Microbial Detection Arrays
Elizabeth Newton
Project Manager
Shayla Stewart
Systems Engineer
Ted Schumacher
Lead Thermal Engineer/Assistant Project Manager
Jeff Childers
Lead Structural Engineer
Charles Vaughan
Lead Electrical Engineer/Chief Safety Officer
Dave Miller
Lead Fabrication Engineer
Steven To
Chief Financial Officer
Sameera Wijesinghe
Webmaster
AES – University of Colorado, Boulder
ASEN 4018 – Senior Projects I: Design Synthesis
Fall Final Report
December 18, 2006
Advisors: Dr. James Maslanik and Dr. Jeffrey Forbes
Customers: BioServe and Tufts University
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
Table of Contents
List of Figures ........................................................................................................................... 5
List of Tables ............................................................................................................................ 7
List of Acronyms ...................................................................................................................... 8
1.0
Project Overview and Requirements .......................................................................... 11
1.1.0
Objective ............................................................................................................. 12
1.2.0
Instrument Operation .......................................................................................... 12
1.3.0
Mars/Earth Comparison ...................................................................................... 13
1.4.0
Design Requirements .......................................................................................... 14
1.4.1.0 Requirement Importance ................................................................................. 16
1.5.0
Deliverables ........................................................................................................ 19
2.0
System Architecture .................................................................................................... 20
2.1.0
Critical Components ........................................................................................... 22
2.1.1.0 Autoclaves....................................................................................................... 22
2.1.2.0 Peristaltic Pumps............................................................................................. 22
2.1.3.0 Reagent Water ................................................................................................. 23
2.1.4.0 Valve ............................................................................................................... 23
2.1.5.0 Test Chambers ................................................................................................ 23
2.1.6.0 Mixers ............................................................................................................. 23
2.1.7.0 Tubing ............................................................................................................. 23
2.1.8.0 Motors ............................................................................................................. 23
2.2.0
Experiment Timeline .......................................................................................... 24
2.3.0
Electrical Subsystem ........................................................................................... 24
3.0
Development and Assessment of System Design Alternatives .................................. 26
3.1.0
System Architecture Pros and Cons .................................................................... 27
3.2.0
System Architecture Options .............................................................................. 29
3.2.1.0 Option A – Monobox ...................................................................................... 29
3.2.2.0 Option B – Single Sterilization, Shared Environment .................................... 30
3.2.3.0 Option C – Single Sterilization, Separate Environment ................................. 31
3.2.4.0 Option D – Dual Sterilization, Separate Environment.................................... 32
3.2.5.0 Option E – Dual Sterilization, Shared Environment....................................... 33
3.3.0
Quantitative Analysis .......................................................................................... 34
3.4.0
Selected System Architecture ............................................................................. 35
4.0
System Design-To Specifications ............................................................................... 36
4.1.0
Reaction Sample Handling ................................................................................. 37
4.1.1.0 Environmental Chamber ................................................................................. 37
4.1.2.0 Support Structure ............................................................................................ 37
4.2.0
Reaction Sample Delivery .................................................................................. 38
4.2.1.0 Clean Room Assembly ................................................................................... 38
4.3.0
Nominal and Peak Power Consumption ............................................................. 38
4.3.1.0 System Insulation ............................................................................................ 38
4.4.0
Unit Disassembly ................................................................................................ 38
4.5.0
Operational Environment .................................................................................... 39
4.5.1.0 Instrument Mass and Volume ......................................................................... 39
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December 18th, 2006
4.5.2.0 Instrument Cost ............................................................................................... 39
4.5.3.0 Component Replacement ................................................................................ 39
4.5.4.0 Instrument Reliability ..................................................................................... 39
4.5.5.0 Field Environment .......................................................................................... 39
5.0
Development and Assessment of Subsystem Design Alternatives ............................. 40
5.1.0
Reaction Chamber ............................................................................................... 41
5.1.1.0 Subsystem Design to Requirements................................................................ 41
5.1.2.0 Requirement Analysis ..................................................................................... 41
5.1.3.0 Internal Volume .............................................................................................. 42
5.1.4.0 Material Requirements .................................................................................... 42
5.1.5.0 Heating Element Trade study.......................................................................... 44
5.1.6.0 Cooling Element Trade Study......................................................................... 46
5.1.7.0 Insulation Trade Study .................................................................................... 47
5.1.8.0 Mixing Trade study ......................................................................................... 49
5.1.9.0 Temperature Sensor Trade study .................................................................... 50
5.1.10.0
Pressure Sensor Trade study ....................................................................... 51
5.2.0
Autoclave ............................................................................................................ 53
5.2.1.0 Subsystem Design to Requirements................................................................ 53
5.2.2.0 Autoclave Techniques ..................................................................................... 53
5.2.3.0 Thermal Analysis ............................................................................................ 53
5.2.4.0 Insulation......................................................................................................... 55
5.2.5.0 Material Selection ........................................................................................... 55
5.2.6.0 Heating and Cooling Apparatus ...................................................................... 56
5.2.7.0 Sensors ............................................................................................................ 56
5.3.0
Sample Transportation ........................................................................................ 56
5.3.1.0 Requirements .................................................................................................. 56
5.3.2.0 Material Selection ........................................................................................... 57
5.3.3.0 Valve Selection ............................................................................................... 57
6.0
Subsystem Design-To Specifications ......................................................................... 59
6.1.0
Overall System Architecture ............................................................................... 60
6.2.0
Subsystem Design ............................................................................................... 66
6.2.1.0 Chassis Design ................................................................................................ 66
6.2.2.0 Autoclave Design ............................................................................................ 66
6.2.3.0 Reagent Water Delivery Design ..................................................................... 67
6.2.4.0 Environmental Design .................................................................................... 67
6.2.5.0 Data Acquisition Design ................................................................................. 67
6.2.6.0 Mass ................................................................................................................ 67
6.3.0
Power requirements ............................................................................................ 68
6.3.1.0 Requirements .................................................................................................. 68
6.3.2.0 Power .............................................................................................................. 71
6.4.0
Component List ................................................................................................... 72
7.0
Project Feasibility and Risk Assessment .................................................................... 74
7.1.0
Autoclave Prototype............................................................................................ 75
7.2.0
Mixing Prototype ................................................................................................ 79
7.3.0
Sample Transportation Prototype ....................................................................... 80
7.4.0
Risk Assessment ................................................................................................. 81
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8.0
Mechanical Design Elements ...................................................................................... 83
8.1.0
Sterilization Chambers ........................................................................................ 84
8.1.1.0 Volume and Dimensions ................................................................................. 85
8.1.2.0 Material and mass ........................................................................................... 87
8.1.3.0 Thermal analysis ............................................................................................. 87
8.2.0
Peristaltic pumps ................................................................................................. 91
8.3.0
Reagent water chamber ....................................................................................... 91
8.4.0
Valve assembly ................................................................................................... 91
8.5.0
Reaction chambers .............................................................................................. 92
8.5.1.0 Volume and Dimensions ................................................................................. 93
8.5.2.0 Material and mass ........................................................................................... 95
8.5.3.0 Thermal control ............................................................................................... 95
8.6.0
Environmentally controlled enclosure ................................................................ 96
8.6.1.0 Thermal analysis ............................................................................................. 96
8.6.2.0 Time and Power required for heating/cooling ................................................ 97
8.7.0
Mixer motors....................................................................................................... 98
8.8.0
External case ....................................................................................................... 98
9.0
Electrical Design Elements ....................................................................................... 100
9.1.0
Electrical Diagram ............................................................................................ 102
9.2.0
Power Input and Supply .................................................................................... 103
9.3.0
Sensor Diagram ................................................................................................. 104
9.4.0
Signal Conditioning .......................................................................................... 107
9.5.0
Control Diagrams .............................................................................................. 107
9.5.1.0 Strip heater Diagram ..................................................................................... 109
9.5.2.0 Thermostat .................................................................................................... 109
9.5.3.0 LEDs ............................................................................................................. 109
9.5.4.0 TEC Control .................................................................................................. 110
9.5.5.0 TEC (Thermoelectric cooler) ........................................................................ 111
9.5.6.0 Fan................................................................................................................. 112
9.5.7.0 Peristaltic Pump ............................................................................................ 112
9.6.0
Mixer Control.................................................................................................... 113
9.6.1.0 Mixer ............................................................................................................. 115
9.6.2.0 Computer....................................................................................................... 116
9.7.0
DAQ .................................................................................................................. 116
9.7.1.0 Wire diagram ................................................................................................ 119
9.8.0
Powered Items ................................................................................................... 121
10.0 Software Design Elements ........................................................................................ 123
11.0 Integration Plan ......................................................................................................... 130
11.1.0
Instrument Assembly ........................................................................................ 131
11.2.0
Autoclave Functional Test Plan ........................................................................ 132
11.3.0
Reaction Chambers ........................................................................................... 133
11.4.0
Data Acquisition and Control ........................................................................... 133
12.0 Verification and Test Plan ........................................................................................ 135
12.1.0
Design Requirement Verification Plan ............................................................. 136
12.2.0
Component Functional Verification and Test ................................................... 138
12.3.0
Subsystem-Level Verification and Test ............................................................ 138
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12.4.0
System-Level Verification and Test ................................................................. 139
13.0 Project Management Plan ......................................................................................... 140
13.1.0
Organizational Responsibilities ........................................................................ 141
13.2.0
Work Breakdown Structure .............................................................................. 142
13.3.0
Schedule ............................................................................................................ 143
13.4.0
Specialized Facilities and Resources ................................................................ 144
13.5.0
Overall Budget .................................................................................................. 145
14.0 Appendix A: Mechanical Design .............................................................................. 146
14.1.0
Mechanical Drawing Tree................................................................................. 146
14.2.0
Sterilization Chamber Lid ................................................................................. 147
14.3.0
Sterilization Chamber Body.............................................................................. 148
14.4.0
Sterilization Chamber Bottom .......................................................................... 149
14.5.0
Sterilization Chamber Assembly ...................................................................... 150
14.6.0
Reaction Chamber Cap ..................................................................................... 151
14.7.0
Reaction Chamber Base .................................................................................... 152
14.8.0
Reaction Chamber Body ................................................................................... 153
14.9.0
Reaction Chamber Assembly............................................................................ 154
14.10.0
Reagent Water Chamber Body ..................................................................... 155
14.11.0
Water Chamber Cap ...................................................................................... 156
14.12.0
Top Support Shelf ......................................................................................... 157
14.13.0
External Case ................................................................................................ 158
15.0 Appendix B: Electrical Design ................................................................................. 159
15.1.0
Electrical Schematic Tree ................................................................................. 159
15.2.0
Overall Electrical Schematic............................................................................. 160
15.3.0
Electrical block diagram ................................................................................... 161
15.4.0
Power Diagram ................................................................................................. 162
15.5.0
Sensor Diagram ................................................................................................. 162
15.6.0
Control Diagrams .............................................................................................. 163
15.7.0
Wire Diagram.................................................................................................... 165
15.8.0
Switch Board ..................................................................................................... 165
16.0 Appendix C: Software............................................................................................... 166
16.1.0
Software Tree .................................................................................................... 166
16.2.0
Software Prototype............................................................................................ 167
17.0 Appendix D: Data Sheets .......................................................................................... 168
17.1.0
Motor................................................................................................................. 169
17.2.0
TEC ................................................................................................................... 170
17.3.0
Motor Control ................................................................................................... 172
17.4.0
Pressure Sensor ................................................................................................. 176
17.5.0
TEC Controller.................................................................................................. 177
17.6.0
Peristaltic Pump ................................................................................................ 189
17.7.0
Voltage Regulator ............................................................................................. 192
17.8.0
CPU ................................................................................................................... 193
18.0 Appendix E: References ........................................................................................... 195
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MiDAs
December 18th, 2006
List of Figures
Figure 1-1NASA Technology Readiness Level Definitions .................................................. 12
Figure 2-1 Overall System Architecture ................................................................................. 21
Figure 2-2 Internal Components ............................................................................................. 22
Figure 3-1 Option A Schematic .............................................................................................. 29
Figure 3-2 Option B Schematic .............................................................................................. 30
Figure 3-3 Option C Schematic .............................................................................................. 31
Figure 3-4 Option D Schematic .............................................................................................. 33
Figure 3-5 Option E Schematic............................................................................................... 34
Figure 3-6 System Architecture Decision Process .................................................................. 35
Figure 5-1 Sonaer S900PIEZO Ultrasonic Processor ............................................................. 49
Figure 5-2 Butterfly Valves .................................................................................................... 57
Figure 5-3 Needle Valve ......................................................................................................... 58
Figure 6-1 Overall System Architecture ................................................................................. 60
Figure 6-2 Top Level Integration Plan.................................................................................... 61
Figure 6-3 Experiment Timeline ............................................................................................. 64
Figure 6-4 Organizational Chart ............................................................................................. 66
Figure 6-5 Mass Analysis ....................................................................................................... 68
Figure 6-6 Power Summary (Full Sterilization Phase) ........................................................... 69
Figure 6-7 Power Summary (Sterilization Phase) - Staggered Autoclaves ............................ 70
Figure 7-1 Autoclave Thermal Analysis ................................................................................. 75
Figure 7-2 Autoclave Prototype Model .................................................................................. 76
Figure 7-3 Autoclave Prototype Setup .................................................................................... 77
Figure 7-4 Autoclave Pressure Results ................................................................................... 77
Figure 7-5 Autoclave Temperature Results ............................................................................ 78
Figure 7-6 Prototype Mixer .................................................................................................... 79
Figure 8-1 Overall System ...................................................................................................... 84
Figure 8-2 Sterilization chamber assembly............................................................................. 86
Figure 8-3 Cut-away view of sterilization chamber ............................................................... 87
Figure 8-4 Butterfly valve ....................................................................................................... 92
Figure 8-5 Reaction chamber .................................................................................................. 94
Figure 8-6 - Reaction chamber lid .......................................................................................... 95
Figure 8-7 Reaction chamber bottom ..................................................................................... 95
Figure 8-8 External case ......................................................................................................... 99
Figure 9-1 Physical Electrical Schematic ............................................................................. 101
Figure 9-2 Overall electrical diagram ................................................................................... 102
Figure 9-3 Power Supply input ............................................................................................. 103
Figure 9.9-4 Voltage Regulator ............................................................................................ 104
Figure 9-5 Sensor circuit diagram......................................................................................... 105
Figure 9-6 PX139 Pressure Sensor ....................................................................................... 105
Figure 9-7 Control Diagram 1............................................................................................... 107
Figure 9-8 Control Diagram 2............................................................................................... 108
Figure 9-9 Strip Heater ......................................................................................................... 109
Figure 9-10 Thermostat......................................................................................................... 109
Figure 9.9-11 LED ................................................................................................................ 109
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Figure 9-12 Wavelength TEC control WEC3243 ................................................................. 110
Figure 9-13 Thermoelectric Cooler ...................................................................................... 111
Figure 9-14 Peristaltic pump controller connection schematic............................................. 113
Figure 9-15 Controller layout ............................................................................................... 114
Figure 9-16 APEX PA75CC ................................................................................................. 114
Figure 9-17 On board computer, an embedded PC104 controller from Kontron ................. 116
Figure 9-18 Data Acquisition................................................................................................ 117
Figure 9-19 Wire Diagram .................................................................................................... 119
Figure 9-20 Switch board...................................................................................................... 119
Figure 10-1 Simplified execution ......................................................................................... 125
Figure 10-2 Autoclave Sensor Diagram ............................................................................... 127
Figure 10-3 Reaction Chamber Sensor Diagram .................................................................. 128
Figure 10-4 LabView vi Autoclave Temperature Control .................................................... 129
Figure 10-5 Software Function Tree ..................................................................................... 129
Figure 11-1 Assembly Flow Diagram................................................................................... 131
Figure 11-2 Overall Assembly .............................................................................................. 132
Figure 11-3 Autoclave Functional Test Plan ........................................................................ 133
Figure 11-4 Reaction Chamber Functional Test Plan ........................................................... 133
Figure 11-5 DAQ Functional Test Plan ................................................................................ 134
Figure 13-1 Organizational Responsibilities ........................................................................ 141
Figure 13-2 Work Breakdown Structure............................................................................... 142
Figure 13-3 Schedule for Spring Semester ........................................................................... 143
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MiDAs
December 18th, 2006
List of Tables
Table 1-1 Mars/Earth Comparison.......................................................................................... 14
Table 1-2 MiDAs Design Requirements................................................................................. 14
Table 2-1 Experiment Timeline .............................................................................................. 24
Table 3-1 Driving Requirements ............................................................................................ 27
Table 3-2 System Architecture Pros and Cons ....................................................................... 28
Table 3-3 Design Alternative Quantitative Analysis .............................................................. 35
Table 4-1 Driving PDD Requirements ................................................................................... 37
Table 5-1 Wetted Material Properties ..................................................................................... 42
Table 5-2 Electric Heating Options ........................................................................................ 45
Table 5-3 Insulation Options .................................................................................................. 48
Table 5-4 Temperature Sensor Comparison ........................................................................... 51
Table 5-5 Pressure Sensor Comparison .................................................................................. 52
Table 6-1 Power Summary ..................................................................................................... 69
Table 6-2 Power Summary (1st Autoclave)............................................................................ 70
Table 6-3 Power Summary (2nd Autoclave) .......................................................................... 70
Table 6-4 Component List ...................................................................................................... 73
Table 7-1 Risk Assessment Chart ........................................................................................... 81
Table 9-1 Sensor system accuracy ........................................................................................ 106
Table 9-2: TEC Pin values .................................................................................................... 111
Table 9-3: TEC specifications .............................................................................................. 112
Table 9-4 Mixer motor specifications ................................................................................... 115
Table 9-5 DAQ system ......................................................................................................... 118
Table 9-6 Drawing Tree ........................................................................................................ 120
Table 9-7 MiDAs Powered Items ......................................................................................... 121
Table 9-8 Electronics Parts List ............................................................................................ 122
Table 10-1: One cycle control............................................................................................... 126
Table 12-1 Design Requirement Verification Plan ............................................................... 136
Table 13-1 Overall Budget.................................................................................................... 145
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List of Acronyms
A
AC
A/D
ADP
AES
Al
ASTID
ASV
BCL
BST
C&DH
CDR
CFO
CFU
CJC
COTS
CPU
CP
CU
CUB
D
DAC
DAQ
DC
DNA
dH2O
dO2
DO
DU
EC
ECTFE
ETFE
FE
FEP
FFR
g
GCMS
GEX
H2O
I
I&T
ISE
JSC
Analysis (verification method)
Alternating Current
Analog to Digital Converter
Acceptance Data Package
Aerospace Engineering Sciences
Aluminum
Astrobiology Science and Technology Instrument Development
Anodic Stripping Voltammetry
Bioanalytical Core Lab
BioServe Space Technologies
Command and Data Handling
Critical Design Review
Chief Financial Officer
Colony Forming Unit
Cold Junction Compensator
Commercial Off the Shelf
Central Processing Unit
Chronopotentiometric
University of Colorado
University of Colorado at Boulder
Demonstration (verification method)
Digital to Analog Converter
Data Acquisition
Direct Current
Deoxyribonucleic Acid
Distilled water
Dissolved Oxygen
Digital Output
Digital Input
Electric Conductivity
Ethylene-Chlorotrifluoroethylene
Ethylene-Tetrafluoroethylene-copolymer
Fabrication Engineer
Fluoroethylene-Propylene
Fall Final Report
Gram, Earth Gravity
Gas Chromatograph/Mass Spectrometer
Gas Exchange
Water
Current, Inspection (verification method)
Integration and Test
Ion Selective Electrode
Johnson Space Center
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kg
LCP
LED
LR
m
MDA
MEA
MECA
MEL
MiDAs
MIL-STD
mL
MOSFET
N/A
NAI
NAR
NASA
ORP
PAB
PAI
PCB
PCTFE
PDD
PDR
PEEK
PEI
PFA
pH
PI
PID
PM
P/N
PPS
PR
PSU
PTFE
PV
PVA
PVC
PVF
PWM
R
RF
RFA
RFA
MiDAs
December 18th, 2006
kilogram
Liquid Crystal Polymer
Light Emitting Diode
Labeled Release
Mass, meter
Microbial Detection Array
Microelectrode Array
Mars Environmental Compatibility Assessment
Master Equipment List
Microbial Detection Arrays
Military Standard
Milliliter
Metal-Oxide-Semiconductor Field-Effect Transistor
Not Applicable
NASA Astrobiology Institute
Not a requirement
National Aeronautics and Space Administration
Oxidation-Reduction Potential
Project Advisory Board
Polyamide-Imide
Printed Circuit Board
Polychloro-Trifluoroethylene
Project Definition Document
Preliminary Design Review
Polyetherketone
Polyetherimide (Ultem)
Perfluoralkoxy
Potential Hydrogen
Polyimide
Proportional Integral Derivative (controls)
Project Manager
Product Number
Polyphenylene Sulfide
Pyrolytic Release
Polysulfone
Polytetrafluoroethylene
Photovoltaics
Photovoltaic Array
Polyvinyl Chloride
Polyvinyl-Fluoride
Pulse Width Modulation
Resistance
Radio Frequency
Recommendation for Action
Request for Action
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RNA
RPM
RTD
SE
SS
SW
T
TEC
TOC
TRL
TRR
USB
V
WBS
WCL
MiDAs
December 18th, 2006
Ribonucleic Acid
Revolution Per Minute
Resistance Temperature Detector
Systems Engineer
Stainless Steel
Software
Test (verification method)
Thermoelectric Cooler
Total Organic Carbon
Technology Readiness Level
Test Readiness Review
Universal Serial Bus
Voltage
Work Breakdown Structure
Wet Chemistry Laboratory
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1.0 Project Overview and Requirements
Author: Shayla Stewart
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1.1.0 Objective
Microbial Detection Arrays (MiDAs) is a component of a larger project focusing on a future
Mars astrobiology mission with an objective to accomplish electrochemical sensing of
metabolic activity in Martian soil. The overall project, funded by an Astrobiology Instrument
Development grant, consists of three research activities: biology testing through NASA
Johnson Space Center (JSC), electrochemical sensing technologies of metabolic activity
through Tufts University, and instrument hardware, which is the focus of this Senior Project.
The MiDAs team objective is to design and build an integrated field instrument that supports
the JSC and Tufts activities above, with meaningful biological and spaceflight constraints,
such as autonomy, size, weight, and materials selection. The project will extend the proof-ofconcept from the laboratory to the field, in an integrated unit, and thus raise the Technology
Readiness Level (TRL) from 1-3 to 4-5. The NASA TRLs are defined in Figure 1-1. This
Earth-based instrument will validate the key functions set forth by the customer, BioServe
Space Technologies, and will enable self-contained, integrated biology research in the lab
(TRL-4) and the field (TRL5) with the electrochemical sensors from Tufts University.
Figure 1-1 NASA Technology Readiness Level Definitions
1.2.0 Instrument Operation
Figure 1-2 shows a simplified functional diagram of the MiDAs instrument. MiDAs
operations begin with its Startup phase when the instrument begins to draw power and takes
initial temperature and pressure readings through the Data Acquisition (DAQ) system. Once
this is complete, a geological sample is split evenly and added into two identical sterilization
chambers with a small amount of water for steam sterilization. The instrument then enters the
Sterilization phase. Once the split samples are individually sterilized, they are transported
into the two reaction chambers, which consist of a test and control chamber. Once the
samples reach the reaction chambers, they are mixed with sterile water and the
electrochemical sensors within the chamber measure an initial baseline as any soluble
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materials reach an equilibrium. An inoculation sample, which has not been sterilized, is then
added into the test chamber and the Testing phase begins under controlled thermal
conditions. This phase continues for approximately 14 days. Any metabolic activity in the
inoculated test chamber should be detectable by changes in the electrochemical sensor
readings relative to the sterile control chamber. The growth or incubation period is
envisioned to last up to 2 weeks. The experiment timeline will be discussed in more detail
later in this document. The scope of this project is to design, build, and validate an integrated
instrument to enable these functions and measurements, but the actual biology
experimentation is outside the scope of this project.
Figure 1-2 MiDAs Operational Diagram
1.3.0 Mars/Earth Comparison
Table 1-1 shows a comparison of the theoretical Mars mission and the MiDAs Earth field
instrument. Complete autonomy is very important for a Mars-based instrument, while this is
not a primary goal for this project. The bold and italicized rows show where the Earth
instrument differs from a theoretical flight-instrument. These are areas where autonomy has
been lost and there is increased reliance on the experimenter to open valves and input the
samples. In these cases, autonomy has been traded for reliability in the field instrument.
Autonomy inherently adds expense, complexity, and failure modes without proving key
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concepts or raising the TRL. The gray indicates the key components where autonomy is vital.
It is noted that the MiDAs instrument meets the key autonomous components. The Mars
instrument will, however, be able to draw on several rover/lander resources such as power,
data storage, thermal control, and communications, which are all required functions for the
field instrument. Given the limited resources and time for the Senior Projects design phase,
there is a careful balance between proving key technology and facilitating integrated field
testing.
Table 1-1 Mars/Earth Comparison
Theoretical Mars Mission
Receive low power from Rover/Lander
Receive startup command from uplink
Rover/lander opens Autoclave lid
Rover/lander inputs sample
Rover/lander closes Autoclave lid
MiDAs Earth Based Apparatus
Receive low power from external source
Press power button
Person opens Autoclave lid
Person inputs sample
Person closes Autoclave lid
Autoclave cycle begins through SW run
Autoclave cycle begins
command
Reaction chamber environment controls begin Reaction chamber environment controls begin
Valve opens
Person opens valve
Water flushes sample out of autoclave
Water flushes sample out of autoclave
Valve closes
Person closes valve
Mixing begins
Mixing begins through SW run command
DAQ begins
DAQ begins through SW run command
Inoculation sample added
Person adds inoculation sample
DAQ runs for 14 days
DAQ runs for 14 days
Data downlink from rover to satellite to Earth Data stored on-board, transfer to PC
1.4.0 Design Requirements
Table 1-2 shows the MiDAs design requirements as defined in the Project Definition
Document (PDD).
Table 1-2 MiDAs Design Requirements
Requirement #
Title
Requirement
PDD 4.1
Reaction Chamber
Volume
MiDAs shall have two chambers with a minimum internal volume
of 50 mL each.
PDD 4.2
Reaction Chamber
Temperature
Each reaction chamber shall be controllable within a range of 4°C
to 37°C with an accuracy of ±1°C.
PDD 4.3
Reaction Chamber
Pressure
Each reaction chamber shall be sealed to a pressure of 1 psi
differential from ambient pressure.
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PDD 4.4
Reaction Chamber
Sensor Capability
PDD 4.5
Reaction Chamber
Mixing Capability
PDD 4.6
Reaction Chamber
Multi-Use Port
PDD 4.7
Reaction Chamber
Material
Each reaction chamber shall be manufactured out of a list of
materials provided by BioServe. This list includes, but is not yet
limited to, Polysulfone, PharMed, 316 stainless steel, and Ultem
1000.
PDD 4.8
Geological Sample
Volume
Each reaction chamber shall receive no less than 5 mL and no more
than 25 mL of geological sample.
PDD 4.9
Inoculation Sample
Volume
The test chamber shall receive a maximum of 1 mL of inoculation
sample.
PDD 4.10
Inoculation Sample
Reception
The test chamber shall receive the inoculation sample through
established aseptic techniques.
PDD 4.11
Reaction Sample
Handling
The reaction samples shall be sterilized in accordance with standard
Autoclave techniques.
PDD 4.12
Inoculation Sample
Handling
The inoculation sample shall not be sterilized. The sample shall
remain in the condition in which it was gathered until it is
introduced into the test chamber.
PDD 4.13
Reaction Sample
Delivery
One pre-measured reaction sample shall be delivered to the test
chamber and one pre-measured reaction sample shall be delivered
to the control chamber. Both samples shall maintain sterility
throughout delivery.
PDD 4.14
Inoculation Sample
Sterility
The inoculation sample shall be aseptically delivered to the test
chamber.
PDD 4.15
Reagent Water
Containment
The sterile reagent water shall be completely contained in both solid
and liquid form.
PDD 4.16
Reagent Water
Delivery
The MiDAs shall aseptically deliver no more than 50 mL (within ±
5% accuracy) of sterile reagent water to each reaction chamber.
PDD 4.17
Reagent Water
Temperature
The reagent water shall be delivered to the reaction chambers at a
temperature not to exceed 60°C.
PDD 4.18
Sensor Integration
The electrochemical sensors shall be placed at a minimum height
within the reaction chambers to mitigate sample sedimentation
effects. This height shall be sufficient to allow the sensors to be
fully submerged with a minimum of 5 mL to 10 mL of fluid.
PDD 4.19
Sensor Data
Collection Rate
The electrochemical sensors shall have a data collection rate of 1
measurement per minute per sensor.
Sensor Data
Acquisition
Sensor Data
Accessibility
All data taken through the sensors shall be collected and stored for
analysis.
The scientific and engineering status data shall be accessible to
users throughout the experiment.
PDD 4.22
MiDAs Status
Warnings
MiDAs shall provide caution, warning, and instrument status to
external ground support equipment.
PDD 4.23
MiDAs Command
MiDAs shall receive commands from external ground support
equipment.
PDD 4.20
PDD 4.21
Each reaction chamber shall be capable of supporting no fewer than
6 and no more than 18 electrochemical sensors.
Each reaction chamber shall have mixing capability such that each
geological sample is evenly distributed within the fluid while
movement is present at each sensor location.
Each reaction chamber shall have a minimum of four multi-use
ports for gas and liquid exchange.
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PDD 4.24
Field Power
MiDAs shall be capable of receiving between 10 W and 30 W from
an external power supply in a field setting.
PDD 4.25
Laboratory Power
MiDAs shall be capable of receiving between 10 W and 30 W from
an external power supply in a laboratory setting.
PDD 4.26
PDD 4.27
Nominal Power
Consumption
Peak Power
Consumption
Nominal power consumption shall not exceed 30 W.
Peak power consumption shall not exceed 30 W for more than 30
seconds.
PDD 4.28
Unit Disassembly
MiDAs shall be able to be taken apart so that it may be sterilized
and reassembled for multiple Earth tests.
PDD 4.29
Operational Cycle
One operational testing cycle shall be 14 standard Earth days, not
including power-up, sterilization, and power-down.
PDD 4.30
Operational
Environment
MiDAs shall be able to operate in environments ranging from
Antarctica to Atacama Valley in Chile.
1.4.1.0
Requirement Importance
4.1 Reaction Chamber Volume
The instrument must have two reaction chambers so that there can be a test and
control simultaneously. This is important for the scientists using the instrument so that they
can discern what changes in temperature or electrochemical activity occur naturally and
which are due to potential metabolic activity in the test chamber.
4.2 Reaction Chamber Temperature
Each reaction chamber must be controllable to a user-selectable set point between
4°C and 37°C and maintained constant at this set point to +/- 1°C. This is assumed to be the
potential range of acceptable growth environments to metabolize and reproduce. The
temperature must be controlled at the desired set point to reduce thermal effects on the
sensors and ensure their long-term stability.
4.3 Reaction Chamber Pressure
Each reaction chamber must be sealed to 1 psi differential from ambient in order to
minimize the gas exchange that might occur between the reaction chambers and the outside
environment, and as a verification method to ensure that there is no fluid leakage and to
maintain sterility.
4.4 Reaction Chamber Sensor Capability
Each reaction chamber has to be able to accommodate the appropriate number of
electrochemical sensors provided by Tufts University in order to collect the desired amount
of measurements.
4.5 Reaction Chamber Mixing Capability
The fluid in the reaction chambers must be mixed as uniformly as possible so that the
sensor readings are accurate. If there is a lot of sample sedimentation, then the solution will
not be homogeneous and the sensors may not be detecting all of the potential metabolic
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activity. There must also be fluid movement at each of the sensors in order to break down the
boundary layer, which is necessary for the sensors to take accurate readings.
4.6 Reaction Chamber Multi-Use Port
Having at least four multi-use ports makes it possible for the user to input/output gas
or liquid to/from the reaction chambers during the experiment.
4.7 Reaction Chamber Material
The list of possible reaction chamber materials is comprised of materials that can all
withstand autoclaving, so that they can be sterilized, have high resistance to corrosion, since
the sample/water solution may be corrosive, are approved for food and pharmaceutical
applications, and are inert so that there is no chemical reaction between the chamber and the
solution within it.
4.8 Geological Sample Volume
The geological sample must be at least 5 mL, which provides enough material to
obtain measurable results. This is a customer specification. The maximum volume of 25 mL
is imposed so that a range of different sample sizes can be accommodated during field testing
and concept evaluation.
4.9 Inoculation Sample Volume
The inoculation sample volume should be less than or equal to 1 mL, which is much
smaller than the reaction sample, so that any reactions that may take place in the test chamber
are not creating false positive readings. The chemistry of the reaction samples may be altered
by autoclaving, and a large volume of non-sterilized yet inert inoculation sample could create
electrochemical changes.
4.10 Inoculation Sample Reception
The inoculation sample must be aseptically delivered to the reaction chambers so that
the user knows that any detected metabolic activity is from life forms already present in the
sample, not transferred to the sample during transportation.
4.11 Reaction Sample Handling
The reaction samples will be sterilized through steam autoclaving, with options for
multiple autoclave cycles upon customer request. This is the sterilization method with the
best chance of killing most known forms of life (e.g. bacteria, viruses, spores, etc.).
4.12 Inoculation Sample Handling
The inoculation sample must remain unsterilized so that any potential living organism
present is preserved.
4.13 Reaction Sample Delivery
Having equal amounts of sample in each reaction chamber helps maintain uniformity
between the test and control. Once the sample is sterilized, it has to remain sterile so that no
life forms are introduced.
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4.14 Inoculation Sample Sterility
The inoculation sample must not become contaminated with any living organisms
from the MiDAs instrument. If metabolic activity is detected, the experimenter needs to
know that the living organisms were originally in the sample or the experiment becomes
obsolete.
4.15 Reagent Water Containment
The reagent water must be contained in both solid/frozen and liquid form so that the
instrument can be transported at a range of temperatures without being powered. Prior to use,
if the instrument is operated in a cold ambient environment, the water must be heated to be a
liquid.
4.16 Reagent Water Delivery
The reagent water delivery must be contained and transported aseptically, so that no
living organisms are transferred to the reagent water.
4.17 Reagent Water Temperature
The electrochemical sensors provided by Tufts University cannot withstand
temperatures above 60°C, so the water must be delivered below this temperature. For
delivery, it must be liquid and thawing may be required prior to use.
4.18 Sensor Integration
The sensors must be able to take readings when the minimum amount of
sample/water solution is in the chamber, so the sensors must be completely submerged in 510 mL.
4.19 Sensor Data Collection Rate
Since the experiment takes place over 14 days, a reading each minute from each
sensor is sufficient to characterize the experiment results.
4.20 Sensor Data Acquisition
The data must be collected and stored so that the experimenter can obtain and study
the data after the experiment is completed.
4.21 Sensor Data Accessibility
The experimenter should be able to access the data during the experiment so as to
observe the status of the experiment while it is in progress.
4.22 MiDAs Status Warnings
Caution, warning, and status signals are necessary to be able to observe the
instrument’s status as well as detect errors throughout the experiment.
4.23 MiDAs Command
The duration of the experiment is such that it is not reasonable to have the user
initiate each step of the process, so the instrument must be capable of receiving software
commands.
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4.24 Field Power
This 30 W power requirement helps pave the way for future space missions. This is
based on predicted wattage for future Mars rover missions.
4.25 Laboratory Power
The instrument needs to be capable of running in a laboratory, as well as the field.
4.26 Nominal Power Consumption
The 30-Watt nominal power consumption is based on predicted wattage provided by
future Mars rovers.
4.27 Peak Power Consumption
The Mars rovers can provide more than nominal power for brief, scheduled periods of
time, so the peak power consumption must not exceed 30 W for more than 30 seconds.
4.28 Unit Disassembly
The instrument must be reusable, so disassembly must be possible for sterilization
purposes.
4.29 Operational Cycle
The 14-day operational testing cycle is the time allotted for the potential living
organisms to reproduce and metabolize.
4.30 Operational Environment
Antarctica and Atacama Valley, Chile are the potential test sites for the MiDAs
instrument, so it must be designed for these environmental conditions. These conditions
include an ambient temperature range between -10°C and 40°C, ambient pressures as low as
70,000 Pa (3000 meter altitude) and a relative humidity of 0-95%, which is just below the
condensation percentage.
1.5.0 Deliverables
The deliverables from the MiDAs senior project team to the customer is the field-ready unit
with a TRL of 4-5 with test data verifying the requirements listed in Table 1-2. The customer
will also receive an operational manual outlining how to assemble/disassemble the
instrument as well as how to operate various components. There will also be a document
proposing design solutions to further raise the TRL to 6-7. This design document will include
ways to increase autonomy in the areas outlined in bold italics in Table 1-1.
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2.0 System Architecture
Author: Sameera Wijesinghe
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Upon analyzing the customer requirements as described in detail in the previous section, the
following design was developed. Figure 2-1 below shows the overall system architecture for
MiDAs. Since sterility was a main concern for this project, the MiDAs unit was designed to
be completely disassembled in a short period of time. This gives the experimenter the added
flexibility of being able to sterilize all the experimental related components in an external
autoclave prior to carrying out any experiments. The relative ease of the disassembly process
can further be seen in the figure below.
Embedded CPU
DAQ
Figure 2-1 Overall System Architecture
It is important to note that the insulation as well as few other non critical components has
been removed for clarity. Highlighted in Figure 2-2 are all the major components that make
up the MiDAs unit.
MiDAs receives 12V from an external power source which will provide power to the motors,
pumps and the heaters. Using a voltage regulator the 12V will be reduced to 5V to
accommodate the electrochemical sensors which are provided by the customer. Since the
temperature in both the autoclaves and also the environment chamber (see figure 2-2 below)
needs to be actively controlled to  1˚, an embedded CPU will be utilized which operates on
custom software for this purpose.
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Peristaltic Pump
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Water Chamber
Heat Sink
Autoclave
Valve
PharMed Tubing
Environment
Chamber
Test Chamber Cap
Mixer
Sensor Ports
Test Chamber
Base
Motor Shaft
Motor Base
Figure 2-2 Internal Components
2.1.0 Critical Components
2.1.1.0
Autoclaves
Each autoclave consists of three strip heaters and a thermoelectric cooler (TEC). The TEC
will only be used in cooling the autoclaves instead of aiding in the process of heating,
although this configuration could be easily changed during adverse weather conditions.
Furthermore, each autoclave will consist of a temperature sensor and a pressure sensor
located inside.
2.1.2.0
Peristaltic Pumps
There are two peristaltic pumps (one per autoclave), each capable of precisely metering out
25mL of reagent water.
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2.1.3.0
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Reagent Water
The peristaltic pumps described above will be used in drawing precisely the required volume
of liquid from the water chamber and pumping it directly into the autoclave chambers once
the autoclaves has completed the sterilization process.
2.1.4.0
Valve
The butterfly valve which is affixed to the base of the autoclave will open manually through
user input once the sterilization has been completed in the autoclaves.
2.1.5.0
Test Chambers
Once the sterilized soil sample has been received by the two chambers the sensors located
along the perimeter of the chambers will acquire data once every minute to detect any
metabolic activity in the sample.
2.1.6.0
Mixers
The custom designed mixers will ensure that no sedimentation of the sample occurs at the
base of the test chambers. The mixers will be continuously operated so that the data acquired
by the sensors will not be subjected to any ambiguity.
2.1.7.0
Tubing
PharMed tubing will transport the mixture of water and soil sample into the test chambers.
The internal diameter of the tubing is approximately one inch and extends directly
downwards for up to three inches to ensure that the soil transportation occurs with minimal
amount of interference.
2.1.8.0
Motors
Two low power motors will be utilized to spin the custom designed mixers. The motors will
operate continuously for the entire duration of the experiment once the sample has been
transported into the test chambers
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2.2.0 Experiment Timeline
The sample will be inserted into the two autoclaves by the experimenter and then sealed.
The melamine insulation will be placed over the two autoclaves and the environment
chamber to prevent heat loss. The required amount of insulation of two inches was based on
the thermal conductivity of melamine. There will be total heat loss of 1.6W though the
insulation. Once the insulation is in place the software will be enabled by the experimenter
to begin the experiment. MiDAs unit is required to operate under various ambient
conditions. Due to this reason it should be noted that the times shown below in Table 2-1 are
for the worst case scenario.
Table 2-1 Experiment Timeline
Subsystem
Description
Autoclave
Raise the temperature of the sample from ambient to 121˚C
Hold at or above 121˚C
Cool the sample to between 4°C and 37˚C
Hold between 4°C and 37°C
Repeat three more cycles (Step1-4)
3.851
0.25
3.232
24
68.32
Accept the soil sample from the autoclaves and begin the testing process
336
Reaction
Chambers
Time (hours)
2.3.0 Electrical Subsystem
Figure 2-3 shows the various electrical interconnections with the hardware components of
MiDAs. There are a total of 10 sensors that will be provided by MiDAs for measuring
temperature and pressure. The electrochemical sensor package which consists of 24 sensors
will be provided by Tufts University.
1
2
Time based on an ambient temperature of -10°C
Time based on a cooling temperature of 20°C
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Computer
x
2
Distribution
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Power
Supply
Power
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x
3
6
Input
Analog
x
0
1
x
0
output
x
1
1
x
Output
x
x
4
x
2
1
TEC
x
1
TEC
AC
2
TEC
2
TEC
AC
1
TEC
RC
Autoclave
Autolcave
x
4
2
x
4
x
1
Control
2
Control
2
TEC
RC
RC
RC
2
H2
For optional
proportional control
Autoclave
x
2
x
4
x
2
LED's
x
2
H1
x
3
1
Control
1
Mixer
2
Mixer
2
Control
Mixer
Mixer
x
2
Autoclave
x
2
x
3
x
2
Pump1
x
2
Pump
2
6
Analog
x
2
Digital
Board
Switch
Number of
wires
2
2
Sensors
DAQ
Figure 2-3 Electrical Subsystem
In addition to the sensors the two peristaltic pumps, the two motors, and the heaters/coolers,
need to be connected to the switch board for on/off control. If proportional control of the
motors or TEC is requested by the customer the mixer motors and TEC can be connected to
the analog outputs of the DAQ.
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3.0 Development and Assessment of System Design
Alternatives
Author: Shayla Stewart
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When developing system design alternatives, there were several driving requirements
considered. These requirements are listed in Table 3-1. The design alternatives examine the
number of sterilization and reaction chambers necessary to fulfill these requirements. This is
a fundamental issue for the MiDAs team because the number and layout of the chambers
drive the thermal analysis, power budget, mass, volume, and cost of the overall instrument.
There were five overall system architectures considered for this instrument.
Table 3-1 Driving Requirements
Requirement #
Requirement
PDD 4.1
Reaction Chamber Volume
PDD 4.2
Reaction Chamber Temperature
PDD 4.3
Reaction Chamber Pressure
PDD 4.5
Reaction Chamber Mixing Capability
PDD 4.7
Reaction Chamber Material
PDD 4.8
Geological Sample Volume
PDD 4.11
Reaction Sample Handling
PDD 4.13
Reaction Sample Delivery
PDD 4.24
Field Power
PDD 4.25
Laboratory Power
PDD 4.26
Nominal Power Consumption
PDD 4.27
Peak Power Consumption
PDD 4.29
Operational Cycle
There were two main parameters considered when establishing the five system architecture
options. The architecture of the sterilization chambers was the first considered and there were
three main options examined. The sample could be sterilized within the reaction chamber,
there could be one separate chamber for sterilization of the geological sample, or there could
be two separate sterilization chambers for each the test and control samples.
The second parameter considered was the environmental controls for the two reaction
chambers. Both the test and control chambers must be maintained at a given pressure and
temperature throughout the testing phase as stated in PDD requirements 4.2 and 4.3. Both
reaction chambers could have separate environmental controls or they could share the same
environment. Separate environments would involve sealing each chamber separately and
having thermal control and insulation around each chamber. In a shared environment, the test
and control chambers would be placed together inside a larger environmental chamber. This
larger chamber would be thermally controlled and insulated, but the reaction chambers
themselves would not.
3.1.0 System Architecture Pros and Cons
The geological sample has to be sterilized using steam autoclave techniques. Using a single
autoclave for the entire sample would involve splitting the sample into two equal volumes to
be transferred into the two reaction chambers once the sterilization is complete. If two
separate autoclaves were used, the sample would be split into equal volumes and placed in
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the autoclaves before sterilization begins. Another decision is whether or not to have a shared
environmental control for both reaction chambers or whether to have one for each chamber.
With some of the overall system architecture options outlined later on, several environmental
sensors (i.e. temperature and pressure sensors) would be necessary in order to obtain accurate
measurements. There are others that would involve the use of only a few environmental
sensors. In either case, the sensors would have to be located in optimum such a way as to
minimize interference with other components within the MiDAs instrument.
The electrochemical sensor package provided by Tufts University has a maximum
temperature limitation of 60°C. As mentioned previously, standard autoclave techniques
require a temperature of at least 121°C. This means that the electrochemical sensors cannot
be within the autoclave during operation. Therefore, if the sample were to be sterilized within
the reaction chamber, some sort of moving sensor package would have to be developed. This
way, the sensors could be moved into the chamber once the sterilization is completed. If the
sterilization and reaction chambers are separate entities, a fixed sensor package in the
reaction chambers would be used.
Table 3-2 shows the pros and cons for each of the system architecture decisions including the
number of autoclaves, number of sensors, whether to have a moving or fixed sensor package,
and whether or not to have a shared environment for the reaction chambers.
Table 3-2 System Architecture Pros and Cons
Option
Separate Autoclave
Shared Autoclave
Few Environmental
Sensors
Several Environmental
Sensors
Moving Sensor Package
Fixed Sensor Package
Separate Environment
Shared Environment
Pros
Eliminates need to split
sample into equal parts
Fewer parts
Less machining time
Fewer parts
Less power consumption
Sensor redundancy
No sample transport
necessary - no
contamination
Reduced complexity – no
extra moving parts
Smaller operational
environment – easier to
thermally control
Easy to keep test and
control under same
conditions
Cons
More machining time
Need to split sample into equal
parts
No redundancy – failure
compromises experiment
Additional parts
More power consumption
Very complex
Failure renders experiment
useless
Sample transport required –
chance for contamination
Difficult to keep test and
control under same conditions
Additional parts
Larger environment – more
power to thermally control
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3.2.0 System Architecture Options
3.2.1.0
Option A – Monobox
Description
This system architecture utilizes a single chamber for sterilization and the
experimental testing. There are two reaction chambers within the autoclave for the test
(marked “Exp” for experiment) and control. The testing is performed in both chambers at the
same time. Figure 3-1 shows a functional schematic of this system architecture. This option
has the pros and cons of a shared autoclave, few sensors, a moving sensor package, and a
shared environment as defined in Table 3-2.
Figure 3-1 Option A Schematic
Experimental Timeline
Stage 1: Receive inoculation sample and geological sample from outside influence
Stage 2: Add the geological sample to each or the reaction chambers (equal parts)
Stage 3: Autoclave to sterilize both reaction chambers
Stage 4: Cool and hold for 24 hrs
Repeat Stages 3 and 4 twice more
Stage 5: Add reagent water to each reaction chamber (equal parts water for both
chambers)
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Stage 6: Use the mixer to fully mix both chambers (the mixer will be used throughout
the duration of the experiment)
Stage 7: Homogenize the environment of the chambers using the environmental
controls
Stage 8: Add the inoculation sample to the test chamber
Stage 9: Add the sensor package to each of the reaction chambers
Stage 10: Test for two weeks
3.2.2.0
Option B – Single Sterilization, Shared Environment
Description
The geological sample in this option is sterilized in a single chamber and divided
equally into the test and control chambers. The test and control chambers are both inside an
enclosed space with shared environmental controls. Figure 3-2 shows a functional schematic
of this system architecture. This option has the pros and cons of a shared autoclave, few
sensors, a fixed sensor package, and a shared environment as defined in Table 3-2.
Figure 3-2 Option B Schematic
Experimental Timeline
Stage 1: Receive inoculation sample and geological sample from outside influence
Stage 2: Add the geological sample to the autoclave
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Stage 3: Autoclave to sterilize sample
Stage 4: Cool and hold for 24 hrs
Repeat Stages 3 and 4 twice more
Stage 5: Separate the sterilized sample into equal parts
Stage 6: Add each sterilized sample to the reaction chambers
Stage 7: Add equal parts reagent water to the reaction chambers
Stage 8: Homogenize the environment of the chambers using the environmental
controls
Stage 9: Add inoculation sample to the test chamber
Stage 10: Test for two weeks
3.2.3.0
Option C – Single Sterilization, Separate Environment
Description
Like Option B, the samples for both reaction chambers are sterilized in a single
sterilization chamber, however, after sterilization, the sample is divided into two separate test
and control chambers with separate environmental controls. Figure 3-3 shows a functional
schematic of the system architecture. This option has the pros and cons of a shared autoclave,
several sensors, a fixed sensor package, and a separate environment as defined in Table 3-2.
Figure 3-3 Option C Schematic
Experimental Timeline
Stage 1: Receive inoculation sample and geological sample from outside influence
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Stage 2: Add the geological sample to the autoclave
Stage 3: Autoclave to sterilize sample
Stage 4: Cool and hold for 24 hrs
Repeat Stages 3 and 4 twice more
Stage 5: Separate the sterilized sample into equal parts
Stage 6: Add each sample to the reaction chambers
Stage 7: Add equal parts reagent water to the reaction chambers
Stage 8: Homogenize the environment of the chambers using the environmental
controls
Stage 9: Add inoculation sample to the test chamber
Stage 10: Test for two weeks
3.2.4.0
Option D – Dual Sterilization, Separate Environment
Description
This option utilizes two separate sterilization chambers. After sterilization, the
sample from each sterilization chamber is placed in a reaction chamber, and each reaction
chamber has its own environmental controls. Figure 3-4 shows a functional schematic of the
system architecture. This option has the pros and cons of a separate autoclave, several
sensors, a fixed sensor package, and a separate environment as defined in Table 3-2.
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Figure 3-4 Option D Schematic
Experimental Timeline
Stage 1: Receive inoculation sample and geological sample from outside influence
Stage 2: Add the geological samples to each autoclave
Stage 3: Autoclave to sterilize samples
Stage 4: Cool and hold for 24 hrs
Repeat Stages 3 and 4 twice more
Stage 5: Add the sterilized samples to the reaction chambers
Stage 6: Add equal parts reagent water to the reaction chambers
Stage 7: Homogenize the environment of the chambers using the environmental
controls
Stage 8: Add inoculation sample to the test chamber
Stage 9: Test for two weeks
3.2.5.0
Option E – Dual Sterilization, Shared Environment
Description
This option also has two separate sterilization chambers. The sample from each
sterilization chamber is placed into separate reaction chambers, but the chambers are kept
together in a shared environment. Figure 3-5 shows a functional schematic of the system
architecture. This option has the pros and cons of a separate autoclave, few sensors, a fixed
sensor package, and a shared environment as defined in Table 3-2.
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Figure 3-5 Option E Schematic
Experimental Timeline
Stage 1: Receive inoculation sample and geological sample from outside influence
Stage 2: Add the geological samples to each autoclave
Stage 3: Autoclave to sterilize samples
Stage 4: Cool and hold for 24 hrs
Repeat Stages 3 and 4 twice more
Stage 5: Add the sterilized samples to the reaction chambers
Stage 6: Add equal parts reagent water to the reaction chambers
Stage 7: Homogenize the environment of the chambers using the environmental
controls
Stage 8: Add inoculation sample to the test chamber
Stage 9: Test for two weeks
3.3.0 Quantitative Analysis
Option A, which involves having the sterilization and testing phases in the same
chamber, was eliminated early on in the design phase due to the fact that it adds complexity
with the necessity of a moving sensor package. The mass, volume, and cost of each of the
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four remaining options were considered as shown in Table 3-3, although the estimates were
far too rough to use in the final system architecture decision. The driving requirements listed
in Table 3-1 became far more important than these three quantities as all four remaining
system architecture options are reasonable within self-imposed constraints.
Table 3-3 Design Alternative Quantitative Analysis
Shared Environment, Shared Sterilization
Separate Environment, Shared Sterilization
Separate Environment, Separate Sterilization
Shared Environment, Separate Sterilization
Mass (g)
900
1200
1400
1300
Volume (mL)
4444
4504
4612
4592
Cost
$150
$1,350
$1,750
$1,350
3.4.0 Selected System Architecture
After developing and analyzing the five different system architecture options, Option
E – Dual Sterilization, Shared Environment has been chosen. The decision process used is
outlined in Figure 3-6.
Figure 3-6 System Architecture Decision Process
First, the differences between shared and separate environments were considered.
Having separate environments had the advantage of more precise thermal control. The shared
environment, however, had more benefits. These benefits included reduced complexity due
to having only one environment to control, a broader range of possible heating options, and
better possible placement of insulation and mixers. After considering the environmental
options, the advantages of each sterilization chamber option were considered. Sterilizing
within the test and control chambers was hard to justify because of the added complexity of
moving the electrochemical sensors into the chamber after sterilization. Using only one large
sterilization chamber was appealing because it only required one thermal control system,
however, it also added complexity by needing to weigh and divide the sample into equal
volumes after sterilization. Having two sterilization chambers eliminates the need to divide
the sample, which greatly reduces the complexity of the design and fabrication. The decision
to implement a shared environment and two sterilization chambers led to the decision to use
Option E defined described previously.
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4.0 System Design-To Specifications
Author: Elizabeth Newton
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After developing the overall system architecture, several system-level design-to requirements
can be determined. These design-to requirements are driven by six PDD requirements, listed
below in Table 4-1.
Table 4-1 Driving PDD Requirements
Requirement #
PDD 4.11
PDD 4.13
PDD 4.26
PDD 4.27
PDD 4.28
PDD 4.30
Requirement
Reaction Sample Handling
Reaction Sample Delivery
Nominal Power Consumption
Peak Power Consumption
Unit Disassembly
Operational Environment
4.1.0 Reaction Sample Handling
This requirement states that steam sterilization is the necessary sterilization procedure for the
geological sample. Steam sterilization requires that the sample be heated to at least 121°C
while maintaining pressure. This is an important driving requirement for the overall system.
Since the ISEs cannot withstand temperatures above 60°C, using autoclave techniques meant
that the sterilization and testing had to occur in separate chambers, as detailed in Chapter 3:
Development and Assessment of System Design Alternatives. Several design-to
requirements flow from this PDD requirement.
4.1.1.0
Environmental Chamber
Because of the very high temperatures achieved by the autoclave chambers, insulation must
be placed between the chambers and the ISEs. This requirement contributed to the
environmental chamber design, which shields the ISEs from the heat of the autoclaves as
well as heats and cools the reaction chambers. Extra insulation must also be added on top of
the environmental chamber to further protect the ISEs.
4.1.2.0
Support Structure
Due to the high heat and pressure of the autoclaves, they had to be made out of an approved
metal, SS 316 stainless steel. They also had to have a minimum wall thickness, as detailed in
Chapter 8: Mechanical Design Elements. These requirements resulted in an autoclave design
that is very heavy. Also, the valve interface from the autoclaves to the PharMed tubing had
to follow the PDD material requirements, and is also made from SS 316 stainless steel. It
also had to withstand the high pressures of the autoclave, so the silicone seat is very sturdy.
This results in a heavy valve that is fairly difficult to open and close. These requirements
flowed down into the need for a sturdy support structure. In order to open and close the
valves without tipping the valve and autoclave assembly, the assembly will be screwed down
onto an aluminum plate, which is attached by thick aluminum spars to the bottom plate. This
design is detailed further in Chapter 8.
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4.2.0 Reaction Sample Delivery
This requirement states that the sterilized sample must remain sterile throughout its delivery
to the reaction chambers. This requirement drove the clean room assembly design-to
requirement.
4.2.1.0
Clean Room Assembly
In order to ensure that the sample pathway through the valve and tubing is sterile, any wetted
surfaces must be autoclaved in a laboratory prior to assembly. These surfaces include the
SS316 valve, PharMed tubing, Ultem 1000 reaction chamber cap, body, and floor, the
impeller for the mixer, and the ISEs. The exceptions to the autoclave requirement are the
ISEs, which cannot withstand autoclaving. Another sterilization method must be used for
these sensors. After these items are sterilized, they must be assembled in a clean room
environment. This assures that no biological material is introduced into the sterile pathway.
Once these items are assembled, they form a sealed unit, which can then be taken into the
field. This sealed, sterile unit is inserted into the rest of the instrument, which does not need
to be assembled in a clean room. The follow-on design-to requirement from this PDD
requirement is that it must be relatively simple to insert the sterile unit into the instrument
without taking it apart. This necessitated the spacing of the assemblies within the chassis and
the slots in the shelves, as seen in the drawings in Chapter 8.
4.3.0 Nominal and Peak Power Consumption
The very low power allotment for the instrument drove many of the subsystem decisions. It
also determined one system-level requirement, which is the addition of insulation throughout
the chassis.
4.3.1.0
System Insulation
Without the benefit of high-powered heating and cooling, every bit of thermal adjustment
must be conserved. This necessitated the addition of insulation throughout the system. Both
autoclaves will be heavily insulated under 2” of melamine insulation. They rest on top of an
aluminum shelf, and cork insulation will be placed between the valve and the shelf to
minimize thermal losses into the shelf. The environmental chamber will also be insulated
with melamine insulation to limit heat loss while the reaction chamber thermal control is
active. These imposed requirements will maximize the thermal control available from 30W
of power.
4.4.0 Unit Disassembly
Disassembly of the unit is important for sterilization. Every wetted surface that is capable of
being autoclaved must be able to be removed from the unit. The design-to requirement for
this PDD requirement is to make the entire unit completely able to be taken apart. This
ensures that it is simple to assemble the unit before an experiment and break it down for
cleaning after an experiment. It also allows access to parts for troubleshooting purposes.
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4.5.0 Operational Environment
The operational environment PDD requirement is two-fold; first, it implies that the
instrument must be capable of performing in a field setting, and second, it defines that
setting. This flows down into several requirements.
4.5.1.0
Instrument Mass and Volume
Because the unit must be useable in a field environment, it must be portable. Portable is
defined as being relatively easy for one person to carry. It can also be defined as the
maximum size allowable as carry-on luggage on a commercial airplane. This flows into the
requirement that the unit must weigh less than 40 lbs. It must also be equipped with handles
to make it easier to move. These are not included in the current design, but will be added to
the chassis along structurally sound points. Also, the volume of the instrument must be small
enough to be carried by one person with a minimal amount of difficulty.
4.5.2.0
Instrument Cost
Since this instrument designed for field use, it must be relatively inexpensive to replace parts.
Damage and wear are inevitable, so minimizing the cost of components is an important
design-to requirement.
4.5.3.0
Component Replacement
As mentioned with instrument cost, damage and wear are inevitable. Therefore, the
instrument must be designed so that parts can be replaced relatively simply. The chambers,
which are a fabricated component, are quite complicated and difficult to machine. The
solution to this is to make the components that are most likely to need replacing easier to
machine. The caps and bottoms to both the autoclave and reaction chambers are
manufactured separately and are generally simpler parts than the chamber bodies. Bearing
wear on the motor can be remedied by purchasing a new collar bearing and manufacturing a
new reaction chamber bottom, which is a fairly simple plastic piece. The autoclave valves
are able to be disassembled so the silicone seals can be replaced if they become worn or
damaged.
4.5.4.0
Instrument Reliability
Field instruments must be very reliable. The inclusion of moving parts must be limited and
where possible, manual backups should be available.
4.5.5.0
Field Environment
As a field instrument, the unit must work in the specified environments. This caused many
design-to requirements related to temperature. Every component of the instrument must be
rated to function at temperatures between -10°C and 40°C.
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5.0 Development and Assessment of Subsystem Design
Alternatives
Author: Ted Schumacher
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5.1.0 Reaction Chamber
5.1.1.0
Subsystem Design-to Requirements
Requirement 4.1. MiDAs shall have two chambers with minimum internal volume of 50mL.
Requirement 4.2. Each reaction chamber shall be controllable within a range of 40C to 370C
with an accuracy of ±1°C.
Requirement 4.3. Each reaction chamber shall be sealed to a pressure of 1 psi differential
from ambient pressure.
Requirement 4.4. Each reaction chamber shall be capable of supporting no fewer than 6 and
no more than 18 electrochemical sensors.
Requirement 4.5. Each reaction chamber shall have mixing capability such that each
geological sample is evenly distributed within the fluid while movement is present at each
sensor location.
Requirement 4.6. Each reaction chamber shall have a minimum of four multi-use ports for
gas and liquid exchange.
Requirement 4.7. Each reaction chamber shall be manufactured out of a list of materials
provided by BioServe. This list includes, but is not yet limited to, Polysulfone, PharMed, 316
stainless steel, and Ultem 1000.
Requirement 4.8. Each reaction chamber shall receive no less than 5 mL and no more than 25
mL of geological sample.
Requirement 4.9. The test chamber shall receive a maximum of 1 mL of inoculation sample.
Requirement 4.10. The test chamber shall receive the inoculation sample through established
aseptic techniques.
Requirement 4.18. The electrochemical sensors shall be placed at a minimum height within
the reaction chambers to mitigate sample sedimentation effects. This height shall be
sufficient to allow the sensors to be fully submerged with a minimum of 5 mL to 10 mL of
fluid.
Requirement 4.24. MiDAs shall provide its own power (between 10 W and 30 W) in a field
setting.
Requirement 4.29. One operational testing cycle shall be 14 standard Earth days, not
including power-up, sterilization, and power-down.
Requirement 4.30. MiDAs shall be able to operate in environments ranging from Antarctica
to Atacama Valley in Chile.
5.1.2.0
Requirement Analysis
The first stage in the design process for the reaction chambers was to look at requirement 4.1.
which determines the first bound on the reaction chamber volume. This set a maximum
volume for the reaction chamber of 50mL. Next requirement 4.2. was looked at stress the
need to minimize volume to maintain an accuracy of ±1°C with our heaters. The pressure
requirement 4.3 shows that they chambers need to be sealed. The reaction chambers need to
be capable of supporting a maximum of 18 electrochemical sensors specific to requirement
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4.4. They also need a mixing apparatus to stir the solution based on requirement 4.5. The
design needs to accommodate 4 multi-use ports for gas and liquid exchange from
requirement 4.6. The thickness of the reaction chamber walls is dependent upon the list of
materials defined in requirement 4.7. The minimum volume bound needs to accommodate
the geological sample from requirement 4.8. The minimum volume bound is increased based
on requirement 4.9.2. A mode of transportation for the inoculation sample must be developed
from requirement 4.10. The placement of the electrochemical sensors is specifically outlined
in requirement 4.18. The reaction chambers must be able to withstand the conditions for the
duration of the experiment based on requirement 4.29. Mass is based upon the need to
operate the field test instrument in the remote areas stated in requirement 4.30.
5.1.3.0
Internal Volume
Now that the requirements were taken into account a specific internal volume of 3.53in3
(57.92cm3) was determined from the placement of the electrochemical sensors and ensuring
all the above requirements were met. The dimensional requirements are satisfied and a trade
study to determine the material to use for the reaction chambers was undertaken.
5.1.4.0
Material Requirements
The greatest limiting requirement for our material selection was requirement 4.7. This is a
pre-selection of materials that BioServe knows to be biocompatible, inert and autoclavable.
MiDAs needs to be transported to remote areas based on requirement 4.30. There is no
specific mass requirement stated, but based on an assumption from Dr. Hoehn we cannot
exceed a mass of 50lbs (22.68kg) to accommodate the checked baggage maximum weight for
air travel. This was important in the selection and the different densities and thermal
properties of our materials are shown below in table 1.
Density
3
Ultem 1000
SS 316
PharMed
Polysulfone
5.1.4.1.0
kg/m
1270
7990
970
1220
Table 5-1 Wetted Material Properties
Autoclavable Min. Temp.
Max. Temp.
yes/no
0
C
0
Thermal Cond.
C
W/m-K
yes
n/a
170
0.22
yes
n/a
1371
16.2 (@ 1000C)
yes
-51
135
n/a
yes
n/a
140
0.12 - 0.26
Ultem 1000
Ultem 1000 is available as rods (0.375" to 6.000” diameter) and plates (0.250" to 4.000"
thick), sheets, cubes, bars, and discs at a cost of $42.98 for a 2” diameter rod and a 6” length.
Ultem 1000 is used for internal components on aircraft, automobiles, pipes, valves, circuit
boards, and microwave applications. It is FDA compliant, NSF certified, and USDA
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approved. Its advantages are that it has a very high specific strength, is easy to machine, and
is available in many different shapes and sizes. It also has a higher operating temperature
than Polysulfone, which may allow it to be used as an autoclave chamber candidate. Ultem
1000 film also has a high impact strength and good weather resistance, which may allow it to
be used as a candidate for the chassis material. It also has flight heritage from various
spaceflight experiments. A disadvantage of Ultem 1000 is relatively expensive and it may not
be able to be used as an autoclave chamber if the heating element is too hot.
5.1.4.2.0
316 Stainless Steel
316 SS is available as tubes, bars, sheets, pipes, many diameters and thicknesses at a cost of
$100 for a 2” diameter rod. PharMed is available as tubes of at least 1 foot, with internal
diameters of 1/16” to 3/4” at a cost of $12.39 for 1 foot with an internal diameter of ¾”. 316
Stainless Steel is used in food and pharmaceutical processing equipment, corrosive chemical
processing, and surgical implants. 316 SS is particularly corrosion resistant due to its higher
molybdenum content. It is meets various ASTM certifications. The advantages of using 316
SS are high strength, a high melting temperature, and excellent corrosion resistance. It is
also readily available in many shapes and sizes. The disadvantages of using 316 SS are high
density and the fact it is more expensive and more difficult to machine than plastics.
5.1.4.3.0
Polysulfone
Polysulfone is available as hexagonal rods, sheets, circular rods (diameters from 0.188” – 6”)
at a cost of $43.39 per foot for a 2” diameter rod. Common applications for this material
include electronic equipment, semiconductor processing, food service, medical, and
pharmaceutical industries (mcmaster.com). This material is FDA compliant, meets UL 94V0
standards for flammability, and is NSF certified. The advantages of using Polysulfone are its
low density, high specific strength, and easy to machineability with no special equipment
required. The disadvantages are that it may not be able to be placed in contact with a heating
element. It is also unavailable in a wide range of shapes and sizes.
5.1.4.4.0
PharMed
PharMed is flexible tubing that is resistant to chemicals and can be autoclaved. It is FDA
compliant and NSF certified and used in the food and biomedical fields. Some diameters are
vacuum-rated. The advantages of PharMed are its low density and it can be autoclaved. It is
inexpensive and available from at least one supplier in small amounts (some suppliers require
a minimum 25’ purchase). It is unable to be machined into a reaction chamber since it is
purchased in tubular form. Therefore Ultem 1000 will be used to machine the test chambers.
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5.1.4.5.0
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Material Selection
The system needs to be heated based on requirement 4.2. Due to Ultem 1000’s high thermal
properties we were able to determine that we could attach heaters directly to the shared
environment. Based on table 5-1, showing Ultem 1000’s thermal properties, it can withstand
the temperatures that will result in the shared environment. We determined to use a shared
environment based on other specifications stated in Chapter 3.
5.1.5.0
Heating Element Trade Study
A trade study for determination of a heating element was conducted. Based on requirement
4.2 and control of the temperature in the reaction chambers within the given range is
important. The temperature control of ±1°C will be delivered through the use of a control
system, not the heating element. The geometry of the chambers and the shared environmental
control area will determine how much actual surface area is available for heating The options
for heating elements are listed below:
1. Heaters using electrical resistance to produce heat.
2. Heaters using a chemical change to produce heat in an exothermal reaction
3. Heat from direct solar exposure.
5.1.5.1.0
Electrical Resistance Heaters
Electrical resistance heaters use the internal resistance of the heater to determine how much
power is dissipated for a given voltage. A heater with a resistance of 4.8 will ideally
dissipate 30W of heat when driven by a 12V supply. Electric heaters can be broken up into
groups depending on the primary type of material they are used to heat. Solid surfaces, gases
or liquids. The different types and information regarding them can be seen in Table 5-2. It
should be noted that the heaters listed in Table 5-2 were chosen from those available off the
shelf using size then power as the primary considerations. Custom heaters are available for
all types that could provide an internal resistance of 4.8, the only exception to this is the
Minco flexible heater. The watt density listed in the table for each heater is the wattage
concentration on the heater surface. This is important for heater life considerations and
material properties of the surface the heater is applied to. Higher watt densities produce
higher surface temperatures and shorter heater life spans. Changes in the internal structure of
the heater can change watt density while still maintaining the same total wattage output. The
advantages of this option are their variety of types and configurations. Their disadvantages
are that they require an electrical power source, they are very small heaters, and some types
are difficult to procure.
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Table 5-2 Electric Heating Options
Tubular
Tape or flexible
Immersion
Gases
Solid surfaces or
Liquids
possibly gases
Cartridge
Solids
Omega
TRI1212/120
Minco
HK5464R4.9L12A
Omega RI100/120
Omega
CSS01235/120
29.39W at 12V
2W at 12V
0.7W at 12V
4W at 12V
14
3.3W at
12V
30
4
31
50
34
57.6
43.6
4.9
72
205.7
36
0.208
0.275
2.45
0.167
0.058
0.334
5.5 x 1 x
1.5
0.246
O.D.x 12
long
3x3
Internal
heating
component =
tube 1.5 long
x 0.625 O.D.
0.124 O.D.
x 2 long
1.25 I.D. x
1.5 width
Weight of
example (lbs)
Price of
example
Advantages
0.4
0.2
0.01
3
0.06
0.87
$30
$28
$33.80
$115
$26
$32
Strong
sheath
Good at
heating air
Strong
sheath
Difficult
to find
small sizes
Custom
length and
resistance
needed
Direct
heating for
substance
Heating
element may
get in the
way of
mixer
High watt
density
Risks
Cheap, easy to
order custom,
Kapton coating
Clamping system
required. Best used
for conduction
heating
Requires
tight
tolerances
for
placement
Small sizes
don’t have
high
wattages
Type
Heating
application
Typical off
the shelf
example –
selected for
size then
power
Power of
example
Watt density
of example
(W/in2)
Internal
Resistance
for example
( )
Current at
12V (amp)
Overall Size
of example
(inches)
5.1.5.2.0
Strip
Gases or
solid
surfaces
Omega
PT512/120
2.5W at
12V
Band
Solids in
cylindrical
form
Omega
MBH1215200A
/120
Chemical Heaters
Chemical heaters use a chemical change to produce heat in an exothermal reaction. This
could be done by adding water to some chemical or mechanically activating the chemical
change. An example of this type of heating is an over the counter hot pack. An advantage of
this option is that they do not use electrical power. Disadvantages are that they are complex if
autonomous, needs a supply of water or mechanical mechanism to initiate chemical change,
require a supply of materials be restocked after use and are difficult to control temperature.
This last disadvantage greatly lowers the feasibility of using option 2, based on our strict
temperature control requirement 4.2.
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5.1.5.3.0
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Solar Exposure
The last option utilizes heat from direct solar exposure. One method would be to use the sun
to provide direct heating through the use of a solar oven configuration. An advantage of this
method is that it does not use electrical heating. The disadvantages are the complexity to
focus energy where needed, its difficulty to control and that the sun does not always shine.
5.1.5.4.0
Conclusion
The determination was made to use internal resistance heaters. They will be the best solution
to heat the environment in the worst case scenario using the limited power supply of 30W.
They also allow for an interface with a control system to stay within the range of ±1°C.
5.1.6.0
Cooling Element Trade Study
A trade study to determine a cooling element was conducted. This was based on requirement
4.2. The temperature control of ±1°C will be delivered through the use of a control system,
not the cooling element. The temperature could exceed 370C in the Atacama Valley in Chile
stated in requirement 4.30. There were two options for cooling shown below.
1. Passive cooling.
2. Cooling through the use of a heat switch.
3. Active cooling through TECs, which are solid state heat pumps.
5.1.6.1.0
Passive Cooling
Radiation and conduction on the outside walls of the chamber were used in the thermal
analysis to create cooling curves to determining if passive cooling was feasible. The
advantages of passive cooling are that it does not use electrical cooling and it’s very simple.
Its disadvantages are that the geometry will determine if there is enough space available for
this to work and it will take a long time. This is unfeasible due to the fact the ambient
temperature could exceed the bounds of requirement 4.2.
5.1.6.2.0
Heat Switch
Cooling through the use of a heat switch is another option. A heat switch is a device that
changes thermal conductivity with varying temperature. A substance melts inside the switch
that would then allow two internal plates to come into contact, increasing thermal
conductivity. A heat switch could be attached to a heat sink that would increase the effective
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surface area available for cooling when needed. An example of a heat switch is the Starsys
Research Diaphragm Thin Plate switch. A 0.13mm gap separates the hot and cold sides. A
paraffin layer melts at a prescribed temperature increasing in volume by over 15%. This
pushes a conducting plate across the gap, increasing the thermal conductance. The thermal
conductance ratio between open and closed configurations is 92:1. The available melting
temperature range for the paraffin is -950C to +860C. Advantages of this option would be that
it does not use electrical cooling, allows most sides of chamber to be insulated while still
allowing a surface to be available for cooling and its space flight tested – currently used on
MER for thermal regulation on batteries. The disadvantages are its more complex
implementation, cost, availability and technical data is unavailable.
5.1.6.3.0
TEC
Active cooling through TECs was another option. TECs are solid state heat pumps. An
example of a typical TEC is a Melcor CP1.0-127-05L-1-W5. This has a maximum
temperature differential between the two sides of the device of 670C when a max voltage of
15.4V is applied. This results in a max current of 3.9 Amps. The total cooling at these
maximums is 33.4W. It is very small at 1.18” x 1.18” x 0.13” (30mm x 30mm x 3.2mm) and
weighs 0.024lbs (0.011) and costs $15.54. Custom TECs are available that cascade individual
units to produce a larger maximum temperature differential. Their advantages are their
concentrated cooling power and that most sides are allowed to be insulated while allowing a
surface to be available for cooling. The disadvantage of this option is the use of electrical
power.
5.1.6.4.0
Conclusion
The ultimate decision to use TECs was based on their ability to satisfy requirement 4.2. They
will be able to heat and cool the environmental chamber within the temperature requirements.
For greater heating capability strip heaters will supplement the TECs.
5.1.7.0
Insulation Trade Study
The decision to use insulation was based on requirement 4.24. Insulation minimizes the
amount of power needed to increase the temperature of the reaction chamber and thus
meeting requirement 4.24. A thermal analysis was conducted to determine the amount and
type of insulation needed. A trade study on insulation was conducted and three options were
determined. These options exclude insulations that are unable to reach a minimum of 1400C
to come in contact with the TECs.
1. Pyrogel 6250.
2. Melamine foam sheets.
3. Fiberglass.
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Table 5-3 shows the Thermal properties of each insulation option.
Pyrogel
Melamine
Fiberglass
5.1.7.1.0
Table 5-3 Insulation Options
Thermal Cond.
Min. Temp.
(W/m-K)
(Celsius)
0.0155
-200
0.53
-50
0.0576
-97.8
Max. Temp.
(Celsius)
350
150
232
Pyrogel 6250
Pyrogel 6250 has a very low Thermal Conductivity or k value. It is also a member of the
Aerogel family and has been flight tested. It is easy to machine and can be cut with scissors.
The only disadvantage with this option is its large cost. We would have to order a minimum
roll of 4.66’ x 30.0’ (1.42m x 9.14m) with a thickness of 0.24” (6mm). This comes at a cost
of $776. Based on the suggestion of the PAB we concluded that Pyrogel is overkill and
decided to go with another option.
5.1.7.2.0
Melamine
Melamine has a higher k value, but this can be overcome by increasing the thickness of the
insulation. A great benefit is that the cost is much lower than that of Pyrogel 6250. It is easy
to machine and can be cut with scissors. We will also receive much more than we can use to
ensure duplication if there is a problem with insulation attachment. A thermal analysis was
conducted and determined that the time would be feasible based on a half inch thickness
along the walls of the reaction chamber’s environment.
5.1.7.3.0
Fiberglass
Fiberglass has a lower k value than Melamine and is very cheap. A roll of fiberglass
insulation was purchased to use for the autoclave prototyping. This was probably enough for
the entire apparatus, but there were concerns about machining the fiberglass. When you cut
fiberglass small particles waft into the air and are a safety hazard. This was a great
disadvantage and the machinist conducting the autoclave prototyping test determined not to
use fiberglass for insulation applications.
5.1.7.4.0
Conclusion
The decision was made to use Melamine to insulate the environmental chamber enclosure.
This was based on the facts that Pyrogel 6250 was deemed overkill for this project and that
fiberglass, while inexpensive, carries safety hazards while machine.
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5.1.8.0
MiDAs
December 18th, 2006
Mixing Trade Study
The decision to mix the solution was based on requirement 4.5. The electrochemical sensors
need mixing to successfully monitor the sample. There are three options to consider for
mixing.
1. Ultrasonic
2. Magnetic
3. Mechanical
5.1.8.1.0
Ultrasonic
The ultrasonic processor of choice is the Sonaer Ultrasonics P/N S900PIEZO shown in
Figure 5-1. The magnetic stirrer is yet to be determined and the mechanical mixer will be a
prototype that was previously tested in space applications.
Figure 5-1 Sonaer S900PIEZO Ultrasonic Processor
This option was unfeasible due to the large size of the mixer. We need this to fit inside the
small reaction chamber at a diameter and length much smaller than the smallest mixers
available to us at a reasonable cost.
5.1.8.2.0
Magnetic
A magnetic mixer is the second option. There is a pending test by Tufts University to
determine whether or not a magnetic mixer will affect the ISEs. If a magnetic mixer does
affect the ISEs that will immediately eliminate that option.
5.1.8.3.0
Mechanical
The third option was a mechanical mixer. A prototype was created and tested with various
types and granularities of samples with water. The test was performed visually to evaluate
the fluid flow and to observe any sedimentation that may be present. The test had some
problems, but was able to achieve the desired results.
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5.1.8.4.0
MiDAs
December 18th, 2006
Conclusion
The end result was that the prototype functioned to the desired result. This verified our
preliminary decision to use mechanical mixers. This will be the choice until we hear positive
feedback from the test at Tufts University. If this information is received then we will reevaluate the effect of a magnetic mixer and implement this in the design if need be.
5.1.9.0
Temperature Sensor Trade Study
The MiDAs project will utilize temperature sensors to verify requirements 4.2. This
verification will be achieved by placing each type of sensor inside the reaction chamber
environment. There are three options for Temperature sensors shown below.
1. Thermocouples
2. Thermistors
3. RTDs
5.1.9.1.0
Thermocouples
The advantages of using thermocouples are a variety of types and configurations, low cost,
widely available, rugged, thoroughly tested, self-powered and do not self-heat. Their
disadvantages are that they require a CJC for calibration and the sensor accuracy can reach
1°C at temperatures between 10°C and 40°C.
5.1.9.2.0
Thermistors
The advantage of using Thermistors is that they are sensitive (typically have better accuracy
then Thermocouples and RTDs). Their disadvantages are that they have a loss of linearity
and temperature curves have not been standardized to the extent of Thermocouples or RTDs.
Thermistors also require shielding from large temperatures and a current to take
measurements resulting in self-heating. These disadvantages greatly increase complexity.
5.1.9.3.0
RTDs
The advantages of using RTDs are their high accuracy, excellent stability and reusability;
they can be immune to electrical noise, they require shielding from large temperatures,
require a current to take measurements which plagues it to self-heating. These options are
shown next to each other for comparison in Table 5-4.
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Table 5-4 Temperature Sensor Comparison
Thermocouples
Model
Cost
Volume
Temp Operation Accuracy
Range Range
(1-40 °C)
Weight Diameter Length
5SRTC-TT
$54 (5
(mini connector) pack)
---
0.51mm
1m
T
---
±1 °C
5LRTC-TT
(standard size)
$58 (5
pack)
---
0.51mm
1m
T
---
±1 °C
5TC-TT (no
connector)
$39 (5
pack)
---
0.51mm
1m
T
---
±1 °C
$92
---
1.6mm
1m
JKTE
---
---
TJ36 (autoclave
probe)
Thermistors
44005
$15
T (Copper) -200 to 350 °C
---
RTD
-80 to
250 °C
2.8
60
Height
Length
Width
---
±1 °C
Self
heating
SA1-RTD
$50
---
25
2m
19
-73 to
260 °C
---
±0.5 °C
FR1328
$15
---
6
22
2.8
-70 to
500 °C
---
±0.2 °C
5.1.9.4.0
Conclusion
In conclusion the general purpose model FR1328 should work well in terms of price and
accuracy. Therefore we chose to use a RTD for the temperature measurement in the reaction
chambers.
5.1.10.0
Pressure Sensor Trade Study
The MiDAs project will utilize the use of pressure sensors to satisfy requirements 4.3. There
are three options for pressure sensors.
1. Gauge
2. Absolute
3. Differential
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5.1.10.1.0
MiDAs
December 18th, 2006
Gauge
The advantages of using gauge sensors are that they are widely available and relatively
cheap. Their disadvantage is that they measure the pressure relative to standard atmosphere.
5.1.10.2.0
Absolute
The advantages of using absolute sensors are that they measure pressure relative to vacuum,
are widely available and relatively cheap. Their disadvantage is that they require additional
sensors to measure local atmospheric conditions.
5.1.10.3.0
Differential
The advantages of using differential sensors are their ability to measure the difference
between two locations. Their disadvantage is that they are slightly more expensive then
gauge and absolute sensors. A comparison of the pressure sensors is shown in Table 5-5.
Table 5-5 Pressure Sensor Comparison
Model
Cost
Wetted
diameter
Height
Length
Width
Temp
Range
Power
Accuracy
***
Threaded
PX138
*
$85
---
26.2
28.1
27.9
0 to
50 °C
8VDC
0.1%
0.5%
No
PX139
*
$85
---
26.2
28.1
27.9
0 to
50 °C
5VDC
@2 mA
0.1%
0.5%
No
PX140
*
$120
---
26.2
28.1
27.9
-18 to
63 °C
8VDC
0.75 %
0.15%
No
Diameter
Length
12
57.9
-54 to
121
°C
24VDC
@15
mA
0.25%
0.25%
Yes
PX209
**
$195
13
* gage, absolute and differential available
** gage and absolute available
*** Linearity/Hysteresis
Note: all parts available in Gage, Absolute and Differential. Dimensions given in mm.
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5.1.10.4.0
MiDAs
December 18th, 2006
Conclusion
Pressure sensors for the reaction chambers will not be required to maintain any seal and
therefore the Model PX139 is recommended for its low power usage. Therefore we will
utilize the gauge sensor option to lower cost and have a wealth of information in respect to
their performance.
5.2.0 Autoclave
5.2.1.0
Subsystem Design-to Requirements
Requirement 4.11. The reaction samples shall be sterilized in accordance with standard
autoclave techniques.
Requirement 4.24. MiDAs shall provide its own power (between 10 W and 30 W) in a field
setting.
Requirement 4.26. Nominal power consumption shall not exceed 30 W.
Requirement 4.27. Peak power consumption shall not exceed 30 W for more than 30
seconds.
5.2.2.0
Autoclave Techniques
Standard autoclave techniques are to heat the sample to 1210C and hold it at that temperature
for 15min. This will kill the organisms that are unable to put up their protection. After the
15min. time period is finished the autoclave will cool to 300C for a period of 24 hours. At
this time the organisms will be given the chance to remove their protection and a second
autoclave cycle will begin. Three cycles will occur before the samples area sterilized and
they consist of heating the autoclave, holding it, cooling it back down and holding it at a
stable temperature of 300C. This process cannot exceed 30W. This is based on requirements
4.24, 4.26 and 4.27.
5.2.3.0
Thermal Analysis
Now that the specific requirements were taken into account a thermal analysis was conducted
to determine the feasibility of creating a chamber and running one autoclave cycle. This
analysis is based on looking at how much internal energy change is required to raise or lower
chamber temperature from -100 C to 1210C which is the required temperature for
sterilization. The various stages of the sterilization process will each have a different
temperature range and calculations for each will be shown in following sections. In general,
knowing the required internal energy change, the amount of energy available that can be
input into the system and the amount of energy that is leaving the system, it is possible to
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December 18th, 2006
calculate the time required to complete the change. The Internal energy change of a chamber
for 316 SS and the contents as a water/air mixture is shown in equations 5-1 and 5-2.
U sys  U steel  U water  Q
(5-1)
Q  [( m)(c p )(T2  T1 )] steel  [( m)(c p )(T2  T1 )] water
(5-2)
The contents of a chamber will be a 1.53in3 (25cm3) sample (modeled as water here),
0.305in3 (5.0cm3) of water (1/2 of which will get vaporized to provide steam for the
sterilization) and 1.70in3 (27.92cm3) of empty space. The mass of the contents composed of
soil (modeled as water), water, and space is 0.13lb (0.058kg). The cp for 316 steel is 452J/kgK while the cp for water is 4,230 J/kg-K. The temperature difference requires vaporizing half
the 5cm3 of water for steam. This will require the heater to supply the energy needed for the
latent heat of vaporization that the phase change requires. The latent heat of vaporization for
water is 2,257KJ/kg. This will be undertaken in five stages.
5.2.3.1.0
Stage 1
The sample is heated from a worst case ambient temperature of -100C to 1210C. This stage
requires some of the water added to the sample to be vaporized and the energy for this is
included in the calculations. The heating requirements based on these temperatures require
52.74KJ.
5.2.3.2.0
Stage 2
The sample is hold at 1210C for 15min. The energy required for this stage will be equal to the
energy lost during this time.
5.2.3.3.0
Stage 3
The sample is cooled to 200C. The water that was vaporized in stage one will condense in
this stage and the energy lost from the system is included in the calculations. The cooling
requirements for temperatures of 1210C and a lower temp of 200C is an energy change of
30.67KJ.
5.2.3.4.0
Stage 4
The sample is held for 24 hours at 200C. The energy required for this stage will be equal to
the energy lost during this time.
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5.2.3.5.0
MiDAs
December 18th, 2006
Stage 5
The sample is heated from the lower holding temperature back to the sterilization
temperature. The heating requires upper temperature of 1210C and a lower temp of 200C
returning an energy change of 41.96KJ. To complete the sterilization phase, stages 2-5 will
need to be completed again followed by another holding and cooling time represented by
stages 2-3.
5.2.3.6.0
Conclusion
The heater and cooler will transfer energy in and out of the system. A TEC operating as a
heat pump was chosen to allow one piece of hardware to perform both functions. It was
calculated that the data system would require 6W of power during the sterilization phase of
the project, leaving a max of 24W available for heating and cooling. The overall system
would require 2 chambers and each one provides samples to the reagent chambers following
sterilization. 24W is available for the heaters and coolers modeling a staggered heating cycle.
It was found that the TEC considered has an efficiency of 56% so that only 13.44W of
energy was available for an energy change to the system from the heater/cooler. A thermal
resistance network was used to model the steady state heat loss through the insulation
surrounding the chambers.
5.2.4.0
Insulation
The same insulation that was purchased and used for the reaction chamber environment will
be used for the autoclave. This Melamine insulation was used in the prototyping of the
autoclave and led to a positive result and the acquisition of the 1210C mark. The decision to
use Melamine is shown in section 5.1.7.
5.2.5.0
Material Selection
The material selection was important in the determination of how to safely seal the autoclave
which is a pressurized chamber. The material for the autoclave must be able to withstand
temperatures of 1400C and a maximum pressure of 35psi (241KPa). The autoclave chamber
material must also be highly corrosion resistant. Soils release salts when mixed with water
and heated, and the chamber must be able to withstand that corrosion. Section 5.1.4 details
some of the wetted materials available for MiDAs based on their biocompatibility and
autoclavable. Based upon the strong anti-corrosive properties and ability to withstand high
temperatures it will be used for the construction of the autoclave.
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5.2.6.0
MiDAs
December 18th, 2006
Heating and Cooling Apparatus
To determine what heating and cooling element needs to be used we looked at a variety of
options shown in section 5.1.4. Using the knowledge from this trade study TECs or passive
cooling must be chosen to feasibly cool the autoclave. A thermal analysis was conducted
using Melamine as our insulation and passive cooling was ruled out due to the large amount
of time it would take to cool (see Chapter 8 for thermal analysis). This made the decision for
us to choose TECs as our cooling option. Therefore we will use the TECs as our heating
option also. Upon further thermal analysis and prototyping (see Chapter 7 for prototyping
results) the solution to heat the side that is not in contact with the TEC to the 1210C
temperature was to use three strip heaters. These will be used in conjunction with the TEC
and allow the internal volume of the autoclave to reach the desired temperature for 15min.
5.2.7.0
Sensors
A trade study on temperature sensors was completed and a sensor was chosen based on the
information in section 5.1.9. For autoclave purposes Model FR1328 was chosen for its
accuracy and low cost (an additional Swagelok (omegalok) adapter is required for sealing the
autoclave). To determine the pressure sensors the trade study in section 5.1.10 was used. For
the autoclave, a gauge sensor will provide the necessary pressure data and will generally cost
the least. The autoclave will be pressurized through the use of a threaded connector creating a
tight seal. The Model PX209 is recommended for use to ensure this pressurization. The small
wetted diameter (13mm) is ideal for fitting an autoclave chamber if need be.
5.3.0 Sample Transportation
5.3.1.0
Requirements
Sample transportation is the act of moving the samples from the autoclave chambers to the
Reaction Chambers. This will be accomplished through the use of a tube design. Trade
studies were conducted to determine the tubing material and valve structure.
Requirement 4.7. Each reaction chamber shall be manufactured out of a list of materials
provided by BioServe. This list includes, but is not yet limited to, Polysulfone, PharMed,
316 stainless steel, and Ultem 1000.
Requirement 4.8. Each reaction chamber shall receive no less than 5 mL and no more than 25
mL of geological sample.
Requirement 4.15. The sterile reagent water shall be completely contained in both solid and
liquid form.
Requirement 4.16. The MiDAs shall aseptically deliver no more than 50 mL (within ± 5%
accuracy) of sterile reagent water to each reaction chamber.
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5.3.2.0
MiDAs
December 18th, 2006
Material Selection
Based on requirement 4.7 biocompatible, materials must be used for the wetted surfaces. To
determine the material section 5.1.4 and the materials trade study was utilized. For the soil
and water transport, PharMed is an excellent choice due to its wide operating temperature
range and availability of sizes.
5.3.3.0
Valve Selection
There is a problem with the amount of the sample trapped between the autoclave and the
valve. This section of the sample runs the risk of not being autoclaved during its cycles
which will disrupt the results of the experiment. Another belief is that too much heat will be
lost through the metal valve and that a ceramic valve should be used. For these reasons it was
determined that the preliminary selection of a ball valve would not satisfy requirement 4.11.
Other options were selected and are listed below.
1. Ceramic valves
2. Ductile iron butterfly valves shown in figure 5-2
Figure 5-2 Butterfly Valves
3. Bronze needle valves shown in Figure 5-3, below.
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Figure 5-3 Needle Valve
5.3.3.1.0
Ceramic Valves
Theoretically we could construct a ceramic valve. The problem with that is pressurizing a
machined valve brings up safety concerns. It would not lose much heat, but due to the fact
that ceramic is very brittle this will be too tough to machine and is unfeasible.
5.3.3.2.0
Butterfly Valve
To decrease the surface area in contact with the autoclave we should use a butterfly valve.
This valve satisfies the pressure and temperature requirements stated in our PDD while
minimizing the surface area conduction will flow through. The valve can also be operated
electronically. The design of a butterfly valve ensures that the sample is very close to the
bottom of the autoclave. This means that the sample with be thoroughly heated and the
Autoclaving cycles will sterilize the entire sample. This was the main problem with the valve
selection and this design will satisfy this criteria.
5.3.3.3.0
Bronze Needle Valve
The bronze needle valve will have to be welded onto the autoclave at the bottom. This would
mean that the tubing will be used with the valve to move the sample. This leaves a small but
unsatisfactory portion of the sample in the tubing. This small part will not be autoclaved and
could skew the results of the experiment.
5.3.3.4.0
Conclusion
The end result is that a butterfly valve was selected. This was ordered and taken apart to
ensure that the sample is as close to the autoclave as possible. It will be screwed onto the
autoclave and therefore be able to be removed to be sterilized separately after each
experimental run.
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6.0 Subsystem Design-To Specifications
Author: Ted Schumacher
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6.1.0 Overall System Architecture
The MiDAs project is composed of 48 parts that require drawings either from the
manufacturer or the MiDAs team. The overall system architecture is shown below in figure
6-1.
Figure 6-1 Overall System Architecture
Here you can see the Autoclaves at the top in lavender, the peristaltic pump in the back in
green, the reagent water chamber next to the pump in silver, the sample transportation
medium under the Autoclaves in yellow, the reaction chamber environment in tan, reaction
chambers in orange and chassis in white. The power system is not shown due to its limited
priority in the overall project. This is due to the fact that we are creating a prototype based on
a theoretical Mars mission. Therefore we can assume we will be receiving power from a
“Mars Rover” when in actuality this will be strictly an Earth laboratory and field instrument.
The power supply will likely come from a wall outlet or a generator. After the trade-studies
were completed each specific subsystem was designed to decrease complexity, usually in the
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form of mechanical parts. By minimizing the amount of stationary and moving parts we limit
complexity for the overall project.
The major subsystems and their corresponding components will need to be integrated into the
final project. A top level integration plan was created to understand the overall picture and
the incorporation of each individual subsystem in the scope of the overall project. The
integration plan is shown in figure 6-2. The integration plan is explained further in Chapter
11.
Figure 6-2 Top Level Integration Plan
As you can see the main structure or chassis is connected to all the main elements of the
project. This flows down from that point onto how each specific subsystem will be
assembled and the parts that make up that assembly. This integration plan breaks down the
work that needs to be completed for the project to be a success. To understand the entire
scope of the project and the vast amount of testing required an experimental timeline was
constructed and is shown in figure 6-3.
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Minutes Description
t=0
Begin
autoclave
Measurement
temperature
Test
Is data being
recorded?
pressure
t=1 to
120
approx.
t = 121
to 135
Heater is on
temperature
Cooler is off
pressure
Temperature
control above
121°C
temperature
Heater is
variable
pressure
Cooler is off
t=136
to 256
approx
t = 257
to 317
temperature
Heater is off
Cooler is on
pressure
Temperature
control
between 437°C for 1
hour
temperature
Yes/No Control
yes --------------
no
Is temperature
>= 125°C?
Is t =135?
Is temperature
<= 123°C?
Begin
cooling
MiDAs
December 18th, 2006
Is temperature
<= 35°C
Is t =317?
pressure
Is temperature
<= 6°C?
Is temperature
>=35°C?
yes
Stop, check for
failure
--------------
no
heater cooler
on
----- increment
time, move
to next
step
----- ----- stop
off
-----
--------------
on
-----
yes
--------------
off
on
no
--------------
-----
-----
yes
--------------
on
-----
no
--------------
off
-----
yes
--------------
-----
off
no
--------------
-----
on
yes
--------------
on
off
no
--------------
-----
-----
yes
--------------
on
off
no
--------------
off
off
yes
--------------
off
on
no
--------------
off
off
increment
time, move
to next
step
increment
time,
repeat until
>= 125°C
increment
time, move
to next
step
perform
next test
increment
time,
repeat until
t = 135
increment
time,
repeat until
t = 135
increment
time,
repeat until
<= 37°C
increment
time, move
to next
step
increment
time, move
to next
step
perform
next test
perform
next test
perform
next test
increment
time,
repeat until
t = 317
increment
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time,
repeat until
t = 317
t = 318
t = 636
t = 954
begin
autoclave
cycle again
begin
autoclave
cycle again
Autoclave
procedure
complete
Is t = 953?
visual
Are heater and
cooler off?
yes
off
off
no
-----
-----
yes
no
Heater is off
Cooler is off
t = 955
t = 956
begin soil
transportation
finish soil
transportation
Are valves
open?
yes
no
temperature
initialize
sensors
pressure
inoculate
Electrochemical
begin mixing
temperature
temperature
control
pressure
Electrochemical
Is pump done?
Is data being
recorded/electrochemical
zeroed?
Is test chamber
inoculated?
no
Stop, check for
failure
close valves,
begin taking
measurements,
zero
electrochemical
sensors
--------------
yes
inoculate
no
Stop, check for
failure
turn on mixers
yes
yes
no
Is temperature
<= 6°C?
Is temperature
>=35°C?
open auto clave
ejection valve
and water
valve
Stop, check for
failure
pump 25mL
water through
autoclave
increment
time, move
to next
step
continue
autoclave
cycle
perform
next test
stop
increment
time, move
to next
step
stop
perform
next test
increment
time,
repeat
increment
time, move
to next
step
stop
perform
next test
yes
stop, check
experiment for
failure
--------------
stop
on
off
no
--------------
off
off
yes
--------------
off
on
perform
next test
perform
next test
increment
time,
repeat until
t = 21116
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no
--------------
off
off
increment
time,
repeat until
t = 21116
Figure 6-3 Experiment Timeline
Now that the amount of testing is determined the work entailed in the entire scope of the
project will be able to be understood. Here the testing can begin when the first Autoclave,
sample transport and reaction chamber and assembled. This gives us the opportunity to begin
testing early in the Spring semester of 2007 and continue it on to the end of the semester.
The work breakdown structure was devised from Figures 6-2 and 6-3.
There are five subsystems that need to be integrated with the Chassis. These are the
Autoclaves, reaction chamber environment, reagent water chamber, DAQ and controls and
the power supply. These require different levels of expertise and vastly different amounts of
work load.
6.1.1.1.0
Autoclave
The Autoclave requires a cap, temperature and pressure sensors and screws for the cap
attachment. These will be interfaced with the cap. The body of the Autoclave utilizes an Oring to pressurize the vessel along with TECs and three strip heaters for heating and cooling.
A heat sink will also be attached to the rear of each TEC. The autoclaves will be machined
first to begin testing as soon as possible. This will require the largest allocation of resources
and when it is completed then the testing schedule can begin. This will give the group the
opportunity to autoclave the soil and determine if sample transport out of the autoclave will
be feasible with the current design.
6.1.1.2.0
Environmental Chamber
The reaction chamber environment houses a pressure sensor along with TECs. This will be
one of the last pieces to be assembled. The testing required will be to heat the environment
with the two reaction chambers inside. A 1psi pressure differential is needed along with
controlling the temperature based on requirement 4.2. The temperature sensors will be
housed in the reaction chambers to ensure the samples are at the exact temperature stated in
requirement 4.2. The reason the environmental chamber was chosen was to eliminate
disparity in the temperature control in both of the reaction chambers. The construction is not
too intensive and it will be able to be pushed back if need be.
6.1.1.3.0
Reaction Chambers
The reaction chambers are inside the shared environmental chamber. These are composed of
the chamber body assembly, body and environmental sensor package defined in requirement
4.4. There will be an interface in the chamber for the environmental sensors as well as a
temperature sensor and multi-use ports defined in requirement 4.6. The mixing apparatus will
be located in the bottom of each reaction chamber. The mixing trade-study is shown in
section 5.6.1. Here a mechanical mixer was chosen that requires a motor, bearing, gears and
an impeller. This system will be tested at first with the autoclave to determine if the sample
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can be transferred to it successfully. Therefore this chamber will be the second part machined
and be able to continue the rigorous testing schedule after the autoclave’s assembly.
6.1.1.4.0
Reagent Water Chamber
The reagent water chamber is needed to more the water to the autoclaves flushing the sample
down to the reaction chambers. This will be accomplished through the use of two peristaltic
pumps attached to two autoclaves. The system will require the machining of the chamber, a
temperature sensor and a strip-heater. This system is low on the priority list and will be the
last chamber to be machined.
6.1.1.5.0
Data Acquisition
The DAQ system requires an embedded CPU and an interface for DAQ. This will include all
of the 10 sensors needed for the project and satisfy the need for an interface connecting the
controls to the sensors.
6.1.1.6.0
Power Supply
The power supply will be modeled as a wall outlet and interface to the system.
6.1.1.7.0
Chassis
The Chassis will require little machining and will be the last part to be created. This will
consist of the body and some type of transportation interface to make it a field unit. The
determination at this time is using handles, but this can change based on customer preference.
Everything will be completed at least one week before the last machining day. This will give
us time for the whole integration. Integration and testing will begin as soon as the first part is
created, but we need to ensure a week lag time for any problems that might occur in the final
attachment of the entire system to the Chassis.
6.1.1.8.0
Organizational Chart
A flow-chart of the organizational chart is shown in figure 6-4. This details the specifics of
who will be working on each sub-system in the Spring Semester of 2007. The organizational
chart is explained further in Chapter 13.
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MiDAs
Project
Management
Fabrication
Design
Document
Verification and
Testing
Project
Manager
Elizabeth
Newton
Lead
Fabrication
Engineer
Dave Miller
Design
Engineer
Chuck
Vaughan
Systems
Engineer
Shayla
Stewart
Assistant
Project
Manager
Ted
Schumacher
Assistant
Fabrication
Engineer
Sameera
Wijesinghe
Design
Engineer
Jeff Childers
Software
Engineer
Steven To
Assistance as
Needed from
Team
Assistance as
Needed from
Team
Assistance as
Needed from
Team
Figure 6-4 Organizational Chart
6.2.0 Subsystem Design
6.2.1.0
Chassis Design
The Chassis component will be assembled using Aluminum. This is due to the
inexpensiveness of Al and its low relative density. Requirement 4.7 states: Each reaction
chamber shall be manufactured out of a list of materials provided by BioServe. This list
includes, but is not yet limited to, Polysulfone, PharMed, 316 stainless steel, and Ultem 1000.
This refers to the wetted materials of the project. The Chassis will not come into contact with
the sample and therefore is not beholden to requirement 4.7. The Chassis is made up of two
plates that are 6.0” x 4.0” with a thickness of ¼” (15.0cm x 0.64cm x 0.16cm). These plates
will be attached by Al L-shaped brackets at each of their four ends. These brackets have
dimensions of 4.0” x 0.5” x ¼” (10.2cm x 1.27cm x 0.64cm). The mass for the entire Chassis
is 1.15Kg. The Chassis will be assembled using screws attached to the L-shaped brackets and
the plates. The Autoclaves, reagent water chamber, reaction chamber environment, DAQ and
control system and power supply will all be attached to the Chassis.
6.2.2.0
Autoclave Design
The Autoclaves will be constructed of 316 Stainless Steel. This determination was shown in
section 5.1.3.1. Through a mass analysis based on the dimensions from the Autoclave
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prototype in Chapter 8 the mass of the Autoclaves is 4.17lbs (1.89Kg). Melamine insulation
was chosen to house the Autoclaves as described in section 5.1.5. There is a 2” diameter to
the insulation which is a mass of 0.0217lbs (9.83g). The TECs will be attached to the flat side
of the Autoclaves. The two TECs have a combined mass of 0.794lbs (360g). Therefore the
entire Autoclave system (Autoclaves, TECs and insulation) has a total mass of 4.99lbs
(2.26Kg).
6.2.3.0
Reagent Water Delivery Design
The reagent water system is made up of the peristaltic pumps, the reagent water chamber,
and the tubing required to transfer the fluid to the autoclaves. The peristaltic pumps are
purchased and weight 0.140lbs (63.5g). The reagent water chamber will be designed with the
dimensions stated in Chapter 8 and has a mass of 0.291lbs (132g). The tubing required to
transfer the reagent water has a small diameter. This relates to a mass of 0.026lbs (12g).
Therefore the total mass of the reagent water system is 0.457lbs (208g).
6.2.4.0
Environmental Design
The reaction chamber environmental system is composed of the reaction chambers,
insulation, TECs and mixers. The reaction chamber environment is Al because it is not
beholden to requirement 4.7. It has the dimensions of 6.80” x 4.70” x 3.92” (17.28cm x
11.95cm x 9.95cm). Based on a 1/8” (0.5cm) thickness for the Al walls, the mass of the
chamber is 1.45lbs (656g). The insulation covers the outside of the chamber and has a mass
of 0.0214lbs (9.72g). The TECs have a mass of 0.794lbs (360g) and the mixers have a mass
of 0.21lbs (95.8g). Therefore the total mass of the reaction chamber environmental system is
2.47lbs (1.12Kg).
6.2.5.0
Data Acquisition Design
The DAQ system and control system are composed of all the sensors, power supply interface,
embedded CPU and the environmental sensor package. We are using a temperature and
pressure sensor to measure the ambient conditions outside the MiDAs apparatus. A pressure
and temperature sensor will be used to measure the conditions inside the Autoclaves.
Temperature sensors will be inside the reaction chambers but there will only be one pressure
sensor in the reaction chamber environment. There will be a temperature sensor inside the
reagent water chamber to ensure liquid conditions. There are a total of 6 temperature sensors
and 4 pressure sensors. Along with the embedded CPU and the DAQ the total mass is 0.64lbs
(292g).
6.2.6.0
Mass
Overall the total mass stands at 30lbs (13.9Kg) and can successfully be transported and used
as a field instrument. A diagram of the mass analysis is shown in figure 6-5.
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2 Pumps
127g
Insulation
9.83g
Water Chamber
132g
2 Autoclaves
1890g
2 Valves
1450g
4 TECs 720g
Environmental
Chamber 656g
2 Reaction
Chambers 173g
Chassis
1150g
2 Mixers
95.8g
CPU and DAq
(not shown)
292g
Internal Mass: 7.10kg (15 lbs)
Total Mass: 13.90 kg (30 lbs)
Sensors
(not shown)
10.0g
Figure 6-5 Mass Analysis
6.3.0 Power requirements
6.3.1.0
Requirements
The power requirements are 4.24, 4.25, 4.26 and 4.27. The power consumption for the
autoclave cycle is listed below. The numbers show the steps in the autoclave process.
1. 5.5 W continuous power consumption by Data Acquisition System (DAQ)
2. 0.5 W continuous power consumption by temperature and pressure sensors
3. 12 W per autoclave heater/cooler (2 autoclaves)
4. Temperature of autoclaves begins at -10°C (worst-case)
5. Time to heat from -10°C to 121°C is 234 min (see thermal analysis)
6. Hold at 121°C for 15 min – consumes 1.4 W
7. Time to cool from 121°C to 20°C is 117 min (see thermal analysis)
8. Hold at 20°C for 24 hrs (1440 min) – consumes 1.4 W
9. Time to heat from 20°C to 121°C is 205 min (see thermal analysis)
Figure 6-6 shows the power summary for the entire sterilization phase of the MiDAs
operational cycle for simultaneous autoclaves. This is based off the nine steps that use power
in autoclave cycle. The autoclaving process must be cycled three times to ensure sterility of
the soil. The maximum power consumption is the maximum allowable at 30W, with no
buffer built in.
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Power Summary (Sterilization Phase)
Power Consumption (W)
35
30
25
Autoclave Heater/Cooler 1
Autoclave Heater/Cooler 2
DAq
Temp/Pressure Sensors
Total Power
20
15
10
5
0
30
0
60
0
90
0
12
00
15
00
18
00
21
00
24
00
27
00
30
00
33
00
36
00
39
00
0
Operation Time (min)
Figure 6-6 Power Summary (Full Sterilization Phase)
The entire sterilization phase takes 3,930mins (65.5 hrs or 2.73 days). A summary of the
power used after each section of the experiment is started.
Heat to 121 C
Hold at 121 C
Cool to 20 C
Hold at 20 C
Heat to 121 C
Hold at 121 C
Cool to 20 C
Hold at 20 C
Heat to 121 C
Hold at 121 C
Cool to 20 C
Table 6-1 Power Summary
Start
Time
Duration
(min)
(min)
0
234
235
15
251
117
369
1440
1810
205
2016
15
2032
117
2150
1440
3591
205
3797
15
3813
117
Stop Time
(min)
234
250
368
1809
2015
2031
2149
3590
3796
3812
3930
Due to figure 6-6 to ensure that peak power consumption is minimized the autoclaves will be
staggered. Figure 6-7 shows the power summary for the entire sterilization phase of the
MiDAs operational cycle for staggered autoclaves. Staggering the autoclaves allows each
autoclave heater/cooler to run on higher power (20W compared to 12W). The autoclaving
process must be cycled three times to ensure sterility of the sample. The maximum power
consumption is 26W, which gives a 4W buffer.
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Power Summary (Sterilization Phase)
Power Consumption (W)
30
25
Autoclave Heater/Cooler 1
Autoclave Heater/Cooler 2
DAq
Temp/Pressure Sensors
Total Power
20
15
10
5
0
30
0
60
0
90
0
12
00
15
00
18
00
21
00
24
00
27
00
30
00
33
00
36
00
39
00
0
Operation Time (min)
Figure 6-7 Power Summary (Sterilization Phase) - Staggered Autoclaves
The entire sterilization phase takes 3,307mins (55.1 hrs or 2.30 days).
Table 6-2 Power Summary (1st Autoclave)
Start Time
Duration
Stop Time
(min)
(min)
(min)
Heat to 121 C
0
90
90
Hold at 121 C
91
15
106
Cool to 20 C
107
46
153
Hold at 20 C
154
1440
1594
Heat to 121 C
1595
72
1667
Hold at 121 C
1668
15
1683
Cool to 20 C
1684
46
1730
Hold at 20 C
1731
1440
3171
Heat to 121 C
3172
72
3244
Hold at 121 C
3245
15
3260
Cool to 20 C
3261
46
3307
Table 6-3 Power Summary (2nd Autoclave)
Start Time
Duration
Stop Time
(min)
(min)
(min)
Heat to 121 C
154
90
244
Hold at 121 C
245
15
260
Cool to 20 C
261
46
307
Hold at 20 C
308
1440
1748
Heat to 121 C
1749
72
1821
Hold at 121 C
1822
15
1837
Cool to 20 C
1838
46
1884
Hold at 20 C
1885
1440
3325
Heat to 121 C
3326
72
3398
Hold at 121 C
3399
15
3414
Cool to 20 C
3415
46
3461
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Figure 6-7 as well as Tables 6-2 and 6-3 show that staggering the autoclaves is beneficial in
more than respect. The autoclave heaters/coolers can run on higher power, which reduces the
time to heat and cool to the desired temperatures. The entire sterilization process then takes
55.1 hrs instead of the 65.5 hrs that the simultaneous autoclaving requires. The maximum
power consumption for sterilization is also reduced to 26 W which leaves buffer for the
maximum power requirement.
6.3.2.0
Power
The power requirements are 4.24, 4.25, 4.26 and 4.27. These must be followed to ensure the
sample remains at the correct temperatures while in the reaction chambers. These require
power for heating and cooling. It was calculated elsewhere that during the testing phase,
electronics and mixers may require 20W of power. This leaves 10W for the thermal control
of the environmental box. Using the geometry defined above with a 10W rated heater/cooler
that is capable of supplying 5.6W of energy (only 56% efficient) and insulation allowing
only 1.55W for a worst case energy loss, a power and time model for the overall sterilization
phase was constructed. A 10W heater/cooler will drawn 0.83 amps (P=VI) at 12V. At 12V, a
1.55W heater or cooler will draw 0.129 amps. This analysis was used for initial and
maintenance cycles.
6.3.2.1.0
Heating
The initial heating problem using the worst case scenario for heating the test chambers and
surroundings is from the coldest ambient temperature (-100C) to the lowest reaction chamber
temperature (40C). A 10W heater with 56% efficiency results in 4.05W heating available
(includes loss through insulation at worst case). The total time required for this energy
change 54.2mins. or 0.9hrs. The power needed assuming a 12V supply is 0.75Amp hrs.
6.3.2.2.0
Cooling
The initial cooling problem using the worst case scenario for cooling the test chambers is
when the reagent water entering into the test chamber is at the highest temperature allowed
(600C) and is needing to be cooled down to the to the highest reaction chamber temperature
(370C). These calculations assume the entire system gets to 600C which is probably not true.
This assumption is made for simplification and will result in a larger energy requirement that
is actually necessary. A 10W heater with 56% efficiency results in 5.6W cooling available
(does not include loss through insulation since highest ambient temperature is 300C, loss of
energy through the insulation will aid this cooling process. It is not taken into account to
provide a worst case scenario). The total time required for this energy change 64.4mins. or
1.07hrs. The power needed assuming a 12V supply is 0.89Amp hrs.
6.3.2.3.0
Thermal Maintenance
The maintenance problem for heating and cooling begins with the establishment of an
equilibrium temperature. This can be established within the environmental control box; the
system may lose or gain 1.55W at a steady rate through the sides of the container. 1.55W will
have to be supplied by the heater/cooler continually over the 2 week testing period for a
worst case situation. This implies 43.34amp hrs over a two week period.
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Heating and cooling will be supplied by a TEC acting as a heat pump. It will draw 10W of
power at most and supply a max of 5.6W energy for heating or cooling. The insulation will
allow for at most 1.55W energy transfer between the inside and outside of the box. The initial
heating or cooling for the worst cases can be accomplished in around an hour and for under 1
amp hour of power each. The maintenance of the temperature for 2 weeks can be
accomplished for 43.34amp hrs. This is deemed feasible under requirements 4.24, 4.25, 4.26
and 4.27.
6.4.0 Component List
A list of the components purchased for the project is shown below in Table 6-4. This list has
received most of its components from BioServe in kind. The component list is shown on the
next page.
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Table 6-4 Component List
Component list for MiDAs project
AC = Autoclave
ST = Sample Transportation
RC = Reaction Chamber
WC = Water Chamber
Component
Autoclave Body (2)
Autoclave Cap (2)
Autoclave Bottom (2)
TEC (4)
Heat Sink (4)
Reaction Chamber (2)
Reaction Chamber Cap (2)
DC Motor (2)
Impeller (2)
Mixer Controller (2)
Reaction Chamber Environment
Peristaltic Pump (2)
Pump Mount (2)
PharMed Tubing (2)
DAQ
Embedded CPU
Chassis
Melamine Insulation (24"x48"x2")
Temperature Sensors (6)
Press Sensors (4)
ISE Package (2)
Ultem 1000 (24"x2" rod)
316 Stainless Steel 2 (12"x2.5"
rods)
Aluminum (48"x48"x0.0625")
Bearing Rotary Shaft
Motors (2)
Syringe
Controller (2)
Test Tubes (2)
Brushless fan
Strip Heater (7)
10μm soil
Peristaltic Pump Tubes (2)
Ball Valve
Butterfly Valve (2)
O-ring
309 SS for AC prototype
Multimeter
Wire Control Switchboard
Procurement
Machined
Machined
Machined
Purchased
Purchased
Machined
Machined
Purchased
Machined
Purchased
Machined
Purchased
Machined
Machined
Purchased
Purchased
Machined
Purchased
Purchased
Purchased
Purchased
Purchased
Subsystem
AC
AC
AC
AC/RC
AC/RC
RC
RC
RC
RC
RC
RC
WC
WC
ST
DAQ
DAQ
Chassis
AC/RC
AC/RC
AC/RC
RC
RC
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Purchased
Screws
Purchased
AC
Chassis
RC
RC
ST
DAQ
ST
Chassis
AC/RC
ST
ST
ST
ST
AC
AC
Prototyping
DAQ
AC/RC
Chassis
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7.0 Project Feasibility and Risk Assessment
Author: Elizabeth Newton
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7.1.0 Autoclave Prototype
The biggest “tall pole” of the MiDAs instrument prior to PDR was autoclaving. The team
was uncertain if the chambers could be heated within the power constraints, if the heat losses
through the insulation were adequately modeled, and if TECs could heat the autoclave
chambers to 121°C. Also, the pressure seal needed to be verified at the elevated
temperatures. To mitigate these risks, an autoclave chamber was fabricated out of SS304
stainless steel and tested using TECs, strip heaters, melamine insulation, and temperature and
pressure sensors. The setup also allowed us to gain familiarity with the instrumentation,
mechanical interfaces between sensors and the chamber, and a rudimentary control system
consisting of a LabView code, sensors, and switches.
Prior to the fabrication of the autoclave, thermal analysis was done on the chamber using
SolidWorks. Figure 7-1 shows the results of that thermal modeling.
Figure 7-1 Autoclave Thermal Analysis
The model in Figure 7-1 shows a steady-state thermal analysis. A heat source was modeled
on the flat, red area and was assumed to reach a temperature of 150°C. The thermal model
also assumed a 2W heat loss from every surface, which is comparable to our insulation
estimates. This model shows that heating the autoclave from one point creates a very large
thermal gradient of nearly 30°C across the chamber. This created a problem because the
largest temperature difference a thermoelectric heat pump can achieve is approximately
130°C. That means that if the ambient temperature is 20°C, the TEC would be sufficient to
heat the flat area of the chamber to 150°C. However, since the instrument must be able to
operate down to -10°C, using only a single-stage TEC to heat will not work.
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The solution to this problem is using strip heaters. Strip heaters are much more efficient than
TECs in heating, and strip heaters can be placed easily under the melamine insulation, and
are easier to integrate with fewer components. Strip heaters placed around the exterior of the
chamber will ensure much more even heating and a lower thermal gradient throughout the
chamber.
After performing this thermal modeling, the chamber was constructed. Figure 7-2 shows a
SolidWorks model of the prototyped chamber with mounting, lid, and seal interfaces.
Sensor Ports
Cap
Screw Holes
O-ring
Body
Figure 7-2 Autoclave Prototype Model
In Figure 7-2, the flat area in front is where the TEC was attached. A silicone O-ring fit into
the groove around the top of the body. Temperature and pressure sensors were inserted into
the #10-32 threaded sensor ports on the cap. SS304 stainless steel was used for the prototype
because SS304 and SS316 stainless steels are very similar, and the aerospace machine shop
had some SS304 on hand that we could readily use.
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Figure 7-3 Autoclave Prototype Setup
Figure 7-3 shows the setup of the autoclave prototype. The autoclave itself is encased in the
grey melamine insulation on the left. The power supply at the top left provides power to the
strip heaters and TEC. The control board and the pressure sensor are shown in the center.
The laptop shows the LabView interface that was used to read the temperature and pressure
sensors, and to control the solid state relay switches. The pressure sensor was mounted to the
cap and read the internal pressure of the autoclave. The temperature sensor was attached to
the exterior of the body on the far side of the heater. Figures 7-4 and 7-5, below, show the
results of the prototype experiment.
35
pressure (psi)
30
25
20
15
10
5
0
0
20
40
60
80
100
120
140
time (min)
Figure 7-4 Autoclave Pressure Results
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Figure 7-4 shows the results of the pressure readings, as read by LabView. The internal
pressure was expected to reach 15 psi (gauge pressure). The actual results showed that the
internal pressure was much higher than expected, reaching a maximum of nearly 35 psi. This
is because the temperature sensor was mounted outside the autoclave chamber, while the
internal pressure is dependent on the highest internal temperature based as tabulated in steam
tables. This indicates that the internal temperature was higher than the external sensor
readout shows, and thus the internal pressure was higher than was expected. For the final
design, the internal temperature can be controlled better to the desired set point of 121°C
with minimal overshoot and hence, with lower pressures. This is done by reducing the
thermal gradients with strip heaters and placing the temperature sensor in a better location.
The pressure dip at around 120 minutes was caused by switching pressure sensors. It was
thought that pressure sensor was reading incorrectly when it continued to climb well past the
expected point, so a different sensor was inserted in parallel to the recording sensor to
validate the sensor reading. Some pressure was released during the addition of the second
sensor. Once the temperature reached steady state, the pressure remained constant, but was
still higher than expected based on the steam tables due to the thermal gradients between the
sensor and the heat source.
140
temperature (deg C)
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
time (min)
Figure 7-5 Autoclave Temperature Results
Figure 7-5 shows the temperature readings from the sensor located on the exterior of the
autoclave. This graph shows that the exterior temperature on the far side of the heater was
able to reach 121°C. This indicates that the heaters are able to heat the autoclave sufficiently,
and that the insulation is sufficient to reach the desired target temperature under our power
constraints at the tested ambient conditions. It took approximately 130 minutes to heat the
exterior of the chamber to 121°C. This time will be extended somewhat when the geological
sample and more water are added due to the added heat capacity.
Overall, the autoclave prototype was a success, both in performance and experience gained.
The strip heaters and TECs will be sufficient to heat the autoclaves to 121°C in a reasonable
amount of time. From the thermal analysis, it was decided that placing strip heaters around
the outside of the autoclave body will provide more even heating, reduce the gradients and
ensure lower pressures with more even temperature distribution at the desired set point.
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7.2.0 Mixing Prototype
The second tall pole from PDR was mixing. The team was concerned that a small, low-RPM
mixer would not be sufficient to mix a 50/50 mixture of small-grain geological sample and
water. To mitigate this risk, a mixer was constructed and tested with soil.
Originally, there were three mixing options under consideration: ultrasonic, magnetic, and
mechanical. Ultrasonic mixing was initially the most promising option due to its heritage in
the MECA project. Ultrasonic mixing works through a probe inserted into the mixing
chamber. The probe vibrates, sending off pressure waves, and these waves mix the solution.
However, the frequency of ultrasonic mixing is dependent on the length of the probe that is
inserted into the mixing chamber, with longer probes having a lower frequency. This is a
problem because frequencies above 18 kHz create pressure waves strong enough to rupture
cell membranes and destroy life. Given the small length of the MiDAs reaction chambers, a
probe length small enough to fit in the chamber creates a frequency above 18 kHz.
Therefore, ultrasonic mixing was not considered a viable option and was discarded.
Our second mixing option was magnetic mixing. Magnetic mixing is common in chemistry
applications. A bar magnet is dropped into the mixing chamber and a varying magnetic field
below it causes the coupled magnet in the solution to spin. This is an attractive mixing
option because there is no complicated interface (rotating shaft seal) between the mixer and
the reaction chamber. However, the spinning magnet may interfere with the performance of
the electrochemical sensors. This option is still pending research by Tufts University, but
until that research is complete, the magnetic mixing option is not being pursued.
The final option for mixing was a mechanical coupled mixer, using a dynamic shaft seal.
Due to the small size of the reaction chamber, no COTS mixer could be found that met our
requirements. Therefore, the MiDAs team designed a mechanical mixer to prototype. The
prototype mixer is shown in Figure 7-6.
Impeller
Chamber
Crossbars
Gasket
Bearing Collar
Motor
Figure 7-6 Prototype Mixer
For the prototype, the impeller and crossbars were made of wood, though in the final design,
they will be made of Ultem 1000. The rubber gasket was press-fit over the impeller. The
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gasket was then press-fit into the central ring of the bearing collar, which freely rotates
within the outer ring. The bearing collar was epoxied into the red chamber lid, which
screwed into the chamber. The small metal drive shaft on the motor fit into a hole drilled
into the bottom of the wooden impeller.
A mixture of approximately 3:1 water and soil was added to the top of the chamber. The soil
was 10-micron grain-size soil of unknown chemical composition, obtained from the
Geotechnical Department at CU-Boulder.
Soon after the mixing prototype was assembled, there was trouble with the way the motor
attached to the impeller. This was due to a poor connection between the motor and the wood,
which will not be a problem with our actual design. However, this necessitated manual
turning of the drive shaft during prototyping.
Despite the hand-turning of the drive shaft, the overall mixing design proved successful. The
crossbars were able to cause fluid movement around the sides of the chamber. Sediment did
accumulate at the bottom of the chamber, however. Therefore, our final impeller design will
employ scoop-shaped crossbars very close to the bottom of the chamber to ensure that soil
does not accumulate on the bottom.
The only concern remaining with the mixing is the bearing collar and shaft seal. Though the
collar is designed to be shielded from dirt, it may accumulate sediment, which will cause
friction within the bearing. If this is determined to be a problem, there are other interfaces
that can be used, such as a sealed gearbox. The floor of the reaction chambers is designed to
be replaceable if a new design is needed.
7.3.0 Sample Transportation Prototype
Though mixing and autoclaving were the only tall poles identified prior to PDR, sample
transportation also proved to be problematic. As more research was done into valves and
tubing, it appeared as though transporting the geological sample from the autoclaves into the
reaction chamber would be difficult due to friction with the tube walls and obstructed flow
through the valve. To mitigate this concern, the MiDAs team performed a prototype
experiment of the sample transportation.
To perform this prototype, a ¾” ball valve and ¾” internal-diameter tubing were obtained.
Some of the 10-micron soil sample obtained from the Geotechnical Department was poured
through the valve and tubing to see how much passed through. The soil was weighed before
and after being poured through the valve to verify how much soil would be captured in the
valve and on the valve and tubing surfaces.
Initially, the sample was poured dry onto the closed valve, which was then opened. The
sample passed through the ball valve and through a clear tube. Using this method, only about
30% of the sample made it through the valve and tube. This indicates that the soil cannot be
satisfactorily transported dry.
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For the second test, the dry sample was again poured onto the closed valve, which was
opened. This time, however, water was trickled onto the soil to flush it through the tube.
Using this method, about 95% of the soil/water mixture passed through the tubing. From
these results, it was determined that using water to flush the soil is a satisfactory solution. To
mitigate the issue with flow obstruction, the inner diameter of the tubing will be increased to
1” for the final design. This will create a straight, 1”-diameter drop from the autoclave,
through the valve and tubing, and into the reaction chamber.
There was also some concern about how steam-sterilization would affect the consistency of
the sample. It was thought that autoclaving the soil could cause it to bake into a solid brick
inside the autoclave, preventing soil transportation. To test this, a sample of 10-micron soil
was autoclaved in a standard laboratory autoclave. Several drops of water were added to the
soil before being placed into the autoclave. After a full autoclave cycle, the soil had not
changed consistency. It was slightly damp, but was still loose and showed no signs of
clumping.
Based on these tests and the changes to the design of the valve and tubing for the final
design, transportation of the soil is less of a concern than it was just after PDR.
7.4.0 Risk Assessment
Though prototyping the autoclaving, mixing, and sample transportation mitigated some of
the risk associated with the design of the MiDAs instrument, some risk still remains. These
risks are shown in Table 7-1.
Medium
Severity
High
Table 7-1 Risk Assessment Chart
•Autoclave
•Mixing
•Sample Transport
•Machining Time
Low
•Budget
•Reaction
Chamber Thermal
Control
Low
Medium
High
Probability
The risks are categorized by low, medium, and high severity and probability. Severity is a
measure of how much impact the risk will have on the project and how difficult it is to work
around the risk. Probability reflects a risk’s chances of actually coming to pass.
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Exceeding our budget is currently the lowest severity and probability risk. With our current
estimates, we remain $3,500 below the allotted budget of $8,000 (see Chapter 13: Project
Management Plan for more details on the budget). The chances of exceeding that budget are
small, but if it is exceeded, there is the possibility of obtaining more funding from BioServe,
the Undergraduate Research Opportunities Program (UROP), or the Engineering Excellence
Fund (EEF).
The autoclaving and mixing are also not greatly concerning. Both risks were mitigated
somewhat during prototyping. Though the consequences of those risks are high, the chances
of them developing into problems are slim. Off-ramps for autoclaving include adding more
heaters and insulating the valve interface more if it fails to achieve the necessary
temperature. Off-ramps for mixing involve changing the interface from the motor to the
reaction chamber through the use of better-sealed bearings and joins. The floor of the
reaction chamber and the interface between the valve and the autoclave are removable, which
will allow easy redesigns if the designs change and a new interface is needed. It is much
easier to fabricate the floor or valve interface than to remake an entire chamber, so time is
saved in the case of redesigns.
Running over on machining time is a high-probability risk. Due to unforeseen difficulties in
the machining process and a general lack of machining experience, it will probably take
longer than expected to fabricate parts. This risk is not very severe, however, due to the
number of off-ramps. First, some machining will be done over Winter Break to get a head
start on the fabrication process. Second, the Lead Fabrication Engineer gained valuable
experience in working with stainless steel during the course of the autoclave prototype
process. This will allow much faster fabrication of the actual autoclave chamber. Third,
extra time for machining has been allotted in the schedule to add a safety factor to the
schedule. Fourth, the MiDAs team has access to BioServe’s machine shop. Their fabrication
engineer, Don Geering, will be available to assist the team in making parts that are complex
or too time-consuming.
Despite prototyping, transportation of the sample is still concerning. Problems could develop
with the valve interface, such as soil becoming stuck in the valve, preventing it from closing
properly. These risks can be mitigated by thoroughly cleaning the valve and its silicone seal
before each test and performing a system check prior to testing to ensure that the valves are
working properly.
Thermal control of the reaction chambers may also be problematic. The TECs should be
sufficient to heat and cool the environmental chamber as necessary, but the actual control of
the temperature may not work as planned. However, the MiDAs team has the assistance of
experts at BioServe who can help improve the design to obtain the specified accuracy and
gradients under the power limitations.
Overall, there are no major concerns to the MiDAs team at this time. The instrument will be
able to be fabricated and tested in the allotted amount of time and money. Though design
changes are inevitable, the current design, as laid out in Chapters 8, 9, and 10, is solid and
should be very close to the final design.
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8.0 Mechanical Design Elements
Author: Dave Miller
Additional SolidWorks models provided by Sameera Wijesinghe, Jake Freeman (BioServe)
and Paul Koenig (BioServe)
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This chapter provides details on the individual components used in the system. Mechanical
drawings for parts that will be manufactured are found in Appendix A. Figure 8-1 shows a
side view of the system with all the insulation removed for clarity. The reaction chamber on
the right side has also been removed to show the mixing mechanism within.
Sterilization
Reagent
chambers
water
chamber
TEC with
heat sink
Tubing
Valve
Peristaltic
pumps
Reaction
chamber
Mixer
impeller
Mixing
motor
Mixer
couplings
Environmental
control chamber
Figure 8-1 Overall System
8.1.0 Sterilization Chambers
The sterilization chambers will sterilize the samples before they enter the reaction chambers.
It was determined from the overall system architecture design that two separate sterilization
chambers will be required.
PDD Requirements:
There are two requirements for the reaction samples that drive considerations for the
sterilization chambers. The first defines the minimum size of the sterilization chamber while
the second helps define the geometry and material needed.
4.13: Reaction Sample Delivery: One pre-measured reaction sample shall be delivered to
the test chamber and one pre-measured reaction sample shall be delivered to the control
chamber. Both samples shall maintain sterility throughout delivery.
o Requirement 4.8: Each reaction chamber shall receive no less than 5 mL and no more
than 25 mL of geological sample.
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4.11: Reaction Sample Handling: The reaction samples shall be sterilized in accordance
with standard Autoclave techniques.
o Standard autoclave techniques implies
o 121 C, hold for 15min
o Cool to 20 C, hold for 24hrs to allow spores to open
o Repeat 3 times
There are several requirements that pertain to the heating, cooling, and power available for
the sterilization chambers. These requirements are directly related to the thermal analysis
performed to model the timeline for the experiment. This analysis is shown after the
geometry and materials have been detailed.
4.26: Nominal Power Consumption: Nominal power consumption shall not exceed
30 W.
4.27: Peak Power Consumption: Peak power consumption shall not exceed 30 W for more
than 30 seconds.
4.30 Operational Environment: MiDAs shall be able to operate in environments ranging
from Antarctica to the Atacama Valley in Chile.
o Ambient temperatures ranging from -10 C to 30 C
8.1.1.0
Volume and Dimensions
Requirements 4.13 and 4.11 define the minimum internal volume required for each chamber.
5mL water will be added to the chamber for use in autoclaving and 10 mL of space will be
provided so the sample is not tightly packed. This implies the total minimum internal
volume for the chamber is 40 mL. The internal sterilization chamber geometry will be a
cylinder with a tapered base to aid in sample transport after sterilization. The internal
diameter of chamber shall be 3.81 cm (1.5 in) to accommodate a 2.54 cm (1.0 in) diameter
sample transport pathway leading to the reaction chambers. The sterilization chambers
require both heating and cooling to produce the required sterilization temperatures. This
directly influences the external sterilization chamber geometry. The chambers shall have
four flat surface areas to accommodate the chosen heaters and cooler. Each of these square
surfaces shall be 4.06 cm (1.6 in) on a side. Along the upper and lower edges of the
chamber, flanges are used for compression fittings for the lid and bottom. Each of these is
0.51 cm (0.2 in) thick. The total height of the chamber is 5.1 cm (2.0in) to accommodate
these features. The internal volume of the chamber with these features is approximately 65
mL. This is well above the minimum of 40 mL required, but is the minimum possible with
the restraints on the external configuration.
The lid to the chambers shall have surface area sufficient to for allow temperature and
pressure sensors as well as a pressure release safety valve. It was determined in the overall
system architecture that reagent water would be used to flush the samples out of the
chambers once the sterilization has been completed. A port for this is also located on the lid.
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All of these ports on the lid are threaded for a #10-32 Berwick fitting. The lid is attached to
the body of the sterilization chamber by six #4 screws that compress a silicone o-ring to
provide sealing. The external diameter of the chamber shall be 6.1 cm (2.4 in) to
accommodate these features.
The bottom of the chamber is attached to a valve interface using a method similar to the one
the lid employs. Six #4 screws are used to provide a compression seal with an o-ring placed
on the bottom of the chamber. The housing for the valve selected has a 8.6 cm (3.4 in)
diameter. This effectively blocks any access to the bottom of the sterilization chamber from
below. Removal of the sterilization chamber from the valve interface is therefore
accomplished from above. A flange on the bottom of the chambers is required to provide the
necessary area for these screws. This flange is 0.64 cm (0.25 in) thick and has an outer
diameter of 8.6 cm (3.4 in). An assembly of the sterilization chamber including the lid, body
and valve interface is shown in Figure 8-2. The drawings for these components are in
Appendix A.
The design of this subassembly which has separate components for the lid, body, and base
will facilitate any future changes needed. The lid can easily be redesigned for alternate
sensor ports, reagent water supply methods, and potentially automated sample supply
methods. The base can also be easily redesigned for interfacing with an alternate valve
assembly. By maintaining the same interface between these components and the body,
reduced manufacturing and testing times can hopefully be achieved.
Temp and Pressure ports
#4 screw holes
O-ring groove
Flange for
connection to valve
interface
4 flat surfaces:
1 cooler
3 heaters
Valve interface
1.0 in sample transport
pathway
Figure 8-2 Sterilization chamber assembly
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Figure 8-3 shows a cut-away view of the sterilization chamber body to illustrate the taper at
the bottom for sample transport as well as the o-ring groove placement. It also shows how
creating flat surfaces on four sides creates thin walls between the heater or cooler surfaces
and the inner chamber. The wall thickness between the flat surfaces and the inner chamber is
0.32 cm (0.125in). Standard autoclave techniques require a temperature of 121 C. The
pressure required for saturated steam at this temperature is 15 psi above standard. This is an
absolute pressure of 29.7 psi or 204774 Pa at sea level on a standard day. For safety
concerns, it was desired to know the minimum wall thickness required to contain this
pressure. To determine this, thin wall pressure formulas were used. The minimum wall
thickness required is 0.03 cm (0.011 in). The chosen wall thickness for the chamber is well
above this minimum.
Heater or
cooler
surface
Sample pathway
O-ring grooves
Figure 8-3 Cut-away view of sterilization chamber
8.1.2.0
Material and mass
The sterilization chamber, lid, and valve interface will be made of 316 stainless steel to
accommodate the high temperatures and moderate pressure required for sterilization as well
as to provide for superior corrosion resistance. The total mass of the lid, chamber and valve
interface made of this material is approximately 1.2 kg or 2.64 lbs.
8.1.3.0
Thermal analysis
The thermal analysis is based on the determination of the internal energy change required to
raise or lower a chamber and its contents from a specified starting temperature to an ending
temperature. The lowest ambient temperature was set forth in the requirements as -10 C and
the highest temperature needed is 121 C for sterilization. The various stages of the
sterilization process will each have a different temperature range and calculations for each
will be shown in following sections. In general, knowing the required internal energy
change, the amount of energy available that can be input into the system and the amount of
energy that is leaving the system, it is possible to calculate the time required to complete the
change.
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Internal energy change
The internal energy change of a sterilization chamber is
U sys  U steel  U water  Q
Q  [( m)(c p )(T2  T1 )] steel  [( m)(c p )(T2  T1 )] water
One chamber has a mass of 1.2 kg (2.64 lb) containing 25.0 cm3 (1.5250 in3) of soil
(modeled as water here), 5.0 cm3 (0.305 in3) of water (1/2 of which will get vaporized to
provide steam for the sterilization). The cp for 316 steel is 452 J/kg K while the cp for water
is 4230 J/kg K.
In addition to the internal energy change the temperature difference requires, vaporizing half
the 5 cm3 of water for steam will require the heater to supply the energy needed for the latent
heat of vaporization that the phase change requires. The latent heat of vaporization for water
is
2257 J/kg.
Stage 1: Heating from worst case ambient temperature to the highest temperature needed for
sterilization. This stage requires some of the water added to the soil be vaporized and the
energy for this is included in the calculations. The heating requirement considering an upper
temperature of 121.0 C and a lower temperature of -10.0 C is an energy change of 115 kJ.
Stage 2: Holding at 121 C for 15 minutes. The energy required for this stage will be equal to
the energy lost during this time. The loss will be detailed in the insulation section that
follows.
Stage 3: Cool to 20 C. The water that was vaporized in stage 1 will condense in this stage
and the energy lost from the system is included in the calculations. The cooling requirement
for an upper temp of 121.0 C and a lower temp of 20.0 C is an energy change of 78 J.
Stage 4: Hold for 24 hours at 20 C. The energy required for this stage will be equal to the
energy lost during this time. The loss will be detailed in the insulation section that follows.
Stage 5: Heat from the lower holding temperature back to the sterilization temperature.
The heating requirement for an upper temperature of 121.0 C and a lower temperature of
20.0 C is energy change of 89 kJ.
To complete the sterilization phase, stages 2-5 will need to be completed again followed by
another holding and cooling time represented by stages 2-3.
Energy transfer through insulation
A thermal resistance network was used to model the steady state heat loss through the
insulation surrounding the chambers. It is assumed that the insulation is in contact with the
chamber so there is no convective zone between the chamber and the insulation. It is also
assumed that a TEC with a heat sink is attached to one of the flat sides. This area will not be
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covered in insulation. The largest heat loss to the surroundings will occur when the there is
the greatest temperature difference. It will be less at other times. The convective heat
transfer coefficient used for the outer surfaces in this model is
h2  25
W
m 2C
This is only an estimate from other examples using natural convection found elsewhere. This
can be increased if forced convection from a fan is used.
The thermal resistance network consists of regions of conduction through the insulation,
conduction through the TEC, natural convection from the outer surface of the insulation and
natural or forced convection from a heat sink attached to the TEC. This heat sink is modeled
as having four, 2.54 cm wide, square fins and as being made of an Al alloy. In general, the
thermal resistances are found from
Rconduction =
Thickness
kA
Rconvection =
1
hAoutside
The conduction resistances for the insulation and the cooler can be considered to be in
parallel since energy loss will occur through both at the same time. The equivalent resistance
is found from
Requiv 
R1 R2
R1  R2
The equivalent conduction resistance and the total convection resistance can be considered to
be in series. The equivalent convection resistance is found from adding up the total surface
area of the insulation and the heat sink. The total thermal resistance is the sum of the series
resistances
Rtotal  Requiv _ conduction  Requiv _ convection
The steady state rate of heat transfer is then given by
Q
Tinside  Tsurroundings
Rtotal
The worst case scenario would be when it is the coldest outside and the hottest inside. The
system will lose the most energy under the worst case situation for as long as that condition
continues. The model that is used assumes the worst case condition is valid throughout the
sterilization process. This will overstate the overall loss in the system, but will provide an
upper limit to energy loss.
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Energy loss through insulation
Using the chamber geometry shown above and the thermal resistance networking model for
the heat loss at worst case temperatures, the following information regarding the sterilization
chamber was found. Melamine insulation can be used. It has a thermal conductivity of
0.03 W/m K and a density of 0.6 lbs/ft3 (9622 g/m3). A 5.08 cm (2 in) thickness of this
insulation can surround the sterilization chambers. The steady state heat loss through the
insulation and TEC for the worst case temperature differentials of an inside temperature of
121 C and an outside temp of -10 C would be 1.6 W. This insulation will be used throughout
the project and the total mass of the insulation was estimated at 383 g (0.844 lbs).
Heater/cooler energy
The heater and cooler will transfer energy into or out of the system. A thermoelectric cooler
(TEC) will provide cooling while strip heaters will provide heating. The TEC considered in
the model is assumed to be 56% efficient while the strip heaters are assumed to be 82%
efficient per manufacturer’s technical papers.
Time and Power required for heating/cooling
Using the geometry defined above and the allowed 12W per chamber for heating or cooling,
a timeline model for the overall sterilization phase was constructed. The power required is
also included here. A 12W heater that is 82% efficient will be able to supply 9.84 W of
energy. A cooler that is 56% efficient will be able to supply 6.7 W of energy. The loss of
energy through the insulation as shown above will be 1.6 W during the times the worst case
temperatures are experienced. A 12W heater/cooler will drawn 1 amps (P=VI) at 12V. At
12V, a 1.6W heater or cooler will draw 0.13 amps.
Stage 1: Heating from worst case ambient to highest temperature needed for sterilization.
This stage requires some of the water added to the soil to be vaporized and the energy for this
is included in the calculations. A 12 W heater with 0.82 efficiency results in 8.2 W heating
available (includes loss through insulation). The total time required for one chamber is
231.11 min or 3.85 hours. The power needed assuming a 12V supply is 3.85 Amp hours
Stage 2: Holding at 121 C for 15 minutes. The energy required for this stage will be equal to
the energy lost during this time and will be at most the energy lost through the insulation
(1.6W). Power needed assuming 12V supply to hold for 15 min at high temperature is 0.03
Amp hours.
Stage 3: Cool to 20 C. The water that was vaporized in stage 1 will condense in this stage
and the energy lost from the system is included in the calculations. A 12 W cooler with 0.56
efficiency results in 6.7 W cooling available (does not include loss). The total time required
for one chamber is 193.89 min or 3.23 hours. The power needed assuming a 12V supply is
3.23 Amp hours.
Stage 4: Hold for 24 hours at 20 C. The energy required for this stage will be equal to the
energy lost during this time and will be at most the energy lost through the insulation (1.6W).
The power needed assuming a 12V supply to hold for 24hrs at the low temperature is 3.2
Amp hours.
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Stage 5: Heating from the lower holding temperature back to the sterilization temperature. A
12 W heater with 0.82 efficiency results in 8.2 W heating available. The total time required
for one chamber is 180.8 min or 3.01 hours. The power needed assuming a 12V supply is
3.01 Amp hours.
To complete the sterilization phase, stages 2-5 will need to be completed again followed by
another holding and cooling time represented by stages 2-3. The actual strip heaters and
cooler are detailed elsewhere.
8.2.0 Peristaltic Pumps
Two peristaltic pumps will be mounted near the sterilization chambers. These will be
purchased parts. They will be connected to the lids of the sterilization chambers through
PharMed tubing and a standard #10-32 fitting. These pumps will allow precisely metered
amount of reagent water to be added to the sterilization chambers. They will also add 5 mL
of water to the sterilization chamber initially for the autoclaving process. Once the
sterilization cycles are complete, they will add 25 mL of reagent water to each chamber to
flush the sample out of the sterilization chamber.
8.3.0 Reagent Water Chamber
A reagent water chamber shall be mounted between the peristaltic pumps. This chamber will
be made of Ultem 1000 and have an internal volume of 60 mL. The lid will contain a #10-32
fitting to connect PharMed tubing from the reagent water chamber to the peristaltic pumps.
This chamber will also be surrounded by a strip heater to maintain the water in a liquid form.
8.4.0 Valve Assembly
The butterfly valve assembly is a purchased product. It provides a 2.54 cm (1 in) sample
pathway and when sealed can withstand pressures over 15 psi gauge and temperatures over
121 C. Figure 8-4 shows a SolidWorks model of the value. The opening in the valve is
welded to the opening in the valve interface piece shown in Figure 8-2. The valve with the
interface piece is then attached to the bottom of the sterilization chambers. During the
sterilization process, it was a concern the sample may harden to a point that it would not be
able to be transported out of the chamber. The butterfly valve mechanism is one way to aid
in the breaking up of the sample before transport. Upon opening, half the valve rotates into
the pathway, providing some way to mechanically break up the potentially compacted
sample.
One area of concern regarding this valve is the initial settling position of the sample in the
sterilization chamber. The distance from the bottom of the sterilization chamber to the valve
flap will be approximately 1.9 cm (0.75 in). During the experiment, once the sample is added
to the sterilization chamber, a portion of it will rest below the inner sterilization chamber on
top of this valve flap. The thermal conduction through the valve interface piece may be
sufficient to allow the appropriate sterilization temperatures to be reached even at this depth.
This will be carefully tested to verify this theory.
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Figure 8-4 Butterfly valve
The valve has a weight of 725g (1.6 lbs). The lower end has tubing attached with a hose
clamp to allow sample transport to the reaction chambers which are positioned below this.
8.5.0 Reaction Chambers
The two test chambers will receive samples from the sterilization chambers in equal amounts.
This sample will be mixed with reagent water in both chambers and a small non-sterile
sample shall be added to one chamber. The chambers shall be environmentally controlled for
2 weeks while science data is being taken. It has been decided that the two testing chambers
will be housed in one environmentally controlled box. This box shall contain both chambers
and all wiring needed for the sensors.
PDD Requirements:
Requirements pertaining to geometry and mass
4.1 Reaction Chamber Volume: MiDAs shall have two chambers with a minimum internal
volume of 50 mL each.
4.4 Reaction Chamber Sensor Capability: Each reaction chamber shall be capable of
supporting no fewer than 6 and no more than 18 electrochemical sensors.
4.5 Reaction Chamber Mixing Capability: Each reaction chamber shall have mixing
capability such that each geological sample is evenly distributed within the fluid while
movement is present at each sensor location.
4.7 Reaction Chamber Material: Each reaction chamber shall be manufactured out of a list
of materials provided by BioServe. This list includes, but is not yet limited to, Polysulfone,
PharMed, 316 stainless steel, and Ultem 1000.
4.18 Sensor Integration: The electrochemical sensors shall be placed at a minimum height
within the reaction chambers to mitigate sample sedimentation effects. This height shall be
sufficient to allow the sensors to be fully submerged with a minimum of
5 mL to 10 mL of fluid.
Requirements pertaining to thermal control
4.2 Reaction Chamber Temperature: Each reaction chamber shall be controllable within a
range of 4°C to 37°C with an accuracy of ±1°C.
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4.8 Geological Sample Volume: Each reaction chamber shall receive no less than 5 ml and
no more than 25 mL of geological sample.
4.16 Reagent Water Delivery: The MiDAs shall aseptically deliver no more than 50 mL
(within ± 5% accuracy) of sterile reagent water to each reaction chamber.
4.17 Reagent Water Temperature: The reagent water shall be delivered to the reaction
chambers at a temperature not to exceed 60°C.
4.30 Operational Environment: MiDAs shall be able to operate in environments ranging
from Antarctica to Atacama Valley in Chile.
 Ambient temperature ranges from -10 C to 30 C
Requirements pertaining to power
4.26 Nominal Power Consumption: Nominal power consumption shall not exceed
30 W.
4.27 Peak Power Consumption: Peak power consumption shall not exceed 30 W for more
than 30 seconds.
4.29 Operational Cycle: One operational testing cycle shall be 14 standard Earth days, not
including power-up, sterilization, and power-down.
8.5.1.0
Volume and Dimensions
Requirement 4.18 states that the lowest row of sensors shall be covered when a minimum of
5 mL of fluid is present. It is assumed that equal portions of fluid and sample are present in
the reaction chambers. This implies that 10 mL of volume will need to cover the lowest row
of sensors. This drives the chamber body dimensions. Assuming a cylindrical shape for the
chamber to minimize sample sedimentation and ease mixing, it is possible with a 2.54 cm
(1.0 in) inner diameter chamber to accomplish this by placing the center points of the lowest
row of sensors 1.9 cm (0.75 in) above the chamber bottom. There will be 4 rows of 6 sensor
ports on the chamber as shown in Figure 8-5. These ports will act as locations for science
sensor or as multi-use ports for the addition of the inoculation sample or as a possible means
for sample removal. There will also be 4 temperature ports, one along each row. The total
length of the reaction chamber body will be 12.7 cm (5.0 in) resulting in a total internal
volume of 64 mL. The reaction chambers will have a wall thickness of 0.635cm (0.25 in) to
accommodate the sensor ports.
The lid will fit over the top of the chamber and seal along an o-ring placed on the outer wall
of the chamber body. The top of the lid will contain a section that a 2.54 cm (1.0 in) I.D.
hose can be clamped to. This 2.54 cm (1.0 in) pathway is the sample transport pathway. A
second view of the lid can be seen in Figure 8-6.
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The base component of the chamber assembly fits over the bottom of the chamber and seals
along an o-ring placed on the outer wall of the chamber. The base will contain a through
hole in the center that will contain a sealed bearing for the mixer impeller. The mixer
impeller shaft passes through this sealed bearing to a coupling for the mixer motor. The seal
between the impeller shaft and the bearing shall be sufficient to hold the sample and reagent
water mixture within the reaction chamber for the two week testing period without leaking.
The base component also has a flange that contains two #4 screw holes for attachment to the
base of the environmental chamber. Figure 8-7 shows the reaction chamber base component.
Sample tube
attachment
Reaction
chamber lid
O-ring
grooves
Reaction
chamber body
Screw
holes
Muli-use and
science sensor
ports
Temperature
ports
Reaction
chamber base
component
Figure 8-5 Reaction chamber
Figure 8-6 shows a view of the reaction chamber lid from underneath.
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Figure 8-6 - Reaction chamber lid
Figure 8-7 shows the base component of the reaction chamber with the central hole for the
sealed bearing visible.
Figure 8-7 Reaction chamber bottom
The chamber body will be produced by BioServe while the cap and bottom will be produced
by the senior projects team. The drawings for these parts are shown in Appendix A. The
design of the reaction chamber subassembly which has separate components for the lid,
body, and base will facilitate any future changes needed in a similar fashion to the
sterilization chambers. The lid can easily be redesigned for alternate sample pathway
methods. The base can also be easily redesigned for interfacing with an alternate mixing
assembly or changed to a solid cap if magnetic mixing is deemed acceptable. By maintaining
the same interface between these components and the body, reduced manufacturing and
testing times can hopefully be achieved with this subassembly as well.
8.5.2.0
Material and Mass
The reaction chambers, lids, and bases are made of Ultem 1000 because of proven biological
and flight tested properties. The total mass of one chamber, lid, and base is 128 g or 0.28 lbs.
8.5.3.0
Thermal Control
The thermal control of the chambers shall be achieved through placing both chambers inside
one larger environmentally controlled enclosure. This shall be detailed next.
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8.6.0 Environmentally Controlled Enclosure
The environmentally controlled enclosure will basically be a box that is well insulated and
has two TEC attached for thermal control. The box will be made of aluminum to provide
thermal conduction pathways to surround the reaction chambers and to give the system some
thermal mass to ease temperature maintenance issues. The dimensions for box are a height
of 15.7 cm (6.17 in), a depth of 19.4 cm (7.64 in), and a width of 30.5 cm (12.0 in) with a
wall thickness of 0.64 cm (0.25 in). It shall have a removable top and side for assembly of
the reaction chambers and sample pathways. The base of the environmental chamber shall
have two 1.27 cm (0.5 in) holes in it as pathways for the mixer impellers. The mixer motors
shall be located below this base. The environmental chamber shall also have an opening
sufficient to allow all the sensor and control wiring to pass through to the outside
components.
8.6.1.0
Thermal Analysis
A method similar to the one used for the sterilization chambers was used to model the
thermal conditions for the environmental box. The system modeled was a box made of
aluminum that contains both reaction chambers, water as the contents for each chamber and a
volume of air surrounding the chambers. The box is insulated on all sides by Melamine
insulation, 5.08 cm
(2 in) thick. Since the testing period is two weeks, the losses through the walls of this box
are the main focus of this thermal analysis.
Internal energy change for environmentally controlled box which contains two chambers:
U sys  U ultem  U water  U air  U Al  Q
Q  2 *[( m)(c p )(T2  T1 )]ultem  2 * [( m)(c p )(T2  T1 )]water  [( m)(c p )(T2  T1 )]air  [( m)(c p )(T2  T1 )] Al
Initial heating
The worst case situation for heating the enclosure is from the coldest ambient temperature to
the lowest reaction chamber temperature. The heating requirement considering an upper
temperature of 4 C and a lower temperature of -10 C is an energy change of 15.5 kJ.
Initial cooling
The worst case situation for cooling the enclosure is when the water entering into the test
chamber is at the highest temperature (60 C) and needing to be cooled down to the highest
reaction chamber temperature (37 C). These calculations assume the entire system gets to 60
C which is probably not true. This assumption is made for simplification and will result in a
larger energy requirement than is actually necessary. The cooling requirement considering an
upper temperature of 60 C and a lower temperature of 37 C is an energy change of 25 kJ.
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Maintenance heating/cooling
Once an equilibrium temperature can be established within the environmental control box,
the system will lose/gain energy through the sides of the box. This is detailed in the next
section.
Heat transfer through walls of environmentally controlled box:
A thermal resistance network will be used once again to model the heat loss through the
walls of the box. The system used consists of an aluminum box, the two chambers, their
contents and the air surrounding the two chambers. This system will lose or gain energy to
the surroundings through the insulation. There will be a convective energy transfer from the
air inside the box to the inner surface, a conductive energy transfer through the enclosure
walls, a conductive energy transfer through the insulation in the box and finally a convective
energy transfer from the outer surface area of the box to the environment. The convective
heat transfer coefficients used in this model are:
W
h1  1 2
for the inside surface area and
m C
h2  25
W
m 2C
for the outside surface area.
Both these are estimates from the examples found elsewhere. The thermal conductivity used
is:
W
W
for the insulation and k  210
for the walls of the enclosure.
mC
mC
The thermal resistance was calculated in a similar fashion to the sterilization chamber model
and resulted in a loss of 2.6 W at a steady state worst case situation. The worst case would
be when it is the coldest outside (-10 C) and the hottest inside (37 C). The system will lose
this much heat under this worst case situation for as long as this condition continues. The
thermal modeling done had many sources of error and will be used only as a general
guideline at this point. Some of the sources or error include the assumption that the
aluminum box, chambers, and contents reach a steady state condition which is probably not
true. Additional thermal mass may also need to be added within the environmental chamber
to actually provide a stable thermal environment for the reaction chambers for the testing
period. The many thermal pathways leading out of the environmental enclosure like wiring,
sample tubing, joints between walls and insulation, etc, where not taken into account either.
k  0.03
8.6.2.0
Time and Power Required for Heating/Cooling
It was calculated elsewhere that during the testing phase, electronics and mixers may require
20W of power. This leaves 10W for the thermal control of the environmental box. Using the
geometry defined above with a 10W rated heater/cooler that is capable of supplying 5.6W of
energy (only 56% efficient) and insulation allowing only 2.6 W for a worst case energy loss,
a power and time model for the overall testing phase was constructed. A 10W heater/cooler
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will drawn 0.83 amps (P=VI) at 12V. At 12V, a 2.6 W heater or cooler will draw 0.217
amps.
Initial heating
The worst case situation for heating the test chambers and surroundings is from the coldest
ambient temperature (-10 C) to the lowest reaction chamber temperature (4 C). A 10 W
heater with 0.56 efficiency results in 3.0 W heating available (includes loss through
insulation at worst case). The total time required for this energy change is 87 min. or 1.45
hours. The power needed assuming a 12V supply is 1.2 Amp hours.
Initial cooling
The worst case situation for cooling the enclosure is when the reagent water entering into the
test chamber is at the highest temperature allowed ( 60 C ) and is needing to be cooled down
to the to the highest reaction chamber temperature (37 C ). These calculations assume the
entire system gets to 60 C which is probably not true. This assumption is made for
simplification and will result in a larger energy requirement than is actually necessary. A 10
W heater with 0.56 efficiency results in 5.6 W cooling available (does not include loss
through insulation since highest ambient temperature is 30 C, loss of energy through the
insulation will aid this cooling process. It is not taken into account to provide a worst case
scenario). The total time required for this energy change 142 min or 2.4 hours. The power
needed assuming a 12V supply is
1.96 Amp hours.
Maintenance heating/cooling
Once an equilibrium temperature can be established within the environmental control box,
the system will lose/gain 2.6W at a steady rate through the sides of the container. 2.6 W will
have to be supplied by the heater/cooler continually over the 2 week testing period for a
worst case situation. 2 weeks is 336 hours. This implies 72.9 amp hours.
8.7.0 Mixer Motors
The mixer motors are purchased parts. They will be used to mix the contents of the reaction
chambers for the two week testing period. They are located below the environmental
enclosure and will be mounted to a base plate. The mixer impeller shaft will protrude below
the surface of the environmental enclosure to interface with these motors. There will be a
coupling between the motor and the impeller shaft for this interface. The impeller shaft has a
T-shaped end which will slide into the coupling and provide for some vertical adjustment
capabilities.
8.8.0 External Case
The entire structure seen in Figure 8-1 will be enclosed in insulation and will slide into an
external case. This can be seen in Figure 8-8 with one of the sides removed and the top
partially opened.
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Figure 8-8 External case
This case can be thought of as a PC type case that is made from thin metal sheets. It has the
overall dimensions of 46 cm x 46 cm x 39 cm (18 in x 18 in x 15 in). It provides protection
for the components inside, is portable and lightweight. The side panels will either slide out
or be easily removable with screws for easy user access.
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9.0 Electrical Design Elements
Author: Charles Vaughan
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December 18th, 2006
The electrical subsystem consists of a power supply and conditioning, power distribution,
sensors, data acquisition, and control system consisting of the heaters, coolers, motors and
water pumps. The figure below is a physical representation of the electrical systems
distributed throughout the MiDAs system.
Electrical Schematic
110VAC
Power Source
12V
+5V
Power
Conditioning/
Protection 12V
Power Distribution/
Switching
CPU
Communication (USB)
T
Dig.Out
T
P
Data Acquisition/
Control
Autoclave 1
T
AHC2
Temp
Control/
Power cut
off
Autoclave 2
P
Water Pump
L1
Control Chamber
AHC 1,2: Autoclave
heater/cooler 1,2
An.In: Analog input
An.out: Analog output
T=Temperature Sensor
P=Pressure Sensor
Dig.Out: Digital Output
Ambient
AHC1 Temp control/
Power Cut off
Reagent Water
Chamber
Control Switch
An.In
An.out
P
T
P
L2
Test Chamber
T
T
Speed control
M1
Electrochemical
Sensors(12)
M2
Speed control
IHC: Incubator Heater/Cooler
L 1,2: Light 1,2
M1,2: Mixer 1,2
Temp control
IHC
Reaction Chamber Environment
Figure 9-1 Physical Electrical Schematic
The diagram illustrates the locations of temperature and pressure sensors as shown in green.
The heaters are shown in red, the black items are the motors/pumps, maroon is the power
supply, with the white being the data acquisition and control system including the CPU. The
torques boxes represent controllers and the light blue boxes represent physical MIDAS
systems. This diagram is based on the MiDAs functional layout, and helps to orient the
reader in the location and function of the electrical components.
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x
Computer
x
3
6
Input
Analog
x
0
1
x
0
output
x
x
1
1
Output
x
x
4
x
2
1
TEC
x
1
TEC
AC
2
TEC
AC
2
TEC
1
TEC
RC
Autoclave
Autolcave
x
4
x
2
x
4
1
Control
2
TEC
RC
2
Control
1
Mixer
RC
RC
2
H2
Autoclave
x
2
x
4
x
2
LED's
x
2
H1
x
3
x
1
Control
2
Mixer
2
Control
Mixer
Mixer
2
Autoclave
x
2
x
3
x
2
Pump1
x
2
Pump
2
6
Analog
x
2
Digital
Board
Switch
2
2
Sensors
2
Distribution
Power
Supply
Power
9.1.0 Electrical Diagram
Figure 9-2 Overall electrical diagram
Figure 9-2 is the top-level electrical system diagram, showing subsystem interconnections as
electrical buses. The numbers on the buses represents the number of wires present. The
power supply is +12VDC and is provided from an external source such as an
110VAC/12VDC power supply, a battery system, or for the Mars instrument, from the lander
/ rover. Two forms of power will be provided to the MiDAs system regulated +5VDC for the
sensors and computer, and +12VDC for all other components. The +5V power will be
conditioned to provide voltage stability, because some of the sensors have ratiometric
outputs. The 12VDC and 5VDC power will be distributed through the Power Distribution
system, which will power the computer, sensors and switch board. All items that receive
power directly from the power distribution will be always on (computer, sensors). The power
consumption of each of these items will be seen further in the report. The switch board
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provides power to all actuators, both on/off and proportional control. The digital outputs will
be used to control any of the 9 optically coupled solid state relays. Both of the autoclave
heaters will be simple on/off devices. These will simply be used to heat the autoclave
chambers up to the desired temperature of 121 degrees C. LEDs will be provided for
photosynthetic organisms and will also be on/off controlled. They will be activated when the
soil enters the Reaction Chambers. The remaining devices will use commercially off the shelf
proportional controllers and will be controlled using the analog outputs. The mixer motors
will be powered using linear power amplifiers, powered from 12VDC and controlled by
analog outputs, for speed control. The TECs will also use +12V but will be controlled by
Pulse Width Modulation (PWM) controllers.
9.2.0 Power Input and Supply
+5VDC
?
LM340-XX
+12VDC
2
T
U
O
N
Breaker
Circuit
?
C
Cap
.1uF
Zener
D
N
D
N
G
G
F
u
0
0
1
Cap
D
1
.22uF
?
D
?
C
Earth
Cap
D
N
G
1
?
C
V
2
1
+
SW-SPST
I
3
Amps
Supply
Power
5
Switch
off
On
U
Requirements
12VDC:
needs 12VDC (10-15VDC) with up to 3 Amps continuous, 5 Amp. Peak.
5VDC:
need 5 VDC (5% accuracy, but .1% stability), <3 Amps
Figure 9-3 Power Supply input
The power input will receive its power from a DC power supply (110AC/12VDC) or
+12VDC from a battery (solar cell, lander, rover, user provided). The voltage level for the
12V power supply is not as important because the items connected don’t have the need for
accurate power input. The only specification is that the voltage can not exceed 15V (damage
to some components may occur). The Zener diode would protect the downstream circuits by
limiting the maximum voltage to 15VDC. The +5V supply does need to be accurate because
some of the sensors have ratiometric outputs, proportional to the excitation voltage. The
power supply will have a manual on/off switch to start the system. It will also have a 5 Amp
circuit breaker protect the system from electrical shorts, which can cause hardware damage
and possible fire hazards. The Zener diode will protect against power surges and reverse
polarity, limiting the maximum voltage to 15VDC. The capacitor will provide some noise
filtering. The +12V will provide power to all the motors and heaters within the system. The
sensors will use +5VDC to provide a power source with stable voltage. Because the motors
and heaters will be connected to the +12V supply this may cause small voltage fluctuation.
This is not a problem for the motors or heaters, but the sensors accuracy relies heavily upon a
stable power source because of their ratiometric outputs. Thus by providing a clean +5V
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power supply it will help ensure the accuracy of the sensor readings. The Voltage Regulator
that creates the +5V can be seen below in figure 9-4.
Figure 9.9-4 Voltage Regulator
(National Instruments)
The voltage regulator has output voltage tolerances of 2% and a line regulation accuracy of
0.01%. This means that the output voltage will be within 2% of 5V (4.9 to 5.1) and the output
voltage will stay within 0.01% of the unit-specific output value. The result will be the need to
calibrate the ratiometric sensors to the to the actual output voltage. Both C1 and C2 help
provide noise filtering to the circuit. Though the output may not be exactly +5V and will vary
from regulator to regulator the voltage will be very steady.
9.3.0 Sensor Diagram
Requirements
Reaction Chamber (PDD doc 4.2)
(PDD doc 4.3)
Ambient
Reaction Sample
(PDD doc 4.11)
(determined via steam tables)
Water Chamber
(PDD doc 4.17)
Temperature range 4°C to 37°C
Temperature accuracy ±1°C
Pressure sealed to 1 psi differential to
Temperature must reach at least 121°C
Temperature range 4°C to 121°C
Pressure will reach at least 18 psi
Temperature range < 60°C
Page 104 of 196
MiDAs
December 18th, 2006
°
K
0
K
0
Thermistor
2
°
K
0
Thermistor
3
°
K
0
Thermistor
4
°
K
0
K
0
Thermistor
5
°
t
°
t
K
0
1
K
Thermistor
6
R
D
N
G
P
R
K
0
2
0
D
N
G
N
Sig
VS
+
Diagram
Sensor
D
PX139
D
N
G
R
1
2
3
Figure 9-5 Sensor circuit diagram
The sensor diagram shows the pressure and temperature sensors. The Pressure Sensors are
the Omega PX139 series and the temperature sensors are 10KOhm thermostats. The pressure
sensors are self contained items that have built in amplification. The output voltage will be
between 0.25 and 4.25VDC. For details on accuracy and minimum resolution within the
12bit A/D system see table 9-1. A picture of the pressure sensor can be seen in figure 9-6.
Figure 9-6 PX139 Pressure Sensor
(Omega.com)
Page 105 of 196
D
N
G
4
5
6
G
AP2
7
8
PX139
9
1
R
1
1
1
1
Sig
VS
+
1
Q
A
D
0
K
0
1
PX139
R
1
R
1
t
Sig
VS
+
R
1
K
0
1
t
D
N
G
AP1
R
PX139
1
K
0
1
t
R
R
1
Sig
VS
+
1
t
Thermistor
1
R
P
A
+5VDC
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
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MiDAs
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Table 9-1 Sensor system accuracy
Sensors
Subsystem
Data
Excitation
Output
Accuracy
Conversion
Sensor
Specification
Pambient
Ambient
PSIA
5Vdc @2mA
0.25 to
4.25 Vdc
+/-0.1% FS
133.33 mV/psia
Tambient
Ambient
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
PX139-030A4V,
Omega, 0 to 30 psia, 0
to 50°C compensated
LM34CAZ, National
Instruments, -45°C to
+148°C
Pautoclave1
Autoclave1
PSID
5Vdc @2mA
0.25 to
4.25 Vdc
+/-0.1% FS
66.66 mV/psi
Tautoclave1
Autoclave1
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
Pautoclave2
Autoclave2
PSID
5Vdc @2mA
0.25 to
4.25 Vdc
+/-0.1% FS
66.66 mV/psi
Tautoclave2
Autoclave2
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
Pchamber
Rx chamber
box
PSID
5Vdc @2mA
0.25 to
4.25 Vdc
+/-0.1% FS
400 mV/psi
Tchamber1
Rx chamber1
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
Tchamber2
Rx chamber2
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
Twater
Water chamber
°C
5 to 30 Vdc
-0.5 to 3
Vdc
+/-0.556°C
18 mV/°C
PX139-030D4V,
Omega, -30 to 30 psid,
0 to 50°C compensated
LM34CAZ, National
Instruments, -45°C to
+148°C
PX139-030D4V,
Omega, -30 to 30 psid,
0 to 50°C compensated
LM34CAZ, National
Instruments, -45°C to
+148°C
PX139-005D4V,
Omega, -5 to 5 psid, 0
to 50°C compensated
LM34CAZ, National
Instruments, -45°C to
+148°C
LM34CAZ, National
Instruments, -45°C to
+148°C
LM34CAZ, National
Instruments, -45°C to
+148°C
The 10KOhm thermistors change resistance as a function of temperature. In order for the
thermistor to function correctly a second 10KOhm resistor with an accuracy of 0.1% will be
placed in series before the thermistor. The result will be a temperature dependent voltage
drop across the thermistor, which will be measured by the analog input. The thermistors will
provide about a 50 mV/degree Celsius signal, and therefore no further amplification is
necessary with the 12bit A/D system.
In addition, prototype experiments were conducted with the larger LM34 temperature sensor.
It provides a linear output voltage of 18mV/C, and covers the entire temperature range of the
autoclave. Due to its relative high output voltage, and less stringent accuracy requirements
for the autoclave (+/-0.5 C), the LM34 should not require any additional signal conditioning.
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9.4.0 Signal Conditioning
Currently, only amplified sensors or sensors with high enough output voltage have been
selected. However to further reduce the noise in the system, low pass filters (1kOhm, 1.0uF)
will be added before the A/D conversion to further reduce noise from the system. Also digital
filtering will be used (average of multiple samples) for the analog input signals. This will
help eliminate higher frequency radiated ‘white noise’ and even some of the 60Hz line noises
easier then with analog filter means.
F
R
Thermistor
IHC1
K
0
1
A
A
IAA
?
RBIAS
D
N
CONTROLLER
WTC3243
TEC
K
0
2
CONTROLLER
8
9
1
7
1
1
1
6
0
1
1
3
4
2
8
9
1
7
1
1
1
6
0
1
2
3
C
R
L
5
4
3
2
1
?
Control
I
R
I
R
2.27MOhm
33.3K
D
N
P
R
P
R
?
D
N
G
D
4.9K
4.9K
?
C
?
Cap
1.5K
1.5K
.22uF
1.5K
D
N
G
D
N
G
D
N
?
D
N
G
+5VDC
Pump
?
Tap
Res
2
LED2
LED1
2
H
R
K
4
5
7
MI
8
MI
D
N
System
?
Motor
Pump
M
B
5
2
6
P
Control
G
CLR
D
N
G
D
N
G
D
N
G
D
N
G
G
+
-
6
PI
DC
PG
PG
1
3
+V(ref)
1
H
R
RWC
SCI
R
-V(ref)1
D
N
G
Peristaltic
1
2
3
4
5
6
7
8
9
+12VDC
Computer
Figure 9-7 Control Diagram 1
Page 107 of 196
K
5
K
5
K
5
K
D
N
G
D
N
G
.22uF
5
Cap
C
2.27MOhm
G
PA75CC
1.5K
.22uF
B
A
O
N
Cap
Vs
+
C
IAB
+
Mixer1
Vs
-
M
B
IAA
+
G
33.3K
IAA
-
2.27MOhm
A
A
O
.22uF
D
Motor
Cap
K
1
K
1
C
Res3
Res3
2.27MOhm
R
L
5
4
3
2
1
C
F
R
I
R
4
1
D
N
G
WTC3243
TEC
K
0
PA75CC
2
B
A
O
G
Vs
+
RBIAS
IAB
+
Mixer1
Vs
-
M
B
IAA
+
-
O
°
t
K
0
1
°
t
Control
D
N
G
N
G
Motor
IHC2
K
1
K
1
Thermistor
Res3
I
Res3
R
9.5.0 Control Diagrams
CONTROLLER
TEC
WTC3243
8
9
1
7
1
1
1
6
I
P
?
1.5K
1.5K
K
5
K
D
N
G
5
D
N
G
.22uF
1.5K
K
5
K
D
N
G
5
D
N
.22uF
1.5K
Cap
C
2.27MOhm
4.9K
R
33.3K
R
R
L
5
4
C
0
1
1
3
4
2
3
2
1
C
I
P
4.9K
R
33.3K
R
R
L
5
4
3
2
1
?
Cap
C
2.27MOhm
G
+5VDC
+12VDC
Computer
9
8
7
6
5
4
3
2
?
Tap
K
3
4
5
6
PI
7
MI
8
MI
D
N
System
?
Motor
Pump
M
B
5
2
6
P
Control
G
CLR
+
-
DC
PG
PG
+V(ref)
1
2
SCI
Res
-V(ref)1
D
N
G
R
Pump
Peristaltic
1
Figure 9-8 Control Diagram 2
The controllers receive 12VDC switched power from the switch board, and are controlled by
analog voltages created by the Diamond-MM32 Digital to Analog Converters. The purely
switched (on/off) items include the strip heaters and the LEDs. The strip heaters that will be
used are the Kapton HK5544R35.2L12A; it has a resistance of 35.2 Ohms. The result is a
power consumption of 4.09 Watts when cold. The LEDS will also run on +12V with a
current limiting resistor, and are set to 20mA for 0.24 Watt of power.
Page 108 of 196
K
0
Thermistor
°
RBIAS
K
0
2
CONTROLLER
8
9
1
7
1
1
1
6
0
1
2
3
4
1
WTC3243
TEC
K
0
2
RBIAS
°
t
1
IHC2
K
0
Thermistor
MiDAs
December 18th, 2006
t
1
IHC2
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
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9.5.1.0
MiDAs
December 18th, 2006
Strip Heater Diagram
Figure 9-9 Strip Heater
(minco.com)
The strip heater is a 35.2 Ohm resistance for a theoretical 4.09Watts that will be drawn from
a 12VDC supply. Losses will be generated from the internal resistance of the switches and
heating. Because 12W of power is necessary to heat the autoclave three heaters will be
attached to each autoclave assembled in parallel.
9.5.2.0
Thermostat
Figure 9-10 Thermostat
(Sensata)
To ensure safety on this project a thermostat will be added to each of the autoclaves. The
thermostat will have the ability to cut the power to the heater in the event the autoclave
becomes too hot. The autoclave will heat to 121C during normal operation. To ensure the
safety of the equipment the thermostat will be activated if it reaches 150 C. 176.7C. The
thermostat that will be used for this operation is the M1 350040112. This part will have a
differential of 22C and a tolerance of 6.7C. The M1 will open on rise, have no mounting
brackets and will be platted with Copper. This will give the MiDAs system more then enough
protection from heat damage.
9.5.3.0
LEDs
Figure 9.9-11 LED
(http://www.china-led-manufacturer.com/images/component_ellipse.jpg)
Page 109 of 196
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December 18th, 2006
The LEDs are only on/off controlled and run at a fixed current of about 20mA, limited by a
series resistor. The white LEDs have about 3.5V forward voltage drop at 20mA. With a
+12V supply a resistance of 420Ohms is needed.
9.5.4.0
TEC Control
The TECs, mixers and Peristaltic pump are initially proportionally controlled, using
commercial of the shelf controllers (TEC) or linear power amplifiers (motors). There will be
a total of 4 TECs, two on the autoclaves and two in the reaction chamber. All the TECs will
have the same design. The TECs will be controlled using the WTC3243 controller from
Wavelength Technologies. The schematic provided by Wavelength Electronics can be seen
below in figure 9-1210.
Figure 9-12 Wavelength TEC control WEC3243
(Wavelength electronics)
Upon examining the provided schematic and the electrical diagram above it can clearly be
seen that the pictures are different. This is because the BANDGAP VOLTAGE
REFERENCE will not be used. The BVR is a built in temperature regulator, based on the
resister values with a +5V input the WTC3243 will determine the temperature that the TEC
will be controlled too. However because of the desired computer control for bench testing for
the MiDAs project, pin 2 will be connected directly to an analog output of the computer
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MiDAs
December 18th, 2006
DAQ system. This will allow for temperature regulation of the TEC directly from the
computer software instead of the trim pot shown in Figure 9-12. This will provide for more
flexibility during initial science testing. A low pass filter will be attached to the analog input
at pin 2 to address any high frequency noise on the DAQ line. The signal will have an
accuracy of 0.083V/C which will allow for temperature control up to +/-0.5C. This is under
the required temperature control of 1 C temperature control. The pin values of the WTC3243
can be seen below:
Table 9-2: TEC Pin values
9.5.5.0
TEC (Thermoelectric Cooler)
The TEC that will be used for this system will be the CP0.8-127-06. The TEC can operate on
up to 16VDC. It can be used for heating or cooling by simply reversing the polarity. A
picture of the TEC can be seen below.
Figure 9-13 Thermoelectric Cooler
(Melcor)
Page 111 of 196
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MiDAs
December 18th, 2006
Because the TEC can switch its polarity it has the ability to both heat and cool the system,
allowing for flexibility on controlling temperatures of the reaction chamber both above and
below the ambient temperature. Combined with the proportional controllers from
Wavelength (WTC3143) will allow for very tight temperature control of the Reaction
chamber. The specifications for this TEC can be seen in the table below.
Table 9-3: TEC specifications
(Melcor)
9.5.6.0
Fan
Because of the large amount of heat that will be generated by the operation of the TECs and
their controllers fans will be needed. In a space flight application the cooling of the TEC and
its control would be the responsibility of the rover thermal control system the fan that will be
used is the Melcor BP401012H. The selected fan will provide enough volumetric flow rate to
properly cool the system even at altitudes of 5000m (5.4*10^4Pa). The fan operates off of
12V at .13A. The addition of this fan to the TEC control will add an additional 1.56W of
power consumption.
9.5.7.0
Peristaltic Pump
The water pump that was chosen for this project was the P625 Peristaltic Pump from Instech.
This pump has been used previously for spaceflight applications. There will be two pumps
operating in the system, one for each autoclave chamber. A single pump design with a pinch
valve was also explored and still may be used because of the high cost of the pump, The
P625 was chosen because it allows accurate fluid metering, and the motor speed control with
feedback is built into the pump assembly. The schematic for the pump controller on the pump
body can be seen below:
Page 112 of 196
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MiDAs
December 18th, 2006
Figure 9-14 Peristaltic pump controller connection schematic
(Instech)
The peristaltic pump will operate off of +12V and will normally use a trim pot to control the
motor speed and therefore the water flow. This means that the water flow can be adjusted by
changing the resistance on the trim pot, and therefore the control voltage to the speed
controller (pin2). There is no need for active control over the water flow from the computer;
therefore this manual control for calibration purposes is acceptable. The water flow is
controlled by time operation of the motor at fixed and known flow rates. The trim pot will be
adjusted during assembly to ensure the desired calibrated water flow.
9.6.0 Mixer Control
Requirements
(PDD 4.1.1)
Each reaction chamber shall have mixing capability such that
each geological sample is evenly distributed within the fluid while
movement is present at each sensor location.
(PDD 4.1.2)
Verification will be through inspection.
The mixers will be initially speed controlled by the computer for development. A later design
after testing may use fixed motor speed. The speed is controlled by a linear power
Page 113 of 196
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MiDAs
December 18th, 2006
operational amplifier (op. amp.), using an analog voltage from the computer to the power op.
amp. input the device that was chosen for the motor control was the APEX PA75CC, which
is a dual power op amp. This will require additional external connections to complete the
motor control device. The schematics of the PA75CC can be seen in the figures below:
Figure 9-15 Controller layout
(from APEX)
Figure 9-16 APEX PA75CC
Figure 9.15 shows the electrical schematic of the control system. Figure 9.16 shows the
connectivity to the pins of the PA75CC. The Rs resisters seen in figure 9.15 are used to
control the current flow, and to ensure the chip does not overload. Because the currents
required for the motor used is small (100mA), these current-resisters were not used and can
be considered 0 Ohm (No current limit). The values of Rf and RI will determine the amplifier
gain. Rf has a value of 20Ohm and RI has a value of 10Ohm, which translates into a gain of
2x. For a gain of this size an input voltage from the analog input will allow for a motor
Page 114 of 196
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MiDAs
December 18th, 2006
voltage of 0-10VDC from a DAQ output of 0-5VDC. The motor specifications can be seen
below.
9.6.1.0
Mixer
The mixer motor that will be used is the Faulhaber 1224. The motor will be run using
+12VDC and will draw approximately 1.95W of power. With at +12VDC input the speed
constant is found to be 1151rpm/V. The torque constant for this motor is 8.3 mNm/A. Further
testing will be done to find the speed and therefore the required torque that will best mix the
soil solution. The table below gives a further description of the motor selected for the mixing.
Table 9-4 Mixer motor specifications
(http://www.micromo.com/uploadpk/1224_SR.pdf)
Page 115 of 196
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9.6.2.0
MiDAs
December 18th, 2006
Computer
Figure 9-17 On board computer, an embedded PC104 controller from Kontron
(MOPSlcd6LX)
The computer that will be used in this project will be the MOPSlcdLX. This is a micro
computer that will be onboard the experiment. It has an AMD LX800 processor, which
operates at 500MHz. It does not require a fan to operate and can be operational in
environments between 0 and 60 degrees C. The MOPSlcdLX operates from only a single
5VDC supply, with less then 200mA current draw (0.9 Watt for CPU without periphery
connected). For external access it is equipped with two USB ports and an Ethernet port. This
computer will have more then enough capacity to provide for the experiment. A solid state
compact flash disk (4GB, power consumption not included in above CPU power draw) with
Windows and LabView will be used initially (flight software would be in C++ and Linux
operating system).
The CPU (MOPSlcdLX) will have a Diamond systems MM32 data acquisition and control
board connected on the PC104 expansion bus. Its power draw (410mA at 5VDC typ.) is also
not included in the 200mA/5V supply to the CPU.
9.7.0 DAQ
Requirements
(PDD 4.19) Sensor Data Collection Rate
(PDD 4.19.1)
The electrochemical sensors shall have a data collection rate of 1
measurement per minute per sensor.
(PDD 4.1.2)
Verification will be through demonstration.
Page 116 of 196
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MiDAs
December 18th, 2006
(PDD 4.20) Sensor Data Acquisition
(PDD 4.20.1)
All data taken through the sensors shall be collected and stored for
analysis.
(PDD 4.20.2)
Verification will be through analysis and demonstration.
(PDD 4.20) Sensor Data Accessibility
(PDD 4.21.1)
The scientific and engineering status data shall be accessible to users
throughout the experiment.
(PDD 4.21.1)
Verification will be through demonstration.
Figure 9-18 Data Acquisition
(Diamond MM-32 from Diamond systems)
The DMM-32X-AT is one of the most advanced data acquisition devices Diamond system
sells. Because of the number of inputs needed for the project two will be used. The DiamondMM32 has 16 bit resolution with a maximum sampling rate of 250 KHz. The circuit has built
in low drift circuitry which will ensure a very accurate voltage reference. The design of the
chip also took into consideration noise problems with digital and analog signals. The chip
was designed to have digital and analog regions so as to minimize noise. Any wires from one
region that cross into the other are heavily shielded. Each DAQ is equipped with 32 analog
Page 117 of 196
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MiDAs
December 18th, 2006
inputs. The analog inputs are where the sensors will read in their voltages. These inputs are
sent into a built in amplifier, which will reduce the error found in the system. There are 4
analog outputs per circuit, but because 2 DAQs will be used a total of 8 will be available for
control. Finally, 24 digital outputs are available per DAQ. The digital outputs will be used to
control the switch board. Further description of the DAQ can be seen in the table below.
Table 9-5 DAQ system
Page 118 of 196
D
N
V
2
1
+
V
5
6
3
5
3
D
N
G
+
0
G
8
3
7
3
4
9
V
5
+
D
N
G
4
3
Distribution
Power
V
5
+
2
3
V
2
1
+
0
3
D
N
G
8
2
V
2
1
+
6
2
D
N
G
4
2
V
2
1
+
2
2
D
N
G
0
2
V
2
1
+
8
1
7
1
Sig
D
N
G
6
1
5
1
Sig
V
2
1
+
4
1
3
1
Sig
D
N
G
2
1
1
1
Sig
V
2
1
+
0
1
9
Sig
D
N
G
8
7
Sig
V
2
1
+
6
5
Sig
D
N
G
4
3
Sig
V
2
1
+
2
1
Sig
Items
Switched
Board
Switch
Output
Digital
Diagram
Wire
System
D
N
G
D
N
G
V
2
1
+
V
2
1
+
Computer
Supply
Power
Sig
D
N
G
Sig
V
5
+
D
N
G
AT2
V
2
1
+
Sig
Pump
D
N
G
D
N
G
V
5
+
V
2
1
+
AT1
Heater2
Sig
D
N
G
D
N
G
V
2
1
+
V
5
+
Heater1
Sig
D
N
G
D
N
V
2
1
+
V
5
Pump
T
Sig
Sig
C
+
V
5
+
T
G
D
N
G
A
Sig
Sig
D
N
G
D
N
G
Sig
V
2
1
+
Sig
V
5
+
D
N
G
D
N
G
Sig
V
2
1
+
D
N
G
V
5
+
D
N
G
V
2
1
+
V
5
+
TEC4
T
T
D
N
G
Sig
Sig
V
2
1
+
Sig
D
N
G
D
N
G
Sig
D
N
G
V
5
+
V
2
1
+
D
N
G
V
5
+
Sig
V
2
1
+
D
N
G
TEC3
T
R
Sig
V
5
+
V
5
+
D
N
G
Sig
Sig
D
N
G
V
2
1
+
D
N
G
D
N
G
V
2
1
+
Sig
V
5
+
V
5
+
D
N
G
Sig
TEC2
P
R
V
2
1
+
D
N
G
V
5
+
V
5
+
Sig
V
5
+
D
N
G
D
N
G
D
N
G
Sig
V
2
1
+
V
2
1
+
V
5
+
D
N
G
V
5
+
V
5
+
TEC1
AP2
D
N
G
Sig
Sig
V
2
1
+
Sig
D
N
G
D
N
G
Sig
D
N
G
V
5
+
V
2
1
+
D
N
G
V
5
+
Sig
V
2
1
+
D
N
G
Mixer2
AP1
Sig
V
5
+
Sig
D
N
G
Sig
Input
DAQ
D
N
G
V
2
1
+
D
N
G
V
2
1
+
V
5
+
inputs
Control
Mixer1
P
A
9.7.1.0
3
V
2
1
+
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
Wire Diagram
Figure 9-19 Wire Diagram
The wire diagram was created to understand how many connections are going to be needed
for the switch board and the computer interface. The switchboard can be seen in figure 9.19
below. The optically coupled MOSFET solid state relays (NAIS ACQ202, 2 Amps each) are
not shown on this wire diagram, but will be shown on a separate circuit board design
drawing.
Figure 9-20 Switch board
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MiDAs
December 18th, 2006
Currently 6 Analog output signals are needed to run the motors and TECs, 10 analog inputs
are needed for the sensors, and 11 digital outputs are needed to run the switch board. When
the voltages and grounds are added to the system a total of 42 connections are needed in the
switch board. The power distribution will need a total of 25 connections to power the
sensors, computer and switch board.
The Drawing Tree summarizes all the parts necessary to construct the electrical system.
Table 9-6 Drawing Tree
Subsystem/Item
Drawing Number
Drawing Name
Drawn by
Electrical Block Diagram
MiDAs-OS-A-200-01
Power Subsystem
Power Supply
Power Distribution
MiDAs-OS-A-210-01
MiDAs-OS-P-211-01
MiDAs-OS-P-212-01
Power System
CV
Sensor Subsystem
Wire Harness
Pressure Sensors
Temperature Sensors
MiDAs-OC-A-220-01
MiDAs-SC-P-221-01
MiDAs-SC-P-222-01
MiDAs-SC-P-223-01
Sensor Schematics
CV
Control
Schematics
CV
Control Subsystem
Mixer/Control 1
Mixer/Control 2
Autoclave TEC/Control 1
Autoclave TEC/Control 2
RC TEC/Control 1
RC TEC/Control 2
Wire Harness
Fan
Switch Board
Strip heaters
LEDs
Wire Harness
Water Pump
Data Acquisition and Control
Computer
Analog input
Digital input
Analog Output
MiDAs-OS-A-230-01
CV
MiDAs-SC-P-231-01
MiDAs-SC-P-232-01
MiDAs-SC-P-233-01
MiDAs-SC-P-234-01
MiDAs-SC-P-235-01
MiDAs-SC-P-236-01
MiDAs-SC-P-237-01
MiDAs-SC-P-238-01
MidAs-OS-A-240-01
Switch Board
Layout
CV
Computer Interface
CV
MiDAs-SC-P-241-01
MiDAs-SC-P-242-01
MiDAs-SC-P-253-01
MiDAs-SC-P-254-01
MidAs-OS-A-250-01
MiDAs-SC-P-251-01
MiDAs-SC-P-252-01
MiDAs-SC-P-253-01
MiDAs-SC-P-254-01
Page 120 of 196
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MiDAs
December 18th, 2006
9.8.0 Powered Items
The following is a list of elements of the Midas project that will require power. The constant
power is the summation of the systems that will always be running. The Switched Power is
the systems that can be turned on and off, and the Controlled power systems are those that
need to have power control similar to a light switch dimmer.
Constant Power
Computer
CF disk, 4GB with IDE
controller
DAQ
Autoclave temp
sensor
Autoclave Pressure
sensor
Reagent Water
Temperature sensor
Test chamber
temperature sensor
Reaction chamber
Pressure Sensor
Control chamber
temperature sensor
Ambient Temperature
Sensor
Ambient Pressure
Sensor
Total Constant
power draw
Number
Table 9-7 MiDAs Powered Items
Voltage(V)
Amps(A)
Power(W)
1
1
5
5
0.200
.02
1.00
2
2
5
5
0.410 x 2
0.0005
4.10 (2.05 ea)
0.0025
2
5
0.002
0.01
1
5
0.0005
0.0025
1
5
0.0005
0.0025
5
0.002
0.01
1
5
0.0005
.0025
1
5
0.0005
.0025
5
0.002
.01
5
1.0485
5.24
1
1
Switched Power
Water Pump
Strip heaters
LEDs
2
7
2
12
12
12
0.125
0.34
0.02
1.5
4.09
0.24
Controlled Power
Mixers
Incubator TEC
Autoclave TEC
2
2
2
12
12
12
.1625
1
1
1.95
12
12
Page 121 of 196
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MiDAs
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Table 9-8 Electronics Parts List
Electronics Parts List
#
used
Power System
On/off switch
Circuit 5Amp Breaker
Capacitor .22uF
Diode
Capacitor .22uF
Capacitor .1uf
Voltage Regulator
18 gage wire (Blue)
Sensors
Pressure Sensor
Temperature Sensor
Resistor 10kOhm
26 gage wire (Blue)
24 gage wire (green)
Control
Motor Control
Company part #
1
1
1
1
1
1
1
Philmore SW-SPST
American Electrical Inc C5A1P
AVX Corporation 08053C224JAT2A
Diodes Inc. SMAJ15A-13-F
AVX Corporation 08053C224JAT2A
AVX Corporation 06033C104JAT2A
National Semiconductor LM340-XX
4
6
6
Omega PX139
2
APEX PA75
Mixer
10Ohm Resistor
20Ohm Resistor
TEC control
2
2
2
2
Faulhaber 1224
TEC
4.99KOhm Resistor 50W
33.3KOhm Resistor 10W
1.5KOhm Resistor 5W
5Ohm Trim pot 10W
Switch
Peristaltic Pump
10KOhm Trimpot 10W
2
4
4
8
8
4
2
2
Melcor CP0.8-127-06
Strip heater
LED
7
2
Kapton HK5544R35.2L12A
Thermostat
7
Fan
18 gage wire (Blue)
18 gage wire (Red)
26 gage wire (Green)
Computer
CPU
DAQ
18 gage wire (red, back)
26 gage wire (white, black)
Flash Drive
4
Klixon M1 350040112
Melcor BP401012H
1
2
Kontron MOPSlcd6LX
Dimond MM-32
1
GE Sensing YM120D370N100
Honeywell SC5E10
Honeywell SC5E10
Honeywell SC5E20
Wavelength WTC3243
Honeywell CMC5010
Honeywell VC10F33
Honeywell SC5E1.5
Honeywell VP10FA5
Philmore SW-SPST
Instech P625
Honeywell VP10FA5
Bourns Inc. 51AAD-B28-D15L
Transcend 4GB
Page 122 of 196
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MiDAs
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10.0 Software Design Elements
Author: Steven To
Page 123 of 196
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Requirements
(PDD 4.2) Reaction Chamber Temperature
(PDD 4.2.1) Each reaction chamber shall be controllable within a range of 4°C
to 37°C with an accuracy of ±1°C.
(PDD 4.3) Reaction Chamber Pressure
(PDD 4.3.1) Each reaction chamber shall be sealed to a pressure of 1 psi
differential.
(PDD 4.5) Reaction Chamber Mixing Capability
(PDD 4.5.1) Each reaction chamber shall have mixing capability such that each
geological sample is evenly distributed within the fluid while
movement is present at each sensor location.
(PDD 4.11) Reaction Sample Handling
(PDD 4.11.1) The reaction samples shall be sterilized in accordance with
standard Autoclave techniques.
(PDD 4.16) Reagent Water Delivery
(PDD 4.16.1) The MiDAs shall aseptically deliver no more than 50 mL (within
±5% accuracy) of sterile reagent water to each reaction chamber.
(PDD 4.17) Reagent Water Temperature
(PDD 4.17.1) The reagent water shall be delivered to the reaction chambers at a
temperature not to exceed 60°C.
(PDD 4.19) Sensor Data Collection Rate
(PDD 4.19.1) The electrochemical sensors shall have a data collection rate of 1
measurement per minute per sensor.
(PDD 4.20) Sensor Data Acquisition
(PDD 4.20.1) All data taken through the sensors shall be collected and stored for
analysis.
(PDD 4.21) Sensor Data Accessibility
(PDD 4.21.1) The scientific and engineering status data shall be accessible to
users throughout the experiment.
(PDD 4.22) MiDAs Status Warnings
(PDD 4.22.1) MiDAs shall provide caution, warning, and instrument status to
external ground support equipment.
(PDD 4.23) MiDAs command
(PDD 4.23.1) MiDAs shall received commands from external ground support
equipment.
Software will be used in several manners. First, the software will be use for data acquisition.
This is to verify sections 4.2, 4.3, 4.11 and 4.17 from the PDD document as well as satisfying
requirements 4.19, 4.20 and 4.21. Second, the software will also have to control all the
necessary components, such as heaters, coolers and motors to satisfy all requirements listed
above.
To achieve these requirements, National Instrument’s LabView was chosen as the
programming language for its ease of use and functionality. To run the software program,
LabView will be installed onto the PC104 embedded CPU (Kontron MOPSlcdLX). The
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Kontron MOPSlcdLX will allow for user access via Ethernet connection or by plugging in a
keyboard and monitor to its respected ports.
Once installed onto the PC104, the software will require a Data Acquisition Card in order to
read the necessary data. Diamond’s MM32 DAQ card will used for its available number of
sensor inputs allowing us to collect data from all sensors as well as for its number of outputs,
to allow for control of our systems.
Control of our system will be achieved in two ways. First is simple on/off control in which
power is turned on or off to the desired component. This is accomplished via the DAQs
digital I/O outputs toggling various switches. Second is proportion control in which power is
proportionally adjust to control the speed or temperature of the desired component. This is
accomplished via the DAQs analogue outputs coupled with an APEX PA75CC controller.
The controller is ideal for the Autoclave temperature control in which various temperatures
will need to be held at different times. In this case, the DAQs analogue outputs send a desired
voltage to the controller which then interprets this voltage as the desired temperature to hold
to.
A simple description of the execution of the software is shown in figure 10-1.
Figure 10-1 Simplified execution
The given times along the time line are approximate values based on initial calculations of
the autoclave thermal properties. Circles indicate user inputs and outputs. A more detailed
description follows in Table 10-1 which outlines all the necessary controls for one testing
system.
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Table 10-1: One cycle control
This table imposes some small safety margins to ensure proper temperatures have been
reached. For example, the autoclave heating temperature is 121°C, but the control specifies
125°C to make sure.
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The sensor diagram to run the experiment is described below in Figure 10-2 and 10-3 to
show the inputs and outputs during heating control of the autoclave and the reaction
chamber.
4| Power (W)
Proportional
control
4| CTemp (V)
5| On/off
Power (W)
4| Temp (V)
Heater
6| Qin (W)
On/off
control
1| Temp (V)
3| High/Low
Autoclave
DAQ
1| Press (V)
2| Yes/no/
CTemp (bin)
2| Temp (bin)
Software control
Is it heating?
Is it cooling ?
Is it holding constant temp?
5| Qout (W)
Cooler
2| Temp (°C)
User
2| Press (psi)
4| Power (W)
Figure 10-2 Autoclave Sensor Diagram
Step 1 The DAQ inputs the sensor data (in the form of analogue volts). Internally, the DAQ
converts the analogue voltage into a digital bit.
Step 2 The DAQ then sends the digital values to the embedded CPU which runs the software
and determines whether to turn the heater or cooler on or off and at what temperature the
proportional control (CTemp) should hold the autoclave to. The software must also be
capable of digitally filtering noise, and converting the digital inputs into a corresponding
measurement (psi, °C, etc) for user to monitor if desired.
Step 3 The DAQ again converts the digital input from the CPU to a digital High/Low signal
for the on/off control
Step 4 The On/off control determines relays power to either the proportional control for the
heater or to the cooler. The DAQ, when applicable, converts the digital input form the CPU
to an analogue volt output for the proportional control.
Step 5 If the heater is on, the proportional control sends power to the heater and continues to
monitor the Autoclave to maintain the correct temperature. If the cooler is on, it begins to
cool the Autoclave by removing heat.
Step 6 The Heater heats the Autoclave as per the proportional controller’s instructions.
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4| Heating/Cooling
Proportional
control
4| CTemp (V)
5| On/off/
Temp (V)
4| Temp (V)
TEC
6| Qin/Qout (W)
Heat/Cool
control
1| Temp (V)
3| High/Low
DAQ
Reaction Chamber
1| Press (V)
2| Yes/no/
CTemp (bin)
2| Temp (bin)
Software control
Is it heating?
Is it cooling?
Is it holding constant temp?
2| Temp (°C)
User
2| Press (psi)
Figure 10-3 Reaction Chamber Sensor Diagram
The reaction chamber diagram is similar to the autoclave sensor diagram except for the type
of input received from the TEC. Since the reaction chamber will be controlled solely by the
TEC the Heat/Cool control must be able to reverse the polarity of the power being provided
to the TEC which can be accomplished with four switches.
Figure 10-4 below is the LabView vi program for the autoclave temperature control. This
serves as an example of how the sensor diagram, Figure 10-2 is implemented via the
procedure of Table 10-1.
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Figure 10-4 LabView vi Autoclave Temperature Control
While Figure 10-4 may appear complicated, most of the components are simply visual
overhead for the user to see what software is doing. Broken down to just the major functions
it becomes a much simpler program Figure 10-5 below.
Figure 10-5 Software Function Tree
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11.0 Integration Plan
Author: Shayla Stewart
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11.1.0 Instrument Assembly
Figure 11-1 shows the assembly flow diagram for the MiDAs instrument. The gray
components indicate the purchased or donated parts, while the white indicates that the
component will have to made or manufactured by the MiDAs team. The assembly starts from
the bottom and moves upward to the integration with the chassis, which is made up of an
outer case and an upper shelf inside.
Figure 11-1 Assembly Flow Diagram
Not every subsystem has to be put into the chassis individually. Figure 11-2 shows the larger
assemblies that will be inserted into the overall chassis. The section marked ‘1’ consists of
the mixer impeller, reaction chamber bottom, body, and cap as well as the PharMed tubing
and autoclave bottom-valve interface used for the sample transport from the autoclave to the
reaction chambers. Each of these components is sterilized in an autoclave provided by
BioServe to kill any living organisms present on each piece. This section is then assembled
outside of the instrument in a clean and sterile environment. This ensures that no
contamination or introduction of living organisms will occur during the assembly process.
This entire section is then slid into the chassis from the side through cutouts in the chassis
shelves and the impeller will be fitted into the motor bearing. This section is a completely
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closed and sterile environment for the experiment, which is then screwed in. The section
labeled ‘2’ shows the overall sterilization assembly including the autoclave cap, body, and
the TEC assembly with the heat sink. This is then screwed onto a shelf attached to the bottom
of the chassis.
2
1
Figure 11-2 Overall Assembly
11.2.0 Autoclave Functional Test Plan
PDD requirement 4.11 states that the reaction samples must be sterilized through standard
autoclaving techniques. This requires that the autoclave chambers be heated to 121°C and
held for 15 minutes before being cooled back down to 20°C and holding for 24 hours. This
cycle must be repeated three times because of the possibility of spores in the sample. Cooling
the sample to close to room temperature and holding allows for the spores to diminish their
protective shells so that they will be killed on the next autoclave cycle.
The sample must be transported from the autoclaves to the reaction chambers once the
sterilization is complete. To ensure that there is enough of the sample to get a good test and
control, at least 90% of the sample must reach the reaction chambers when the reagent water
is pumped through.
Figure 11-3 shows the functional test plan for the autoclaves. The thermal control on the
autoclaves consists of three strip heaters wired in series and a thermoelectric cooler (TEC).
The sample transport from the autoclave to the reaction chambers involves a butterfly valve
at the bottom of the autoclave and is also a function of the sample consistency. If the soil is
too dense or sticky, it may be difficult to move it in the chamber. The thermal control and
sample transport will need to be tested prior to integrating the autoclave into the entire
system. The details of the testing will be outlined in section 12 of this report.
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TEC
Thermal
Control
Autoclave
Sample
Transport
Strip
Heaters
Butterfly
Valve
Heat from -10°C to 121°C
Hold for 15 min
Cool to 20°C
Repeat 3 times
Transport 90% of sample
when reagent water
pumped through
Sample
Consistency
Figure 11-3 Autoclave Functional Test Plan
11.3.0 Reaction Chambers
PDD Requirement 4.2 states that each reaction chamber must be controllable within a
temperature range of 4-37°C with an accuracy of ±1°C. Aside from the chamber thermal
control, there is a mixing requirement as stated in PDD requirement 4.5. The sample/water
solution in the chambers must be mixed so as to distribute the sample and minimize sample
sedimentation at the bottom and sides of the chamber. There also must be fluid movement at
each of the sensor on the side so that accurate readings are possible.
Figure 11-4 shows the functional test plan for the reaction chambers. The thermal control for
the reaction chambers is performed within the reaction chamber environment with two TECs
placed near the reaction chambers. The mixing within the chambers involves a small motor
and the designed impeller. The thermal control and mixing capability will need to be tested
prior to integrating the reaction chambers into the entire system. The details of the testing
will be outlined in section 12 of this report.
Reaction
Chamber
Thermal
Control
TEC
Motor
Mixing
Impeller
Maintain temperature
between 4°C and 37°C
Maintain fluid movement
around sides; Maintain
minimal sedimentation on
sides and bottom of chamber
Figure 11-4 Reaction Chamber Functional Test Plan
11.4.0 Data Acquisition and Control
PDD requirement 4.20 states that all of the data taken through the sensors shall be collected
and stored for analysis. The instrument must also be able to receive commands and provide
caution, warning, and instrument status as specified in PDD requirements 4.22 and 4.23.
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Figure 11-5 shows the functional test plan for the Data Acquisition and Control subsystem.
The collection, storage, and command capabilities are dependent on the hardware as well as
the interface and LabView software. These capabilities must be tested prior to its overall
integration into the system. The details of the testing will be outlined in section 12 of this
report.
DAQ &
Control
Collection
& Storage
Command
Interface
Software
Collect & store data from
each sensor
Receive commands from SW
Provide caution, warning,
status signals
Figure 11-5 DAQ Functional Test Plan
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12.0 Verification and Test Plan
Author: Shayla Stewart
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12.1.0 Design Requirement Verification Plan
Table 12-1 shows the verification plan for each requirement stated in the PDD and in Table
1-2. The verification methods are defined as analysis (A), test (T), inspection (I), and
demonstration (D).
Table 12-1 Design Requirement Verification Plan
Verification
Requirement
Method
Reqt. #
Title
PDD 4.1
Reaction
Chamber Volume
≥ 50 mL
PDD 4.2
Reaction
Chamber
Temperature
4 – 37°C
±1°
A, T
1 psi
differential
A, T
6 – 18 sensors
A, I
Analysis and design of the chamber
geometry and by visual means
Fluid
movement,
minimal
sediment
A, I
Analysis of the flow pattern generated during
mixing and by visual/video means.
≥ 4 multi-use
ports
A, I
Analysis and design of the chamber
geometry and by visual means
Polysulfone,
PharMed, 316
SS, Ultem 1000
A
Structural and thermal analysis of the
reaction chambers.
5 – 25 mL
I, D
Simple volume measurement prior to
insertion into autoclave
≤ 1 mL
I, D
Aseptic
delivery
A, T
PDD 4.3
PDD 4.4
PDD 4.5
PDD 4.6
PDD 4.7
PDD 4.8
PDD 4.9
PDD 4.10
Reaction
Chamber
Pressure
Reaction
Chamber Sensor
Capability
Reaction
Chamber Mixing
Capability
Reaction
Chamber MultiUse Port
Reaction
Chamber
Material
Geological
Sample Volume
Inoculation
Sample Volume
Inoculation
Sample
Reception
I, D
Verification
Simple volume measurement.
Thermal analysis of the environmental
chamber geometry; Test by means of
temperature sensors within the reaction
chamber environment
Pressure decay of sealed chamber by means
of pressure sensors within the reaction
chamber environment
Simple volume measurement prior to
insertion into reaction chamber
Analysis of sample transport; Sterile
swabbing of wetted surfaces with biological
culture test
Thermal analysis of the autoclave chambers;
Testing by means of temperature/pressure
sensors through cap and autoclave indicator
tape
PDD 4.11
Reaction Sample
Handling
Steam
autoclave
sterilization
A, T
PDD 4.12
Inoculation
Sample Handling
No sterilization
A, D
Thermal analysis making sure sample does
not get near autoclaves; Demonstration
PDD 4.13
Reaction Sample
Delivery
Aseptic
delivery, equal
volume to each
chamber
A, T
Analysis and testing of sample transport
through valve; Sterile swabbing of wetted
surfaces with biological culture test
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Analysis of sample transport; Sterile
swabbing of wetted surfaces with biological
culture test
Thermal analysis of reagent water chamber;
Test by means of temperature sensors within
chamber
Analysis of peristaltic pump with volume and
flow control; Simple volume measurement
after flow through pump
PDD 4.14
Inoculation
Sample Sterility
Aseptic
delivery
A, T
PDD 4.15
Reagent Water
Containment
Contained as
solid & liquid
A, T
PDD 4.16
Reagent Water
Delivery
≤ 50 mL ±5%,
aseptic delivery
A, I
PDD 4.17
Reagent Water
Temperature
< 60°C
A, T
Thermal analysis; Test by means of
temperature sensors within chambers
PDD 4.18
Sensor
Integration
A, I
Analysis of reaction chamber geometry;
Simple volume measurement
PDD 4.19
Sensor Data
Collection Rate
A, T
Analysis and testing of the DAQ/command
software
PDD 4.20
Sensor Data
Acquisition
A, T
Analysis and testing of the DAQ/command
software.
PDD 4.21
Sensor Data
Accessibility
PDD 4.22
MiDAs Status
Warnings
PDD 4.23
MiDAs
Command
PDD 4.24
Field Power
PDD 4.25
Laboratory Power
PDD 4.26
PDD 4.27
Nominal Power
Consumption
Peak Power
Consumption
Bottom row
submerged in
5 – 10 mL
1 measurement
per min per
sensor
All data
collected &
stored
Accessible
during
experiment
Provide caution,
warning, status
signals
Receive
commands
Operate on 10 –
30W @ 12VDC
in field
Operate on 10 –
30W @ 12VDC
in lab
≤ 30W @
12VDC
> 30W for
≤ 30 sec
Taken apart,
sterilized,
reassembled
D
A, T
A, T
Demonstration of data transfer from
embedded CPU
Analysis and testing of the DAQ/command
software with set max temperature and shutoff abilities
Analysis and testing of the command
software
A, T
Analysis of the power consumption; Test
using multimeter within circuit
A, T
Analysis of power consumption; Test using
multimeter within circuit
A, T
A, T
PDD 4.28
Unit Disassembly
A, D
PDD 4.29
Operational
Cycle
14 standard
Earth days
A, T
PDD 4.30
Operational
Environment
Antarctica to
Atacama Valley
(-10 to 40°C)
A, T
Analysis of power consumption; Test using
multimeter within circuit
Analysis of power consumption; Test using
multimeter within circuit
Analysis of unit assembly; Demonstration of
instrument disassembly
Test of shortened operational cycle; Analysis
of instrument stability of control/drift over 3
days
Thermal analysis of the surrounding
environment; Testing instrument in
temperature-controlled environment
(BioServe)
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12.2.0 Component Functional Verification and Test
The sensors that are to be used (e.g. temperature and pressure sensors) will need to be
calibrated with known calibration laboratory instruments. This will ensure that the readings
taken will be sufficiently accurate. Each powered component will also need to be tested for
functionality prior to integration into each subsystem. This includes the motors for the
mixers, as well as every TEC, strip heater, and peristaltic pump used. The safety
mechanisms, such as the pressure release valve on the autoclave, the sensors, and any and all
switches used must also be tested in the laboratory to detect any possible faulty or broken
components. These will need to be tested again once installed in the instrument to make sure
that all of the proper connections are made and the desired voltages are achieved.
12.3.0 Subsystem-Level Verification and Test
PDD 4.11 requires that the reaction sample be steam sterilized up to three times in order to
achieve thorough sterilization. To verify that the autoclave and the Data Acquisition and
command software can handle repetitive cycles, the autoclave will be run three times prior to
integration into the entire system. The temperature limits must be reached in order to verify
that the autoclave is successful. Once completed, a portion of the sterile sample will be
culture tested at BioServe to ensure that there are no living organisms left in the sample.
The DAQ and control software will also be tested prior to system-level integration using a
simulator provided by BioServe that allows the user to set an analog input voltage and to
display the digital and analog output voltages. This simulator allows testing of the software
without any instrument hardware, which permits parallel development of the software and
hardware.
The DAQ and control software will also be tested during the autoclave testing. The
temperature and pressure sensors within the autoclave will be connected to the DAQ during
testing in order to collect and store the heating and cooling data. The control software will be
responsible for commanding the TEC and the strip heaters to heat or cool as necessary to
achieve the appropriate temperatures within the autoclave. The ability of the software to
provide caution, warning, and status signal will also be tested by setting a maximum
temperature and/or pressure within the autoclave. When the autoclave approaches this
maximum, a caution or warning signal should appear. If the autoclave exceeds the maximum,
there will be an emergency shut-off.
The mixer within each reaction chamber will also be tested prior to system-level integration
as mentioned in section 11. As mentioned in Table 12-1, this will be through visual and video
verification. The appropriate volume of the sample to be tested will be mixed with water and
put in the reaction chambers with the sensors in place. The mixer will then be powered on
and the tester will examine the chambers and verify that there is fluid movement around the
sides of the chamber and that the amount of sedimentation will not affect the sensor readings.
The solution does not have to be completely homogeneous, but there should be enough of the
sample moving around the sensors to achieve accurate readings. The sensors do not need to
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take readings during this mixing test, although they must be in place to maintain the seal
around the holes in the reaction chamber.
12.4.0 System-Level Verification and Test
Once the entire instrument is assembled, system-level testing will begin. The instrument will
be placed in BioServe’s temperature-controlled testing environment. For a worst-case test,
this environment will be set to -10°C. The desired sample will be placed in the autoclave
through the top of the chassis and the autoclave cap will be screwed on. Then the autoclaving
process will begin. Since the autoclave repetition requirements will have been verified prior
to system-level testing, only one autoclave cycle will be performed. Once this cycle is
complete, the software will alert the experimenter who will then open the butterfly valve. The
reagent water will flush through the autoclave pushing the sample into the reaction chambers.
Once the sample is in the reaction chambers, the mixing and data acquisition for the
experiment will begin. PDD requirement 4.29 states that the experiment takes place for 14
days. The MiDAs instrument, however, will only be tested for three complete days while
varying the temperature in BioServe’s testing environment. This verifies that the command
software and the thermal control in the MiDAs environmental chamber satisfy the
temperature requirement (4-37°C). Three full days is sufficient to verify the requirements set
forth in the PDD.
The MiDAs instrument will be tested under three ambient conditions during the testing phase
to ensure that steady state can be reached. There are two worst-case conditions that must be
tested. The first is maintaining the reaction chamber environment at 37°C with an ambient
temperature of -10°C, which is the low end of the potential operational environment outlined
in PDD requirement 4.30. The other worst-case to test is maintaining the chambers at 4°C
with an ambient temperature of 40°C. The third test is a nominal case, which will be
controlling the environmental chamber between 4° and 37°C with an ambient temperature of
about 20°. For these conditions, the current and power draw will be measured using a
multimeter to ensure that the MiDAs environmental set points can be maintained within the
required accuracy and stability. If the system is stable for three days, then it is assumed stable
over 14 days.
During the 3-day testing period, the sensor drift will also be monitored. If the drift is very
small in this time frame, then the drift over two weeks will not be detrimental. The DAQ
memory will also be investigated at the end of the testing phase. If it is possible that the
memory would be full after two weeks, then the data may have to be downloaded from the
onboard computer periodically throughout the experiment.
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13.0 Project Management Plan
Author: Elizabeth Newton
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13.1.0 Organizational Responsibilities
MiDAs
Project
Management
Fabrication
Design
Document
Verification and
Testing
Project
Manager
Elizabeth
Newton
Lead
Fabrication
Engineer
Dave Miller
Design
Engineer
Chuck
Vaughan
Systems
Engineer
Shayla
Stewart
Assistant
Project
Manager
Ted
Schumacher
Assistant
Fabrication
Engineer
Sameera
Wijesinghe
Design
Engineer
Jeff Childers
Software
Engineer
Steven To
Assistance as
Needed from
Team
Assistance as
Needed from
Team
Assistance as
Needed from
Team
Figure 13-1 Organizational Responsibilities
Figure 13-1, above, shows organizational responsibilities for the fabrication and testing phase
of the project. It is broken up into four components: project management, fabrication, design
document work, and verification and testing. The responsibilities of each team are
summarized in the work breakdown structure in the next section.
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13.2.0 Work Breakdown Structure
MiDAs
Project
Management
Fabrication
Design
Document
Verification and
Testing
Scheduling
Fabricating
Chambers
TRL 6-7 Design
Subsystem
Integration and
Testing
Organizing
Meetings
Fabricating
Chassis and
Supports
Preliminary
Drawings of
Designs
System
Integration and
Testing
Interface with
Customer
Integrating
Electrical
and
Mechanical
Systems
Creating
Design
Document
Creating Testing
Software
Maintaining
Technical
Drawings
Creating
Instrument
Software
Figure 13-2 Work Breakdown Structure
Figure 13-2 shows the work breakdown structure. Each team is responsible for various tasks,
which are outlined in the figure and explained below.
The responsibility of the project management team is to ensure that the rest of the project
runs smoothly. This includes duties such as scheduling, organizing and running meetings,
and interfacing with the customer. These tasks will be performed by the project manager
and the assistant project manager.
The fabrication team is in charge of the actual creation of the parts. This includes
maintaining and updating SolidWorks models and drawings, as well as machining the parts.
These tasks will be primarily performed by the fabrication engineer and the assistant
fabrication engineer, but the rest of the MiDAs team will assist with less complicated parts.
The MiDAs team also has access to BioServe’s machine shop, which can fabricate some
parts as well.
The design document team is in charge of upgrading the field instrument to be more Marsapplicable. These upgrades will not be implemented, but will be included in a design
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document to be delivered to the customer. This document will provide design suggestions to
future teams working on this project on how to make the instrument more automated and
able to survive in a Mars-like environment. The whole MiDAs team will work on this
document as necessary.
Verification and testing includes development of testing and integration plans as well as
actually assembling and testing the system and subsystem. The team must show that each
requirement in the PDD is verified appropriately. All members of the MiDAs team will
assist in the integration and testing of the instrument.
13.3.0 Schedule
Figure 13-3 Schedule for Spring Semester
Figure 13-3, above, shows the schedule for the MiDAs team for the second phase of the
project. This phase will include the fabrication, integration, and testing of the MiDAs
project.
There are three primary tasks for the group as a whole. First, all parts will be ordered during
Winter Break and the first two weeks of the semester. Priority will be given to the
components that go into fabricating the autoclave and test chambers, since these are
machined first. Second, the entire team will assist with the component integration. Third,
everyone will work on the users’ manual. Creating the manual spans about seven weeks of
the second semester, and will be written concurrently with the integration of the components.
This will help ensure that users’ manual is as clear and precise as possible.
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The fabrication team will be in charge of manufacturing all the components for the project.
In order to facilitate integration and iron out problems early, each “path” of the instrument
will be manufactured separately. This means that one autoclave, one reaction chamber, and
the attachments between them will be made first, followed by the second set. The fabrication
team will also help with the electrical connections and integration towards the end of the
semester.
The testing and verification teams will be in charge of assembling and integrating the various
components. They will then test the components according to the testing and verification
plan. The testing team will also be in charge of writing LabView code both for testing and
for actual instrument functionality.
13.4.0 Specialized Facilities and Resources
The MiDAs team has access to several special facilities and resources. In addition to the
aerospace machine shop and electronics shop, BioServe is providing assistance in many
ways. BioServe is providing the team with matching funds, bringing our total budget to
$8,000. BioServe can also provide small parts, such as screws, wires, and spare materials if
they are available. BioServe also has its own machine shop, which is run by Don Geering.
Mr. Geering is available to help the fabrication team by making parts if we run short on time,
or by fabricating delicate or complicated parts, such as the sensor ports on the reaction
chambers.
For testing purposes, BioServe has several facilities available for the MiDAs team. They
have a temperature-controlled testing chamber where the instrument can be tested in
variable-temperature environments to ensure that the thermal controls function properly.
They also have a biological lab available to test the sterility of the soil transportation. Also,
BioServe can provide a clean room to assemble the sterile components.
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13.5.0 Overall Budget
The overall budget for MiDAs is shown in Table 13-1. This table includes all known parts.
The numbers shown are raw and do not include a safety factor. The total budget is just over
$4,550, which is $3,450 below our total allotted budget.
Item
Thermal Control
Melamine
Insulation
Strip Heater
Thermoelectric
Cooler (TEC)
Heat Sink
Sensors
Mechanical
Quantity
Cost
1
(24”x48”x2”)
7
$50
$237
4
$107
Melcor
HX6-201-L-M
4
$46
Temperature
National
SA1-RTD
6
$300
Pressure
Omega
PX139
4
$340
ISE Package
Tufts
--
2
--
Ultem 1000
8686K81
$155
6384K44
1
(24”x2” rod)
2
(12”x2.5” rod)
2
(48”x48”x.0625”)
2
Rotary Shaft
Ring Seal
Pumps
McMasterCarr
McMasterCarr
McMasterCarr
McMasterCarr
McMasterCarr
Instech
9562K41
2
$7
P625/275.133
2
$690
Motors
Micromo
1224
2
$600
Butterfly Valve
McMasterCarr
Dimond
Systems
Kontron
4820K31
2
$174
DMM-37X-AX
2
$480
MOPSlcdLX
1
$450
PA75CC
2
$25
WTC3243
4
$348
TOTAL
$4554
316 Stainless
Steel
Aluminum
Bearing
Computer/DAQ
Table 13-1 Overall Budget
Vendor
Vendor Part
Number
McMaster86145K27
Carr
Minco
HK5544R33.1L1
2B
Melcor
CP-0.8-127-06L
DAQ
Embedded CPU
Mixer Controller
Thermoelectric
Controller
Apex Microtechnology
Apex Microtechnology
89325K673
89015K53
$300
$230
$15
Page 145 of 196
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MiDAs
December 18th, 2006
14.0 Appendix A: Mechanical Design
Drawings for the parts that will be manufactured are shown on following pages.
14.1.0 Mechanical Drawing Tree
Page 146 of 196
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MiDAs
December 18th, 2006
14.2.0 Sterilization Chamber Lid
MiDAs-SC-101-01 – Sterilization chamber lid - SolidWorks part and drawing by DM
Page 147 of 196
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MiDAs
December 18th, 2006
14.3.0 Sterilization Chamber Body
MiDAs-SC-201-01 – Sterilization chamber body - SolidWorks part and drawing by DM
Page 148 of 196
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MiDAs
December 18th, 2006
14.4.0 Sterilization Chamber Bottom
MiDAs-SC-401-01 – Sterilization chamber bottom - SolidWorks part and drawing by DM
Page 149 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
14.5.0 Sterilization Chamber Assembly
MiDAs-SC-A-000-01 – Sterilization chamber assembly - SolidWorks part and drawing by
DM
Page 150 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
14.6.0 Reaction Chamber Cap
MiDAs-RC-P-301-01 – Reaction chamber cap - SolidWorks part and drawing by DM
Page 151 of 196
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MiDAs
December 18th, 2006
14.7.0 Reaction Chamber Base
MiDAs-RC-P-401-01 – Reaction chamber base - – SolidWorks part and drawing by DM
Page 152 of 196
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MiDAs
December 18th, 2006
14.8.0 Reaction Chamber Body
MiDAs-RC-P-101-01 – Reaction chamber body – SolidWorks done by JF and PK at
BioServe
Drawing done by DM based on that part
Page 153 of 196
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MiDAs
December 18th, 2006
14.9.0 Reaction Chamber Assembly
MiDAs-RC-A-000-01 – Reaction chamber assembly – body from SolidWorks from
BioServe, cap, bottom and overall drawing by DM
Page 154 of 196
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
14.10.0
MiDAs
December 18th, 2006
Reagent Water Chamber Body
MiDAs-WC-P-101-01 – Reagent water chamber body – SolidWorks part by SW, drawing by
DM
Page 155 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
14.11.0
MiDAs
December 18th, 2006
Water Chamber Cap
MiDAs-WC-P-102-01 – Water chamber cap - – SolidWorks part by SW, drawing by DM
Page 156 of 196
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
14.12.0
MiDAs
December 18th, 2006
Top Support Shelf
MiDAs-OC-P-101-01 – top shelf holding sterilization chambers - – SolidWorks part by SW,
drawing by DM
Page 157 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
14.13.0
MiDAs
December 18th, 2006
External Case
MiDAs-OC-P-102-01 – External case, basic dimensions only - – SolidWorks part by SW,
drawing by DM
Page 158 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.0 Appendix B: Electrical Design
15.1.0 Electrical Schematic Tree
Subsystem/Item
Drawing Number
Electrical Block Diagram
MiDAs-OS-A-200-01
Power Subsystem
Power Supply
Power Distribution
MiDAs-OS-A-210-01
MiDAs-OS-P-211-01
MiDAs-OS-P-212-01
Sensor Subsystem
Wire Harness
Pressure Sensors
Temperature Sensors
Control Subsystem
Mixer/Control 1
Mixer/Control 2
Autoclave TEC/Control 1
Autoclave TEC/Control 2
RC TEC/Control 1
RC TEC/Control 2
Wire Harness
Fan
Switch Board
Strip heaters
LEDs
Wire Harness
Water Pump
Data Acquisition and
Control
Computer
Analog input
Digital input
Analog Output
MiDAs-OC-A-220-01
Drawing
Name
Drawn by
CV
Power System
CV
Sensor
Schematics
CV
Control
Schematics
CV
MiDAs-SC-P-221-01
MiDAs-SC-P-222-01
MiDAs-SC-P-223-01
MiDAs-OS-A-230-01
MiDAs-SC-P-231-01
MiDAs-SC-P-232-01
MiDAs-SC-P-233-01
MiDAs-SC-P-234-01
MiDAs-SC-P-235-01
MiDAs-SC-P-236-01
MiDAs-SC-P-237-01
MiDAs-SC-P-238-01
MidAs-OS-A-240-01
Switch Board
Layout
CV
Computer
Interface
CV
MiDAs-SC-P-241-01
MiDAs-SC-P-242-01
MiDAs-SC-P-253-01
MiDAs-SC-P-254-01
MidAs-OS-A-250-01
MiDAs-SC-P-251-01
MiDAs-SC-P-252-01
MiDAs-SC-P-253-01
MiDAs-SC-P-254-01
Page 159 of 196
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ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.2.0 Overall Electrical Schematic
Electrical Schematic
110VAC
Power Source
12V
+5V
Power
Conditioning/
Protection 12V
Power Distribution/
Switching
CPU
Communication (USB)
T
Dig.Out
T
P
Data Acquisition/
Control
Autoclave 1
T
AHC2
Temp
Control/
Power cut
off
Autoclave 2
P
Water Pump
L1
Control Chamber
AHC 1,2: Autoclave
heater/cooler 1,2
An.In: Analog input
An.out: Analog output
T=Temperature Sensor
P=Pressure Sensor
Dig.Out: Digital Output
Ambient
AHC1 Temp control/
Power Cut off
Reagent Water
Chamber
Control Switch
An.In
An.out
P
T
P
L2
Test Chamber
T
T
Speed control
M1
Electrochemical
Sensors(12)
M2
Speed control
IHC: Incubator Heater/Cooler
L 1,2: Light 1,2
M1,2: Mixer 1,2
Temp control
IHC
Reaction Chamber Environment
Page 160 of 196
1
TEC
AC
2
TEC
AC
1
TEC
RC
2
TEC
RC
1
Mixer
2
Mixer
2
Control
2
TEC
1
TEC
Autolcave
x
4
x
2
x
4
x
2
x
4
Autoclave
1
Control
RC
x
2
x
4
x
2
x
3
x
2
RC
1
Control
Mixer
x
3
x
2
2
Control
Mixer
H2
Autoclave
LED's
H1
Autoclave
Pump1
2
Pump
6
x
Output
Analog
x
1
1
x
x
output
Digital
x
3
6
Board
Switch
2
2
x
2
x
2
x
2
x
2
Input
Analog
x
0
1
x
0
2
Sensors
x
2
Computer
Distribution
Power
Supply
Power
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ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.3.0 Electrical block diagram
Page 161 of 196
Diagram
Sensor
D
Sig
G
5
6
Page 162 of 196
D
N
D
N
R
4
N
VS
+
3
G
PX139
2
G
D
N
G
1
AP2
7
8
PX139
9
0
1
R
1
1
2
1
°
t
°
K
0
1
t
K
1
0
Thermistor
6
R
P
R
K
K
0
1
D
N
G
0
1
Sig
VS
+
Q
A
D
PX139
Thermistor
5
R
K
0
1
R
K
0
1
°
t
Sig
VS
+
Thermistor
4
R
K
0
1
K
0
1
°
t
D
N
G
AP1
Thermistor
3
R
PX139
K
0
1
K
0
1
°
t
R
Thermistor
2
R
K
0
1
Sig
VS
+
K
0
1
°
t
Thermistor
1
R
P
A
+5VDC
D
N
G
D
N
G
F
u
0
0
1
Cap
Zener
D
1
.1uF
.22uF
?
C
?
D
Earth
Cap
Cap
D
N
G
1
15.5.0 Sensor Diagram
?
C
?
C
V
2
1
+
Breaker
Circuit
SW-SPST
T
U
O
N
I
2
3
Supply
Power
Amps
5
+5VDC
LM340-XX
+12VDC
Switch
off
On
?
U
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.4.0 Power Diagram
Motor
Pump
M
?
B
5
2
6
P
System
Control
D
N
G
CLR
8
MI
+
7
MI
-
6
PI
DC
5
PG
4
PG
1
3
+V(ref)
RWC
2
SCI
R
-V(ref)1
Pump
Peristaltic
5
6
7
8
9
+12VDC
+5VDC
G
G
D
N
G
.22uF
5
Cap
?
C
2.27MOhm
G
PA75CC
1.5K
.22uF
B
A
O
D
N
G
D
N
G
D
N
G
D
N
G
K
1
H
G
Tap
Res
LED2
LED1
2
H
R
?
D
N
D
N
Page 163 of 196
K
5
K
5
K
5
K
D
N
G
D
N
G
D
N
1.5K
1.5K
1.5K
.22uF
D
4
N
R
3
D
2
N
G
D
N
G
1
Computer
Cap
Cap
Vs
+
?
C
?
C
IAB
+
4.9K
4.9K
Mixer1
Vs
-
M
P
R
P
R
?
B
IAA
+
D
N
G
33.3K
33.3K
IAA
-
2.27MOhm
2.27MOhm
A
A
O
I
R
I
R
.22uF
Control
Motor
Cap
K
1
?
C
Res3
Res3
2.27MOhm
R
R
L
L
C
C
8
9
1
1
1
1
1
7
0
1
2
3
4
6
5
4
3
2
1
8
9
1
1
1
1
1
7
0
1
2
3
4
6
5
4
3
2
1
F
R
I
R
D
N
G
WTC3243
WTC3243
CONTROLLER
TEC
CONTROLLER
TEC
PA75CC
K
0
2
K
0
2
B
A
O
D
N
G
Vs
+
RBIAS
RBIAS
IAB
+
Mixer1
Vs
-
M
?
B
IAA
+
IAA
-
A
A
O
°
t
K
0
1
°
t
D
N
K
1
G
D
N
G
Control
Motor
Thermistor
IHC1
K
0
1
IHC2
K
1
K
1
Thermistor
Res3
Res3
F
R
I
R
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.6.0 Control Diagrams
Motor
Pump
M
?
B
5
2
6
P
System
Control
D
N
G
CLR
8
MI
+
7
MI
-
6
PI
DC
5
PG
4
PG
3
+V(ref)
K
1
2
SCI
Tap
Res
-V(ref)1
D
N
G
?
R
Pump
Peristaltic
1
2
3
4
5
6
7
8
9
+12VDC
Computer
+5VDC
D
N
G
D
N
G
Page 164 of 196
K
5
K
5
K
5
K
5
D
N
G
D
N
G
.22uF
.22uF
1.5K
1.5K
1.5K
1.5K
Cap
Cap
?
C
?
C
2.27MOhm
2.27MOhm
4.9K
4.9K
P
R
P
R
33.3K
33.3K
I
R
I
R
R
R
L
L
C
C
8
9
1
1
1
1
1
7
0
1
2
3
4
6
5
4
3
2
1
8
9
1
1
1
1
1
7
0
1
2
3
4
6
5
4
3
2
1
WTC3243
WTC3243
CONTROLLER
TEC
CONTROLLER
TEC
K
0
2
K
0
2
RBIAS
RBIAS
°
°
t
t
K
0
1
K
0
1
Thermistor
IHC2
Thermistor
IHC2
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
D
N
V
2
1
+
V
5
6
3
5
3
D
N
G
+
0
G
8
3
7
3
4
9
V
5
+
3
V
2
1
+
D
N
G
4
3
Distribution
Power
V
5
+
2
3
V
2
1
+
0
3
D
N
G
8
2
V
2
1
+
6
2
D
N
G
4
2
V
2
1
+
2
2
D
N
G
0
2
V
2
1
+
8
1
7
1
Sig
D
N
G
6
1
5
1
Sig
V
2
1
+
4
1
3
1
Sig
D
N
G
2
1
1
1
Sig
V
2
1
+
0
1
9
Sig
D
N
G
8
7
Sig
V
2
1
+
6
5
Sig
D
N
G
4
3
Sig
V
2
1
+
2
1
Sig
Items
Switched
Board
Switch
Output
Digital
Diagram
Wire
System
D
N
G
D
N
G
V
2
1
+
V
2
1
+
Computer
Supply
Power
Sig
D
N
G
Sig
V
5
+
D
N
G
AT2
V
2
1
+
Sig
Pump
D
N
G
D
N
G
V
5
+
V
2
1
+
AT1
Heater2
Sig
D
N
G
D
N
G
V
2
1
+
V
5
+
Heater1
Sig
D
N
G
D
N
V
2
1
+
V
5
Pump
T
Sig
Sig
C
+
V
5
+
T
G
D
N
G
A
Sig
Sig
D
N
G
D
N
G
Sig
V
2
1
+
Sig
V
5
+
D
N
G
D
N
G
Sig
V
2
1
+
D
N
G
V
5
+
D
N
G
V
2
1
+
V
5
+
TEC4
T
T
D
N
G
Sig
Sig
V
2
1
+
Sig
D
N
G
D
N
G
Sig
D
N
G
V
5
+
V
2
1
+
D
N
G
V
5
+
Sig
V
2
1
+
D
N
G
TEC3
T
R
Sig
V
5
+
V
5
+
D
N
G
Sig
Sig
D
N
G
V
2
1
+
D
N
G
D
N
G
V
2
1
+
Sig
V
5
+
V
5
+
D
N
G
Sig
TEC2
P
R
V
2
1
+
D
N
G
V
5
+
V
5
+
Sig
V
5
+
D
N
G
D
N
G
D
N
G
Sig
V
2
1
+
V
2
1
+
V
5
+
D
N
G
V
5
+
V
5
+
TEC1
AP2
D
N
G
Sig
Sig
V
2
1
+
Sig
D
N
G
D
N
G
Sig
D
N
G
V
5
+
V
2
1
+
D
N
G
V
5
+
Sig
V
2
1
+
D
N
G
Mixer2
AP1
Sig
V
5
+
Sig
D
N
G
Sig
Input
DAQ
D
N
G
V
2
1
+
D
N
G
V
2
1
+
V
5
+
inputs
Control
Mixer1
P
A
Fall Final Report
ASEN 4018 – Senior Projects I: Design Synthesis
MiDAs
December 18th, 2006
15.7.0 Wire Diagram
15.8.0 Switch Board
Page 165 of 196
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MiDAs
December 18th, 2006
16.0 Appendix C: Software
16.1.0 Software Tree
AIn = Analog Input:
Acquires pressure and temperature data
DBit Out = Digital Bit Out: toggles output high or low to
control the switch board
Err Msg = Error message: displays error message if output
is not configured right
To Eng = Converts binary inputs from levels to voltage level
ToEngArray= Converts array of binary inputs to voltage level
= Autoclave
temperature/pressure.vi
= Elapse Timer: Counts amount of time elapsed after specific case
= Time Delay: Waits specified time before taking next
sensor data
= Write File: Writes data to measurement
file
Page 166 of 196
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December 18th, 2006
16.2.0 Software Prototype
Page 167 of 196
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MiDAs
December 18th, 2006
17.0 Appendix D: Data Sheets
Page 168 of 196
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MiDAs
December 18th, 2006
17.1.0 Motor
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17.2.0 TEC
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December 18th, 2006
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17.3.0 Motor Control
Page 172 of 196
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17.4.0 Pressure Sensor
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17.5.0 TEC Controller
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December 18th, 2006
17.6.0 Peristaltic Pump
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MiDAs
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17.7.0 Voltage Regulator
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17.8.0 CPU
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18.0 Appendix E: References
Cengel, Yunus. Introduction to Thermodynamics and Heat Transfer. McGraw-Hill.
University of Nevada, Reno. 1997
Gilmore, David. Spacecraft Thermal Control Handbook. Aerospace Press. El Segundo,
California. 2002
Mankins, John C. “Technology Readiness Levels.” April 6, 1995.
<http://ipao.larc.nasa.gov/Toolkit/TRL.pdf.>
www.dimondsystems.com
www.kontron.com
www.matweb.com
www.mcmaster.com
www.melcor.com
www.minco.com
www.omega.com
www.sonaer.com
www.sonozap.com
www.claybornlab.com
www.thomasnet.com
www.coleparmer.com
www.taycoeng.com
www.watlow.com
www.aerogel.com
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