Getting the Most from
your Sensors and
Transducers
How to make fast, reliable
sensor measurements with
your data logger system
Presenter: Mark D. Bailey
Product Marketing Manager
Modular Data Acquisition and Switching Platforms
Agilent Technologies
© Agilent Technologies, 2012
1
Reliable Measurement of Sensors/Transducers
In this seminar, we will cover:
1. Common Sensor Types; their advantages and disadvantages
2. Techniques to reduce Sources of Error and Noise
3. Interfacing Transducers to a Data Logging System
4. Using a Web Interface to quickly set up & debug a Data Logger
5. Fast and easy instrument control and automation using Agilent’s Command Expert S/W
At the end of the seminar, you should be able to:
1. Select the correct sensors for your application
2. Reduce measurement errors due to noise and other factors
3. Identify the necessary characteristics/specs for your data logger system
4. Recognize the benefits of an instrument’s built-in web server and data logging software
5. See the benefits of Agilent’s Free Command Expert Software
2
Data Logger System Architecture
Our focus today …
Transducer
Signal
Conditioning
…and we will also touch on these
Multiplexer
Digital
Multimeter
(DMM)
A/D
Display
Analysis &
Reporting
SCAN
MON
VIEW
3
28.32 C
Data Logger Systems - Transducers
Transducers or sensors convert a physical phenomena to an electrical signal
Physical Parameters
•
•
•
•
•
•
•
Temperature
Flow
Pressure
Strain
Position
Weight
Speed
Electrical Signals
Transducer
DC Volts
AC Volts
DC Current
AC Current
Resistance
Frequency
• Choose the correct sensor
Agilent Application Note 290:
“Practical Temperature Measurements”
4
• Mount it correctly
• Position it correctly
Physical Transducers
Rotation
Pressure
5
Linear Voltage Displacement Transducer (LVDT)
Strain
Temperature
US Distribution Training March 2012
© 2012 Agilent Technologies
Temperature Sensors
Thermocouples
RTDs
Galileo Thermometer
Thermistors
IC Sensors
Agilent Application Note, “How to Select the Correct Temperature Sensor”
http://cp.literature.agilent.com/litweb/pdf/5990-9793EN.pdf
6
Thermocouples
Thermocouples made from two Dissimilar Metals
(e.g.; Iron and Constantan)
Metal A
• J-type thermocouple @ room temp < 1mV
• A 1 C change at 0 C = 50.38 V
• To see a 0.1 C change in a J-type
thermocouple at 0 C, your instrument must
be able to resolve down to 5 V.
+
V
AB
Metal B
-
Watch for:
• Good junctions
• Thermal shunting
• Noise and leakage current
• Thermocouple specs
• Calibration of TC
7
How to measure a Thermocouple
•
Create a reference junction
•
•
Measure Tref using a thermistor
Lookup Vref for Thermocouple
at reference junction
•
Compute Vx = V+Vref
•
Solve for Tx using Vx
 Need sufficient resolution to make
accurate thermocouple measurements;
22-bit or better A/D converter (DMM)
 Does the Data Logger have internal
reference junction compensation?
 Does the Data Logger have thermocouple conversion routines built-in?
Metal A
VX
Metal B
Tref
Vx
V
Vref
0
8
Metal C
+
V
Metal C
o
Tref
Tx
Thermistors
Better accuracy than thermocouples, but more expensive
• They measure absolute temperature
• A common thermistor type measures
5K at 25 C, with a 4% change per C
• Therefore, a 1 C change = 200 change
• 10 ohms of lead resistance would cause
an insignificant 0.05 C error
Does the Data Logger have built-in
conversion routines for all the
common thermistor types?
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Thermistor
R = V/I
• Often physically small mass
• Won’t cause thermal loading
• A large measurement current
will cause self heating
Resistance Temperature Detector
(RTD)
• Absolute temperature measurement
• Highly accurate measurement
• Platinum RTD has 100
with 0.385 / C
at 0 C
• 10 of lead resistance would cause
a 26 C error (very significant!)
• Avoid self heating - a 5 mA current source
would create 2.5 mW of power in our RTD
• At 1 mW/ºC, that is an error of 2.5/ºC
Does the Data Logger have built-in
conversion routines for the common
RTD types?
10
Integrated Circuit Temperature Sensor
Linear change in voltage or current
with a change in temperature
• Absolute measurement
• 10 mV/K (voltage IC)
• 1 A/K (current IC)
• At room temperature, the output
is approximately 3V with a
10mV/°C change
• Limited temperature range < 150 C
• Fairly large mass
• Requires external power
11
Temperature Sensor Summary
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Humidity Sensors
Common humidity sensors include:
– Capacitive (RH)
– Resistive (RH)
– Thermal Conductivity (Absolute)
The sensor elements require circuitry for signal conversion, linearization, and
buffering. A separate bias supply is needed for power.
A capacitive sensor is well suited for measuring an environmental chamber’s humidity.
Its DC voltage output signal is in turn easily measured by the data acquisition
equipment’s DMM.
Do you need to measure Absolute Humidity or Relative Humidity?
13
Strain Gage Measurements
Use a Wheatstone bridge to provide offset nulling, increased gain
and temperature drift compensation.
You can also use a four-wire ohm measurement.
See a YouTube video at AgilentTube; Search on
“Static and Dynamic Forces Overview”
14
Pressure Sensors
15
Rotational Speed Sensors
RPM Sensor
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Rotational Speed Sensors
Variable Reluctance
Sensor
Hall Effect Sensor
See a YouTube video at AgilentTube;
Search on “Measuring Rotational Speed, Revolutions Per Minute”
17
Sensor Summary
The Data Logger needs to be able to measure and convert all these different
signal levels to meaningful measurements like temperature, humidity, rpm, etc.
18
Using 4-20 mA current loops
Use a 250Ω termination resistor:
20 mA = 5 volts = wide open
4 mA = 1 volt = fully closed
0 mA = 0 volts = open circuit
19
Dealing with noise
Thermocouples are highly
susceptible to noise:
• Very low output voltage
• Very long physical runs
Types of noise:
1. Common mode noise, generated by ground loops
2. Normal mode noise, generated by electromagnetic fields
3. Electrostatic noise, generated by rotating equipment, etc.
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Reducing Common Mode Noise
Eliminate Ground Loops
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Reducing Normal Mode Noise
Minimize coupling, add filtering
MEASUREMENT TIPS
• Reduce the field strength interfering with
the measurement. It is better to run more
wire and avoid the field.
• Minimize the size of the measurement
loop. Use twisted-pair cabling; it’s like
making a smaller receiving antenna.
• Run the measurement wires perpendicular
to high-current wires.
22
• Reduce normal mode currents with a filter.
• Use an integrating A/D. Normal mode noise is
typically the same frequency as the line
frequency.
• Trade speed for reading rate with the
integrating A/D. For 60 Hz line frequency,
60 readings per second can be achieved using
1 PLC; only 6 readings per second can be
achieved using 10 PLCs.
Reducing Electrostatic Noise
Shielding is your friend
Application Note, “Optimizing
Thermocouple Measurements in a
Noisy Environment”
http://cp.literature.agilent.com/litweb/
pdf/5990-9794EN.pdf
23
Converting Sensor Outputs to Useful Results
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Data Logger Instrument Requirements
 Wide variety of signal types to measure
(Voltage, current, resistance, frequency, etc.)
 Wide variety of signal levels to measure
(µV to 100V, µA to 3A, etc.)
 Need to convert raw measurements into meaningful results
 Need sufficient speed, accuracy and resolution
 Should be easy to connect and re-configure sensors
 Easy to set up, troubleshoot and program
 Easy to transfer and analyze acquired data
25
Data Logging Options
Product Flexibility
High
M9000-series
34980A
Multifunction Switch
Measure Unit
34970A/72A
Data Logger
Low
Just Enough
Performance:
Up to 60 channels,
3 slots, 8 modules
Price
26
Higher Level
Performance:
Up to 560 channels,
8 slots, 21 cards
Decision Criteria
Balanced Throughput &
Performance:
High Density,
High Speed,
Many modules
Performance
Agilent 34980A Multifunction Switch/Measure Unit
• 8-slots, up to 560 2-wire channels
• Internal 6 ½ digit DMM
• Display to monitor setup and measured values
• Front panel for setup, control and debug
• Up to 1000 channels/second
• GPIB, USB, LAN (LXI)
• Remote access via built-in web interface
• Twenty-one plug-in modules
• Data Logger software included
34980A Demo System
Slot 1:
Slot 2:
Slot 3:
Slot 4:
Slot 5:
Slot 6:
Slot 7:
Slot 8:
Dual 4x16 Armature MUX
20-Ch 5A switch
N/C
40-Ch MUX w/ thermocouples
Multi-function module
4-Ch Isolated DAC
Quad 1x4 RF 50ΩMUX
N/C
“Okay, but how do I set it up and use it ??”
27
It’s Video Time !!
Internal Web Server Demo
28
Great, but how about programming and analysis??
Free BenchLink Data Logger Software
29
34826A BenchLink Data Logger
High-speed data logging software with
quick and easy access to measurements
 Supports high-performance data logging
for 34980A Switch/Measure unit
 Quick and easy test setup and execution
 Collect, monitor and manage data
 Set alarms and execute scans
 Present data on a single channel or
multiple channels
 Export data to other applications for
analysis
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34832A BenchLink Data Logger Pro
See Data Logger Pro videos at;
http://www.youtube.com/watch?v=EomiMQQivfY
http://www.youtube.com/watch?v=KPi9CUFB8zY
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Fine, but how about multiple instruments
and different programming languages?
What are the
instrument
commands?
Why is it so hard to get
the instrument
command sequence
into my programming
environment?
What are all of
the command
parameters?
?
?
What is the correct
command syntax?
?
32
Command Expert:
A new tool to help with instrument programming
Agilent Command Expert is a FREE software application that provides
fast and easy instrument control in many PC application environments
Command Expert combines
instrument command sets,
documentation, syntax
checking, command execution
and debugging all in one
interface.
33
Command Expert Key Capabilities
Assists in finding:
Integrates in:
• Right instrument commands
• Excel®
• Setting the correct parameters
• MATLAB
• Passing data and variables
• LabVIEW
• Visual Studio®
Combines in one interface:
• SystemVue
• Instrument commands
• VEE
• Documentation
• Syntax checking
• Command execution
Command Expert Overview - SCPI
Connect to instruments
Search for commands
Perform commands
using correct
syntax and
parameters
View detailed command documentation
Build, execute and debug sequences of commands
It’s Video Time Again!!
35
Integrating into Excel
MATLAB integration
37
Similar Experience in VEE and LabVIEW
EASY INSTRUMENT CONTROL NOW!
www.agilent.com/find/commandexpert
39
For more information on Command
Expert….
Download the software at
www.agilent.com/find/commandexpert
40
Reliable Measurement of Sensors/Transducers
We’ve talked about the following:
 Selecting the correct sensors for your application
 Reducing measurement errors due to noise and other factors
 Identifying the necessary characteristics for your data logger system
 Recognizing the benefits of an instrument’s built-in web server
and Data Logging Software
 Seeing the benefits of Agilent’s Free Command Expert Software
Questions ?
41
Thank you for attending !!
1. Find out more: www.agilent.com/find/34980temp
2. Watch the 34980A in Action on YouTube
3. Get a Quick Quote
4. Contact a Distribution partner
Buy from an
Authorized Distributor
www.agilent.com/find/distributors
42
31 May 2012
11:00 AM MDT
13 July 2012
11:00 AM MDT
06 Sept 2012
11:00 AM MDT
Focus on Switching: Multiplexers, Matrices and
System Performance
Focus on Control: Digital and Analog Control Tips
and Techniques
Focus on Data Acquisition: Setup, Programming,
Debugging and Maintaining a Reliable System