ECE40275 - Data Acquisition
Systems
Victor Kolesnichenko
UCSD Extension
Fall 2014
Course Objectives:
• Provide students with the knowledge required to specify, design,
and implement a Data Acquisition System (DAS)
• Learn common architecture of a Data Acquisition System and its
components
• Apply basic principles of sampling and digitizing theory
• Design a simple DAS based on a Cortex-type microcontroller. This
includes hardware and firmware design.
• Collect and analyze data from the DAS
• Evaluate “build versus buy” option
Grading and withdrawal policy – read
Buy STM32F4-Discovery board from ST Microelectronic
Buy USB to USB To RS232 TTL UART PL2303HX Auto Converter from eBay
The main book: Data Conversion Handbook, Analog Devices, 2005, ISBN : 0750678410
http://hotfile.com/dl/19138498/ca230e6/0750678410.rar.html - does not work anymore
Roster Sheet – to sign
victork@ca-consulting.us, 858-500-6088
Prerequisites:
• Students must have a basic understanding of C programming, circuit
analysis, analog and digital electronics, and microprocessor-based
design.
Audience:
• Instrumentation engineers / electronics engineers in manufacturing
and process industries;
• Data Acquisition & Control (DA&C) system designers / integrators;
• Control and Instrumentation Engineers;
• Students taking Embedded Engineering courses;
• Electrical, mechanical, software, and chemical engineers and
technicians wishing to understand the essentials of data acquisition.
Demo Board Selection
• Criteria: price less than $50, easy
to add sensors and memory,
several IDEs
• TI TMDX28027USB Piccolo
ControlStick $39.00, now $40.5
• Microchip DM330011 - MPLAB
Starter Kit for dsPIC DSC
$59.98
• Futurlec dsPIC30F2010
Development Board $44.90
Demo Board Selection, 2
• Futurlec STM32F103
Development Board
$39.90
Coridium Super-PRO
board - $49.00
(LPC1756)
STM32F4-Discovery
Features of STM32F4-Discovery
• STM32F407VGT6 microcontroller featuring 32-bit ARM
Cortex-M4F core, 1 MB Flash, 192 KB RAM in an
LQFP100 package
• On-board ST-LINK/V2 with selection mode switch to use
the kit as a standalone ST-LINK/V2 (with SWD
connector for programming and debugging)
• Board power supply: through USB bus or from an
external 5 V supply voltage
• External application power supply: 3 V and 5 V
• LIS302DL or LIS3DSH ST MEMS 3-axis accelerometer
• MP45DT02, ST MEMS audio sensor, omni-directional
digital microphone
• CS43L22, audio DAC with integrated class D speaker
driver
Features of STM32F4-Discovery, 2
•
•
•
•
•
•
•
•
•
Eight LEDs:
LD1 (red/green) for USB communication
LD2 (red) for 3.3 V power on
Four user LEDs, LD3 (orange), LD4 (green), LD5 (red)
and LD6 (blue)
2 USB OTG LEDs LD7 (green) VBus and LD8 (red)
over-current
Two push buttons (user and reset)
USB OTG FS with micro-AB connector
Extension header for all LQFP100 I/Os for quick
connection to prototyping board and easy probing
Price - $14.58 (Direct from STM)
Terminology
• Accuracy - The extend to which a given measurement
agrees with the defined value.
• Accuracy Class - The maximum allowable error of
measurement at reference conditions.
• ADC
Analog-to-Digital Converter is a
device that converts a continuous quantity (usually –
voltage) to discrete digital numbers.
• ANSI
American National Standards Institute
is a nonprofit, privately funded membership organization
that coordinates the development of U.S. voluntary
national standards and represents the U.S. in
international standards organizations. The institute
promotes and facilitates the development and integrity of
voluntary consensus standards and conformity
assessment systems.
Terminology, 2
• ASCII
- American Standard Code for Information
Interchange
• ASIC
- Application-Specific Integrated Circuit
• b
- Bit
• B
- Byte
• bps
- Bits per second
• CMRR
- Common-Mode Rejection Ratio
• DAQ
- Data Acquisition
• DAS
- Data Acquisition System
• dB
- decibel (?) (Graham Bell invented a phone)
• DIO
- Digital Input/Output
• DSP
- Digital Signal Process(or/ing)
Terminology, 3
• EEPROM - Electrically Erasable Programmable ROM
• ENOB
- Effective Number Of Bits
• Firmware - Software that is embedded in the electronic
device.
• FRAM
- Ferroelectric Random Access Memory
• Giga
- A prefix meaning 1,000,000,000. Example:
2.4GHz.
• GPIB
- General Purpose Interface Bus
• GUI
- Graphical User Interface
• Hertz or Hz
- Cycles per Second. The practical
unit of frequency measurement.
• I/O
- Input/Output
Terminology, 4
• I2C
- Inter IC (Integrated Circuits) Communication
• IEC
- International Electrotechnical Commission, a
worldwide organization preparing and publishing
international standards for electrical, electronic, and
related technologies. The members of IEC have national
committees in each country.
• kilo or k - the prefix meaning 1000. Use small letter k,
for example, kV.
• LAN
Local Area Network. A network
consisting of nodes that are confined within a localized
area. For example, a floor of a building, or the building
itself.
Terminology, 5
• LSB
least significant bit
• Mega A prefix (capital M) meaning
1,000,000. 10MW, for example.
• Micro (u) A prefix (small u) meaning
1/1,000,000. 100uA, for example.
• Milli (m) A prefix (small m) meaning 1/1000. 5
mA, for example.
• N.E.C.
National Electric Code. A regulation
covering the electric wiring systems on the customer’s
premises with regards to safety.
• PGA
- Programmable Gain Amplifier
• RMS
- Root-Mean-Square
• SCADA - Supervisory Control And Data Acquisition
Terminology, 6
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•
•
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S/H
- Sample-and-Hold
SNR
- Signal-to-Noise Ratio
SPI
- Serial Peripheral Interface.
USB
- Universal Serial Bus – industry standard
defining physical connections, power supply, and
protocol of communication between master and slave
• ZigBee
- ZigBee™ is the standards-based wireless
networking technology for reliable, secure, cost-effective,
low-power monitoring and control solutions. ZigBee™
provides the network, security and application profile
software layers for the IEEE 802.15.4 global wireless
standard.
Google Search Results on
Data Acquisition System
Google Search Results on
Data Acquisition System, 2
Data Acquisition System –
Definition from Wikipedia
• Data Acquisition is the process of sampling of real
world physical conditions and conversion of the resulting
samples into digital numeric values that can be
manipulated by a computer.
The components of data acquisition systems include:
Sensors that convert physical parameters to
electrical signals.
Signal conditioning circuitry to convert sensor
signals into a form that can be converted to digital
values.
Analog-to-digital converters, which convert
conditioned sensor signals to digital values.
Communication channel for transmission data to a
computer.
Data Logger (From Wikipedia)
• A data logger (also datalogger or data recorder) is an
electronic device that records data over time or in
relation to location either with a built in instrument or
sensor or via external instruments and sensors.
Increasingly, but not entirely, they are based on a digital
processor (or computer). They generally are small,
battery powered, portable, and equipped with a
microprocessor, internal memory for data storage, and
sensors. Some data loggers interface with a personal
computer and utilize software to activate the data logger
and view and analyze the collected data, while others
have a local interface device (keypad, LCD) and can be
used as a stand-alone device.
Applications of DAS:
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–
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Automotive: Crash-, Drive-Tests (DAS or Logger?)
Aerospace: “black boxes” - Data ?
Industrial: AMI, SCADA, Monitoring…
Medical: Patient diagnostic, observation, (including
remote), etc…
Scientific Research
Semiconductors Testing
Transportation: traffic statistics, schedule control,
traffic violations…
Weather forecasting
Your examples:
Architecture of a Typical DAS/Data
Logger
Sensors/
Transdu
cers
cers
Signal
Conditio
ners
Analog
to
Digital
Conver
ters
Microcon
troller
Memory
Other components – Firmware and Software
Commu
nication
Channel
Sensors or Transducers
•
There is no agreement among scientists and engineers on this definition, for
example one well known states: Transducer: 1. A device that is intended to
transform an electrical signal into acoustic, biological, chemical, electrical,
magnetic, mechanical, optical, radiational, or thermal stimuli for the purpose of
transmitting information. (Information in biological form??) 2. A device that is
intended to transform energy in one form into energy in another form for the
purpose of transmitting power. (Hydro-electro station??) Sensor: A device
that is intended to transform acoustic, biological, chemical, electrical,
magnetic, mechanical, optical, radiational, or thermal stimuli into an electrical
signal for the purpose of transmitting information.
Rich Gorczyca:
• “In a control system, sensors are on the input side and they sense specific
phenomena in the environment. Actuators are on the output side and they
manipulate or adjust phenomena in the environment. Both sensors and
actuators are transducers in that they convert one form of energy into another
form. Sensors typically convert physical energy (??) into electrical energy (??).
Actuators convert electrical energy into physical energy. A microphone is a
sensor that converts sound waves into electrical signals. A speaker is an
actuator that converts the electrical signals into sound waves. Both are
transducers.”
Overview of Sensors/Transducers
• Sensors (give me your examples)
• Transducers (piezoelectric mike or speaker,
electromechanical…- 2-way, photovoltiac,
electrochemical…- 1-way)
• Gauges (pressure, vacuum, RPM…)
• Detectors (photo, ion, alpha, beta, gamma, XRay…)
• Indicators: Test the pH of a substance by means
of the dye litmus (see also indicator )
Sensors from
http://www.sensorsportal.com/HTML/Sensor.htm
•
Optical sensors
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Biosensors
•
Torque sensors
•
Chemical sensors
•
Position sensors
•
Level sensors
•
Rotation speed
sensors
•
Proximity sensors
•
Ultrasonic sensors
•
Displacement sensors
•
Load Cells
•
Resonant sensors
•
Vacuum sensors
•
Flow sensors
•
Magnetic sensors
•
TEDS (Transducer
Electronic Data Sheet)
(IEEE 1451 plug-andplay) sensors
•
Viscosity sensors
•
Mechanical sensors
•
Wireless sensors
•
Moisture sensors
•
Yaw sensors
•
Temperature
sensors
•
Pressure sensors
•
Gas sensors
•
Nano-sensors
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Accelerometers
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Oxygen sensors
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Acoustic sensors
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pH sensors
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Humidity sensors
Tilt sensors
Inclination sensors
Sensor(s) Selection
We will operate with the term “sensor” for our DAS.
The sensor(s) selection is dictated by the requirements to
the DAS (MRD -> Functional Specs -> Hardware
Requirements Specification):
• What physical phenomenon(s) to be measured?
• What is the range of the parameter change?
• What is the required accuracy of measurements?
• Any requirements to (non)linearity (calibration)?
• Speed of measurements (samples per second),
• What type of interface does the sensor have to provide?
• What is the price limit?
Sensors Deviations (from Wikipedia)
• The sensitivity may in practice differ from the value specified. This is
called a sensitivity error, but the sensor is still linear.
• Since the range of the output signal is always limited, the output signal
will eventually reach a minimum or maximum when the measured
property exceeds the limits. The full scale range defines the maximum
and minimum values of the measured property.
• If the output signal is not zero when the measured property is zero, the
sensor has an offset or bias. This is defined as the output of the sensor
at zero input.
• If the sensitivity is not constant over the range of the sensor, this is
called nonlinearity. Usually this is defined by the amount the output
differs from ideal behavior over the full range of the sensor, often noted
as a percentage of the full range.
• If the deviation is caused by a rapid change of the measured property
over time, there is a dynamic error. Often, this behavior is described with
a bode plot showing sensitivity error and phase shift as function of the
frequency of a periodic input signal.
• If the output signal slowly changes independent of the measured
property, this is defined as drift (telecommunication).
Sensors Deviations (from Wikipedia), 2
• Long term drift usually indicates a slow degradation of sensor properties
over a long period of time.
• Noise is a random deviation of the signal that varies in time.
• Hysteresis is an error caused by when the measured property reverses
direction, but there is some finite lag in time for the sensor to respond,
creating a different offset error in one direction than in the other.
• If the sensor has a digital output, the output is essentially an
approximation of the measured property. The approximation error is also
called digitization error.
• If the signal is monitored digitally, limitation of the sampling frequency
also can cause a dynamic error, or, if the variable or added noise
changes periodically at a frequency near a multiple of the sampling rate, it may induce aliasing errors.
• The sensor may to some extent be sensitive to properties other than the
property being measured. For example, most sensors are influenced by
the temperature of their environment.
• All these deviations can be classified as systematic errors or random
errors. Systematic errors can sometimes be compensated for by means
of some kind of calibration strategy. Noise is a random error that can be
reduced by signal processing, such as filtering, usually at the expense of
the dynamic behavior of the sensor.
Functional Requirements
Specification for the Project Design
• Data Acquisition System capable of logging and storing
data from two temperature sensors (inside and outside
the building, for example)
• Samples are 8-bit long (what is the accuracy?)
• Temperature range from 0 to 100F (what is the
resolution?)
• Max number of records - >=10000 (how much memory?)
• Each record must have a time stamp
• Price of the DAS must not exceed $50.00
• The DAS must be reprogrammable and reconfigurable
via RS-232
• Data must be stored in non-volatile memory
• The DAS must be able to work as a stand-alone unit
Temperature Sensors
• Semiconductor Diode (−2 mV/˚C at low constant
current through the diode, needed additional
circuitry)
• Integrated Circuit (analog or digital output)
• RTD – Resistive Temperature Detector (carbon,
platinum layer on substrate): NTC, PTC (needed
additional circuitry)
• Thermocouple - Junction of different metals or
alloys (needed some methods of cold-junction
compensation to adjust for varying temperature
at the terminals and amplifiers)
Signal Conditioning
• In most practical cases a proper interface
between a sensor and an ADC is required.
• The goals of the interface is to provide the ADC
with:
– Full-scale signal (voltage) corresponding to the
maximum of the measured parameter
– Low-pass frequency filtering of the input signal equal
or lower than maximum sampling frequency of ADC
– If necessary – differential and/or isolated from the
sensor signal
– Phase correction – in case of simultaneous sampling
or S&H from different kinds of sensors (Wattmeter)
– Linearization of sensor’s characteristic, if necessary
Components of Signal Conditioners
• Operational Amplifiers (OpAmps)
• Passive components:
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Resistors
Capacitors,
Inductors (warning),
Transformers,
Optoisolators.
• Example of R-C low-pass filter
– Time Constant; error vs. time
– Graphical Interpretation with an input step function