getting the most from your sensors and transducers · 2012-03-23 · getting the most from your...
TRANSCRIPT
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
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© Agilent Technologies, 2012
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
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Data Logger System Architecture
Transducer Signal
Conditioning Multiplexer
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting
A/D 28.32 C MON
VIEW
SCAN
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…and we will also touch on these Our focus today …
Data Logger Systems - Transducers
• Temperature
• Flow
• Pressure
• Strain
• Position
• Weight
• Speed
Transducer
DC Volts
AC Volts
DC Current
AC Current
Resistance
Frequency
Physical Parameters Electrical Signals
Transducers or sensors convert a physical phenomena to an electrical signal
• Choose the correct sensor • Mount it correctly • Position it correctly
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Agilent Application Note 290:
“Practical Temperature Measurements”
5 © 2012 Agilent Technologies
US Distribution Training March 2012
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Physical Transducers
Rotation Linear Voltage Displacement Transducer (LVDT)
Pressure Strain Temperature
Temperature Sensors
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Thermistors
Galileo Thermometer
RTDs
Thermocouples
IC Sensors
Agilent Application Note, “How to Select the Correct Temperature Sensor”
http://cp.literature.agilent.com/litweb/pdf/5990-9793EN.pdf
Thermocouples
Thermocouples made from two Dissimilar Metals
(e.g.; Iron and Constantan)
• 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.
VAB + -
Metal A
Metal B
Watch for: • Good junctions • Thermal shunting • Noise and leakage current • Thermocouple specs • Calibration of TC
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• 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
0 Tref
Vx
Vref
Tx
V
o
How to measure a Thermocouple
Tref
VX
Metal A
Metal B
Metal C
Metal C
V +
-
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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 thermo-
couple conversion routines built-in?
Thermistors
• 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
Thermistor
• Often physically small mass • Won’t cause thermal loading • A large measurement current will cause self heating
Better accuracy than thermocouples, but more expensive
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Does the Data Logger have built-in
conversion routines for all the
common thermistor types?
R = V/I
Resistance Temperature Detector
(RTD)
• 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
• Absolute temperature measurement
• Highly accurate measurement
• Platinum RTD has 100 at 0 C
with 0.385 / C
• 10 of lead resistance would cause
a 26 C error (very significant!)
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Does the Data Logger have built-in
conversion routines for the common
RTD types?
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
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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?
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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”
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Pressure Sensors
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Rotational Speed Sensors
RPM Sensor
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Rotational Speed Sensors
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See a YouTube video at AgilentTube;
Search on “Measuring Rotational Speed, Revolutions Per Minute”
Variable Reluctance
Sensor
Hall Effect Sensor
Sensor Summary
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The Data Logger needs to be able to measure and convert all these different
signal levels to meaningful measurements like temperature, humidity, rpm, etc.
Using 4-20 mA current loops
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Use a 250Ω termination resistor:
20 mA = 5 volts = wide open
4 mA = 1 volt = fully closed
0 mA = 0 volts = open circuit
Dealing with noise
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.
Thermocouples are highly
susceptible to noise:
• Very low output voltage
• Very long physical runs
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Reducing Common Mode Noise
Eliminate Ground Loops
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Reducing Normal Mode Noise Minimize coupling, add filtering
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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.
• 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
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Application Note, “Optimizing
Thermocouple Measurements in a
Noisy Environment”
http://cp.literature.agilent.com/litweb/
pdf/5990-9794EN.pdf
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
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Data Logging Options
Pro
duct F
lexib
ility
High
Low
Just Enough
Performance:
Up to 60 channels,
3 slots, 8 modules
Higher Level
Performance:
Up to 560 channels,
8 slots, 21 cards
Balanced Throughput &
Performance:
High Density,
High Speed,
Many modules
34980A Multifunction Switch
Measure Unit
34970A/72A Data Logger
Price Performance Decision Criteria
M9000-series
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Agilent 34980A Multifunction Switch/Measure Unit
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• 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: Dual 4x16 Armature MUX
Slot 2: 20-Ch 5A switch
Slot 3: N/C
Slot 4: 40-Ch MUX w/ thermocouples
Slot 5: Multi-function module
Slot 6: 4-Ch Isolated DAC
Slot 7: Quad 1x4 RF 50ΩMUX
Slot 8: N/C
“Okay, but how do I set it up and use it ??”
It’s Video Time !! Internal Web Server Demo
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Great, but how about programming and analysis??
Free BenchLink Data Logger Software
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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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?
? ?
Why is it so hard to get
the instrument
command sequence
into my programming
environment?
What are the
instrument
commands?
What is the correct
command syntax?
What are all of
the command
parameters?
Fine, but how about multiple instruments
and different programming languages?
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Command Expert combines
instrument command sets,
documentation, syntax
checking, command execution
and debugging all in one
interface.
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
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Command Expert Key Capabilities
Assists in finding:
• Right instrument commands
• Setting the correct parameters
• Passing data and variables
Combines in one interface:
• Instrument commands
• Documentation
• Syntax checking
• Command execution
Integrates in:
• Excel®
• MATLAB
• LabVIEW
• Visual Studio®
• SystemVue
• VEE
Command Expert Overview - SCPI
Connect to instruments
Build, execute and debug sequences of commands
Search for commands
Perform commands
using correct
syntax and
parameters
View detailed command documentation
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It’s Video Time Again!!
Integrating into Excel
MATLAB integration
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Similar Experience in VEE and LabVIEW
E A S Y I N S T R U M E N T C O N T R O L N O W !
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www.agilent.com/find/commandexpert
For more information on Command
Expert…. Download the software at
www.agilent.com/find/commandexpert
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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
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Questions ?
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
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Thank you for attending !!
Buy from an
Authorized Distributor
www.agilent.com/find/distributors
31 May 2012 11:00 AM MDT Focus on Switching: Multiplexers, Matrices and
System Performance
13 July 2012 11:00 AM MDT Focus on Control: Digital and Analog Control Tips
and Techniques
06 Sept 2012 11:00 AM MDT Focus on Data Acquisition: Setup, Programming,
Debugging and Maintaining a Reliable System