Select your temperature sensor
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 4/1/2007 2:00:00 AM
Temperature is the most common physical measurement in electronics. Today's sensors—thermocouples, RTDs, and thermistors—serve different purposes and are based on different technologies.
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Download a copy of Dale Cigoy's paper: How to select the right temperature sensor. Also: Useful temperature measurement links |
Thermocouples, for example, are small, easy to use, require just two wires, and cover a wide temperature range. They do, however, require linearization and a reference sensor.
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Four-wire RTDs use two wires for sensor excitation and two for measurements. Using four wires removes voltage drops in the sensor wires caused by excitation current and lead resistance. |
RTDs are more linear and more accurate than thermocouples, but they often require three or four wires (figure) and are subject to self-heating. Thermistors are the most sensitive to temperature changes but have the smallest temperature range.
Dale Cigoy, senior applications engineer at Keithley Instruments, has written a paper that covers the technologies and applications of these temperature sensors. “How to select the right temperature sensor” explains how each sensor works, describes error sources, and helps you select the right kind of sensor for an application. Cigoy also discusses the pros and cons of each sensor and explains how to avoid common mistakes when connecting temperature sensors.
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Useful temperature measurement links Mangum, B.W., et al., “The Kelvin and Temperature Measurements,” National Institute of Standards and Technology, Gaithersburg, MD, 2001. ts.nist.gov/MeasurementServices/Calibrations/upload/106-1-01.PDF Schraff, Fred, "The Principles and Methods of Using Thermocouples," www.iotech.com/mcjun96.html. Steinhart-Hart Equation spreadsheet from YSI for calculating thermistor resistance. www.reed-electronics.com/tmworld/software/stinhart.zip. Swanson, Cal, “Sensor Selection 101, Optimal Temperature Sensor Selection: The First Step in Achieving Accurate Temperature Measurement,” ECN, January 1, 2007. www.ecnmag.com/article/CA6404009.html. “Temperature Measurement Basics,” National Instruments, www.ni.com/temperature/temp_basics.htm. Temperature reference from Omega Engineering, www.omega.com/temperature/z/zsection.asp. Temperature sensor, calibration, and measurement resources, www.temperatures.com. Temperature technical reference from YSI, www.ysitemperature.com/tech-home.html. |
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