Sunday, May 17, 2009

Thermistors for Temperature Measurement

Thermistors for industrial temperature measurements? Sure - we just took a repeat order from an OEM customer (for instruments - we don't sell the thermistors themselves). So, I thought I'd write about them.

Let me identify myself - Harry Trietley, President & Chief Engineer. In the 1980s I worked at YSI (formerly Yellow Springs Instruments) who had once pioneered precision interchangeable thermistors. (They no longer make them - sold the product line off.) So, I had the opportunity to learn how to apply them. We now have two regular OEM customers.

You won't find thermistor info on our web site - maybe we should add it. For now, this blog is a start.

Thermistors are resistance thermometers but much different from RTDs (Resistance Temperature Detectors). RTDs are linear (approximately), wide range, relatively low sensitivity (about 0.4% per deg C) and increase with temperature. Thermistors are highly nonlinear, narrow range, high sensitivity and decrease with temperature (about 4% per deg C).

There are many types of thermistors - small, large, highly accurate, loose accuracy, many shapes. This blog is about NTC (Negative Temperature Coefficient) thermistors. There also are PTC (Positive Temperature Coefficient) thermistors that act more like thermal switches - increasing resistance rapidly in just a few degrees near the switching point. PTCs are not used for linear temperature measurement.

Precision NTC thermistors excel in moderate temperature, narrow range applications. They are very sensitive, and some have tighter accuracy specs than RTDs. One of our customers uses them in heating/air conditioning control; the other, precision measurements related to integrated circuit manufacturing processes. They also see wide use in medical and laboratory temperature measurement.

We have made simple adaptations of our signal conditioners (temperature transmitters) for use with thermistors. So far we haven't published standard spec sheets, but they are very similar to our other instrument styles. (See

If you have an application let us know. Each application is different as there are many thermistor types. We would need to start by knowing your measurement temperature range - also the thermistor type if you have chosen one yet. If not, we can help you find the right one. Probably best to ask for Harry.

e-mail:, US phone (941) 927-0300 or toll-free (800) 808-0300.


  1. Ummmm... can I have that in English please? LOL!

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