Common Temperature Sensing Technologies

[Barley_Li]

Temperature sensing is one of the more common technologies in today’s product applications.
To make a reliable temperature measurement, it is important to carefully select the right temperature sensor for the application. Understanding the advantages and disadvantages of the different types of temperature sensors will help to make the proper selections before a measurement.

Thermocouples, Thermistors (NTC / PTC), Resistance Temperature Detectors (RTDs) and Temperature sensing ICs are the most common temperature sensors used in the measurement.

	Thermocouple	Thermistor	RTD	Temperature Sensing IC
Low/High Temperature Range	-270°C / 1800°C	-85°C / 600°C	-250°C / 900°C	-55°C / 300°C
Linearity	Poor	Worst	Good	Best
Accuracy	Good	Calibration dependent	Great	Good
Advantages	*Self-powered, rugged	Fast response to temperature changes, high sensitivity	*Most accuarate, most stable	*Most Linear, digital interface
Disadvantages	*Non-linear, reference required, least stable, least sensitive	*Non-linear, limited temperature range, current source required	*Current source required, small resistance change, slow	*Power supply required, self-heating, limited temperature range
Typical Applications	Extreme temperature sensing - oven, test equipment	Low precision, moderate temperature range - hair dryer, protection circuits	High precision, extended temperature - gas and fluid flow	Computers, wearable devices, data logging

Low / High range given bases on commonly available through Digi-Key at time of post.

[Robert_Fay]

Recently I had a chance to speak with some of the representatives from Amphenol
Advanced Sensors and though they may be a little bias as manufacturers of thermistors they shared some excellent information on thermistors with me and I wanted to share it with you.

Thermistor Accuracy: There really is a range and the thermistor could be listed as “Best”.

Currently the RTD is listed as “Great” however, if you use the Digi-Key filter for accuracy, the best you can select with a RTD is ±0.1°C, which would be a class 1/3 Din B. For the thermistor filter you can select ±0.01°C with a part like USP3986 or MC65F103AN that has a tolerance of ±0.05°C, which is much better than the RTD.

Advantages: You could even add “Customization” to the thermistor list above.

The beauty of thermistors is that there are different ways to manufacture them, which allows them to achieve the various accuracies. It is not that they are calibrated to tighter tolerances, but they are manufactured to tighter tolerances.

With a thermistor, the geometry plays a big part in the accuracy. A bead or disc thermistor that has a large variation in size will have a tolerance of about ±5°C. (The Typical thermistor mentioned in the table above) A standard chip thermistor that is diced to a precise dimension will have a tolerance of about ±0.3°C. A ground chip thermistor, that is sized to achieve a specific resistance window will allow for tolerances down to ±0.05°C.

This adds to the number of options as well. Looking at the Digi-Key site if I type RTD into the search I get 405 items, PMIC - Thermal Management has 741 items, Thermocouple is 1325 items, but Thermistor gives you 10614 items (combining NTC and PTC).

Typical Applications: can really vary will all the thermistor options as well. While it may be true they are used in some hair dryer there are more advanced applications for the higher accuracy parts. For example: Thermometers, Harsh Environment, Battery / EV / EVH.

One of the Amphenol reps shared that the MC65 and SC30 / SC50 style thermistors listed from them are the base thermistors for three of the largest predictive thermometer OEMs in the US. The JS8746 and NKA style thermistors are an example that is suitable for immersion (Harsh Environment). The CTTS-203856-S02 and GE-1920 style thermistors are an example that are used for battery pack or coolant systems related to EV.