Thermistors

Arroyo Instruments uses thermistors in many of its temperature-controlled mounts, and also offers them for individual sale for custom applications (see p/n 1600-10K). Thermistors work by translating temperature into resistance, with resistance decreasing as temperature increases (sometimes referred to as a ‘negative temperature coefficient’, or NTC, thermistors).

The graph below illustrates the resistance of the thermistor as a function of the temperature:

Thermistor Resistance vs. Temperature Graph

As can be seen in the graph, the resistance of the thermistor drops very quickly. In the typical control range (0°C to 40°C), 10K thermistors offer good sensitivity to changes in temperature, and this is the range in which most 10K thermistors are typically used. 10K thermistors can be used at much higher temperatures but will suffer poorer temperature stability performance because of the lower sensitivity.

The Steinhart-Hart Equation

Resistance varies inversely with temperature in a non-linear fashion. This relationship can be accurately modeled by the Steinhart-Hart equation:

Where:

A = 1.12924E-03
B = 2.34108E-04
C = 0.87755E-07
R = actual thermistor resistance, in ohms

By default, all Arroyo Instruments temperature controllers use these constants, but our controllers will work with any set of Steinhart-Hart constants. If you are using a different thermistor, contact your thermistor manufacturer for their Steinhart-Hart constants.

Thermistor Resistance vs Temperature Chart