Thermistor

The Thermistor calculator returns the resistance at an end temperature based on the base temperature and resistance, an operating temperature and thermistor B coefficient.

INSTRUCTIONS: Choose units and enter the following:

• (T₁) Base Temperature
• (R₁) Base Resistance
• (T₂) Operating Temperature
• (B) Thermistor B Coefficient

Operating Resistance (R₂): The calculator returns the resistance in kilo-ohms ( kΩ ).  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The thermistor's resistance is a function of temperature, so that they can be used as temperature sensing devices.  This formula calculates the resistance of a thermistor given:

• Base temperature (T1; typically 25° C = 298 K);
• Base resistance (R1; default 10 k);
• Operating temperature (T2);
• B coefficient (different for different thermistors; default = 3988 K

The thermistor equation typically refers to the relationship between the resistance of a thermistor and its temperature. Thermistors are temperature-sensitive resistors, meaning their resistance changes with temperature. There are various types of thermistors, but the most common equation used to describe their behavior is the Steinhart-Hart equation, which is given by:

`T = 1 / (A+Bln(R)+C(ln(R))^3​)  −  273.15`

where:

• T = Temperature in Kelvin
• R = Resistance of thermistor at temperature T in ohm.
• A, B, C are Steinhart-Hart coefficients.

The Steinhart-Hart coefficients are determined experimentally and are specific to each thermistor. They are typically provided by the manufacturer or can be determined through calibration. The equation is nonlinear, but it can be linearized over a small temperature range if necessary.

Plot Notes

The calculator is set up to display a plot of the operating resistance across different values of operating temperatures (T₂).  Enter the range of temperatures, number of points between them and select PLOT to see the graph.