Electronic – How to measure temperature using a NTC thermistor

NTC (negative temperature coefficient) thermistors change their effective resistance over temperature. The most common equation used to model this change is the Steinhart-Hart equation. It uses three coefficients to characterize the NTC material with great accuracy.

The Steinhart–Hart equation is a model of the resistance of a semiconductor at different temperatures. The equation is:

$${1 \over T} = A + B \ln(R) + C (\ln(R))^3$$

where:

• \$T\$ is the temperature (in kelvins)
• \$R\$ is the resistance at \$T\$ (in ohms)
• \$A\$, \$B\$, and \$C\$ are the Steinhart–Hart coefficients which vary depending on the type and model of thermistor and the temperature range of interest. (The most general form of the applied equation contains a \$(\ln(R))^2\$ term, but this is frequently neglected because it is typically much smaller than the other coefficients, and is therefore not shown above.)

— Steinhart-Hart equation - Wikipedia, The Free Encyclopedia

Many manufacturers provide application notes (e.g. here) detailing on how to calibrate a given NTC if you desire accuracy better than the quoted manufacturing tolerance.

The provided B-coefficient can be used in a simplified Steinhart-Hart equation as described on the Wikipedia Thermistor article under "B parameter equation".