This Demonstration considers a full set of measurements of a negative temperature coefficient thermistor and lets you select the approximation method and the data points to be used for a corresponding version of the Steinhart–Hart approximation. The computed Steinhart–Hart coefficients are displayed along with a plot of the difference between the measured and approximated values (the temperature error).
Specification of a negative temperature coefficient thermistor is commonly expressed in terms of the coefficients in a Steinhart–Hart approximation. There are three common sets of coefficients: the beta coefficient that is computed from two measurement data points at two specified temperatures, the three-coefficient approximation that requires three measured data points and the four-coefficient approximation that requires four data points for curve fitting.
Two coefficients (beta constant):
Three coefficients (Steinhart–Hart equation):
Four coefficients (Steinhart–Hart equation):
, , and are Steinhart–Hart coefficients and is a constant commonly specified for thermistors. The coefficients for fitting the four-coefficient equation are not necessarily the same as those for fitting the three-coefficient equation.
is the thermistor resistance in ohms at temperature .
is the thermistor temperature in degrees Kelvin.
is a reference temperature used for one of the measured data points used to calculate the constant. Commonly, this is 25 °C.
is the thermistor resistance at the reference temperature .
The measured data  is taken from the manufacturer's data for the model TDK part number NTCG063JF103FTDS.