Figure 35 Thermistor Resistance Verus Temperature - Newport 6100 User Manual

122 Principles of Operation
The following section contains an explanation of the Steinhart-Hart equation
and the values of these constants for some common thermistors.
Two terminal thermistors have a non-linear relationship between temperature
and resistance. The resistance versus temperature characteristics for a family
of similar thermistors is shown in Figure 35. It has been found empirically
that the resistance versus temperature relationship for most common negative
temperature coefficient (NTC) thermistors can be accurately modeled by a
polynomial expansion relating the logarithm of resistance to inverse
temperature. The Steinhart-Hart equation is one such expression and is given
as follows:
3
1/T = C1 + C2 (Ln R) + C3 (Ln R) (Eq. 1)
where T is in Kelvin. To convert T to C, subtract 273.15.
Figure 35 Thermistor Resistance verus Temperature
Once the three constants C1, C2, and C3 are accurately determined, only
small errors in the calculation of temperature over wide temperature ranges
exist. The equation will produce temperature calculation errors of less than
0.01C over the range -20 C to 50 C.
The constants C1, C2, and C3 are expressed in the form n.nnnn, simplifying
entry into the 6100.