NTC Thermistor
Calculating the Temperature Coefficient of a Thermistor

The temperature coefficient of a thermistor is defined as the relative change in resistance referred to the change in temperature. The easiest way to calculate the temperature coefficient is by using the below equation.  

a = -b/ T²    eqn 2 

where 

b = Ln(R_t1/ R_t2) / (1/T₁ – 1/T₂) 

The temperature coefficient of thermistor is used when calculating the tolerance of a thermistor in terms of temperature. This unit is measured in terms of the percent per degrees celsius (%/°C). 

(EX): Suppose a customer orders a 10,000 W thermistor with an accuracy of ± 0.5°C.

(Q) How would we translate this in terms of resistance tolerance at different temperatures?

(A ) The specified part number would be NT03 10391, with a beta of 3950°C. The tolerance at 25°C would be: 

-3950°K / (298.15) ² = -4.44%/ °C X ± 0.5°C = ± 2.22 % @ 25°C. 

In this manner you can find the tolerance at any temperature for any given value of beta. Also the reverse is true if you need to find the accuracy of a part in terms of temperature.