NTC Thermistors are non-linear resistors that alter their resistance characteristics with temperature. Simply put, as temperature increases the thermistor’s resistance decreases. The manner in which the resistance of a thermistor decreases is related to a constant known in the thermistor industry as beta (b). Beta is measured in °K and is computed based on the formulation given below.
b = Ln(R t1/ Rt2) / (1/T1 – 1/T2)
Rt1 = the resistance at temperature 1
Rt2 = the resistance at temperature 2
T1 = Temperature one in °K
T2= Temperature two in °K
The beta value of an NTC Thermistor is calculated using only two temperatures over a given range and is not the most accurate way to calculate the R vs. T curve. A more accurate method is to use the Steinhart and Hart method, it uses three temperatures over a given range.