NTC Thermistor
Calculating Beta

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/ R_t2) / (1/T₁ – 1/T₂)

 where
     R_t1 = the resistance at temperature 1
     R_t2 = 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.