Basically, characteristics of a thermistors is represented by four constants: resistance R, B constant B, thermal dissipation constantand thermal time constant.
Zero-power resistance ( R T )
The zero-power resistance is the value of a resistance when measured at a specified temperature, under conditions such that the change in resistance due to the internal generation of heat is negligible with respect to the total error of measurement.
Rated zero-power resistance ( R25 )
The rated zero-power resistance is the nominal value at the standard temperature of 25℃ no other specified..
The constant which shows the change in the resistance calculated by the following formula using the resistance at 2 points at a specified ambient temperature. B=ln (R/R0) / (1/T-1/T0) R: Resistance when ambient temperature is T(K), R0: resistance when the ambient temperature is T0 (K)
Dissipation constant ( δ )
The dissipation constant is the quotient (in W/K), at a specified ambient temperature in a specified medium of a change in power dissipation in a thermistor to the resultant body temperature change.
Thermal time constant ( τ )
The time (in sec) required for a thermistor to change its body temperature by 63.2% of a specific temperature span when the measurements are made under zero-power conditions in thermally stable environments.