Although a thermistor is measured under controlled ambient temperature, self-heating (as a result of the measurement current) makes it impossible to measure the theoretical resistance accurately. The Zero-Power Resistance is the measured DC resistance with a power dissipation sufficiently low that the resistance variation caused by self-heating is very small compared to the overall resistance change (power <5% of the dissipation constant). The Zero-Power Resistance at an ambient temperature of 25°C is the Nominal Zero-Power Resistance.
Standard tolerances of Nominal Zero-Power Resistance are shown in Table 1 below. Tolerances for temperature sensing are normally selected from F to K, and tolerances for temperature compensation are usually selected from J to L.
