Analysis of NTC thermistors self-heating effect in multiple thermal environments

This study analyzes the self-heating effect of the negative temperature coefficient thermistors in multiple thermal environments. Six thermistors were tested to explore the influence of excitation current, temperature, and mediums on the self-heating effect. The thermistors were measured at the water triple point (0.12 mK, k = 2) and the melting point of gallium (0.45 mK, k = 2) cells. Subsequently, a thermostatic bath equipped with a heat pipe was used to calibrate the thermistors and measure their self-heating effect within -5 degrees C-35 degrees C. The calibration uncertainty was estimated to be 0.60 mK (k = 2). The self-heating effect of thermistors increases with higher current and decreases with rising temperature. The temperature difference between currents of 0.01 mA and 0.05 mA was approximately 50 mK at the water triple point and 15 mK at the gallium fixed-point. Self-heating in the thermostatic bath was about one-third of that in fixed points. Computational fluid dynamics simulation results corroborated these findings, aligning well with experimental measurements. To ensure accurate measurements, it is crucial to maintain consistent conditions and medium when calibrating and using the thermistors.