Research on sub-mK-level precision temperature measurement based on negative temperature coefficient thermistors

Purpose Negative temperature coefficient (NTC) thermistor temperature sensors are gaining widespread application in high-precision temperature measurement because of their high stability. This paper aims to propose a comprehensive traceability method to ensure that NTC thermistors can achieve sub-mK-level accuracy. Design/methodology/approach The temperature–resistance relationship of the negative temperature coefficient thermistors was accurately measured by using the water triple point cell, the melting point of gallium apparatus and the high-precision thermostat bath with an isothermal block. The Steinhart–Hart equation-fitting parameters of the three negative temperature coefficient thermistors were obtained by the least squares method. The verification of the fitting results and the temperature cycling experiment showed that the error and stability are less than 1 mK, and the extended uncertainty of the measurement results is 0.8 mK. Findings The results show that the measurement method used in this paper is suitable for high-precision temperature measurement of millikelvin-level NTC thermistors. It is feasible to use NTC thermistors for sub-millikelvin temperature measurement. Research limitations/implications In the measurement process, the uniformity and stability of the thermostat bath are still the main sources of measurement uncertainty. In the subsequent work, the authors will further improve the structure of the thermostat bath and the isotherm device to enhance the uncertainty level so as to further improve the measurement accuracy level. Practical implications This study used a combination of fixed-point devices and thermostats to achieve sub-mK calibration of NTC thermistors, providing a reference method for the application of NTC in high-precision temperature measurement. Originality/value This study uses a combined approach using fixed-point apparatus and a thermostat to achieve sub-mK-level calibration for NTC thermistors, serving as a reference for their application in high-precision temperature measurement fields.