Development of a Milli-Kelvin Thermostatic Bath for High-Precision Temperature Sensor Calibration

For most temperature sensors, measurement traceability must be established via a comparison method within a thermostatic environment. To address the limitations of domestic constant temperature baths in meeting the calibration requirements for high-precision temperature sensors in fields such as semiconductors, a thermostatic bath device with milli-kelvin (mK) level temperature control capability has been developed. First, a novel system scheme was designed to create a sub-cooled condition using a refrigeration machine, while temperature balance was maintained by adjusting the heating power. Second, a high-precision temperature measurement module was designed using a thermistor sensor and a resistance ratio measurement method; measurement accuracy was improved by employing a bidirectional constant current source. Finally, an optimized temperature control logic was proposed to achieve rapid temperature regulation. Experimental results demonstrate that the device operates effectively within a (5–50) °C range, with stability better than 0.003 °C/h and uniformity superior to 0.003 °C. The device has been calibrated by a professional organization and meets the verification requirements for high-precision temperature sensors.