Reducing the Uncertainty of Self-heating in High-accuracy Cryogenic Temperature Measurements

Abstract

Listen

Translate article

Self-heating of resistance thermometers is a well-known phenomenon, which occurs when the measuring current additionally heats up the sensing element. The following paper describes the influence of the self-heating of a Cernox thermometer on the uncertainty in cryogenic temperatures (8K and 10K). The self-heating temperature difference is related to the thermal resistance between the sensor and its surroundings.The self-heating temperature increase can be corrected by the basic two-current method. However, in measurements ofhigh accuracy, uncertainty of the self-heating correction, achieved by the basic two-current method, may not be sufficient. More advanced methods for self-heating correction are proposed, based on the use of more than two different currents. Uncertainty of the self-heating for four methods (basic two-current method, three-current method, four-current method and five-current method) at different cryogenic temperatures is calculated. We can find that using the advanced methods we can decrease the uncertainty from 0.7 to 0.5 mK at 8K, and from 0.84 to 0.64 mK at 10K. This decrease may not be significant in common cryogenic temperatures measurement, but it can present an improvement in measurements of the the highest accuracy. The calculation results also show that there is no remarkable difference between the three-current method and the four-current method. The facts indicate that accuracy only slowly improves with the increasing number of different currents when the number of current is more than three.