Methods of reducing the uncertainty of the self-heating correction of a standard platinum resistance thermometer in temperature measurements of the highest accuracy

Self-heating of resistance thermometers is a well-known phenomenon, which occurs when the measuring current additionally heats up the sensing element. In the paper, the self-heating of standard platinum resistance thermometers (SPRTs) is studied with special emphasis on the investigation and evaluation of factors which contribute to the uncertainty of the self-heating correction. The basic two-current method for self-heating correction is analysed and additional correction methods are proposed, based on the optimal selection of currents and the use of more than two different currents. Using the advanced methods we can decrease the uncertainty of the self-heating correction from 0.04 to 0.01 mK. This decrease may not be significant in routine SPRT calibrations, but it can present an improvement in measurements of the highest accuracy, such as intercomparisons.