Realization of PLTS-2000 for Low-Temperature Resistance Thermometer Calibration Services Below 650mK

摘要

In this study, the Provisional Low Temperature Scale of 2000 (PLTS-2000) was realized below 650mK for the purpose of launching low-temperature resistance thermometer calibration services in Japan. A Straty-Adams-type He-3 melting pressure thermometer (MPT) and a dilution refrigerator were used to realize the PLTS-2000. Offsets due to hydrostatic pressure head in a filling capillary line of the MPT were adjusted using the minimum pressure fixed point on the 3He melting curve. A rather large MPT hysteresis between the decreasing and increasing pressures was observed during pressure calibration of the MPT and was the main source of uncertainty. The combined standard uncertainty (k = 1) between 50mK and 650mK was estimated to be in the range of 0.40mK to 2.62mK. The MPT and a number of resistance thermometers with negative temperature coefficients were mounted on the experimental platform with a thermal connection to a mixing chamber and compared in a multiple-temperature-point calibration. The temperature range around the melting pressure minimum, 250mK to 400mK, was not used for the calibration. The expanded uncertainty (k = 2) in the calibration based on realization of the PLTS-2000 between 50mK and 650mK was estimated to be in the range of 0.86mK to 5.25mK.