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

Abstract

In this study, the Provisional Low Temperature Scale of 2000 (PLTS-2000) was realized below 650 mK for the purpose of launching low-temperature resistance thermometer calibration services in Japan. A Straty–Adams-type \(^{3}\)He 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 \(^{3}\)He 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 50 mK and 650 mK was estimated to be in the range of 0.40 mK to 2.62 mK. 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, 250 mK to 400 mK, was not used for the calibration. The expanded uncertainty (\(k = 2\)) in the calibration based on realization of the PLTS-2000 between 50 mK and 650 mK was estimated to be in the range of 0.86 mK to 5.25 mK.