Cryogenic fixed point: The effect of bushings at the triple point of argon.

Metal sheath Standard Platinum Resistance Thermometers (SPRTs) are used in different industrial sectors because of their low cost and robustness. Calibration of them at cryogenic temperatures remains a challenge due to heat conduction effects through their stainless-steel stems. Research papers on the triple point of water express that the use of tubular bushings made of good thermal conductivity materials decreases the self-heating (SH) effects and improves the thermal contact between the sensor and the cell. Žužek et al. [1] conducted tests at the fixed points from Zn to Hg, observing the same behaviour when bushings are used. At the time of writing this paper, no reported work has been found for the triple point of argon (TP-Ar) and the performance of bushings and their associated SH effects. Therefore, the main goal of this work was to investigate the effect of bushings on the SH of metal sheath SPRTs at the TP-Ar. The measurements were carried out comparing metal sheath SPRTs from different end-users and hand-made bushings of copper, aluminum, and brass. In addition, the effect of heat flux (HF) at two immersion depths using currents of 1 mA and √2 mA was studied. Finally, the results of different tests with bushings are presented. [ABSTRACT FROM AUTHOR]