Precision AC measurements of temperature below 90 K

Specially designed sealed cells filled with ultrapure gas have been utilized for the realization of thermodynamic fixed points in the Primary Standards Laboratory. Accurate determination of the triple-point temperatures of Ar, N/sub 2/, O/sub 2/, Ne, and D/sub 2/ was accomplished with a high-precision AC resistance bridge operating at a frequency of 30 Hz. Detailed data obtained for platinum resistance thermometers (PRTs) and rhodium-iron (Rh-Fe) sensors are presented. The levels of accuracy and precision achieved are evaluated.<
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