A new calorimeter for the simultaneous calibration of SPRTs and CSPRTs at the triple point of mercury

Abstract

The LNE-Cnam has recently developed a new quasi-adiabatic calorimeter for the realization of the triple point of mercury (234.3156 K) at the highest degree of accuracy. The device can accommodate long-stem Standard Platinum Resistance Thermometers (SPRTs) and capsule-type SPRTs (CSPRTs). It can be used to realize simultaneous calibrations of SPRTs and CSPRTs, and to study the temperature evolution of the triple point when the fraction of melted substance changes. The device is composed of a triple point cell installed in a vacuum-tight adiabatic calorimeter, where CSPRTs are mounted, with a central reentrant well for housing long-stem SPRTs. The well is surrounded by a shield cell filled with mercury and its upper part is at the ambient temperature. Five mercury triple point cells have been recently filled and characterized at the LNE-Cnam. Measurements have been carried out with both long-stem and capsule-type SPRTs. Triple point uncertainties of 0.2 mK for the calibration of CSPRTs, and of 0.3 mK for the calibration of long-stem SPRTs have been obtained.