Comparison between the 5960A Fluke and the Ar-IMGC system for the realization of the triple-point of Argon at INRiM

In 2018 a new cryostat (Ar-Fluke) for the realization of the triple-point of the argon, a defining fixed point of the International Temperature Scale of 1990 (ITS-90), was acquired at INRiM. The new system, manufactured by Fluke, was intended to substitute the current National reference, a model developed at BNM-INM in the 1975 (Ar-IMGC). The Fluke system has many advantages over the other system, such as the possibility to calibrate four long-stem Standard Platinum Resistance Thermometers (SPRTs) simultaneously and to have much longer plateau, so reducing the time for customer’s calibration. This technical report describes the working principle and the typical phase transitions obtained with the two argon systems. Then, the result of the direct comparison between the two systems is reported. A complete uncertainty budget was evaluated, for the first time, for the new Ar-Fluke system and compared with that of the National standard.