Degree of Equivalence of Realizations of the Triple Points of Argon and Oxygen Between NIS and LNE-Cnam

Abstract

This paper describes the results of an investigation for the degree of equivalence of realizations of the triple points of argon and oxygen between the “National Institute of Standards -Egypt (NIS)” and “Institut Nationale de Metrologie - France (LNE-Cnam).” The investigation was carried out through measurements of the argon and oxygen triple points (83.8058 K and 54.3584 K, respectively), as defining fixed points on the ITS-90 that are used in the calibration of capsule standard platinum resistance thermometers. The main objective of this work was to compare the realizations of both of the fixed-point cells and to establish the degree of equivalence between the two laboratories. As defined by the MRA, the degree of equivalence between two measurements (each consisting of a measured value \(m_{i}\) and its uncertainty \(u_{i})\) is expressed by the difference between the measured values, \(m_{1} - m_{2}\), and the expanded pair uncertainty of this difference \(U_\mathrm{p}\). Two cells, containing argon and oxygen, which had been fabricated and filled at LNE-Cnam, were used as artifacts exchanged between the two laboratories. The comparison measurements revealed temperature differences of 0.28 mK and 0.39 mK with expanded pair uncertainties of 0.66 mK and 0.74 mK for the argon and oxygen points, respectively. A detailed description of the equipment used in the two laboratories and an analysis of the comparison results will be presented in this paper.