Comparison of Argon Triple Point between NIS-Egypt and LNE-INM/CNAM-France

This paper describes the results of a bilateral comparison of the triple point of argon (83.8058 K), one of the defining fixed points on the ITS-90 and the lowest temperature fixed point used in the calibration of the long-stem Standard Platinum Resistance Thermometers (SPRTs) used in most national metrological institutes (NMIs), as realized and maintained at the National Institute of Standards Egypt (NIS) and Institut Nationale de Metrologie - France (LNE-INM/CNAM). The main objective of this work was to compare the realizations of the argon triple-point cells for longstem thermometers and to establish the level of agreement between the results from the two laboratories. The comparison measurements revealed a slightly higher temperature of the NIS argon "Constant Heat Flux" (CHF-device) than that of the LNE-INM/CNAM device by about 0.2 mK. The difference found is significantly smaller than its expanded combined uncertainty (coverage factor k = 2). The detailed analysis of the results and the uncertainty budget related to the measurements are presented. Calculation of the normalized error ratio (NER) gave a value of 0.25 ≤ 1 which shows that the measurements at the two laboratories are compatible.