Bilateral comparison of the realisations of the ITS-90 at the freezing points of Al (660,323 °C) and Ag (961,78 °C)

Project Description

The thermometry section of the Belgian national Metrology institute (SMD) extended in 2008 the realization of ITS90 international temperature scale by adding Al and Ag fixed points to its range of services. SMD needs to confirm the quality of those realizations through a bilateral comparison, both for introducing CMCs and extending the accreditation scope.

From 1998 to 2000 CCT organised a comparison of the local realization of ITS-90 temperatures using aluminium and silver freezing-point cells for all participating national laboratories. LNE-INM (formerly BNM-INM) took part in that comparison. The corresponding EUROMET regional key comparison took place in 2004 and 2005. LNE-INM was co-pilot in this comparison.

The procedure of EUROMET-T-K4 is not identical with the procedure of CCT-K4: While CCT-K4 was a direct comparison of Al and Ag fixed point cells, EUROMET-T-K4 requires the calibration of HSPRTs. The EUROMET.T-K4 report concluded that HSPRT usage as travelling standards for intercomparisons should be avoided. Therefore the bilateral comparison will follow the CCT-K4 cell comparison procedure and will compare the travelling Al et Ag cell with the local national standard cells. LNE-INM will pilot this bilateral comparison.

Final Report 2014-03-24

The goal of the project was to support CMCs claims for SMD.The bilateral comparison followed the CCT-K4 cell comparison procedure and compared one travelling Al et Ag cell with the local national standard cells. LNE-INM piloted this bilateral comparison.

Measurements were made during 2010 and 2011. Several technical problems (unstable plateau of the Al travelling cell and deviation of HSPRTs) occurred during the measurements, the result beeing that  measurement uncertainties were larger than expected. Therefore the results of this comparison were not reported to BIPM and SMD postponed the foreseen CMC extension.