NRC measurement set-up and preparatory work for CCT-K7.2021 key comparison of triple-point-of-water cells

This paper describes the NRC measurement set-up and the preparatory work for the CCT-K7.2021 key comparison (KC) of triple-point-of-water (TPW) cells. The preparatory work at NRC (charged with piloting the KC) included a comprehensive testing of the measurement set-up, the definition of the new NRC national standard for the TPW temperature, and the evaluation of the uncertainty budgets relevant for this KC. The new NRC TPW national standard is composed of an ensemble of ten fused silica TPW cells, characterized in both their isotopic composition and impurity content. Three uncertainty budgets were evaluated, corresponding to three different cases involved in the measurements at the pilot laboratory: (a) the temperature difference between two TPW cells, which amounted to 26 mu K (k = 2), (b) the temperature difference between a TPW cell and NRC national reference, which amounted to 35 mu K (k = 2) and (c) the temperature difference between a comparison participant's transfer cell and the comparison reference, composed of the average of two NRC national reference cells, which amounted to 19 mu K (k = 2).