The CCT has completed the guide summarizing the uncertainties in the realization of the SPRT subranges of ITS-90 between the triple point of neon (24.5561 K) and the freezing point of silver (961.78 • C). This article identifies aspects of standard platinum resistance thermometry where either data or models are lacking and further research is required. In the calibration of SPRTs, the two main concerns are the need for data on liquidus slopes for the different impurities in the fixed points and improved understanding of the impact of the thermal environment of the fixed point on the realized temperature. In the use of SPRTs, the two largest sources of uncertainty are Types 1 and 3 non-uniqueness and oxidation. The causes of Type 3 non-uniqueness are not yet understood, especially at low temperatures, and there is a paucity of data for the high-temperature subranges. In respect of oxidation, there is a need for validation of the models developed in the 1980s, especially in light of the reduced partial pressure of oxygen used in modern SPRTs. A range of other effects including vacancy effects in SPRTs, isotopic effects in fixed points, and improved statistical methods are discussed.

Working Group 3 of the Consultative Committee for Thermometry is responsible for recommending methods to assess uncertainties in contact thermometry. Accordingly, it has now completed a guide summarizing the uncertainties in the realization of the standard platinum resistance thermometer subranges of ITS-90 between the triple point of neon (24.5561 K) and the freezing point of silver (961.78 • C). The document provides guidance to assess the uncertainties of both SPRT calibrations and temperature measurements. The document describes all known sources of uncertainty and influence variables, identifies key references in the literature that discuss, model or evaluate each effect, gives an indication of the typical magnitudes of the uncertainties, and provides propagation laws. This article is an overview of the guide emphasizing aspects that may be different from common practice, which includes: associating all uncertainty terms with a physical cause to ensure they can be propagated and to prevent double counting; uncertainty due to the oxidation state of the SPRT; uncertainty due to the isotopic composition of fixed-point substances; uncertainty due to impurities in fixed-point substances; and uncertainty due to nonuniqueness of the SPRT interpolations. The article gives a graphical summary of the total uncertainties in ITS-90 over the SPRT temperature range.

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From 2002 to 2004 the Consultative Committee for Thermometry (CCT) carried out a Key Comparison (KC) of water triple point cells (CCT-K7). In 2005 the Regional Metrology Organization (RMO) EURAMET decided to initiate an additional KC of water triple point cells, EUROMET.T-K7, to extend the metrological equivalence to a larger number of national metrology institutes (NMIs) from the EURAMET region.The EUROMET.T-K7 comparison was carried out in 2006–2008 with the coordination of VSL and the participation of 24 EUROMET NMIs, 9 of them having participated in CCT-K7 as well (8 out of 9 used the same transfer cell they had used in CCT-K7).This report presents the results of this comparison, provides detailed information of the measurements performed by all participating laboratories and links the comparison results to the CCT-K7 comparison.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

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