Final report on EUROMET.T-K4 (EUROMET Project 820): Comparison of the realizations of the ITS-90 at the freezing points of Al (660.323 °C) and Ag (961.78 °C)

KEY COMPARISON: The comparison EUROMET.T-K4 is the regional extension of CCT-K4: an intercomparison of the realisations of the freezing points of Al (660.323 °C) and Ag (961.78 °C). The intercomparison was organized in four loops with long stem standard platinum resistance thermometers (SPRTs) as travelling standards: One 25 O thermometer to be used only at the Al freezing point and two high temperature SPRTs to be used only at the Ag freezing point in each loop. Parallel to the measurements with thermometers the pilot and sub-pilots organized an internal intercomparison using an Ag fixed point cell. Most HTSPRTs showed a strong drift which is mainly due to mechanical stress and poisoning of the sensor by impurities. This drift can partly be compensated by a correction applying Matthiessen's rule. An evaluation of the data taking into account both HTSPRTs in each loop, the linkage of the sub-pilots by measurements at the Ag freezing point and a possible compensation according to Matthiessens's rule allows to calculate the results of the participants also for the measurements at the Ag freezing point. European reference values (ERV) were calculated for measurements at the Al and Ag freezing points. The difference between these ERVs and the corresponding KCRVs of CCT-K4 is also given, which allows the linking of the different comparisons.