Final report on the APMP regional comparison of type R thermocouples calibration at Cu, Co-C and Pd fixed points, APMP.T-S16

Main text Platinum based thermocouples are widely used to provide traceability to accredited laboratories for high temperature contact thermometry (up to 1560 °C). Different NMI's have adopted a very diverse range of methods to calibrate these thermocouples, such as gold and palladium (Au and Pd) 'melt wire' techniques (in both air and argon), mini fixed point of copper, cobalt-carbon eutectic and palladium-carbon eutectic points, and comparison with reference thermocouples or radiation thermometers. Although a successful comparison, APMP.T-S1-04, up to 1100 °C was performed in 2005-2006, no equivalent comparison has so far been made over the higher temperature range to 1560 °C. The study here fills this gap: 9 NMI's from the APMP region participated in an inverted-star comparison using their normal calibration procedures. The impact of reversible hysteresis was minimised by specifying the thermocouple annealing state, and the impact of irreversible heat treatment minimised using the inhomogeneity analysis methods developed in APMP.T-S1-04, based on detailed knowledge of the participants' furnace temperature profiles. Despite the wide variation in calibration techniques used by the participants, comparison reference values with uncertainties comparable to that of ITS-90 itself could be achieved: ± 0.06 °C ( k = 2) at Cu point (1084.62 °C), ± 0.19 °C (k = 2) at Co-C point (1324 °C), and ± 0.15 °C (k = 2) at Pd point (1554.8 °C). This resulted in calculated of degrees-of-equivalence comparable to participants claimed uncertainties. The results also showed En ratios <1 at all comparison temperatures for all participants, supporting the equivalence between the wide range of calibration references and methods adopted. 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 https://www.bipm.org/kcdb/ . The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).