International Key Comparison CCT-K9 (ITS-90 SPRT Calibration from the Ar TP to the Zn FP) - Report on measurements at INRIM

During the 2010 session of the Consultative Committee for Thermometry to the CIPM it was decided to repeat, after about 10 years, the preceding Key Comparison CCT-K3. Unlike CCT-K3, which operated in the temperature range from the Argon Triple Point (Ar TP) up to the Aluminium Freezing Point (Al FP), the temperature range for the new KC - denominated CCT-K9 - would be limited up to the Zinc Freezing Point (Zn FP), in order to avoid the (still unresolved) issues that arose between the results at the Al FP from CCT-K3 and CCT-K4 (comparison of the Aluminium and Silver fixed points). As pilot laboratory, NIST accepted to organize the comparison where the number of participants would be limited to 4 (four) in the case of Euramet and similar limitations for the other RMOs. The comparison would be performed by using two standard platinum resistance thermometers (SPRTs) to be hand-carried to NIST after a calibration over the full temperature range at the participant's laboratory, and another full calibration when the SPRTs were hand-carried back. See also the attached appendix with the measurement protocol.