Report on the CCM key comparison of kilogram realizations CCM.M-K8.2019

Abstract

This report describes the first CCM key comparison of realizations of the kilogram definition based on the fixed numerical value of the Planck constant, which came into force on 20 May 2019. The objectives were to determine the level of agreement between realizations of the kilogram using Kibble and joule balances and the X-ray crystal density (XRCD) method and to provide input for the calculation of the first "consensus value" of the kilogram. The consensus value will serve as the basis for an internationally coordinated dissemination of the kilogram which will continue until sufficient agreement between realization experiments has been achieved. The comparison was organized by the BIPM and had seven participants. The BIPM, KRISS, NIST and NRC operated Kibble balances, the NIM used a joule balance and the NMIJ and the PTB participated using 28Si spheres, the masses of which were determined with the XRCD method. These realization methods were used to calibrate 1 kg mass standards under vacuum. The standards were sent (in air) to the BIPM where they were compared under vacuum with each other and with BIPM Pt-Ir working standards. The latter were calibrated (in air) traceable to the International Prototype of the Kilogram (IPK), the mass of which served as the definition of the kilogram until 20 May 2019. The results of the weighings at the BIPM together with the measurement results communicated by the participants allowed comparison of the values attributed to mass standards of 1 kg using the participating realization experiments. The level of agreement between mass determinations with the realization experiments and the BIPM as-maintained mass unit, traceable to the Planck constant through the mass of the International Prototype of the Kilogram can also be deduced. 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 CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Reproducibility of the Realization of the Kilogram Based on the Planck Constant by the XRCD Method at NMIJ

“…The international equivalence of the realization by NMIJ was confirmed in the key comparison CCM.M-K8.2019 [24]. In addition, the reproducibility of the realization was evaluated in this study.…”

“…The pilot laboratory, Bureau International des Poids et Mesures (BIPM), has already carried out mass comparisons among the transfer standards from all participants. Details of the mass comparisons are given in [24].…”

Dissemination of the Kilogram Following Its Redefinition

“…It has a deviation of -0.019 mg with respect to the mass unit maintained by the BIPM working standards, with a standard uncertainty of 0.008 mg. The results of this comparison are shown in Figure 1 [8]. The chisquared test for consistency of the data set was passed, although the two results with the smallest uncertainties were not in agreement with each other.…”

On modelling of artefact instability in interlaboratory comparisons

“…In a recent and highly relevant key comparison for the new definition of the kilogram [6][7][8], a star-type comparison between the pilot laboratory and the other participants was employed. Here, each participant measures its individual travelling artefact and then sends it to the pilot, which measures and returns it after examination.…”