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CCEM capacitance comparison successfully completed using a new scheme

For the second time since the implementation of the CIPM Mutual Recognition Arrangement (CIPM MRA), the Consultative Committee for Electricity and Magnetism (CCEM) has organized a key comparison of electrical capacitance calibrations, CCEM-K4.

The comparison was piloted by the BIPM and had seven NMI participants from four Regional Metrology Organizations: METAS, NIM, NIST, NMIA, NPL, PTB and VNIIM. The BIPM participated in the comparison with its own realization of the capacitance unit, the farad.

This was the first CCEM comparison which adopted the star scheme which consists of a set of parallel bilateral comparisons carried out between the participating NMIs and the BIPM. Each participant provided a set of capacitance standards and the BIPM served as a common reference for the comparison. The measurands were the capacitance values at 10 pF and optionally at 100 pF. All participants carried out measurements at both values.

Four of the participants, including the BIPM, took their traceability from the dc or ac quantum Hall effect, the other four from a calculable capacitor. The comparison results agreed within ± 5 parts in 108 at 10 pF and within ± 10 parts in 108 at 100 pF, consistent with the claimed uncertainties.

The comparison also allowed the evaluation of the difference between the value of the von Klitzing constant RK measured by electrical means - based on the calculable capacitor - and the value recommended in the CODATA fundamental constants adjustment of 2014. The latter value is dominated by measurements of the anomalous magnetic moment of the electron and atomic recoil. A difference of (43 ± 23) parts in 109 (k=1) has been found.

The use of the star scheme was a great success. The comparison has been completed within a period of only one year and the results are excellent. The CCEM community will consider if this model can be applied to comparisons of other quantities.

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