Mechanical and electrical power in SI units have been equated by measurements made on a coil part of which is in a strong magnetic field. The force due to a current I flowing in the coil, is weighed by opposing it with a mass M subject to the earth's gravitational acceleration g. This is combined with a separate measurement in which a voltage V is generated in the coil when it is moved vertically with velocity U through the relationshipIf the current produces a voltage V across a resistor whose value R is known in SI units [I], then

In 2017 the Consultative Committee for Electricity and Magnetism (CCEM) commissioned a key comparison of electrical capacitance standards, the second time this quantity has been compared since the implementation of the Mutual Recognition Agreement by the Comité International des Poids et Mesures (CIPM—MRA) in 1999. This comparison—CCEM-K4.2017—was piloted by the Bureau International des Poids et Mesures (BIPM) and included seven National Metrology Institutes (NMI) belonging to four Regional Metrology Organizations. The measuring scheme adopted for the comparison was that of a star comparison consisting of a set of bilateral comparisons between the participating NMIs and the BIPM, whose capacitance reference base served as a common reference. For each of the bilateral comparisons, the measurands were the capacitance values of 10 pF travelling standard capacitors belonging to the NMIs and, optionally, the values of 100 pF standards. All the participants have been chosen from those able to realize and maintain a representation of the farad at the best known level of accuracy. Four of them, including the BIPM, were taking their traceability from dc or ac quantum Hall effect standards and, the four others, from a calculable capacitor. The comparison results analysis have evidenced an agreement within about ±5 parts in 108 for the mandatory 10 pF measurements and within about ±10 parts in 108 for the optional 100 pF measurements. Also, excepted for one of the participants, a good agreement has been found for the ratio 100 pF:10 pF (within ±5 parts in 108). In addition to the comparison, it has been possible to evaluate the difference between the value of R K (von Klitzing constant) measured by electrical means from calculable capacitors and its last CODATA recommended value (CODATA 2014 adjustment). A difference of (43 ± 23) parts in 109 (k = 1) has been found which is consistent with the difference that can be computed from the experimental data used in the CODATA 2014 adjustment of fundamental constants. This report presents the details of the measurements and analysis having led to these results. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

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An international comparison of 10 pF and 100 pF capacitance standards has taken place within the framework of EUROMET. The comparison, which was piloted by the National Physical Laboratory (NPL, UK), involved seventeen laboratories, including several which are members of other regional organizations. The agreement demonstrated by the comparison provides confidence in maintaining traceability for the farad, via either a calculable capacitor or a quantum Hall resistance (QHR) standard and the internationally agreed value of RK-90. However, the results appear to show that there are slight but significant differences between the representation of the farad for some laboratories. A full report of the comparison has been published by the NPL.

This report describes a comparison of 10 pF and 100 pF capacitance standards organized within the framework of EUROMET Project No. 345 between 1995 and 1998. Piloted by the National Physical Laboratory (NPL, UK), the comparison involved sixteen national metrology institutes (NMIs), several of which are members of other regional metrology organizations, and the Bureau International des Poids et Mesures. The results show that there are significant differences between representations of the farad by some NMIs. However, the agreement demonstrated by the comparison gives confidence in maintaining traceability for the farad via either a calculable capacitor or a quantum Hall reference standard and the consensus value of the von Klitzing constant, R K-90 .