Electrical Units in the New SI: Saying Goodbye to the 1990 Values

Nick Fletcher, Gert Rietveld, James Olthoff, and Ilya Budovsky, “Electrical Units in the New SI: Saying Goodbye to the 1990 Values”, NCSLi Measure J. Meas. Sci., Vol. 9, no. 3, pp. 34 – 39 (2014).

The proposed redefinition of several International System (SI) base units is a topic that has been on the metrology agenda for the last decade. Recent progress on several determinations of the fundamental constants means that we now have a good idea of the defined numerical values that will be given in the new system to the Planck constant, h, and the elementary charge, e. This is especially relevant to electrical metrology as new numerical values for the von Klitzing and Josephson constants, given by the relations RK = h/e2 and KJ = 2e/h, will replace the existing 1990 ‘conventional’ values, RK‑90 and KJ‑90. The implementation of the new system cannot be done without introducing small step changes into sizes of the electrical units that are disseminated using Josephson and quantum Hall intrinsic standards. At the time of writing it looks likely that the relative change from KJ‑90 to KJ will be of the order 1 × 10−7, and that from RK‑90 to RK will be approximately 2 × 10−8. This paper discusses the practical impact of these changes on electrical metrology and highlights the long term benefits that will come from the updated system. The CCEM (Consultative Committee for Electricity and Magnetism) of the International Committee for Weights and Measures is now taking the first steps to ensure a smooth implementation, most probably in 2018.

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