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



Nick Fletcher, Gert Rietveld, James K. Olthoff, Ilya F. Budovsky


The proposed redefinition of several SI base units is a topic that has been on the metrology agenda for the last decade. The general principles and the motivation for the changes have been presented at the NCSLI several times. However, recent progress on several determinations of the fundamental constants means that we are now in a position to start discussing the details of the implementation. In particular, we 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. It is now clear that the implementation of the new system cannot be done without introducing small step changes into sizes of the electrical units disseminated using Josephson and quantum Hall intrinsic standards. This paper discusses the likely sizes of these changes, and their practical impact on electrical metrology. 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. This is small enough to trouble only a few ‘top-level' users that maintain an in-house Josephson reference, but large enough that the change needs to be well planned and communicated. The relative change from RK 90 to RK will be smaller, of the order 2×10−8. We discuss the long term benefits that will come from the updated system and why these changes are necessary. 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.
Proceedings Title
NCSLI 2014 Workshop & Symposium and Tutorial Program
Conference Dates
July 28-31, 2014
Conference Location
Orlando, FL, US
Conference Title


Fletcher, N. , Rietveld, G. , Olthoff, J. and Budovsky, I. (2016), Electrical Units in the New SI: Saying Goodbye to the 1990 Values, NCSLI 2014 Workshop & Symposium and Tutorial Program, Orlando, FL, US (Accessed May 27, 2024)


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Created May 11, 2016, Updated October 12, 2021