From the Mise-en-pratique for Mass to the Future of Metrology for the SI
Carl J. Williams
The two most troublesome issues with the SI as currently defined involve the artifact kilogram (kg) and the electrical units. Defining the kg as exactly equal to the mass of the International Prototype Kilogram (IPK) poses severe difficulties in scaling, because measurement uncertainties increase by orders of magnitude the farther the desired scale is from the 1 kg range. Moreover, the worlds standard masses are known to change over time. In 2013, in preparation for the SI redefinition, the International Bureau of Weights and Measures (BIPM) conducted an extraordinary comparison of its working standards with the IPK. In the 25 years since the 3rd periodic verification, the unit of mass as maintained by the International Bureau of Weights and Measures (BIPM) through its working standards was found to be 0.035 mg too high relative to the IPK1. Only one of the SI base units is electrical -- the ampere. It is nearly impossible to realize under the present definition. Yet the volt and the ohm, which are based on quantum phenomena (the Josephson effect for the volt; the quantum Hall effect for the ohm), are so metrologically robust that in 1987 the General Committee on Weights and Measures (CGPM) established conventional electrical units. The net effect is that since 1990 the SI electrical units have deviated slowly from conventional electrical units.
Proceedings of the International Summer School Enrico Fermi Vol 196
IOS Press, Amsterdam, -1
International System of Units, Quantum Based Measurements, Quantum Metrology, Mise-en-pratique for mass
From the Mise-en-pratique for Mass to the Future of Metrology for the SI, Proceedings of the International Summer School Enrico Fermi Vol 196, IOS Press, Amsterdam, -1
(Accessed September 23, 2021)