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Crucial test for the kilogram redefinition

The future definition of the kilogram, expected to be approved at the time of the 26th CGPM in 2018, will lead to a fundamentally new situation in mass metrology, because it will allow NMIs, in principle, to realize the mass unit independently and at any nominal value of mass. It will therefore become necessary to verify the uniformity of mass units realized in different NMIs.

The Consultative Committee for Mass and Related Quantities, the CCM, has requested that a comparison of the future realizations of the kilogram, based on experiments which will become primary methods in the new SI, shall be carried out. The BIPM will serve as the pilot laboratory for this CCM Pilot Study.

At the beginning of April 2016, mass standards from six NMIs, calibrated using watt balances or 28Si-Avogadro spheres will be sent to the BIPM. They will be compared with each other in a precision mass comparator, under vacuum, which will allow testing of the uniformity of the mass units realized by each participant. The continuity between mass realization based on the present and the future kilogram definition will also be evaluated.

The weighing campaign at the BIPM is expected to be finished in June 2016. The standards will then be sent back and the mass stability will be evaluated by the NMIs. The results of the Pilot Study will be available in early 2017.

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