Present and future mass standards for the LNE watt balance and the future dissemination of the mass unit in France

Abstract

The value of the Planck constant h was determined in 2014 by means of the LNE watt balance experiment. The relative standard uncertainty was 31 parts in 10 8 . This first determination was performed in air with a 500 g mass standard made from XSH Alacrite. The main uncertainty components in air associated with the mass involve the calibration, the mass stability, the buoyancy correction and the magnetic interaction correction. The combined relative uncertainty due to the mass is 7.2 parts in 10 8 . The use in 2016 of a mass standard made from platinum iridium alloy significantly reduces the component of uncertainty arising from the mass standard for a Planck constant measurement either in air or under vacuum. The relative uncertainty due to this contribution is estimated to be about 3 parts in 10 8 in air and one part in 10 8 under vacuum. The future system for the dissemination of the mass unit using the LNE watt balance will be based on a primary realization with three 500 g mass standards made from platinum-iridium alloy, pure iridium and Udimet 720 respectively, coupled with a pool of kilograms made from different materials. Pure iridium and Udimet 720 are new materials to make reference mass standards proposed by CNAM and LNE respectively and have never been used by any NMI for manufacturing mass standards until now. Some new results concerning their surface behavior are given.

Precise determination of the ratioh/mu: a way to link microscopic mass to the new kilogram

“…We have also presented the state of the art for measurements of fundamental constants and physical quantities that are involved in the determination of this ratio. Nowadays the relative uncertainty on the CODATA 2014 the value of the ratio h/m u is of 4.5 × 10 −10 , which complies with the recommendations of the Consultative Committee for Mass and Related Quantities (CCM) for the redefinition of the kilogram ( [47] and ref herein). However the lack of overlap between the value deduced from the photon recoil measurements and the one determined from α(a e ) makes the resulting value of ratio h/m u less reliable.…”

A determination of the Planck constant using the LNE Kibble balance in air

“…Measurements have been carried out with a 500 g mass of pure iridium labeled DB1. This material was selected about 10 years ago for its qualities of density, hardness, magnetic susceptibility and chemical resistance [35]. The artefact which is a cylinder of about 40 mm radius and 20 mm height was supplied by Johnson-Matthey and subsequently machined and manually polished with a diamond paste at LNE in 2015.…”