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A determination of the Planck constant h using the LNE Kibble balance in air was carried out in the spring of 2017. Substantial improvements since 2014, chiefly related to the mass standard, mechanical alignments, voltage measurements and type A evaluation uncertainties, leads to a h value of 6.626 070 41(38) × 10 -34 J • s, with a relative standard uncertainty of 5.7 × 10 -8 .

After separate developments of the different elements with continuous characterizations and improvements, the LNE watt balance has been assembled. This paper describes the system in detail and gives its first measurements of the Planck's constant h. The value determined in air is h = 6.626 068 8(20) × 10 −34 Js which differs in relative terms by −0.05 × 10 −7 from the h 90 value and by −1.1 × 10 −7 from that of the 2010 CODATA adjustment of h. The relative standard uncertainty associated is 3.1 × 10 −7 .

The mass comparator for primary standards of the INM is a high level metrological set. Recently, its balance has been put into a thermally isolated and airtight chamber and this has led us to engage in an experimental study concerning the independence of the measured parameters. This study has revealed that the independence hypothesis must be rejected. The different correlation coefficients have been determined.

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Alignments of watt balance experiments are necessary to achieve a relative uncertainty at a level of few parts in 10 8 . This paper briefly describes the LNE watt balance and concentrates on adjustments made to minimize the coil movements during weighing mode. The parasitic forces and torques involved in these movements are estimated by a mathematical model. Some of the calculated parasitic forces are compared with an evaluation done by studying the yaw movement of the beam.

In 2000, the Bureau National de Métrologie (BNM, France) decided to develop a new watt balance experiment. Among numerous design studies, the choice of the transfer mass is particularly important. Because of the proximity to a source of high magnetic intensity, this mass must have a magnetic susceptibility as weak as possible. Gold-platinum alloy seems to meet this requirement, as well as additional requirements for density and hardness values, making it a possible candidate for mass standard realization. Five different gold-platinum alloys were studied, their volume magnetic susceptibility ranging from −2.8 × 10 −5 to −2.1 × 10 −5 for two of them and from +1.1 × 10 −5 to +8.8 × 10 −5 for the other three.