In a Kibble balance experiment, the mass value is determined by calculating the geometric factor of the magnetic circuit-coil set up. This factor is calculated using two different interleaved methods: the weighing phase and the dynamic phase. This article presents improvements in the noise measurement of the geometric factor in both the dynamic and static phases from 2017 to 2024, ultimately reducing the noise associated with the determination of the value of a mass of the LNE Kibble balance (LNE KB) to a value of 410(-8) for an integration time of 1 day (a 6 fold improvement with respect to 2017).

The determination of a mass value in a Kibble balance type experiment requires the determination of the geometric factor of the magnetic circuit - coil set by two different methods. One of these phases requires the simultaneous acquisition of voltage and speed, the associated measurement noise must be reduced to the lowest possible value. This paper presents the improvement in the signal-to-noise ratio of the geometric factor by replacing the existing screw motor with a linear motor. The noise of the geometrical factor is reduced by a factor of five, which ultimately decreases the noise associated with the determination of the value of a mass in the LNE Kibble balance by a factor of five.

The LNE is developing a measuring device using an electrostatic force generator for the realization of small masses and forces in the International System of Units (SI). The weighing mechanism is completely monolithic and can support two capacitive actuators. In this paper, we have focused on two methods for measuring the capacitance gradient dC/dz: by applying the known weight of a standard mass or by measuring the capacitance at different vertical position.

Main text This report describes the second CCM key comparison of realizations of the kilogram definition based on the fixed numerical value of the Planck constant, which came into force on 20 May 2019. The objectives were to determine the level of agreement between realizations of the kilogram using Kibble and joule balances and the x-ray crystal density (XRCD) method and to provide input for the calculation of the second "consensus value" of the kilogram. The consensus value serves as the basis for an internationally coordinated dissemination of the kilogram and is updated after each new key comparison. Its use will continue until satisfactory agreement between realization experiments has been achieved. Another objective was the determination of the reproducibility of the realization experiments by comparing the new results with those of the first key comparison of kilogram realizations, CCM.M-K8.2019. The comparison was organized by the BIPM and had nine participants. The BIPM, LNE, METAS, NIST, NRC and UME operated Kibble balances, the NIM used a joule balance and the NMIJ and the PTB participated using 28Si spheres, the masses of which were determined with the XRCD method. These realization methods were used to calibrate 1 kg mass standards under vacuum or in air. The standards were sent to the BIPM where they were compared with each other and with BIPM Pt-Ir working standards. The latter were calibrated traceable to the International Prototype of the Kilogram (IPK), the mass of which served as the definition of the kilogram until 20 May 2019. The results of the weighings at the BIPM together with the measurement results communicated by the participants allowed comparison of the values attributed to 1 kg mass standards using the realization experiments of the participants. The level of agreement between mass determinations with the realization experiments and the BIPM as-maintained mass unit, traceable to the Planck constant through the mass of the International Prototype of the Kilogram, could also be deduced. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This paper describes the main improvements on the LNE Kibble balance in order to eliminate significant mechanical problems which prevent measurements under vacuum conditions: they will allow kilogram realizations in vacuum in some months.

La 26e Conférence générale des poids et mesures (CGPM) s’est réunie à Versailles du 13 au 16 novembre 2018. Elle a rassemblé les représentants de la plupart des 59 États membres du Bureau international des poids et mesures (BIPM) et des 43 États associés.

Determination of the Planck constant in the Kibble balance experiment requires, among other things, a precise control and knowledge of the speed and position of its major sensor: a coil immerged in a magnetic field. This paper presents our method to measure the coil unwanted angular movements during its vertical travel and a way to reduce it by controlling piezoelectric actuators. By this way we were able to reduce the contribution to the global uncertainty of the angular parasitic forces from 2μrad/s to less than 1μrad/s.

The definition of the kilogram in the International System of Units (SI) is expected to be revised in 2018. The present definition of the kilogram, the mass of the International Prototype of the Kilogram (IPK), adopted in 1889, would then be replaced by a definition based on a fixed numerical value of the Planck constant. The Consultative Committee for Mass and Related Quantities has requested that, as one of the essential steps before the redefinition, a comparison of kilogram realizations based on future realization methods, Kibble(9) balances and x-ray crystal density (XRCD) experiments, be organized. This comparison was carried out during 2016 in the form of a 'Pilot Study'. One aim of the study was to determine the uniformity of mass dissemination after the redefinition by comparing mass calibrations based on different future realization experiments. Another aim was to test the continuity of the mass unit across the redefinition by comparing mass calibrations based on Kibble balances and XRCD experiments with those based on the IPK. This paper describes the organization of the comparison and presents its results.

Le kilogramme est la dernière unité du Système international d'unités (SI) encore définie par un artefact : le prototype international du kilogramme (International Prototype of the Kilogram ou IPK).En 100 ans, des comparaisons entre l'IPK, ses copies officielles et les prototypes nationaux ont montré une variation relative de masse de l'ordre de 5 × 10 -8 .Après un bref rappel sur l'unité de masse, cet article expose la nécessité de redéfinir le kilogramme.Il explique le choix de la constante de Planck h comme base d'une définition telle qu'envisagée par la CGPM en 2018.L'article présente les derniers résultats obtenus avec les balances du watt qui permettent aujourd'hui d'établir un lien entre h et une masse macroscopique avec des incertitudes relatives de quelques 10 -8 .Enfin, l'article présente la position adoptée en France par le laboratoire national de métrologie pour la « mise en pratique » du kilogramme et sa dissémination après sa redéfinition en 2018.

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) x 10(-34) J . s, with a relative standard uncertainty of 5.7 x 10(-8).

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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.

This paper describes some mechanical and electrical improvements in the LNE watt balance experiment. A new single-piece balance beam has been developed and the electrical system to servo-control its equilibrium position during the static phase has been modified.

The Planck constant h was determined in 2014 by means of the French watt balance experiment at the LNE (Trappes).The relative standard uncertainty was 3.1×10 -7 .This first French determination was performed in air with a 500 g mass standard made from a Co-based superalloy.The two main corrections are the buoyancy correction of the order of 66 mg, and the magnetic interaction correction of about 37 µg.This interaction force appears between the mass artifact and the residual magnetic field coming from the permanent magnet used in the experiment.The main uncertainty components associated with the mass are the calibration uncertainty, the stability uncertainty, the buoyancy correction uncertainty and the magnetic interaction correction uncertainty.The combined uncertainty component due to the mass is about 36 µg, i.e. 7.2×10 -8 in relative value.

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) x 10(-34) Js which differs in relative terms by -0.05 x 10(-7) from the h(90) value and by -1.1 x 10(-7) from that of the 2010 CODATA adjustment of h. The relative standard uncertainty associated is 3.1 x 10(-7).

Since 2005, the French watt balance experiment, installed at the LNE, has been using a balance beam with removable flexure hinges designed at the CNAM. With this balance, a first determination of the Planck constant in air was performed in 2014. This balance beam presents some drawbacks. First, it is difficult to mount and adjust the hinges. Secondly, the use of clamped flexure strips used as pivots limits the beam sensitivity and measurement repeatability, moreover the central flexure strip twists under the effect of unwanted horizontal forces at the ends of the beam, which leads to a potential measurement error. For these reasons, a new, single-piece balance beam has been designed. It is not only easier to mount and adjust than its predecessor, but also free of unwanted stresses such as shear force on the hinges. This ensures that, once the beam is loaded, the rotation axes are by construction parallel and coplanar. In addition, the use of a double central hinge strongly reduces the torsion effect.

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.

The misalignments of the LNE watt balance experiment have been studied. This paper presents the evaluation of unwanted horizontal forces and torques applied to the coil and describes the experimental set-up that will be used to measure the vertical velocity and all the unwanted velocities.

L'article présente le nouvel étalon primaire du LNE pour les mesures des valeurs efficaces et des taux de distorsion harmonique de signaux périodiques contenant une composante fondamentale à 50 Hz et des harmoniques quasi-stationnaires jusqu'au rang 50.La méthode de mesure est basée sur l'échantillonnage des signaux par un voltmètre numérique et le traitement des échantillons par transformée de Fourier discrète.La traçabilité aux unités SI est assurée par des comparaisons avec un convertisseur thermique.Les incertitudes types sur la valeur efficace et le taux de distorsion sont respectivement de 22 μV/V et 0,002 5 % pour tous les signaux déformés étudiés.