Paul-André Meury

Micro-mass standards to calibrate the sensitivity of mass comparators

In mass metrology, the standards currently used are calibrated by a chain of comparisons, performed using mass comparators, that extends ultimately from the international prototype (which is the definition of the unit of mass) to the standards in routine use. The differences measured in the course of these comparisons become smaller and smaller as the standards approach the definitions of their units, precisely because of how accurately they have been adjusted.One source of uncertainty in the determination of the difference of mass between the mass compared and the reference mass is the sensitivity error of the comparator used. Unfortunately, in the market there are no mass standards small enough (of the order of a few hundreds of micrograms) for a valid evaluation of this source of uncertainty. The users of these comparators therefore have no choice but to rely on the characteristics claimed by the makers of the comparators, or else to determine this sensitivity error at higher values (at least 1 mg) and interpolate from this result to smaller differences of mass.For this reason, the LNE decided to produce and calibrate micro-mass standards having nominal values between 100 µg and 900 µg. These standards were developed, then tested in multiple comparisons on an A5 type automatic comparator. They have since been qualified and calibrated in a weighing design, repeatedly and over an extended period of time, to establish their stability with respect to oxidation and the harmlessness of the handling and storage procedure associated with their use. Finally, the micro-standards so qualified were used to characterize the sensitivity errors of two of the LNEs mass comparators, including the one used to tie Frances Platinum reference standard (Pt 35) to stainless steel and superalloy standards.

Metallurgical characterization of materials for the reference mass standard of the French watt balance experiment

Watt balance experiments are intended to link the mass unit to the Planck constant. Therefore, in these experiments, a reference mass standard is necessary. However, in the French apparatus, the platinum–iridium alloy that forms the international prototype of the kilogram cannot be considered because of its magnetic susceptibility. Consequently, new materials were investigated, according to stringent specifications. This led to the selection of alloys based on precious metals. The stability of the materials used in mass metrology is strongly dependent on bulk homogeneity and cleanliness: after the investigation of different production modes and heating treatments, microstructural and analytical studies were performed. The critical properties of the different materials were examined and discussed in comparison with the platinum–iridium alloy.

Progress on the LNE watt balance project

This paper describes the main progress on the LNE watt balance project since 2004. Development of different parts and structure of the watt balance including starting their assembly are presented.

Determination of the density of air: a comparison of the CIPM thermodynamic formula and the gravimetric method

Today, the determination of the density of air is the main source of uncertainty (10??g) in a comparison of a platinum?iridium alloy national prototype with a stainless steel reference standard. The method currently recommended by the BIPM is to calculate this density, using a formula developed in 1981 and revised in 1991 by the CIPM, from the measured values of the pressure, temperature, hygrometry and molar fraction of CO2 in air. Recent work has found significant differences between the values given by this formula and those given by a method using artefacts having identical masses and very different volumes (6.4 ? 10?5 with a relative uncertainty of 1.2 ? 10?5). To investigate this difference, the BIPM asked the member laboratories of the Consultatitve Committee for Mass (CCM) to investigate two lines of approach: check the composition of the air, in particular the argon content, which may explain the discrepancies found; this is the object of a study by the chemical metrology unit of LNE (see the article by Sutour et al in this issue), study the behavior of artefacts during the air?vacuum transfer in a comparator that can work both in a controlled atmosphere and in a vacuum, to confirm or not confirm the discrepancies; this latter study is the object of this paper.

CCM.M-K3.1 comparison / 50 kg mass

This comparison is a subsequent key comparison to the comparison CCM.M-K3 performed in 2001–2002 and published in 2005. This comparison is between the CEM (Spain) as participating laboratory and the LNE (France) as pilot laboratory. The aim of this comparison was to compare the results obtained by each laboratory when calibrating the same two 50 kg stainless steel mass standards, one provided by CEM and one by LNE. Main text. 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 kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).