Pierre Gournay

The BNM Watt balance project

A new watt balance project is now developed by the BNM: the general configuration and the main parts of the experimental set-up in development are presented. Its aim is to contribute to the international effort in monitoring the kilogram towards a new definition of the mass unit with an accuracy of 10-8 or better

Magnetic circuit design for the BNM Watt balance experiment

BNM has started since 2001 the development of a watt balance experiment. The authors present in this paper the design of the magnetic circuit intended to equip it

The NIST project for the electronic realization of the kilogram

The project Electronic Realization of the Kilogram has rebuilt the National Institute of Standards and Technology (NIST) watt balance, which has been fully operational for nine months. Short-term noise is at an all-time low with overnight runs exhibiting standard deviations of parts in 10/sup 8/. Recent improvements are discussed that have led to this enhanced performance, as are several significant error tests. Present watt results (i.e., Plancks constant) are now within 1 /spl mu/W/W of CODATA values, but error checking to report a more precise value has not been completed.

Balance Pan Damping Using Rings of Tuned Sloshing Liquids

This paper describes a new method to damp out balance pan oscillations, even when the balance is operated in a vacuum. The key is to tune the wavelength of the damping liquid by adjusting the depth. The liquid is sealed in a vacuum-compatible container attached above the pan, and the time that the wave travels from one side of the container to the other can be adjusted for maximum damping at the natural pendulum frequencies of the pan. We are investigating the practical application of this damping approach in our respective watt-balance experiments. It is shown that the channels in the shape of rings filled with liquids to the optimum depth work well.

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.

A measuring machine for the magnetic circuit of the LNE watt balance

This paper describes the measuring machine built to measure the direction of the axis of revolution of the magnetic field in the magnetic circuit of the LNE watt balance. It is also used to measure the air gap geometry and the flux density in the air gap.

Testing the new generation of low-frequency current comparators

Improved magnetic materials open the perspective of operating room-temperature current comparators at lower frequency without compromising metrological accuracy. Two prototypes of low-frequency current comparator (LFCCs) have been successfully tested in precision resistance ratio measurements at drive frequencies of 0.5 Hz and 1 Hz using the BIPMs bridge setup with a recently realized frequency extension. These measurements have been performed using standard resistors of 10 kΩ, 1 kΩ and 100 Ω nominal values as well as the quantized Hall resistance (QHR) of GaAs and graphene devices.

A new CCEM-K4 comparison of capacitance at 10 pF

The CCEM-K4 key comparison of capacitance at 10 pF was last carried out between 1996 and 1999. The Consultative Committee for Electricity and Magnetism of the International Committee for Weights and Measures decided that it should be repeated in 2016. We present here the main technical choices adopted for the next comparison.

Experimental study of carrier density tuning in epitaxial graphene QHR devices

Adjustment of the charge carrier density in quantized Hall resistance (QHR) devices based on epitaxial SiC graphene films can be performed using photochemical and chemical gating. Our experiments show that the carrier concentration in fabricated graphene devices can be reversibly varied by either treatment with UV light or using molecules from aqua ammonia. Treatment of SiC graphene QHR devices in such a way provides tuning of carrier concentration to optimum values, in the range (1-3) × 1011 cm-2, at which the dissipation in QHR regime is reduced and the full quantization of Hall resistance is expected.

Progress report on measuring the von Klitzing constant at the BIPM

A project aiming at measuring the von Klitzing constant with an uncertainty of the order of one part in 108 is currently ongoing at the BIPM. This measurement will be performed by linking a calculable cross-capacitor to a quantum Hall resistor through a quadrature transfer. The main parts of the overall measuring setup as well as the current status of the project are presented.