EMRP - e-Mass: The watt balance route towards a new definition of the kilogram

• Unité de recherche: METAS
• Numéro de projet: 5211.08.FP.061
• Titre du projet anglais: EMRP - e-Mass: The watt balance route towards a new definition of the kilogram

Mots-clé (Anglais)

Watt balance, kilogram, unit of mass, absolute gravimeter, International System of Units SI

Description succincte (Anglais)

Several laboratories around the world participate actively in the search for a new definition of the kilogram in the International System of Units SI. One possible approach consists in a virtual comparison between a mechanical and an electrical power with by means of a watt balance. The Laboratoire National de Métrologie et d'Essais LNE (France), the Istituto Nazionale di Ricerca Metrologica INRIM (Italy), and the Federal Office of Metrology METAS (Switzerland) have decided to join their efforts and their expertise in a "Joint Research Project" (JRP T1.J1.1) in the frame of the "European Metrology Research Programme" (EMRP - iMERA Plus). LNE and METAS have identified topics where both experiments would benefit from a collaboration. The activity has been organized in 3 experimental work packages summarized below:

• Experimental improvement of critical parts of watt balances (passive damping system, alignment tools and techniques, study of magnetic field behaviour, noise reduction in electrical and velocity measurements)
• Gravimetry
• Establishment of guidelines for the realisation of an optimized watt balance

 INRIM does not have a watt balance and is only involved in the gravimetry work package.

This project is partly funded by the European Community’s Seventh Framework Programme, ERA-NET Plus under Grant Agreement No 217257.

Objectifs du projet (Anglais)

Bring together the resources from LNE, METAS and INRIM to study and develop the experimental techniques which are needed for the realization and operation of watt balances with an accuracy level of a few parts in 10⁸.

Résumé des résultats (Abstract) (Anglais)

The experimental work was focused on the following topics: development of tools and techniques for the alignment of the apparatus, study of the magnetic field behaviour, reduction of the noise level in electrical measurements, measurement of the gravimetric field

The main result is the development and the integration of a new type of optical detector. It allows to measure the attitude of the measuring coil with a sub-micrometer resolution during both phases of the measurement. This detector is fully non-magnetic and can be operated in vacuum. The magnetic study has shown that it is possible to design a magnet based on SmCo material with a very small temperature coefficient. Such a magnet will be implemented in the next generation of watt balance.

During the time of the project, it has been possible to run the METAS experiment for extended sets of measurements in a satisfactory stable mechanical situation. A value for the Planck constant has been extracted from these data to be h = 6.626 069 1(20) x10^-34 Js [0.29x10^-6]. This value differs from the CODATA 2006 value by 0.024 µW/W.

Mise en oeuvre et application (Anglais)

The tools and techniques needed to reach a relative uncertainty of a few parts in 10⁸ in the determination of the Planck constant were developed in the framework of this project. The results are implemented in a new generation watt balance experiment at METAS. 

Publications / Résultats (Anglais)

• A. Eichenberger, G. Genevès; P. Gournay, “Determination of the Planck constant by means of a watt balance”, Eur. Phys J. Special Topics 172, 363-383.
• A. Louchet-Chauvet, S. Merlet, Q. Bodart, A. Landragin and F. Pereira Dos Santos, H. Baumann, G. D’Agostino and C. Origlia, “Comparison of 3 absolute gravimeters based on different methods for the e-MASS project”, accepted by IEEE Trans. Instrum. and Meas., under press
• Eichenberger A., Baumann H., Jeanneret B., Jeckelmann B., Richard P., Beer W, “Determination of the Planck constant with the METAS watt balance”, Metrologia, 2011, 48, n°3, 133-141.
• F. Bielsa, A. Eichenberger, O. Gilbert, P. Juncar, G. Genevès; “Characterization of the coil displacement in the LNE and METAS watt balance experiments”, Digest, 2010 Conference on Precision Electromagnetic Measurement, June 13-18, 2010, Daejon, Korea
• F. Bielsa, A. Eichenberger, O. Gilbert, P. Juncar, G. Genevès, “Optical alignment tool for the LNE and METAS watt balance projects”; Digest, 2010 Conference on Precision Electromagnetic Measurement, June 13-18, 2010, Daejon, Korea
• G. Genevès, F. Bielsa, A. Eichenberger, O, Gilbert, P. Juncar, F. Villar, G. D’Agostino, S. Merlet, P. Pinot, H. Baumann, F. Pereira dos Santos; “The e-mass euramet joint research project : the watt balance route towards a new definition of the kilogram”, Digest, 2010 Conference on Precision Electromagnetic Measurement, June 13-18, 2010, Daejon, Korea