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The BIPM Watt Balance: Improvements and Developments

This paper summarizes the various improvements to and new developments for the Bureau International des Poids et Mesures (BIPM) watt balance, which have been implemented over the past two years. The main distinctive feature of the BIPM apparatus is its capability for simultaneous force and velocity measurements. Our first campaign of measurements in air at atmospheric pressure has been carried out with simultaneous force-velocity measurements. The results obtained among 11 series showed a relative reproducibility of the Planck constant h of 5.0 × 10-6. The relative difference between our Planck constant result and the CODATA 2006 recommended value is -4.8 × 10-6, with a relative uncertainty of 4.8 × 10-5.

A watt balance based on a simultaneous measurement scheme

The International Bureau of Weights and Measures (BIPM) is developing a novel watt balance based on a simultaneous measurement scheme for the forthcoming redefinition of the kilogram. The two distinct measurement phases in a conventional watt balance are carried out in a single phase where all quantities are measured simultaneously. The main characteristics of this simultaneous measurement approach are described. An analysis of the advantages and the drawbacks is carried out.

Alignment Procedure Used in the BIPM Watt Balance

The Bureau International des Poids et Mesures (BIPM) is developing a watt balance to measure accurately the Planck constant h by linking it to the kilogram. The kilogram is currently the only base unit of the International System of Units still defined by a material artifact. A fixed numerical value of h could be the basis for the expected future redefinition of the kilogram in terms of fundamental constants. One main concern of the watt balance experiment is the alignment of the involved vectors. In particular, the electromagnetic force exerted on the watt balance coil needs to be carefully aligned parallel to the gravitational force exerted on the test mass. To address this requirement, we have developed an original experimental procedure that has been validated with a test coil which is a prototype for the ultimate watt balance coil. The result is accurate enough to enable a determination of the Planck constant with a relative uncertainty of about 1·10-8 , which is the ultimate goal of the BIPM watt balance.

Final Report on the International Comparison of Luminous Responsivity CCPR-K3.b

During its 13 th meeting in 1994 the Consultative Committee for Photometry and Radiometry (CCPR) decided to carry out a comparison of luminous responsivity to be organized by the BIPM. This comparison was classified as a key comparison by the 14 th CCPR in 1997 and subsequently named CCPR-K3.b. Fifteen laboratories took part in this comparison by sending calibrated photometers to the BIPM. The photometers were compared with a common set of reference photometers to deduce the relative differences between the calibrations made in the participating laboratories. In this report the details of the procedure and the results are presented.

Superconducting moving coil system to study the behaviour of superconducting coils for a BIPM cryogenic watt balance

The BIPM has built an experimental setup dedicated to the study of the physical behaviour of a superconducting coil during the dynamic phase of a watt balance experiment. We have compared it with the behaviour of a normal conducting coil. First experimental results are presented and preliminary conclusions are drawn.

Comparison of the Josephson voltage standards of the EIM and the BIPM

A comparison of the 10 V Josephson array voltage standard of the Bureau International des Poids et Mesures (BIPM) was made with that of the Hellenic Institute of Metrology (EIM), Greece, in March 2010. For this exercise, the option B of the BIPM.EM-K10.b comparison protocol was applied, in which the BIPM only provides a reference voltage that has to be measured by the EIM using its Josephson voltage standard and its own measuring device. The results of the two participants are in very good agreement and the overall relative standard uncertainty is 2.0 parts in 1010. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Final report on the bilateral comparison of 1 Ω standards (ongoing BIPM key comparison BIPM.EM-K13.a) between the NIST (USA) and the BIPM

This report describes the results obtained from a NIST?BIPM bilateral comparison of 1 ? resistance standards in 2007. The comparison was carried out in the framework of the BIPM ongoing key comparison BIPM.EM-K13.a. Three BIPM 1 ? travelling standards of CSIRO type were calibrated first at the BIPM, then at the NIST and again at the BIPM after their return. The stability of the transfer standard was such that the uncertainty associated with the transfer was significantly smaller than the uncertainty arising from the calibrations. The NIST and the BIPM calibrations were found to be in good agreement, with a mean difference smaller than one standard uncertainty of the comparison. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Bilateral comparison of 1 Ω standards (ongoing BIPM key comparison BIPM.EM-K13.a) between the NMIA (Australia) and the BIPM

This report describes the results obtained from a NMIA(Australia)?BIPM bilateral comparison of 1?? resistance standards in the period 2008?2009. The comparison was carried out in the framework of the BIPM ongoing key comparison BIPM.EM-K13.a. Three BIPM 1?? travelling standards of CSIRO type were calibrated first at the BIPM, then at the NMIA and again at the BIPM after their return. The stability of the transfer standards was such that the uncertainty associated with the transfer was significantly smaller than the uncertainty arising from the calibrations. The BIPM results are based on the conventional value RK-90. Those from the NMIA are traceable to a calculable capacitor. The uncertainty of the comparison includes therefore the standard uncertainty of 1???10?7 that applies to the use of the quantum Hall effect as a representation of the ohm. The NMIA and the BIPM calibrations were found to be in agreement, with a mean difference smaller than the expanded uncertainty (k = 2) of the comparison. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Comparison of the Josephson Voltage Standards of the INM and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the Institutul National de Metrologie (INM), Bucuresti, Romania, was carried out in June 2014 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by INM using its Josephson standard with its own measuring device. Option A required INM to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement loop. Since no sufficiently stable voltage could be achieved in this configuration, a digital detector was used. In all cases the BIPM array was kept floating from ground. The final results were in good agreement within the combined relative standard uncertainty of 2.6 parts in 1010 for the nominal voltage of 10 V. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Bilateral comparison of 10 V standards between the NSAI?NML (Ireland) and the BIPM, March to April 2011 (part of the ongoing BIPM key comparison BIPM.EM-K11.b)

As a part of the ongoing BIPM key comparison BIPM.EM-K11.b, a comparison of the 10?V voltage reference standards of the BIPM and the National Standards Authority of Ireland?National Metrology Laboratory (NSAI?NML), Dublin, Ireland, was carried out from March to April 2011. Two BIPM Zener diode-based travelling standards (Fluke 732B) were transported by freight to NSAI?NML. At NSAI?NML, the 10?V output EMF of each travelling standard was measured by direct comparison with a group of characterized Zener diode-based electronic voltage standards. At the BIPM, the travelling standards were calibrated before and after the measurements at NSAI?NML, with the Josephson Voltage Standard. Results of all measurements were corrected for the dependence of the output voltages on internal temperature and ambient pressure. The comparison results show that the voltage standards maintained by NSAI?NML and the BIPM were equivalent, within their stated expanded uncertainties, on the mean date of the comparison. 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).