Bureau International des Poids et Mesures BIPM

Sèvres, France

Bureau International des Poids et Mesures BIPM

Sèvres, France

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Wallard A.,Bureau International des Poids et Mesures BIPM
Metrologia | Year: 2011

Bureau International des Poids et Mesures (BIPM) is a French organization that conducts scientific work based around the operation of reference facilities on behalf of national metrology institutes (NMI) in the States that are Parties to the Meter Convention, international liaison, planning, and administration. The main activities of the BIPM are scientific works, maintenance and updating the International System of Units SI, liaison with other bodies with similar or complementary missions and promotion of metrology. The Mass Department is heavily involved in the International Avogadro Coordination (IAC) project, where the BIPM takes a lead role in mass measurements of the silicon spheres used in this work. The work of the Electricity Department is focused on its comparison program to validate national primary standards for fundamental electrical quantities. The BIPM has started to investigate pure material characterization methods for analytes of higher molecular weight and complexity that are of direct relevance to the Consultative Committee for Amount of Substance (CCQM).


Davis R.S.,Bureau International des Poids et Mesures BIPM | Barat P.,Bureau International des Poids et Mesures BIPM | Stock M.,Bureau International des Poids et Mesures BIPM
Metrologia | Year: 2016

The very first definition of the kilogram was in terms of a constant of nature, although this idea could not be fully realized at the end of the 18th century. Instead the kilogram was defined by an artefact whose mass was made to approximate as closely as possible a physical constant with unit kg m-3 - the maximum density of distilled water at atmospheric pressure. For the next two centuries, mass comparators improved greatly as did the materials from which artefacts could be constructed. These improvements put tighter constraints on the realization of a non-artefact definition of the kilogram. However, it is now expected that the goal of redefining the kilogram in terms of fundamental constants will be achieved in 2018. We present a history of the kilogram with emphasis on continuity of this unit of mass each time it has been redefined and the stability of a unit defined by the mass of an artefact. © 2016 BIPM & IOP Publishing Ltd.


Richard P.,Federal Institute of Metrology METAS | Fang H.,Bureau International des Poids et Mesures BIPM | Davis R.,Bureau International des Poids et Mesures BIPM
Metrologia | Year: 2016

The redefinition of the kilogram, expected to be approved in the autumn of 2018, will replace the artefact definition of the kilogram by assigning a fixed numerical value to a fundamental constant of physics. While the concept of such a change is pleasing, the mass community as represented by the Consultative Committee for Mass and Related Quantities (CCM) was faced with a number of technical and procedural challenges that needed to be met in order to profit in any meaningful way from the proposed change. In the following, we outline these challenges and how the CCM has met and is meeting them. We focus especially on what the mass community requires of the new definition and the process by which the CCM has sought to ensure that these needs will be met. © 2016 BIPM & IOP Publishing Ltd.


Jiang Z.,Bureau International des Poids et Mesures BIPM
2015 Joint Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum, FCS 2015 - Proceedings | Year: 2015

In almost all the studies, the differential receiver calibration and the link calibration had been discussed separately as if the two calibrations were completely independent. In fact, in the sense of the total delay for UTC time transfer, the difference between the receiver and link calibrations is not how to perform the calibration measurement but how to use the measurement data. The two calibration results are convertible to each other under certain condition. We discuss the features, advantages and disadvantages of the link and receiver calibrations, their uncertainties, and in particular, their applications in the computation of [UTC-UTC(k)]. © 2015 IEEE.


Stock M.,Bureau International des Poids et Mesures BIPM
Metrologia | Year: 2013

Since 1889 the international prototype of the kilogram has served as the definition of the unit of mass in the International System of Units (SI). It is the last material artefact to define a base unit of the SI, and it influences several other base units. This situation is no longer acceptable in a time of ever increasing measurement precision. It is therefore planned to redefine the unit of mass by fixing the numerical value of the Planck constant. At the same time three other base units, the ampere, the kelvin and the mole, will be redefined. As a first step, the kilogram redefinition requires a highly accurate determination of the Planck constant in the present SI system, with a relative uncertainty of the order of 1 part in 108. The most promising experiment for this purpose, and for the future realization of the kilogram, is the watt balance. It compares mechanical and electrical power and makes use of two macroscopic quantum effects, thus creating a relationship between a macroscopic mass and the Planck constant. In this paper the background for the choice of the Planck constant for the kilogram redefinition is discussed and the role of the Planck constant in physics is briefly reviewed. The operating principle of watt balance experiments is explained and the existing experiments are reviewed. An overview is given of all presently available experimental determinations of the Planck constant, and it is shown that further investigation is needed before the redefinition of the kilogram can take place. © 2013 BIPM & IOP Publishing Ltd.


Wallard A.,Bureau International des Poids et Mesures BIPM
Metrologia | Year: 2010

Andrew Wallard, director, Bureau International des Poids et Mesures (BIPM), Sèvres, France, has presented its report for the year 2009. The report states that the International Committee for Weights and Measures (CIPM) has approved a number of policy documents including the Rules of Procedure for Consultative Committees and their working groups, and the criteria for membership of the CCU. BIPM has also strengthened its links with a number of intergovernmental organizations and international bodies and its work with the World Meteorological Organization continues to increase and the two bodies will hold a joint symposium on metrology and climate change in March-April 2010. The BIPM continues to provide a limited number of measurement services to national metrology institute (NMI) from Member States. The calibration service of BIPM continues to support requests from Member States, have enhanced the service through a re-evaluation of the masses of working standards and is in the process of adding new capabilities for the calibration of relative humidity sensors.


Jiang Z.,Bureau International des Poids et Mesures BIPM | Lewandowski W.,Polish Academy of Sciences
Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI | Year: 2014

UTC is represented by the differences [UTC-UTC(k)] between UTC and the UTC realization of a laboratory k, to which uncertainties are associated. The dominant part of the uncertainty comes from the time transfer. Because PTB is the only pivot of the present UTC time transfer network, the estimation of the uncertainty in [UTCUTC( k)] becomes therefore that of the time links of Lab(k)-PTB. The uncertainty consists of two parts: The Type A component (uA) is estimated by statistical means and the Type B component (uB) is estimated by other methods, mainly the calibration. The value of uA depends on the time transfer techniques and has been carefully investigated in an early study [4]. The results have been applied in the BIPM Circular T since Nov. 2011. The value of uB depends on the calibration technique. In the present Circular T, the uB are about 1 ns for the TWSTT (Ywo-Way Satellite Time Transfer) links and 5-7 ns for the GNSS links. These conventional uB are the values corresponding to the moments when the calibrations were performed. Are they still valuable? Or are not they overestimated or underestimated? We try to answer the question in this paper. In this paper, we first review the last global uA evaluations made in 2011, of which the result is still valuable; and then we estimate the accuracy of [UTC-UTC(k)] using the newly developed accurate time link calibration techniques of which the uB is about 0.6 ~ 1.5 ns. After proving the dependence of the uncertainty in [UTCUTC( k)] on that of the related time transfer link Lab(k)- PTB, we analyze the uncertainties of the TWSTT and GNSS time link calibrations performed in the recent years by several independent organizations, such as the TimeTech, PTB, USNO, ROA and BIPM etc. Some seventeen leading UTC laboratories in Europe, Asia and North America are involved which contribute 84% clock weight in the UTC generation. We evaluate the real uncertainty in [UTC-UTC(k)] which is of 2.5 ns in general for both of the TWSTT and GNSS links. It is bigger than the uB(TW)=1 ns and much smaller than the uB(GPS)=5 ns. The evolution of the uB(TW) may explain the first and the overestimation the latter. By this study, we do not find convincible examples proving that the firmware variation in the TWSTT or GNSS receivers may cause the calibrations change bigger than 2 ns. It is however easy to find evidences that most of the outliers > 2 ns in the calibration corrections are probably caused by the equipment setups changes and/or sub-delay measurement errors/biases in the UTC laboratories as well as the events such as the satellite or frequency changes, etc.


Andreo P.,University of Stockholm | Burns D.T.,Bureau International des Poids et Mesures BIPM | Salvat F.,University of Barcelona
Physics in Medicine and Biology | Year: 2012

A systematic analysis of the available data has been carried out for mass energy-absorption coefficients and their ratios for air, graphite and water for photon energies between 1 keV and 2 MeV, using representative kilovoltage x-ray spectra for mammography and diagnostic radiology below 100 kV, and for 192Ir and 60Co gamma-ray spectra. The aim of this work was to establish an envelope of uncertainty based on the spread of the available data. Type A uncertainties were determined from the results of Monte Carlo (MC) calculations with the PENELOPE and EGSnrc systems, yielding mean values for ν en/ with a given statistical standard uncertainty. Type B estimates were based on two groupings. The first grouping consisted of MC calculations based on a similar implementation but using different data and/or approximations. The second grouping was formed by various datasets, obtained by different authors or methods using the same or different basic data, and with different implementations (analytical, MC-based, or a combination of the two); these datasets were the compilations of NIST, Hubbell, JohnsCunningham, Attix and Higgins, plus MC calculations with PENELOPE and EGSnrc. The combined standard uncertainty, u c, for the ν en/ values for the mammography x-ray spectra is 2.5%, decreasing gradually to 1.6% for kilovoltage x-ray spectra up to 100 kV. For 60Co and 192Ir, u cis approximately 0.1%. The Type B uncertainty analysis for the ratios of ν en/ values includes four methods of analysis and concludes that for the present data the assumption that the data interval represents 95% confidence limits is a good compromise. For the mammography x-ray spectra, the combined standard uncertainties of (ν en/) graphite,airand (ν en/) graphite,waterare 1.5%, and 0.5% for (ν en/) water,air, decreasing gradually down to u c= 0.1% for the three ν en/ ratios for the gamma-ray spectra. The present estimates are shown to coincide well with those of Hubbell (1977 Rad. Res. 70 5881), except for the lowest energy range (radiodiagnostic) where it is concluded that current databases and their systematic analysis represent an improvement over the older Hubbell estimations. The results for (ν en/) graphite,airfor the gamma-ray dosimetry range are moderately higher than those of Seltzer and Bergstrom (2005 private communication). © 2012 Institute of Physics and Engineering in Medicine.


Stock M.,Bureau International des Poids et Mesures BIPM
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Since 1889, the international prototype of the kilogram has served as the definition of the unit of mass in the International System of Units (SI). It is the last material artefact to define a base unit of the SI, and it influences several other base units. This situation is no longer acceptable in a time of ever-increasing measurement precision. It is therefore planned to redefine the unit of mass by fixing the numerical value of the Planck constant. At the same time three other base units, the ampere, the kelvin and the mole, will be redefined. As a first step, the kilogram redefinition requires a highly accurate determination of the Planck constant in the present SI system, with a relative uncertainty of the order of 1 part in 10 8. The most promising experiment for this purpose, and for the future realization of the kilogram, is the watt balance. It compares mechanical and electrical power and makes use of two macroscopic quantum effects, thus creating a relationship between a macroscopic mass and the Planck constant. In this paper, the operating principle of watt balance experiments is explained and the existing experiments are reviewed. An overview is given of all available experimental determinations of the Planck constant, and it is shown that further investigation is needed before the redefinition of the kilogram can take place. Independent of this requirement, a consensus has been reached on the form that future definitions of the SI base units will take. © 2011 The Royal Society.


Davis R.S.,Bureau International des Poids et Mesures BIPM
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Since 1889, the international prototype of the kilogram has served to define the unit of mass in what is now known as the International System of Units (SI). This definition, which continues to serve mass metrology well, is an anachronism for twenty-first century physics. Indeed, the kilogram will no doubt be redefined in terms of a physical constant, such as the Planck constant. As a practical matter, linking the quantum world to the macroscopic world of mass metrology has, and remains, challenging although great progress has been made. The international prototype or, more likely, a modern ensemble of reference standards, may yet have a role to play for some time after redefinition, as described in this paper. © 2011 The Royal Society.

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