About
118
Publications
39,501
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
3,751
Citations
Introduction
Richard Davis is an honorary principal research physicist of the International Bureau of Weights and Measures (BIPM).
Current institution
Additional affiliations
June 1990 - October 2010
July 1972 - June 1990
Publications
Publications (118)
The International System of Units (SI) [1] was inaugurated in 1960, following years of discussions interrupted by world wars. At that time, a consensus did not yet exist on whether the SI unit of plane angle, the radian (symbol: rad), should be treated as a base unit with its own dimension A, independent of all other base dimensions, or as a unit d...
The values of Newton’s constant of gravitation, G, reported by determinations at the Interna- tional Bureau of Weights and Measures (BIPM) in 2001 [1] and in 2013 [2] are some 200 parts per million (ppm) larger than the value of 6.67430 × 10−11 m3 kg−1 s−2 which was recommended by CODATA in 2018 [3]. The CODATA value has an assigned uncertainty of...
In a useful introduction to “natural units” [1], the author contrasted natural units to the SI as it existed at the time of writing (2016). The SI was characterized in [1] as a system that “relies heavily on precision measurements of standard prototypes, objects or systems that define a physical unit.” In particular, the SI indeed relied on one sta...
Article "Techniques de l'Ingénieur" R50 : https://www.techniques-ingenieur.fr/base-documentaire/mesures-analyses-th1/organisation-et-vocabulaire-de-la-metrologie-42421210/etalons-metrologiques-fondamentaux-r50/
Le Système international d'unités (SI) qui a été adopté par la Conférence générale des poids et mesures en 1960 est l'aboutissement de pl...
2019 was a big year for metrology. The international system of units was revised on World Metrology Day, May 20
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup>
, that year [1]. What will 2020 bring? In this article we discuss five promising advances that we have on a watchlist for 2020. First,...
Following the revision of the International System of Units (SI), that takes effect on 20 May 2019, the unit mole is defined by using a fixed number of elementary entities. This number is the fixed numerical value of the Avogadro constant, which is the defining constant of the unit mole. This definition was made possible because the determination o...
In November 2018, the General Conference on Weights and Measures (CGPM) gave its unanimous approval to Resolution 1, a major revision of the SI to take effect on May 20, 2019 [1]. The intentions of the CGPM had already been set out in a resolution adopted in 2011. All of the work needed to meet the requirements of the 2011 resolution was monitored...
On 16 November 2018 a revision of the International System of Units (the SI) was agreed by the General Conference on Weights and Measures. The definitions of the base units were presented in a new format that highlighted the link between each unit and a defined value of an associated constant. The physical concepts underlying the definitions of the...
As part of a revision to the International System of Units (SI) approved in2018 and to take effect in May 2019, the seven base units will be defined bygiving fixed numerical values to seven defining constants. This article shows howthe definitions of all seven base units can be derived efficiently from thedefining constants, with the result appeari...
The hardness of materials can be measured in many different ways, but the oldest method which is still influential relies on the Mohs scale devised by Friedrich Mohs in about 1822 as an aide to identifying and classifying minerals based on their hardness. (An English translation of Mohs' treatise on mineralogy was published in 1825 and includes a d...
In 1967, the Soviet Union's Venera-4 space mission to Venus sent back the first tantalizing temperature measurements of the Venusian atmosphere; Veneras -5 and -6 were launched in January 1969. A few months later, a famous lowtemperature physicist whimsically said, "I think it is a sad reflection on our civilization that while we can and do measure...
As part of a revision to the SI expected to be approved later this year and to take effect in May 2019, the seven base units will be defined by giving fixed numerical values to seven “defining constants”.
The report shows how the definitions of all seven base units can be derived efficiently from the defining constants, with the result appearing a...
Measuring the speed of light, and ultimately using this speed to define the meter in the International System of Units (SI), has much to teach us about basic metrology. These lessons will gain new relevance later this year if the revised SI gains final approval, as expected. The history culminating in the last measurement of the speed of light is r...
In 2011 the General Conference on Weights and Measures (CGPM) noted the intention of the International Committee for Weights and Measures (CIPM) to revise the entire International System of Units (SI) by linking all seven base units to seven fundamental physical constants. Of particular interest to chemists, new definitions for the kilogram and the...
Material properties are affected by temperature. This can be a major obstacle when, for instance, measuring precise lengths with a metal ruler. If the ruler was calibrated by one laboratory at a reference temperature— say 15°C—but then used at a different temperature in another laboratory, then the calibration certificate might include the value of...
The engineering of stability into a wide variety of commonly- used devices and systems is a well-known necessity. Inherently unstable mechanical systems are often stabilized by the addition of servocontrol, a well-known historical example being the addition by James Watt of a “governor” to his steam engine. The governor is a mechanical servocontrol...
In the proposed new SI, the kilogram will be redefined in terms of the Planck constant and the mole will be redefined in terms of the Avogadro constant. These redefinitions will have some consequences for measurements in chemistry. The goal of the Mole Project (IUPAC Project Number 2013-048-1-100) was to compile published work related to the defini...
The revised International System of Units (SI), expected to be approved late in 2018, has implications for physics pedagogy. The ampere definition, which dates from 1948, will be replaced by a definition that fixes the numerical value of the elementary chargee in coulombs. The kilogram definition, which dates from 1889, will be replaced by a defini...
The most reproducible measurements of dc resistance are made with a four-terminal circuit. Two of the terminals carry electrical current through the resistive element and two are used to pick off the potential difference, or voltage, between opposite ends of the element. If the resistance is known and the voltage is measured, then the current flowi...
Eighty-five years ago, the journal Science published »The Romance of the Next Decimal Place» by F.K. Richtmyer. The essay cites specific historical examples to show how improved measurement accuracy (the next decimal place) has driven scientific discovery in many areas, and predicts that this will continue at an increasing pace. As his title sugges...
The revised International System of Units (SI), expected to be approved late in 2018, has implications for physics pedagogy; the ampere definition which dates from 1948 will be replaced by a definition that fixes the numerical value of the elementary charge, e, in coulombs. The kilogram definition which dates from 1889 will be replaced by a definit...
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 Quantiti...
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 atmo...
Recent proposals to re-define some of the base units of the SI make use of
definitions that refer to fixed numerical values of certain constants. We
review these proposals in the context of the latest results of the
least-squares adjustment of the fundamental constants and against the
background of the difficulty experienced with communicating the...
The definition of the kilogram, the unit of mass in the International System of Units (SI), has not changed in more than 125 years. The kilogram is still defined by the mass of a Pt–Ir cylinder conserved at the International Bureau of Weights and Measures. Science and technology have progressed to the point where it is likely the kilogram will be r...
Until a new definition of the kilogram has been adopted, the SI unit of mass remains defined in terms of an artefact, the international prototype of the kilogram K, which is not readily available for regular recalibration of BIPM prototypes used for the calibration of national prototypes. Since 1889 the working hypothesis has been that the platinum...
This report presents the results of the first phase of the campaign of calibration carried out with respect to the international prototype of the kilogram (IPK) in anticipation of the redefinition of the kilogram (Extraordinary Calibrations). The definition of the kilogram was realized according to the procedure outlined in the 8th Edition of the S...
This paper is a complement to the two short papers published in 2001 and 2013 in which we presented the results of the two BIPM determinations of the Newtonian constant of gravitation G. While this review contains no new results, it includes more detailed descriptions of certain key parameters that enter into the determination of G. Following a des...
DOI:https://doi.org/10.1103/PhysRevLett.113.039901
In 2011, the General Conference on Weights and Measures (CGPM) confirmed its intention to adopt new definitions for four of the base units of the SI based on fixed numerical values of selected constants. These will be the kilogram, the ampere, the kelvin and the mole. The CGPM was not able to adopt the new definitions at that time because certain e...
In the International System of Units (SI), the definition of the mole sets the value of the molar mass of carbon-12, M(12C), exactly equal to 0.012 kg mol−1 whereas the Avogadro constant, NA, which is the molar number of entities, is measured experimentally. In the proposed 'new SI' the principles underlying these relationships will be reversed. Ho...
A watt balance is an electromechanical device that allows a mass to be determined in terms of measurable electrical and mechanical quantities, themselves traceable to the fundamental constants of physics. International plans are well advanced to redefine the unit of mass, the kilogram, in terms of a fixed numerical value for the Planck constant. A...
This Letter describes new work on the determination of the Newtonian constant of gravitation, G, carried out at the BIPM since publication of the first results in 2001. The apparatus has been completely rebuilt and extensive tests carried out on the key parameters needed to produce a new value for G. The basic principles of the experiment remain th...
This paper describes new work on the BIPM G experiment carried out since publication of the first results in 2001. The apparatus has been completely rebuilt and extensive tests carried out on the key parameters needed to produce a new value for G. The basic principles of the experiment remain the same, namely a torsion balance suspended from a wide...
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 consta...
A cleaning method using ultraviolet activated ozone has been developed at the National Physical Laboratory (NPL). A comparison to test the effectiveness of this cleaning method with nettoyage-lavage cleaning on platinum–iridium artefacts and kilogram mass standards was undertaken at the Bureau International des Poids et Mesures (BIPM). Three cleani...
The principal analytical techniques for measuring mass and density are presented. These are put in the broader context of the meaning of these quantities and the units in which they are commonly measured. The importance of legal metrology to analytical weighing is emphasized. The basic features of servocontrolled analytical balances are presented,...
The International System of Units (SI) is widely used in science, industry, and commerce because it caters simultaneously
to the needs of all. In the early twenty-first century, this means defining the units of time, length, mass, and electricity
in terms of the fundamental constants of physics, and then “realizing” these definitions to sufficient...
Measuring Newton's constant of gravitation is a difficult task, because gravity is the weakest of all the fundamental forces. An experiment involving two simple pendulums provides a seemingly accurate but surprising value.
The mise en pratique (“practical realization”) for the definition of the kelvin (MeP-K) was created by the Consultative Committee for Thermometry (CCT) in 2006 to give practitioners of thermometry a guide to
the realization of the kelvin, i.e., measurement of temperature in kelvins, in accord with the International System of Units.
In this article,...
This contribution discusses the relative roles of the standard formulation for the density of liquid water recommended for metrology by the International Committee for Weights and Measures (CIPM) in 2001 and the thermodynamic property formulation adopted by the International Association for the Properties of Water and Steam (IAPWS) in 1995. The two...
A redefinition of most of the base units of the International System (SI) has been proposed and may be approved as early as autumn, 2011. In particular, it is proposed that the kilogram, which currently is defined by the mass of an artifact maintained at the BIPM, should be redefined in terms of a fundamental constant of physics. The paper reviews...
This paper gives the final results of the Mk II version of the BIPM torsion-balance G experiment. Results of the Mk I version were published in 2001 and the apparatus was entirely rebuilt in the years 2001 to 2003. The key feature the BIPM approach is that a value of G can be obtained by up to three different methods. The 2001 result came from two...
Measurements of air density determined gravimetrically and by using the CIPM-81/91 formula, an equation of state, have a relative deviation of 6.4 × 10−5.This difference is consistent with a new determination of the mole fraction of argon xAr carried out in 2002 by the Korea Research Institute of Standards and Science (KRISS) and with recently publ...
LNE and BIPM compared their pressure standards equipped with 20 cm2 effective area piston–cylinder units in the absolute pressure range from 80 kPa to 110 kPa.The pressure standards, the method for calculating the reference values and the comparison results are presented. The results of the comparison can be considered as satisfactory as the deviat...
The 20th IMEKO-TC3 Congress was held in Merida from November 27 through November 30, 2007. In the final Plenary Session, Prof. A. Cruz Serra (President of IMEKO) and Prof. Dae-Im Kang (President-Elect of IMEKO and Vice-President of KRISS – Korea) provided the final data of the Congress thanking the institutions present who, with their scientific co...
A revised draft of OIML Recommendation 111 has been approved recently. Among the many notable changes to the previous edition are specific requirements for both the magnetic susceptibility and residual magnetization of weights used in legal metrology. The highest class of such weights is E1, for which a 1kg weight has a manufacturing tolerance of ±...
The ubiquitous technology of magnetic force compensation of gravitational forces acting on artifacts on the pans of modern balances and comparators has brought with it the problem of magnetic leakage from the compensation coils. Leaking magnetic fields, as well as those due to the surroundings of the balance, can interact with the artifact whose ma...
OIML Recommendation R-111 (2004), now publicly available, specifies the magnetic properties of standard weights as a function of class and nominal value. This note aims to show why these specifications are necessary and how a manufactured weight can, in principle, be tested to verify that it is in compliance. A risk analysis can then help individua...
The kilogram is the unit of mass in the International System. Its definition dates from 1889 and, therefore, predates most of modern physics. The definition simply states that the 'kilogram' is the mass of an object known as the international prototype. Thus, we have the extraordinary situation that certain fundamental physical constants (the Planc...
Introduction ..................................................................................................................................................... 2
Criteria for membership of the Consultative Committees of the CIPM.......................................................... 3
Consultative Committee for Electricity and Magnetism (CCEM...
TOPICS 1 - Instrumentation and Methods 1.1 Force standards 1.2 Mass standards and balances 1.3 Torque standards 1.4 Density Standards 2 - Fundamental aspects 2.1 Force metrology 2.2 New concepts in mass metrology 2.3 Torque metrology 2.4 Density metrology and redefinition of the mass unit 2.5 Dynamic force and torque measurements 2.6 Multi-componen...
This paper describes the design and construction of a novel form of equal-arm balance. The balance has been designed to study the performance of flexure strips for use as pivots in a 1 kg mass comparator working at the highest accuracy. The beam of the balance is servo controlled using optical detection of angular position and electromagnetic contr...
A redetermination of the argon mole fraction in air has been undertaken in two samples of dried natural air using mass spectrometric analysis with reference to a suite of gravimetrically prepared synthetic dry air mixtures. The resulting measurement of the argon mole fraction was 9.332 mmol mol−1 with a combined standard uncertainty of 3 µmol mol−1...
The BIPM torsion-strip balance used to produce a value for G published in 2001 has been modified with a view to reducing the uncertainty from the 2001 value of about 40 ppm down to about 10 ppm. The poster will not contain a new value for G
[This corrects the article on p. 209 in vol. 100.].
We report a key comparison of 1 kg stainless steel mass standards carried out between February 1995 and October 1997. Organized within the Consultative Committee for Mass and Related Quantities (CCM), the participants included 14 national metrology institutes (NMIs) and the BIPM, with the BIPM serving as pilot laboratory. The 14 NMIs were divided i...
Unwanted magnetic effects must be minimized and quantified in precision weighing and mass metrology. To this end, methods of measuring magnetic fields and of characterizing the magnetic properties of bodies such as weights are reviewed. The results of comparisons between weights made of ferromagnetic and weakly magnetic materials as well as modelli...
The present definition of the unit of mass in the International System (SI) is based on the international prototype of the kilogram, an artefact dating back to the 1880s. At present there is considerable effort worldwide aimed at replacing this artefact definition by one based on physical constants. This paper gives a brief history of the SI unit a...
In 2000, the Bureau National de Métrologie (BNM, France) decided to develop a new watt balance experiment. Among numerous design studies, the choice of the transfer mass is particularly important. Because of the proximity to a source of high magnetic intensity, this mass must have a magnetic susceptibility as weak as possible. Gold–platinum alloy s...
We report on the design and preliminary performance of a novel torsion balance for the measurement of the Newtonian gravitational constant. The design takes advantage of the properties of a wide, heavily loaded torsion strip to enhance the ratio of gravitational signal-to-noise torques beyond that achievable by the traditional Cavendish torsion bal...
The volume magnetic susceptibility of moist air χm(ma) is needed to correct the results of certain experiments to vacuum conditions. This paper derives an appropriate equation for χm(ma) for which pressure, temperature, relative humidity, and carbon dioxide content are variable parameters. The derived equation also depends sensitively on the molar...
Changes in the display of a mass balance caused by the effect of the earth's magnetic field were measured at the Korea Research Institute of Standards and Science (KRISS) using the Bureau International des Poids et Mesures (BIPM) susceptometer operating in a Helmholtz coil system. The experimental results concerning this effect generally agreed wit...
Experimental results from four recent research reports on the determination of the density/temperature relationship of Standard Mean Ocean Water (SMOW) under a pressure of 101 325 Pa are analysed and a new formula is recommended for metrological applications. This paper determines the formulae of density and relative density, with their uncertainti...
A magnetic susceptometer developed at the Bureau International des Poids et Mesures (BIPM) is used by many national laboratories to determine the magnetic properties of stainless-steel mass standards. This device relies on a small, cylindrical magnet to simulate a magnetic point dipole. According to simple theoretical considerations, (a) the uncert...
A method is described to determine the volume of a mass standard from weighings made in air of differing density against a reference volume artefact. Standard uncertainties in volume of 2 parts in 105 (at 1 kg) or better are readily achievable with this method, using adequate measuring facilities. The advantages of the method are that volume determ...
Magnetization of a mass standard can lead to weighing errors. This is because most modern balances are sources of non-uniform magnetic induction. Although the problem of unwanted magnetic forces is well known, the characterization of the magnetic properties of mass standards and balances can be problematic. This paper compares the kind of informati...
Reports progress of a programme to measure the Newtonian constant of gravitation, G, with a torsion strip balance using several different methods. We have recently published a result with an uncertainty of 41 parts per million (ppm). The present efforts are aimed at reducing this uncertainty to about 10 ppm.
Recent letters have explained why the overall force on a pendulum bob as it passes through its lowest point is directed towards the hanging point (August p22). It turns out that this tension is important in classical beam-balances. Such balances have suspended pans that are essentially pendulum bobs. The extra tension in the suspension as the pans...
We present the results of a measurement of G made with a torsion-strip balance used in two substantially independent ways. The two results agree to within their respective uncertainties; the correlation coefficient of the two methods is -0.18. The result is G = 6.675 59(27)x10(-11) m(3) kg(-1) s(-2) with a standard uncertainty of 4.1 parts in 10(5)...
We have determined the inhomogeneities in the density of prototype STEP test masses made from HIPed beryllium and niobium using the hydrostatic weighing method developed at BIPM. 13 samples are taken from a HIPed beryllium rod (approximately 140 mm long by 90 mm) and 24 samples from a niobium rod (approximately 225 mm long by 45 mm). The maximum re...
A susceptometer developed at the Bureau International des Poids et Mesures is used by many national laboratories to determine the magnetic properties of stainless-steel mass standards. This device relies on a small, cylindrical magnet to simulate a magnetic point dipole. According to simple theoretical considerations, a) the magnetic moment of the...
A new measurement of G is presented having an uncertainty close to 1 part in 104. It results from work at the BIPM using a novel torsion balance and its aim is to help resolve the discrepancy produced by the 1995 result from the PTB that differed by 0.6% from the then Codata value
We develop a model for damping of a mechanical oscillator when subjected to an electrostatic force applied via electrodes with resistive losses. The model predicts viscous damping that varies as the inverse of oscillation frequency and that is proportional to a dimensionless constant Δe, which depends on the surface properties of the electrodes. Pr...
We briefly review the results of experimental and theoretical studies of anelasticity at low frequencies and we discuss the essential features of models that explain consistently the key aspects of this behaviour. In our original paper on this topic we reported that damping in a compound pendulum at frequencies in the range 10-3-10-2 Hz was consist...
The BIPM is undertaking a determination of the Newtonian gravitational constant, G using a torsion balance with a thin, heavily loaded strip as the suspension element. This apparatus uses four 1.2 kg test masses and four 15.5 kg source masses to produce a gravitational torque of 2 × 10-8 N m. A preliminary determination of G has been made with a re...
A convenient new force method for the measurement of volume magnetic susceptibility is described. It is based on a commercial balance that is used to measure the force between a magnet placed on the pan of the balance and the sample supported just above. Samples of almost arbitrary shape and size can be measured quickly. The sensitivity of the devi...
A synopsis is given of the fourth meeting of the Consultative Committee on Amount of Substance (CCQM). This is preceded by
a brief description of the origins of the various consultative committees that report to the Comité International des Poids
et Mesures (CIPM). In addition to invited guests, the attendees included experts on metrology in chemi...
The Chairman, Dr. Manfred Peters, gave a welcoming address, thanking UKAS for the organisation of the meeting. He introduced his successor to the chair, Dr. Carlo Ferrero from IMGC, Turin. With just two topics on the agenda, Dr. Peters suggested that the first day be spent, under his chairmanship, on the document EA-Gxx, to finalise the draft after...
Revised values are given for the stress-dependent damping in Cu-Be torsion strips [Phys. Lett. A 197 (1995) 197; 198 (1995) 474 (E)]. New work has shown that the relation then taken for the restoring torque of a heavily loaded strip in torsion failed to include a load dependent (gravitational) term. Its inclusion removes the inconsistency then note...
A magnetic resonance imaging method for volume magnetic susceptibility estimate of materials immersed in a liquid containing resonant nuclei is proposed. The method uses either the standard spin-echo Fourier imaging technique or the projection-reconstruction technique. Image distortions of cylindrical macroscopic susceptibility inhomomogeneities ar...
Magnetic interactions may lead to errors in precision mass metrology. An analytical description of such magnetic errors is presented in which the roles of both the volume magnetic susceptibility and permanent magnetization are discussed. The same formalism is then used to describe in detail the calibration and operation of a susceptometer developed...
Stress-dependent damping in CuBe torsion and flexure suspensions has been measured at stresses up to 1.1 GPa, 95% of the yield stress. The modulus defects of CuBe increases from 4.3 × 10−5 to only 6 × 10−6 in this range. A much larger additional damping, orginating at the clamping interface between the suspension and its support, was identified and...
Small rare-earth magnets have remarkable properties that can be exploited in the construction of simple measuring devices. Examples are a torsion pendulum that measures the earth's horizontal magnetic field and a gravimetric pendulum that responds to the small susceptibilities of various "nonmagnetic" materials. These preliminary demonstrations lea...
Mass measurements made in air generally require corrections for the effects of buoyancy. In applying these corrections, the BIPM and most national laboratories now use the same equation for the determination of ρ, the density of moist air [1, 2]. The formalism presented in [1, 2] is often, though unofficially, referred to as the CIPM-81 equation to...
We report a new determination of the Universal Gas Constant R: (8. 314 471 plus or minus 0. 000 014) J multiplied by (times) mol** minus **1K** minus **1. The uncertainty in the new value is 1. 7 ppm (standard error), a factor of 5 smaller than the uncertainty in the best previous value. The gas constant was determined from measurements of the spee...
We report a new value for the universal gas constant R: (8.314 471+/-0.000 014) J mol-1K-1. The standard error of R has been reduced by a factor of 5 to 1.7 ppm. R was determined from the speed of sound in argon contained within a thick, spherical shell at the temperature of the triple point of water Tt. The volume of the shell was measured by our...
