Prototype Of Kilogram Research Articles

Evaluation of the accuracy, consistency, and stability of measurements of the Planck constant used in the redefinition of the international system of units

The Consultative Committee for Mass and related quantities (ccm), of the International Committee for weights and measures (cipm), has recently declared the readiness of the community to support the redefinition of the international system of units (SI) at the next meeting of the General Conference on Weights and Measures (cgpm) scheduled for November, 2018.Such redefinition will replace the international prototype of the Kilogram (ipk), as the definition and sole primary realization of the unit of mass, with a definition involving the Planck constant, h. This redefinition in terms of a fundamental constant of nature will enable widespread primary realizations not only of the kilogram but also of its multiples and sub-multiples, best to address the full range of practical needs in the measurement of mass.We review and discuss the statistical models and statistical data reductions, uncertainty evaluations, and substantive arguments that support the verification of several technical preconditions for the redefinition that the ccm has established, and whose verification the ccm has affirmed. These conditions relate to the accuracy and mutual consistency of qualifying measurement results.We review also an issue that has surfaced only recently, concerning the convergence toward a stable value, of the historical values that the task group on fundamental constants of the committee on Data for Science and Technology codata-tgfc has recommended for h over the years, even though the ccm has not deemed this issue to be relevant.We conclude that no statistically significant trend can be substantiated for these recommended values, but note that cumulative consensus values that may be derived from the historical measurement results for h seem to have converged while continuing to exhibit fluctuations that are typical of a process in statistical control.Finally, we argue that the most recent consensus value derived from the best measurements available for h, obtained using either a Kibble balance or the xrcd method, is reliable and has uncertainty no larger than the uncertainties surrounding the current primary and secondary realizations of the unit of mass, hence that no credible technical impediments stand in the way of the redefinition of the unit of mass in terms of a fixed value of h.

The SI Redefinition to Come into Force from 20 May 2019

The 19th Meeting of the Directors of National Metrology Institutes (NMIs) and Member State Representatives of the International Bureau for Weights and Measures (Bureau international des poids et mesures, BIPM) was held at its office at Sevres, France during 18 and 19 October 2017. Before we discuss the major outcome of this meeting, it is worth understanding the International Convention on SI and derived units and formation of National Metrology Institutes (NMIs), which is schematically shown in Figure 1. On 20 May 1875, 20 industrially developed nations met for the ‘Convention of the Metre’ and signed the ‘Treaty of the Metre’ under which three bodies were set up to take custody of the international prototype kilogram and metre, and to regulate comparisons with national prototypes.

Review of quantum electrical standards and benefits and effects of the implementation of the ‘revised SI’

In the present International System of Units (SI), the Josephson effect and quantum Hall effect have been utilized for voltage and resistance primary standards, and the electrical current standard has been derived from a combination of the two quantum standards. In 2018, it is planned that the SI will be revised based on the latest measurements results of the Planck constant, elementary charge, Avogadro constant, and Boltzmann constant. The adoption of the ‘Revised SI’ means we shall finally terminate the traceability of the kilogram tied to an artifact (the international prototype of the kilogram) and start a new traceability of the kilogram to the Planck constant h. In electricity and magnetism metrology, and related precision measurements, the traceability presently based on the ‘conventional values’ of the Josephson constant and the von Klitzing constant is going to be switched to the revised traceability based on the Planck constant and elementary charge. In this article, the foundation of the quantum electrical measurements and how the Revised SI, which is based purely on fundamental physical constants and quantum effects, will bring us a long‐term benefit with negligible impact to industry are detailed. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Progress on vacuum-to-air mass calibration system using magnetic suspension to disseminate the Planck-constant realized kilogram.

The kilogram is the unit of mass in the International System of units (SI) and has been defined as the mass of the International Prototype Kilogram (IPK) since 1889. In the future, a new definition of the kilogram will be realized by fixing the value of the Planck constant. The new definition of the unit of mass will occur in a vacuum environment by necessity, so the National Institute of Standards and Technology (NIST) is developing a mass calibration system in which a kilogram artefact in air can be directly compared with a kilogram realized in a vacuum environment. This apparatus uses magnetic suspension to couple the kilogram in air to a high accuracy mass balance in vacuum.

Comparison of Duplicate Standards with the National Primary Standard for the Unit of Mass in 2014–2015

Results of comparisons of the national prototype kilogram No. 12 in 2013–2014 with the international kilogram prototype are discussed. Comparisons of secondary duplicate standards with the National Primary Standard for the unit of mass GET 3-2008 in 2015 by the method of combined measurements are reported. Work on improving the national primary standard for the unit of mass in light of the transition to a new definition of the kilogram is analyzed.

Calibration campaign against the international prototype of the kilogram in anticipation of the redefinition of the kilogram, part II: evolution of the BIPM as-maintained mass unit from the 3rd periodic verification to 2014

In 2014 the Bureau International des Poids et Mesures (BIPM) carried out a calibration campaign using the international prototype of the kilogram (IPK). This is the second part in a series of publications describing the results of that campaign. As reported (Metrologia 52 310–6), following the comparisons between the IPK and its official copies, it was found that the BIPM ‘as-maintained mass unit’ was offset by 35 μg from the mass of the IPK in 2014. We report here the results of an investigation into this offset that has considered all data available from internal BIPM mass comparisons carried out between 1992 and 2014. This has enabled us to model the evolution of the offset in the as-maintained mass unit and to identify some possible reasons why it has developed. We also report how the model has been used to estimate corrections to all 1 kg mass calibration certificates issued by the BIPM during this period.

Air–vacuum transfer; establishing traceability to the new kilogram

The redefinition of the kilogram, along with another three of the base units of the International System of Units (SI), is scheduled for 2018. The current definition of the SI unit of mass assigns a mass of exactly one kilogram to the International Prototype of the kilogram, which is maintained in air and from which the unit is disseminated. The new definition, which will be from the Planck constant, involves the realisation of the mass unit in vacuum by the watt balance or Avogadro experiments. Thus, for the effective dissemination of the mass unit from the primary realisation experiments to end users, traceability of mass standards transferred between vacuum and air needs to be established and the associated uncertainties well understood. This paper describes a means of achieving the link between a unit realised in vacuum and standards used in air, and the ways in which their use can be optimised. It also investigates the likely uncertainty contribution introduced by the vacuum–air transfer process.

On the Trigonometric Descriptions of Colors

<p class="1Body">An attempt is presented for the description of the spectral colors using the standard trigonometric tools in order to extract more information about photons. We have arranged the spectral colors on an arc of the circle with the radius R = 1 and the central angle θ = π/3 when we have defined cos (θ) = λ<sub>380</sub>/λ<sub>760</sub> = 0.5. Several trigonometric operations were applied in order to find the gravity centers for the scotopic, photopic, and mesopic visions. The concept of the center of gravity of colors introduced Isaac Newton. We have postulated properties of the long-lived photons with the new interpretation of the Hubble (Zwicky-Nernst) constant H<sub>0</sub> = 2.748… * 10<sup>-18</sup> kg kg<sup>-1 </sup>s<sup>-1</sup>, the specific mass evaporation rate (SMER) of gravitons from the source mass. The stability of international prototypes of kilogram has been regularly checked. We predict that those standard kilograms due to the evaporation of gravitons lost 8.67 μg kg<sup>-1</sup> century<sup>-1</sup>. The energy of long-lived photons was trigonometrically decomposed into three parts that could be experimentally tested: longitudinal energy, transverse energy and energy of evaporated gravitons. We tested the properties of the long-lived photons with the experimental data published for the best available standard candles: supernovae Type Ia. There was found a surprising match of those experimental data with the model of the long-lived photons. Finally, we have proposed a possible decomposition of the big G (Newtonian gravitational constant) and the small kappa κ (Einsteinian gravitational constant) in order to get a new insight into the mysterious gravitational force and/or the curvature concept.</p>

Establishment of the platinum–iridium kilogram mass standards at NMIJ after the Extraordinary Calibrations

The Bureau International des Poids et Mesures has carried out calibrations of the platinum–iridium kilogram mass standards by referencing the international prototype of the kilogram for the first time since the third periodic verification of national prototypes of the kilogram was carried out in 1988–92. This calibration campaign was designated ‘Extraordinary Calibrations’ in the second phase, in which two platinum–iridium kilogram mass standards of the National Metrology Institute of Japan were calibrated with a standard uncertainty of 3.5 μg. By adding these new calibration data into our data sets from 1991, we established our mass unit with a standard uncertainty of 3.3 μg by least-squares analysis using an exponential model, which is useful for compensating for mass increase after cleaning the mass standards. Moreover, it was found that our established mass unit following the Extraordinary Calibrations shifted against our previously maintained mass unit by −20.8 μg as of the beginning of 2015. The analysis with a linear model revealed that the amount of mass increase over time of some standards was significantly smaller than that suggested at the third periodic verification of national prototypes of the kilogram. The analysis with the exponential model gave an exponent of 0.217 with a standard uncertainty of 0.057. This suggests that the mass increase due to surface contamination cannot be explained by a diffusion-limited process.

Improving traceability to the international prototype of the kilogram

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 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–iridium prototypes are stable mass standards, although mass comparisons indicate that this is not entirely true. In this paper we present a method for improving metrological traceability to the international prototype by modelling the change in mass of prototypes over time and evaluate the model parameters by a weighted least squares adjustment. The method has been applied to comparisons between 18 prototypes performed at the BIPM in the period 1889–2009. The mass values predicted by the model are compared to the mass values assigned by BIPM in the period 1992–2009 and to results of the Extraordinary Calibrations performed at BIPM in 2014 using the international prototype as reference standard.

Calibration campaign against the international prototype of the kilogram in anticipation of the redefinition of the kilogram part I: comparison of the international prototype with its official copies

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 SI Brochure. Thus the IPK and its six official copies have been cleaned and washed following the BIPM procedure.The mass comparisons carried out during this campaign showed a very good repeatability. The pooled standard deviation of repeated weighings of the prototypes was 0.4 µg. The effect of cleaning and washing of the IPK was to remove a mass of 16.8 µg. The effect of cleaning and washing of the six official copies was found to be very similar, giving an average mass removed from the seven prototypes of 15 µg with a standard deviation of 2 µg.The differences in mass between the IPK and the official copies have changed by an average of 1 µg since the 3rd Periodic Verification of National Prototypes of the Kilogram (1988–1992). These results do not confirm the trend for the masses of the six official copies to diverge from the mass of the IPK that was observed during the 2nd and 3rd Periodic Verifications.All BIPM working standards and the prototypes reserved for special use have been calibrated with respect to the IPK as part of this campaign. All of them were found to have lower masses than when they were calibrated during the 3rd Periodic Verification. As a consequence, the BIPM ‘as-maintained’ mass unit in 2014 has been found to be offset by 35 µg with respect to the IPK. This result will be analyzed in a further publication.

Recent Developments in the Study of the Surface-Stability of Platinum and Platinum-Iridium Mass Standards

We review developments in the study of the stability of platinum-iridium standard weights, in particular the kilogram prototypes manufactured from alloy supplied by Johnson Matthey in the 1880s that still stand at the heart of the International System of Units (abbreviated SI from the French: Systeme international d’unites). The SI has long since moved on from length standards based on physical artefacts fabricated from this alloy, but the SI unit of mass is still defi ned in this way, as the mass of a real physical object. The stability of these reference masses has been a concern since the 1930s, with mass loss or gain at the surface being the principal concern. In recent years X-ray photoelectron spectroscopy (XPS) has been particularly valuable in elucidating the types of contamination present and the mechanism by which contamination takes place. While direct studies on the International Prototype Kilogram are understandably diffi cult, at Newcastle University we have examined the surfaces of six Pt mass standards also manufactured in the mid-19th century, using XPS to identify contamination chemically. XPS shows a signifi cant quantity of mercury on the surfaces of all six. The most likely source of Hg vapour is the accidental breakage of thermometers and barometers, and the mechanism of contamination may be similar to the poisoning of platinum group metal (pgm) catalysts by Hg, an effect known for almost a century.

The Dissemination of Mass in the United States: Results and Implications of Recent BIPM Calibrations of US National Prototype Kilograms.

The National Institute of Standards and Technology (NIST) is responsible for the dissemination of the unit of mass within the United States of America through the national prototype kilogram K20 and its check standard K4. These platinum-iridium artifacts have been in use since 1889 and are periodically sent to the International Bureau of Weights and Measures (BIPM) for recalibration. The following is a brief description of the roles of the national prototype kilograms in the dissemination of mass in the United States of America, and the implications for NIST mass calibration customers of the most recent recalibrations of K20 and K4.

Stability of reference masses: VI. Mercury and carbonaceous contamination on platinum weights manufactured at a similar time as the international and national prototype kilograms

The stability of prototype kilogram reference masses has been a long-standing question within the SI, with mass loss or gain at the surface being the principal concern. In papers I, III and IV of this series we showed mercury and organic carbonaceous contamination to be significant in sample surfaces exposed to typical prototype kilogram storage environments. In this work, we have examined the surfaces of six platinum mass standards manufactured in the mid-19th century. We used x-ray photoelectron spectroscopy in order to identify mercury and carbonaceous contamination, and assess the validity of our previous models for the rate of increase. We use white-light interferometry to study surface roughness and polishing damage. We see mercury on all six of the 19th century polished prototypes we analysed. For one weight, manufactured around 1830, we see a quantity of mercury roughly equivalent to 250 µg if present on the surface of a prototype kilogram at the same mass per unit area. The quantities of these contaminations calculated from our XPS spectra are in good agreement with the theoretical models developed in papers III and IV for the growth of mercury and carbonaceous contamination, respectively, and increase our confidence that these processes are indeed happening at the surface of polished kilogram prototypes in most (if not all) cases. We discuss some potential sources of mercury contamination, though the most likely source remains the accidental breakage of thermometers and barometers containing mercury in the past. Mercury in laboratory air can adsorb and diffuse into defects and grain boundaries, especially at polished surfaces. We consider some possible ways to improve the situation, for example by placing a gold foil in the proximity of a prototype to act as a ‘getter’ that will preferentially adsorb mercury.

The New Kilogram Definition and its Implications for High-Precision Mass Tolerance Classes.

The SI unit of mass, the kilogram, is the only remaining artifact definition in the seven fundamental units of the SI system. It will be redefined in terms of the Planck constant as soon as certain experimental conditions, based on recommendations of the Consultative Committee for Mass and Related Quantities (CCM) are met. To better reflect reality, the redefinition will likely be accompanied by an increase in the uncertainties that National Metrology Institutes (NMIs) pass on to customers via artifact dissemination, which could have an impact on the reference standards that are used by secondary calibration laboratories if certain weight tolerances are adopted for use. This paper will compare the legal metrology requirements for precision mass calibration laboratories after the kilogram is redefined with the current capabilities based on the international prototype kilogram (IPK) realization of the kilogram.

Design of the new METAS watt balance experiment Mark II

The kilogram is the last unit of the international system of units (SI) still based on a material artefact, the international prototype of the kilogram (IPK). The comparisons made in the last hundred years have clearly revealed a long-term relative drift between the IPK and the official copies kept under similar conditions at the Bureau International des Poids et Mesures. A promising route towards a new definition of the kilogram based on a fundamental constant is represented by the watt balance experiment which links the mass unit to the Planck constant h. For more than ten years, the Federal Institute of Metrology METAS has been actively working in the conception and development of a watt balance experiment. This paper describes the new design of the Mark II METAS watt balance. The metrological characteristics of the different components of the experiment are described and discussed.

A one-kilogram quartz resonator as a mass standard

The SI unit of mass, the kilogram, is defined by a single artifact, the International Prototype Kilogram. This artifact, the primary mass standard, suffers from long-term instabilities that are neither well understood nor easily monitored. A secondary mass standard consisting of a 1-kg quartz resonator in ultrahigh vacuum is proposed. The frequency stability of such a resonator is likely to be far higher than the mass stability of the primary mass standard. Moreover, the resonator would provide a link to the SI time-interval unit. When compared with a laboratory-grade atomic frequency standard or GPS time, the frequency of the resonator could be monitored, on a continuous basis, with 10(-15) precision in only a few days of averaging. It could also be coordinated, worldwide, with other resonator mass standards without the need to transport the standards.

ABOUT “SI” TRACEABILITY OF MICROMASSES AND/OR MICROFORCES

Over the last period, increasing attention has been paid to measurement of small forces which play a more important role in nanotechnology and other significant areas such as MEMS (Micro-Electro-Mechanical Systems) and NEMS (nano-electro-mechanical systems) which can be found into everyday products (mobile phones, MP3 players, PCs, cars). In this respect, the development of mass standards and measurement techniques below the current limit of 1 milligram is vital to provide traceability to the SI for such measurements. In Romania, the Mass laboratory of INM considered it necessary to extend the dissemination of the mass unit below 1 mg, in order to meet current needs. Using the subdivision method and starting from the national prototype kilogram No. 2, all necessary experiments were performed for the first time in Romania to extend mass unit traceability till 100 μg. This extension also supports the provision of mass calibrations for low force measurements. The associated measurement procedure and measurement uncertainty results obtained in the calibration are described. In the article are also presented some of the worldwide methods currently used for measuring small forces.

In situ direct determination of air density using Pt-Ir and stainless steel standards

The density of air was directly measured using a Pt-Ir kilogram prototype and a stainless steel kilogram as buoyancy artifacts (BA) in a balance using an automatic weight exchanger capable of handling four weights. The mass values of two other stainless steel weights as test objects placed on the same weight exchanger were determined by comparing them with the prototype of kilogram and using the air density measured in situ. The in situ BA method produced less uncertainty in obtaining the mass values of test weights than that by the BIPM equation method. The accuracy of the in situ direct determination of the air density could be improved by utilizing a stainless steel BA whose true mass and volume could have been known more accurately. BA then could measure the mass of any object with less uncertainty in situ.

The role of the international prototype of the kilogram after redefinition of the International System of Units

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.