Re-defining the kilogram via a moving-coil apparatus

Kibble, B P; Robinson, L. A.; Belliss, J H

doi:10.1109/cpem.1990.109978

Cited by 7 publications

(5 citation statements)

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“…It is perhaps a quirk of history that two experiments were already planning to measure electrical power in SI units just as a more fundamental prospect was discovered. Kibble's suggested alteration to ampere balances caused the NPL in England [79] and the NBS in the United States [80] to redesign their existing ampere balances to take advantage of the motion mode. They had yet to complete either system when the QHE was discovered in 1980.…”

Section: A Direct Link To H Via Quantum Electronicsmentioning

confidence: 99%

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History and progress on accurate measurements of the Planck constant

Steiner

2012

Rep. Prog. Phys.

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The measurement of the Planck constant, h, is entering a new phase. The CODATA 2010 recommended value is 6.626 069 57 × 10(-34) J s, but it has been a long road, and the trip is not over yet. Since its discovery as a fundamental physical constant to explain various effects in quantum theory, h has become especially important in defining standards for electrical measurements and soon, for mass determination. Measuring h in the International System of Units (SI) started as experimental attempts merely to prove its existence. Many decades passed while newer experiments measured physical effects that were the influence of h combined with other physical constants: elementary charge, e, and the Avogadro constant, N(A). As experimental techniques improved, the precision of the value of h expanded. When the Josephson and quantum Hall theories led to new electronic devices, and a hundred year old experiment, the absolute ampere, was altered into a watt balance, h not only became vital in definitions for the volt and ohm units, but suddenly it could be measured directly and even more accurately. Finally, as measurement uncertainties now approach a few parts in 10(8) from the watt balance experiments and Avogadro determinations, its importance has been linked to a proposed redefinition of a kilogram unit of mass. The path to higher accuracy in measuring the value of h was not always an example of continuous progress. Since new measurements periodically led to changes in its accepted value and the corresponding SI units, it is helpful to see why there were bumps in the road and where the different branch lines of research joined in the effort. Recalling the bumps along this road will hopefully avoid their repetition in the upcoming SI redefinition debates. This paper begins with a brief history of the methods to measure a combination of fundamental constants, thus indirectly obtaining the Planck constant. The historical path is followed in the section describing how the improved techniques and discoveries in quantum mechanics steadily reduced the uncertainty of h. The central part of this review describes the technical details of the watt balance technique, which is a combination of the mechanical and electronic measurements that now determine h as a direct result, i.e. not requiring measured values of additional fundamental constants. The first technical section describes the basics and some of the common details of many watt balance designs. Next is a review of the ongoing advances at the (currently) seven national metrology institutions where these experiments are pursued. A final summary of the recent h determinations of the last two decades shows how history keeps repeating itself; there is again a question of whether there is a shift in the newest results, albeit at uncertainties that are many orders of magnitude less than the original experiments. The conclusion is that there is room for further development to resolve these differences and find new ideas for a watt balance system with a more universal application. Sin...

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Section: A Direct Link To H Via Quantum Electronicsmentioning

confidence: 99%

“…The lever arm for motion control was preserved. The magnet was redesigned to incorporate a horizontal circular coil to reduce the field interactions between the coil and magnet in place of the figure 8 induction coil, as related in [122]. The coils and balance apparatus were built into a vacuum chamber.…”

Section: Npl Mark Ii-in Vacuum New Coil Designmentioning

confidence: 99%

History and progress on accurate measurements of the Planck constant

Steiner

2012

Rep. Prog. Phys.

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“…The final result of this set-up with a relative standard uncertainty of 2×10 −7 was published in 1990 [32,42]. An improved apparatus, described in the next sections, was presented during the same year [43,44]. In the mean time, this experiment has reached a short-term reproducibility in the order of one part in 10 8 [45], and a new result for the Planck constant may be expected in the near future.…”

Section: The Existing Projects and Their Main Characteristicsmentioning

confidence: 99%

Tracing Planck's constant to the kilogram by electromechanical methods

2003

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Among the priority tasks in the further development of the International System of Units is the redefinition of the kilogram based on fundamental constants. One of the strategies pursued today is to relate mass to Planck's constant h using the equivalence between mechanical and electrical energies. In this paper, possible experimental approaches in this direction are described. The approach which promises to reach the required uncertainty at the earliest is the concept of the moving-coil watt balance. The status of the different watt balance experiments is reviewed in detail.

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“…The main contributors to the quoted u , , ~ of 13,6 x 10" for h were (in parts in lo8): induced voltage U in terms of the Josephson effect, 11,2; experimental standard deviation of the mean of 50values of WwJW, 4,8; index of refraction of air, 4,8 (the velocity was measured interferometrically); optical fringe frequency, 2,O; and buoyancy correction for the standard masses, 2,O. Kibble and colleagues have now built a "next generation" apparatus that operates in vacuum and that has been designed to reduce these uncertainties significantly; a u ~, ~ of less than 1 x lo4 is eventually anticipated [38].…”

Section: Watt Balance Nplmentioning

confidence: 99%

Determining the Avogadro Constant from Electrical Measurements

Taylor

1994

Metrologia

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It is now possible to obtain indirect values of the Avogadro constant NA having comparatively small combined standard uncertainties by appropriately combining the values of a number of other fundamental physical constants. These constants, whose values in several important cases can be obtained from electrical measurements, include the Rydberg, fine-structure, Josephson, von Klitzing, Planck, and Faraday constants, the molar mass of the proton, the proton-electron mass ratio, and the shielded proton gyromagnetic ratio. This paper gives the expressions that relate NA to these other fundamental constants and the values of NA that can be obtained from these expressions using the currently available data. It also briefly discusses the prospects of obtaining an indirect value of NA with a combined standard uncertainty that is small enough to allow the redefinition of the kilogram.

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Re-defining the kilogram via a moving-coil apparatus

Cited by 7 publications

References 0 publications

History and progress on accurate measurements of the Planck constant

History and progress on accurate measurements of the Planck constant

Tracing Planck's constant to the kilogram by electromechanical methods

Determining the Avogadro Constant from Electrical Measurements

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