Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

Seifert, F.; Panna, Alireza R.; Li, Shisong; Han, Bing; Chao, Leon; Cao, A.; Haddad, D.; Choi, Hyemi; Haley, Lori; Schlamminger, Stephan

doi:10.1109/tim.2014.2323138

Cited by 55 publications

(119 citation statements)

References 13 publications

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“…Two Sm 2 Co 17 disks oriented in repulsion generate, in a 30 mm wide air gap, a 0.55 T radial magnetic field guided by the iron yoke. 29,30 While the magnetic flux density is mostly oriented along the radial direction, there is a small vertical component. This vertical field is caused by the finiteness of the gap (fringe fields at the end of the gap) and an asymmetry in the air-yoke boundary.…”

Section: Figmentioning

confidence: 99%

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Invited Article: A precise instrument to determine the Planck constant, and the future kilogram

Haddad

Seifert

Chao

et al. 2016

Review of Scientific Instruments

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A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and the Planck constant is established by the practical realization of the electrical units derived from the Josephson and the quantum Hall effects. We describe in this paper the fourth-generation watt balance at the National Institute of Standards and Technology (NIST), and report our initial determination of the Planck constant obtained from data taken in late 2015 and the beginning of 2016. A comprehensive analysis of the data and the associated uncertainties led to the SI value of the Planck constant, h = 6.626 069 83(22) × 10−34 J s. The relative standard uncertainty associated with this result is 34 × 10−9.

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Section: Figmentioning

confidence: 99%

“…See Ref. 30 for details on the shimming procedure. Prior to winding the coil, the coil former was painted with a static dissipative coating.…”

Section: -6mentioning

confidence: 99%

Invited Article: A precise instrument to determine the Planck constant, and the future kilogram

Haddad

Seifert

Chao

et al. 2016

Review of Scientific Instruments

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“…(1) Its maximum magnetic permeability is about 8300, which is much higher than the steel used in a watt balance, e.g., NIST-4, the 4th generation of watt balance in the National Institute of Standard and Technology (NIST) [5]. This would lead to a better boundary condition of the air and the yoke.…”

Section: Design Of the Electromagnetmentioning

confidence: 99%

Coils and the Electromagnet Used in the Joule Balance at the NIM

Zhang

Han

et al. 2015

IEEE Trans. Instrum. Meas.

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Abstract-In the joule balance developed at National Institute of Metrology (NIM), the dynamic phase of a watt balance is replaced by the mutual inductance measurement in an attempt to provide an alternative method for the kg redefinition. But for this method a rather large current in the exciting coil, is needed to offer the necessary magnetic field in the force weighing phase, and the coil heating becomes an important uncertainty source. To reduce coil heating, a new coil system, in which a ferromagnetic material is used to increase the magnetic field was designed recently. But adopting the ferromagnetic material brings the difficulty from the nonlinear characteristic of material. This problem can be removed by measuring the magnetic flux linkage difference of the suspended coil at two vertical positions directly to replace the mutual inductance parameter. Some systematic effects of this magnet are discussed.

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“…However, limited to the mechanical realization, only several vertical profiles of B r (z) at different horizontal coordinates can be determined by the gradient coil (GC) method [20] or a high resolution magnetic probe. Knowing a set of subjected information, a natural question is: how can we solve the whole filed in the air gap by using minimum measurable quantities?…”

Section: Introductionmentioning

confidence: 99%

Field representation of a watt balance magnet by partial profile measurements

Yuan

Zhao

et al. 2015

Metrologia

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Abstract. Permanent magnets with high-permeability yokes have been widely used in watt balances for supplying a robust and strong magnetic field at the coil position. Subjected to the mechanical realization, only several B r (z) (radial magnetic field along the vertical direction) profiles can be measured by coils for field characterization. In this article, we present an algorithm that can construct the global magnetic field of the air gap based on N (N ≥ 1) additional measurements of B r (z) profiles. The proposed algorithm is realized by polynomially estimating the B z (r) function with analysis of basic relations between two magnetic components in air gap, i.e., B r (r, z) and B z (r, z), following the Maxwell's equations. The algorithm, verified by FEM simulations, can characterize the three-dimensional contribution of the magnetic field for a watt balance magnet with acceptable accuracy, which would supply basic field parameters for alignment and misalignment corrections.

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Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

Cited by 55 publications

References 13 publications

Invited Article: A precise instrument to determine the Planck constant, and the future kilogram

Invited Article: A precise instrument to determine the Planck constant, and the future kilogram

Coils and the Electromagnet Used in the Joule Balance at the NIM

Field representation of a watt balance magnet by partial profile measurements

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