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A simultaneous moving and weighing technique for a watt balance at room temperature,

Robinson, I A (2012) A simultaneous moving and weighing technique for a watt balance at room temperature,. Metrologia, 49 (1). pp. 108-112.

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Abstract

Measurements made with watt balances are paving the way to a new definition of the kilogram based upon a fixed value of the Planck constant. A conventional watt balance measures virtual power in a two-part experiment that requires stability of a few parts in 109 in the strength of a magnetic field which links the two parts of the experiment. This limits the technique to those laboratories with the specialised facilities to support this requirement. The BIPM has suggested that the stability requirement could be relaxed, by exploiting the properties of superconductors, to perform the two parts of the experiment simultaneously. This requires cryogenic operation of parts of the balance introducing some significant disadvantages. This letter suggests a novel modification to the watt balance which avoids these disadvantages by allowing the BIPM technique to be implemented at room temperature, with an uncertainty comparable to the best conventional watt balances. A bifilar winding replaces the single conductor winding on a conventional watt balance; the measurement proceeds using the BIPM technique, but with one strand of the bifilar winding carrying the weighing current, whilst the other is used to measure the voltage induced by the motion of the coil in the magnetic field. The roles of the two strands are alternated to eliminate errors arising from small differences between them.

Item Type: Article
Keywords: kilogram, watt balance, SI, redefinition
Subjects: Engineering Measurements
Engineering Measurements > Mass, Force, Pressure
Identification number/DOI: 10.1088/0026-1394/49/1/015
Last Modified: 02 Feb 2018 13:14
URI: http://eprintspublications.npl.co.uk/id/eprint/5305

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