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Coil motion effects in watt balances: a theoretical check



Stephan Schlamminger, Shisong Li, Darine El Haddad, Frank C. Seifert, Leon S. Chao, Jon R. Pratt


A watt balance is a precision apparatus for the measurement of the Planck constant that has been proposed as a primary method for realizing the unit of mass in a revised International System of Units. In contrast to an ampere balance, which was historically used to realize the unit of current in terms of the kilogram, the watt balance relates electrical and mechanical units through a virtual power measurement and has far greater precision. However, because the virtual power measurement requires the execution of a prescribed motion of a coil in a fixed magnetic field, systematic errors introduced by horizontal and rotational deviations of the coil from its prescribed path will compromise the accuracy. We model these potential errors using an analysis that accounts for the fringing field in the magnet, creating a framework for assessing the impact of this class of errors on the uncertainty of watt balance results.


fundamental electrical measurements, watt balance, Planck constant, SI units, mass metrology, revised SI


Schlamminger, S. , Li, S. , El, D. , Seifert, F. , Chao, L. and Pratt, J. (2016), Coil motion effects in watt balances: a theoretical check, Metrologia, [online], (Accessed May 22, 2024)


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Created February 10, 2016, Updated October 8, 2019