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



Frank Seifert, Alireza Panna, Leon Chao, Bing Han, Shisong Li, Yusi A. Cao, Darine El Haddad, Stephan Schlamminger, Heeju Choi, Lori Haley


The magnet system is one of the key elements of a watt balance. For the new watt balance currently under construction at the National Institute of Standards and Technology a permanent magnet system was chosen. We describe the detailed construction of the magnet system, first measurements of the field profile, and shimming techniques that were used to achieve a flat field profile. We further characterize the most important aspects of the magnet and give order of magnitude estimates for several systematic effects that originate from the magnet system.
IEEE Transactions on Instrumentation and Measurement


mass, permanent magnet, Planck constant, watt balance, SI units


Seifert, F. , Panna, A. , Chao, L. , Han, B. , Li, S. , Cao, Y. , El Haddad, D. , Schlamminger, S. , Choi, H. and Haley, L. (2014), Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System, IEEE Transactions on Instrumentation and Measurement, [online],, (Accessed June 13, 2024)


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Created June 5, 2014, Updated October 12, 2021