Field representation of a watt balance magnet by partial profile measurements

摘要

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 or a magnetic probe 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 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.