Designing Model and Optimization of the Permanent Magnet for Joule Balance NIM-2

The permanent magnet with yokes is widely used in watt and joule balances to measure the Planck constant for the forthcoming redefinition of the unit of mass, the kilogram. Recently, the permanent magnet has been in consideration for a further practice of National Institute of Metrology (NIM)-2, the generalized joule balance. In this paper, an analytical model to design the permanent magnet system is proposed. This model can be solved to obtain the preliminary parameters and then used as guidance for the finite element analysis software to optimize the parameters of such a magnet system. As an instance of the application of this designing model, the permanent magnet system for NIM-2 is described. The special shape of the contact areas minimizes the effect of misalignment of the top and middle yokes on the vertical component of the magnetic field.