A preliminary magnet nonlinear research on the joule balance

The joule balance experiment has been carried out at the National Institute of Metrology, China (NIM) since 2007. To reduce the measurement uncertainty further, the major parts of the second generation of the joule balance apparatus system is built already. A new magnet system using electromagnet is being adopted to reduce self-heating in the coils. However the results on the measurement show that the nonlinearity and hysteresis of the ferromagnetic material will bring a considerable measurement uncertainty. In this paper, the nonlinear effect is reduced by one order of magnitude by an experimental method. The nonlinearity and hysteresis effect is about 10-6 in the relative standard uncertainty.