The interaction between the magnetized coil-suspension system and the compensation coil in the joule balance

Abstract

The joule balance is one of the mass traceability devices in the revised International System of Units, and its smooth operation relies on a compensation coil to reduce the effect of the external magnetic field. In this paper, the interaction between the magnetized coil-suspension system and the compensation coil is theoretically analyzed and experimentally verified. First, an additional induced voltage can be detected in the compensation coil when it moves relative to the magnetized coil-suspension system, which will lead to a measurement deviation of several parts in 10 6 in the moving phase. Second, if the excitation current also flows through the compensation coil in the weighing phase, then an additional magnetization force which can not be canceled out by the mass-on and mass-off measurements will be applied on the coil-suspension system. Theoretical analysis indicates that the deviations introduced in the two phases are nearly equivalent, so that the final mass measurement result will not be affected at least on the magnitude of 10 −9 . However, this conclusion can only be verified at 10 −8 level due to the current measurement limitations of the joule balance.