Precision Control of Resistive Power in Kibble Balance Coils: An Advanced Method for Minimizing Temperature-Related Magnetic Errors

Abstract

Temperature changes affect the coercivity of permanent magnets, thereby impacting the $Bl$ factor and potentially introducing systematic errors in Kibble balance measurements. While the thermal-magnetic effect is negligible in large magnet systems, it increases substantially as the magnet size decreases, posing an engineering difficulty for tabletop Kibble balance systems. We discuss the mechanism of thermal-magnetic effects through finite element analysis, which has not been sufficiently emphasized in previous studies. A bifilar-coil power regulator is proposed to eliminate thermal-magnetic errors in Kibble balances. The approach aims to keep the power of the internal heating source -- coil ohmic power -- constant over time, allowing the $Bl$ drift to be mitigated through ABA or ABBA measurement sequences. Experimental results validate the proposal, demonstrating that the thermal effect can be reduced by more than two orders of magnitude compared to the conventional two-mode, two-phase measurement scheme, and by about one order of magnitude compared to the one-mode, two-phase scheme. The proposed approach can eliminate the influence of thermal-magnetic effects on the measurement results, thus further breaking down the limitations on the minimum size of tabletop Kibble balances.