Toward a Calculable Standard Shunt for Current Measurements at 10 A and Up To 1 MHz

Electrical current shunts are widely used as a resistance standard in metrology laboratories and precision instruments with the aim of measuring a high level of alternative and direct currents (ac and dc) with high accuracy. These ac current sensors are characterized by a broadband operating frequency bandwidth and are commonly calibrated up to 100 kHz. The use of a current shunt requires the preliminary knowledge of its magnitude deviation from dc and phase angle according to the frequency. The determination of these parameters is challenging at high frequencies and for high levels of current: typically beyond 100 kHz and 1 zA. For a current level of 10 A, existing current shunts exhibit a strong variation in magnitude and phase. The best magnitude performances of 10-A current shunt standards published so far are limited to 2 μΩ/Ω at 100 kHz. In this paper, we detail the theoretical basis of innovate shunts for current measurements from 50 mA to 10 A up to 1 MHz. The electrical modeling is valid from 50 mA to 10 A: only the Rdc value must be changed to get the electromagnetic response of any shunt standards designed for this range of current levels. For a 10-A shunt standard, the relative deviation from dc obtained by calculation is less than 0.2 and 20 μΩ/Ω in magnitude at 100 kHz and 1 MHz, respectively. The design as well as the electromagnetic modeling of the shunt is profoundly described in this paper.