Self-Calibration Method for Accurate Direct-Current Ratio Calibration

A self-calibration method is proposed for determining the current ratio for DC current ratio devices. To demonstrate the feasibility of the proposal, an experimental test with nominal current ratios of 10:1 100:1 and 1000:1 is performed, and a three-step calibration procedure is used: Firstly, eleven magnetic modulator-based DC current transducers (DCCTs) with a nominal current ratio of 10:1 are used to realize the self-calibration of a 10:1 current ratio through the reference current method; secondly, the eleven DCCTs are series-parallel to achieve the current ratio build-up from 10:1 to 100:1; finally, another DCCT with a 100:1 auxiliary current ratio is used to realize the 1000:1 current ratio calibration, combining the two steps before. The merit of the proposed self-calibration method is that the measurement does not need a high-precision current source or ammeter. Current ratio calibration based on this technology offers a lower-cost, more robust alternative to those using other devices. The experimental results show that the uncertainty of the calibration, mainly dominated by the noise and the stability of the magnetic modulator used, is within a few parts in 10⁻⁷ or better in the 1000 A range.