The development of the current comparator, a high-accuracy A-C ratio measuring device

The current comparator is a stable, sensitive, and reliable magnetic device, which may be used for a-c ratio measurements of high accuracy. The sources of error in such a device are discussed, and methods are proposed for minimizing their effect. The design of a 2,000-amp (ampere) feed-through current comparator based on these investigations is described, and test results are given which indicate that its over-all accuracy at 60 cps (cycles per second) is better than 0.2 ppm (part per million) for all ratios from 1:1 to 400:1, irrespective of distribution of the primary winding.