The Current Comparator and Its Application to the Absolute Calibration of Current Transformers

The current comparator is a passive magnetic current-ratio device of exceptionally high inherent stability and proportionately high sensitivity. Methods are presented for calibration of such devices to an accuracy of 0.1 ppm (part per million). The design and construction of a multiratio comparator, which covers various ratios from 1 to 1 to 12 to 1, and which has errors of less than 1 ppm, is given. The use of the comparator, whose error is independent of current magnitude, for the absolute calibration of current transformers is described, and its extension to frequencies higher than the usual power frequencies discussed.