A current-comparator-based system for calibration of optical instrument transformers with analog and digital outputs

An overview of the development of a system comprising of instruments, based on the current-comparator technology, for calibration of optical instrument transformers with analog and digital outputs is presented. The instruments include a transimpedance amplifier for operation of input currents from 1 A to 10,000 A, a high voltage active divider for operation of input voltages from 1 kV to 500 kV, a current-comparator bridge, and two sampling voltmeters. The current comparator is used in a feedback loop to correct the magnitude and phase of the outputs of the transimpedance amplifier and the high voltage active divider to an accuracy of better than 10 parts per million and 10 murad, respectively. The sampling voltmeters are effectively used as 18-bit A/D converters.