A microprocessor-controlled current-comparator-based DC voltage calibrator

A microprocessor-controlled current-comparator-based dc voltage calibrator is described. A self-balancing dc comparator is used to establish voltages proportional to a reference signal. The calibrator features an automatic self-calibration mode, two ranges of −10 to +10 V and −120 to +120 V with an output uncertainty of less than 2 and 3 parts per million (ppm) of full scale, respectively, a resolution of 1 ppm, and a linearity error of less than 1 ppm of full scale.