Power-factor calibrator

A power-factor calibrator, using a precise wattmeter as a calibration tool to obtain short- and long-term stability and accuracy, is described. The wattmeter's zero reading indicates that the actual phase angle at the output of the calibrator is 90/spl deg/ or -90/spl deg/. The phase difference between 90/spl deg/ (-90/spl deg/) and the calibrator setting is considered as the correction for the subsequent calibrator settings over the whole phase angle measuring range. An autocalibration procedure is developed for the determination of the phase-angle correction. By frequently applying an autocalibration procedure, most of the parasitic factors are eliminated and accuracy depends mainly on the wattmeter's error at zero power factor. The calibrator covers the frequency range from 30 Hz to 1 kHz, its output voltage and current are up to 120 V and 5 A, and an uncertainty of /spl plusmn/0.0025/spl deg/ is achieved.