An electronic supply for use in the calibration of instruments

A brief review is given of some of the features of supplies that are suitable for use in the calibration of a.c. instruments, and an account is then given of a high-power oscillator-amplifier set that has been built for this purpose. The set consists of an oscillator, two amplifiers and a phase-shift unit. An output of at least 700VA is available at unity power factor within the range 30c/s-5kc/s from each amplifier, and if necessary the two outputs can be connected in series. The output voltage is free from random variations greater than 0.01%, drifts at maximum power output by not more than 0.003% per minute, and has a supply-frequency component not greater than 0.01%. The output voltage is therefore always constant to 0.01% for the time taken to calibrate a point on an instrument scale. The distortion in the outputs of the oscillator-amplifier set is never greater than 0.45% of the fundamental at any frequency or power output within its rating.