Measuring of slowly changing AC signals without sample-and-hold circuit

Abstract

The measurement method described in this paper can be applied fur the accurate determination of slowly changing AC signals during the period of one second. Measurements of voltage and current are made in successive periods by a stroboscopic technique (synchronous undersampling). Assuming steady state of the observed system (electric utilities) in the stated one-second interval, it is proved that precise digital processing can be achieved without using a sample-and-hold circuit. The necessary synchronization is achieved by software measurements of the frequency of the measured signal. The suggested measuring system was practically built and tested, and the obtained results completely confirmed the starting postulates. A processing precision of 0.01% was achieved.