New improvements in accurate measurement of synchronously sampled AC signals

A digital algorithm design approach, based on the use of a dual-slope ADC, is described in this paper. The main advantage of this approach is the determination of all electric values in an electric utility signal by the same algorithm. The algorithm has a high accuracy and regular structure. Measurements of voltage and current are made in successive periods by a stroboscopic technique (synchronous undersampling). The assumed stationarity of the electric utility signal is validated by measurements with an experimental set-up, consisting of a fast high precision sigma-delta ADC. The necessary synchronization is achieved by software measurements of the frequency of the measured signal. Assuming stationarity of the observed system (electric utility), in the stated one-second interval, it is proved that precise digital processing can be achieved without using a sample-and-hold circuit. The suggested measuring system was simulated, practically realized, and tested. Obtained results confirmed completely the starting postulates. Processing precision of 0.01% was achieved.