New digital multimeter for accurate measurement of synchronously sampled AC signals

An approach to the design of a digital multimeter based on the use of dual-slope ADC is described in this paper. Based on this approach, a new technique for algorithm design is developed. The main advantage of this approach is the determination of all electric values in electric utilities by the same algorithm. The algorithm has high accuracy and a regular structure. Measurements of voltage and current are made in successive periods by a stroboscopic technique (synchronous undersampling). The assumed stationarity of the electric utilities is validated by measurements with an experimental setup, consisting of a fast high-precision sigma-delta ADC. The necessary synchronization is reached by software measurements of the frequency of the measured signal. Assuming stationarity of the observed system (electric utilities) in the stated 1-s interval, it is proved that precise digital processing can be achieved without using a sample-and-hold circuit. The suggested measuring system was simulated, realized in a practical setup, and tested. The obtained results completely confirmed the starting postulates. A processing precision of 0.01% was achieved.