Abstract: An electricity metering transducer is disclosed which samples voltages and currents at an innerconnection terminal of an electrical energy distribution system, converts those samples to digital form and computes selected electricity metering quantities. In a multiphase system current and voltage signals are multiplexed to a pair of codecs, one for current signals and one for voltage signals. The period of the signals being sampled is detected and used to generate a substantially nonsynchronous sampling signal so that a sample migration system is created which provides a large number of samples of a composite wave form. The steps of a digitally generated stepwise approximation of a sawtooth waveform are summed with the sequential analog samples and then removed from the digital value of each sample by software operation in order to increase the resolution of the digital to analog conversion.

Abstract: Voltage and current signals in a power distribution system are converted to digital data by scaling and sampling the signals and simultaneously comparing all the samples to a digitally generated ramp converted to analog form. When a sample intersects the ramp, the digital number representing the ramp amplitude is loaded into storage without interrupting the ramp generation sequence. A zero cross detector detects a zero crossing for a voltage or current. Sampling is initiated by a programmable, interval timer which is loaded with a selected time interval from a microcomputer and initiates the sampling a selected time interval after the zero cross is detected. The samples are taken during representative, repetitive cycles at angularly spaced positions in a composite cycle to form a group of samples for the composite cycle for each of the signals of the power distribution system.