Ac mains test system for measuring current harmonics and voltage

Abstract

A digital system measures cyclic disturbance signals on an electrical line that are induced by a connected unit under test (UUT). The system includes a digital to analog (D/A) converter which receives and converts a first train of digital signals to a cyclic analog test signal and applies that signal to the electrical line. An analog to digital (A/D) converter receives and converts analog cyclic disturbance signals from the electrical line to a second train of digital signals. A synch generator applies a train of synch pulses, concurrently, to synchronizing inputs of the D/A converter and the A/D converter so that their respective conversion operations are based upon a common time-base signal. A processor is coupled to the D/A converter and A/D converter and outputs the first train of digital signals to the D/A converter and receives the second train of digital signals from the A/D converter. The processor subjects a portion of the second train of digital signals to signal analysis, with the portion of the second train being representative of an integer number of cycles of the cyclic disturbance signal sensed from the electrical line. The clock frequency which causes generation of the synch pulses is selected so that the synch pulses have a precise, predetermined relationship to a predetermined number of cycles of the cyclic signal (in the case of a power spectrum analysis) or a predetermined number of half cycles (in the case of an amplitude analysis).