1. Field of the Invention
The invention is concerned with signal monitoring arrangements and, more particularly, with a signal loss detector for three-phase circuits.
2. Description of the Prior Art
Prior signal monitoring arrangements to detect a signal or phase loss in a three-phase circuit have rectified the individual phase signals and utilized magnitude comparisons to indicate the occurrence of a signal or phase loss. A particular arrangement utilizing this technique is disclosed in U.S. Pat. No. 2,800,621 issued to Harold G. Carlson et al on July 23, 1957. The Carlson patent disclosed a three-phase voltage monitoring circuit to sense unbalanced conditions in a three-phase circuit. The monitoring circuit includes three single-phase auto transformers coupled respectively to each phase. Each transformer winding includes a high voltage tap and a relatively low voltage tap. The outputs of the high voltage tap are rectified and a DC average voltage is derived therefrom. A peak voltage level is derived from the output of the relatively low voltage taps. During normal balanced condition, the magnitude of the average voltage is greater than the peak voltage. In the event of an imbalance condition, the magnitude of the peak voltage exceeds the average voltage thereby providing an indication of the imbalance condition.