APPARATUS FOR PRODUCING A SIGNAL WHEN A SELECTED PHASE RELATIONSHIP EXISTS BETWEEN TWO ALTERNATING CURRENT VOLTAGES OF DIFFERENT FREQUENCIES

摘要

A signal is produced when a selected phase relationship exists between two alternating current voltages of different frequencies by converting the alternating current waveforms to square waves, combining the square waves to produce a rectangular waveform, and utilizing the rectangular waveform to produce a triangular beat frequency signal having a linear relationship between phase difference and time, and a level detector has the triangular beat frequency signal applied thereto and produces an output signal when the triangular beat frequency signal exceeds in amplitude a selected level in the level detector.