Digital phase shift circuit signal generator for rip detectors

Abstract

A circuit for generating plural AC signals, at least two of which may be relatively shifted in phase by a selected amount, includes a frequency divider for dividing the frequency of an AC input signal to derive a first AC signal at a relatively reduced second frequency, and a digital phase shifter responsive to the progress of the frequency divider for producing a second AC signal shifted in phase a selected amount from such first AC signal. The circuit is especially suited for use in a conveyor belt rip detector in which input and output coupling means couple an AC transmitter signal to antennas carried by the conveyor belt and receive an AC transmitter signal transmitted by respective antennas, and a detector monitors such AC signals received by said output coupling means and an AC reference signal to detect the integrity of the conveyor belt, for the circuit of the invention may be used to generate such AC signal and such reference signal relatively shifted in phase by a selected amount. Synchronous demodulation using a lock in amplifier technique may be employed effectively to improve substantially the signal to noise ratio and/or signal discernment in the rip detector. The invention lends itself to computer control and self diagnosis of faults of the rip detector by use of the AC transmitter and reference signals and an AC test signal, also produced by the noted circuit.