Patent ID: 6867596

Claim:
A system for detecting faults in a cable disposed in a conducting medium, said system comprising: a. a transmitter that applies a composite signal to the cable, wherein the composite signal comprises a low frequency first component that alternates at a first frequency and that defines a phase, and a low frequency second component that alternates at a second frequency higher than the first frequency and that defines a duty cycle having a predetermined relationship with the phase of the first component, wherein the composite signal returns to the transmitter through the conducting medium from a fault in the cable; b. a probe that, when inserted into the conducting medium proximate the cable, receives the composite signal leaked from the fault; and c. receiver circuitry that receives the composite signal from the probe and that filters the first component, filters the second component, defines an alternating reference signal having a phase based on the duty cycle of the filtered second component, and compares the phase of the reference signal with the phase of the filtered first component.