Apparatus for detecting faults in buried cables including means for applying a composite signal having fundamental and even harmonic frequency components

Claim 1

A SYSTEM FOR LOCATING FAULTS IN A CABLE HAVING A METALLIC SHEATH COVERED BY A LAYER OF INSULATING MATERIAL AND BURIED IN A CONDUCTING MEDIUM, SAID SYSTEM COMPRISING MEANS FOR APPLYING TO THE METALLIC SHEATH A COMPOSITE SIGNAL CONTAINING A FIRST COMPONENT HAVING A FUNDAMENTAL FREQUENCY AND A SECOND COMPONENT HAVING AN EVEN HARMONIC FREQUENCY OF SAID FIRST COMPONENT, AND FAULT DETECTOR MEANS INCLUDING: (A) MEANS TO DETECT SIGNALS ALONG THE CABLE AT PAIRS OF LOCATIONS SPACED LONGITUDINALLY OF THE CABLE, WHICH SIGNALS ARE REPRESENTATIVE OF THE DIFFERENCES IN POTENTIALS AT EACH OF SAID PAIRS OF LOCATIONS DUE TO THE COMPOSITE SIGNAL; (B) TUNED CIRCUIT MEANS CONNECTED TO THE SIGNAL DETECTING MEANS TO SEPARATE EACH DETECTED SIGNAL INTO SAID FIRST AND SECOND COMPONENTS; (C) MEANS TO CONVERT THE FREQUENCY OF THE SEPARATED FIRST COMPONENT TO EQUAL THE FREQUENCY OF THE SECOND COMPONENT; (D) MEANS FOR COMPARING THE PHASE RELATIONSHIP BETWEEN SAID CONVERTED FREQUENCY AND THE FREQUENCY OF THE SEPARATED SECOND COMPONENT; (E) AND MEANS RESPONSIVE TO A CHANGE IN PHASE RELATIONSHIP TO INDICATE THE LOCATION OF THE FAULT.

Claim 2

A SYSTEM FOR LOCATING FAULTS IN A CABLE HAVING A METALLIC SHEATH COVERED BY A LAYER OF INSULATING MATERIAL AND BURIED IN A CONDUCTING MEDIUM, SAID SYSTEM COMPRISING MEANS FOR APPLYING TO THE METALLIC SHEATH A COMPOSITE SIGNAL CONTAINING A FIRST COMPONENT HAVING A FUNDAMENTAL FREQUENCY AND A SECOND COMPONENT HAVING AN EVEN HARMONIC FREQUENCY OF SAID FIRST COMPONENT, AND FAULT DETECTOR MEANS INCLUDING: (A) MEANS TO DETECT SIGNALS ALONG THE CABLE AT PAIRS OF LOCATIONS SPACED LONGITUDINALLY OF THE CABLE, WHICH SIGNALS ARE REPRESENTATIVE OF THE DIFFERENCES IN POTENTIALS AT EACH OF SAID PAIRS OF LOCATIONS DUE TO THE COMPOSITE SIGNAL; (B) TUNED CIRCUIT MEANS CONNECTED TO THE SIGNAL DETECTING MEANS TO SEPARATE EACH DETECTED SIGNAL INTO SAID FIRST AND SECOND COMPONENTS; (C) MEANS TO CONVERT THE FREQUENCY OF THE SEPARATED FIRST COMPONENT TO EQUAL THE FREQUENCY OF THE SECOND COMPONENT; (D) MEANS FOR COMPARING THE PHASE RELATIONSHIP BETWEEN SAID CONVERTED FREQUENCY AND THE FREQUENCY OF THE SEPARATED SECOND COMPONENT; (E) AND MEANS RESPONSIVE TO A CHANGE IN PHASE RELATIONSHIP TO INDICATE THE LOCATION OF THE FAULT.