Eddy current apparatus for testing the hardness of a ferromagnetic material

Claim 1

IN A MAGNETIC HARDNESS TESTING APPARATUS FOR TESTING THE HARDNESS OF A TEST PIECE, THE COMBINATION COMPRISING: (A) AN ALTERNATING COIL COUPLED TO SAID SOURCE; (B) A FLUX PRODUCING COIL COUPLED TO SAID SOURCE; (C) A DETECTION COIL COUPLED MAGNETICALLY TO SAID TEST PIECE, AND TEST PIECE BEING COUPLED MAGNETICALLY TO SAID FLUX PRODUCING COIL; (D) MEANS CONNECTED TO SAID FLUX PRODUCING COIL FOR GENERATING A FIRST SIGNAL INDICATIVE OF THE ZERO REFERENCE CROSSOVER OF THE CURRENT THROUGH SAID FLUX PRODUCING COIL; (E) MEANS CONNECTED TO SAID FLUX PRODUCING COIL FOR PRODUCING A SECOND SIGNAL INDICATIVE THE ZERO REFERENCE CROSSOVER OF THE CURRENT THROUGH SAID FLUX PRODUCING COIL AND PHASE SHIFT MEANS COUPLED TO SAID LAST MENTIONED MEANS TO PROVIDE A PREDETERMINED PHASE SHIFT OF SAID SECOND SIGNALS; (F) MEANS CONNECTED TO SAID DETECTION COIL FOR PRODUCING A THIRD SIGNAL INDICATIVE OF THE ZERO REFERENCE CROSSOVER OF THE VOLTAGE PRODUCED BY THE FLUX INDUCED IN SAID DETECTION COIL; AND, (G) MEANS CONNECTED TO SAID FIRST SIGNAL GENERATING MEANS AND SAID THIRD SIGNAL PRODUCING MEANS FOR COMPARING SAID FIRST AND SAID THIRD SIGNALS TO PRODUCE A COMPARSION SIGNAL AND MEANS CONNECTED TO SAID COMPARING MEANS AND SAID SECOND SIGNAL PRODUCING MEANS FOR COMPARING SAID COMPARISON SIGNAL WITH SAID SECOND SIGNAL INCLUDING A METER FOR GIVING A VISUAL INDICATION OF THE RESULT OF THE COMBINATION OF SAID SIGNALS.