Means and techniques for eliminating effects of varying water path lengths in metal inspection

Claim 1

IN A METAL INSPECTION SYSTEM OF THE CHARACTER DESCRIBED WHEREIN ENERGY PULSES ARE TRANSFERRED TO AND FROM A TEST PIECE THROUGH A WATER PATH, A TIMING MULTIVIBRATOR, PULSE GENERATING MEANS OPERATED BY SAID TIMING MULTIVIBRATOR, A TRANSDUCER COUPLED TO SAID GENERATING MEANS, A WATER PATH COUPLING SAID TRANSDUCER TO SAID TEST PIECE TO SUPPLY ENERGY FROM SAID GENERATING MEANS TO SAID TEST PIECE, RECEIVING MEANS COUPLED TO SAID TRANSDUCER FOR RECEIVING AND AMPLIFYING ENERGY PULSES CORRESPONDING TO REFLECTIONS FROM THE FRONT AND BACK FACES OF SAID TEST PIECE, A DELAY MONOSTABLE MULTIVIBRATOR COUPLED TO SAID TIMING MULTIVIBRATOR AND OPERATED THEREBY IN TIMED RELATIONSHIP THEREWITH, A FIRST BISTABLE MULTIVIBRATOR COUPLED TO SAID MONOSTABLE MULTIVIBRATOR, A COINCIDENCE CIRCUIT HAVING AN INPUT CIRCUIT, MEANS COUPLING THE OUTPUT OF SAID FIRST BISTABLE MULTIVIBRATOR TO SAID INPUT CIRCUIT, MEANS COUPLING SAID ENERGY PULSES TO SAID INPUT CIRCUIT, SAID COINCIDENCE CIRCUIT FUNCTIONING TO PRODUCE AN OUTPUT SIGNAL UPON A TIME COINCIDENT CONDITION OF SAID OUTPUT OF SAID BISTABLE MULTIVIBRATOR AND AN ENERGY PULSE CORRESPONDING TO REFLECTION FROM SAID FRONT FACE, A SECOND BISTABLE MULTIVIBRATOR COUPLED TO THE SAID COINCIDENCE CIRCUIT AN OPERATED BY SAID OUTPUT SIGNAL, A CATHODE RAY TUBE CIRCUIT INCLUDING A PAIR OF QUADRATURELY ACTING BEAM DEFLECTING MEANS, MEANS COUPLING ONE OF SAID BEAM DEFLECTING MEANS TO SAID RECEIVING MEANS, SWEEP GENERATING MEANS COUPLED TO THE OTHER ONE OF SAID BEAM DEFLECTING MEANS, AND MEANS APPLYING SAID OUTPUT SIGNAL TO SAID SWEEP GENERATING MEANS TO INITIATE OPERATION OF THE SAME.