Ultra-sonic flaw detection

Claim 1

ULTRASONIC FLAW DETECTION APPARATUS FOR DETECTING FLAWS IN A TEST PIECE BY COMPARISON WITH A DUMMY WORK PIECE, COMPRISING IN COMBINATION CONTAINER MEANS FOR LIQUID, FIRST AND SECOND ELECTRIMECHANICAL VIBRATION TRANSDUCER MEANS ARRANGED IN SAID CONTAINER MEANS TO TRANSMIT PULSES OF ULTRASONIC WAVE ENERGY THROUGH LIQUID TO BE CONTAINED IN SAID CONTAINER MEANS AND TO RECEIVE ECHO SIGNALS, SAID CONTAINER MEANS ALSO BEING ADAPTED TO CONTAIN A TEST WORK PIECE AND A DUMMY WORK PIECE IMMERSED IN THE LIQUID AT EQUAL DEPTHS BELOW SAID FIRST AND SECOND TRANSDUCER MEANS RESPECTIVELY, PULSE GENERATING MEANS FOR ENERGIZING SAID FIRST AND SECOND TRANSDUCER MEANS, RESULTANT SIGNAL PRODUCING MEANS COUPLED TO SAID FIRST AND SECOND TRANSDUCER MEANS TO PROVIDE A COMBINED OUTPUT SIGNAL BY COMBINING THE OUTPUTS OF SAID FIRST AND SECOND TRANSDUCER MEANS IN OPPOSITION TO EFFECT CANCELLATION OF UNWANTED ECHO SIGNALS FROM THE FRONT SURFACES OF THE WORK PIECE, SAID RESULTANT SIGNAL PRODUCING MEANS COMPRISING GAIN CONTROLLED AMPLIFYING MEANS COUPLED TO ONE OF SAID FIRST AND SECOND TRANSDUCER MEANS, A SECOND PULSE GENERATOR MEANS, AND GATING MEANS RESPONSIVE TO THE COMBINED OUTPUT SIGNAL WHEN MADE OPERABLE IN RESPONSE TO A SIGNAL FROM SAID SECOND PULSE GENERATING MEANS, SAID SECOND PULSE GENERATING MEANS ACTUATED BY THE FIRST PULSE GENERATING MEANS AND CONNECTED TO THE GATING MEANS TO ACTUATE THE GATING MEANS AT A TIME TO SELECT THE PORTION OF THE COMBINED OUTPUT SIGNAL CORRESPONDING TO ECHOES FROM THE FRONT SURFACES OF THE WORK PIECE AND GAIN CONTROL MEANS COMPRISING SAID GATING MEANS COUPLED TO SAID GAIN CONTROLLED AMPLIFYING MEANS TO VARY THE GAIN OF SAID AMPLIFYING MEANS IN ACCORDANCE WITH THE MAGNITUDE OF THE SELECTED ECHO SIGNAL.