Apparatus for ultrasonic flaw detection

Claim 1

APPARATUS FOR THE ULTRASONIC INSPECTION OF AN ARTICLE COMPRISING FIRST AND SECOND TRANDUCER PROBES, MEANS TO PASS ELECTRICAL IMPULSES INTO SAID PROBES TO BE CONVERTED INTO BEAMS TO IN-PHASE PULSES OF ULTRASONIC VIBRATIONS AND DIRECTED TOWARDS SAID ARTICLE THEREFROM, FIRST AND SECOND RECEIVER MEANS CONNECTED RESPECTIVELY TO SAID FIRST AND SECOND PROBES TO CONVERT ECHOES OF SAID PULSES OF ULTRASONIC VIBRATIONS RECEIVED BACK AT SAID FIRST AND SECOND PROBES INTO FIRST AND SECOND SETS OF DISCRETE ELECTRICAL SIGNALS RESPECTIVELY, A DIFFERENCE AMPLIFIER COMPRISING A GATE VALVE HAVING A CONTROL GRID AND A SUPPRESSOR GRID, SAID CONTROL GRID BEING NORMALLY BIASED TO CUT-OFF, MEANS INVERTING THE FIRST SET OF DISCRETE ELECTRICAL SIGNALS TO PRODUCE NEGATIVE BIASING SIGNALS AND APPLYING SAID NEGATIVE SIGNALS TO THE SUPPRESSOR GRID, MEANS APPLYING THE SECOND SET OF DISCRETE ELECTRICAL SIGNALS TO THE CONTROL GRID, WHEREBY A RESULTANT SIGNAL REPRESENTING THE DIFFERENCE BETWEEN SAID FIRST AND SECOND SETS OF DISCRETE ELECTRICAL SIGNALS IS PRODUCED BY SAID DIFFERENCE AMPLIFIER, AND MEANS, RECEIVING SAID RESULTANT SIGNAL, FOR INDICATING WHETHER A FLAW IS PRESENT IN THE ARTICLE.