GB933564A - Improvements in and relating to ultrasonic flaw-detectors - Google Patents

Abstract

933,564. Ultrasonic inspection devices. J. OBRAZ. July 12, 1960 [Aug. 19, 1959], No. 24282/60. Class 40 (7). A device for automatically adjusting the sensitivity of ultrasonic flaw detection apparatus comprises a first memory circuit which registers the sum of the amplitudes of all impulses fed to it in a preselected time interval of not less than the flaw echo time plus the final echo time, and a second memory circuit connected to receive information from the first memory circuit and to control the sensitivity of the detection apparatus, the contents of the first memory circuit being cancelled upon the emission of the succeeding ultrasonic pulse to the material under test and the contents of the second memory circuit being cancelled when the sensitivity has been controlled. Thus undesired increase of receiver sensitivity which would otherwise arise if the " bottom echo " alone were used for automatic gain control (A.G.C.) purposes is avoided. Reflected signals from transmitted pulses of constant p.r.p. are fed to video amplifiers 5, 6 after detection; amplifier 5 output is gated in valve 10 by a pulse from monostable multivibrator 9 of such timing and duration as to embrace flaw and bottom echoes. Valve 10 output is accumulated on capacitor 13 which is discharged at each pulse transmission from transducer 3. The simultaneous charging of capacitor 16, which is discharged by a pulse generated at the termination of the sawtooth time base of cathode-ray oscilloscope 7, provides a voltage which is compared with the adjustable voltage across potentiometer 22 tap and cathode follower 25 feeds the ensuing A.G.C. voltage to amplifier 6. Thyratron-controlled relay 28 actuates an alarm when no flaw or bottom echo is present at amplifier 4 output; the relay may also stop the supply of material being tested when automatic and continuous testing is being employed.