GB815071A - Improvements in or relating to ultrasonic flaw detecting apparatus - Google Patents

Abstract

815,071. Ultrasonic flaw detection. GLASS DEVELOPMENTS Ltd., and SPROULE, D. O. Feb. 8, 1957 [Feb. 10, 1956], No. 4276/56. Class 118 (2). In an ultrasonic flaw detector the specimen (see Fig. 1) is supported in a tank filled with suitable liquid (e.g. water) sufficient to cover it and a movable trolley 12 (see also Figs. 2 to 5 (not shown)) carries the transmitter-receiver probe head 22 which is movable across it; the angle of the probe relative to the surface of the specimen is maintained constant (see Figs. 7 and 8 (not shown)). The probe 22 (sec Fig. 9) reciprocates successively in adjacent narrow strips along the specimen and the received pulse echoes are fed via gate circuits to amplitude discriminators whose outputs are recorded by styli PS1 ... PS4 on a reciprocating web of electro-sensitive paper; cathode-ray displays of the received echoes are also given. 2 Mc/s. trigger pulses at a repetition frequency of 50 c/s. are fed to a transducer T (see Fig. 9) and to a transmitting coil TC associated with a delay line DL on which are provided receiver coils RC1 ... RC4, so dimensioned that each one products a square output pulse of a duration equivalent to the range of possible echo times from a region of predetermined thickness, and so located that successive thickness regions of the specimen are examined. The output of coil RC1 (for example) opens gate G1 (see also Fig. 10 (not shown), for the period corresponding to the first quarter of an inch thickness of the specimen and permits linearly amplified receiver signals to pass to amplitude discriminator AD1 (see also Fig. 10 (not shown)) which has four discrimination levels each having an associated memory circuit such as a capacitor charged through a rectifier so that in accordance with the amplitude of the received echo some or all of the fixed brushes B1 are given a sustained potential. The distributer switch DS carries metallic contacts CT2 connected to the recording styli; contact sets CT1 or CT3 are earthed via arm A, depending on the direction of traverse. The reciprocation of the distributer switch and of the recording paper follows that of the probe by the use of servomotors SA; the perpendicular stepping of the styli follows that of the probe by means of servomotors SB. The form of record obtained is illustrated by Fig. 11 (not shown). Cathode-ray tube AS provides a range-amplitude form of display and tube BS, a rectangular plan-position display with the horizontal dimension representing the length of the specimen and the occurrence of bright spots in the vertical direction indicating the positions of discovered flaws. The number of gate circuits G, and the number of amplitude discriminator levels, may be changed. The probe head may comprise a combined transmitter/receiver transducer; and several probes and their associated apparatus may be used to provide the simultaneous inspection of several regions.