Patent GB-968798-A (GB)
Title: Apparatus for signal reflection ultrasonic flaw testing
IPC: G01N29/22
Filed: 1963-03-06
Abstract: 968,798. Ultrasonic flow detection; transistor pulse circuits. I. L. JOY. March 6, 1963 [March 9, 1962], No. 9005/63. Headings H3T and H4D. In an ultrasonic flaw detection arrangement of the signal reflection type, the transmitting and receiving transducer assembly 25 (see Figs. 1 and 2) is carried by a plate 14 resiliently coupled by means 16 ... 18 to a shaft 12 provided with a dead centre for engagement with the test object (e.g. with the centre of an axle A) and with a crank handle 13 which, in combination with a loosely mounted wooden sleeve 15, enables an operator to effect radial scanning of the end face of the test object. The transducer assembly 25 is mounted in an aperture in plate 14 (Fig. 3, not shown), each transducer (preferably of the piezo-electric type) being recessed in a holder with its operative face covered by a wear resistant layer, which may project slightly beyond the plane of the plate, comprised of a mixture of an epoxy resin and silicon carbide. Additionally, plate 14 is provided with a series of concentric grooves on its contact face for retention of a coupling liquid (Fig. 3, not shown). In operation, the dead-centre (which is spring urged outwards) is pressed against the test object by means of the sleeve 15 and the sliding motion of the latter along shaft 12 operates a switch 26 which completes the power supply circuit for the solid state transmitting and receiving circuitry carried in a casing 24 mounted on shaft 12 for rotation therewith. Fig. 4 shows details of the latter and comprises a rate generator 40 consisting of a blocking oscillator supplying trigger pulses 40P of one to five microsecond duration at a rate of 2000 per second to pulse a signal generator 41 operating in the range 2 to 5 mc/s. and the output of which is supplied to the transmitting transducer crystal 28. The output of generator 40 is also fed to a delay generator comprising a one-shot multivibrator 50 producing an output pulse 50W, the length of which is determined by a potentiometer 56 (controlled by knob 33 calibrated in terms of the depth in the test object to be examined) and which is fed to a differentiator and amplifier 51 producing in response to its trailing edge, a pulse 51P which is fed to a gating interval generator 52 (similar to delay generator 50), the length of the output pulse 47G of which is also determined by a potentiometer 56 (controlled by knob 34). In the generators 50 and 52 (Fig. 4), the signal at the end of the timing potentiometer 56 is amplified by a transistor 57 before application to the transistor 54 which with transistor 55 forms a one-shot multivibrator to ensure sufficient signal strength for driving transistor 54 to saturation when the timing resistance is set at its maximum resistance of one megohm. The output pulse 47G of generator 52 is then utilized to control a gate 47 which receives the echo signals picked up by the receiving transducers 29 (after conversion to an I.F. frequency of 15 mc/s., detection and amplification in elements 42... 46) and passes them to a pulse stretcher 48, the output of which is fed to a solid state switch 49 controlling indicator lamp 30 carried by shaft 12 (Fig. 1). The position of the transducer assembly 25 when the lamp lights up indicates the angular position of the flaw and the time interval during which it remains lighted gives an approximation of the size of the flaw. Instead of employing separate transducers for transmission and receptions a single transducer may be employed and in addition to the indicator lamp 30 a cathode-ray tube indicator (70, Fig. 4) producing an A or B- scan may be employed. In a modification the casing 24 may be remotely positioned and connected to the crank mounted assembly by means of conductors co-operating with commutator contacts carried by the crank (Fig. 5, not shown).