GB1311291A - Material tester - Google Patents

Abstract

1311291 Ultrasonic inspection devices AUTOMATION INDUSTRIES Inc 3 April 1970 [4 April 1969] 15934/70 Heading H4D In a pulse-echo ultrasonic tester for testing a workpiece, an attenuator connected between the probe and the echo receiver is controlled so that, following a transmitted ultrasonic pulse, the first echo pulse in the resulting echo pulse train is passed to the receiver in attentuated form and the attenuation is terminated, a predetermined time after said first echo pulse. In the Fig. 1 embodiment, transducer probe 13 is energized with pulses from transmitter 10 at a rate determined by a generator 12 which also synchronizes the time base sweep of cathode ray tube 26. Echoes from workpiece 16 in a water couplant 17 are applied to tube 26 via electronic attenuator 50, receiver 52, controlled reject and detector circuits 54 and vertical deflection amplifier 20. To prevent overloading of receiver 52 by the interface echo from workpiece 16 (which would mask any subsequent echoes from flaws near the interface), attenuator 50 is switched on by a control pulse to attenuate all of the interface echo except for its leading edge. This control pulse is derived by applying a rate generator 12 pulse to a delay monostable 60 which " sets " bi-stable 62 just before the interface echo arrival and so provides a first input to AND gate 64; the second input to gate 64 is the start of the interface echo from receiver 52. A pulse commencing at the start of the interface echo is thus provided by monostable 66 (which is triggered by the AND gate output), and is inverted at 70, shaped at 72, and amplified at 80 to give the control pulse. The time constant of network 72 prevents abrupt removal of the attenuation and thus avoids spurious signal generation. Control 76 sets the degree of attentuation. Further controlled attenuation of the interface echo is provided by circuits 54, the degree of attentuation being set by control 69 and the time for which the attentuation is effective being determined by variable delay monostable 68.