GB699796A - Improvements in or relating to the detection of cracks in engineering components - Google Patents

Abstract

699,796. Ultrasonic inspection devices. PARSONS & MARINE ENGINEERING TURBINE RESEARCH & DEVELOPMENT ASSOCIATION. March 21, 1951 [March 24, 1950], No. 7468/50. Class 118 (ii). In a pulse-echo flaw detector operating at an audio pulse recurrence frequency and comprising separate transmitting and receiving electromechanical transducers 3 and 4, the output from the receiving transducer 4 is applied to an aural indicator, e.g. telephone earpiece 10, through a gate circuit 6 which is opened when the transmitted pulse ends and is closed before reception of echoes from the boundaries of the work piece 1 by a positive gating pulse of adjustable duration from a phantaltron circuit 7, V2, Fig. 3 (not shown), which is triggered by the trailing edge of the directly received pulse. The pulse recurrence frequency is chosen to allow the effect of each pulse to die away between successive pulses. According to the Provisional Specification, the transmitter may comprise a mechanically actuated hammer. Specification 641,081 is referred to and a known system is also described in which the receiver is rendered inoperative for a short period after generation of the transmitted pulse in order to render the detector insensitive to reflections from the near boundary of the medium.