GB1391175A - Electrical circuit means for use in acoustic emission detecting and or recording apparatus - Google Patents

Abstract

1391175 Electric selective signalling CAMBRIDGE CONSULTANTS Ltd 2 Aug 1972 [4 Aug 1971] 18943/71 Heading G4H [Also in Division H4] Apparatus for detecting faults in stressed structures comprises transducers 2 arranged to detect acoustic emissions produced during testing, each transducer being connected to a respective counter 10 (or other detecting and/or recording medium), by a logic circuit 8 which ensures that only the signal from the first of the transducers to detect a stress wave is allowed to pass to the counter. Transducers 2 are accelerometers whose output waveforms take the form of sets of decaying sinusoids (Fig. 2, not shown); these pass to a device 6 which produces a square-wave pulse each time the input exceeds a threshold value. In the embodiment of Fig. 6, each device 6 and counter 10 is separated by an AND-gate 16 whose other input is a "1" from an inverter 22. The first pulse to arrive at any of the gates 16 passes through it to trigger a retriggerable monostable 26 and (via a gate 20), a monostable 18: the output from 18 acts through inverter 22 and OR-gates 24 to inhibit all the gates 16 except the first, which is kept open via its gate 24 and monostable 26 so that the remainder of the signal can be counted. The output from 26 is of shorter duration than that from 18 but it is longer than the interval between the pulses of the signal, so that these can continually re-trigger the monostable. Other embodiments are described (Figs. 3-5, not shown), wherein different arrangements of gates and monostables allow only the first pulse to pass to a counter, all the gates 16 being subsequently blocked.