A system for flaw detection during a continuous welding process uses a transducer to provide a signal burst for each acoustic burst from an article being welded. The signal burst is amplified and filtered to pass frequencies between about 100 and about 550 KHz. The ring-down counter counts signals of the filtered signal burst. The first signal of the filtered signal burst initiates a timing circuit that times out to provide a reset pulse to reset the ring-down counter. If the decimal count exceeds 100 but does not exceed 1000, the ring-down counter operates circuitry to provide a latched signal to an output of a flip-flop to enable a gate before the counter is reset by the reset pulse of the timing circuit. That reset pulse is also provided to the gate to provide at its output a pulse representing one filtered signal burst having more than 100 and no more than 1000 signals during the timing operation. The pulses from the gate are inputs to a pulse counter in the counter mode and a retriggerable monostable multivibrator that, if not retriggered by the next pulse before a predetermined time, resets another flip-flop and resets the pulse counter. If the pulse counter counts a predetermined number of pulses before it is reset, it sets that another flip-flop to provide a signal to an alarm device that turns on a light indicating that there is a weld flaw.
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