Automatic Noise-Blanking, Pulse-Timing Discriminator for Ultrasonic Nondestructive Testing

摘要

A new, easy to operate, pulse-timing discriminator has been developed for production inspection of parts. This instrument combines the noise-blanking advantages of threshold discrimination with the echo-timing precision of zero-crossing discrimination by using a shaped threshold detector output to enable a zero-crossng discriminator only when the RF ultrasonic signal exceeds an adjustable threshold. Flip-flops are then used to separate the echoes. Discriminator timing walk for a 30-dB amplitude change of a 5-MHz transducer waveform is only 200 psec, while timing jitter is only 30 psec. Long-term timing stability is 100 psec. In thickness gaging, a 200-psec timing error corresponds to an error of 0.64 micrometer in aluminum. An automatic polarity selection system corrects for pulse polarity inversions A time-to-pulse-height converter allows operation as a B-scan instrument capable of detecting flaws at depths of 0.25 mm in aluminum. (ERA citation 05:010491)