Ultrasonic fault testing method - uses discriminator having two threshold levels for statistical interference suppression

摘要

The signal derived from a fault detected by an ultrasonic testing apparatus exhibits an amplitude variation (A) which varies with time (t). The variation depends on the relative velocity of the sound between the test object and the test head and the nature of the fault. In order to permit discrimination between signals from a fault and interference signals, a second threshold is introduced in addition to the discriminator threshold usually specified. The two discriminator threshold levels permit two modes of statistical suppression of interference signals which are, by definition, sporadic and non-recurrent. In the first method the statistical suppression commences immediately the second threshold level (2) is exceeded and either the signals exceeding the first threshold level are read directly as fault signals or they are stored for long enough to permit the statistical suppression to be carried out. In the second method, statistical suppression commences when the first threshold level (1) is exceeded.