GB1366050A - Ultrasonic thickness measurement - Google Patents

Abstract

1366050 Ultrasonic thickness measuring BRITISH STEEL CORP 14 Sept 1973 [14 Sept 1972] 42732/72 Heading H4D In measuring thickness by the ultrasonic pulse-echo method, particularly of thin tube walls, extraneous signals between "major" reflections may lead to error. According to the invention the time span T 1 of a predetermined plurality of reflected pulses, and, separately, the time span T 2 of a predetermined lesser number of reflected signals within the predetermined plurality, are measured, T 1 and T 2 are compared, at least one set of reflections are processed before the comparison such that resultant T 1 and T 2 are, for correct comparison, equal, and the comparator controls the thickness signal output. In one embodiment reflected pulses after shaping are passed to a counter 3 the third and fourth pulses of the reflection train being passed to a bi-stable 1 the output of which, 26, Fig. 2, is passed to a stretcher 8, 27, Fig. 2, to actuate gate 1, 29, Fig. 2; clock pulses passed by the latter are counted, and the count held, by pulse counting unit 1. The time interval between the third and sixth reflection pulses, 28 and 30, Fig. 2, yields clock pulses into pulse counting unit 2. The clock pulse counts are compared in unit 10 and, if equal, a "valid measurement" is fed to enable recorder 11. The counters are then reset for like operation in the next transmitter pulse repetition period. In another embodiment pulse stretcher 8 is replaced by a divide-by-three circuit in the clock pulse output to gate 2, Fig. 3 (not shown). Measurement may be in error if the sixth reflection pulse is small; the seventh pulse is therefore extracted and additionally utilized in enabling the recorder.