NDTnet 1998 Aug, Vol.3 No.8

Abstract

The modem Russian MIA flaw detectors use pulse version of the method, which permits to produce very portable (0.7 - 1.5 kg) and simple instruments, convenient especially for in-service testing. The objects to be tested are multilayer structures of reinforced plastics, metals and other materials: honeycomb panels, antenna fairings, propellers, helicopter rotors and so on. In mentioned instruments amplitude-frequency analog signal processing is used.

In this report problem of information processing in MIA pulse flaw detectors by means of mutual correlation function is considered. Such processing promises to increase the sensitivity and to reduce the noises, mainly the frictional ones.

The mutual correlation function is



where f₁ (t) is obtained in sound area of tested object and stored in memory averagesignal (the reference signal), f₂ (t) is the current signal.
The MCF were calculated for pulses



where q(t) consists of a few first periods only. The s(t) pulses are typical for single contact probes, the q(t) pulses - for twin contact probes. The flaws in tested objects decrease carrier frequencies of both pulses and change their amplitudes.

Influences of all the signal parameters on MCF for both signals have been estimated. It was shown that the most important of them is the difference of initial phases between current and reference signals. The calculations confirm that the processing by means of MCF can increase the sensitivity and especially reduce the level of frictional noises. Some requirements to MIA flaw detectors using correlative signal processing are formulated.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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