Extraction of crack indications from detection signals based on signal phase characteristics in eddy current testing

This paper shows phase characteristics of crack indications obtained with a 48-channel ECT system, and proposes a method to reduce noise and extract crack indications from detection signals of this ECT system based on these phase characteristics. Because this ECT system performs two kinds of scanning patterns: U-scan and T-scan, and obtains two sets of signal distributions for one scanning area simultaneously, the proposed method uses a two-stage process that includes so-called a main filter and a sub filter. While the main filter uses the phase information of the same scanning pattern by which the target signals are obtained, the sub filter uses the phase information of the other scanning pattern for the target signals. Using these two filters imposes more strict conditions on extracting crack indications so as to reduce more noise. The results of a round robin test shows that this filtering method is effective to extract crack indications from the background of complicated noises. (author)