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概要

This paper proposes a methodology of lift-off measurement using optical system embedded in Eddy Current Testing (ECT) system. Firstly, the influence of lift-off on ECT signal was evaluated. Secondly, both ECT signal with lift-off shifting and the lift-off signal were acquired by means of an ECT probe with an optical displacement sensor. Then two cases of the crack shapes reconstructions were carried out using inverse analysis code. One was computed with taking the measured lift-off into account and the other was calculated with lift-off same length as initial condition of experiment. The maximum error between actual crack depth and reconstructed one is decreased from 45% to 12% when the measured lift-off was taken into consideration to the calculation. Finally, the lift-off measurement using an optical system composed of objective lens and photodiode which can be applied to ECT system is performed. The results suggested that the optical system has feasibility of lift-off measurement when optimum lens is selected.

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