We developed eddy current testing (ECT) devices with saw-wave excitation. The saw wave has many harmonics, which can be used to get more information about defects. Multi-frequency digital lock-in amplifier for the harmonics was developed based on labview program. Using the saw-wave ECT, we did the experiments of crack detection for CFRP cable. An excitation coil and differential receiver coil were wrapped around a tube. The CFRP cable was moved through the tube for crack detection. The diameter of the CFRP cable was 1.3 mm and the diameter was 2.5 mm with the plastic coating. Three artificial defects with the interval of 50 mm were made. The depths of the cracks were about 1/4, 2/4, and 3/4 of the diameter of the cable respectively. Using the saw-wave ECT with the fundamental frequency of 200 kHz and the excitation current of 20 mA, the artificial defects in the CFRP cable was successfully detected.
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