Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-operated eddy current testers are able to recognize defects in conductive materials. The objective of our work is to overcome this problem by implementing a microcomputer based system to detect and estimate the size of cracks and other defects in conductive non magnetic material, with minimum operator intervention. In order to reach the best solution different hardware implementations have to be investigated. This paper compares the results obtained with three techniques already essayed: using a commercial lock-in amplifier, a dedicated electronic signal conditioning circuit and a data acquisition board (DAQ).
The implementation using the DAQ requires more digital signal processing after the analog conversion than the other methods. In particular, cross correlation and sine-fitting of the sampled signals are used to estimate the phase difference between the excitation current and the sensing coils output signals. The results obtained are presented and compared within the paper.