A Fast ECT Measurement Method for the Thickness of Metallic Plates

This contribution focuses on the nondestructive evaluation of the thickness of metallic plates, by means of eddy-current testing. Specifically, we present a method for reducing/optimizing the measurement time for the approach presented in (Yin and Peyton, 2007), while keeping a high accuracy suitable for industrial applications. In (Yin and Peyton, 2007), the key feature for estimating the thickness of plates is the value of the frequency where a proper quantity achieves its minimum value. To get a proper accuracy in measuring the thickness of the plate, this minimum needs to be located in an accurate manner. In turns, this requires 'many' measurements at different frequencies, which make the approach time-consuming and not suitable for almost real-time applications, as those of interest for industry. The proposed patent pending strategy combines a multisine approach to collect the data onto a proper set of frequencies, plus proper techniques for interpolating the data at all the frequencies required to locate accurately the minimum of the response. The combination of the multisine to allocate efficiently the measurement frequencies with the data interpolation results in a reduction of the number of required measurements and, in ultimate analysis, of the overall measurement time. Specifically, the measurement time for a typical situation was reduced of a factor of about 4 (from 13 to 2.66 s) with the same accuracy level of the order of 3%. Finally, we highlight that both design and testing of the new measurement method were carried out by combining numerical simulations and experimental results.