Measurement of coating thickness using lift-off point of intersection features from pulsed eddy current signals

Abstract

In industries, the thickness measurement of non-ferromagnetic coatings on a ferromagnetic substrate is a difficult problem. In this paper, we proposed a simple but liftoff insensitive method for measuring the thickness of non-ferrous coatings using lift-off point of intersection (LOI) extracted from pulsed eddy current (PEC) signals. Firstly, an analytical model was formulated to calculate PEC signals using Fourier transform. Then, the simulations were carried out to investigate the characteristics of LOI points and the applicability of the presented method for measurement of coating thickness. Subsequently, the critical factors on coating thickness measurement were discussed. The results show that the developed new method is feasible for measurement of nonferrous coating thickness. The rising time of pulse excitations could balance the sensitivity and accuracy. The results demonstrate that the relative error for measurement of coating thickness is 4.9% when the rising time increases to 90 μs