A Method for Comparing the Metrological Properties of Eddy Current Probes

This article describes a method for comparing the metrological properties of air-cored and solid-cored coils designed as eddy current probes. The approach suggested in this article assumes that a pair of equivalent parameters of an ideal filamentary coil can be assigned to any contact coil so that the impedance variations in both coils are identical. These two parameters include the coil radius and its distance from the surface of a test piece. The experiments performed demonstrate that for equivalent parameters defined in such a way, impedance variations in a real and filamentary coil are the same for a broad frequency range of excitation current and conductivity of the material being tested. Therefore, comparisons between parameters of eddy current probes such as sensitivity, depth of penetration, or inspection coverage can be made with the use of a simple model of an ideal filamentary coil defined by only two parameters. The solution proposed in this article substantially simplifies the calibration process of the measuring instrument, the adjustment and optimization of parameters for newly designed probes, and the development of efficient and reliable mechanisms to eliminate undesired effects (e.g., lift-off).