Investigations on eddy current sensors regarding inline-capability of zinc coating monitoring using a model-based estimator

This work deals with preliminary investigations for the reliable thickness determination of a conductive, nonmagnetic metal coating on ferromagnetic steels. For this purpose, an eddy current sensor system is used. Different analytical coil models are compared: a normal solenoid, a differential coil and a rectangular coil. Thus, a sensitivity analysis regarding interfering influences, e.g., liftoff fluctuations, is done. Based on this, the advantages and disadvantages of the analyzed coil geometries are discussed. Finally, an model-based estimator is used to determine the coating thickness from simulation data at different operating points.