Non-Contact and In-Process Measurement of Film Coating Thickness by Combining Two Principles of Eddy-Current and Capacitance Sensing

A non-contact and in-process measurement method of film thickness coated with dielectric materials on a base metal is suggested. A dual sensor based on the combination of the principle of eddy-current sensing and the principle of capacitance sensing is developed. The dual sensor is mathematically modelled in consideration of the physical characteristics of both sensing elements against the base metal as well as the coating film. The simulation results from the suggested model provide some information regarding the optimum gap distance for real applications. The developed dual sensor is proven to be accurate to less than ±1 μm through experiments for three base metals with polyvinyl coatings of three different thickness.