Low-cost accurate inductive system for thickness measurement of industrial ferromagnetic plates

This paper deals with profile thickness measurement of ferromagnetic slabs for industrial applications, by means of inductive proximity sensors. A low-cost accurate measurement system was realized, based on an embedded microcontroller and exploiting two inductive probes facing each other. Such system was designed to operate with moving plates, passing through the probe assembly mounted in a fixed position. The developed system was properly calibrated, following a procedure implemented ad hoc, and its performance was assessed using sample ferromagnetic test objects. The achieved accuracy of the thickness estimation is about 20 mu m at 2 readings/s measurement speed. The accuracy of the system does not depend on the type of ferromagnetic material (i.e on the value of the magnetic permeability, provided it is large). Afterwards, an experimental campaign was conducted, characterizing the thickness of solid and laser beam machined ferromagnetic slabs.