Non-contact sensor for determining moving flat steel strip shape profile

摘要

Method and apparatus for monitoring the flatness characteristic of a moving electrically conducting strip of material by continuously measuring the change in capacitance between the strip surface and a fixed point adjacent the surface. The capacitance is measured by means of a sensor having an active plate surrounded by a guard plate for eliminating stray capacitance, both plates being impressed with a high frequency signal. Changes in capacitance associated with both plates are eliminated while changes in capacitance associated with only the active plate are covered to a voltage proportional to the inverse of the spacing between the active plate and the strip surface. A plurality of the sensors may be spaced across the width of the plate for providing a profile of the strip flatness characteristics. The sensor finds particular application for monitoring and characterizing bottom buckles in steel strip following high temperature annealing.