Patent ID: 6448764
Filing Date: 2002-09-10
Classification: G01B

Abstract:
A process for contactless determination of planarity of a ferromagnetic metal strip in transit along a strip-processing or cold-rolling line, said process comprising the steps of:(a) exciting in said metal strip a magnetic field having a hysteresis loop with a exciter driven by alternating current and juxtaposed with said strip and periodically repeating at a frequency of said alternating current; (b) detecting a tangential magnetic field strength resulting from said magnetic field at a surface of said metal strip with a magnetic field strength sensor while said hysteresis loop is driven by said exciter; (c) producing a signal whose time course represents a time course of said tangential magnetic field strength while said hysteresis loop is driven by said exciter; (d) detecting changes in a beat permeability (&mgr;&Dgr;=&Dgr;B/&Dgr;H) as function of the tangential magnetic field strength and determining as measurement parameters at least two parameters selected from a maximum (&mgr;&Dgr;max) of the changes in beat permeability, an associated value (Hc&mgr;) of the tangential magnetic field strength and a width of a curve representing change (&Dgr;H&mgr;) in said beat permeability of the magnetic field strength as a function of time; (e) from variations in said measurement parameters as functions of mechanical stresses in said strip, determining at least one stress distribution from among a longitudinal stress distribution and a transverse stress distribution of the longitudinal stress integrated over a strip thickness; and (f) from the determined stress distribution, determining a corresponding longitudinal residual intrinsic stress distribution and a resulting degree of nonplanarity of the metal strip.