| 摘要 |
Method and device for measuring, in a non-destructive way and without contact, as well as by a direct and continuous route, the thickness of a coating on an elongated ferromagnetic substrate which is moving past by determination of the Joule-effect losses of the Foucault currents induced in the coated product by an alternating magnetic field. An excitation frequency of the alternating magnetic field is chosen such that the natural penetration of the Foucault currents in the coating material is sufficiently close to the intended thickness of the coating to be applied and the measurement frequency is varied as a function of the conductivity of the coating metal with respect to that of the substrate. The measurement device consists of an oscillator composed of an LC circuit and of an amplifier with variable gain connected in closed loop. <IMAGE> |
