Patent ID: 8154277
Filing Date: 2012-04-10
Classification: G01B

Abstract:
1. A method for measuring the thickness of a metal layer provided on a metal object, wherein the metal layer has a resistivity (ρ 1 ) that differs from the resistivity (ρ 2 ) of the metal object, and the method comprises: generating a constant magnetic field in close vicinity of the metal layer, generating a sudden variation of the magnetic field so that a current is induced in the surface of the metal layer, measuring the changes of the magnetic field outside the metal layer due to the induced current during a time period that is longer than the time it takes for the current to propagate through the metal layer, detecting when the measured values of the changes of the magnetic field deviate from expected values of changes of a magnetic field for a homogeneous object with the same resistivity as the layer, and, on the basis thereof, estimating the time it takes for the induced current to propagate through the layer and reach the boundary between the metal layer and the metal object, and determining the thickness (d) of the layer based on a mathematical relation between the thickness of the layer and the time it takes for the induced current to reach the boundary between the metal layer and the metal object.