Patent ID: 6788050
Filing Date: 2004-09-07
Classification: G01B

Abstract:
A method for determining a component of an eddy current sensor (ECS) signal attributable to a substrate comprising:placing a substrate in a first position relative to an ECS at a first distance from the ECS, the substrate including a conductive film on a first surface of the substrate; detecting a first ECS signal with the substrate in the first position; inverting the substrate relative to the ECS such that the substrate is in a second position relative to the ECS at a second distance from the ECS, the second distance equal to the first distance less about a thickness of the substrate; detecting a second ECS signal with the substrate in the second position; determining a difference signal equal to a difference between a first signal level on a calibration graph for the ECS and the second signal level, the second signal level being shifted a distance about equal to the thickness of the substrate; and calculating a first substrate component of the first ECS signal equal to a product of the first distance and the difference signal, divided by the thickness of the substrate.