Metod för tjockleksmätning av metallskikt med från underlaget föga avvikande egenskaper

摘要

A bridge coupling is used with an AC source and measures the deviations in impedance using a coil (15) directed towards the measurement object on the side of the surface layer (12). A second measurement coil (16) is directed towards a normal metal part (14) and is coupled to the bridge. The magnetic field from the coils is directed at right-angles towards the surface layer - The measurements occur at a frequency such that the penetration depth for the field in the measurement object remains at least 1.0 and at most 4.0 times the layer thickness. The components in the deviations are measured which lie 90 degrees phase-displaced in relation to the line which represents the deviations. The deviations can be measured when the distance is varied between the second coil (16) and the normal part or between the first coil (15) and the measurement objects surface layer. - (Dwg.1/2)