device for measuring the thickness of a non-magnetic layer on a magnetic or magnetisierbaren document

摘要

The arrangement for measuring the thickness of a non-magnetic layer on a magnetic or magnetisable substrate contains a probe in contact with the layer and a reference body of similar characteristics to the substrate. The distance is displayed between the reference probe and a compensation probe whose separation is variable. Calibration of the device is less susceptible to stray fields and temp. variations than with conventional arrangements and to magnet ageing, shock and vibration. It is more suitable for series production applications. The measurement pole of a permanent magnet rests on the layer. The reference body is adjusted w.r.t. the opposite pole until the fields in the measurement and compensation gaps are equal. The reference position is adjusted by a drive unit.