Detecting distance changes

摘要

A device for detecting a change in the distance between two opposed surfaces (20, 30) and which, in particular can be used for detecting the increased thickness of a double sheet feed comprises a ferromagnetic material (58) associated with one of the surfaces and a giant magneto resistance effect sensor (70) associated with the other surface. A current source applies a current to the sensor (70) to read the magnetic field that impinges on the sensor so that changes in the distance between the surfaces (20, 30) are reflected in the change in the detected magnetic field.