Abstract: An apparatus for testing the wall thickness of a moving tube of plastics or other electrically non-conducting material being produced by an extruder, comprises an electrically conductive measurement body arranged in the moving tube, a ferromagnetic holding member which is arranged in the tube within effective range of a holding magnet located outside the tube and which has a tie connection to the measurement body to locate the measurement body axially within the effective range of a measuring sensor located outside the tube. The holding member and the measurement body may be introduced into the tube through a channel in the extruder head, shot into the tube from a forward position, or inserted through an aperture cut in the tube wall.

Abstract: A method and device for contactless measuring of the thickness of layers, particularly of insulating layers on metallic parts whereby a contactless pneumatic servo-mechanism approaches to and maintains a measuring head at a predetermined distance from the layer and whereby the thickness of the layer is ascertained by a measuring pick-up located in the measuring head.