GB1144538A - Improvements in or relating to devices for measuring the thickness of members of ferromagnetic material - Google Patents

Abstract

1,144,538. Measuring thickness. H. NIX and E. STEINGROEVER. Jan.16, 1968 [Sept.6, 1967], No.2274/68. Heading G1N. In apparatus for measuring the thickness of a member or layer of ferromagnetic material such as iron, nickel or cobalt, the magnetic flux of a permanent magnet 4 is divided between a measuring path 14 including a portion of the member or layer 10 the thickness of which is being measured and a shunting path 15, the flux in one of the paths being measured to determine the thickness, and the flux in the measuring path being removable so that the apparatus may be easily applied to and removed from the member or layer. The embodiment shown in Fig. 1, comprises a permanent magnet 4 having polepieces 5, 6 and being mounted for axial movement within a magnetically soft iron housing 1, the lower part of the wall of which is divided by a brass ring 7 to define the two flux paths. When the magnet is raised, Fig. 2 (not shown), no flux flows through the lower portion of the housing. Stops (not shown), may be provided to limit the downward movement of the magnet so that the sensitivity and range of measurement may be adjusted to suit different thicknesses of materials. A Hall probe or a magnetostrictive element 11, disposed in a slot in the brass ring 7 is connected into a measuring bridge circuit. A switch 13 automatically disconnects the battery from the bridge circuit when the magnet is raised. In a modification, the magnet remains stationary and a ferromagnetic shunt is displaced or rotated to vary the flux in the measuring path. In another embodiment, Fig. (not shown), the flux in the measuring path is adjusted by varying the current flowing in a winding (24) disposed around a magnetically soft ferromagnetic polepiece (20) having a high saturation, e.g. an iron-cobalt alloy containing 20 to 60% cobalt. The form of the external pole surfaces may be suited to the form of the member, e.g. the external or internal profile of tubes, tanks, and ships sides. Preferably the member or layer is fully saturated.