GB691384A - Improvements in or relating to electromagnetic measuring instruments - Google Patents

Abstract

691,384. Transformers. GENERAL ELECTRIC CO., Ltd., MATTHEWS, A., and POLGREEN, G. R. July 30, 1951 [Aug. 11, 1950], No. 20029/50. Class 38 (ii). [Also in Group XXXVIII] An electro-magnetic pick-up head for measuring small displacements comprises two symmetrical transformers totally enclosed by an iron dust core except for two or more short air gaps which are varied by movement of a movable part of the core, the change in inductance of the secondary windings being indicative of the magnitude of the displacement. An embodiment for measuring pressure (Fig. 1) comprises a diaphragm 1 rigidly clamped at the outer edge and supporting two metal discs 5 at the centre, dividing a gas-tight chamber into two sections 6, 7, the forward section 7 being connected via a tube 8 to the space whose pressure is to be determined, and the other section 6 being evacuated. The discs 5 are assembled on a metal rod 9, carrying the movable parts 26, 27 of an iron dust core totally enclosing two spools carrying two primary windings 43 and two secondary windings 42. Air gaps 30, 31 are allowed between the movable cores 26, 27 and fixed cores 18, 19 separa.teci by a phosphor-bronze spider 22, which prevents lateral movement of cores 18, 19, the air gaps 30, 31 being adjustable by a metal cap 33 threaded on to the rod 9, altering the position of a metal sleeve 34 carrying the movable cores 26, 27. A gas-tight bellows 11 allows for longitudinal movement of the rod 9 while maintaining the vacuum in section 6. The two primary windings 43 are connected in series aiding and fed with A.G., the two secondary windings 42 being connected in series opposition across a milliammeter. The gaps 30, 31 are initially balanced by adjusting the cap 33, and subsequent movement of the diaphragm 1 produces a proportionate reading on the milliammeter. In a modification (Fig. 4) for more general use, the rod 9 is supplied with a tapped end 49 for coupling to any moving part, and a resistance winding 56 is assembled inside the head to provide temperature compensation. An over-travel alarm is also provided by the addition of an adjustable end stop 58 screwed into the casing, and closing an alarm circuit when rod 9 contacts the casing. The pick-up head may be employed in the arrangements described in Specification 677,355, [Group XXXVIII].