GB643324A - - Google Patents

Abstract

643,324. Electromagnetic ammeters and voltmeters. GREIBACH, E. H. Feb. 18, 1947, No. 4715. Convention date, Feb. 20, 1946. [Class 37] [Also in Group XIX] In a moving coil instrument the moving system and magnetic core are formed as a self-supporting detachable unit, the moving coil being supported by a bifilar suspension tensioned by cantilever springs. To the polepieces 36, Fig. 5, are attached two' 'flanged brass tubular mounts 62, 63 into which can be inserted a brass tube 61 carrying the moving coil 31 and its suspensions and also the magnetic core 37. The moving coil 31 is supported by two bifilar suspensions 51 tensioned by cantilever springs 76, each of which consists of a pair of flat opposite-handed spirals. The springs may be of bimetal for temperature compensation. The springs 76 are mounted in upper and lower suspension heads 71, 72 which fit into screwed adjusting collars 74 by which the tension of the bifilar suspensions may be adjusted. Each suspension head 71, 72 may be rotated relatively to its adjusting collar 74 without disturbing it in its axially adjusted position so as to effect zero adjustment of the moving coil 31 and its pointer. The bifilar suspension 51 may be formed from a rolled strip with thickened edges 53-1, 54-1, Fig. 7, forming the two wires joined by a thin web 51-1 which may be weakened by perforations 51-2. The moving coil 31 may consist of a number of winding sections, the suspension members serving as connecting leads. The air gap extends over an arc about 50 per cent greater than the maximum deflection range of the coil so that the coil always moves in a uniform field. Magnetic impurities in the moving coil do not then produce any torque and their effect on the sensitivity of the instrument is eliminated. The instrument is supported in its case by a ring of rubber-like material.