GB456988A - - Google Patents

Abstract

456,988. Current and pressure meters. NALDER BROS. & THOMPSON, Ltd., 97, Dalston Lane, and LIPMAN, C. L., 9, Stamford Grove East, Stamford Hill, both in London. May 21, 1935, No. 14842. [Class 37] [See also Group XXXVII] A permanent magnet moving - coil measuring instrument or relay has a bar magnet carrying a supporting member, which may be a magnet, extending across an end face of the first magnet and spaced therefrom to form an airgap in which the coil moves and embraces the member. The magnet may have a varying cross-section and may have polepieces of soft magnetic material. Materials of high coercivity such as aluminium-nickel and aluminium-nickelcobalt alloys may be used, and these may be magnetized longitudinally or across their diameter. Fig. 1 (Prov.) shows a cylindrical magnet Mo and an annular magnet Mi spaced by a magnetic washer W and clamped in a frame F, the moving coil C being balanced by the pointer P. Adjustment of the gap G can be effected by shims under the magnet Mo or by changing the washer W. The magnet Mo is magnetized across the diameter Y, Y giving a flux distribution indicated in Fig. 5 (Prov.), or it may be slotted at one side and magnetized across a line at rightangles to Y, Y. The magnet Mi is also slotted at one side to permit assemblage of the coil C, and, as in Fig. 9 (Prov.), it can have a tapering cross-section. The washer W can be integral with either Mo or Mi. In a modification, a second magnet Mo is arranged above the coil C giving an instrument of greater sensitivity. The bores of the magnets may be enlarged to permit illumination of the dial from behind. In Fig. 12 (Prov.), the magnet Mo is magnetized longitudinally giving a flux distribution shown in Fig. 16 (Prov.), and the part Mi is either of soft-iron, in which case the frame F is magnetic, or is a permanent magnet. The magnet Mo may comprise two separate half cylinders, and one form of the part Mi is shown in Fig. 21 (Prov.), with its flux distribution. An edgewise instrument, Fig. 23 (Prov.), has the part Mi lying in a recess in the magnet Mo. Damping is effected by the aluminium or copper coil former, or by a metal disc on the instrument spindle. Fig. 1 (Comp.) has a polepiece I on the magnet Mo, the part Mi being secured by screws E by which the moving system, Fig. 3 (Comp.), can be readily detached. The moving system can be pivoted eccentrically with respect to the magnets to give a desired scale law.