GB627327A - - Google Patents

Abstract

627,327. Moving-coil meters. NALDER BROS. & THOMPSON, Ltd., and LIPMAN, C. L. Jan. 7, 1947, No. 539. [Class 37] [Also in Group XXXVII] An electromagnetic meter or relay with at least two moving coils, has a core plate with a plurality of coaxial, ring-shaped members so that one coil embraces one ring, and the other coil or coils embraces one or more of the rings, one coil being adapted to carry an external current and the other also carrying an external current or short-circuited to carry induced eddycurrents. Figs. 1 and 8 show forms of core plates used in the assemblies shown in Figs. 18 and 20 respectively. The moving coils may consist of one active coil and one short-circuited coil on a common spindle, or two active coils on a common spindle in line or otherwise angularly displaced from one another, for use as ratiometer or dynamometer, or one active coil and one short-circuited coil on separate coaxial spindles to provide facility for indicat, ing maximum deflection, or two active coils on separate coaxial spindles to provide two independent instruments. Where two active coils are provided, theirampere-turns may be proportioned in any desired ratio, and the effects may be aiding or opposing as required. The active coils may be wound on closed ring metal formers to enhance the damping effect, or, for A.C. meters, they may be wound without formers. The rings forming the core plate may lie in the same or parallel planes. The crosssection of the rings may-be uniform or may vary round the circumference, the variations being in opposite directions for ratiometers. A ring-shaped magnetic shield may be placed between two active coils, or ridges may be provided between the rings to concentrate the flux in the air gaps. The core plate may itself be a permanent magnet or electromagnet. The shape of the core plate is such that means are provided for assembling the coils round the rings by bringing the gaps to the edges of the plate, or by making the core plate in more than one piece. The rings forming the core plate may be fixed to or form an integral part of one or more fixing plates which are attached to the main body of the magnet. The rings may be convex or concave with respect to their fixing plates, and the coils may be on the same or opposite sides of the spindle. The magnet may be a permanent magnet or electromagnet energized by a fixed coil, as used on dynamometer type wattmeters. The magnet may be provided with two or more polepieces, the core plates being interleaved with the polepieces. Specification 574,894 is referred to. Specifications 456,988, 469,938 and 530,698 also are referred to in the Provisional Specification.