GB441908A - - Google Patents

Abstract

441,908. Permanent magnets. SHEVLIN, J. T., 15, South Street, Finsbury, London.- (Deuta-Werke Vorm. Deutsche Tachometerwerke Ges. ; 25, Oranienstrasse, Berlin) Feb. 1, 1935, No. 3373. [Class 35] [See also Group XXXVI] An instrument has a moving coil 5 carried by a spindle 8 and enclosing a laminated magnetic core 2, the magnetic circuit of which is completed through laminated poles 1, 3. The laminations forming the core 2 and poles 1, 3 are shaped as shown in Fig. 2 with a circular head having a central hole and a slot 17. The spindle 8 carrying the coil 5 and pointer 11 is mounted between bearing screws 18. The hook ends of the laminations forming the core 2 are then introduced singly into the coil 5, the slots 17 of alternate laminae being preferably arranged on opposite sides of the centre line so as to form a closed annular core for the coil 5. Alternatively all the slots may face in the same direction. The laminae forming the poles 1, 3 may be similarly arranged. The instrument shown in Fig. 1 is for alternating current, the magnet having flat coils 4 mounted between the core 2 and the poles 1, 3. The air gaps 6, 7 between the plates 1, 2, 3 are determined by distance pieces 14, 15, which may be of chrome nickel so as to form a magnetic shunt the permeability of which is dependent on temperature. For direct-current instruments a permanent magnet is formed by replacing the coils 4 by magnetic material of high retentivity. This is used in the form of powder in conjunction with a binder such as shellac or artificial resin and is tamped into the spaces between the plates 1, 2, 3.