Patent GB-1177631-A (GB)
Title: Improvements in or relating to Electromagnetic Indicating Devices.
Inventor: DUDLEY DENNIS WILLIAM
IPC: G09F9/40
Filed: 1966-01-20
Abstract: 1,177,631. Electric motors; arrangement of leads; terminals. SMITHS INDUSTRIES Ltd. 20 Jan., 1967 [20 Jan., 1966], No. 2746/66. Heading H2A. [Also in Division G4] In an electromagnetic device, preferably for use as an indicator, a permanent magnet is mounted for angular displacement about an axis normal to its magnetization and ferromagnetic elements spaced angularly from one another about the axis extend towards the magnet from a ferromagnetic yoke member spaced from the magnet along the axis; the yoke member provides low-reluctance magnetic interconnection of the elements such that when the magnet is brought into register about the axis with any one of the elements its own magnetization acting via the relevant element and the yoke member restrains it in this position ; electrical windings are inductively coupled to the elements for use in temporarily magnetizing the elements selectively; energization of different ones of the windings brings the magnet into register with different ones of the elements, and an indicia-bearing element is coupled to the magnet to provide an indication of angular position.  As shown in Fig. 3, the winding 22 (only one shown) on each ferromagnetic element 18 is wound in opposite senses on either side of a central tooth-piece 21 to produce a common magnetic pole there. The elements 18 are equally spaced around the permanent magnet rotor 10 and are odd in number (e.g. 11) so that when one pole of the rotor is aligned with a tooth-piece 21, the other pole is aligned with the gap between two tooth-pieces. The rotor is brought to any one position by supplying a pulse of D.C. to one winding 22 to produce a north pole at the tooth-piece 21 and thereby attract the south pole of the rotor, as shown. Half the flux path is then as shown by the dashed lines. At the end of the pulse, the permanent magnetization of the rotor is sufficient to hold it in position. The rotor is brought to any other position by supplying a D.C. pulse to the appropriate winding 22. An aluminium drum 15, Fig. 1, bearing the ten digits 0 to 9 and a blank or a decimal point, is secured to the rotor; the appropriate digit &c. appears at a window (not shown) at the front of the casing 16. Preferably the rotor is damped by silicone oil introduced into the bearings 11. Preferably a printed circuit board 23 is provided to connect the windings 22 to eleven terminal-contacts and one common terminalcontact (not shown) at the rear of-the casing 16. In another embodiment the magnet 10 is arranged above the circle of electromagnets 18, 22, and is long enough to extend nearly to the pins above the windings, the pins in this case protruding above the windings and the upper yoke ring 20 being omitted. Each winding is wound in one direction only to give a N-pole at the top when energized. Tooth pieces 21 may be provided as before to reduce the air gaps between the free ends of the pins and the magnet. The magnet carries an aluminium drum as before. In either case, the S-pole end of the permanent magnet may extend radially further out than the N-pole and to provide better switching between index positions. A number of such drum indicators, each with a decimal point in the eleventh position, may be arranged with axes and viewing windows respectively aligned; the decimal point may then be made to occur at any position along the length of the display.