GB543919A - Improvements in rheostat devices - Google Patents

Abstract

543,919. Variable resistances. SONOTONE CORPORATION. Nov. 7, 1940, No. 16222. Convention date, Nov. 9, 1939. [Class 37] A resistance element is contained in a shallow casing having a relatively movable cover which carries the contact element. A circular metal casing 10, Fig. 1, has a cover 11 of synthetic resin or other insulation material. The cover 11 is formed with a circular groove 13 and a central hole 14 which fit over the run 15 of the casing and a central cylindrical portion 16 so as to exclude dust. The bottom of the casing 10 is covered by a thin insulating washer 17 of paper. A shouldered bushing 18 of insulating material is placed round the central portion 16 of the casing and around the lower flange of this is a flat annular resistance element 19 having a rigid body of synthetic resin or other insulating material. This is fastened to the bottom wall of the casing 10 by two rivets 20 which also serve as terminals and as stops for the contact arm. An arcuate resistance film is coated on the insulating body between the rivets 20, or alternatively a wire-wound resistance element may be employed. To the underside of the cover 11 there is fastened by rivets 26 'a contact arm 28 having at its end a stud 29 which presses a flexible contact plate 44 into contact with the resistance strip at any selected point. The cover 11 is revolubly joined to the casing 10 by a central screw 32 engaging a screw-thread in the part 16. The rim of the cover 11 serves as a grip for adjusting the resistance. The rheostat may be mounted by means of a supporting strip 50 of metal secured to the bottom wall of the casing. Alternatively the casing 10 may be screwed externally and secured in an opening in a supporting plate by a ring nut, or the screw 32 may have a threaded extension which is clamped in a hole in a support by a nut. Fig. 7 shows a method of mounting the rheostat behind a panel 54 for actuation by a shaft 65 extending through a hole in the panel. A rectangular clamp 60 is formed of a bent metal strip having at its centre a threaded hole engaging a screwed nipple 61 which fits a hole in the panel 54 and is clamped by a nut 62. The rheostat 10, 11 is placed within the clamp 60 and held against the inwardly bent rear ends 64 thereof by a stub shaft 65 passing through the nipple 61. The inner end of the shaft 65 has a key stud fitting a keyhole in an arm 67 having lugs 68 engaging depressions in the cover 11 so that this is rotated by rotation of the shaft 65. A spring washer 69 having inwardly projecting lugs 70 is sprung into a groove 71 of the shaft 65 in order to press the casing against the ends 64 of the clamp. Outwardly bent projections 73 may be formed on the casing to prevent rotation.