GB922881A - Improvements in variable resistors - Google Patents

Abstract

922,881. Variable resistors. BOURNS Inc., and M. E. BOURNS. April 20, 1959, No. 13355/59. Class 37. In a variable resistor which includes a rotating lead screw, a linear resistance element arranged parallel with the lead screw and a slider movable by the lead screw along the element, the slider comprises oppositely indined interconnecting spring portions, each encircling the lead screw, and spring pressed into driving engagement with it, the inclined portions being yieldable under excessive pressure to ride over the thread if the lead screw is turned when the slider is prevented from moving. In one embodiment, Figs. 2, 3, a twopart casing 11 of for example phenolic resin material has mounted within it a conductive member 14 and a cylinder 15 of insulating material having a resistive film 16, both being held in position by the ledges 17. Electrical connections to the member and cylinder are made by means of the resilient contacts 20 which project through the casing walls. A lead screw 24 extends through the casing and is retained within the semicircular depressions 25 by insulated caps 28 in which are provided screwdriver slots 28 for adjustment of the potentiometer. A contact member 30 formed by stamping, is bent to have sides 31 and 32 which are apertured to take the lead screw, the shape of the apertures being such that when the sides 31 and 32 are pressed together the lead screw may be easily inserted, and when they are released the top and bottom edges of the openings engage with the screw thread. The side 32 has a portion 36 which is in contact with the resistive coating and a further part 38 is bent to engage with the member 14. The two parts of the casing may be held together by rivets 12 or by adhesive. In a second embodiment (Figs. 4, 5, not shown) the member 14 is replaced by a cylinder with a resistive coating and the resistive element by a moulded piece of resistive material, the casing being divided in a plane perpendicular to that of the first embodiment. In a third form (Figs. 6, 7, not shown) the contact to the slider is obtained through the lead screw and the case is provided with a transparent cover, a projection from it engaging with the lead screw to retain it in position. In a fourth form (Figs. 8, 9) the resistive element includes a generally oval cross-section body 118 of insulating material around which are wound a number of turns 119 of resistive wire, connected at one end to a larger group of turns 120 thus forming a large resistance value coupled to a fine adjustment. The element is held in position by means of spring clips 121 positioned in the housing at opposite ends to make contact with a portion of the winding. A lid 111 of the housing has a conductive metal layer 112 secured to it to provide the connection between the grouping contact and the terminal 125.