GB923607A - Variable resistor - Google Patents

Abstract

923,607. Variable resistors. BOURNS Inc. June 10, 1959 [April 29, 1959], No. 19881/59. Class 37. A variable resistor has an elongate casing 11, Figs. 1, 4, in which a slider 65 is movable along a resistance element 53 by means of a rotatable lead-screw 21, the resistance element being mounted on a lid 13 so that it is brought into contact with the slider 65 when the lid is assembled on the casing 11. The slider 65 includes a wire driving member 74, a portion 74<SP>1</SP> of which normally engages the thread of the lead-screw 21 but slips on the threads when it reaches the end of its travel along the leadscrew 21. Driving member 74 is carried by a U- shaped part of sheet metal which embraces lead-screw 21 and includes a base 70 and sides 71, Fig. 2. The slider 65 also includes a spring contact 66 which engages the resistance element 53. The lead-screw 21 is held against axial movement by a retainer 30. One end 24 of the lead-screw 21 is provided with a socket 31 into which is tightly fitted one end of a ceramic coupling 32. The other end of coupling 32 is tightly held in a socket 33 in a head 34 provided with a slot 36 to receive a screwdriver blade. An elastomeric O-ring 40 encircles coupling 32. Resistance element 53 may be a composition element but is preferably wire on a ceramic mandrel 54, Fig. 2, apertured centrally to receive a terminal strip 56. End 57 of strip 56 is bent and soldered to one end of resistance element 53. The other end of strip 56 is soldered to a terminal wire 60. Resistance element 53 is connected to a second terminal wire 62 and wires 60, 62 lie within channel 44 of lid 13 one on each side of projection 63. Lead-screw 21 serves as an electrical return from contact 66, connection to a terminal wire 81 being made through a clip 84 having a bowed spring finger 87 which presses against lead-screw 21.