GB1035521A - Improvements in or relating to variable electric resistances, variable transformers and the like - Google Patents

Abstract

1,035,521. Variable resistors; transformers. MINIATURE ELECTRONIC COMPONENTS Ltd., and O. T. LEWIS. Jan. 11, 1963, No. 1348/63. Headings HIS and H1T. [Also in Division H2] In a variable electric component such as a resistor or transformer having an element along which a contact slide to vary the component value, a spring contact is supported and balanced by forces acting at four spaced-apart regions, two of these forces acting between the element and the sliding surface of the contact and between a take-off conducting member and an abutting surface of the contact respectively. In a rotary potentiometer, Fig. 1, an arrow-shaped spring contact 5 has a contact surface 6 which bears on a circular resistance track 4, a central surface 7 which bears on the underside of a slot 10 formed in the stem 11 of a mushroom-shaped conducting stud 12, and two upturned triangular lugs 8, 9 which are located in arcuate recesses 15, 16 in the underside of the mushroom head 13 and are pressed down upon by head 13, so providing the third and fourth balancing forces. When stud 12 is turned to vary the resistance, lugs 8 and 9 co-operate with recesses 15, 16 to turn the contact 5, whereupon the surface 6 travels round track 4. Variations in the shape of contact 5 and in the positions of application of the balancing forces are described (Figs. 2 to 5, not shown). In a linear potentiometer, Fig. 6 (not shown), a contact 5 has one spring finger with a contact tip 6 bearing on a linear resistance track 4, a second spring finger with a contact surface 7 which co-operates with the thread of a lead screw 23, and two flat surfaces 8, 9 which bear down upon insulating surfaces 21, 22. When the screw 23 is turned, the surface 7 moves along the screw thread and so contact surface 6 travels along track 4.