GB1189067A - Variable Resistance Device - Google Patents

Abstract

1,189,067. Variable resistors. BECKMAN INSTRUMENTS Inc. 26 June, 1968 [3 July, 1967], No. 30420/68. Heading H1S. A variable register (e.g. a trimming resistor) comprises a housing 6 having a threaded shaft 12 and a resistance element 31, a block 23 having spring contact 26 mounted thereon which presses on element 31 and urges the block 23 so that a threaded channel in its upper face engages the thread of the shaft 12 to enable rotation of the shaft to move the contact over the resistance element. The shaft is secured in the housing by spring clip 17 being inserted between the shoulder 18 formed by the annular recess 16 in the shaft 12 and two wedge-shaped projections 19 on the inner wall of the housing on either side of the opening 11 for receiving the shaft, the head 45 of the shaft being forced into firm engagement with the outer wall of the housing. 0-ring 22 maybe mounted in a second recess 22a in the shaft. The V-shaped spring contact 26 which may be coated with a palladium-silver-copper alloy is push-fitted into engagement with the boss 28 of the block 23, flanges 23a about the side walls of the housing to prevent rotation of the block 23. The resistor element may be in the form of a helically wound resistance wire or a resistive film (30, Fig. 2, not shown), e.g. of carbon or conductive plastics material, on an insulating substrate 31, e.g. of refractory, glass or plastics material. A conductive collector strip (29, Fig. 2) is also mounted on the substrate 31 parallel to but spaced from the resistive element to which contact is made via the spring contact 26 which is also the tapping contact. External electrical connections are made via tags 40 and terminals 33 and 35 to the resistive strip and 34 to the collector. The substrate 31 is held into place in the housing 12 by base member 10 which is bonded to the housing 12, e.g. by ultrasonic welding the members 10 and 12 and block 23 being of filled plastics material.