GB1445452A - Variable resistors - Google Patents

Abstract

1445452 Variable resistors ITW-ATECO GmbH 5 Nov 1973 [4 Nov 1972] 51250/73 Heading HIS A variable resistor comprises a plurality of resistance elements 8, Fig. 1, 60-62, Fig. 2, which within a region 26 are contacted by a pivoted slider, the resistance elements, and preferably also their contact portions, being produced by etching grooves 13 out of a chromenickel steel sheet which is mounted on a metal plate 11 electrically, but not thermally, insulated by a layer 10; the resistance elements are covered, except for region 26, by a further layer 8, both layers 8 and 10 being of a composite mica material, e.g. mica and polyamide fibres. The chrome-nickel steel, which may additionally contain molybdenum, is preferably laminated to layer 10 with adhesive. The resistive tracks may be connected in series or in parallel. To avoid sparking contact portions 65, 66 and/or slider contacts 3a, 3b are staggered, e.g. the contact portions may be disposed radially and offset circumferentially (Fig. 5 not shown) or they may be S-shaped and the slider contacts are staggered (Fig. 6 not shown). The metal plate 11 may be mounted in a supporting unit by means of through holes (24, Fig. 3 not shown). Arcuate slots (23) in the plate may be provided adjacent holes 24 to protect them from excessive heating. In addition the part of the plate beneath the region 26 may be punched-out to prevent short-circuiting to the plate. In another arrangement (Fig. 7 not shown) the edges of the plate are bent upwardly and two edges have inwardly bent sections (73, 74) beneath which the slider is mounted. The slider is actuated by a lever (14) pivoted on a holder (15) which is screwed to the plate. Various modifications of the slider and slider contacts are described with reference to Figs. 10-18 and 22-25, not shown. The resistors may be used as series resistors for the fan motors of car heaters. In Fig. 29 (not shown) the actuating lever can occupy three alternative positions defined by projections from the side of an aperture through which it passes. A further lever, e.g. for actuating an air valve, may be mounted adjacent the first lever. In the embodiment of Fig. 30 (not shown), resistive tracks which are relatively highly loaded are mounted vertically to improve the convective cooling thereof.