GB813274A - Improvements relating to mechanical-electrical transducers - Google Patents

Abstract

813,274. Variable resistors. BRISTOL CO. May 28, 1956, No. 16490/56. Class 37. [Also in Groups XXX and VIII] In a mechanical electrical transducer, a wire wound resistor has a brush support arm carrying at least one elongated brush equally resilient in all transverse directions, the end of the brush being constrained to follow the end of the brush support arm but is free to flex in a direction normal to the surface of the resistor. As shown, the free end of a Bourdon spring 18 is attached to the hub 22 of a spindle pivoted between two journal screws 15. An aluminium alloy brush arm 25, carrying a wire brush 26 over the resistive track 12 is balanced by a counterweight 32 and is attached to the spindle but insulated from it by a collar 24. A hair-spring 33 is used to connect the brush 26 to the terminal 34. The wire brush 26 which is preferably made from a heat-hardened palladium alloy is passed through a hole in the stud 29 and wound into a short spring 30 to provide bias against the resistive track 12. It is positioned radially by the slotted guide 31 at the end of the brush arm 25. In a modification, Fig. 4, two brushes 40, 41 are similarly mounted. The ends are bent reciprocably to enable each wire to contact a different part of the lower side of the same turn. The brushes 40, 41 are connected to the inside of the hair-spring 33<SP>1</SP> by two electrically connected anchoring lugs 28<SP>1</SP> and 42. Resistive track (Fig. 6). An aluminium strip 36 having an anodized oxide coating 37 is wound with a single layer of bare nickel chrome wire, the turns being spaced by 0.0005 to 0.001 inch. The wire is secured by a hightemperature polymerizing varnish 38 such as silicone varnish which, on setting, forms a concave meniscus between turns. Varnish is later removed from the outer surface of the track by a fine abrasive. The track may be formed into an arc of radius different from that described by the brush, thus distributing wear along part of the brush axis. This principle may also be utilized to compensate for non- linearity of the sensitive element 18.