GB895226A - Improvements in or relating to variable electrical resistors - Google Patents

Abstract

895,226. Variable resistors. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Feb. 12, 1960 [Nov. 21, 1958], No. 37514/58. Class 37. The current path between terminals 2 and 3, Fig. 1, of a variable resistor of the meandered film type includes secondary excursions defined by cuts 8 arranged transversely of the primary excursions defined by cuts 4 and 7, which latter extend from respective opposite edges 5 and 6 of the resistive film. A wiper contact 9 can move along a track 10 along which the primary cuts are of increased width, 7A. In a second embodiment, Fig. 2, the film is of annular form, and the secondary cuts are omitted in the neighbourhood of the circular wiper track 10. In a third embodiment, Fig. 3, the film is of a metal oxide, and the wiper track 10 is again circular and intersects the cuts at right angles. The meandering film configuration may be produced by the partial removal of a film formed on an insulating base, by spraying the resistive material through a shaped mask, by the silk screen printing technique, or by the photographic technique disclosed in Specification 845,453. Templates, Figs. 4 and 5 (not shown), may be employed for producing the films. The parts of the resistive film upon which the wiper contact bears can be strengthened by the application of a metal layer, or the wiper may contact strips of strong and good conducting material extending from the points at which one primary excursion ends and another begins.