GB377315A - Improvements in or relating to variable electrical resistance devices - Google Patents

Abstract

377,315. Variable resistances ; coatings and deposits ; sets of, and wire, resistances. GRAMOPHONE CO., Ltd., Hayes, Middlesex, and WHITE, J., 26, Connaught Gardens, Palmer's Green, London. April 28, 1931, No. 12566. [Class 37.] A variable electric resistance comprises resistance elements 1, 2 having different resistivities, and widths or cross-sectional areas which vary along their length, the widths or cross sections of adjacent elements at their surface of interconnection being proportional to their resistance per unit length at that surface. The elements 1, 2 may be of granular resistance material such as granular carbon with or without a graphite binding possessing different resistivities. The resistance elements are mounted on the frusto-conical base 3 of a hard cylindrical insulating container 4 and a wiper 7 is attached to a spindle 6, the end 8 of the wiper 7 bearing on a resilient disc 9 which makes contact with the entire width of the part of the resistance under the end 8. The granular resistance elements may be formed by applying a colloidal suspension of graphite to strips of paper or other fibrous supports, which are dried and then cut into the desired shape. The resistance elements may be formed of wire of metals or alloys having different resistivities and tapered sections, in which case the wire may be wound in a helical groove on a cylindrical member and sliding contact established by a brush, or the wire may be wound on a flexible strip of insulating material which may be bent to form an arc on which a rotatable contact arm, with or without an interposed resilient contact disc, may bear.