GB495799A - Improvements in or relating to variable electric resistances - Google Patents

Abstract

495,799. Variable resistances. STANDARD TELEPHONES & CABLES, Ltd., and HELLIER, W. H. M. May 21, 1937, No. 14179. [Class 37] A variable resistance in which a contact member is movable over a resistance wire is arranged so that the displacement of the slider is a logarithmic function of the resistance between one terminal and the slider by making the resistance wire of contiguous lengths having different resistances per unit length, e.g. by forming them of different materials or different gauges. In the construction shown, two cylindrical formers 1, 2 are disposed between end plates 3, 4 in which is mounted a screwed rod 5 passing through a nut 6, which carries flat resilient wipers 7, 8 having contact studs 9. One or both ends of the rod 5 are slotted for insertion of a screwdriver. Each of the windings on the formers 1, 2 consists of successive lengths of wire having such resistances per unit length that an approximately logarithmic relation exists between the displacement of the slider 6 and the resistance between this and one end of the former. In an example each winding on the formers 1, 2 consists of four successive lengths of wire, the first and second consisting of constantan wire of 37 and 40 S.W.G. respectively, and the third and fourth of wire of the material known under the Registered Trade Mark " Nichrome," of 40 and 43 S.W.G. respectively. The first and third sections are enamelled, the others being double silk covered, the increased thickness of insulating-material compensating for the decreased gauge of wire and thereby enabling the slider to pass smoothly from one section to another.