GB384731A - Improvements relating to rheostats - Google Patents

Abstract

384,731. Variable resistances. MACKINTOSH, F., 10, Springvale Terrace, Glasgow. Oct. 2, 1931, No. 27418. [Class 37.] The contacting means comprises a flexible conducting travelling belt or belts 4 embracing a resistance helix 2 wound on a rotatable insulating cylinder 1. The belt 4 consists of a helically wound phosphor bronze or other wire and passes over a grooved pulley 5 revolubly and axially movable on a conducting rod 6, so that as the cylinder 1 is revolved by the handle 11 the belt 4 traverses the cylinder from end to end. Terminals 12, 13 are connected respectively to one end of the resistance wire 2 and to the rod 6. One or two convolutions of copper wire may be incorporated in the wire 2 between the terminal 12 and the adjacent end of the resistance wire 2 so that the resistance is completely cut out when the belt 4 is at one end of its travel. Connections may be made by means of slip-rings at each end of the resistance wire 2 so that the resistance may be employed as a potentiometer. Two similar resistances may be mounted coaxially or side by side and geared together so as to form a double potentiometer or a series resistance. A three-phase motor starter may be formed by mounting three resistance units with their axes parallel and forming an equilateral triangle, a single belt wrapping the three cylinders and forming the neutral or star point. Two or more conducting belts in parallel may be employed to increase the carrying capacity.. The resistances may be immersed in oil. Instead of a spring, the belt may consist of a stranded or woven conductor, means being provided for keeping the belt tensioned. According to the Provisional Specification the pulley 5 may be ungrooved and substantially the same length as the rod 6, so that the belt traverses the pulley from end to end.