GB512650A - Improvements in and relating to rheostats or potentiometers - Google Patents

Abstract

512,650. Variable resistances. INTERNATIONAL RESISTANCE CO. Jan. 7, 1938, No. 20997/39. Convention date, Jan. 7, 1937. Divided out of 511,178. [Class 37] A variable resistance or potentiometer particularly for use as a volume control for radio apparatus comprises an insulating support 43, Fig. 2, with inner portions 46, 47 and a narrow annular coating 80, e.g., one-eighth, of an inch wide, of resistance ink, with which engages a sliding contact formed with a number of individual contact arms 61, Fig. 6, of phosphor bronze wire of circular cross section bent to a curve at the point 61a at which they engage the resistance strip so as to provide point contact between each contact finger and the resistance strip. These wires are clamped at one end by a strap 59b on a rotatable insulating arm 39 and are free to move vertically at their other ends. The ends of the resistance strip are of high and low potential and are connected to terminals 27, 28 respectively. The sliding contact is connected to a third terminal 29 by means of a coil 58 of spring wire having a substantial number of turns. Riveted to the centre terminal 28 is a member 38 which is bent down at one end 38a so as to make contact with the low potential end of the resistance strip. The member 38 has also a raised portion 38c which extends over the head of the rivet 36 that secures the terminal 27 to the high potential end of the resistance, so as to serve as an electrostatic shield between this and the sliding contact. Points on the resistance strip are connected by ribbons 50, 51 of highly conductive coating material to rivets 41, 40 situated in the portions 46, 47 of the support within the resistance ring 80. These rivets secure and make contact with terminals 26, 25. Specification 511,178 is referred to.