GB251694A - Improvements in or relating to variable resistance devices - Google Patents

Abstract

251,694. Igranic Electric Co., Ltd., and Wright, S. R. Feb. 6, 1925. Resistance coatings; variable resistances. - A filament rheostat is combined in a single unit with a high variable resistance which functions as either a potentiometer or a grid leak and which is of the kind having its resistance in the form of a film of graphite or other soft material. The movable contactor of the high resistance and one end of the resistance element of the filament rheostat are in permanent electrical connection with a common terminal which may be the earth terminal. The filament rheostat may comprise a spiral spring 1 on a drum rotated by a hollow shaft 11 and knob 12 and held in position by a. spring washer 22, the drum comprising an insulat. ing annulus 18 and metal parts 19, 20. One end of the resister 1 is connected to the metal disc 19 and so to a terminal 7 through the metal hub 20, the metal frame 15, and a metal rod 15<a>. The tangential contactor 3 for the resister 1 is mounted on and insulated from the rod 15a, carries a terminal 8, and may be lifted out of contact with the resister 1 by an insulating piece connecting the ends of the resistor 1. The potentio meter comprises a graphite deposit in grooves on a raised circular track in a fixed insulating base 5 secured to the frame 15 by screws 23, and a graphite contactor 6 in a socket 27. A resilient metallic arm 28 carrying the socket 27 is rotated by a central shaft 13 and knob 14 and is connected through this shaft and the frame 15 to the terminal 7. The ends of the graphite deposit are connected to separate terminals 10 through plates 25 and conducting pillars 26 passing through the base 5 and limiting the movement of the arm 28. The knobs 12, 14 are separated by a metallic washer 33, and the knob 14 has a metal core 34. In a unit comprising a filament rheostat and a grid leak, one of the terminals 10 is omitted, an insulating stop being provided to limit the movement of the contactor at this end of the graphite deposit. This deposit is now formed on a nearly plain surface and is burnished to form a hard path by rubbing with metal, the plunger 6 being then of hard metal to continue the burnishing. The Provisional Specification refers to Specification 195,903 and 228,432.