GB721952A - Improvements relating to wire wound potentiometers and variable resistors - Google Patents

Abstract

721,952. Variable resistors. COLLINSON, R. F. March 9, 1953 [Dec. 7, 1951], No. 28779/51. Class 37. In a wire-wound potentiometer using a single control member fine adjustment occurs when a first slider takes up lost-motion and moves over an axuillary resistance element and coarse adjustment occurs when the first slider drives a second slider over the main resistance element. In the rotary potentiometer shown an auxiliary resistance segment 22 bridges contact fingers 20, 21 which, one in advance of the other, ride along the main resistance toroid 11. If coarse and fine adjustment are successively required the control spindle 25 sweeps contact finger 30 along resistance segment 22 and finger 30 engages stop 23 or 24 and then drives contact fingers 20, 21 along toroid 11 to give the required coarse adjustment and this is followed by reverse rotation of spindle 25 so that contact finger 30 is shifted along segment 22 until the required fine adjustment is attained. The resistance segment 22 is located in a recess in cylindrical insulating rotor 14 which carries spring arms 18, 19 terminating in the contact fingers 20, 21 and connected to the segment 22 via stops 23, 24. The spindle 25 supports by nut 26 and key member 27 a disc 28 so that the latter may be rotated with respect to rotor 14. The disc 28 carries a contact ring 29 which has on one side the contact finger 30 and diametrically opposite this finger 30 there is a second contact finger 31 engaging a current collector ring 15 encircling the rotor 14. With movement. of rotor 14 during coarse adjustment the current collector ring 15 rides against a stationary springy contactor 16. In a modification the contact ring 29 is replaced by a U-shaped member having a contact finger (similar to 30) for travel along resistance segment 22 and a pair of contacts like 20, 21 for travel along a contact segment fixed diametrically opposite the re- . sistance segment 22 and connected to current collector ring 15. If desired as an emergency or permanent alternative to stops 23, 24 which are in reality metal links the insulating rotor may have pins 32, 33 for co-operation with contact finger 31.