Patent GB-726578-A (GB)
Title: Improvements in or relating to variable resistance devices
IPC: H01C10/32
Filed: 1953-03-19
Abstract: 726,578. Variable resistors; multi-unit potentiometer assemblies. HELIPOT CORPORATION. March 19, 1953 [April 18, 1952], No. 7599/53. Class 37. A variable resistor is provided with two co-operating shorting elements for producing a constant output resistance throughout a selected range of relative movement between a wiping contact and the resistance element. In the diagrams of Figs. 10 and 11a the potentiometer wiper traverses the entire length of the resistance element and throughout a first zone A and a final zone C the output resistance is constant and this is accomplished in Fig. 10 as an auxiliary wiper 20 moving synchronously with potentiometer wiper 15 contacts successively shorting bars 21, 24. The desired effect is obtained conversely in Fig. 11a, i.e. by using stationary auxiliary wipers 34, 37 and movable shorting bars 32, 33. The invention is described with reference to multiple or ganged rotary-type potentiometers wherein constant and variable voltages are delivered as a driving shaft is continuously rotated. A first embodiment, Figs. 1 to 3, is based on Fig. 10 and a second embodiment, Figs. 7 and 8, realizes Fig. 11a. In the five-unit assembly of Fig. 1 the units 41-44 are provided with shorting elements and the end unit 45 is not as it is required for this unit that the whole of the resistance be active. Each unit has its own surrounding casing wall 46 having a shoulder 72 against which rests the ring resistance element 17, Fig. 2, and in units 41-44 there is also an insulating ring 76, Fig. 3, with arcuate shorting bars 21, 24 mounted against the resistance element 17. The driving rotor 89 comprises slip-rings 90 and pairs of wipers 15, 20 for units 41-44 and a single wiper 15 for unit 45. The slip-rings 90 are provided with annular grooves 101 and each wiper assembly, Fig. 4, is of springy metal and has two curved arms 103 which are flexed and snapped home friction-tight into groove 101 and the assembly is then swung round within groove 101 to the phase position required and there anchored to the corresponding slip-ring 90 by soldering lug 105. The current collecting brush assembly 88, Fig. 4, comprises two wire arms 96 looped at 97 and terminating in cylinders 98 which rest in a curved groove 95 in slip-rings 90. The casing wall 46 and end covers 47, 50 are tongue-and-groove coupled as at 54 and held fast together by bracket clamps 56, Figs. 5 and 6 (not shown), and this arrangement of interconnection permits any unit to be rotated for phase adjustment. In the second embodiment shown in Figs. 7 and 8 the movable shorting bars 32, 33 are in effect travelling wipers in an assembly 130 similar to Fig. 4 and fitted into an annular groove 128. These shorting bars may extend, e.g., 225 and 9 degrees respectively (zones A and C) and cooperate with stationary wipers 34, 37 mounted on conducting arms 135, 145 which are adjustable to the required position from dummy terminals 136, 146. Fig. 12 shows a moving shorting bar acting as a switch in conjunction with fixed wipers 151, 152. The resistance element 17 comprises a split metallic ring 74, Fig. 2, coated with insulating material and wound with resistance wire 75.