Patent GB-735856-A (GB)
Title: Improvements relating to potentiometers and variable resistors
Inventor: SEDGFIELD HUGH BROUGHAM
IPC: H01C10/16
Filed: 1951-08-29
Abstract: 735,856. Resistance networks; variable resistors and potentiometers. SPERRY GYROSCOPE CO., Ltd. Oct. 9, 1952 [Aug. 29, 1951], No. 20382/51. Class 37. A variable resistor or potentiometer cooperates with an output law correction device comprising an auxiliary variable resistor or potentiometer. In the example sine or cosine construction of Fig. 1, the driving gearing 11 rotates primary resistance winding 1 and lead screw 7 so that roller contact 9 travels along resistance winding 1 and a cam-follower 19 moves along curved slot 18 in cam bracket 17. The slider 14 belonging to auxiliary resistance winding 13 is secured to cam bracket 17 which pivots about the axis of resistance winding 1 whereby as cam-follower 19 follows the contour of cam slot 18 the slider 14 is adjusted along auxiliary winding 13 thereby introducing the required correction. The main resistance winding 1 is wound on a spool 2 shaped to conform within manufacturing tolerances to the sine/ cosine function required and the selected part of the auxiliary winding 13 applies the appropriate correction for each position of roller contact 9 along main resistance winding 1 so that the total resistance or voltage drawn from the device more closely conforms to the chosen output law. The construction of Fig. 1 is represented in a cosine 0 to +90 degree potentiometer diagram, Fig. 3, and the required zero rate of change of voltage (at 0 degree) is obtained in Fig. 1 by utilizing a short length of cylindrical spool from either side of 0 degree and winding with resistance conductor of appropriately varied cross-section. This conductor may be obtained by electroplating a uniform section conductor and varying the rate of withdrawal from the plating bath or varying the rate of plating so that the conductor diameter decreases from a large diameter at 0 degree until it becomes equal to the conductor 1 at the points 1a, 1b where the spool shaping commences. In Fig. 3, + potential to earth is applied across winding sections 1<1>, 1<11> and the output taken from roller contact 9 and earth and connected Œ by slider 14 moving one or the other side of centre tap 141 of auxiliary potentiometer 13 is delivered across output terminals 25, 26. Fig. 3 may be modified or adapted to provide (i) a sine function 0-180 degree output with in this case 0, 90 and 180 degree at 31, 41 and 51; (ii) a sine 0-Œ90 degree output with negative voltage fed in at 41, Fig. 5 (not shown); (iii) only a + correcting voltage taken from a non-centretap potentiometer 13 and winding 1/roller contact 9 output never exceeding the functional value required, Fig. 4 (not shown); (iv) in place of auxiliary potentiometer 13 a variable resistor 13; Fig. 6, series-connected in the input so that slider 14 as moved by cam bracket 17 increases or decreases the vo tage fed to terminal 4. Fig. 2 demonstrates the use of Fig. 1 as a rheostat wherein winding section 1<1> cooperating with roller contact 9 produces an output equal to or less than the required function value and the series auxiliary winding 13 introduces the necessary plus correction. In a modified Fig. 2 with the main rheostat output never less than the theoretical function requirement a selected part of auxiliary winding 13 is in parallel with winding 1<1> to apply the minus correction.