Patent GB-858191-A (GB)
Title: Improvements in or relating to electrical systems
Inventor: WORSWICK BERNARD AUGUSTINE
IPC: G01D9/30
Filed: 1956-05-04
Abstract: 858,191. Multi-indicating systems. BAILEY METERS & CONTROLS Ltd. May 3, 1957 [May 4, 1956], No. 13858/56. Class 40 (1). An indicating, recording or controlling system comprises a series of networks each having a component whose electrical characteristic varies in accordance with an external value and another component whose characteristic can be changed to restore the condition of the network to its former state, and a single resetting means connected sequentially to the various networks to restore their condition, the indication, record or control being obtained from the position of the resettable component. The preferred method is to restore the null point of a bridge circuit (A.C. or D.C.) by means of a potentiometer, which may also be fitted with limit switches to give an indication or control when the variable reaches an undesirably high or low value. The invention is described in connection with four temperature-sensitive elements 471, 473, 475, 477 (Fig. 12) connected in four Wheatstone bridges whose outputs are joined to the inputs of the 4-way switch 279. This switch connects the bridge outputs in sequence via the amplifier 461 to the motor 145 which rotates in a direction dependent on the sense of unbalance of the bridge in circuit at the time. Although all four resetting potentiometers 431, 433, 413, 447 are shown coupled to the motor, the mechanism described below ensures that only that one belonging to the bridge that is coupled to the amplifier at that instant is actually moved, and the balance of the other bridges is not disturbed. The bridges are energized by an A.C. supply at 487. The motor 251 which operates the switch 279 also (Fig. 8) operates four cams 271, 273, 275, 277 set 90 degrees apart on the shaft 259, and these in turn operate four rocker arms 283, 293, 283, 293. The other ends of the latter (Fig. 6) move connecting rods 307, 351 which first allow the clutch levers 101, 125 to rotate under the influence of the spring 361 and then disengage brakes 327, 357 on the potentiometer shafts (see below). Thus once per revolution of the shaft 259 each potentiometer is connected for a short period to the motor 145 and is rotated if the corresponding variable has changed since the last time of connecting (e.g. one cycle in 28 sec.). Each potentiometer is provided with a cam 75, 129, 131, 175 (Fig. 3) which operates a corresponding pen on a continuously rotating chart, and any variation in the potentiometer setting causes the trace to deviate from its straight line. The four potentiometers 41, 43, 45, 47 are driven by an endless band 113 in the manner shown in Fig. 4 (where only two are visible), the actual resistance wire being indicated at 413. The potentiometer 41, cam 75  and brake disc 83 are mounted on a shaft 51 which also carries the pulley 109 normally spaced apart from the disc 83. When the clutch lever 101 is operated the threaded element 95 (having a quick multi-start thread) rotates in the nut 53 and presses the pulley sideways into contact with the disc 83 so that the potentiometer 41 is rotated relative to its slider if the motor 145 is being energized. Potentiometers 43 and 47 (not shown in Fig. 4) are operated similarly, but the drive to potentiometer 45 (lower part of Fig. 4) is different since it is coaxial with the motor 145. The pulley 209 always rotates with the motor shaft 141, but is capable of axial movement in or out of engagement with the disc 183 by the action of the clutch lever 201 in the same way as for the pulley 109. The brake devices shown in Fig. 6 at 327, 357 operate on the milled edges of the discs 83, 183 so that the potentiometers cannot rotate except when they are coupled to the driving motor 145. Fig. 11 (not shown) explains how rotation of the potentiometers causes movement of the respective pens. Fig. 5 (not shown) gives mechanical details of the clutch surface. The indications can be transmitted to a remote point by providing an additional slider engaging a second slide-wire on each potentiometer at 411 (Fig. 4). The indicating instrument itself forms the subject of Specification 858,192.