Patent GB-731224-A (GB)
Title: Improvements in systems for supervising a plurality of variables
IPC: G08B26/00
Filed: 1953-07-31
Abstract: 731,224. Electric indicating systems. BAILEY METERS & CONTROLS, Ltd. July 31, 1953 [Aug. 2, 1952], No. 21300/53. Class 40 (1). In a system for supervising a number of variables, each of a number of resistances whose values correspond respectively to the variables, is connected in turn, simultaneously to at least two potential comparison circuits. One of these circuits may indicate the values of the variables and the other when the variables reach predetermined high and low values. As shown, three comparison circuits are used for indicating, respectively, the value and when the predetermined high and low values are reached. Variable resistors 40, 41, 42, ... , Fig. 2, sensitive, e.g., to temperature, are scanned sequentially by a stepping switch 31 advanced automatically by a drive magnet 38 pulsed through a rectifier 39 by a motor drive cam-actuated switch 45. Each variable resistor 40,41 ... is energized through a transformer A, and is connected simultaneously to potential comparison circuits 49, 50, and also to a further comparison circuit 80 if a manual selector switch 67 is in the " automatic " position. In the circuit 49 the P.D. across each resistor 40, 41 ... is compared with the P.D. across a corresponding preset resistor 53 in series with a fixed resistor 79 energized over a transformer B1. The difference voltage is applied to an amplifier 99 in an electronic relay 55 including a normally operated relay 56. Should the resistance 40, 41, ... increase so that the difference voltage is zero, corresponding to a predetermined high temperature, the relay 56 is de-energized to stop the stepping switch 31 at contact P, light a red alarm lamp 63 at contact Q in parallel with the green lamp G normally operated over the wiper 34 of switch 31 and operate an audible alarm 86 over contact S. The comparison circuit 50 functions similarly to the circuit 49 except that the normally energized relay 58 is de-energized when a predetermined " low temperature " resistor 40, 41, ... is read. by the selector 31. In this case the selector 31 is stopped at contact L, an audible warning 87 operated at contact T and a yellow alarm lamp 63A lit over contact N. To restart the selector 31, a switch 48 is momentarily operated. In the comparison circuit 80 the P.D. across the resistor 40, 41, ... is compared with the P.D. across a resistor 98<SP>1</SP> in series with a portion of a potentiometer 98 which is adjusted by a motor 97 actuated through an amplifier 96 by the difference voltage until balance is achieved. A pointer 83 rigid with'the potentiometer wiper then indicates the temperature in question on a scale 68. Thus, with selector 67 at " auto matic " the pointer 83 indicates the temperatures represented by the respective resistors 40, 41, ... as they are scanned by the selector 31. By moving the selector 67 to any one of its other positions 1 ... 24 the temperature corresponding to the associated resistor 40, 41, ... is indicated continuously at 83. The switch 31 may be stepped manually by repeated actuation of the switch 48. D.C. may be used in lieu of A.C.