Patent GB-622203-A (GB)
Title: Improvements in controlling systems for regulators
IPC: G05B11/01
Filed: 1945-10-22
Abstract: 622,203. Automatic control systems. DEHN, F. B. (Automatic Temperature Control Co., Inc.). Oct. 22, 1945, No. 27802. [Class 38 (iv)] Variation of a quantity to be maintained constant (e.g. temperature, pressure, humidity) produces corresponding movement of a slider to unbalance a bridge, the out-of-balance currents varying the controlling quantity (e.g. fuel supply) and causing a further slider to move to re-balance the bridge; the out-ofbalance currents also act upon the supply sliders to the bridge to vary adjacent arms in opposite senses so that the bridge re-balances with an asymmetrical relation between the sliders controlled by the variable and controlling quantities, and when the supply sliders reach their limiting positions they are automatically brought back to their mid-positions. The invention is described with reference to maintaining constant the temperature of a furnace. Variation of temperature causes movement of contact 32, Fig. 2, over resistance 28, thus producing out-of-balance current in relay windings 54, 56 to actuate contact 57; if contacts 57, 60 are made, field winding 17 of motor 18 is actuated over contact 153 of relay 131, while if contacts 57, 58 are made, field winding 16 of motor 18 is energized over contact 148 of relay 142. Motor 18 actuates the valve of the fuel supply to the furnace in accordance with the variation of temperature, and actuates slider 23 on resistance 24 to re-balance the bridge to a condition with contact 57 midway between contacts 60, 58. Should the load in the furnace change, however, it will be necessary to open the valve further when the temperature is at the optimum, i.e. slider 23 must be displaced relatively to 32. To attain this the supply tappings 65, 79 to the bridge are equally and oppositely displaced by a motor 73 which is brought into operation whenever slider 32 is moved, so that the bridge re-balances with slider 32 at its centre position and slider 23 displaced. Relays 131, 142 are normally energized over limit switches 20, 21, but one is de-energized by the opening of one of the switches by motor 18 whenever the valve is completely open or completely shut. When both relays 131, 142 are energized, i.e. when the valve is not either wholly open or shut, the motor 18 can respond to any variation of temperature and relay 46 is operated. The slider 32 is arranged also to close contacts 35, 166 or 34, 166, for short periods of time determined by an interrupter 107, thus energizing either field winding 74, 75 of motor 73 over contacts of relay 46. Motor 73 thus adjusts sliders 65, 79. Motor 73 also drives a cam 139, so that when the supply valve is wholly open or shut, and relay 46 is de-energized, the field windings of motor 73 are energized over contacts 118, 125 or 118, 120, until the cam brings contact 118 midway between contacts 120, 125 so that the sliders 65, 69 are brought back to the central position. When either relay 131, 142 is de-energized, unbalance of the bridge can only result in the motor 18 being actuated to open or close the supply valve according as it is closed or open. Resistances 70, 78 are manually adjustable to vary the effective length of resistance 24 and thus the range of adjustment of asymmetrical relationship of sliders 32, 23. Switch 85 and press-buttons 93, 100 allow motor 18 to be run by hand to any position. In a modification, Fig. 3 (not shown), the bridge output between sliders 32 and 23 is applied to two thermionic valves whose output actuates a relay completing contacts 57, 60, or 57, 58; while slider 32 at its limits of travel closes contacts to actuate relay 46 to centre the bridge input contacts on their resistances. In a further rnodification, the bridge 28, 72, 24, 66, Fig. 4, is completed at intervals over contact 285 of a relay 271 actuated by an interrupter 107. Alternately, with the completion of this bridge, contact 283 of relay 271 completes a second bridge comprising resistances 315, 28 and their sliders 316, 32. The output of each bridge is applied alternately over thermionic amplifiers 200, 201 to actuate relay 170. Relay 170 alternately controls motor 18 (controlling the supply valve and slider 23) and motor 287 (controlling the slider 315) in accordance with the actuation of relay 271. The slider 32 is moved by the temperature registering device, and the input tappings 65, 79 to the bridge are moved by motor 73 controlled from cam 295 and contacts 301, 275, 302 operated by motor 287. In this arrangement, the slider 316 follows the movement of slider 32, and it provides a convenient attachment to an existing pyrometer instrument.