Patent GB-804812-A (GB)
Title: Improvements relating to control systems
IPC: G05D27/02
Filed: 1954-06-02
Abstract: 804,812. Automatic control systems. ELECTROFLO METERS CO., Ltd., and ENGEL, F. V. A. E. Aug. 31, 1955 [June 2, 1954; June 17, 1954], Nos. 16339/54 and 17878/54. Class 38 (4). [Also in Group XXXVIII] In a control system for a plant a force dependent on a variable condition in the plant deflects a member to influence electronic means which control (a) electromagnetic means producing an opposing force to re-balance the member, and (b) two or more means controlling a condition or conditions in the plant. In Fig. 2 a plant condition, e.g. boiler pressure, is detected by a transducer 2 which sends an electric current, dependent in magnitude on the pressure, through potentiometers 4, 5 thereby developing voltages which operate electric or fluid-pressure servo units 8, 9<SP>1</SP>, 9<SP>2</SP> controlling, for example, the inputs of forced draught, secondary air and fuel to the boiler. The relative adjustment effected by servo units 9<SP>1</SP>, 9<SP>2</SP> is automatically varied in a predetermined manner by a distributer 13. A differential component of control may be introduced into one or more of the servo units by apparatus of the type described in Specification 723,540, [Group XXIX]. Transducer 2 comprises a bellows 26, Fig. 3, responsive to boiler pressure, acting on a lever 27 pivoted at 28 and operating a shutter 31 between a light source 33 and a photo-cell 32. Photo-cell 32 is associated with an amplifier valve 36 which, in energizing an electromagnet 30 to maintain lever 27 balanced, develops an anode current which is applied through terminals 43, 44 to potentiometers 4, 5, Fig. 2. Resistance-capacity circuits including condensers 38, 41 introduce adjustable integral components of control. Additional solenoids energized from terminals 43, 44 and acting on lever 27 through fluid-pressure links having adjustable leakage or transmission restrictions to introduce a differential or integral component of control, are described. In a modified form of controller responsive to fluid flow, lever 27 varies the coupling between coils of an oscillator, of the type described in Specification 616,551, [Group XXXVIII], the output of which serves to balance the lever by energizing an A.C. solenoid. Distributer 13, Fig. 7, comprises an electric motor 101 the speed of which is controlled through an amplifier by the voltage from potentiometer 5. Motor 101 and a constant-speed motor 102 drive a differential gear 103 the output shaft of which, by adjusting a potentiometer 123 applying a voltage to the input of amplifier 119, takes up a position corresponding to the voltage from potentiometer 5 and thus positions potentiometers 111, 112 controlling servo units 91, 9<SP>2</SP>, Fig. 2. Cams 105, 106 in the drives to potentiometers 111, 112 are shaped to produce the desired relationship between the adjustment of the two potentiometers. Arrangements for changing over to manual control without shock and safety devices which operate on failure of transducer output or on incorrect operation of the distributer are described. Specifications 404,012, [Group XXXVIII], 463,326, 463,549, [both in Group XXIX], also are referred to.