GB691396A - Improvements in or relating to control systems - Google Patents

Abstract

691,396. Automatic temperature control systems. BAILEY METERS & CONTROLS. Ltd. Oct. 26, 1950 [Oct. 26, 1949], No. 26105/50. Class 38 (iv). [Also in Groups XXIV and XXXVIII] Relates to control systems utilizing magnetic fluid clutches of the type comprising driving and driven members of magnetic material separated by a fluid containing particles of magnetic material whose apparent viscosity increases when subject to a magnetic field, thereby increasing the torque transmission. According to the present invention a variable fluid pressure is converted into a corresponding voltage or current which is applied to control the magnetic field in the clutch. The control fluid pressure may be dependent on some other variable, e.g. level, temperature or flow. Fig. 1 illustrates a system for automatically controlling the vapour temperature in a vapour generator in which measuring devices 1 and 2 respectively sensitive to vapour flow and temperature individually position pilot valves 3 and 4 of the type disclosed in Specification 425,507, [Group XII], producing air pressures in conduits 5 and 6 proportional to the measured flow and temperature. Conduit 6 is connected to a standardizing relay 7 which establishes in. conduit 8 a further pressure proportional to the temperature and conduits 5 and 8 are connected to an averaging relay 9 producing in conduit 10 a final pressure dependent on the required control effect which is applied via a manual-automatic selector switch 11 to bellows 13 controlling the position of the movable core 14 of a transformer comprising primary 15 and two series-opposed secondaries 16, 17 which are connected to the secondaries 18, 19 of a similar remotely located transformer 18-21. Relays 7 and 9 may be of the type disclosed in Specification 461,389, [Group XXIX]. When the two cores 14 and 21 are in corresponding positions there is no resultant voltage between the centre taps of the two secondaries, but any departure from this balanced condition produces an A.C. error voltage of amplitude and phase proportional to the magnitude and direction of the unbalance which is applied through an amplifier and phase-sensitive device 26 to energize the forward or reverse windings of the reversible magnetic fluid clutch 22, Figs. 6 and 7 (not shown, see Group XXIV), interposed between a constant speed unidirectional motor 24 and a reduction gear coupled to a linkage 25 operating a damper 23 which controls the vapour temperature, the linkage 25 being also coupled to the transformer core 21 so that the damper and core move in correspondence with movements of core 14. The phase-sensitive device 26, Fig. 3, comprises two push-pull A.C. energized tutrodes 65, 66 with the forward and reverse clutch windings 60 and 61 as anode loads, the amplified error voltage being applied in parallel to the control grids. In a modification, Fig. 4 (not shown), transformer 18-21 is replaced by a variable potentiometer and in Fig. 5 (not shown), the connections to the secondary centre taps are omitted the device 26 being inserted in series with one of the outer connections. Details of the bellows-transformer transducer 13-17 are illustrated in Fig. 2 (not shown). In another embodiment, Fig. 8 (not shown), the variations in final fluid pressure in conduit 10 are converted into corresponding variations in D.C. current of a magnetic fluid clutch transducer of the type disclosed in Specification 691,392, [Group XXXVIII], the output current being applied through the control winding of a unidirectional magnetic fluid clutch, Fig. 9 (not shown), coupled to a constant speed motor. The motor is also coupled via reduction gearing to one input of a differential gear whose other input is coupled to the clutch output and the differential output is linked to the temperature controlling damper so that for a particular value of the control current the damper is stationary but for other values of the current the damper will move continuously in one direction or the other.