Patent GB-607605-A (GB)
Title: Improved control system for regulating a number of variable quantities, for example the speeds of boiler auxiliaries
IPC: G05B11/32
Filed: 1945-09-17
Abstract: 607,605. Automatic control systems for boiler equipment. BRITISH THOMSON-HOUSTON CO., Ltd., and POOL, W. J. Sept. 17, 1945, No. 23911. [Class 38 (iv)] [Also in Groups XXXVI and XXXVIII] Boiler equipment comprises two or more auxiliary groups, each including one or more fans or blowers and means for controlling their output comprising a regulating device for each group, these devices being coupled together in such a manner that they are capable alternatively of relative positional adjustment or of simultaneous adjustment, each device being so graded as to give a logarithmic relationship between the quantity regulated and the mechanical movement of the regulating device, so that simultaneous change of the regulated quantities may be produced in the same proportion whatever their relative proportions were before the change was made. Fig. 11 shows a boiler control installation in which two fans 36 operating on parallel and similar air circuits are driven by induction motors 37 through eddy current couplings 38 having exciting windings 39. An independently controlled fan 40 is driven from an induction motor 41 through an eddy-current coupling 42 with exciting winding 43. A stoker 44 is driven by an A.C. commutator motor 45, the speed of which is regulated by adjusting a spindle 47. A master control shaft 1 is rotatable by a hand wheel 34 to vary the speed of the motors 37, 41, 45 in the same proportion, to compensate for a change in the demand for steam. Attached to the shaft 1 is a disc 1c to which may be engaged a sleeve 35c so that the angular position of 1c and 35c may be changed and they may then be locked together. The sleeve 35c carries the slider of a rheostat 2c in series with the windings 39 of the couplings 38 to control the speed of the fans 36. A similar disc 1d, sleeve 35d and rheostat 2d control the speed of the fan 40. The speed of the motor 45 is controlled by a rheostat 2e having its slider rigidly fixed to the shaft 1. This controls the current in a coil 21 of a balanced relay 22, the other coil 23 being controlled by a rheostat 27  coupled to the spindle 47. The relay 22 controls a pilot motor 46 which rotates the spindle 47 in such direction as to cause the speed of the motor 45 to correspond to the setting of the rheostat 2e. The coil 23 may, alternatively, be supplied from a tacho-generator driven by the motor being controlled. The shaft 1 may be replaced by mechanical or electrical devices such as a system of chains and sprockets, or a system of selsyns. The hand wheel 34 may be replaced by a device responsive to boiler pressure. If it is desired to adjust the relative speeds of two motors in accordance with some other function of the boiler, the relative positions of the rheostat 2d and the disc 1d may be adjusted by an automatic controlling device, such as epicyclic gearing. Fig. 5 shows a controlling device for a pulverized fuel feeding fan in which it is necessary that the reduction in speed shall not proceed beyond a given limit. A controlling disc 2 is adjustably driven from the shaft 1 and drives a disc 2a through a spring 14, relative rotation between the discs 2, 2a being prevented by a stop 16 attached to 2a co-operating with a stop 15 attached to 2. If 2 rotates clockwise, the stop 15 drives 2a through the stop 16. If 2 rotates counterclockwise, its stop 15 tends to move out of engagement with the stop 16 but is held in engagement by the spring 14. The disc 2a is provided with another stop 17 which, when the minimum permissible speed is reached, cooperates with a fixed stop 18 so that further movement of the disc 2 tensions the spring 14. For controlling an A.C. commutator motor in which speed is controlled by movement of the brush gear, this may be effected by means of cams. The hand wheel 34 may be coupled to the shaft 1 through a scroll 31, Fig. 10, fixed to the shaft 1 and driven by a chain 32 engaging a sprocket 33, which is driven by the hand wheel 34. The chain operates on a larger radius of the scroll for high motor speeds than for low, thus causing the change in motor speed to be more nearly proportional to movement of the hand wheel.