Patent GB-368282-A (GB)
Abstract: 368,282. Control systems for boiler installations. WARREN, T. R., Beechwood, Gaskell Road, Altrincham, Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Nov. 28, 1930, No. 35903.- [Class 51 (i).] Apparatus for maintaining a desired functional relation between two quantities, one or both of which may vary, in boiler installations, such as the steam flow and air flow or steam flow and furnace pressure or the steam flow from two boilers or groups of boilers, comprises a pair of resistance potentiometers the positions of the tapping or movable members of which are governed by the magnitudes of the two quantities respectively, an electrically operated central off-position relay device forming with the resistance potentiometers and a source of direct current a Wheatstone bridge whereof a pair of conjugate terminals are connected to the operating element or coil of the relay device which is operated in accordance with variations in one or both quantities and an electric controller through the medium of which the relay is periodically associated with apparatus for effecting variation in the boiler operating conditions, the controller also forming part of an impulse generator whereby periodic adjustments of the operating conditions may be made by current impulses depending on the departure of another quantity, such as steam pressure, from the desired value. In applying the invention to a boiler plant, steam flow, air flow and furnace pressure meters Ps, Pa, Pf, Fig. 1, in the form of potentiometers are employed each comprising a pointer p normally biased so that it may move freely over the dial of the meter, its contact part e being caused to engage at intervals with tappings t of a resistance unit r by an annular segment a operated by a solenoid. The potentiometers Ps, Pa, Pf are connected respectively to direct current supply conductors L, L1 through resistances R1, R2, variable resistances R3, R4 and resistances R5, R6. Electromagnetic relays Rsa, Rsf are connected across the pointers p of the meters Ps, Pa and Ps, Pf respectively, or if it is desired to maintain the furnace pressure constant the relay Rsf may be omitted and the pointer p of the meter Pf may be connected through a relay R/ to a resistance R7 across the conductors L, L1. A similar set of meters Ps<1>, Pal, Pf<1> for another boiler or group of boilers is employed, the pointers of the steam flow meters Ps, Ps<1> of the two boilers being connected through relays Rls and Rls<1> which are associated with apparatus such as mechanical stokers for maintaining the steam flow from the boilers in the desired relation. The relays Rsa, Rsf are connected to apparatus for effecting changes in the operating conditions such as forced and induced draught fans. Fig. 2 shows a control system in which the plant is also controlled by steam pressure as well as by the above described apparatus. In the event of a departure of the steam pressure of the boiler installation from normal an arm 16 of a selector switch DS is moved from its central position so as to bridge one contact of groups of contacts 21, 22 and contact strip 19 or 20 according to the departure of the pressure from normal. A continuously rotating drum controller DC driven by a motor 2 is provided with a continuous ring of conducting material formed with a V-shape projecting portion 4, a V-shape contact 5 and rectangular contact 6 all electrically connected through the contact brush 8 with the supply main C. During the rotation of the controller the contact brushes 9 .. 12 engage with the contact 4 and in the event of the arm 16 bridging one of the contacts of the groups 21, 22 and one of the strips 19, 20, a current impulse flows from the main C to one of the conductors 23, 24 and to the operating coils IDR, IDL, &c. for raising or lowering the induced draught, forced draught or fuel supply. When the brush contact 14 engages with the contact 6 current flows through the conductor 26 to energize coils CPs, CPa, CPf for releasing the segments a of the steam flow, air flow and furnace pressure meters to condition the various bridges. Should the steam flow and air flow not be in the desired relation one of the contacts Rsa1, Rsa2 will be closed according as to whether an increase or decrease of induced draught is desired and upon the engagement of the contact brush 13 with the contact strip 5 current will flow through the conductor 25 through the contact Rsa1 or Rsa2 to the inducing draught raising or lowering apparatus. Similarly the forced draught and fuel supply apparatus is operated upon a departure from the normal of the furnace pressure or steam delivery from different boilers. The contactor coils IDR, IDI., &c. are disconnected from the mains 23, 24 by opening the contacts T1 .. T6 by the operating coil T which is energized when the brush 14 engages with the contact strip 6. A modification of the bridge arrangement shown in Fig. 1 consists in connecting the conductors for the meters of one boiler to the conductors for the meters of another boiler by adjustable resistances operated in tandem.