US2216534A

US2216534A - Control apparatus

Info

Publication number: US2216534A
Application number: US154001A
Authority: US
Inventors: David B Kirk
Original assignee: Brown Instr Co
Current assignee: Brown Instruments Co
Priority date: 1937-07-16
Filing date: 1937-07-16
Publication date: 1940-10-01
Anticipated expiration: 1957-10-01

Description

Oct. 1, 1940. B, KlRK CONTROL APPARATUS 2 Sheets-Sheet 1 Filed July 16, 1937 .m, Rl MK m M W w l A D M 4 m 5 F 1 Y 9 I I 2 B 5 3 3 3 4 ll 3 3 fk I If n 9 m 2 m n i 7 1 H v6 n 7 "8 A. Aw 7 M n 6 A n l\v\. L L 4 i 6 v v Oct. 1, 1940.

D. 4B. KIRK 2,216,534

CONTROL APPARATUS Fileduul 16, 195': 2 Sheets-Sheet 2 INVENTOR.

DAVID B. KIRK W 34/ W R 75,

A TTORNEY Patented Oct. 1 1940 UNITED STATES PATENT OFFICE CONTROL APPARATUS Application July 16, 1937, Serial No. 154,001

17 Claims.

The present invention relates to improved control instrumentalities, and more particularly it relates to improved fuel combustion control systems of the type adapted for use with a plurality of fuel 5 fired furnaces in distinguishing between normal and abnormal conditions of combustion in all of the furnaces. I

It is a specific object of the invention to provide a system of the class described in which the combustion conditions in a plurality of fuel-fired furnaces may be controlled 'by means of a single control system.

Another object of the invention is to provide an improved fuel combustion control system for a plurality of fuel fired furnaces wherein means are provided for simultaneously distinguishing between actual conditions of combustion and simulated conditions of combustion in all of the furnaces. I

A further object of the invention is to provide such combustion checking means which operate upon the occurrence of an abnormal condition even after initial combustion has taken place, to shut down the fuel supply means.

In combustion control systems which have been proposed heretofore, various means have been employed for determining if combustion conditions are proper, and whether combustion actually takes place, one such means comprising an burner and which is so connected in the system as to provide a conductive path of relatively low resistance to ground through the flame. The variation in the electrical conductivity of this path to ground when a flame is present and when a flame is not present is commonly employed to change the bias on the control grid of an electronic valve for controlling a thermal safety switch. Since there is a possibility that a low resistance path may be set up from the electrode to ground through other agencies than by means of the flame, for example, a lowresistance path which may be established between the flame electrode and ground by reason of carbonization, by accidental'touching of the electrode to ground, or by other abnormal conditions simulating combustion, provisions have been made in devices of the prior art for preventing the fuel supply and ignition from being turned on when such abnormal conditions exist.

Since an abnormal condition of this character simulating combustion may arise after the system is already in operation, it is desirable to provide means for distinguishing between such abelectrode which extends into the flame of the normal conditions and natural combustion while the system is in operation. For example, in a thermostatically controlled house heating system, if the control system is insensitive to the presence of the flame after initial ignition of the flame, the fuel feeding means will be operated continuously as long as the room thermostat is closed. If the flame should then be extinguished, the furnace will be flooded with atomized fuel and a highly explosive mixture of the latter will be permitted to accumulate.

In a combustion control system in which a plurality of burners operate together, as for example for heating in unison and supplied with a common fuel line, it will be apparent that it is relatively important that an abnormal or dangerous condition of any of the burners be guarded against. In such a system, failure of any one of the burners to ignite or accidental extinguishing of the flame after it has ignited may result in an explosion.

The various features of novelty which characterize my invention are pointed out with particularity. in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, and the advantages possessed by it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a diagrammatic view illustrating one embodiment of the invention as adapted for use with a plurality of furnaces; and

Figs. 2 and 3 each illustrate a modification of a portion of the arrangement of Fig. 1.

In Fig. 1 of the drawings a plurality of gas burners l, 2, and 3, are shown as supplied with gas through a conduit 4 and the flow of gas to the burners is controlled by an electrically operated or other suitable valve 5. A respective pilot burner 6, I, and B is provided at each of the burners I, 2, and 3 and the flow of gas to all of the pilot burners is controlled by an electrically operated or other suitable valve 8. Means are provided for igniting the fuel at each of the pilot burners including pairs-of electrodes III, II, and I2 which are connected in parallel to the terminals of a secondary winding I3 of an ignition transformer ll having a primary winding l5 which is adapted to be energized from the alternating current supply conductors L and L The fuel valve operating circuit of my control system is controlled by means of a thermostat I6 which may be located in a room or space to be heated. The thermostat I6 may be of any bloclr 25 2t, wle he l ice:

' cult v. rib

gizatioof time, el

combine two triodes in each bulb.

to s. S.

arm :5. the latte; Element lee direction a 1g other to separate nterrupting the circuit The switch it w n until c osed position. current 1i connected by conductors Q to the heater filaments and of el

tronic valves

38 and 43, which as shown are of a "min amplifier type and Valve 36 includes an anode a control grid 38, and a cathode 38 as one triode and an anode 45, a control grid 4| and the cathode 38 as the second triode. Similarly, the valve 43 includes an anode 44, a control grid 45, a cathode 46 as one triode, and an anode 4?, a control grid 48 and the cathode 46 as the second triode. For convenience in describing the circuit operation the triodes including the

anodes

31, 40, 44, and 41 will be referred to hereinafter as the triodes A, B, C, and D, respectively.

As illustrated, the

anodes

31, 44, and 41 are connected together and are connected by a con ductor 49 to one end of the transformer secondary winding 30. The other end of winding 30 is connected by a conductor 50, in which a resistor 5| is inserted, to one end of the transformer secondary winding 3|, and the other end of this winding is connected to the

cathodes

39 and 46 of

valves

36 and 43 by a conductor 52. It is noted the transformer secondary windings 30 and 3| are so connected that the voltages induced across their terminals by the primary winding 28 assist each other, being additive, and together supply anode voltage to the triodes A, C, and D.

The control grid 4| of the triode B is connected by a conductor 53 to the conductor 5|! and the anode 40 is connected by a conductor 54 to one end of the transformer secondary winding 32. The other end of winding 32 is connected by a conductor 55, in which a relay winding 56 is inserted, to one end of the transformer secondary winding 3| and the other end of winding 3| is connected by conductor 52 to the cathode 39. Thus, one end of the resistor 5| is connectedthrough the transformer secondary winding 3| to the cathode 39, and the other end of the resistor 5| is connected to the control grid 4|. The anode currents conducted by the triodes A, C, and D pass through the resistor 5| and in the proper direction to impr ss a potential on the control grid 4| which is negative with respect to the potential of cathode 39 so that when the triodes referred to are conductive, the triode B will be rendered non-conductive. To this end the voltages produced across the terminals of the trans former secondar 3C 3| are so re t r El and the con- C and I that than the ratio oi the ratio of V /V is grea Brion/R wher V and V the voltages of gs 33 ,EACD is the cornbined anode 1 E is L 55% The relay U atively associated. with a pair of s and 5E, and when "haf- Lav the relay winding ed and the switch blades 51' lode B is n be de-ene the and US will be in the positions shown. The switch blades El and 5c biased by spring means or 7 other means in an upward direction and po ition the switch blade 5'! is in engageaction oi their opposing spring biases into engagemen 'th contacts Gil and Si, respectively. As *7 be apparent the output current of triode will be pulsating, and for the purpose of since g out the pulsating current hows through tl relay winding 56 and thereby preventing chattering of the contacts 51 and 59, a condenser 82 of suitable value may desirably be connected across the terminals of the winding 56.

When the temperature of the room or space to be controlled falls below the value it is desired to maintain, the thermostat It? operates to move the switch blade i9 into engagement with the contact 20 to close an energizing circuit to the transformer primary winding 28, the ignition transformer l4, and the operating means for the pilot valve 9. The energizing circuit to the transformer primary winding 28 may be traced from the alternating current supply line L conductor l8, bimetallic element I1, switch blade l9, contact 20,

blades

22 and 23 of the thermal safety switch 2|, the heating coil 28, conductors 53 and B3 to one end of the transformer primary winding 28, through winding 28, and a conductor 64- the thermal safety switch 2|, heater winding 26,

switch blade 51, contact 58, conductor 65 to one end of the ignition transformer primary winding I5, through winding l5, and conductor 64 to the alternating current supply conductor L The energizing circuit for the pilot valve operating means may be traced from the supply line L conductor I8, bimetallic element switch blade l9, contact 20,

switch blades

22 and 23 of the thermal safety switch 2|, heating coil 26, conductor 63, the pilot valve operating means, and

conductors

64, and 64 to the supply conductor L Fuel will then be supplied to the various pilot burners and simultaneously an igniting spark will appear across the electrodes III, II, and I2 to ignite the fuel at each of the respective pilot burners.

As was previously pointed out the energization of relay winding 56 is adapted to be controlled by the triode B and this triode in turn is adapted to be controlled by the flow of current through the triodes A, C, and D and as will become apparent the flow of anode current through each of the last mentioned triodes is adapted to be controlled by an individual circuit of which a respective pilot flame is a. component part. The control grid 38 of triode A is connected by a conductor 66 to an electrode 61 which is insulated from the burner and extends intothe pilot flame. The conductor 86 is preferably encased in a shield 68 of any suitable type and the shield is connected to the cathode 39. The conductor 66 is also connected to the cathode 39 through a parallel circuit including a condenser 69, and a resistor '18. By way of illustration, the condenser 69 may have a value of .002 microfarad and the resistor 18 may have a value of 25 megohms. Similarly, the

control grid 45 is connected by a'conductor 66" to an electrode 81 which is insulated from the burner and extends into the burner flame. The conductor 66', as shown, is encased in a shield 68' and the shield is connected to the cathode 46. A condenser 69' and a resistor 10 which may have identical values as the condenser 69 and resistor 10 are connected in parallel relation between the conductor 66' and the cathode 48. The control grid 48 is also connected by a conductor 66 to an electrode 61 which extends into the pilot flame and is insulated from burner. The conductor 86 is encased in a shield 68 which is connected to the cathode 46 and a condenser 69 and a .resistor H! are connected in parallel relation between the control grid 48 and the cathode 46. The condenser 69 and resistor I0 may be identical in value with the condenser 69 and resistor 10.

When the system is de-energized the various switch blades are in the positions shown and the

control grids

38, 45, and 48 are at substantially 4 the same potential as the

cathodes

39 and 46, which, as noted are connected together. The triodes A, C, and D will then be conductive and pulsating current will flow through the resistor 5| producing a pulsating potential drop there-.

across. Since the positive end of resistor 5| is connected through the transformer secondary winding 3| to the

cathodes

39 and 46 and the negative end of the resistor 5| is connected by conductor 53 to the control grid 4|, a negative potential will be applied to the control grid 4| when the triodes A, C, and D are conductive whereby the triode B will be rendered non-conductive, resulting in de-energization of the relay winding 56. The phase relation of the winding 32 is such that the alternating voltage main tained on the anode 48 will be in phase with the alternating voltages maintained on

anodes

31, 44, and 41.

As soon as a flame appears at each of the pilot burners, individual circuits are established through the respective flames which operate to bias the

control grids

38, 45, and 48 negatively and thereby to render the triodes A, C, and D less conductive. When a flame appears at the pilot burner 6, for example, a circuit is established from the control electrode 38 to the conductor 86, electrode 61, the flame resistance, the pilot burner 6, to ground H, to ground 12, resistor 13, relay winding 56, and the transformer secondary windtive.

secondary winding 3| will tend to charge the condenser .69 positively, but, due to the flow of grid current, and the high resistance of the flame, the control grid 38 will not be permitted to swing very far positive, if at all, and as a result the negative charge remaining on the condenser 69 from the preceding half cycle will be greater than the positive charge being impressed thereon so that the control grid 38 will remain somewhat nega- Thus, as long as there is a flame at the pilot burner 6 the control grid 38 will be negative with respect to the cathode 39 and as a result the triode A will be rendered less conductive. Similarly, when a flame appears at the pilot burners and 8 the

control grids

45 and 48 will be biased negatively and the triodes C and D will be rendered less conductive.

When the triodes A, C, and D are thus rendered less conductive the pulsating potential drop across the resistor 5| will be reduced whereby the potential on the control grid 4| will become less negative. The flow of anode current through the triode B will thus be increased resulting in energization of the relay winding 56 and actuation of the switch blades 51 and 59 into engagement with the

contacts

68 and 6|, respectively. It is noted that the flow of anode current through the relay winding 56 produces a potential drop across the winding which is in the proper direction to bias the

control grids

38, 45, and 48 negatively and thereby causes a further reduction in the anode current conducted by the valves A, C, and D.

Movement of the arm 51 out of engagementwith the contact 58 causes the previously traced circuit through the primary of the ignition transformer to be interrupted so that the ignition means is de-energized. At the same time movement of the arm 51 into engagement with the contact 60 establishes an energizing circuit to the main valve actuating means 5 which may be traced from the alternating current supply conductor L conductor l8, bimetallic element l1, switch blade I8, contact 28,

switch blades

22 and 23 of the thermal safety switch, conductor 14, contact 6|, switch blade 59, switch blade 51, contact 60, conductor 15, the valve actuating means 5, and conductors 84' and 64 to'the supply conductor LP. The main fuel valve 5 is then opened and fuel is admitted to the burners 2 and 3, which is subsequently ignited by the individual pilot flames.

It should be noted the energization of the relay 56 with the resultant movement of arm 59 into engagement with contact 6| establishes an energizing circuit from the thermostat to the transformer primary winding 28, the pilot valve 9 and the main valve 5 which does not include the heater resistance 26 of the thermal safety switch but shunts that resistance. Short circuiting of the resistance 26 in this manner operates to render the thermal safety switch 2| inoperative and the system will then remain in operation as long as normal combustion conditions exist and the thermostat i is in closed position.

If, for any reason, any one of the pilot burners should not become lighted, the potential of the control grid controlled by the respective burner flame will not be rendered negative with respect to its corresponding cathode to thereby make the average potential of those grids more positive than they were with normal flame resistance from the electrode 5'! to ground and as a result the pulsating potential drop across the resistor 5i will not be sufliciently reduced. The control grid 4| will thus be maintained negative with respect to the cathode 39 and as a result the relay winding 56 will remain de-energized and the shunt circuit around the heater winding 26 will not be established. After a predetermined period of time, this will cause the bimetallic element 24 .to be heated sufficiently to result in separation of

switch arms

22 and 23. The separation of the

switch arms

22 and 23 opens the circuit to the transformer primary winding 28 and de-energizes the entire system. As was previously noted,

the

switch arms

22 and 23 connot be automatically reset so that it is necessary for an attendant to investigate the condition which prevents ignition of the pilot burner before the system can again be put into operation.

As was mentioned previously, if a condition simulating combustion should be established after the system is in operation, the system will operate to close the main fuel supply valve. If a low resistance path is established be ween any one -of the electrodes 81" or and its respective burner after the system is already in operation, the potential on the respective control grid 5, or 3-8 be increased sufficiently in the positive direction to render the corresponding triode conductive to the necessary extent to prodrop across resistor 5i suflicycle when the anode o indi idual thereto more conduc tive charge,

W it would through a normal fi accordingly the average poten al of the control grid will be more positive it is when resistance of the path from the electl to ground is that of a normal flame. This i creased potential drop across resistor l operae to render the triode 3 non-conduc e result'ng in de-energization of 5S and conseq to limit the flow of grid current through the tr' 'hese triodes in the event any or? the con r'ds is connected directly to ground.

In Fig. 2 2 have illustrated, more or less diagrammatically, a modification of the arrangement disclosed in Fig. l in which the triodes C and D have been omitted. In this modification, as illustrated, the ends of

conductors

65, 66 and 66 remote. from their respective flame electrodes have been connected together and the

shields

68, 58 and 68 have also been connected together. The conductor 66 is connected to the control grid 38 of triode A, and the shields are connected to the cathode 39. A condenser B9 and resistor 10 of suitable value are connected in parallel relation between the control grid 38 and cathode 39.

Thus, when all of the flames are extinguished the control grid 38 will be at substantially the same potential as the cathode 39 whereby the triode A will conduct suflfioient anode current to render the triode B non-conductive and the relay 56 will be de-energized. 'When a flame appears at each of the pilot burners, however, a circuit path will be closed from the bottom end of the transformer secondary winding 3! through the resistor 13 and the respective pilot flames to the control grid 38, and it is noted that the effect of the appearance of each pilot flame is to increase by a. proportionate amount the negative bias applied to the control grid 38. For example,

when only one flame is present a negative charge of a magnitude determined by the flame resistance will be stored on the condenser B9 and when a second flame appears the negative charge will be increased proportionately. It will be readily apparent that condenser 69 and resistor 70 may be so proportioned with respect to the other circuit constants that the flow of anode current conducted by triode A will not be reduced siuiiciently to cause the triode B to become conductive until all of the pilot flames have been ig ited. Thus, failure of any of the pilot flames to ignite will operate to prevent the main fuel supply valve from being opened and subsequently to ale-energize the system. Similarly, should any of the pilot flames become extinguished while the system is in operation, the triode A will be rendered sufliciently conductive to render the triode non-conductive or at least sumciently less con ductive to cause de-energization of the relay 56 and thereby closure of the main fuel supply valve. she establishment of an abnormally low resistflame electo de-eneror less diad C and D have been omitted all of the nilot flames and 13.22116 electrodes have been cond in series relation. With this modification it will become apparent that failure of any one or" the pilot flames to appear will operate to maintain the main fuel supply valve closed and similarly extinguishment of any or" the pilot flames will operate close the main fuel supply valve.

Specifically thconductor 66 is connected to the flame electrode 6'? and circuit connections are cvided including flame electrodes 37 Si, 61 Bi and 87 whereby when the pilot burners 6, l, and 8 have been i nited a circuit path will be closed between flame electrode 6? and ground I i. With this modification the tips of pilot burners 5, l and 8 are of electrical insulating material or are electrica y insulated from the pilot burners supply pipe and as illustrated the flame electrode 61 is inserted in the path of the flame of burner 6 near the flame electrode 61 and the electrode 61 is connected to the flame electrode 61 which is inserted in the path of the flame of burner 1. The flame electrode 61 is positioned adjacent the electrode 61' in the path of the flame of burner I and is connected to the flame electrode 61 which is inserted in the path of'the flame of burner 8. connected to ground as indicated at 1| so that whena flame is present at each of the pilot burners 6, l, and 8 a circuit path will have been established between the control grid 38 and ground H. As illustrated the conductors connecting the flame electrodes 61? and 61', and 61 and 61 are preferably run in shielded

cables

68 and 68 respectively, which may be connected to the cathode 39 of valve 36, and a condenser 69 and a resistor 10 are connected between the control grid 38 and the cathode 39.

Thus, when a flame is present at all of the pilot burners a circuit path including all of .the pilot flames in series will be established between control grid 38 and ground whereby the triode A will be rendered non-conductive, resulting in energization of the relay 56 and consequently in' safety switch 2| (not shown in this arrangement).

heats up sufficiently the entire system will be de-energized.

Similarly, if any of the pilot burner flames should be extinguished while the system is in operation, the circuit path including the burner flames will be opened and the triode A will be rendered conductive whereby the system will subsequently be de-energized. Similarly, if a condition simulating combustion, such for example, as a low resistance path between any one of the flame electrodes and ground by reason of carbonization or direct connection therebetween, should be established after the system is in operation, the potential of control grid 38 will be increased sufficiently in the positive direction to render the triode A conductive and thereby to subsequently cause de-energization. of the system.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form oi the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage Without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A control system comprising, a plurality of isolated burners having a flame normally burning at each of said burners, a single electrode associated with each of said flames and adapted to be connected to ground thereby, means for controlling the condition of combustion of said flames in one sense to maintain said flames and in another sense to discontinue said flames if burning or to prevent their existence if not burning, an electronic valve having an input circuit and an output circuit, electrical circuit means including the output circuit of said valve to control said The flame electrode 61 is c second mentioned means, and means responsive to low, intermediate, and high electrical resistance values in the electrode to ground connections to continuously control said valve in said one sense responsively to said intermediate value and in said other sense responsively to said low and high values.

2. A control system comprising, a plurality of isolated burners having a flame normally burning at each of said burners, a single electrode associatedwith each of said flames and adapted to be connected to ground thereby, means for controlling the condition of combustion of said flames in one sense to maintain said flames and in another sense to discontinue said flames if burning or to prevent their existence if not burning, an electronic valve having an input .circuit and an output circuit, electrical circuit means including the output circuit of said valve to control said second mentioned means, and electrical circuit means including electronic valve means responsive to low, intermediate, and high electrical'resistance values in the electrode to ground connections to continuously control said first mentioned valve in said one sense responsively to said intermediate value and in said other sense responsively to said low and high values.

3. A control system comprising, a plurality of isolated burners at each of which a flame is normally burning, a single electrode associated with each of said flames, means for controlling the condition of combustion oi. said flames in one sense to maintain said flames and in another sense to discontinue said flames if burning or to prevent their existence if not burning, an electrical energizing supply source, a plurality of conductive paths energized from said source and each normally including one of said electrodes and one of said flames, an electronic valve having. an input circuit and an output circuit, means controlled by the output circuit of said valve for controlling. said second mentioned means, and means jointly responsive to all of said conductive paths and electrically connected to the input circuit of said valve to continuously control said valve in said other sense on the establishment of an abnormal condition of said conductive paths.-

4. A control system comprising, a plurality of isolated burners having a flame normally burning at each of said burners, a single electrode associated with each of said flames, means for controlling the condition of combustion of said flames in one sense to maintain said flames and in another sense to discontinue said flames if. burning or to prevent their existence if not burning, an electrical energizing supply source, a plurality of conductive paths energized from said source and each normally including one of said electrodes and one of said flames, an electronic valve having an input circuit and an output circuit, means including the output circuit of said valve to control said second mentioned means, and a single electronic valve connected to the input circuit of said first mentioned electronic valve and responsive to low, intermediate and high electrical resistance values in all of said means, a single electrode associated with each of said burners and separated therefrom by a gap adapted to be bridged by the individual burner flames, electronic valve means having an input circuit and an output circuit, means to continuously control the input circuit of said electronic valve means including an electronic valve individual to each of said electrodes and controlled in accordance with the resistance of the gap between the electrode and burner associated therewith, and electrical circuit means including the output circuit of said electronic valve means to control said burner fuel control means.

6. In a fuel burner system, a plurality of isolated burners having a flame normally burning at each of said burners, burner fuel control means, a single electrode associated with each of said burners and separated therefrom by a gap adapted to be bridged by the individual burner flames, electronic valve means having an input circuit and an output circuit, means to continuously control the input circuit of said electronic valve means including an electronic valve individual to each of said electrodes and responsive to low, intermediate, and high resistance values of the gap between the electrode and burner associated therewith, and electrical circuit means including the output circuit of said electronic valve means to control said burner fuel control means to maintain said flames responsively to said intermediate value and to discontinue or prevent the existence of s flames responsively to said low and high resis" ance values.

ing at each of said burners, a single electrode asscciated with each of said burners separated therefrom by a gap adapted to be br dged the dividual burner flames, b rans to control the supply or one! to s ers, a device jointly responsive to the of. sistance values of the gap between each or electrodes and its associated an elec Zing supply source, and continuously of said device to control said burner conuol means in a safe sense upon direct nection of any of said electrodes to its associated A control system comprising, a plura isolated burners having a dame norms ing at each of said burners, a single elect as sociated with each of said Flames and ada ted be connected to ground tnereby, ixea'is 1 trolling the condition o combustion 1 in one sense to maintain said a other sense to discontinue said flame prevent their existence ctronic valve having an input circui output circuit, electrical circuit means inch 3113 output circuit of said valve to control second mentioned means, electrical means including a device join .respon low, i.termediate, and high electrical vali es in the electrode to groun continuously control soonsively to interm 1 other sense responsively t A combustion safeguard control system ising, a plurality of isolated burn name normally burning eac"- of single electrode associated v itlthereby, means for controlling the condition of combustion of said flames in one sense to maintain said flames and in another sense to discontinue said flames if burning or to prevent their existence if not burning, an electronic valve common to all of said electrodes to continuously control said second mentioned means and adapted to be controlled in said one sense in response to intermediate resistance values in the electrode to ground connections and to be controlled in said other sense in response to low and high resistance values in the electrode to ground connections.

10. In a fuel burner system, a plurality of isolated burners having a flame normally burning at each of said burners, burner fuel control means, a'single electrode associated with each of said flames and adapted to be connected to ground thereby, an electronic valve having an electrode common to all of said flame electrodes, an electronic valve having an input circuit and an output circuit, electrical circuit means including the output circuit of said second mentioned electronic valve adapted to cause said burner fuel control means to assume a fuel feeding position to maintain said flames when each of the electrode to ground connections includes the resistance of a respective burner flame, and continuously effective electrical circuit means including said first mentioned valve adapted to render the first mentioned circuit means ineffective in re sponse to two widely separated resistance values in the electrode to ground connections.

11. prising, a plurality of isolated burners hav' g lame normally burnat each of said burners, of electrodes d flames, means for I till a one sense to A sense to disc ing 0; to prevent their e burnin an ene gizing supply source, a conductive path said source an.

Moi second ass when said s and to corn means in conductive path inch trol second me sense upon the estabu slrunt connection abet any com

nes and soo ne said flames if stence if not burni anot burning ing, an

path energized by d so me and normally including said flames connected in series relation, an input cicuit and out circuit being con tinuously controlled by said conductive path, and electronic means unde; control of the output circuit of said electronic alve adapted to control said second mentioned in said one sense when conductive path includes said flames and to control said second mentioned means in said other sense upon the establishment of a low resistance shunt about one of said flames.

13. in a control system, a plurality of burner means, a plurality of resistances each of which is modified by a respective one of said burner means, each of said resistances normally varying over a predetermined intermediate range of values and abnormally adapted to assume two widely displaced high and low values, means for effecting a control operation in one sense to maintain said resistances within said intermediate range of values and for effecting a control operation in another sense upon the occurrence of said resistances assuming one of said widely displaced values, an electronic valve having an input circuit and an output circuit, electrical circuit means including the output circuit of said electronic valve to control said first mentioned means, and means responsive to said resistances to continuously control the input circuit of said valve in said one sense when the values of said resistances are within said intermediate range of values and in said other sense when the values of said resistances are either one of said widely displaced values.

14. In a control system, a plurality of burner means adapted to cooperate with a plurality of variable conditions, each condition adapted to be modified by a respective one of said burner means, each of said conditions normally varying over a predetermined intermediate range of values and abnormally adapted to assume two widely displaced values, means for efi'ecting a control operation in one sense to maintain said conditions within said predetermined range of values and in another sense upon the occurrence of said conditions assuming one of said widely displaced values, an electronic valve havingan input circuit and an output circuit, electrical circuit means including the output circuit said ,electronic valve adapted to control said first mentioned means, and means responsive to said conditions to continuously control the input circuit of said valve in said one sense when the values of said conditions are within said intermediate range of values and in said other sense when the values of said conditions are one or the other of said widely displaced values.

15. In a control system, a plurality of burner means adapted to cooperate with a plurality of variable conditions, each condition adapted to be modified by a respective one of said burner means, each of said conditions normally varying over a predetermined intermediate range of values and abnormally adapted to assume two widely displaced values, means for effecting a control operation in one sense to maintain said conditions within said predetermined range of values and in another sense upon the occurrence of said condition assuming one of said widely displaced values, an electronic valve having an input circuit and an output circuit, electrical circuit means including the output circuit of said electronic valve to control said first mentioned means, and'electronic valve means responsive to said conditions to continuously control the input circuit of said valve in said one sense when the values of said conditions are within said intermediate range of values and in said other sense when the values of said conditions are one or the other said widely displaced values.

16. In a control system, a plurality of burner means adapted to cooperate with a plurality of variable conditions, each condition adapted to be modified by a respective one of said burner means, each of said conditions normally varying over a predetermined intermediate range of values and abnormally adapted to assume two widely displaced values, means for controlling said first mentioned means in one senseto maintain said conditions within said predetermined range of values and in another sense upon the occurrence of said conditions assuming one of said widely displaced values, an electronic valve having an input circuit and an output circuit, electrical circuit means including the output circult of said electronic valve to control said second mentioned means, and a single electronic valve common to and responsive to said conditions to continuously control the input circuit of said valve in said one sense when the value of said conditions is within said intermediate range of values and in said other sense when the value of said conditions are one or the other of said widely displaced values.

17. In a fuel burner system, a plurality of main burners, a pilot burner associated with each of said main burners, a flame normally burning at each of said pilot burners, fuel control means for said main and pilot burners, a single electrode associated with each of said pilot burners and separated therefrom by a gap adapted to be bridged by the individual pilot burner flames,

CERTIFICATE oF, CORRECTION;

Patent No. 2,216,531 Y October 1, 191m.

DAVID B. KIRK.

It is hereby certified. that error appears in the printed specification ofthe above humber ed patent requiring correction as follows: Page 14., first column, l ines atoll inclusive; strike out the words Yto thereby makethe 'a veragefpotentia l of those grids more positive than. they were with normal flame resistance from'the electrode 6'? to il dand insertthe same after "winding 51" in-line 1; epithet the S -1 Letters Eatent should be read with this correction there-in thet thesame may conform to the record of the casein the Patent Office.

Signed and se aledthis Zhth day of December, A. D. 19l .0.

Henry Van Arsdale, Q (Seal) Acting Commissionerof Patents.

CERTiFICATE oF CORRECTION;

Patent Not 2,2165%.- October 1, 191m.

DAVID B. KIRK.

It is herebyeertifie'd that error appears in the printed specifioetion ofthe above nu'mbered petent requiring correction as follows: Page 14., first column, iines 8 t0 'l 1 inclusive; strike out the Words "to thereby make the *averagepotentielof those grids more positive thanv they were with normalflame resistance from the electrode 67 to groin; and insert the same after "winding 51" ih-line 1 a dwht the Se-1 Letters Batent should be read with this correction therein thet thesame mayconf orm to the record of the case in the Patent Offiee.

Signed and sealedfthis 214th dey of December, A. D. 19140.

Henry Van Arsdale (Seal) Acting Commissioner of Patents.