US2626657A - Burner control apparatus with component checking means - Google Patents

Description

Jan. 27,1953 J. M WILSON 2,626,657

BURNER CONTROL APPARATUS WITH COMPONENT CHECKING MEANS Filed June 27, 1949 2 SHEETS-SHEET l ll 3nventor b 1 I 1 I I JOHN M.W|LSON (Ittorneg Patented Jan. 27, 1953 UNITED STATES PATENT OFFICE BURNER CONTROL APPARATUS WITH COMIONENT'CHECKING MEANS Application June 27, 1949, Serial No. 101,507

18 Claims. 1

The present invention relates to burner control apparatus and particularly to that type of burner control apparatus employing condenser timing for obtaining safety shutdown and proper sequencing of the burner control. This application is a continuation in part of an application filed by the present inventor for Burner Control Apparatus, on March 10, 1948, Serial No. 13,981, now abandoned.

In some present day burner installations, particularly those employing gas as a fuel, it is desirable to have almost immediate shutdown in the event, that upon initiation of operation, combustion is not established or upon the occurrence of a flame failure. This may be accomplished by usin an electronic flame detector 'to regulate the charging time of a condenser through resistor. When the condenser is charged suffi'ciently, the charge may be used to bias an electron discharge device out of conduction to render the apparatus inoperative. When combustion is detected by the electronic flame detector the charging circuit of the condenser is rendered ineffective.

By using an electronic flame detector in the present invention it is possible to shut the burner down the instant it is determined combustion is not present. The electronic flame detector that has been employed responds almost instantly to the presence or absence of flame. As the flame detector employs an electron discharge devic which is subject to failure, it is necessary to provide a control apparatus which will be quickly rendered inoperative upon the flame failure and which will check the circuit components in the event that the flame detector should be inoperative or should be operating falsely.

It is therefore an object of th present invention to provide a burner control apparatus of the electronic type which will quickly respond to the presence or absence of flame and which will be maintained inoperative in the event there is a component failure in the control apparatus.

Another object of the present invention is to provide a burner control apparatus which employs resistor-condenser timing to accomplish shutdown of a burner when there is a flame failure and which checks the components of the control apparatus to maintain the burner inoperative when there is a false indication of flame.

Still another object of the present invention is to provide a control apparatus employing an electron discharge device which is rendered operative upon the need for operation of a burner and inoperative upon the occurrenc of a flame failure by a biasing voltage charging a condenser associated with the discharge device and further biasing the discharge device to be maintained inoperative when a flame detection device falsely indicates flame.

A further object of the present invention is to provide a burner control apparatus employing an electron discharg device which is rendered operative upon the need for operation of a burner and an electronic flame detector which will render the discharge device inoperative when there is a flame failure and maintain the discharge device inoperative when there is a false indication of flame.

A still further object of the present invention is to provide a burner control apparatus employing an electron discharge device which is biased to be inoperative upon a flame failure by one biasing circuit and to be biased to be inoperative by a second circuit when there is a false indication of flame and where the latter biasing circuit will be maintained continuously until the fault causin the false indication of flame is removed.

These and other more detailed and specific objects will be disclosed in the course of the following specification, reference being had to the accompanying drawings of which:

Figure 1 shows in detail one embodiment of the invention as applied to a gas burner control. and

Figure 2 shows the invention in slightly modifled form.

Referring to Figure 1, the numeral Ill represents a gas burner which is adapted to be supplied fuel through a conduit II. Controlling the flow of fuel through the conduit 1 l is a valve [2 which is electrically operated. The fuel of the burner is ignited by a pair of ignition electrodes l3 and 14 which are operatively energized by an ignition transformer i5 consisting of a primary winding 16, energized from a common source of power, and a secondary winding H. An electric spark between the ignition electrodes will ignite the gas flowing from a pilot nozzle l8. Supplying fuel to the pilot nozzle [8 is a conduit I9 which has controlling the flow of fuel therein, a further electrically operated valve 20. Both valves l2 and 20 are of the type which are maintained open as long as energized and moved to closed position upon deenergization.

To indicate the need for operation of the burner ID, a thermostat 2| has been provided which may be seen to consist of a bimetal 22 which is operable upon the temperature falling and rising to move a switch blade 23 into and out of engagement respectively ith an associated switch contact 24. Located within a housing 3?, indicated by dotted lines, are the control circuits for actuating the valves I2 and 20 and ignition transformer I5 upon the demand for heat as indicated by thermostat 2I. Energized by the actuation of the thermostat 2| is a control relay I20 having a relay winding I2I which is operable when energized to move an associated switch blade I22 from engagement with a switch contact I23 into engagement with a further contact I24. Energized by the control relay I2!) is a main control electron discharge device 25 in the form of a triode having an anode 25, a control electrode 21, and a cathode 28. Energized by the current flow through the triode 25 is a relay 29 which may be seen to consist of a relay winding 3!], adapted to move a pair of switch blades El and 32 which are normally biased so that the switch blade'3l engages a contact 33 and the switch blade 32 'is biased out of engagement with the contact 34. When relay 3a is energized, the switch blades 3| and 32 engage contacts 35 and 34 respectively. A condenser 36 is connected across the relay winding 38 to function in a normal manner to by-pass th alternating current flowing in the energizing circuit for triode 25.

Energized by the transformer '45 is an electron discharge device 50 in the formof a triode having an anode 5|, a control electrode 52, and a cathode 53. Also energized by the transformer 45 is a further electron discharge device 54 in the "form of a triode having an anode 55, a control electrode 56, and a cathode 51. Associated with the inputof triode 50 is a biasing condenser 58,

"a filter network consisting of a resistor 59 and condenser 60, and a biasing resistor 6I.

Associated with the input of triode 54 are a pair of resistors 62 and 63. The output circuit of the triode 54 includes a relay 65 having a relay winding 66 which is adapted to move a pair of switch blades 61 and 68. The switch blades 61 and 68 are normally biased so that the switch blade 67 engages a switch contact 69 and the switch blade '68 is biased out of engagement with an associated contact Ill. When the relay is energized the switch blade 61 moves into engagement with an associated contact ll and the switch blade 63 moves into engagement with the associated contact Ill. A condenser I2 is provided to by-pass the alternating current around the relay winding 66. Also associated with the flame detectionportion of the control apparatus is an electrode I5 which is positioned ina manner to intersect the flame from either the pilot nozzle I8 or the burner Ill.

Normal operation of Figure 1 In considering the normal operation of the subject control'apparatus it will be assumed that control relays I20 and-Minor the'flame detection relay are energized. Under these conditions the ignition transformer will not be energized, the pilot valve 26 will not be energized and the main control valve I2 will not be energized. The thermostat 2I is used to indicate the need for operation of the burner It and upon such need the bimetal 22 will move the switch blade 23 into engagement with its associated contact 24. With blade 23 engaging switch contact 24 an energizing circuit is completed to the control relay I20 from the input power line Bil through conductors 8| and 82, contact 24, blade 23, bimetal 22, conductor 33, relay winding I2I, and conductors and ill to the other input power line 88. When this relay becomes energized, the switch blade I22 will move into engagement with contact I24 to complete an energizing circuit to the main control triode 2 5. This circuit to triode 25 may be traced from the input power line 88 through conductors B7, 85, and 84, relay winding '30, anode 26, cathode 28, conductor I25, switch blade I22, switch contact I24, and conductors I26 and 8 I back to the other input power line 86. It will be noted that this last traced circuit includes the relay winding 39. In the absence of any biasing voltage on the input of the triode 25 the resultant current flow will cause relay winding 30 to move the switch blades 3| and 32 into engagement with their associated switch contacts 35 and 3d respectively.

When switch blade 32 engages switch contact 35. an energizing circuit is completed to the ignition transformer is and the pilot valve 26. This circuit may be traced from the input power line '88 through conductors 8?, 85 and 85, switch blade 32, switch contact '34, conductors 90 and 9 I, switch blade 5?, switch contact 69, conductor 92, ignition transformer primary winding I6, and conductors 93 and 9 back to the other input power line 80. The energizing circuit to the pilot valve 20 is almost identical to the last traced circuit except relay I55 and this circuit may be traced from the that it does not include switch contacts of the input power line 88 through conductors 81, B5 and 89, switch contact 32, switch contact 34, conductors 9B and 95, pilot valve 26, and conductors S3 and'S i to the other input power line 813. With pilot valve 20 and ignition transformer I5 energized, fuel will pass through the conduit I9 to the pilot nozzle I8 where the spark across the ignition electrodes I3 and 54 will ignite the fuel.

The flame detector employed in the subject control apparatus is of the type that is adapted to utilize the rectifying characteristics of a flame bridging a pair of flame electrodes. It is a well known phenomenon that when a pair 0': flame electrodes are positioned in the path of a flame and voltage is applied to those electrodes there will be a current flow through the flame. The current flow through the flame will be greater in one direction than it is in the other, the direction of greatest electron conductivity being in the direction of propagation of the flame. Just how this is utilized in the present control apparatus will be understood from the discussion of the flame detector which follows.

The flame electrode circuit is used to bias triode 50 into and out of conduction in accordance with the presence or absence of flame that may be existing between the pilot nozzle I 8 and the flame electrode ?5. The flame detection circuit may be traced from the lower terminal or secondary 41 through conductors I0! and Itil, ground 99 ground 98, pilot nozzle i8, electrode 15, conductor -9'i,-condenser"58 and conductor 95 to the tap 48 5 of the secondary 41. As there'is alternating current on the secondary 4! there will be alternating current applied across the gap between the flame electrode I5 and the pilot nozzle I8 which will mean that there will be a unidirectional component of current flow through the last traced circuit which will tend to charge the condenser 58 to a predetermined voltage of a polarity which will be negative on the lower terminal and positive on the upper terminal. The condenser 58 will be so charged during the half cycle of the alternating power supply when the tap 48 is positive with respect to the lower terminal of secondary 41. On the following half cycle, the condenser 58 will discharge in a circuit that may be traced from the lower terminal of condenser 58 through resistors 59 and GI, conductor I01, secondary 41, tap 48 and conductor 96 to the upper terminal of condenser 58. The current flow through resistor BI will result in condenser 60 assuming a charge which will be negative on the upper terminal and positive on the lower terminal. The resistor 59 and the condenser 60 form a filter network which serves to smooth out any flame fluctuation occurring at the flame electrode I5 and changes in the charging rate of condenser 58. With condenser 89 being effectively charged by the charge on the condenser'58 the triode 50 will be biased to be nonconductive since the condenser 60 is connected directly between the control electrode 52 and the cathode 53. When triode 50 is nonconducting the triode 54 will be biased into conduction and will energize relay 85 in a manner to be explained hereinafter. The energizing circuit for the triode 54 may be traced from the upper terminal of the secondary 41 through conductor I06, relay winding 68, conductor I07, anode 55, cathode 51, and conductors I08, I03 and I02, back to the tap 48 of the secondary 41. The triode 54 will be conducting since the control electrode 56 is connected to a voltage divider consisting of resistors 62 and 63 connected across the upper half of the secondary 47, and is biased to be conductive since the control electrode will be positive with respect to the cathode on the conducting half cycle of the power source.

When the relay 85 becomes energized the relay winding 88 will move the switch blades BTI and 68 into engagement with their associated switch contacts TI and I respectively. When the switch blade 8i engages switch contact II and opens the switch contact 69 the ignition circuit to transformer I is deenergized as the energizing circuit for the transformer I5 was completed through switch blade 67 and switch contact 89, and the main control valve I2 will be energized by switch blade 8i engaging switch contact II. This energizing circuit may be traced from the input power line 88 through conductors 8'5, 85 and 89,'switch blade 32, switch contact 34, conductors 90 and 9|, switch blade 61, switch contact ii, conductor I09, main control valve i2, and conductors lit and 94 back to the other input power line 80. The system is now operating normaily with pilot valve 20 energized and the main control valve I2 energized.

As soon as the burner I0 has operated for a sufficient length of time the thermostat 2| will no longer indicate a need for operation of the burner so that the switch blade 23 will be moved out of engagement with the associated switch contact 24 by bimetal 22. This will open the energizing circuit to the control relay I20 so that the switch blade I22 will move from engagement with contact I24 into engagementwith contact I23. When blade I22 moves from engagement with contact I24, the energizing circuit to the main control tube 25 is openedand the relay 29 will become deenergized. When the blade I22 engages contact I23, the control electrode 21 of device 25 is connected to the cathode 28 by a circuit that may be traced from control electrode 21, through conductor I30, switch contact I23, switch blade I22 and conductor I25 to cathode 28. This circuit is provided to insure that the control electrode will be at the same potential as the cathode upon a subsequent demand for burner operation, as indicated by the reoperation of the thermostat 2|.

When relay 29 becomes deenergized, the switch blades 3| and 32 will move to their deenergized positions so that the switch blade 32 will be no longer engaging switch contact 34 and the energizing circuit to the pilot valve 20 and the main control valve I2 will be broken and the fuel supply to the burner I0 will be discontinued. With fuel no longer supplied to the pilot nozzle I8 there will be no flame emitting from the nozzle to intersect the flame electrode I5. With no rectifying action taking place in the flame electrode circuit the condenser 58 will not be charged to bias the triode 50 to be nonconducting. With triode 50 conducting its energizing circuit may be traced from the secondary 41 at tap 48 through conductors I02 and I03, resistor 63, conductors I04 and I05, anode 5|, cathode 53, and conductors I00 and I0! back to the lower terminal of the secondary 41. It will be noted that the last traced circuit includes the resistor 63 which will have a voltage drop across it on the conducting half cycle of the triode 50 such that the upper terminal will be negative. This voltage drop is utilized to maintain the triode 54 to be efiectively nonconducting when the triode 50 is conducting, since the triode 54 is phased to be conducting on the same half cycle as the triode 50. With both relays 29 and deenergized the control apparatus is in a condition for a further operating cycle.

Operation of Figure 1 on flame failure In the operation discussed so far no consideration has been given to the safety features of the control apparatus. One such feature provides for automatic shutdown in the event that there is a failure of the electrode I5 to detect the presence of flame. Assume that there is a need for operation of the burner and the thermostat 2| is closed so that the switch blade 23 engages switch contact 24 which action completes the energizing circuit to relay I20 and thereby to triode 25. With triode 25 energized the relay 29 will become energized so that the switch blades 3| and 32 will move into engagement with their associated switch contacts 35 and 34 respectively.

As explained above, when switch blade 32 engages switch contact 34 on the starting portion of the operating cycle the ignition transformer I5 is energized as well as the pilot valve 20. Normally fuel would emit from the burner nozzle I8 and the ignition electrodes I3 and I4 would ignite the same. In the event that there was no ignition of the fuel coming from pilot nozzle I8 there would be no flame intersecting the flame electrode I5 and there would be no rectification in the flame detection circuit to charge the condenser 58. With no charge on the condenser 58 the triode 50 will be biased in its conducting range so that there will be a current flow through the resistor 63 whichwill effectively bias the triode 54 to be .nonconclucting so that it will not energize the relay .65.

As noted above, the voltage drop across the resistor 63 is such that its upper terminal is negative and its lower terminal is positive. This voltage drop is utilized in the biasing circuit for the .main control triode .25 .by reason of its connectionto the biasing condenser 39. Inasmuch as it is desired to bias the main control triode 25 below the point necessary to maintain the relay 2'9 energized when there is no flame present in the burner it or the pilot nozzle I8 a biasing circuit must be established between the resistor 63 and. the biasing condenser 39. This circuit may be traced .from the upper terminal of the condenser 39 through conductor III, resistor 42, conductors H2 and we, resistor 63, conductors I03, 3, and I26, switch contact I24, switch blade I22, and conductor I25 back to the lower terminal of the condenser 39. It will be noted that this last traced charging circuit for the condenser 39 includes a resistor 42. The function of this resistor is to .delay the charging time of the condenser '39 a predetermined amount. If the condenser 39 is charged sufficiently negative by the voltageacross the resistor 63 the control electrode 2'! will bias the main control tube 25 below the point necessary to maintain the relay 29 energized and the control system will be rendered inoperative. To put the apparatus back in operation it is necessary to depress the manual 'reset lever 40 so that it engages switch contact 4!. This will effectively short circuit the condenser 39 so that it will discharge 'and'the main control tube 25 will once again become conductive to reenergize the relay 29 and attempt to start the burner in operation again.

charged sufficiently negative to cut the tube off or a flame is establishedat the burner.

The flame failure considered so far has been only in connection with the starting cycle. If flame is established prior to the time that the condenser 39 becomes fully charged, the condenser will be effectively shorted out and the control electrode 2'! and cathode28 of the main control tube 2 will beconnected directly together so that the control tube will remain conductive. This shunting circuit will occur only when both the main control relay 2% and the flame detection relay B5 are energized so that the switch blade 3! of relay 29 engages switch contact 35 and the switch blade 68 of relay 65 engages switch contact 13. With these two relays energized, a circuit may be traced from the control electrode 21 through conductors II! and H5, switch blade 68, switch contact 13, conductor I I 6, switch blade 3|, switch contact 35, and conductor H3 back to the oathode 23. This circuit is actually a short circuit connection which connects the control electrode 21 to the cathode 28 and with such a connection triode 25 will continue to conduct and maintain relay'29 energized.

Should the apparatus be operating normally so that thereis fuel being suppliedto both .the

pilot nozzle l8 and the burner I0 and there is a subsequent flame failure, the flame detection relay 65 will become deenergized. With the relay becoming deenergized the switch blad 51 will engage switch contact 69 so that the energizing circuit to the ignition transformer I5 will once again be completed. The energizing circuit to the main control valve I2 will be broken by the movement of the switch blade 61 out of engagement with its associated switch contact II and the shunting circuit for condenser 39, associated with the input of control tube 25, will be opened by the movement of the switch blade 68 out of engagement with its associated switch contact Ill. In the event that the reenergization of the ignition transformer I5 fails to establish combustion at the pilot nozzle I8 within a predetermined time the condenser 39 will be charged sufficiently through resistor 32 to bias the triode 25 below the point necessary to maintain relay 29 energized and when this occurs the switch blades 3i and 32 will move out of engagement with their associated contacts 35 and 34 respectively so that the pilot valve 23 and the ignition transformer I5 will be deenergized and the system will be inoperative until such time as the manual reset lever at is pushed into engagement with switch contact GI to once again discharge the condenser 33. With condenser 39 discharged by the reset lever actuation the control tube will once again become conductive and attempt to initiate operation of the burner andif combustion fails to take place the condenser 39 will once again be charged to a point where it will bias the control tube 25 to be effectively nonconducting.

Operation of Figure 1 on ground out As it ispossible to have .a condition where the flame electrode 55 will be short-circuited with the pilot nozzle I8, which condition is referred to as a ground out condition, it is desirable to see that the control apparatus does not become operative. With the electrode l5 shorted to the pilot nozzle i8 there can be no rectification of the flame detection circuit and therefore the condenser 58 will not be charged so that it will have no biasing effect on the triode 55 which will remain conductive sufficiently to maintain the triode 54 nonconductive as explained above. With the triode 54 effectively nonconductive, the relay will not become energized so that the shunting circuit around the condenser 39 will not be completed and the condenser 39 will be charged by the voltage existing across resistor .63, as explained above, to bias the main control tube 25 below the point necessary to maintain relay 29 energized; When relay 29 becomes deenergized both the ignition transformer 65 and the pilot valve 20 will become deenergized and the system will remain inoperative until such time as the manual reset lever is depressed to discharge the condenser 39.

Operation of Figure 1 upon false indication of flame As the control apparatus employs an electronic flame detector, it is desirable to employ some means of preventing operation of the control apparatus when that flame detector is falsely indicating flame as might occur should some of the elements within the triodes 50 or 54 become shorted or open circuited in such a manner that the triode 54 remains conductive and the relay 65 energized. This is accomplished in the present invention by applying an alternating current bias voltage to the control electrode 21 of the main control tube 25 whenever the relay 95 is energized and there is no demand for operation of the burner or when the relay 29 is deenergized. When the relay 29 is deenergized so that the switch blade 3I engages switch contact 33 and when the relay 55 is energized falsely indicating the presence of flame so that the switch blade 68 is engaging switch contact 10 it is possible to complete the biasing circuit to the control electrode 21 of the main control tube 25. This circuit may be traced from the tap 49 of the secondary 41 through conductor II9, switch contact 33, switch blade 3I, conductor I I6, switch contact 10, switch blade 68, and conductors H and III to the control electrode 21. To establish a common potential between the biasing voltage on the control electrode 21 and the voltage on the oathode 28 it is necessary to have the cathode 28 effectively connected to a point on the transformer secondary 41. This is done by direct connection of the cathode 28 through conductor I25, switch blade I22, switch contact I24, and conductors 82, H3, and I02 to the tap 48 of the secondary 41. It will be noted that this last traced circuit is completed only when the thermostat 2I is closed to energize the relay I20 upon a demand for more heat but since the control relay 29 is deenergized when the thermostat is open it will make no differenoe since the relay will not become energized due to the completion of the last traced biasing circuit. The voltage between the taps 49 and 48 of the secondary 41 are of such phase with respect to the alternating current voltage on the triode 25 that the control electrode 21 will be negative with respect to the cathode 28 on the normally conducting half cycle of the triode 25. This voltage will remain biasing the control electrode 21 until the' fault has been removed from the flame detection portion of the control apparatus. With triode 25 so biased, the current flow through the triode will not be sufficient to energize relay 29. It will be impossible to appreciably affect this biasing voltage by depressing the reset lever 43 because of the fact that the resistor 42 is tapped at 43 and there is suflicient resistance in the circuit shunting the control electrode 21 of the cathode 28 when the lever is depressed that the alternating current biasing voltage will not be short-circuited to permit en- 0 ergization of the main control relay 29.

As soon as the fault has been cleared from the flame detection portion of the control apparatus the relay 65 will become deenergized so that the switch blade 68 will move out of engagement with its associated switch contact and the alternating current biasing circuit will be interrupted to thereby permit operation of the control apparatus in the normal manner.

Figure 2 The apparatus shown in Figure 2 accomplishes the same type of control as that of the apparatus shown in Figure 1. In Figure 2, the components Which correspond to those of Figure 1 carry the same reference numerals. The circuits in Figure 2 have been slightly modified in the timing circuit and in the component checking circuit.

In Figure 2, the room thermostat 2I is effective to control appropriate electrical circuits within the housing I31, the latter of which initiate and check the operation of the pilot burner I8 and the main burner I0. Located within the housing I31 is a flame detection circuit which corresponds identically to that of Figure 1 except that a modifled relay I65 has been added in the output circuit of the discharge device 54. This relay comprises a relay winding I65, a plurality of switch blades I61, I60, I69 and I10. The switch blade I61 is normally biased by means not shown into engagement with an associated switch contact I12. When the relay is energized the switch blade moves into engagement with a contact I1I. Switch blade I68 is normally biased out of engagement with an associated contact I13 and switch blade I69 is normally biased out of engagement with a contact I14. Switch blade I10 is normally biased into engagement with a contact I15. Supplying power to the flame detection circuit is a transformer I45 having a primary winding I46 and a pair of secondary windings I41 and I48. The secondary winding I41 is tapped at I49. The secondary I48 is used to supply the filament voltages for the discharge devices of the flame detector and for the main control tube 25. This transformer is also used for alternating current biasing purposes in a manner which will be understood when the operation of the present figure is considered.

The operation of the flame detector shown in Figure 2 is the same as that of the flame detector shown in Figure 1 and the output control relay I65 will be energized when a flame is detected and will be deenergized when there is no flame or there is faulty operation at the flame rod 15.

A control relay I29 has been added to the output circuit of the main control tube 25 and this relay comprises a relay winding I30, and a plurality of switch blades I3I, I32 and 233. The switch blades are normally biased out of engagement with associated contacts I34, I35 and I36 and the blade I32 is biased into engagement within associated contact I31.

An additional control relay I50 is associated with the timing circuit on the input of the main control tube 25. This control relay comprises a relay winding I5I, a plurality of switch blades I52, I53 and I54 which are normally biased out of engagement with their associated switch contacts I55, I58 and I51. Associated with the relay I50 is a current limiting resistor I60.

Associated with the input of the main control tube 25 is a timing condenser I6I, a timing resistor I62 and a grid lead resistor I63. A pair of filament heaters I64 are connected to the sec ondary winding I48 and are utilized for heating the cathodes of triodes 25, 50, and 54.

Operation of Figure 2 In considering the operation of Figure 2, it will be noted that the apparatus as shown upon the drawing is in the deenergized position with the room thermostat not calling for burner operation and the control relays all deenergized. Also deenergized are the ignition device, the pilot valve and the main valve. When there is a need for burner operation the room thermostat 2I will close and will complete an energizing circuit to the main control tube 25. This energizing circuit may be traced from. the lower terminal of secondary I41 through conductors I and I8I, relay winding I30, conductor I82, anode 26, cathode 28, conductors I83, 226 and I84, bimetal 22, switch blade 23, switch contact 24, and conductors I and I88 to tap I49 on secondary I41. With this last traced energizing circuit complete, the current flow therethrough will be sufficient to energize the control l 11 relay I23 so that the switch blades I3 I, I32 and I 33 will moveinto engagement with their associated contacts I33, I33 and I33, respectively.

When switch blade I 33 engages contact I36, an energizing circuit is completed through the ignition transformer I5 and the pilot valve 23. This energizing circuit may be traced from the input power line 33 through conductors I33, I9I, and H12, switch contact I36, switch blade I33, conductor I93, switch contact I15, switch blade I'Ill, conductor I34, primary I5 of ignition transformer I5, andconductors I35. and I96 back to the other input power line 88,

The energizing circuit for the pilot valve 23 is almost identical to the above traced circuit except that the circuit does not include any contacts of the flame indicating relay I35. This circuit may be traced from the upper input power line 80 through conductors I93, ISI and I32, switch contact I33, switch blade I33, conductors I33 and I91, pilot valve 23, and conductors I35 and [-33 to'the. lower input power line 88.

Also energized, upon the energization of the control relay I23 is the control relay I53. The energizing circuit for this relay may be traced from the input power line 8i! through conductors I90 and I9I', switch contact I34, switch blade I3 I, conductors 200, switch contact I12, switch blade I61, conductor 2I1I, conductor 2E3, relay winding I5 I and conductors 234 and 235 to the other input power line 83. When relay I38 becomes energized a holding circuit therefor is completed which is independent of the relay contacts of either relays I29 and I35 and this holding circuit may be traced from the input power line 33 through conductors I93 and 2&2, switch blade I52, switch contact I55, resistor I53, conductor 233, relay winding I5I, and conductors 2G4 and 235 to the other input power line 38. The further circuit. completed by the energization of the relay I5!) is a charging circuit for the timing condenser IBI. It will be recalled that in considering the operation of the flame indicator in Figure 1, there was a voltage drop across the load resistor 63. such that the upper terminal of the resistor was negative and the lower terminal was positive when the triode 5!! is on the conducting half cycle of the power supply. With a condenser E l connected in parallel with the resistor I53, the polarity across the resistor I53 will then be maintained there by the fact that on the half cycles in which the tube 53 is not conducting, the condenser 64 will be discharging through the re sistor 63 and will be maintaining the polarity thereon. This charging circuit may be traced from the lower terminal of resistor 63 through conductors 2H} and I 35, switch contact 25, switch blade 23', bimetal 22, conductor I34, condenser IBI, conductor 2, switch contact I56, switch blade I53, conductor 2 I2, switch blade I53, switch contact I51, timing resistor I 62, and conductor 2I3 back to the upper terminal of resistor 33. This charging circuit, when completed, will start charging the timing condenser I6! so that its upperterminal will be negative with respect to its lower terminal.

If a flame is established at the pilot nozzle I3, the presence of the pilot flame will be detected by the flame rod assembly and will be indicated by the operation of the relay I63. When this flame, indicating relay becomes energized the switch blades I61, I38, I69 and I19 will all move to the energized position where the blade I31 will engage switch contact I1I, blade I68 will engage contact I13 and blade I69'wil1 engage contact I 14. The blade I10 will move'out. of. engagement with contact I15. When blade I'GS engages contact I14 the control electrode 21 is connected" directly to the cathode 28 of the main control tube 25 so that any charge upon the timing condenser I6I will have no efiect upon the operation of the control tube. This shorting circuit may be traced from the control electrode 21' through conductors 2I5 and 2I6, switch blade I63, switch contact I14, conductor 2I1, switch blade I32, switch contact I35, conductor 2I8 to cathode 28. With this shorting circuit complete, the control tube will stay conducting and will maintain the control relay I29energized.

When the flame indicating relay I65 becomes energized the energizing circuit to the ignition transformer I5 is broken by the movement of switch blade I 13 out of engagement with its contact I15. Inasmuch as thepilot valve is energized independently of this last switch contact, the pilot valve will remain energized. When the switch blade I63 engages contact I13, an energizing circult-is completed tothe main valve I 2 and this energizing circuit may be traced from the input power line 83 through conductors I93, I9I and [32, switch contact I36, switch blade I33, conductors I 93 and 2223, switch contact I13, switch blade I38, conductor 222, main valve I2, and conductors 223 and I93 back to the other input power line 83. When the switch blade I61 engages contact ill, a short circuit is completed across the relay winding I 5i so that the relay I50 willbecome deenergized. This shorting circuit may be traced from the input power line 88 through conductors 263 and 225, switch contact I1 I, switch blade I61, conductor 23!, conductor 233, relay winding I5I and conductor 234. back to conductor 205. When relay I53 becomes deenergized, the switch blades: will move out of engagement with their associated contacts and the charging circuit for the timing condenser ISI will be opened and the holding circuit for the. relay itself will be opened.

The apparatus is now operating normally with the main control. relay I23 energized, the flame indicating relay I35 energized and the control relay I53 deenergized. Further, the ignition transformer is deenergized and the main pilot valve and main valve are energized.

As soon as the thermostat 2I no longer indicates the need for burner operation, the switch blade I23 will move out of engagement with contact 24 and this will open the energizing circuit to the main control tube 25. With the control tube 25 deenergized, the main control relay I29 will become deenergized. When the control relay I 29 becomes deenergized the switch blade I33 will move out of engagement with contact I36 to open the energizing circuit through the main valve I2 and the pilot valve ZIlso that the burner assembly will be shut down. When flame is no longer detected by the flame rod 15, the flame indicating relay I65 will become deenergized. When this occurs, the apparatus will be completely shut down and will be ready for another operating cycle upon a further demandfor burner operation as indicated by the operation of the room thermostat 2I l Operation of Figure 2 on flame failure If the operating cycle is started in a normal manner by the room thermostat first closing to indicate a need for burner operation, the control relay I 29 and the control relay I53 will become energized, in the manner described above. When the relay I29 becomes energized the pilot valve 20 and the ignition transformer I will be energized to attempt to establish a flame at the pilot nozzle I8. When the relay I50 becomes energized the charging circuit to the timing condenser IEI is completed from the load resistor 63. If no flame is detected by the flame rod I5, the flame indicating relay I65 will remain in the deenergized position and the charging circuit to condenser I6I will not be interrupted. This will mean that after a predetermined time, a time dependent upon the size of the timing resistor I62 and the timing condenser IBI, the condenser IBI will assume a charge which is negative on the upper terminal and positive on the lower terminal and of sufficient magnitude to bias the main control tube 25 below the conducting point necessary to maintain the control relay I29 energized. When the relay I29 becomes deenergized the ignition transformer and the pilot valve will be deenergized. Inasmuch as the control relay I52 establishes a holding circuit for itself, independent of any contact with either relay I29 or IE5, this relay will remain energized and when so energized the charging circuit to the timing condenser IGI will remain intact and will maintain the bias on the control group 25 below the point necessary to pull in the control relay I29. The apparatus will stay in this condition until such time as the reset button is actuated so that the switch blade 40 moves into engagement with contact 4|. When this occurs, the condenser I6I will be shorted out by a circuit that may be traced from the upper terminal of condenser IGI through conductor 2| I, switch contact I55, switch blade I53, conductor 2I2, switch blade I54, switch contact I51, switch contact II, switch blade 40, and conductor 226 to the lower terminal of condenser IBI.

When the condenser Itl has been discharged, it is possible to reenergize the main control relay I29 since the control electrode 21 will have the same potential as the cathode 28 and the current flow through relay 25 should be suincient to energize the main control relay I29. This will mean that a further attempt will be made to establish flame at the pilot nozzle I8. If flame is established, the operation of the apparatus will be as explained above, and the flame will be indicated by the operation of the flame indicating relay I65 which in turn will energize the main valve I2 so that the apparatus will be operating normally.

In the event that the apparatus should be operating normally and there should be a subsequent flame failure so that the flame indicating relay I65 became deenergized, it is also desired that the apparatus be rendered inoperative and the control valve be deenergized. It will be noted that as soon as the flame indicating relay I85 becomes deenergized, with the room therstat 2| still calling for operation of the burner, the short circuit around the relay winding I5I will be removed and the relay will become energized. When the relay does become energized the charging circuit for the timing condenser IBI is completed and, after a predetermined time, the condenser will charge and will bias the control tube 25 to a point where its conductivity will no longer maintain the control relay I29 energized. When the relay I29 becomes deenergized the energizing circuit to the main valve and pilot valve will be deenergized and the burner apparatus will be completely shut down. In order to put the apparatus back in operation it is necessary that the reset switch 40 be actuated to discharge the timing condenser IGI and when this occurs, a further attempt will be made to establish burner operation and if this fails, the apparatus will again be shut down.

Operation of Figure 2 upon false indication of flame In the event that there is a false indication of flame as would occur if the flame indicating relay I55 were to remain in the energized position after the burner has been shut down by the opening of the room thermostat 2I, it is desired that there be no further operation of the control apparatus until the fault causing operation of the flame indicating relay is removed. The maintaining of the apparatus inoperative is accomplished in somewhat the same manner as was accomplished in the apparatus shown in Figure 1. In the present figure, when there is a false indication of flame, an alternating current bias is obtained from the secondary winding supplying energizing voltages for the filaments I54. This alternating bias from filament secondary I48 is applied between the control electrode 21 and cathode 28. The circuit from the secondary I48 may be traced from the upper terminal of the secondary through conductor 23E, switch contact I31, switch blade I32, conductor 2I'I, contact I'M, switch blade I59, and conductors 2 I 8 and M5 to the control electrode 2?. The connection of the secondary I48 to the cathode may be traced from the lower terminal of secondary I48 to conductor 23I, conductor I85, conductor I85, switch contact 24, switch blade 23, and conductors I84, 225 and I83 to cathode 28. It will be noted that this last traced circuit is completed only upon the closing of the room thermostat 2 I. This will be of no significance inasmuch as soon as the biasing circuit is completed, a negatively phased alternating current bias is supplied between the control electrode 21, cathode 28, such that the control electrode 21 will be negative with respect to the cathode 28 on the half cycle when the anode 26 is positive with respect to the oathode, or on the normally conducting half cycles. With the control electrode biased negatively with respect to the cathode on the conducting half cycle of the tube, the current flow will not be suflicient to energize the control relay 29 and the apparatus will stay in a shutdown position until the fault causing fake operation of the relay IE5 is removed. As in Figure l, the depressing of the reset switch will have no effect upon the operation upon a component failure. This will be understood when it is noted that the relay I50 will be deenergized with relay I65 operating due to the short circuit around the relay. With relay I50 deenergized, it is impossible to complete a shorting circuit between the cathode 28 and control electrode 2'! by the depressing of the reset switch 40.

Conclusion From the foregoing it can be seen that I have provided a burner control apparatus which is operative to shut the burner down upon a flame failure, to provide against ground out conditions of the flame detection circuit, and to maintain the control apparatus inoperative when there is a false indication of flame by the flame detection relay. Further it may be seen that I have provided a control apparatus which employs condenser timing for establishing the safety shutdown of the control apparatus and provi ing with that feature a fail safe circuit which can be rendered ineffective upon a flame failure or canbemaintained eifective continuously upon a false. indicationof flame.

Although I have described my invention in connection with a gas burner control, and while it is particularly well adapted for use there, it will be obvious to those skilled in the art that my invention could be applied to any burner control apparatus where it is desired to use an electron discharge device and a condenser timed input safety biasing circuit. Therefore, I intend to be limited solely by the scope of the appended claims in which I claim:

1. Apparatus for controlling a fuel burner having a control means for indicating the need for burner operation comprising in combination, an electron. discharge device adapted to be energized by the control means, relay means, said relay means having switch. contacts adapted to energize means for initiating operation of the burner, means connecting said relay means in the energizing circuit of said discharge device, biasing means, a source of biasing potential, time delay means, means connecting said biasing means, said time delay means and said source of biasing potential in biasing relation to said discharge device so that said discharge device will be rendered inoperative after a predetermined time delay, electric switching means adapted to be actuated by means indicating proper burner operation, means including said electric switching means for rendering said biasing means ineffective when said electric switching means is actuated and indicating the presence of combustion, additional biasing means, and means including said electric switching means connecting said additional biasing means to said dis charge device when said electric switching means is in actuated position and indicating the presence of combustion and there is no demand for operation of the burner to maintain said discharge device inoperative upon a subsequent demand for burner operation.

2. Apparatus for controlling a fuel burner having a control means for indicating the need for burner operation, comprising in combina tion, an electron discharge device having input and output terminals, a source of power, an electric circuit adapted to be completed by the control means for connecting said discharge device to said source of power, a relay, means connecting said relay to the output terminals of said discharge device so that said relay is energized when the current flow in said discharge device is greater than a predetermined value, means actuated by said relay for initiating operation of a burner when said relay is energized, a condenser, means connecting said condenser in biasing relation to the input terminals of said discharge device, a charging circuit connected to said condenser by means including the control means for charging said condenser after a predetermined time delay to a potential which will bias said. discharge device below the point necessary to maintain said relay energized, electric means adapted to be energized by means indicating proper burner operation, switch means actuated by said electric means for rendering inoperative said charging circuit so that said discharge device vwill remain operative, a out 01f circuit including said source of power, means connecting said cut off circuit to said discharge device, and further switch means actuated by said electric means for completing said out off circuit only when. said relay is deenergized and said switch means is in actuated position so that said discharge device will be maintained inoperative upon a subsequent demand for. burner operation by the control means.

3. In a control system for a fuel burner. having a control means associated therewith for in.-- dicating, the need for burner operation, in combination, an electron discharge device adapted to be energized by the. control means, a relay having switch contacts for initiating operation of the burner, means connecting said relay in. circuit with said. discharge device, a condenser, means connecting said condenser in current. controlling relation to said discharge device, a charging circuit connected to said condenser, said charging circuit being operable to. charge said condenser after a predetermined time delay following the. operation of the control means. so. that said. condenser will. reduce the. current. flow in said. discharge device below the point necessary to maintain said. relay energized, electrically operable means having switch contacts. and. adapted to be energized by combustion responsive means, means including switch contacts actuated by said electrically operable means for rendering said charging circuit ineffective, biasing means, circuit means connecting. said biasing. means to. said. discharge device, and means including switch contacts of said electrically op-- erable means and switch contacts of said relay for completing an electrical circuit from said biasing means to said discharge device to maintain said device inoperative when there has been no need for operation of the burner and saidcombustion responsive means is indicating the presence of combustion and the control means subsequently indicates a need for burner operation.

4. Apparatus for controlling a fuel burner system having a fuel burner and a control means for indicating the need for operation. of the burner, comprising in combination, a source of power, an electron discharge device, a relay, an electric circuit adapted to be completed by the control means for connecting said discharge device and said relay in an energizing circuit to said source of power, means actuated by said relay when energized for initiating operation of the burner, electric means adapted to be energized by combustion responsive means, first and second biasing circuit means, means including said electric means and said relay for connecting said first biasing circuit means in current controlling relation to said discharge device to render said device inoperative after a predetermined length. of time when only said relay is operative, and means including said second biasing circuit means to maintain said device inoperative when said combustion responsive device is falsely indicating the presence of flame following a normal burner shutdown and the control means is subsequently actuated.

5. A control apparatus for a fuel burner system having a fuel burner and a control means for indicating the need for burner operation, comprising in combination, a source of power, an electron discharge device, a relay having in and out switch contacts, an electric circuit connecting said discharge device and said relay in an energizing circuit when said circuit is completed by means including the control means, means actuated by certain of the in contacts of said relay for initiating operation of the burner, combustion responsive means having in switch contacts actuated when a burner flame is present, first and second biasing means, first circuit means including the control means for connecting said first biasing means to said discharge device in current controlling relation to render said device inoperative after a predetermined length of time, second circuit means including in contacts of said relay and said combustion responsive means for rendering said first biasing means inefiective when a burner fiame is present, third circuit means including in contacts of said combustion responsive means and out contacts of said relay connecting said second biasing means to said discharge device to maintain said device inoperative when said combustion responsive means is operating falsely and there is a subsequent indication of a need for burner operation by the control means.

6. Control apparatus for a fuel burner system having a fuel burner and a control means for indicating the need for burner operation, comprising in combination, first and second electron discharge devices, first and second relays having a plurality of switch contacts, a source of power, a first electric circuit including said control means for connecting said first relay and said first discharge device to said source of power, switch means actuated by said first relay for initiating operation of the burner, a second electric circuit connecting said second relay and said second discharge device to said source of power, a burner flame responsive circuit, means connecting said circuit in current controlling relation to said second discharge device so that said discharge device will render operative said second relay on the presence of flame, first and second biasing means, circuit means connecting said first biasing means to said first discharge device when said first circuit is completed so that after a predetermined length of time said first discharge device will be rendered inoperative, a third electric circuit including switch means actuated by said first and second relays for short circuiting said first biasing means, and a fourth electric circuit including switch means actuated by said second relay connecting said second biasing means to said first discharge device to maintain said first discharge device inoperative when said flame responsive circuit is falsely maintaining said second discharge device operative and there is a subsequent indication of a need for burner operation by the control means.

7. Control apparatus for a fuel burner system having a fuel burner and a control means for indicating the need for burner operation, comprising in combination, an electron discharge device having an anode, cathode and control electrode, an alternating current source of power, a relay, a first electric circuit for connecting said relay and the anode-cathode circuit of said discharge device to said source of power so that said device is conductive on alternate half cycles of said source of power, switch means actuated by said relay for initiating operation of the burner, a condenser, means connecting said condenser between the control electrode and cathode of said discharge device, a source of charging current, time delay resistive means, a second electric circuit connecting said source of charging current through said time delay resistive means to said condenser so that said condenser is slowly charged to bias said discharge device below the point necessary to maintain said relay energized, combustion responsive means actuated on the presence of flame, means including said combustion responsive means when actuated for discharging said condenser to maintain said discharge device operative, a third electric circuit for effectively connecting said source of power to the control electrode of said discharge device only when said combustion responsive device is actuated and said relay is deenergized, said third circuit having an alternating current phase opposite the phase of said first circuit,

8. In a safety control system for apparatus normally operable when energized to establish a predetermined condition, in combination, means including an electron discharge device having an input circuit and controllin said apparatus so that said apparatus is energized only when said discharge device is conductive, first means responsive to a condition indicative of the need for conduction of said device for operating said controlling means, means including a condenser in the input circuit of said device for controlling the conductivity of said device to cause the current flow to maintain a predetermined level for a predetermined time following a call for operation by said first responsive means, second means independent of said controlling means responsive to the establishment of said predetermined condition for shunting said condenser so as to maintain said discharge device conductive, and biasing means connected to said device for maintaining said device nonconducting when said first responsive means becomes operative indicating the need for operation of said control means and said second means is operating falsely.

9. Control apparatus for a fuel burner system having a fuel burner and a condition responsive means for indicating the need for burner operation, comprising in combination, means for initiating operation of the burner, control means for said initiating means including an electron discharge device having an input circuit and an output circuit, said control means being effective to operate said operation initiating means only when said discharge device is conductive, and means for controlling the conductivity of said discharge device, said last named means comprising said condition responsive means operable to complete an energizing circuit for said discharge device upon the need for operation of a burner, a first biasing circuit which is operable to deenergize said discharge device after a predetermined time when the burner fails to operate, a combustion responsive means which is operable to shunt out said first biasing circuit when said combustion responsive means and said responsive means are operative, and a second biasing circuit includin said combustion responsive device connected to the input of said discharge device to maintain said discharge device inoperative only when said combustion responsive means is operating falsely and there is a subsequent demand for burner operation by the condition responsive means.

10. Control apparatus having means for controlling a fuel burner to establish combustion, comprising in combination, means including a normally conducting electron discharge device having a control electrode for initiating operation of the burner controlling means when said discharge device is conductive, and regulating means for controlling the conductivity of said discharge device, said regulating means including switch means for completing the conductive circuit of said discharge device upon need for operation of said burner controlling means to establish combustion, means responsive to establishment of combustion for maintaining said discharge device conductive when said apparatus is functioning properly, biasing means, and means including said conductive when combustion responsive means connecting said biasing :means to the control electrode of said discharge device for maintaining said device nonsaid combustion responsive means indicates establishment of combustion and when said switch means are not indicatin need for operation of said burner controlling mean to establish combustion.

:nection, means including combustion responsive means for maintaining said relay means operative upon the establishment of combustion, a biasing voltage, and means including said combustion responsive means for connecting said biasing voltage to said control electrode to apply a voltage thereto and prevent operation of said discharge device when said combustion responsive .means is falsely indicating the presence of combustion.

12. Control apparatus for a fuel burner, comprising in combination, an electron discharge device having an anode, a cathode and control electrode, a source of power, means connecting said source of power in energizing relation to said anode and said cathode, relay means connected in said last named connection adapted when energized to initiate operation of the burner, a condenser timing circuit, means connecting said timing circuit in current fiow controlling relationship to said discharge device, combustion responsive means for indicating proper operation of the burner, said combustion responsive means comprising a source of signal potential which is indicative of the presence or absence of combustion, means connecting said combustion responsive means to said timing circuit so that upon failure of said combustion responsive means to indicate the presence of combustion said timing circuit will be charged after a predetermined time delay by said signal potential to render said discharge device nonconductive and said relay means deenergized, and further means including said combustion responsive means for shunting said timing circuit when there is a flame at the burner.

13. Control apparatus for a fuel burner having control means for indicating the need for operation of the burner, the combination comprising, a source of power, an electron discharge device having an input and output circuit, a, first control relay for initiating burner operation, means connecting said relay in the output circuit of said device, circuit means adapted to be completed by the control means for connecting said device in an energizing circuit to said source of power, biasing means, a timing condenser, a second control relay, means including said first relay when energized for connecting said second relay to said source, means including said second relay for connecting said biasing means to said icondenser, means connecting said condenser to said input of said device for rendering said device inoperative after a predetermined time following the energization of the second relay, and further means for rendering said biasing means ineffective to charge said condenser when there is an indication of burner flame.

14. Control apparatus for a fuel burner having control means for indicating the needfor operation of the burner, the combination comprising,

a source of power, an electrondischarge device having an input and output circuit, a first control relay for initiating burner operation, means connecting said relay in the output circuit of said device, means adapted to be'energized by the control means for connecting said device in an energizing circuit to said source of power, biasing means, a timing condenser, a second control relay, means including said first relay when energized for connecting said second relay to said source, means including said second relay for connecting said biasing means to said condenser, means connecting said condenser to said input of said device for rendering said device inoperative after a predetermined time following the energization of said second relay, and further means for rendering said biasing means ineffective to charge said condenser when there is an indication of burner flame and to render inoperative said second relay means.

15. Control apparatus for a fuel burner having control means for indicating the need for burner operation, the combination comprising, a source of power, an electron discharge device, a control relay for initiating burner operation connectedin circuit with said device, means adapted to be energized by the control means for connecting said device and said relay in an energizing circuit to said source, energizable means for indicating proper burner operation, first biasing circuit means including said burner operation indicating means for rendering inoperative said device after a predetermined time delay upon a failure of burner operation, a reset switch associated with said first biasing circuit means for rendering said device and relay operative to attempt to initiate a further burner operation, and second biasing circuit means for rendering said device inoperative upon said indicating means operating falsely, said reset switch being ineffective to initiate operation of said device when said indi cating means is operating falsely.

16. Control apparatus for a fuel burner having control means for indicating the need for operation of the burner, the combination comprising, a source of power, an electron discharge device having an input and output circuit, a first control relay for initiating burner operation, means connecting said relay in the output circuit of said device, means adapted to be energized by the control means for connecting said device in an energizing circuit to said source of power, biasing means, a timing condenser, a second control relay, means including said first relay when energized for connecting said second relay to said source, means including said second relay for connecting said biasing means to said condenser, means connecting said condenser to said input of said device for rendering said de vice inoperative after a predetermined time following the energization of said second relay, a reset switch for shunting said timing condenser to initiate operation of said device following deenergization of said device by said timing condenser, means responsive to proper burner operation for rendering said second relay inoperative and for shuntin said input, and means including said second relay for rendering said reset switch ineifective when said burner operation responsive means is operating falsely.

17. Control apparatus for a fuel burner having control means for indicating the need for operation of the burner, the combination comprising, a first electrical-switching means adapted to be energized by thecontrol means, an electron discharge device, a source of power, a second electrical switching means, means including said first switching means when energized for connecting said device and said second switching means in an energizing circuit to said source, means actuated by said second switchin means when energized for energizing the burner, a third electrical switching means adapted to be energized upon proper operation of the burner, first and second biasing circuit means, means including said third switching means and said second switching means for connecting said first biasing circuit means in current controllin relation to said discharge device to render said device inoperative aiter a predetermined length or time when onl said first and second switching means are operative and said third is inoperative, and means including said second biasing circuit means to maintain said device inoperative when said third switchin means is falsely indicating proper burner operation, said first switching means is energized and said second switching means is deenergized.

18. Control apparatus for a fuel burner having control means for indicating the need for operation of the burner, the combination comprising, a first electrical switching means adapted to be energized by the control means, an electron discharge device, a source of power, a second electrical switching means, means including said first switching means when energized for connecting said device and said second switching means in an energizing circuit to said source, means actuated by said secon" switching means when energized for initiating burner operation, a third electrical switching means adapted to be energized upon pr per operation of the burner, biasing means, and means said third switching means and said second switching means for connecting said biasing means in current controlling relation to said 0 scharge device to render said device inoperative after a predetermined time when only said first and second switching means operative said third switching means is inoperative, and means in cluding said first switching for rendering ineffective said biasing means when said first switching means is rendered inoperative upon the energizing circuit therefor being opened by the control means.

J OHN lvl. VIIIEON.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,170,497 Gille Aug. 22, 1939 2,243,071 Crago May 2'7, 1941 2,293,474 Schneider Aug. 18, 1942 2,368,893 Spangenberg et 'al. Feb. 6, 1945

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