US2964102A

US2964102A - Ignition safety control for fluid fuel burners

Info

Publication number: US2964102A
Application number: US721070A
Authority: US
Inventors: Irving S Cassell; Lewis D Eckard
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-03-12
Filing date: 1958-03-12
Publication date: 1960-12-13
Anticipated expiration: 1977-12-13

Description

Dec. 13, 1960 l. s. cAssl-:LL ET AL 2,964,102

IGNITION SAFETY CONTROL FOR FLUID FUEL BURNERS 2 Sheets-Sheet 1 Filed March l2, 1958 INVENTORS y Cassell Le s DEC/17d BY AUDE/VIK? Dec. 13, 1960 s, CASSELL ET AL 2,964,102

IGNITION SAFETY CONTROL FOR FLUID FUEL BURNERS 2 Sheets-Sheet 2 Filed March 12, 1958 United States Patent O l 2,964,102 IGNITION SAFETY CONTROL FOR FLUID FUEL BURNERS Irving S. Cassell, Fairfax, Va. (704 Tall Oak Court,l Annandale, Va.), and Lewis D. Eckard, 1857 Newton St.,

NW., Washington 10, D.C.

Filed Mar. 12, 1958, Ser. No. `721,070 6 Claims. (Cl. 158-28) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes Without the payment of any royalty thereon.

This invention relates to electric control systems particularly suitable for burners using fluid fuel, including gas and liquid fuels.

In the past, electric control systems have been devised to supervise the flame in liquid fuel burners. Such systems require a time delay commonly known as a trial for ignition period, before the fuel is cut off in the event of ignition failure. Explosions in these liquid fuel burners have been attributed to variations in the amount of air or fuel supplied within the time delay period.

For gas fuel burners, electric control system have been devised to supervise the pilot flame, but these systems have not included means for supervising the igniting of the pilot. In control systems utilizing a spark as the igniting means, gas has been permitted to enter the pilot before sparking and, in the event o-f spark failure, the fuel is not immediately shut olf. Further, in many control system no means is provided for shutting off the gas when the pilot goes out and purging the combustion chamber in the event the spark does not ignite the fuel flame.

It is the principal object of this invention to provide an electric control system which assures complete safety during ignition, operation, and shut off of all types of fluid fuel burners.

Another object of this invention is to provide an electric control system which will prevent fuel from entering a combustion chamber in the event of ignition failure.

It is another object of this invention to provide an electric control system which requires the presence of an igniting means before fuel is permitted yto enter the combustion chamber or pilot.

It is another object of this invention to provide an electric control system for a burner which requires the presence of `all the necessary components for assuring the ignition of the fuel such as ythe igniting means, fuel pressure, air and if desired components outside the burner, but on which the burner is to act.

It is another object of this invention to provide an electric control system which is a combination of a primary control system and a secondary control system. The primary system requires the means for ignition before fuel enters the combustion chamber and the secondary system thereafter providing a trial for ignition period for the main burner.

Another object of the invention is to provide an electric control system which will instantaneously cut off the fuel supply in the event of flame failure.

Still another object of this invention is to provide an electric control system having a trouble shooting circuit providing a time delay period for purging the combustion chamber of combustible products in the event of failure of the electric control system.

Specific embodiments of this invention are shown 1n the accompanying drawings in which- Fig. 1 illustrates diagrammatically an arrangement of apparatus and electrical circuits as the same might be employed in a liquid fuel spark ignited burner; and Fig. 2 illustrates diagrammatically an arrangement of apparatus and electrical circuits as the same might be employed in a gas fuel spark ignited burner.

Referring now more specifically to the drawings, cor-v responding reference numerals represent corresponding parts in each of the several views. In the liquid fuel ignited by spark form shown in Fig. l, the burner mechanism includes a motor 10, a blower 11, and a duct 12 which conducts ,air to a combustion chamberf14 and through which the fuel inlet duct 16 leads to a nozzle 18. The supply of fuel to the burner is controlled by a fuel solenoid actuated valve 20 which is closed unless opened for operation of the burner `as will be hereinafter explained.

The flame issuing from the burner is indicated at 22. The burner is equipped with ignition electrodes 23 energized by a secondary winding 24 of a transformer 26 whose primary Z8 is connected across a source of power 30.

A photoconductive cell 32 of the lead sulfide type, is mounted in a housing 34 having walls defining a passage to the photoconductive cell. The passage is so positioned in relation to the fuel burner nozzle 18, the electrodes 23 and the photoconductive cell 32 that the photoconductive cell will receive energy lfrom the sparking electrodes 23 only when the spark is in the exact position to ignite fuel which will be entering the combustion chamber in response to the spark exciting the photoconductive cell, and after ignition from the burner flame 22. This particular type of photoconductive cell has a resistance -which varies in proportion to the intensity of the energy, eg. infrared, ultra violet, radiating from the spark or burner flame or from a torch. This variable resistance permits the use of an electronic circuit which amplifies only the pulsating frequency peculiar to flame or spark radiation and therefore is not affected by hot refractory or other sources of infrared energy.

The electrical control system may include any of the usual limit controls, or circuit interrupters, which for a steam cleaner or a steam heating system may include a high pressure switch 36, a Ilow water flow switch 38, a low fuel pressure switch 40, a thermostat 42, and an air flow switch 44. The high pressure switch 36 is normally closed but is actuated by excessive steam pressure of the steam cleaner or heater to provide a safety control. The low water flow switch 38, the low fuel pressure switch 4f), and the air flow switch 44 are normally open but are actuated responsive to the delivery of* their respective components in proper amounts to the steam cleaner or heater system. The thermostat 42 is normally closed and calling for heat from the combustion chamber.

The power line from the source of alternating current 30 is represented by

conductors

46 and 48 and when a main switch 50 is closed, the ignition transformer 26 is energized, the current passing through conductor 46, main switch 50,

conductors

60 and 51, to a time delay relay 52 normally closed' and conductor 54 to the primary 2S of the ignition transformer 26 and returning through conductors 56, '76, and 48. Energization of the ignition transformer 26 produces a spark between the burner electrodes 23.

Simultaneously with the closing of the main switch 50, the motor 10 is energized through a circuit which may be traced as follows: From lthe source of power 30 through conductor l46, main switch 50, conductor 60 to the motor 10 and return to the source of power 30 through conductor 66 to the normally closed high pressure switch 36 and conductor 48. In heating systems, water and fuel may be gravity fed to the system or operation of the motor 10l may cause a water pump to pump water to a heating coil, a fuel pump to pump fuel to the combustion chamber, as well as actuate a blower to force air into the aircombustion chamber.

As these operations are peculiar to all systems of this type', the pumps and sources of water and fuel are not shown in the drawings.

l When -thewater and fuel pumps, not shown, and blower 11 meet the minimum requirements of their respective switches, or if the water and fuel are gravity fed when the water andv fuel are present in the minimum amount, these switches close and with the water in the heating coil calling forheat, the thermostat switch is already closed completing a circuit to energize an amplitier 72.. This powercircuit maybe traced in Fig. l as follows: From thesource of power 30 through conductor 46, main switch 50,

conductors

60 and 70 to the normally opened low water flow switch 38 which is connected in series with the normally opened low fuel pressure switch 40, which in turn is connected in series with the normally closed thermostat 42, which in turn is connected in series with the normally open air flow switch 44 connected to an amplifier 72 by conductor 74; and from the amplifier back to the source of power 30 through return conductors'75, 76, and 48.

When the spark of the electrodes 23 is in proper position to ignite fuel entering the combustion chamber, the photoconductive cell is excited and the cells output is applied to the input of amplifier 72 where it is amplified. The amplified signal is applied to a relay coil 79 to close immediately relay contacts A and B of a circuit control relay 78 for the fuel solenoid 8S and ignition time delay relay 52. Relay contact A is slow opening and in this form of the invention is preferably designed to remain closed tive 'seconds after deenergization of the coil 79. l kClosing theY circuit control relay 78 completes two circuits, one to the fuel solenoid valve 20 through contact B whereby the valve is opened to permit fuel to enter the combustion chamber, and the other through contact A to the ignition time delay relay 52 which, being a slow opening type relay, acts in two and onehalf seconds to break the ignition circuit to cut olf the spark of the sparking electrodes 23.

The circuit to the fuel solenoid may be traced as follows: From the source of power 30 through conductor 46, main switch 50,

conductors

60 and 82 to contactor B of the circuit control relay 78, conductor 84 to a solenoid 85 of the fuel solenoid actuated valve 20 and return through

conductors

86, 76, and 48.

The circuit to the time delay relay 52 may as follows: From the source of power 3ft through conductor 46, main switch 50,

conductors

60 and 82 to the time delay contact A of the circuit control relay 78, through conductor 88 to a coil 80 of the ignition time delay relay 52 and return to the source of power through

conductorsv

90 and 48.

In operation, the main switch 50 is closed energizing simultaneously the sparking electrodes to produce a spark in the combustion chamber and the motor to operate the water pump, fuel pump, and air blower. When proper amounts of water, fuel, and air are available to their respective switches, they close, and with the thermostat calling for heat the power circuit to the amplifier is closed and the amplifier is energized. With the Yamplifier energized, the signal resulting from exposure of'the cell to the spark is amplified and this amplified signal is applied to the relay coil 79 of the circuit control relay. The relay coil operates to close immediately contacts A and B. The closing of contact B permits the source of power to energize the solenoid of the solenoid actuated fuel valve to open the valve and permit fuel to flow into the combustion chamber where it is ignited by the spark. The closing'of contact A of the circuit control relay permits current tovenergize the coil of the ignition time delay relay which acts in two and one-half seconds to' break the ignition circuit cutting ol the spark in `the combustion chamber. During this sparking period, fuel owing into the `combusbe I traced 4 tion chamber should have been ignited and when th spark goes off the burner flame should take over the function of the spark for the photoconductive cell. However, if the fuel has not been ignited, with the spark cut off there is no amplilied signal applied to the circuit control relay coil 79, and contacty B opens immediately permitting the fuel solenoid actuated valve to close cutting off the flow of fuel to the combustion chamber. Relay contact A, being a slow-to-open contact, delays five seconds before opening. This five second delay permits the source of `power to continue energization of the ignition time delay relay 512 to keep the ignitioncircuit open for ive seconds. The motor is still running, therefore, during this tive second period, air from the blower clears the combustible mixture from the combustion chamber. After this ve second period, the ignition time delay relay 52 is de-energized and the ignition circuit closes to begin a new cycle of operation. At any stage, after the main switch is closed, a shortage of water, fuel, or air will operate one of the

switches

38, 40, or 44 to open the power circuit to the amplifier to stop the iiow of fuel to the combustion chamber. The thermostat 42, when its heat requirement is satisfied, will also open the powerA circuit to the amplifier 72, and should the steam cleaner develop excessive steam pressure, the high pressure switch 36 in circuit with the motor 10 will open to stop the motor causingthe amplifier power control switches 38, 40, 44, which are responsive to the operation of the motor, to open to cut oi the amplifier.

In the gas pilot ignited by spark form shown in Fig'. 2, the combustion chamber 14 is provided with a pilot burner 92 and nozzle 94 in addition to the burner mechanism described above for Fig. l. The flame issuing from the pilot burner nozzle 94 is indicated at 96. The pilot burner receives gas from a gas supply pipe, not shown. The supply of gas to the' pilot burner is controlled by a pilot fuel solenoid actuated valve 98 which is closed, unless opened for operation of the pilot burner as will be hereinafter explained.

ln this form (Fig. 2) the pilot burner is provided with the electrodes 23 and the photoconductive cell 32 is so positioned that the spark must be in the exact position to ignite the fuel entering the combustion chamber through the pilot burner before it will excite the cell 32. The cell when positioned to be excited by the spark must also be in position to be excited by the pilot burner iiame and the main burner flame 22. i

The circuits and operation of the form shown in Fig. 2 are identical to the form shown in Fig. l down to the closing of the circuit control relay 78 by the application of the amplified signal of the photoconductive cell 32 to the coil 79 of the circuit control relay 78. However, the Vclosing of the circuit control relay 78 in Fig. 2 closes three circuits instead of the two circuits described for Fig. 1. Accordingly, the circuit control relay 78, as shown in Fig. 2, is provided with a contact Cin addition to the coil 79, and contacts A and B of Fig. 1.

The contacts A, B, and C of the circuit control 4relay 78 are in the following circuits: Contact A of relay 78 is in circuit with the coil of the ignition time delay relay 52, contact'B is in circuit with the solenoid 99 of the pilot fuel solenoid 'valve 98, and contact C is in circuit with coils lill) and 102 of a second time delay relay 104 which includes two sets of time delay relay contacts A and B and the coils and 102. Contact A of the second time delay relay 104 is fora normally closed, slow-opening relay having a ten second delay'and is in the pilot fuel solenoid actuated valve circuit to be described. Relay contact Bof the second time delay relay 104 is a normally open, slow-closing relay having a ve second delay and is in the fuel burner solenoid actuated valve circuit..-

The circuit energizing the coil 80 of the time delay relay 52 is that described for Fig. 1 and need not be traced again. However, the contact A of relay 78 in this form (Fig. 2) is a normally open, slow-opening relay contact having a ten second delay rather than the five second delay of the relay contact A of relay 78 for the form shown in Fig. l.

The circuit energizing the pilot fuel solenoid 99 of the pilot fuel solenoid actuated valve 98 may be traced as follows: From the source of power 30 through conductor 46, main switch 50,

conductors

50 and 82 to relay contact B of the circuit control relay 78, conductor 106 to pilot fuel solenoid 99 and the ten second time delay relay contact A of time delay relay 104, and return to source of power 30 through

conductors

1110, 86, 76, and 48.

The circuit energizing the coils 100 and 102 of the time delay relay 104 may be traced in Fig. 2 as follows: From the source of power 30 through conductor 46, main switch 50,

conductors

60 and 82 to relay contact C of the circuit control relay 78, through conductor 112 to coil 100 for the A contact of the time delay relay 104 and coil 102 for the B contact of the time delay relay 104 and return t6 the source of power through

conductors

114, 86, 76, and 48.

Contact B of the time delay relay 104 is in circuit with the source of power 30 and solenoid 85 of the burner fuel solenoid actuated valve 20. This circuit may be traced in Fig. 2 as follows: From the source of power 30 through conductor 46, main switch 50,

conductors

60, 82, and 118 to contact B of the time delay relay 104 and burner fuel solenoid 8S and return to the source of power through

conductors

124, 86, 76 and 48.

The simultaneous operation of the circuits is as follows: When the coil 79 of the circuit control relay 78 is energized by the amplified signal output of the photoconductive cell 32, the contacts A, B, and C are closed immediately. The closing of contact B energizes the pilot fuel solenoid 99 to open the pilot fuel solenoid actuated valve and permits fuel to enter the pilot fuel burner where it is ignited by the spark of the sparking electrodes 23. The closing of the ten second time delay contact A of the circuit control relay 78 causes energization of the coil 80 of the normally closed ignition time delay relay 52 to open the ignition transformer circuit after two and one-half seconds have elapsed to shut off the spark of the sparking electrodes 23 in the cornbustion chamber. The closing of contact C energizes coil 100 for the ten second delay contact A and the coil 102 for the five second delay contact B of the time delay relay 104. Energization of the coil 102 closes the contact B of the time delay relay104 after a five second time delay to close the circuit to the vburner fuel solenoid V85 opening the burner fuel solenoid actuated valve 20 permitting fuel to flow to the combustion chamber fuel burner where it is ignited by the pilot flame. Energization of the coil 100 opens the circuit to the pilot fuel solenoid actuated valve 93 after a ten second delay to cut off the flow of fuel to the pilot burner 94 cutting off the pilot burner llame. The fuel burner flame is now exciting the photoconductive cell to keep the circuit control relay coil 79 energized to maintain the liow of fuel to the burner. However, should the spark of the electrodes 23 fail to ignite the pilot burner or should the pilot burner fail to ignite the combustion chamber fuel burner 12, the photoconductive cell is no longer excited and the coil 79 of the circuit control relay 78 is deenergized causing contacts B and C of the circuit control relay 78 to open immediately to cut off the flow of any fuel to the pilot and/or main burner. However, as contact A of the circuit control relay 78 is a slow-to-open ten second` delay relay, the coil 80 of the time delay relay 52 is energized for ten additional seconds, thereby keeping the ignition transformer circuit open for ten additional seconds during which the blower 11. continues operation to purge the combustion chamber of any combustible mixture after'which the time delay relay 52 opens permitting the ignition transformer circuit to close to begin a new sparking period in the combustion chamber and another cycle of. operation.v The control switches or circuit interrupters of Fig. l are included in this form and provide safety control features for the forni identical te those of the form described for Fig. 1.

Although having described two specific embodiments of this invention, it will be understood that numerous details of the constructions shown may be altered or omitted without departing from the spirit of this invention as defined by the following claims.

We claim:

l. In combination with a fluid fuel burner apparatus having a burner extending into a combustion chamber, draft-producing means to supply air to the burner, fuel feeding means arranged to supply fuel to the burner, and spark-producing ignition means arranged to ignite the fuel and air emanating from the burner, the improvement comprising a safety ignition and control system having means actuated by the spark for controlling the introduction of fuel to the burner, said last named means comprising an amplifier, a source of power, electrical circuit means coupling said amplifier to said source of power to apply operating potentials to said amplifier, a photoconductive cell directed at the fuelcombustion zone and responsive to varying intensity of infrared radiation from the spark, a circuit connecting said photoconductive cell to the input of said amplifier, a circuit control relay including a coil and a pair of contacts, one of which is slower to open than the other, means for applying the output of the amplifier to energize the coil of the circuit control relay, a solenoid actuated fuel valve connected in series with the faster opening contact of the circuit control relay and said source of power, and an ignition time delay relay including a coil and a slow opening contact, the coil of said time delay relay being connected in seriesr with the circuit control relay slow opening contact and said source of power, the contacts of the circuit control relay being closed upon energization of the coil thereof to thereby supply current to the solenoid of the fuel valve to open said fuel valve and simultaneously closing the slow opening contact of the circuit control relay to supply current to the coil of the ignition time delay relay to open the time delay contact to cut off the sparking means, and thereafter said photoconductive cell remaining operative during periods of combustion.

2. In combination with a gas fuel burner apparatus having a main gas fuel burner extending into a combustion chamber, draft-producing means to supply air to the main burner, fuel feeding means arranged to supply fuel to the burner, and spark-producing ignition means arranged to ignite a gas fuel pilot burner which is arranged to ignite the main burner, the improvement comprising a safety ignition and control system having means sequentially actuated by a spark from the sparking means for controlling the introduction of fuel to the pilot burner, the flame of the pilot burner for controlling the introduction of fuel to the main burner, and by the llame of the main burner for controlling the continued introduction of the fuel to the main burner, said sequentially actuated means comprising an amplifier, a source of power, said amplifier being connected to said source of power to apply operating potentials to said amplifier, a photoconductive cell directed at the fuel combustion zone and actuated responsively to varying intensity of infrared radiation radiating sequentially from the sparking means, pilot burner flame and main burner flame, a circuit connecting said photoconductive cell to the input of said amplifier, a circuit control relay including a coil and a plurality of relay contacts, one of which is slower to open than the others, means for applying the'output of the yamplifier 7 to energize the coil of the circuit control relay to close the relay contacts, a solenoid actuated pilot fuel valve connected in series with 'one of the faster opening contacts of the circuit control relay and the source of power, a first time delay relay including a coil and a slow opening, normally closed contact having the coil thereof in series with the slow opening circuit controlrelay contact and the source of power, a second time vdelay relay including two coils and two contacts, one of said contacts being normally closed and the other open, the coils of saidsecond time delay relay being in`- series with another of the faster opening contacts of the circuit control relay and the source of power, the normally closed contact of the second time delay relay being in circuit with the solenoid actuated pilot fuel valve, and a burner solenoid actuated fuel valve having the solenoid thereof connected in series with the normally open contact of the second time delay relay and the source of power, energization of the coil of the circuitV control relay closing the contacts thereof and simultaneously supplying current to .the solenoid of the pilot fuel valve, to the coil of the rst time delay relay, and to the coils of the second time delay relay, one of the coils of said second time delay relay operating subsequently to open the pilot fuel valve solenoid circuit to close the solenoid actuated pilot fuel valve, and the remaining coil thereof operating thereafter to close the circuit to the burner fuel solenoid to open the burner solenoid actuated fuel valve, any deenergization of the burner fuel solenoid through failure of spark, pilot burner flame, or burner iiame operating immediately to break the circuit'to the solenoid of the pilot fuel valve permitting the latter valve to close, to open the slower opening contact, to de-energize, after a brief interval, the coil of the iirst time'delay relay permitting the contact of the ignition time delay relay to close, and to de-energize the coils of the second time delay relay to immediately open the circuitto the fuel burner solenoid permitting the fuel burner valve to close.

3. In combination, an ignition and control system'and a iiuid fuel burner apparatus; said burner apparatus having a burner extending into a combustion chamber, a blower for supplying air to the burner, fuel feeding means for supplying fuel to the burner having an electrically actuated normally-closed fuel valve, and yspark-producing ignition means arranged to ignite the fuel air mixture from the burner; said control system including a photoconductive resistance cell having a conducting capacity proportional to the quantity of infred radiation contacting the cell and being physically positioned to receive inf-rared radiation both from the sparks produced by the ignition means andtfrom the flame of the burner; an ampliiier electrically connected to said cell, said amplifier providing an amplified electrical power `output based upon the frequencies of energy conducted by said cell which are characteristic of the frequenciesof electrical spark and ame infrared radiation; means for energizing said amplifier, actuating the blower, and actuating the spark-producing ignition means; and circuit means including relay means actuated by the amplified power output Which opens the fuel valve for the duration of the amplified power output, interrupts after a time delay the spark-producing ignition means, and thereafter maintains the ignition means inoperative for ther duration of the ampliiied power output and for a period of time after cessation thereof,l at which time thev ignition means automatically commences operating again.

4. The combination of an ignition and control system and a fluid fuel burner apparatus as set out in claim 3 wherein said relay means includes a normally-open control relay which is closed by the power output of said amplifier, said control'relay having a'quick-op'ening oontact and a delayed-opening contact, the quick-opening contact being connected upon closing to open the fuel valve, the delayed-opening `contact being connected upon closing to energize a normally-closed delayed-opening re lay which. thereupon opens after`a time delay and is connected to interruptv operation of the spark ignition means, said fuel valve remaining open and said spark ignition means remaining inoperative during continued amplified power output by the amplifier and upon cessation of the amplifiedl powerl output each valve and relay returning to normal condition.

5. In combination, anignition and control system and a uid fuel burner, main burner fuel feeding means for supplying fuel to the main burner having an electrically actuated normally-closed main burner fuel valve, a pilot burner arranged to ignite the'fuel actuated normallyclosed pilot burner fuel valve, and spark-producing ignition means arranged to ignite the fuel from the pilot burner; said ignition and control system including a photoconductive resistance cell having a conducting capacity proportional tothe quantity of infrared radiation contacting the cell and being physically positioned to receive infrared radiation from the sparks produced by the ignition means, from the llame ofthe pilot burner, and from the flame of the main burner; an amplier electrically connected to said cell, said amplifier providing an ampliiied electrical power output based upon the frequencies of energy conducted by the cell which are characteristic of the frequencies of electrical spark and iiame infrared radiation; means for energizing said amplifier, actuating the blower, and actuating the spark-producing ignition means; and circuit means including relay means actuated upon excitation of said amplifier, which relay means sequentially opens the pilot fuel valve, interrupts operation of thefspark-producing ignition means, opens the main burner fuel valve, and closes the pilot burner fuel valve, the main burner fuel valve remaining open for the duration of the amplified power output and the spark-producingignition means remaining inoperative for the duration of the amplilied power output and for a period ofl time thereafter.

6. The combination of an ignition and control system and a iiuid fuel burner apparatus as set out in claim 5 wherein said relay means includes a normally-open master control relay which is closed upon excitation of said amplier for the duration of the power output therefrom, said master control relay having a delayed-opening contact and iirst and second quick-opening contacts, said iirst quick-opening contact being connected upon closing to open the normally-closed pilot fuel valve, said second quick-opening contact being connected to energize a second relay havinging a normally-closed delayed-opening contact and a normally-open delayed-closing contact wherein the delays are of such relative duration that the normally-open contact closes before the normally-closed contact opens, the normally-open contact being connected upon closing to open the main burner fuel valve, the normally-closed contact being connected upon opening to de-energize the pilot fuel valve whereby the 'valve returns to normally-closed position, said delayed-opening contact of said master control relay connected to energize a third relay having a normally-closed ,delayedopening contact which thereupon opens after a time delay but before the normally-open contact of said second relay closes, and said third relay being connected to interrupt operation of the spark ignition means for the duration of output from said amplifier and for/a period of time thereafter when the delayed-opening contact of said master control relay opens.

References Cited in the iile of this patent UNITED STATES PATENTS 2,335,655 Dickey Nov. 30, 1943 2,412,990 Kruse Dec. 24, 1946 2,490,095 Rosche Dec. 6, 1949 2,635,813 Schlenzl Apr. 21, 1953 2,771,942 Miller Nov. 27, 1956 v 2,805,652 l Stout Sept. 10, 1957