US3589848A

US3589848A - Oil burner control system

Info

Publication number: US3589848A
Application number: US750657A
Authority: US
Inventors: William F Potts
Original assignee: Liberty Combustion Corp
Current assignee: Liberty Combustion Corp
Priority date: 1968-08-06
Filing date: 1968-08-06
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29

Abstract

Oil burner control system employing a control transformer the primary impedance of which varies in response to secondary loading by a temperature controller, whereby the variation causes energization of the control circuit. The full specification should be consulted for an understanding of the invention.

Description

hich varies in g by a temperature controller,

whereby the variation causes energization of the control circuit. The full specification should be consulted for an un derstanding of the invention.

Inventor William F. Potts Liverpool, N.Y. Appl. No. 750,657 Filed Aug. 6, 1968 Patented June 29, 1971 Assignee Liberty Combustion Corporation Syracuse, N.Y.

4 Claims, 6 Drawing Figs. [52] U.S. 431/78, 317/79,431/1 16 United States Patent [54] OIL BURNER CONTROL SYSTEM IGNITION IGNITION ew 8 GM ,3 V R LM A w he. 5 m

INVENTOR.

PATENTED JUN29 I97! IGNITION VOLTAGE SHEET 1 BF 3 a) GENERATOR 4 54 IGN m o N c: RCUIT I i CONTROL WILLIAM F, POT TS,

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INVIiNTOR. WILLIAM F. POTTS.

ATTORNEY OIL BURNER CONTROL SYSTEM The present invention comprises improvements in a fluid fuel igniter control system as disclosed in my copending US. Pat. application Ser. No. 586,583 filed Sept. 26, I966.

In that application there is described a combined oil burner ignition and control circuit employing a capacitor discharge ignition voltage generator and a control circuit employing semiconductors. The combined circuit is composed of circuit elements permitting the entire circuit to be contained in a single housing of smaller size and less weight than that of an ignition transformer used heretofore to provide ignition voltage alone. In substance, the ignition control circuit of that applica tion comprises circuitry employing semiconductor devices for directly controlling'flow of power, but the circuit complexity and number of circuit elements result in relatively high equipment costs which make thecircuit noncompetitive in the oilheating market at this time.

My present invention comprises partly in combination with a capacitor discharge spark voltage generator, a burner control circuit that is lower in cost, employs fewer circuit elements and has improved fail-safe characteristics over the oil burner control circuit described in my copending application. Further, my invention illustrates a method of combining the spark voltage generator and the control circuit as independently housed units on a common connecting board, the whole contained in a space smaller than that of the ignition transformer used formerly on most generator-type oil burners. In addition, the development of an oil burner not part of my invention and generally referred to as a blue flame burner, that is, one which more thoroughly reduces combustion products to carbon dioxide and water vapor so that a blue flame rather than a yellow flame results, has been brought about by the oil heating industry. The blue flame burner requires constant ignition, however lower ignition spark energy may be used since the deflection of the spark plasma by an airstream, as described in my copending application, is not required. Since the flame from this burner is blue, the cadmium sulfide photocell, commonly used as an oil flame sensor on gun-type burners, is no longer suitable, since blue flame contains virtually no yellow to which the cadmium sulfide cell is largely responsive. Consequently, the burner control circuit must be responsive to heat responsive switches or ultraviolet flame detector systems as well as the cadmium sulfide photocell so that an appropriate sensor may be used with the blue flame.

The physical separation of the burner control circuit and the spark voltage generator is desirable under certain field servicing conditions and my invention describes how they may be housed separately and used independently of each other or in combination on a common connecting base.

An object of the invention is to provide an oil burner control circuit, for use with ignition means such as a high voltage transformer or a capacitive discharge voltage generator, having few, low cost, circuit elements.

A further object of the invention is to provide an oil burner control circuit having the capability to disable a capacitive discharge spark voltage generator in response to presence of flame at the burner.

Yet another object of the invention is to provide an oil burner control circuit in which component failure or malfunction will not result in an unsafe or undesirable condition of the burner which it controls.

Another object of the invention is to provide an oil burner control circuit adaptable to altering component values to operate on different magnitudes of alternating current voltage and frequency.

A yet further object of the invention'is to provide an oil burner control circuit having facilities to provide a choice between constant ignition and interrupted ignition.

Yet another object of the invention is to provide a combined spark voltage generator and oil burner control circuit in which the two circuits are physically separate items interconnected by a common connecting base and occupying a volume smaller than that used heretofore by most ignition transformers alone.

Another object of the invention is to provide an oil burner control circuit responsive to any flame sensor having characteristics such that in the absence of flame at the burner, the flame sensor has a high resistance and in the presence of flame, the flame sensor has a low resistance, for example, a heat responsive switch, a flame responsive relay system, or a photocell.

The above and other novel features of the invention will appear more fully hereinafter from the following detailed description when taken in' conjunction with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings, wherein like reference characters indicate like parts:

FIG 1 is a schematic oil burner assembly with ignition control and generator indicated as blank diagram;

FIG. 2 is a circuit diagram of the ignition control and generator of FIG. I;

- FIG. 3 is a circuit illustrating a variation of a portion of the circuit of FIG. 2;

FIG. 4 is a schematic diagram of the burner; and

FIG. 5 is a plan view of the arrangement of the spark control and generator assembly, and FIG. 6 is an illustrated view of the assembly of FIG. 5.

In FIG. 1, there is shown an oil burner control system for oil burner assembly 20, arranged to be supplied with oil by an oil supply line 22 under the control of a fuel pump, not shown, forming part of the burner assembly, and driven by the burner motor 24 to provide a diverging spray cone of oil 25 at nozzle 26 when the motor is running, the motor being supplied with alternating current power by a combined circuit 28 to be described.

Input terminals

30 and 32 of burner control circuit 33 are connected to a source of alternating current voltage and

terminals

34 and 36 are connected to a thermostatic switch 38, the latter controlling the turning on and off of the combined circuit 28 in response to demand for heat. Spark gap electrodes 40 and 42 in burner assembly provide spark discharges for ignition of the oil spray and are connected to spark voltage generator 44 which forms part of the combined circuit 28, the electrodes being connected to

terminals

46 and 48 wherewith they are supplied with spark voltage when generator 44 is operating. Flame detector 50, located in burner assembly 20 or adjacent to the burner combustion chamber, not shown, senses the presence or absence of flame issuing from burner 20, developing a high resistance in the absence of flame and a low resistance in the presence of flame.

Burner control circuit 33 controls the flow of power from the alternating current source to the generator 44 via line 52 and line 54, and to motor 24 via terminal 56, motor 24 also being connected to terminal 32 by line 59.

With line voltage applied to terminals and 32 and thermostatic switch 38 open, combined circuit 28 is inoperative and the burner is off. When switch 38 is closed, burner control circuit 33 will apply power to line 52 and terminal 56 provided that flame sensor 50 is not at low resistance, and will thereby energize generator 44 to produce sparking voltage at

terminals

48 and 46 for sparking at electrodes and 42 and causing motor 24 to operate. Motor 24 drives an air blower fan, not shown, to provide combustion air and as mentioned previously also drives a pump which provides a cone of oil spray 25 from nozzle 26. Spark discharges from electrodes 40 and 42 ignite the oil spray, ignition takes place, the resulting flame is detected by flame sensor and burner control circuit 33 causes generator 44 to cease operating. So long as switch 38 is closed and flame sensor 50 is sensing the presence of flame, the burner will continue to operate until switch 38 opens. However, in the event that flame ceases to be detected initially or on a flame-out during a burning period, sensor 50 acts on burner control circuit 33 to reactivate generator 44 in an attempt to reignite the burner, while at the same time a circuit breaker trip switch in ignition control circuit 33 will act after a predetermined period of time to shut combined circuit 28 off, thus stopping the operation of the burner and requiring manual reset of the trip switch.

As common practice in the oil heating industry, prior to my invention described in application No. 586,593 and my present invention, the burner control and the spark voltage generator were necessarily separate equipments located separately and apart from each other and interconnected by appropriate wiring. While my invention describes them being used as a combined circuit it is nevertheless practical and sometimes desirable to use them as separate equipments as will be illustrated hereinafter.

In FIG. 2, I have shown a specific embodiment of the burner control circuit 33 and the spark voltage generator 44 of FIG. 1. In FIG 2 parts corresponding to those shown in FIG. I are given corresponding reference numerals. As shown, the input supply terminal 30 of control circuit 33 is connected to the rest of the apparatus through a circuit breaker generally designated as 60 and in the drawing shown as 60A encompassing a normally closed

breaker contact

62 and 60B comprising heater resistance 64. The circuit breaker 60 is of the thermally responsive heater resistance-type with a bimetallic tripping element to open the normally closed contacts when heated by its heater. The circuit breaker is of the conventional type which, once tripped, must be manually reset before further operation.

Input terminal 30 is also connected through normally open contact 66 of relay 68 to terminal 56 and thence to motor 24, and to line 52 and thereby to generator 44. Thus, to operate the burner and provide it with ignition voltage, contact 66 must close. Relay 68 must be energized to close contact 66. Relay winding 69 is connected in a series circuit between

input terminals

30 and 32, the circuit comprising from terminal 30, breaker contact 62, the primary winding 70 of transformer 72 which has a secondary winding 74 connected to ter' minals 34 and 36, relay winding 69, the anode and cathode of silicon-controlled rectifier 76, in that order, and the heater winding 64 of circuit breaker 60. Line 78 connecting primary winding 70 relay winding 69 is also connected through the series connection of

resistors

80 and 82 to terminal 32.

Resistors

94 and 96 are series connected in that order between line 78 and the cathode of SCR-76 and their midpoint is connected to line 58 to control the operation of generator 44. Resistor 98 is connected across the anode and cathode SCR-76 to bias the cathode of SCR-76. Triggering voltage to the gate of SCR-76 is provided from the series circuit of

resistors

86, 88 and 90 between line 78 and terminal 32, the gate being connected to the junction of resistors 88 and 90. Terminal 53 is connected at the junction of resistors 86 and 88 to provide a bypass path for current from resistor 86 through flame sensor 50 to terminal 32 via terminals SI and 53 when flame sensor 50 has a low resistance.

When switch 38 is open, the reactance of primary winding 70 is very high due to thesmall magnetizing current of transformer 72, and consequently the voltage existing between line 78 and terminal 32 is approximately one third of the voltage applied between

terminals

30 and 32, this fraction of the input voltage being insufficient to operate the circuitry. However, when switch 38 is closed, thus representing a load or short circuit on secondary winding 74, the reactance of winding 70 drops to a very low value and the voltage between line 78 and terminal 32 increases to approximately 90 percent of the input voltage at

terminals

30 and 32. This use of transformer 72 serves two purposes. First, the thermostatic switch 38 is isolated from the input supply voltage at

terminals

30 and 32 and second, the secondary short circuit current is considerably higher than the primary load current, in proportion to the turns ratio, thus providing the typical room space thermostat switch 38 with adequate current for heat anticipation, this being common practice to prevent unnecessary and undesirable fluctuations of room temperature. Thus when switch 38 is closed, the gate of SCR-76 will draw current through resistors 86 and 88 causing SCR-76 to conduct each time that line 78 is positive.

During the conduction period relay 68 is energized and pulls in to close both normally

open contacts

66 and 84, at the same time causing current to flow in heater 64 with consequent heating of the associated bimetal element of circuit breaker 60. When contact 84 closes, relay winding 69 will draw energizing current through contact 84 and resistor 82 regardless of whether or not SCR-76 is in a conducting state, thus insuring that relay 68 remains energized so long as switch 38 is closed. When switch 38 is opened, the reactance of winding 70 will increase sufficiently to cause relay 68 to drop out due to low voltage.

Terminals

51 and 53 being connected to flame sensor 50 will allow SCR-76 to be triggered into conduction on succeeding half cycles when line 78 is positive thus causing heater 64 to continue heating so long as there is absence of flame at burner 20. However, when the burner ignites, flame sensor 50 develops a low resistance and bypasses the current around resistor 88 and the gate cathode of SCR-76 so that the latter will no longer be triggered into conduction solong as flame sensor 50 is sensing flame. It will be noted that resistor in parallel connection with the gate cathode of SCR-76 is preferably an adjustable resistor, the adjustment being used to set the threshold value of the resistance at which sensor 50 will prevent further triggering of SCR-76. Capacitor 92 serves to prevent transient voltages from triggering SCR-76 into conduction. Resistor 98 provides a bias on the cathode of SCR-76, the main purpose of this being to make for wider latitude in the values used in

resistor

86, 88 and 92 so that the cutoff point of triggering to SCR-76 will not be too critical relative to variations in the input voltage applied to

terminals

30 and 32. The value of resistor 98 is sufficiently high however, so that when SCR-76 is not conducting heater element 64 will not heat sufficiently to cause the circuit breaker contact 62 to trip open.

From this description it will be apparent that so long as flame sensor 50senses theabsence of flame at burner 20, SCR-76 will continue to be triggered, causing heater 64 to heat to the point where it will warp the bimetallic element of breaker switch 60 thus tripping open breaker contact 62, the latter remaining open until breaker 60 is manually reset. it will also be apparent that'when switch 38 is first closed, should flame sensor 50 have a low resistance for any reason, SCR-76 will not be triggered into conduction because flame sensor 50 bypasses the triggering current with the consequence that relay 68 will not pull in and the burner will not operate until flame sensor 50 reverts to a high resistance at which time SCR-76 will be triggered to pull in relay 68 and normal operation will resume.

The circuit of ignition voltage generator 44 illustrates how interrupted ignition may be provided by control circuit 33 and how generator 44 may be altered for continuous ignition.

When input voltage from

terminals

30 and 32 is applied to generator 44 via contacts 66 and line 52, capacitor 100 charges unilaterally with the polarity shown through resistor 102, rectifier diode 104 and primary winding of 106 of transformer 108 which has a secondary winding 110 connected to

terminals

46 and 48. The anode of a silicon-controlled rectifier 112 is connected to the cathode of diode 104, the cathode of SCR-1I2 being connected via line 54 to terminal 32. Rectifler diode. 114 is reverse connected across the anode and cathode of SCR-112. Although capacitor 100 will charge to the peak of the line voltage applied to

terminals

30 and 32, SCR-l12 will not conduct until it is triggered into conduction by the discharge of capacitor 116 through breakdown device 118 and resistor 120. Thus, to trigger SCR-112 into conduction to cause the currents of pulses of spark voltage at

terminals

46 and 48, capacitor 116 must charge to the breakdown voltage of breakdown device 118, resistor 120 being a current limiting device so that the discharge current does not exceed a safe value for the gate of SCR-112. Capacitor 116 will be unilaterally charged from the voltage at reference line '58 through terminal 112, switch blade 124 and terminal 126 and the anode and cathode of rectifier diode 128, to a value depending upon the voltage between

lines

58 and 54. This value will in turn depend on the relative values of

resistors

94, 96 and heater 64. The values of

resistors

94 and 96 are chosen so that when SCR-76 is not conducting, the charge on capacitor 116 will not reach the breakdown voltage of breakdown device 118 and consequently SCR-112 will not be triggered into conduction and spark voltage will not be produced. However, when SCR-76 is triggered into conduction, the, voltage across heater 64 will be approximately half the voltage between line 78 and line 54 and this will allow the voltage at line 58 to increase to a value high enough so the charge on capacitor 116 will repetitively reach the breakdown voltage of breakdown device 118, thus allowing spark voltage pulses to be produced at

terminals

46 and 48. The rate at which SCR- 112 is triggered may be varied to any desired spark rate by the adjustment of the value of resistor 94. To provide constant ignition rather than interrupted ignition, switch blade 124 is shifted to connect terminals 126 and 130, thereby allowing capacitor 116 to charge from the voltage on capacitor 100 through resistor 132. So long as contacts 66 areclosed and thereby apply input voltage to generator 44, the generator will produce spark voltage pulses at

terminals

46 and 48, with the triggering rate of SCR-1l2 being determined primarily by the value of resistor 132.

It will be apparent from foregoing that generator 44 being connected to burner control circuit 33 by three distinct lines, 52, 54 and 58, may be assembled as a separate unit and mounted remote from burner control circuit 33, interconnections being made by appropriate wiring. It will also be apparent that generator 44 and burner control circuit 33 may be assembled as separate units but mounted on a common connecting board so that the two units may be independently removed and replaced, connections being made to the common board by plug-in connectors.

A partial diagram of burner control circuit 33 is shown in FIG. 3 to illustrate another method of providing control operating voltage at line 78 by means of a voltage stepdown transformer 134 and a relay 136 having normally open contacts 138. The schematic diagram of burner control circuit 33 is not shown in full in FIG. 3 since all functions, components and connections are identical with that illustrated in FIG. 2 with the exception of the means of providing line 78 with operating voltage. In this arrangement the primary winding of transformer 134 is connected between terminals and 32 so that it is energized with input voltage at all times. The secondary winding of transformer 134 is in series connection with the winding of relay 136, terminal 34, switch 38 and terminal 36, so that when switch 38 is closed, relay .136 will be energized to close its normally open contact 138, thereby connecting reference line 78 to terminal 30 via normally closed contact 62 of circuit breaker 60. Thus when switch 38 is closed to operate the burner, the control circuit operating voltage between line 78 and line 54 is obtained directly from input terminal 30. This method of controlling the voltage at reference line 38 may be desirable in certain instances where wide variations in the input voltage at

terminals

30 and 32 would otherwise adversely affect the operation of the circuit described in FIG. 2 at the extreme ranges of the voltage variations.

FIG. 4 is a longitudinal cross-sectional sketch of the tubular combustion section of a blue flame oil burner illustrating how gases released by combustion of the oil-air mixture are recirculated to be burned again thus greatly reducing the amount of unburned hydrocarbon issuing from the burner and consequently providing a blue flame instead of the typical yellow flame of the gun-type oil burner.

Combustion chamber 200 comprises a recycling tube 202 concentrically mounted within combustion chamber 200 to form a recirculating chamber 204, the assembly being mounted within a cylindrical housing 206. A baffle ring 208 in the expanded portion 209 of chamber 200 is provided to aid in recirculating combustion gases.

A mixture of oil and compressed air is sprayed into chamber 200 from a nozzle 210 and is ignited by sparks occurring at electrode assembly 212 which is located in the oil spray. The burning mixture 214, expands rapidly in the expanded portion 209, and combustion gases 216 deflected by baffle 208 and passback to the fuel input area 217 through recirculating chamber 204 to be mixed with the incoming mixture from nozzle 210 and burned again in chamber 200. The result of this action is that flame 218 issuing from chamber 200 has a blue flame rather than yellow or orange flame, typical of the virtually complete reduction of hydrocarbons by combustion to carbon dioxide and water vapor.

Although electrode assembly 212 is located in the stream of the oil-air mixture and oil droplets will impinge thereon, the problem of carbon forming on'the electrodes as experienced in gun-type oil burners does not occur in the blue flame burners because the recirculating gases 216 are hot enough to evaporate the oil on the assembly 212 without leaving a residue.

Since the electrode gap is in the oil-air mixture there is no need to have the spark discharges deflected into the mixture, and consequently the energy delivered by a capacitor discharge ignition voltage generator may be greatly reduced from that required for a gun-type oil burner.

Because of the construction of combustion chamber 200 the flameresulting from ignition of the oil-air mixture will burn downstream of the nozzle 210 with the result that with interrupted ignition the incoming fuel mixture would tend to blow the flame out because the recirculated gases 216 may not be hot enough when they reach area 217 to ignite the fresh oilair mixture. Thus to avoid flame blowouts constant ignition is desirable.

It is obvious from the description that combustion chamber 200 will get hot from heat released by the combustion therein;

A second supply of air 218 is forced through the annular space between combustion chamber 200 and housing 206 to cool chamber 200.

Flame sensor 220 is located adjacent to the burner to detect the presence of blue flame, for instance an ultraviolet detector tube connected through an appropriate amplifier actuated relay to the ignition control circuit via

lines

222 and 224, or to detect the presence of heat from the flame such as a heat sensitive switch.

In FIG. 5 there is shown the arrangement of the elements of the ignition control circuit 33 of FIG. 2, mounted on a printed board 150, like numbers indicating like components. The dimensions of board are 2 5/16 inches wide by 3 3/34 inches long by one-sixteenth inch thick. Similarly the elements of ignition voltage generator 44 of FIG. 2 are mounted on joined

circuit boards

152 and 153. The dimensions of board 152 being 2 H6 inches wide by 3% inches long by one-sixteenth inch thick and of board 153 being 2% inches wide by 3% inches long by one-sixteenth inch thick. Board 150 with the elements of circuit 33 and connecting pins extending out of the underside of the board to represent

terminals

30, 32, 34, 36, 51, 53 and 56, and

line

52, 54 and 58 of combined circuit 28 of FIGS. 1 and 2, and

boards

152 and 153 with the elements of generator circuit 44 and connecting pins extending out the bottom of board 152 representing

terminals

46 and 48 and

lines

52, 54 and 58 of combined circuit 128 of FIG. 1, are both mounted on and connected to a common connecting board 154 whose dimensions are 4 inches wide by 5 inches long by one-eighth inch thick, to form a completed assembly of combined circuit 28 but without housing.

FIG. 6 is an elevation view of the arrangement of FIG. 5, with a section view of housing 162 containing board 150 with the elements of circuit 33 mounted thereon, and housing 164 containing

boards

152 and 153 with the elements of generator 44. The height of

housing

162 and 164 is 2 13/ 16 inches measured from the upper surface of board 154 on which the housings rest.

From the foregoing, it will be seen that the combined circuit 28 comprising control circuit 33 in housing 162, generator 44 in housing 164 and common connecting board 154, is contained in the space volume measuring 4 5 2 15/ l 6 inches, of nearly 60 cu. inches. The housing for most line operated ignition transformers alone and as used on gun-type oil burners v occupies a space volume, measuring very nearly 3% inches X 4% inches X 5% inches, of nearly 87 cu. inches.

While a single embodiment with variations of the invention has been illustrated and described, it is to be understood that I the invention is not limited thereto. As various changes in the construction and arrangement may be made without departing from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits of the invention.

I claim:

1. For use in an .oil burner control system comprising a source of alternating current having one line and another line, an oil burner having a blower and pump motor, an air spark gap disposed adjacent the oil burner to ignite fuel issuing therefrom, a spark-generating apparatus connected to said air spark gap, a thermostatic switch, a flame sensor having low resistance in presence of flame and high resistance in absence of flame, a burner control circuit comprising connections extending to said source of alternating current, to said motor, to said air spark gap, to said generating apparatus, and to said flame sensor, a series circuit disposed across said source of alternating current comprising from said one line the normally closed contacts of a heat actuated circuit breaker, one winding of a two winding control transformer having a high impedance when the other winding is open circuit, and a low impedance when said other winding is short-circuited by said thermostatic switch, the winding of an electromechanical relay, the anode and cathode of a silicon-controlled rectifier in that order and the heater of resistance of said circuit breaker, to said other line, a first resistance means having a tap connection connected across said relay winding and said silicon controlled rectifier to provide a voltage between said tap connection and said other line, said voltage having a higher value when said silicon-controlled rectifier is conducting than otherwise, means for triggering said silicon-controlled rectifier when said thermostatic switch is closed and said sensor senses the absence of flame on each half cycle when said one line is positive, a second resistance means comprising two resistors in series disposed across said relay winding, silicon-controlled rectifier and heater resistance, their midpoint being connected through a first normally open contact of said relay to the anode of said silicon-controlled rectifier, whereby when said relay is initially energized by the conduction of said siliconcontrolled rectifier and said first normally open contact closes said relay remains energized through said second resistance means regardless of the conduction state of said silicon-controlled rectifier, so long as said thermostatic switch is-closed and said circuit breaker contact is closed.

2. For use in an oil burner control circuit, a two-winding control transformer to electrically isolate said control circuit from a heat demand switch as a thermostatic actuated switch, comprising a transformer having a first winding and a second winding and a ratio of first winding turns to second winding turns of at least four to one, said second winding having connections extending to said demand switch, said first winding being connected in series with other circuit elements of said control circuit acrossa source of alternating current power, whereby when said demand switch is open said first winding limits the current flow to said other circuit elements to prevent the operation of said control circuit, and when said demand switch is closed the impedance of said first winding is greatly reduced by short circuiting effect of said closed demand switch, to increase the flow of current tosaid other circuit elements to permit the operation of said control circuit.

3. An oil burner controlcircuit as set forth in claim 1 wherein the voltage between said tap connection and said other line may be extended to the trigger circuit of the discharge means of a capacitive-discharge ignition voltage generator comprising said spark-generating apparatus whereby sparking occurs at said air spark gap when said flame sensor senses the absence of flame at said burner.

4. For the ignition and control of an oil burner of the blue flame-type burriing, in addition to a mixture of oil and air, recirculated combustion gases and oil otherwise evaporated by heat, including an air spark gap and a flame-responsive device; in combination, a source of alternating current power; a spark generator apparatus comprising a capacitance, a stepup transformer the primary of which is in series with the capacitance and the secondary of which is connected across the air spark gap, means to unilaterally charge the capacitance from said source of power and unidirectional means for repetitively discharging said capacitance through the transformer primary and disposed in a first housing; a burner control circuit including connecting means extending to said source of power, to said generator apparatus, to said flame-responsive device and to a heat demand switch, relay switching means initially responsive to said demand switch demanding heat and to said flame-responsive device indicating the absence of flame at the burner to apply said source of power to said generator apparatus and to said blue flame burner, said switching means responsive thereafter to said demand switch only, means to terminate the operation of said generator apparatus when said flame-responsive device indicates the presence of flame at the burner and safety shutoff means having contacts adapted to open the circuit to said source of power after a predetermined period when energized, said shutoff means being energized in the absence of flame indication and not energized in the presence of flame indication, said control circuit disposed in a second housing; both said first and second housings disposed on a common interconnecting base, the whole occupying a space volume less than that occupied alone by a line-operate oil burner ignition transformer. 1

Claims

1. For use in an oil burner control system comprising a source of alternating current having one line and another line, an oil burner having a blower and pump motor, an air spark gap disposed adjacent the oil burner to ignite fuel issuing therefrom, a spark-generating apparatus connected to said air spark gap, a thermostatic switch, a flame sensor having low resistance in presence of flame and high resistance in absence of flame, a burner control circuit comprising connections extending to said source of alternating current, to said motor, to said air spark gap, to said generating apparatus, and to said flame sensor, a series circuit disposed across said source of alternating current comprising from said one line the normally closed contacts of a heat actuated circuit breaker, one winding of a two winding control transformer having a high impedance when the other winding is open circuit, and a low impedance when said other winding is short-circuited by said thermostatic switch, the winding of an electromechanical relay, the aNode and cathode of a silicon-controlled rectifier in that order and the heater of resistance of said circuit breaker, to said other line, a first resistance means having a tap connection connected across said relay winding and said silicon controlled rectifier to provide a voltage between said tap connection and said other line, said voltage having a higher value when said silicon-controlled rectifier is conducting than otherwise, means for triggering said silicon-controlled rectifier when said thermostatic switch is closed and said sensor senses the absence of flame on each half cycle when said one line is positive, a second resistance means comprising two resistors in series disposed across said relay winding, silicon-controlled rectifier and heater resistance, their midpoint being connected through a first normally open contact of said relay to the anode of said silicon-controlled rectifier, whereby when said relay is initially energized by the conduction of said silicon-controlled rectifier and said first normally open contact closes said relay remains energized through said second resistance means regardless of the conduction state of said silicon-controlled rectifier, so long as said thermostatic switch is closed and said circuit breaker contact is closed.

2. For use in an oil burner control circuit, a two-winding control transformer to electrically isolate said control circuit from a heat demand switch such as a thermostatic actuated switch, comprising a transformer having a first winding and a second winding and a ratio of first winding turns to second winding turns of at least four to one, said second winding having connections extending to said demand switch, said first winding being connected in series with other circuit elements of said control circuit across a source of alternating current power, whereby when said demand switch is open said first winding limits the current flow to said other circuit elements to prevent the operation of said control circuit, and when said demand switch is closed the impedance of said first winding is greatly reduced by short circuiting effect of said closed demand switch, to increase the flow of current to said other circuit elements to permit the operation of said control circuit.

3. An oil burner control circuit as set forth in claim 1 wherein the voltage between said tap connection and said other line may be extended to the trigger circuit of the discharge means of a capacitive-discharge ignition voltage generator comprising said spark-generating apparatus whereby sparking occurs at said air spark gap when said flame sensor senses the absence of flame at said burner.

4. For the ignition and control of an oil burner of the blue flame-type burning, in addition to a mixture of oil and air, recirculated combustion gases and oil otherwise evaporated by heat, including an air spark gap and a flame-responsive device; in combination, a source of alternating current power; a spark generator apparatus comprising a capacitance, a stepup transformer the primary of which is in series with the capacitance and the secondary of which is connected across the air spark gap, means to unilaterally charge the capacitance from said source of power and unidirectional means for repetitively discharging said capacitance through the transformer primary and disposed in a first housing; a burner control circuit including connecting means extending to said source of power, to said generator apparatus, to said flame-responsive device and to a heat demand switch, relay switching means initially responsive to said demand switch demanding heat and to said flame-responsive device indicating the absence of flame at the burner to apply said source of power to said generator apparatus and to said blue flame burner, said switching means responsive thereafter to said demand switch only, means to terminate the operation of said generator apparatus when said flame-responsive device indicates the presence of flame at the burner and safety shutoff means havinG contacts adapted to open the circuit to said source of power after a predetermined period when energized, said shutoff means being energized in the absence of flame indication and not energized in the presence of flame indication, said control circuit disposed in a second housing; both said first and second housings disposed on a common interconnecting base, the whole occupying a space volume less than that occupied alone by a line-operated oil burner ignition transformer.