US3519376A - Fuel burner control using silicon controlled rectifier spark generation and thermocouple actuated reed switch - Google Patents

Description

July 7, 1970 G. E. DIETZ 3,519,376

FUEL BURNER CONTROL USING SILICON CONTROLLED RECTIFIER SPARK 'GENERATION AND THERMOCQUPLE ACTUATED REED SWITCH Filed May 24. 1968 GERALD E. DIETZ INVENTOR.

AT TORNE K United States Patent 3,519,376 FUEL BURNER CONTROL USING SILICON CONTROLLED RECTIFIER SPARK GENERA- TION AND THERMOCOUPLE ACTUATED REED SWITCH Gerald E. Dietz, Milwaukee, Wis., assignor to Penn Controls, Inc., Oak Brook, Ill., a corporation of Delaware Filed May 24, 1968, Ser. No. 731,822 Int. Cl. F23q 3/00 U.S. Cl. 431-43 7 Claims ABSTRACT OF THE DISCLOSURE Gaseous fuel is fed through an electromagnetically actuated main valve to a main burner for ignition thereat from a standing pilot flame, under conditions where the pilot flame is sensed by a thermocouple. The thermocouple generates suflicient current to actuate magnetically a reed switch to closed condition to energize the main valve. Under conditions where the pilot flame is extinguished inadvertently, the reed switch, after the thermocouple has cooled sufliciently reopens the energizing circuit of the main valve, stopping the flow of fuel to the main burner. Simultaneously, the thermocouple actuated reed switch, in reopening, activates a spark generator, The generator provides a continuous high voltage spark by means of a silicon controlled rectifier oscillating circuit for relighting the pilot flame. When the pilot flame is successfully relit and the thermocouple reheated, the reed switch contacts again close, simultaneously deenergizing the spark generator circuit and preparing the main valve for reenergization through thermostat contacts, upon the next successive call for heating. Two embodiments are disclosed, one for operation from a 120 volt alternating power source and the other for operation from a 25 volt alternating power source; both utilizing the same silicon controlled rectifier oscillator circuit for spark generation.

The invention relates to fuel burner controls and, more particularly, to such a control for automatically generating a high voltage electric spark for igniting a pilot flame, under conditions where such flame is inadvertently extinguished, while simultaneously causing deenergization of main burner fuel feeding means.

Fuel burners are often located in difficult to reach locations. For example, infrared heaters are sometimes located high in ceilings of shops or plants. In such situations fuel at the main burner is often lit through a standing pilot flame. In the event of inadvertent outage of the pilot flame (due to wind gusts or a momentary interruption of the gas supply), it is desirable that the main burner fuel feeding mechanism be quickly caused to shut off the fuel supply to the main burner. At the same time relighting of the pilot flame should be automatically and quickly initiated. It is also desirable that such an automatic safety control be economical to manufacture and maintain and be substantially trouble free.

It is, therefore, an object of the invention to provide a fuel burner control system in which a standing pilot ignites fuel at a main burner, which control monitors the pilot flame and provides automatic electric reignition thereof 3,519,376 Patented July 7, 1970 in case of outage, while simultaneously shutting off fuel fed to the main burner.

It is also an object of the invention to provide such a control which, upon successful relighting of the pilot flame, effects simultaneous deenergization of the electric ignition means for the pilot and reenergization of the fuel feeding means for the main burner through a single pair of electrical contacts.

The invention involves providing a thermocouple in position to monitor the pilot flame. The thermocouple, when sufliciently heated, magnetically energizes a reed switch to closed position. The reed switch contacts control energization of main burner fuel feeding means and an electric spark generator. The electric spark generator comprises a silicon controlled rectifier oscillator, utilizing capacitor discharge through its anode-cathode circuit to pulse the primary winding of a high voltage spark transformer. The transformer provides a continuous spark across a pair of spaced apart electrodes for igniting the pilot flame. The pilot flame is sensed by the thermocouple which causes the reed switch contacts to be closed. Closing of the contacts simultaneously energizes the fuel feeding means of the main burner, while applying a short circuit between the gate and cathode electrodes of the silicon controlled rectifier of the oscillator. Such short circuit places the 0scillator in nonoscillating condition, shutting down the spark generator.

Features and advantages of the invention may be seen from the above, from the following description of the preferred embodiment when considered in conjunction with the drawing and from the appended claims.

In the drawings:

FIG. 1 is a simplified, schematic wiring diagram of a fuel burner control using a standing pilot flame for igniting fuel fed to a main burner and utilizing an electric continuous spark generator for lighting the pilot flame, and embodying the invention; the control being arranged for operation from a volt alternating power source; and

FIG. 2 is a simplified, schematic wiring diagram of another embodiment of the invention similar to that of FIG. 1, but operable from a 25 volt alternating power source.

With reference to the preferred embodiment of FIG. 1, 12.0 volts at 60 cycles per second from any convenient source (not shown) is applied to the circuitry over supply lines L1, L2. A main gas valve, generally designated MGV, is shown diagrammatically as being of the electromagnetic actuated type, having an actuating coil SEL. When coil SEL is energized, the valve opens permitting the flow of gaseous fuel from gas inlet IP to gas outlet OP, as indicated by directional arrows, for supplying fuel to a main burner (not shown) for ignition thereat from a standing pilot flame. The standing pilot flame is designated FL, fuel being supplied therefor through a manual rotorcock RC, controlling the flow of pilot fuel through a gas line GL.

A thermocouple TC is positioned to be heated by pilot flame FL and is connected across an energizing coil RSW of a reed switch indicated in broken line outline as RS. Reed switch RS includes a pair of normally open contacts RSC connected in series with main valve actuating coil SEL and a pair of thermostat contacts T positioned in the space to be heated, the series circuit being connected across supply lines L1, L2 through manual line switch MS.

Means for generating a continuous spark for igniting fuel at the pilot is provided. This spark generator includes a silicon controlled rectifier SCR connected in an oscillating circuit for pulsing the primary winding PR of a. high voltage spark transformer, generally designated ST. The secondary winding SEC of high voltage spark transformer ST is connected across a pair of spaced apart electrodes, designated SG, positioned to ignite fuel at the pilot outlet. Rectifier SCR (having an anode a, a cathode c and a gate g electrodes) has its anode electrode a connected through a diode D2 in series with a current limiting resistor R3 and switch MS to supply line L2. Its cathode electrode c is connected through a resistor R2 to a point intermediate reed switch contacts RSC and main valve actuating coil SEL. Another resistor R1 is connected shunting the anode-cathode circuit of rectifier SCR, the shunted circuit including resistor R2, diode D2 and resistor R3. A second diode D1 is connected between the cathode c and gate g electrodes of rectifier SCR so as to permit current flow only from the cathode c to gate g electrodes. A charging capacitor C is connected in series with primary winding PR of sparking transformer ST from the gate g to anode a electrodes of rectifier SCR in the named order.

In operation, assume that line switch MS is closed, applying power to the circuit, While rotorcock RC is manually rotated to permit the flow of gas through line GL to the pilot outlet. As the voltage on supply line L2 becomes positive with respect to supply line L1, capacitor C charges to fully charged condition through line switch MS, resistor R3, diode D2 and primary winding PR to supply line L1. As supply line L1 becomes positive with respect to supply line L2, during the start of the next negative half cycle of the applied power, the potential at gate electrode g of rectifier SCR with respect to its cathode electrode (the potential appearing across diode D1) becomes sufliciently positive to cause rectifier SCR to conduct through its anode-cathode circuit, discharging previously charged capacitor C through primary winding PR of the high voltage spark transformer ST. Such pulsing of primary winding PR causes generation of an output spark across spark gap SG to ignite the pilot flame.

Next assume that thermocouple TC senses the pilot flame FL and is heated sufliciently to generate enough current to actuate reed switch RS by means of its energizing coil RSW. Switch RS closes its contacts RSC, applying a relatively low impedance path across diode D1. This low impedance path prevents the development of a sulficient voltage across the gate-cathode electrodes of rectifier SCR to fire the rectifier. Rectifier SCR is thus maintained in nonconducting condition, stopping the spark generator oscillator circuit from generating sparks across gap SG.

It may be noted that, until reed switch contacts RSC are actuated closed (by the sensing of the pilot flame by the thermocouple TC) capacitor C charges every positive half cycle of the applied voltage and discharges at the start of each negative half cycle of the applied voltage, producing a spark at spark gap SG once every negative half cycle of the applied voltage.

As reed switch contacts RSC close, they also prepare an energizing circuit for the actuating coil SEL of main gas valve MGV, preparing the main gas valve for operation subject to a call for heat from thermostat T.

Next assume that heat is called for by the closing of standing pilot flame FL is inadvertently extinguished. Under such condition, as thermocouple TC cools sufiiciently, insuflicient power is applied to actuating coil RSW of reed switch RS to maintain reed switch contacts RSC closed. Contacts, RSC, thus, return to their normally open condition, interrupting the energizing circuit of coil SEL of main gas valve MGV. Main gas valve MGV closes, shutting off the supply of fuel to the main fuel burner (not shown) which is, thereby, extinguished. Simultaneously, this reopening of contacts RSC removes the low impedance path previously applied between the gate g and cathode c electrodes of silicon controlled rectifier SCR. Under such conditions, as was previously described, the spark generator immediately again provides a continuous spark every negative half cycle of the applied voltage across spark gaps SG to relight the pilot flame FL.

Next assume that the pilot flame is relit, reheating thermocouple TC sufiiciently to reclose reed switch contacts RSC, thereby causing reenergization of main gas valve MGV and stopping the spark generator, as was previously described.

The embodiment of FIG. 2 operates exactly the same as that of FIG. 1 with the exception that, instead of voltpower, power at the relatively low voltage of 25 volts, 60 cycles per second may be applied from any convenient source (not shown) to the circuitry over supply lines L1, L2. This 25 volt, 60 cycle power is transformed by TR to 120 volt power for the spark generator. Transformer TR has a primary winding PR-l connected across supply lines L1, L2 through line switch MS, and a secondary winding SE connected to supply line L1 at one end and at its, other end to the right hand side of resistor R3 in the anode circuit of silicon controlled rectifier SCR. Transformer TR is wound to provide the polarities indicated by the dots. In addition, a second capacitor C2 is connected between the anode of diode D1 and the right hand end of resistor R2 in the cathode circuit of rectifier SCR. With this arrangement the spark generator oscillator of rectifier SCR is supplied with a steppedup voltage of 120 volts by transformer TR, as in the FIG. 1 embodiment, but is triggered (through resistors R1 and R2 and diode -D1) at 25 volts; the voltage at which the main gas valve MGV is operated in this embodiment. This beneficially enables the same continuous spark generator to be utilized in a gas control using a 25 volt actuated gas valve and one using a 120 volt actuated gas valve, as in FIG. 1.

The circuit operation is the same as that previously described for the FIG. 1 continuous spark generator with reed switch contacts RSC functioning exactly the same to provide a low impedance path across the gate-cathode electrodes of rectifier SCR to stop continuous spark generation, under conditions where thermocouple TC is heated sufliciently by pilot flame FL.

The remainder of the FIG. 2 circuit operation is exactly the same as that of the FIG. 1 circuit with the exception that transformer TR provides across its winding SE the voltage polarity which causes, when resistor R3 is positive with respect to the cathode c of rectifier SCR, capacitor C1 to charge through resistor R3, diode D2, primary winding PR, to line L1. Under conditions where the voltage applied by secondary winding SE to resistor R, becomes negative with respect to the voltage applied to the gate electrode g of rectifier SCR, rectifier SCR fires, causing capacitor C1 to discharge through primary winding PR in the anode-cathode circuit of rectifier SCR, pulsing the primary winding PR and causing a spark across gap SG.

Capacitor C2 is provided between resistor R2 and the cathode electrode c of rectifier SCR to isolate reed switch contacts RSC from rectifier SCR to insure that, when the reed switch contacts close, the silicon controlled rectifier is maintained in nonconducting condition.

Satisfactory operation was obtained in one tested embodiment of the FIG. 1 circuit using the following components: resistors R1 and R2 at kilohms, resistor R3 at 150 ohms, capacitor C at 1 microfared and rectifier SCR of the GEC106B type.

Satisfactory operation was obtained in one tested embodiment of the FIG. 2 circuit utilizing the following circuit components: resistor R1 at 4.7 kilohms, resistor R2 at 1.5 kilohms, resistor R3 at 270 ohms, capacitor C1 at 1 microfarad, capacitor C2 at .33 microfarad and rectifier SCR of the GEC106B type.

It may be noted that with either embodiment of the subject control a single pair of reed switch contacts (RSC) are utilized to control spark generation and actuation of main valve MGV, thereby providing an efficient automatic burner control.

As changes can be made in the above described construction and many apparently different embodiments of this invention can be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown on the accompanying drawing be interpreted as illustrative only and not in a limiting sense.

What is claimed is:

1. A control for a fuel burner system having a main burner comprising:

fuel feeding means operative when energized for causing fuel to flow to said main burner for ignition thereat,

pilot flame means positioned for transferring ignition from the pilot flame to said main burner,

an electric igniter means operative for lighting said pilot flame,

a thermocouple positioned for monitoring said pilot flame for generating current when heated by said pilot flame,

thermostat means for calling for energization of said fuel feeding means,

a single pair of normally open contacts in series with said thermostat means for causing energization of such fuel feeding means through said thermostat means under conditions where said contacts are actuated closed,

magnetic actuating means responsive to said thermocouple for actuating said normally open switch con tacts to closed condition when energized sufficiently by said thermocouple current,

said single pair contacts when actuated closed preventing operation of said igniter means while automatically causing reoperation thereof when in open condition.

2. A control as set forth in claim 1 wherein said electric igniter means includes a pair of spaced apart electrodes positioned for igniting said pilot flame, and

continuous spark generating oscillating means for providing at said pair of spaced apart electrodes a continuous igniting spark for said pilot flame.

3. A control as set forth in claim 2 wherein said pair of normally open contacts and said magnetic actuating means comprise:

thermocouple responsive reed switch means including i normally open reed switch contacts and magnetic actuated coil means connected for energization by said thermocouple for causing closing of said reed switch contacts under heated conditions of said thermocouple.

4. The control as set forth in claim 3 wherein said spark generating means comprise a silicon controlled rectifier having anode, cathode, and gate electrodes,

a first diode connects said cathode electrode to said gate electrode permitting current flow only from the cathode to gate electrodes,

a second diode connected in the anode circuit of said silicon controlled rectifier for providing half-wave rectified power thereto from an alternating power source,

an ignition transformer having a primary winding and a secondary winding, said secondary winding being directly connected across said spark electrodes positioned for igniting said pilot flame,

said primary winding being connected in series with a capacitor across the anode-gate circuit of said silicon controlled rectifier for providing high voltage pulses through said primary winding for igniting said pilot flame under conditions where said capacitor discharges through said silicon controlled rectifier,

said reed switch contacts being connected between the cathode and gate electrodes of said silicon controlled rectifier for providing a low impedance shunt path therebetween for maintaining said rectifier in nonoscillating condition under conditions where reed switch contacts are closed for energizing said fuel feeding means.

5. A control as set forth in claim 4 wherein step-up transformer means are provided between said applied power and said silicon controlled rectifier oscillating means for providing a predetermined increased voltage energization of said oscillator under conditions where said fuel feeding means is operable at the lower input voltage to said stetrup transformer means.

'6. A control for a main fuel burner comprising:

a pilot burner,

a thermocouple positioned in the flame of said pilot burner for generating current when heated,

fuel feeding means operative when energized for causing fuel to flow to said rnain burner for ignition thereat by said pilot flame,

means for calling for energization oof said fuel feeding means,

a silicon controlled rectifier having anode, cathode and gate electrodes,

a pair of normally open electrical contacts,

means responsive to current generated by said thermocouple for actuating said contacts closed under heated conditions of said thermocouple and for returning said contacts to open condition under cold conditions of said thermocouple,

said fuel feeding means being connected in series circuit with said contacts for energization from an alternating power source in response to said means calling for said energization,

said silicon controlled rectifier having its said cathode electrode connected through a resistor to a point intermediate said contacts and said fuel feeding means in said series circuit,

said rectifier having its anode-cathode circuit connected through a first diode and said contacts across said alternating power source for applying unidirectional power through the anode-cathode circuit of said rectifier through said contacts,

said gate electrode of said rectifier being connected shunting said contacts,

said gate electrode also being connected to the anode electrode of said rectifier through a capacitor,

a second diode having an anode and cathode with its anode electrode connected to said rectifier cathode and its cathode electrode connected to the gate electrode of said rectifier,

ignition transformer means having primary and secondary windings,

said primary winding being connected in series with Eaid capacitor in the gate-anode circuit of said rectithe said secondary winding of said ignition transformer being connected across a pair of electrodes spaced apart and in a position to ignite fuel at said pilot burner, under conditions where said energization calling means calls for energization of said fuel feeding means,

said thermocouple means causing, under conditions of being heated sufficiently by said pilot fuel burner, actuation of said contacts to closed condition for energization of said fuel feeding means and simultaneously providing a low impedance path across the gate-cathode circuit of said rectifier maintaining said rectifier in nonfired condition.

7. A control as set forth in claim 6 wherein said pair of normally open electric contacts and means for actuating said contacts closed comprise a reed switch having a pair of normally open contacts and a magnetic actuating coil connected for energization by said thermocouple means.

References Cited UNITED STATES PATENTS EDWARD G. FAVORS, Primary Examiner US. Cl. X.R.

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