US3619097A

US3619097A - Safety timed burner control system

Info

Publication number: US3619097A
Application number: US14956A
Authority: US
Inventors: Homer B Clay; William Lloyd Hewitt
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1970-02-27
Filing date: 1970-02-27
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09
Also published as: CA949165A; GB1334245A; JPS5018619B1; DE2107912A1; NL7102169A

Abstract

A burner control system adapted to be connected to a fuel burner wherein a safety timing circuit is used to assure ignition of the burner fuel and subsequent proper operation of the burner. The safety timer circuit utilizes a capacitive voltage divider network that initially is supplied with energy at start up of the system, and which is subsequently supplied with energy from a flame rectification sensor in order to assure the ignition and continued operation through an ignition control means and a silicon-controlled spark-generating circuit. The sensing of flame also causes the shutdown of the silicon controlled spark ignition portion of the system.

Description

United States Patent [72] inventors Homer B. Clay Minneapolis, Minn.; William Lloyd Hewitt, Harbor City, Calif. [21] Appl. No. 14,956 [22] Filed Feb. 27, 1970 [45] Patented Nov. 9, 197] [73] Assignee Honeywell Inc.

Minneapolis, Minn.

[54] SAFETY TIMED BURNER CONTROL SYSTEM 9 Claims, 2 Drawing Figs.

[52] U.S.Cl 431/80 [5 1] Int. Cl F23n 5/10 [50] Field of Search 43 H78, 80, 264

[56] References Cited UNITED STATES PATENTS 3,348,104 10/1967 Zielinskietal. 431/78 X 3,445,l72 5/l969 Zielinski 3,520,645 7/l970 Cotton et al.

Primary Examiner- Edward G. Favors Attorneys-Lamont B. Koontz and Alfred N. Feldman ABSTRACT: A burner control system adapted to be connected to a fuel burner wherein a safety timing circuit is used to assure ignition of the burner fuel and subsequent proper operation of the burner. The safety timer circuit utilizes a capacitive voltage divider network that initially is supplied with energy at start up of the system, and which is subsequently supplied with energy from a flame rectificationsensor in order to assure the ignition and continued operation through an ignition control means and a silicon-controlled spark-generating circuit. The sensing of flame also causes the shutdown of the silicon controlled spark ignition portion of the system.

I I6 i SENSOR BURNER SAFETY TIMED BURNER CONTROL SYSTEM BACKGROUND OF THE INVENTION In fuel burner control systems it is necessary to supply an inexpensive and reliable means of obtaining ignition, response to the existence of flame, and a safety shutdown in case there is a failure of the burner to ignite. This can be accomplished in many different ways but the present invention is directed to a particularly economical arrangement where safety is accomplished along with multiple use of components for economy.

SUMMARY OF THE INVENTION The present invention has particular utility in the burner control art as a means of obtaining safe operation of a fuel burner. An input circuit in the form of a capacitive voltage divider is provided that is initially charged at a called for operation of the burner and this initial charge causes a field effect transistor to in turn operate a silicon controlled rectifier through which a fuel valve or a fuel controlled relay is energized. Simultaneously, a relaxation type of silicon controlled oscillator is operated for generation of a spark at the fuel burner to ignite the fuel issuing upon opening of the fuel valve. The subsequent generation of flame at the burner is sensed by a rectification flame-sensing means in the form of a flame rod. The flame rod supplies a rectified current back to the input of the capacitive voltage divider network to keep the network properly charged for continued operation of the system. This rectified voltage also is utilized to control a rectification sensitive means in the input circuit of the silicon-controlled sparkgenerating arrangement. When the flame rod senses the existence of flame, the silicon controlled relaxation type oscillator is deactivated to remove the generation of spark at the burner.

All of the equipment utilized forms a completely fail safe system in that the malfunction of a component in the system shuts the fuel valve, as does the loss of flame or grounding at the flame sensor since a continuous flow of energy from the flame rod is necessary to keep the system in operation.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of a complete system; and FIG. 2 is a complete schematic representation including some numerical values of a preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I a block diagram of a complete burner control system is disclosed and is adapted to be connected to a fuel burner shown generally at and a source of alternating current voltage connected between conductors 11 and 12. The fuel burner 10 includes a grounded burner member 13, a pair of

spark electrodes

14 and 15, and a sensor 16 in the form of a rectification flame sensing means that supplies a rectified alternating current when a flame is present at the burner member 13. These members are all conventional and have been disclosed as a means of explaining the operation of the burner control system itself.

Conductor 11 is connected to a controller or thermostat 20 so that energy can be controllably supplied to the burner control system. Thermostat 20 is further connected to conductor 21 that supplies energy to a safety timer means 22 that includes and energy storage means and which is connected between the

conductors

21 and 12. The safety timer means 22 becomes operative on the application of an alternating current voltage thereto by having a set amount of energy stored in the energy storage means so that a timing function can be initiated along with a control signal on conductor 23 to a fuel control means generally shown at 24. The fuel control means 24 includes a current control device O2 in the form of a silicon controlled rectifier that is conductive whenever a control signal is applied on conductor 23 and which conducts through a fuel supply means 25 which is a valve or relay controlling a valve. Also, as part of the fuel control means 24, a resistor 26 is supplied so that whenever current flows in the silicon controlled rectifier Q2, a voltage is developed across the resistor 26.

The voltage that is generated across resistor 26 is applied to a conductor 27 to an ignition means generally shown at 30. The ignition means 30 includes a rectification sensitive means 31 that normally receives the signal on conductor 27 and controls it for application to a conductor 32 that in turn energizes a spark ignition device 33. Spark ignition device 33 includes a silicon controlled rectifier Q4 in a well known type of relaxation type of spark ignition circuit. The spark ignition device 33 includes an output transformer 34 which is grounded at conductor 35 and connected to the spark electrode 15 by conductor 36. The previously described spark electrode 14 of the fuel burner 10 is also grounded so that energy from the transformer 34 is applied as a spark between the

electrodes

14 and 15 to ignite fuel from the burner member 13. To complete the ignition means 30, a step-up transformer 37 is disclosed as being connected across

conductors

12 and 21 to supply a higher voltage to the ignition means 30 than would be available on conductors l1 and 12 which are connected to a relatively low voltage supply. The transformer 37 has one of its secondary windings grounded at 38 and the other of its windings 39 connected to the conductor 12. The transformer 37 is phased to apply current to the ignition means 30 during the half cycle when safety timer means 22 is not drawing current.

In order to complete the system, the rectification flame sensor means 16 is connected by a conductor 40 to a pair of

conductors

41 and 42. The conductor 41 connects to the ignition means 30 at the flame rectification sensitive means 31, while the conductor 42 is connected to the safety timer means 22 at its input. The conductor 42 supplies energy from the rectification flame sensitive means 16 to the energy storage means contained in the safety timer means 22.

OPERATION-FIG. l

The general operation of the schematic disclosed in block form in FIG. 1 is accomplished by a call for heat by the thermostat 20 closing to apply energy on

conductors

21 and 12 to the safety timer means 22. The energy storage means contained therein takes on a fixed amount of energy by charging a pair of capacitors, that will be disclosed in detail in connection with FIG. 2. This operation provides a signal on conductor 23 to the silicon controlled rectifier Q2 that starts it into conduction to energize the fuel supply means 25 which supplies fuel to the burner 10. The conduction of Q2 generates a voltage across resistor 26 that is applied to the rectification sensitive means 31 of the ignition means 30. Simultaneously, through conductor 32, the capacitor spark ignition device 33 is energized to provide a high voltage spark across the

electrodes

14 and 15. With fuel issuing from the burner member 13 and a spark existing between the

electrodes

14 and 15, a flame is generated. The generation of flame causes a rectified alternating current to flow between the rectification flame sensor means 16 and ground. This rectified alternating current is supplied through conductor 40 to

conductors

41 and 42. The voltage supplied on conductor 41 is conducted to the rectification sensitive means 31 which senses the presence of the rectified alternating current and removes the triggering signal for the silicon controlled rectifier Q4 that is part of the spark discharge or ignition device 33. This turns off the spark.

The rectified alternating current supplied on conductor 42 supplies energy to the storage means in the safety timer means 22 to prevent the flame safety timer means 22 from having the energy stored on the energy storage means depleted. As long as energy is available, a control signal is available through conductor 23 to keep the silicon controlled rectifier O2 in conduction thereby keeping the fuel supply means 25 energized. This is a normal start-up and operation of the system.

If, for some reason, the system fails to create a flame at the burner member 13, the rectification flame sensor means 16 fails to sense the existence of flame and no rectified alternating current is supplied through

conductors

41 and 42. Without a rectification signal on conductor 41, the ignition means 30 continues to supply a spark. At the same time there is no energy supplied through conductor 42 to restore the energy being drained in the safety timer means 22 from its energy storage means. As soon as the energy in the energy storage means is depleted, the signal on conductor 23 is removed and the silicon controlled rectifier Q2 ceases to conduct. This closes the fuel supply means 25 and removes the source of operating signal for the ignition means 30 thereby turning off the ignition means 30. This then shuts the system down in a safe mode upon the failure of a flame to be generated at the burner member 13.

A detailed disclosure of the entire circuit including all of the components and wiring of the block diagram of FIG. 1 is disclosed in FlG. 2. The same reference numerals are utilized in both figures to identify the identical components or conductors.

The schematic diagram disclosed in FIG. 2 has been referenced with numerical values for some of the components. The capacitors are in microfarads and the resistors are in ohms in order to put the values of a typical embodiment of the invention into perspective. The values stated are illustrative only and are not intended to be limitations in any way.

The supply voltage is again disclosed between

conductors

21 and 12 and in the embodiment disclosed would be typically 24 volts as is obtained from a conventional control transformer in a fuel burner system for residential or similar types of applications. The safety timer means 22 is disclosed as including a pair of

capacitors

50 and 51 connected in series through a pair of

diodes

52 and 53 across the

conductors

21 and 12. This series arrangement makes up the energy storage means for the safety timer means 22. A common junction 54 between the

capacitors

50 and 51 is applied through a resistor 55 to the gate 56 of a field effect transistor Q1 that operates as a current control means in the safety timer means 22. A drain 57 of the field effect transistor 01 is connected through a resistor 58 to a capacitor 60 which in turn is connected back to a junction 61 between the

diodes

52 and 53. A source 62 of the field effect transistor 01 is connected to the conductor 12 to provide the main operating circuitry for the safety timer means 22.

The input of the field effect transistor 01 also contains a very high resistance bleeder network of

resistors

73 and 64 along with bypass capacitors 65 and 66 that are used to shunt high frequency pulses. A further high resistance bypass resistor 67 is disclosed which is used to bleed off the energy stored in the

capacitors

50 and 51 when the unit is not in operation.

Part of the output circuitry for the safety timer means 22 includes a pair of diodes 70 and 71 that are connected in series with a resistor 72 to connect the drain 57 of the field effect transistor O1 to conductor 12. This circuitry is used to discharge the capacitor 60 at an appropriate time to provide an energizing signal on conductor 23 for the fuel control means 24. The diodes 70 and 71 also provide a fail safe function in the event that the transistor Q1 fails. The conductor 23 is connected to the gate 73 of the silicon controlled rectifier 02 which has a cathode 74 connected to resistor 26 which in turn is connected to the conductor 12. The anode 75 of the silicon controlled rectifier Q2 is connected through conductor 76 to the fuel supply means of valve 25 which in turn is connected by conductor 77 to conductor 21. The fuel supply means or valve 25 is shunted by a diode 78 and a resistor 79 for freewheeling and proper impedance matching of the silicon controlled rectifier 02 to the fuel valve means 25.

The cathode 74 of the silicon controlled rectifier O2 is connected by conductor 80 to a resistor 81 that is selected to provide a timing function in the discharge of the capacitor 50 through the resistor 81 and the resistor 26 to shut the system down in the event that flame is not sensed at the burner 10. The resistor 26 and the resistor 81 provide for approximately a or 11 second delay before the charge on capacitor 50 is depleted sufficiently to deactive the safety timer means 22 in the event that flame is not established at the fuel burner 10.

The cathode 74 of the silicon controlled rectifier O2 is connected by conductor 27 through resistor 82 to the previously mentioned rectification sensitive means 31 which is a field effect transistor Q3. The gate 83 of the field effect transistor 03 is connected through a resistor 84 and a resistor 85 to the conductor 41 and is the control path for the receipt of rectified alternating current from the sensor means 16 when flame is sensed. The gate 83 is further connected by resistor 86 to the conductor 12 to complete the gate control circuit for the field effect transistor Q3.

A source 87 of the field effect transistor O3 is connected through a resistor 88 and a diode 90 to the conductor 12 and from the input means to silicon controlled rectifier 04 that forms part of a conventional relaxation type oscillator spark igniter circuit. This circuit includes the transformer 34, a storage capacitor 91, a diode 92, and a current-limiting resistor 93. The energy storage capacitor 91 receives a charge through the diode 92 and resistor 93 on alternate haif cycles of the applied line voltage, and the capacitor 91 is then periodically discharged through the silicon controlled rectifier O4 in a conventional fashion. The transformer 34 is connected by conductors 35 to ground and 36 to the electrode 15 to complete the circuitry.

OPERATION OF FIG. 2

Upon application of an alternating current voltage to

conductors

12 and 21 through such a device as a controller or thermostat, current flows through the circuit made up of the

capacitors

50, 51 and

diodes

52 and 53 to charge the capacitors S0 and 51 with equal voltage values. Subsequently, no further charge enters the capacitor 50 but various resistive networks begin discharging the capacitor 50. The various discharge paths are made up of the high resistance network of

resistors

63 and 64, the timing

resistors

26 and 81, the resistors in the gate circuit 56 of the field effect transistor 01, and the

circuit including resistors

63, 85, 84, and 86. All of these resistive networks are quite high in value with the exception of the

timing resistors

26 and 81 and, therefore, the only resistors of real consequence in a normal operating circuit are the

resistors

26 and 81 which provide a discharge time for operation of the field effect transistor Q1 of about 10 or 11 seconds.

Through the resistor 55 the field effect transistor 01 receives a negative voltage at its gate 56 and this voltage is used to turn the field effect transistor O1 to an off condition when the source potential on conductor 12 is negative. When the source potential becomes positive by a reversal in the voltage on

lines

12 and 21, the field effect transistor Q1 conducts and allows the capacitor 60 to take on a charge through the source 62 to drain 57 connection of the field effect transistor ()1 by way of the resistor 58. The energy stored in capacitor 60 can be discharged only through the diodes 70 and 71 through the resistor 72 to provide a trigger signal to the silicon controlled rectifier Q2. This function occurs every half cycle after the initial application of power and, therefore, a trigger signal is applied to gate 73 of the silicon controlled rectifier Q2 causing the silicon rectifier O2 to conduct through the fuel supply means 25. This conduction generates a potential across the resistor 26 which is applied through conductor 27 and resistor 82 to the field efi'ect transistor Q3. The application of the potential generated across the resistor 26 to the field effect transistor Q3 prior to the establishment of a rectified alternating current at the sensor 16 allows the field effect transistor Q3 to conduct through the resistor 88 to trigger the silicon controlled rectifier Q4 into conduction. The conduction of the transistor Q4 dumps energy that has been previously stored in capacitor 91 through the transformer 34 to generate a spark across the

electrodes

14 and 15. The capacitor 91 has received a charged on half cycle of the applied voltage from the transformer 37 through the resistor 93 and diode 92 in a conventional fashion.

As long as an adequate charge is available on the

capacitors

50 and 51, the field effect transistor Q1 alternately charges the capacitor 60 and allows the capacitor 60 to discharge through the resistor 72 to trigger the silicon controlled rectifier Q2 into conduction along with the operation of the ignition means 30. The ignition means 30 generates a spark between

electrodes

14 and 15 until one of two events occur.

In the event that the spark between

electrodes

14 and 15 along with the fuel issued from the fuel supply means 25 is ignited at the fuel burner 10, the system is in normal operation. A rectified alternating current is then generated between ground at the burner member 13 and the rectification flame sensor means 16. The rectified alternating current is applied through conductor 40 to the

further conductors

41 and 42. The energy supplied on conductor 41 flows through

resistors

85, 84 and 86. This energy is sufficient to bias the field effect transistor Q3 to an off" state thereby removing the voltage drop across resistor 88 which was used to trigger the spark between the

electrodes

14 and 15 by turning the silicon controlled rectifier Q4 off. The energy supplied on conductor 42 from the rectification of flame supplies energy to keep the balance of energy in the

capacitors

50 and 51 in a state wherein the field effect transistor Q1 will conduct on alternate half cycles. This supplies a charging current to the capacitor 60 so that the discharge of capacitor 60 can trigger the silicon controlled rectifier Q2 into conduction to keep the fuel supply means 25 energized for a continuous flow of fuel.

ln the event that the spark at

electrodes

14 or 15 is absent or insufficient to ignite fuel, there is no rectified alternating current voltage supplied between the burner member 13 and the rectification flame sensor means 16 and no voltage is supplied on conductor 40 to either 41 or 42. The lack of energy being supplied to conductor 42 allows the capacitor 50 to be discharged through the

timing resistors

26 and 81 in approximately or 11 seconds. This deactivates the field effect transistor Q1 and prevents a flow of current from the source 62 to the drain 57 to charge the capacitor 60. When the capacitor 60 is no longer charged, the silicon controlled rectifier O2 is no longer triggered into operation and the fuel supply means 25 closes. This also turns off the operation of the ignition means 30.

The burner safety timer control circuit described is dependent on a safety timer means 22 that has some form of energy storage means for use in timing a safe start and operating period. In the event that a failure to start occurs in the safety timing means operational time, the fuel supply means 25 closes and the system locks itself out. In the event that flame is provided at the sensor means 16 prior to the timing out of the discharge of capacitor 50, the silicon controlled rectifier O2 is kept in conduction and the fuel supply means 25 is kept open until energy is removed from

conductors

12 and 21 to shut the burner off.

The present system provides for a fail safe operation of a fuel burner system. In the event that a proper flame is not established within a predetermined time, the system will shut itself down. Also, the existence of a flame in the proper time turns off the generation of the electric spark between

electrodes

14 and 15 by operating through an ignition means 30 and particularly through the rectification sensitive means 31 which is in the gate circuit of the silicon controlled rectifier Q4. The present system provides a unique double function and safety arrangement for the operation of fuel burners and has been disclosed with one particular circuit arrangement that would accomplish this end. The circuitry can be altered in any number of ways in order to carry out the present invention and the applicants wish to be limited in the scope of their invention solely by the scope of the appended claims.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A burner control system adapted to be connected to a fuel burner and a source of alternating current voltage for safe operation of said fuel burner, including: safety timer means ininitially energized to an operable stage by application of said altematrng current voltage to said system; said safety timer means having an input connected to rectification flame sensor means which upon sensing the existence of flame is capable of supplying energy to said energy storage means at a faster rate than said energy drain means is capable of depleting energy from said energy storage means; said safety timing means further having output circuit means; fuel control means and ignition means connected to said output circuit means to initiate operation of said system as long as said energy storage means maintains an adequate energy level; and said ignition means including rectification sensitive means connected to said rectification flame sensor means with said rectification sensitive means disabling said ignition means upon the existence of flame at said rectification flame sensor means.

2. A burner control system as described in claim 1 wherein said energy storage means is capacitive voltage divider means and rectification means connected to said alternating current voltage source.

3. A burner control system as described in claim 2 wherein said energy drain means is at least one resistive electrical circuit.

4. A burner control system as described in claim 3 wherein said fuel control means includes a silicon controlled rectifier for operation of a fuel supply for said fuel burner, and said ignition means includes a relaxation oscillator type of silicon controlled rectifier spark ignition circuit.

5. A burner control system as described in claim 4 wherein said safety timer means includes a field effect transistor for control of said fuel control means and said ignition means with said capacitive voltage divider means connected to a gate of said field effect transistor to control the operation of said transistor when sufficient energy is received from said rectification flame sensor means.

6. A burner control system as described in claim 5 wherein said silicon controlled rectifier relaxation oscillator of said spark ignition circuit includes an input circuit controlled by a second field effect transistor of said rectification sensitive means in response to current from said rectification flame sensor means to disable said ignition means when flame is present at said flame sensor means.

7. A burner safety timer control circuit adapted to be connected to a source of alternating current voltage and to rectification flame sensor means of a fuel burner, including: capacitive voltage divider means and rectification means connected to said alternating current voltage source upon energization of said burner control circuit to supply an initial charge to said capacitive voltage divider means; current drain means connected to said capacitive voltage divider means to slowly drain said capacitive voltage divider means of said initial charge; high impedance solid-state current control means having an input connected to said capacitive voltage divider means and output means adapted to be connected to operate said fuel burner when said capacitive voltage divider means charge is maintained; and connection means adapted to connect said rectification flame sensor means to said capacitive voltage di vider means to supply a charge to said capacitive voltage divider means when said fuel burner has a proper flame to maintain said charge and keep said solid-state current control means output means operating said fuel burner.

8. A burner safety timer control circuit as described in claim 7 wherein said high impedance solid state current control means is a field effect transistor having a gate as said input connected to said capacitive voltage divider means.

9. A burner safety timer control circuit as described in claim 7 wherein said capacitive voltage divider means includes a pair of capacitors, and said rectification means is diode means in series circuit with said pair of capacitors.

Claims

1. A burner control system adapted to be connected to a fuel burner and a source of alternating current voltage for safe operation of said fuel burner, including: safety timer means including energy storage means having slow energy drain means initially energized to an operable stage by application of said alternating current voltage to said system; said safety timer means having an input connected to rectification flame sensor means which upon sensing the existence of flame is capable of supplying energy to said energy storage means at a faster rate than said energy drain means is capable of depleting energy from said energy storage means; said safety timing means further having output circuit means; fuel control means and ignition means connected to said output circuit means to initiate operation of said system as long as said energy storage means maintains an adequate energy level; and said ignition means including rectification sensitive means connected to said rectification flame sensor means with said rectification sensitive means disabling said ignition means upon the existence of flame at said rectification flame sensor means.

7. A burner safety timer control circuit adapted to be connected to a source of alternating current voltage and to rectification flame sensor means of a fuel burner, including: capacitive voltage divider means and rectification means connected to said alternating current voltage source upon energization of said burner control circuit to supply an initial charge to said capacitive voltage divider means; current drain means connected to said capacitive voltage divider means to slowly drain said capacitive voltage divider means of said initial charge; high impedance solid-state current control means having an input connected to said capacitive voltage divider means and output means adapted to be connected to operate said fuel burner when said capacitive voltage divider means charge is maintained; and connection means adapted to connect said rectification flame sensor means to said capacitive voltage divider means to supply a charge to said capacitive voltage divider means when said fuel burner has a proper flame to maintain said charge and keep said solid-state current control means output means operating said fuel burner.