US3541549A - Self-checking flame detection apparatus - Google Patents

Description

Nov. 17., 1970 lD. L. GRAVES 3,541,549

SELF-CHECKING FLAME DETECTION APPARATUS .Filed Aug. 19, 1968' INVENTOR DONALD L. GRAVES United States Patent O 3,541,549 SELF-CHECKING FLAME DETECTION APPARATUS Donald L. Graves, Montville, NJ., assignor to McGraw- Edison Company, Elgin, Ill., a corporation of Delaware Filed Aug. 19, 1968, Ser. No. 753,387 Int. Cl. G0811 29/00; F23q 23/08 U.S. Cl. 340--410 12 Claims ABSTRACT OF THE DISCLOSURE lf the flame fails in a fuel burner and th fuel valve is not closed shortly thereafter, and explosion hazard may occur. It is therefore essential from a safety standpoint that each fuel burner installation be provided with a safeguarding apparatus which will close the fuel valve with little delay when a flame failure occurs. However, such safeguarding apparatus may itself become defective and no longer perform its safeguarding function. The present system includes a comprehensive safety means which checks the detector by intermittently shielding the detector from the sensed flame characteristic to simulate a condiion of flame failure and then reacts to initiate closing of the fuel valve if either the detector or the checking apparatus does not function properly.

Prior fail-safe systems such as are taught by Rowell Pats. Nos. 2,798,213, 2,807,009 and 2,807,011 are characterized typically by feedback-operated shutter systems which may intercept the sensed flame characteristic by as much as fifty percent of the time leaving them as much as fifty percent dead time when the flame detector is inoperative to perform its intended function, and by energy storage devices (condensers) which are switched intermittently with the operation of the shutter between a D.C. voltage source and the protective relay to operate such relay directly by the stored energy. These systems are characterized by frequent operation of the switching means, causing heavy wear and tear on the apparatus, particularly since the checking operation is carried on continuously day and night. In the present improved system, a burner control relay is not operated directly by stored energy but is operated by a generated power supply controlled by stored energy in a high impedance circuit allowing periods of continuous operation of up to two minutes between recharging of acomparatively small condenser. Also, the shutter operation is not controlled by a feedback circuit but by timing means which can be set to reoperate the shutter at inervals approaching the discharge period of the condenser, with the duration of each shutter operation being set as low as one second or less. Thus, the dead time is reduced and the rate of shutter and switch operation is less frequent, causing the wear and tear on the apparatus to be reduced and enabling accordingly a higher checking and performance reliability.

An object of the invention is therefore to provide a novel safety apparatus for a fuel burner which checks intermittently the operability of the flame detector system and of the checking apparatus itself while imposing a dead time on the detector system of generally less than ten percent, and without incurring excessive wear and tear 3,541,549 Patented Nov. 17, 1970 on the apparatus whereby to enable a higher reliability in detection and in checking performance to be attained.

Another object is to provide such improved safety apparatus which can be preset to check the detector at intervals ranging from a few seconds to two minutes or more.

These and other objects and features of the invention will be apparent from the following description and the appended claims.

ln the description of the invention, reference is had to the accompanying schematic circuit diagram showing a preferred embodiment of the invention.

The primary power supply for the system comprises an input power transformer T1 having a primary winding connected through an on-off power switch 10 to a pair of power leads 11 to be connected to a 120 volt A.C. source not shown. The secondary winding of the transformer T1 is center tapped and connected through a fullwave rectifier D1-D4 to provide a primary 24 Volt D.C. supply. The positive side of this 24 volt D.C. supply is filtered with respect to a center tap line 12 by a series resistor R1 and a shunt capacitor C1 and the full 24 volts are filtered with respect to the negative side 13 by series resistors R1 and R2 and a shunt capacitor C2. The 24 volt supply provides the operating power for the electronic components of the system except for an oscillator Q1 and a trigger amplifier Q2 connected to the center tap line 12. The oscillator is operated from the charge stored in a condenser C3. The condenser is initially charged by connecting it between the center tap line -12 and the plus side El, and is recharged intermittently to keep the oscillator running as necessary by connecting it to a voltage supply variably intermediate that of the center tap line 12 and the plus side El. As will appear, the oscillator must be kept running in order to permit sustained energization of a burner control relay KF.

The A.C. power supply 11 is connected also through the on-off power switch 10 by leads 14 and 15 to the series connected primaries of a coupling transformer T3 and a voltage step-up transformer T4 which is associated with an ultraviolet flame detector 16. The secondary of the transformer T4 is connected through a resistor R28 to a U-V detector tube 17 preferably of the type disclosed in the Howling Pat. No. 3,047,761, dated July 31, 19612. This detector tube comprises two symmetrical electrodes 18 enclosed in a glass envelope 19 containing an ionizing gas such as hydrogen. The tube is capable of passing alternating current when a firing potential of 700 volts is applied across the electrodes and the electrodes are subjected to ultraviolet radiation. Once the tube is fired it continues to pass current until the applied potential falls below a sustaining value of around 330 volts. Thus, when the tube is operated from alternating current supply it is quenched automatically after each half cycle. The tube is housed in one compartment of a box 20 subdivided by a partition wall 21. Exposure of the detector tube to a flame area 22 of the burner is via an aperture 23 in the partition wall 21 and a lens 24 in an outside wall of the box 20. In the second compartment of the box 20` is a shutter 25 operable across the aperture 23 by a coil 26 to intercept the U-V radiation from the flame area to the detector tube whereby to simulate a flame failure. The coil 26 is connected to an electronic timing circuit 27 diagrammatically indicated which can be manually set as by a knob 28 to cause the shutter to be operated intermittently at adjustable intervals and to be held operated for a given period of relatively short duration.

The A.C. power supply 11 is also connected through the on-off power switch 10 to a lead 29 to provide A.C. power with reference to the lead 15 for a flame-out indicator 30, a flame-on indicator 31 and an alarm device 32. A trial for ignition timer TFI, an igniter fuel valve 33, a main fuel valve 34 and an ignition transformer 35 are connected also between the power leads 15 and 29 under control of a manual start switch 36 as is hereinafter described.

The burner control relay KF must be held operated in order to keep the main fuel valve 34 open and the burner running. A generated D.C. current supply is made available to the relay KF so long as the condenser C3 has a charge thereon above a predetermined level to keep the oscillator Q1 running. The oscillator Q1 feeds through an amplifier stage Q2 to trigger a flip-flop circuit Q3-Q,1, and the flip-flop circuit feeds through amplifier transistors Q5 and Q3 to the primary winding of a transformer T2. The secondary winding of this `transformer feeds through a full-Wave rectifier D7-D13 into a circuit including the relay KF, a small resistor R16, a switching transistor Q7 and a diode D6, One terminal of the diode D3 is connected to the negative side 13 of the primary voltage supply.

The switching transistor Q7 is coupled to the U-V detector tube 17 through the coupling transformer T3, a pair of rectifiers D14 and D15, and an amplifier transistor Q3. When the detector tube is rendered intermittently conductive by incident U-V radiation, a sufficient current ows through the coupling transformer T3 and the amplier transistor Q3 to charge a biasing condenser C in the input circuit of the transistor Q7 whereby to render the transistor Q7 conductive within about .4 second after the detector tube is triggered. Thus, to keep the burner control relay KF operated, not only must the condenser C3 bear a sufficient charge but the U-V detector tube 17 must also be repetitively triggered to hold the transistor Q7 conductive except for the short check periods.

The oscillator Q1 has a high impedance input so that a condenser C3 of the order of 40G-500 microfarads is capable of keeping the oscillator Q1 running for a period exceeding two minutes after each recharging of the condenser before the energy stored in the condenser falls below the level necessary for operation. It is to be noted that the discharge time of condenser C3 establishes the maximum time between the successive periods for checking the detector system since the power to the condenser is shut off during the normal operating periods of the detector system and the condenser is recharged only when the shutter 25 is operated to simulate a flame failure and the transistor Q7 is nonconductive. A condenser C3 is connected across the burner control relay KF to hold this relay operated at least for a normal checking period.

It will be seen that when the power switch 10 is closed, the llame-out indicator 30 and the alarm device 32 are energized, a striking voltage is made available through transformer T1 to the detector tube 17 so that the tube will trigger as soon as it is excited by U-V radiation from a flame of the burner, and power is supplied to the shutter timer control 27. Also, the condenser C3 is charged from the line E1 through contacts KL1 of a load relay KL and center line 12 to start the oscillator Q1 running. However, the burner control relay KF is not operated yet because the switching transistor Q7 is still nonconducting.

If the operator presses the button of the start switch 36 while the relay KF is not operated, the switch pole 36a closes contacts 36b to activate the relay KL via switch contacts KF1 of the relay KF. Operation of the relay KL opens its contacts KL1 to cut olf the initial charge circuit for the condenser C3, closes contacts KL3 paralleling initially closed contacts KF1 of the relay KF to provide one element of a hold circuit for the KL relay, opens KL3 to deenergize the alarm device 32 and closes contacts KL4 to activate the ignition transformer 35 and an ignition timer TFI from the line 29 through contacts 36a` and pole 36d of the start switch 36. Also, the closing of the contacts KL1 provides power from the line 37 through a contact of the ignition timer TFI to open the igniter fuel valve 33. Since fuel is now supplied to the igniter burner and the ignition transformer 35 is activated, a flame is ignited. If the llame ignition does not occur the detector tube 17 is not triggered and the burner control relay KF is not operated, with the result that the circuit for the relay KL is opened at the contacts 36b to drop out the relay KL and shut down the burner when the start switch 36 is released. On the other hand, if flame ignition occurs the detector tube 17 is triggered, and if the coupling of the detector tube to the switching transistor Q7 is functioning properly the transistor Q7 is rendered conductive to operate the relay KF. Operation of the relay KF opens contacts KF1 to make continued operation of relay KL dependent on its hold contacts KL2, closes contacts KF2 to keep the relay KL operated when the start switch 36 is released and makes continued operation of the relay KL dependent on relay KF, opens contacts KF3 to shut off the flame-out indicator 30 and closes contacts KF4 to activate the flame-on indicator 31. Upon now releasing the start button of switch 36, the ignition transformer 35 and the coil of ignition timer TFI are cut olf by the opening of contacts 36C, and switch pole 36d makes with contacts 36e to activate the main fuel valve 34 from the line 38 via the contacts KL1 of the relay KL and the contacts 36e of the start switch. With ignition llame and main fuel present, the main flame is ignited. A predetermined time after the coil of the TFI timer is deenergized (typically 10 seconds), the switch contact of TFI opens to cause the igniter fuel valve to close. Although the igniter flame is shut off, the detector 17 continues to be triggered by the main llame. The burner is now in normal running condition.

Within a preselected interval after the power switch 10 is closed, the shutter timer control 27 operates the shutter 25 and holds the shutter operated for typically one second. This operation of the shutter intercepts the U-V radiation from the burner llame to the detector tube 17 to start a checking operation. Firstly, if the detection tube is functioning properly so that it ceases to trigger when the radiation is intercepted, it will be quenched the instant the applied A.C. voltage falls below a sustaining value of about 330 volts, and if the coupling circuitry from the detector and switching transistor Q7 is returned to off condition about 1A second thereafter kby the discharge of bias condenser C10 through resistor R23 to cut off flow from the generated current supply to the relay KF. However, the charge on the condenser C3 will hold the KF relay operated at least for a normal checking period. Should some malfunction occur causing the checking period to be extended beyond a normal time, the relay KF will drop out which in turn will drop out the relay KL by the opening of the contacts, KF3, and the drop out of the relay KL will shut olf the main valve 34 to stop the burner. On the other hand, if the shutter 25 is returned to off position after a normal checking period, the switching transistor Q7 is returned to on position at the end of the checking period to close again the primary energizing circuit for the KF relay before the charge on condenser C3 drops below the hold-in requirement of relay KF.

Also, the instant the shutter 25 is shifted to operated position, a switch KS1 is closed in a recharge circuit 39 for the condenser C3. This recharge circuit runs from a junction point 40 between the relay KF and the switching transistor Q3 and includes a diode D11 poled positively in the direction from the junction point to the condenser. This junction point 40 is connected through a resistor R17 to the plus side E1 of the 24 volt primary voltage supply. When the transistor Q7 is conducting, the potential of the junction point 40 is below that of the center tap line 12 with the result that no charging current flows into condenser C3. Discharge current from condenser C3 is prevented from dissipating through transistor Q7 because the polarization of diode D11 prevents current flow in that direction. However, when the transistor Q7 is nonconducting, the potential of the junction point 40 rises above that of the center line 12 to permit charging current to flow to the condenser C3 provided the switch KS1 is then closed. Thus, if the detector apparatus is functioning properly to shift the transistor Q7 to off position shortly after the shutter is operated, the condenser C3 will be recharged to enable it to keep the oscillator Q1 running for a period exceeding the interval between checking operations. However, if the detector apparatus is not functioning properly and the transistor Q7 is not shut off responsive to the operation of the shutter, the condenser C3 will not be recharged with the result that shortly after the shutter is returned to its non-intercepting position the oscillator Q1 will stop to cut oif the supply of generated current to the relay KF. Under these conditions the relay KF will soon drop out and shut down the burner even though the shutter is properly returned to its non-intercepting position.

If the timing control 27 should malfunction and fail to reoperate the shutter within the predetermined discharge period of the condenser C3, the charge on the condenser will fall -below the necessary predetermined level and will stop the oscillator to drop out the KF relay and shut down the burner. Any malfunctioning of the timer control causing it to reoperate the shutter at a faster rate will not shut down the burner but will have the detrimental effect only of increasing the dead time when the detector is ineffective to perform its llame detecting operation.

The embodiment of my invention herein particularly shown and described is intended to be illustrative and not necessarily limitative of my invention since the same is subject to changes and modifications without departure from the scope of my invention, which I endeavor to express according to the following claims.

1 claim:

1. A fuel burner control system comprising a burner control relay, an oscillator and rectifying means for providing a D.C. current supply for operating said relay, sensing means for detecting a `flame of said burner, means for intermittently intercepting said sensing means from said flame, and means responsive to said lintercepting means for maintaining said oscillator running only if said intercepting means is reoperated within a predetermined interval.

2. The fuel burner control system set forth in claim 1 including means responsive to said sensing means for disconnecting said current supply from said relay when said sensing means is not activated, and means for delaying the drop out of said relay for a predetermined period after said current supply is disconnected from said relay.

3. A fuel burner control system comprising a burner control relay, flame sensing means, means for intercepting the sensing means from the llame of said burner, means for intermittently Operating said intercepting means, current supplying means for said relay including a condenser for maintaining the supplying means in operative condition for a predetermined interval after each charging of the condenser, and a charge circuit for said condenser controlled independently by said interceptor operating means and said sensing means to cause the charge circuit to be rendered operative only when said intercepting means is operated and said sensing means is not activated.

4. The fuel burner control system set forth in claim 3 including timing control means settable to recycle said intercepting means within said predetermined interval and to hold the intercepting means operated for a predeterminedperiod of relatively short duration, means for disconnecting said voltage supplying means from said relay when said sensing means is not activated, and a shunt condenser across said relay adapted to hold the relay operated at least for a time period of said predetermined duration after the relay is disconnected from said supplying means.

5. A fuel burner control system comprising an ultraviolet detector tube for detecting the flame of the burner, a burner control relay required to be operated to keep the burner running, current generating means for operating said relay including a condenser adapted to keep the generating means operative as long as the condenser bears at least a given charge, a shutter for intermittently intercepting transmission of U-V radiation from said flame to said detector tube, an electronic switch device required to receive an amplified signal from said detector tube in order to place the device in conductive condition, and means rendered operable to charge said condenser only when said shutter is operated and said switch device is non-conducting.

6. The burner control system set forth in claim 5 wherein said electronic switch device is connected in the current supply circuit of said burner control relay to require the electronic switch device to be in conductive condition to enable current to be supplied to said relay, including a condenser connected across said relay for holding the relay operated at least for a predetermined period While said shutter is operated and said switch device is non-conducting.

7. A fuel burner control system including a burner control relay required to be operated to keep the burner running, a U-V detector tube for detecting the flame of the burner, a shutter for intermittently shielding the detector tube from said flame, an energy storage condenser, an oscillator rendered operative by said condenser so long as the condenser bears a charge above a predetermined level, means connected to the output of said oscillator for making D.C. operating power available to said burner control relay, means for recurrently operating said shutter within the time interval said condenser is capable of operating said oscillator after each recharging thereof, and means rendered operable with each operation of said shutter for recharging said condenser.

8. The fuel burner control system set forth in claim 7 including circuit means for providing an alternating firing potential capable of producing a pulsating glow discharge in said detector tube when the tube is excited by incident ultraviolet radiation, a switching transistor connected in the power circuit of said burner control relay, means supplying a potential to the junction between said transistor and burner control relay capable of charging said storage condenser only when the transistor is nonconductive, and means connecting the control electrode of said transistor to said detector tube to render the transistor conductive only when said detector tube is triggered into a conductive state.

9. The fuel burner control system set forth in claim 8 including a primary D.C. voltage supply having a center tap to which the negative side of said condenser and oscillator are connected, means connecting said transistor between said burner control relay and said negative side of said primary D.C. voltage supply, resistance means connecting the plus side of said primary D.C. voltage supply to the junction between said transistor and said burner control relay to provide a potential at said junction above that of said center tap when said transistor is in a non-conducting state and below that of said center tap when the transistor is in a conducting state, and a charge circuit for said storage condenser connected to said junction.

10. The fuel burner control system set forth in claim 9 including a diode in said charge circuit poled to prevent current from flowing from said storage condenser when said transistor is conducting, and a switch in said charge circuit operated in timed relation with said shutter to permit charge current to flow to said condenser only when said shutter is operated.

11. A fuel burner control system comprising a burner control relay, current supplying means for said relay including a condenser required to be charged above a predetermined level to keep said supplying means operative, llame sensing means, a shutter for intercepting the flame from said sensing means, electronic switch means in said current supplying circuit responsive to said sensing means for supplying current to said relay only when said condenser is charged and said sensing means is activated, a charge circuit for said condenser rendered operable by said electronic switch means as the switch means is rendered non-conducting, a switch in said charge circuit timed with said shutter to close as the shutter is operated, and a diode in said charge circuit poled to prevent current flow from said condenser when said electronic switch means is conducting.

12. A condition-responsive apparatus comprising means for sensing the presence of a selected condition, an electronic switching device controlled by said sensing means to cause the switching device to be conductive when said sensing means is activated and relatively nonconductive when said sensing means is not activated, a first power supply, an energy storage device, means for charging said storage device from said first power supply, an oscillator operable by said storage device for a first time period after each recharging of said storage device, means connected to said oscillator for providing a second power supply only so long as said oscillator is operating, an electrically operable switching device connected to said second power supply via said electronic switching device to assume an unenergized state when said condition is not being sensed and an energized state when said electronic switching device is conductive and said oscillator is operating, means to delay for a second time period less than said first time period a return of said electrically operable switching device to an unenergized state after said electronic switching device becomes nonconductive or said oscillator stops operating, means for intercepting said sensing means from said selected condition for a third time period shorter than said second time period, means for repetitively recycling said intercepting means at intervals shorter than said first time period and longer than said second time period, and means for preventing simultaneous energization of said electrically operable switching device from said second power supply and charging of said storage device from said iirst power supply.

References Cited UNITED STATES PATENTS 3,143,161 8/1964 Graves et al 340-410X 3,143,162 8/1964 Graves et al S40-410x 3,190,341 6/1965 Giuffrida et al. 340-410X 3,263,730 8/1966 Giuffrida 431-26 2,798,214 7/1957 Rowell 340-410 2,798,213 7/1957 Rowell 340-410 STANLEY M. URYNOWICZ, JR., Primary Examiner U.S. Cl. X.R. 431-24

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