US2537293A - Burner safety control apparatus - Google Patents

Description

Jan. 9, 1951 DU WAYNE J. PETERSON BURNER SAFETY CONTROL APPARATUS Filed May 6, 1948 3nventor 00 WflY/VE J PETE/750 U m H 0 W l w Patented Jan. s, 1951 f j 2,531,293" umrso STATES PATENT ori ice-- t 2,537,293 1 p I BURNER SAFETY comer. APPARATUS Du Wayne John Peterson, Grosse Pointe, Mich,

assignor to, Minneapolis-Honeywell Regulator Company, llinneapoligllinm, a corporation 'of Delaware Application Mi, 6, ms. Seth! No. 25.331 a cum. (01458-28) The present invention is concerned with a fuel burner control apparatus and more particularly with a burner control apparatus of the type to be associated with'a burner having a standing pilot.

In the present day fuel burner controls, especially those employing electronic flame detectors,

it is customary to provide for checking the opera.- tion of the components to insure that the apparatus is operating properly. In a copending application of John M. Wilson for Fuel Burner Control System," Serial No. 731,998, filed March 3, 1947, there is described a burner control ap- 1 pa'ratus wherein the burner control is rendered inoperative whenever the flame detection device fails to operate or the flame detection device is falsely indicating the presence of flame. This is accomplished by employing a safety switch cutout device whichv is energized whenever there is a demand for operation of the burner and the flame detector does not detect flame. The safety switch cutout device is'a-l'so operated whenever there is no demand for operation of the burner and the flame detection device indicates the presence of flame falsely. When such an arrangement is employed in a burner having a standingpilot flame, it is necessary to make provisions for keeping the pilot flame from operating the flame detection device when there is' no demand for op-' eration of the burner and still have the control apparatus retain the circuit checking features.

It is therefore an object of the present invention to provide a burner control apparatus which fuel through a conduit ll. Controlling the flow of fuel in the conduit H is an electrically operated gas: valve I! which is operable when energized to permit fuel to flow to the burner III. A pilot burner nozzle 13 having a flame i4 emitting therefrom is provided to ignite the fuel supplied to burner It. The burner nozzle I! receives a continuous supply of fuel from the conduit ll through a pilot conduit [-5.

For indicating the need for operation of the burner I 0 a thermostat I 6 is provided. This ther-' mostat It may be seen to consist of a bimetal I! which is adapted on temperature changes to move the switch blades l8 and l9'into and out of engagement with the associated switch, contacts 29 and 2| respectively. located within the housing indicated at 22 are the main components of the control apparatus. The power supply of my control apparatus consists of a transformer. 25

having a primary winding 25 connected to any suitable power source, a secondary winding 21 tapped at 28 and a. further secondarywinding 29 having a tap at 30. Adapted to be energized by the secondary winding 27 is a control relay 3| having a relay winding 32 and switch blades 33. 34 and 35 normally biased out of engagement with the associat d switch contacts 36, 31 and 38.

Energized by the secondary winding 29 is an electronic flamedetection device which may be seen to consist of a pair of electron discharge devices and 4| having operative circuits therefor. The discharge device 40 maybe seen to consist of an anode 42. a control electrode 43,.and a cathode 44, the latter of which is energized to be electron emissive by a suitable cathode heater 45. The discharge device 4! consists of an anode 46, a control electrode 41, and a cathode 48, the latter of which is heated to be electron emissive by cathode heater filament 49. Associated with 40 the input to discharge device 40 are a pair of is no combustion'afl'ecting the device.

A still further object of the present invention I proved type of failsafe circuit employed with an electronic flame detector;v and Figure 2 shows a modification of the circuit shown in Figure 1 with a photoelectric cell act- ,7

ing as the flame sensingdevice.

Referring to Figure 1, the numeral 10 represents a. gas burner which receives its supply of condensers 50 and 5| and a pair of resistors 52 and 53. Resistors 54 and 55 are associated in a. biasing relation with the input to discharge device 4|.v Energized by the discharge device 4| is a relay 56 having a relay winding 51 which is adapted to move switch blades 58 and 59, normally biased out of association with switch contacts 60 and BI respectively. Switch blade i .is normally biased into contact with a contact 62. A bypass cond nser 63 is connected across the relay winding 51 to function in the normal manner by filtering the pulsating direct current flowing in the energizing circuit of triode 4|. A

flame electrode 15 is provided to detect the presrate and open an electrical circuit. A reset button 18 is provided to put the safety device back in a circuit closing position. A resistor 18 is provided for use in the energizing circuit of the heater 61 under certain conditions of operation.

Operation of Figure 1 In discussing the operation of the present control apparatus it will be assumed first that all the components are deenergized and in a position shown on the diagram of Figure 1. It will further be assumed that the pilot flame I4 is present at the pilot nozzle I3 and is intersecting the flame sensing electrode 15. Upon a demand for heat in a space being controlled the thermostat I6 will become operative so that the bimetal I1 will sequentially move switch blades I8 and I9 into engagement with their associated switch contacts 28 and 2| respectively. This sequential movement and engagement of contacts is used to prevent any chattering tendencies in the thermostat and the relay controlled thereby. When switch blade I8 engages contact 28 and switch blade I9 engages contact 2| an energizing circuit for the relay 3| will be completed so that the switch arms 33, 34 and 35 will move into engagement with their associated switch contacts 36, 31 and 38. This energizing circuit may be traced from the upper terminal of the secondary section 21 through conductor 88, relay winding 32, conductor 8|, switch contact 28, switch blade I8, switch blade I9, switch contact 2 I, conductor 82, switch contact 62, switch blade 58, conductor 83, conductor 84, safety switch heater 81, switch blades 88 and 69, and conductor 85 back to the lower terminal of the secondary section 21. When the relay 3| becomes energized a holding circuit for the relay is established independent of the switch blade 58 and switch contact 82 of the relay 58. This holding circuit may be traced from the upper terminal of the secondary section 21 through conductor 88, relay winding 32, conductor 8|, switch contact 28, switch blade I8, bi-- metal I1, conductor 86, switch contact 31, switch blade 34, conductor 81, conductor 84, safety switch heater 61. switch blades 68 and 69, and conductor 85 back to the lower terminal of the secondary section 21. It will be noted that both of the last traced circuits pass through the safety switch heater 61. This safety switch heater when energized for a predetermined length of time will move the bimetal 66 toward the right so that the switch blades 68 and 69 will open circuit and open the electrical circuit to control relay 32. To prevent continued energization of the safety switch heater 61, the relay 56, whose operational circuit will be explained hereinafter, is provided to eflectively bypass the energizing current for relay 32 around the safety switch heater 61. This is accomplished by the switch blade 58 moving in o engagement with switch contact 68 so that with relay 56 energized the energizing circuit for the relay 32 ma be traced from the upper terminal of the secondary section 21 through conductor 80, relay winding 32, conductor 8|, switch contact 28, switch blade I8, bimetal I1, conductor 86, switch contact 31, switch blade 34, conductors 81 and 83, switch blade 58, switch contact 68, conductors 88 and 89, switch contact 36, switch blade 33, and conductors 98 and 85 back to the lower terminal of the secondary section 21. Under normal operating conditions the relay 58 is energized only when there is a flame detected by the input circuit to the name detection apparatus.

In understanding the operation of the flame detection apparatus employed with the present in- 4 vention it is necessary to know that a flame has certain electrical characteristics which make it more conductive in one direction than it is in another so that as far as alternating electric current passing through the flame is concerned there will be a certain amount of rectification which may be utilized to bias a control tube into and out of conduction in accordance with the presence or absence of flame. The direction of greatest electron conductivity in a flame is generally in the direction of propagation of the flame. The flame electrode 15 associated with the burner nozzle I3 serves as the flame detecting element which is operable when bridged by the flame I4 to act as a rectifier of any alternating current appearing across the gap between the electrode 15 and nozzle I3. The alternating current supplied across the gap is supplied from the lower section of the secondary 29 and the conventional current flow path may be traced from the tap 38 of secondary 29 through conductors 9| and 92, condenser 58, conductor 93, switch contact 38, switch blade 35, conductor 94, electrode 15, flame I4, burner nozzle I3, ground 95, ground 96 and conductor 91 back to the lower terminal of the secondary section 29. With alternating current flowing in the last traced circuit and flame |4 acting as a rectifier it may easily be seen that the condenser 58 will become charged so that upon the presence of flame the lower terminal of the condenser 58 will become negative and the upper terminal will be positive. This charge on condenser 58 is used to bias the triode 48 and is coupled to the input circuit of the triode 48 by a fllter network consisting of a resistor 52 and condenser 5|, the latter of which is connected directly between the control electrode 43 and cathode 44 of triode 48. The grid resistor 53 connected in parallel with the condenser 5| functions in the normal manner. With condenser 58 charged as described above the control electrode 43 will be biased negative with respect to the cathode 44 so that the triode 48 will be effectivel non-conducting. The energizing circuit for the triode 48 may be traced from the tap 38 of the secondary 29 through conductors 9| and 98, resistor 55, conductor 99, anode-42, cath ode 44, and conductors I88 and 91 back to the lower terminal of the secondary 29. When there is no current flow in the last traced circuit there will be no voltage drop across the resistor 55 which is connected directly across the input circuit to triode 4| by direct connections to the control electrode 41 and to cathode 48. With no bias voltage on the triode 4| the tube will pass current and will energize relay 56. This energizing circuit for the relay 58 may be traced from the upper terminal of the secondary 29 through conductors I8| and I82, relay winding 51, conductor I83, anode 48, cathode 48, and conductors 98 and 9| back to the center tap 38 of the transformer 29. When the relay 56 becomes energized the switch blades 58 and 59 move into engagement with their associated contacts 88 and 6| to complete the above described safety switch heater bypass circuit and an energizing circuit to the electrical fuel valve I2. The energizing circuit for fuel valve 2 may be traced from the input power line I84 through switch contact BI, switch blade 59, conductor I85, and valve I2 back to the other input power line I86. With valve I2 energized fuel will be supplied through conduit II to burner I8 so that the burner I8 will be operative to supply heat to the space where the temperature is being controlled by the thermostat I8.

As soon as the temperature in the space being heated has been satisiied the thermostat it will be operative so that the bimetal II will. move'the switch blade ll out 01- engagement with its asfore leak out through the resistors 52 and It so that there will be effectively no biasing voltage on the input to trlod ll and the control electrode ll will be at approximately the same potential as the cathode 44 since they are directly connected bya' resistor 53. This will meanthat the triode II will now be conducting sufliciently to put a voltage across resistor 55 which will be negative at its upper terminal and positive at its lower terminal. This voltage on resistor 55 etfectivel biases the triode 4| so that its current flow is decreased below a point necessary to maintain the relay It in an energized position. When relay It becomes deenergized the switch blade 59 moves out of engagement with its associated switch contact ii to open the energizing circuit a the electric valve l2. With valve i2 deenersizedthe flow of fuel to the burner III will be cut on and will remain cut oil until the valve I2 is not become energized. As noted above. when relay It is deenergized the energizing circuit for the relay II is completed through the safety,

switch heater 6'! which is operable after a pre-v determined time delay to move the bimetal 66 toward the right and permit the switch contact {I to separate from the switch contact 69. When the switch contact I separates from contact 69 V the energizing circuit for the relay II is broken and will remain so until the reset button 10 is manually depressed and the contacts are once again engaging. Also deenergized by the opening of the contacts 68 and 89 are the cathode heater circuits for the triodes 40 and 4|; The cathode heater circuit may betraced from the tap 280i the secondary 21 through conductor lll,- cathode once again energized. With relay II and 5t deen- .erglzed, the apparatus, is'back in the position shown in the diagram and is ready ior another heating cycle to take place. It will be noted that; the triodes 40 and 4| are continuously maintained" in an operative circuit even though the thermostat I6 is not closed and rela 3| is deenergized. This will mean that the electrical apparatus for indicating a flame will be ready to operate whenever the flame rectifier is connected to the [input of the indicating apparatus. Thus, the triode;

when not connected'to the flame rectifier lljwill be conducting and will maintain the triode'll non-conducting, and relay 56 will bedeene'rgized.

The flame rectifier will be cut into the circuit,

56 will become energized to close an energizing circuit to the gas valve I 2.

Operation upon flame failure Assume that there is a demand for heat in the space being controlled by the thermostat it so that the bimetal ll actuates the switch blades I8 and I9 into engagement with their respective contacts 20 and II and so that the relay 3| will become energized. as explained above. Assume. further that there is no pilot flame ll existing at the nozzle It. It may be seen that when switch blade 35 engages switch contact 38 upon relay 3| becoming energized and closes the flame detection circuit, with the flame H not present, there will be no charge placed upon the condenser 50 so that the triode 40 will be biased into the conductive range-and will be maintaining triode 4| effectively noneonductive so that the relay it will 75 open circuited as when the conductor 94 should "heater ll, conductor I08, cathode heater 4!, conductor I, switch contacts 68 and 69, and-conductor back to the lower terminal of the secondary 21. With the cathode heater circuit to the triode 4| and 4| deenergized it will be impossible under any conditions to energize the relay i6 and to bring into operation-the electric valve |2.'

.In the event that theapparatus is operating normally when there is a demand for operation of the burner l0 and when relays 3| and 58 are energized in their normal manner let it be assumed that the flame from the burner III and from the burner nozzle l3 are accidentally ext ished for any reason. This will result in the relay 56 becoming deenergized since the flame ll will no longer be charging the condenser 50 so that the triode Ill now conducting will function to bias the triode 4| below the point necessary tov maintain relay 56 energized. With relay 56 deenergized the circuit bypassing the safety switch heater 61 will be opened and the'relay 3| will have its energizing circuit once again completed through the safety switch heater 61 since 'the switch blade 58 is now engaging switch contact 62. If the pilot flame is not reignited within a predetermined time the safety switch heater 61 will have wa'rped the bimetal 66 sufliciently so that switch contact 88 and 69 will separate and deenergize relay 3| and the cathode heater circuits for the triodes 40 and 4| as explained above.

Operation on component failure The present apparatus is further capable of detecting component failures and rendering the apparatus inoperative when such fahures occur. These component failures may involve such conditions as the grounding out or shorting out of electrode I5 to burner nozzle i3, open circuiting of the electrode 15 and conductor 94, or relay 56 remaining energized even though no flame is present.

In the event that there is a ground out condition where the electrode 15 shorts with the pilot nozzle l3 it is believed that it will be quite obvious that there will be no rectification in the flame detection circuit so that the condenser 50 will not be charged and triode 40 will be conducting suiflcientiy to eiiectively bias the triode 4| below the point necessary to maintain relay 55 energized. With relay v5t deenergized the safety switch heater 6'! will have the holdingcurrent for the relay 3| passing therethrough so that the safety switch contacts 68 and 69 will open to A similar apparatus shutdown would occur in the event that the flame detection circuit were open circuit with the electrode I5. Such an open circuit would mean that no rectification would be detected by condenser 50 and triode 40 would bias vtriode 4| to be effectively nonconducting so that the relay 56 is .deenergized. As in every other situation described thus far with relay 3| energized and relay 56 deenergized, the safety switch heater 6'! will be operative after a predetermined length of time to deenergize the entire control apparatus.

Should the relay 56 remain in the energized position due to faulty operation 'of the input circuit of the flame detector or faulty operation of the triode control tubes 40 and 4| with relay 3| deenergized due to the opening of the switch contact 20 and switch blade IS, the apparatus will still be rendered inoperative. This may readily be seen since an energizing circuit to the safety switch heater 6'! may be traced independently of the relay 3|. This circuit may be traced from the upper terminal of the secondary 2'! through conductor 80, resistor 16, conductor 88, switch contact 60, switch blade 58, conductors 83 and 84, safety switch heater 61, switch contacts 68 and 69, and conductor 85 back to the lower terminal of the secondary section 21. With the safety switch heater 6! energized the switch blade 66 will once again move out from under the switch contacts 68 and 69 so that they will open circuit as explained above. With the open circuiting of the switch contacts 88 and 69 the cathode heater filaments for triodes 40 and 4| will be open and when the cathodes 44 and 48 have cooled below the electron emissive point the relay 55 will become deenergized to open the energizing circuit to the electric valve |2.

In considering the above it will be noted that the subject control apparatus is one which has a component checking feature which will render the apparatus inoperative should the flame detection relay 55 stay in the energized position when the relay 3| is deenergized. By using a circuit having component check, as the above-mentioned Wilson application discloses, with a standing pilot, the apparatus would have a safety shutdown after each start for the standing pilot would maintain the flame detection relay energized. By providing an arrangement, as here, for opening the circuit of the flame rod this condition is prevented. Further, the apparatus is still able to function in the normal manner by distinguishing from open or short conditions and flame conditions at the flame rod, and because of this there will be no operation of the flame detection relay 56 or the main valve l2 under short or open conditions at the flame rod assembly. This will be true whether occurring during operation or on shutdown.

In Figure 2, I have shown a photocell substituted in the flame electrode circuit of Figure 1. Components corresponding to components in Figure I carry the same reference numeral in Figure 2. The functioning of the control apparatus employing a photocell is the same as Figure 1 since the photocell will detect the presence of flame at the standing pilot and due to its rectifying action will operate in the same manner as the flame electrode in Figure 1 and will not indicate a flame when an open or short circuit occurs in the photocell circuit. The flame detection circuit of Figure 2, like the flame detection circuit of Figure 1, includes the switch contact 38 and switch blade 35 of relay 3| because of the use of a standing pilot and the fact that the control apparatus comprises component checking features. The flame detection circuit in Figure 2 may be traced from the switch contact 38 through switch blade 85, conductor 94, anode cathode H2, and ground conductor The ground out, fail-safe on flame failure, and component checking features will be the same in a control apparatus employing a photocell as well as the control apparatus employing a flame electrode.

It may therefore be seen that I have provided a burner control apparatus for association with a burner having a standing pilot which will have component checking features for maintaining the apparatus inoperative should the flame detection relay remain energized after there is no further need for operation of the burner. I have further combined with the above-mentioned feature a control apparatus that-will fail safe on flame failure or circuit failure in the flame detection circuit.

Although I have described my invention in connection with a particular type of burner control apparatus and while it is well adapted for use there, it will be obvious to those skilled in the art that my invention could be applied to any type of control apparatus to be associated with a burner having a standing pilot flame. Therefore, I'intend to be limited solely by the scope of the appended claims in which I claim:

1. A burner control apparatus for use with a fuel burner having a continuously burning pilot flame, a continuously operating flame indicating device, said indicating device comprising a first relay and an electric circuit which is adapted when a portion thereof is bridged by a flame to effect energization of said first relay, a second relay adapted to be energized by means indicative of the need for operation of the burner, means including said first relay adapted to render the burner operative when said first relay is energized, and means controlled by said second relay for rendering said electric circuit effective only when said second relay is energized.

2. A burner control apparatus for use with a fuel burner having a continuously burning pilot flame, a continuously operative flame indicating device, said device comprising a first relay and an electric circuit adapted to be completed through a photocell which when subjected to a flame will efiect with said circuit energization of said first relay, a second relay adapted to be energized by means indicative of the need for operation of the burner, means including said first relay adapted to render the burner operative when said first relay is energized, and means controlled by said second relay for rendering said photocell and the electric circuit effective to detect a flame only when said second relay is energized.

3. A burner control apparatus for use with a fuel burner having a continuously burning pilot flame. a combustion indicating relay, a flame indicating apparatus operating continuously and operable to energize said indicating relay on the presence of a flame, a control relay adapted to be energized by means indicative of the need for operation of the burner, means including said combustion indicating relay adapted to render the burner operative when said combustion responsive relay is energized, means common to said control relay for rendering said flame indicating apparatus effective to detect a flame only when said control relay is energized, safety cutout means for deenergizing said control apparatus, means for energizing said safety cutout means, and electrical circuit means including said relays connecting said energizing means to said cutout means when either of said relays becomes energized and the other is deenergized.

4. A burner control apparatus for use with a burner having a continuously burning pilot flame,

a flame indicating apparatus, said apparatus comprising a first relay and an electric circuit which is adapted when a portion thereof is connected to means exposed to a flame to energize said first relay, a second relay adapted to be energized by means indicative of the need for operation of the burner, means including said first relay adapted to render the burner operative when said first relay is energized, safety cutout means for deenergizing said control apparatus after a predetermined time delay, means for energizing said safety cutout means, switch means common to either of said relays for completing the energizing circuit of said safety cutout means when only one of said relay means becomes energized, and means controlled by said second relay for rendering said electric circuit effective to indicate a flame only when said second relay is energized to prevent said electric circuit from energizing said first relay when said second relay is deenergized.

5. A burner control apparatus for use with a burner having a continuously burning pilot flame, flrst relay means adapted to be energized by means indicative of the need for operation of the burner, an electron discharge device having a cathode heater, a second relay, an electrical circuit adapted to have a portion thereof affected by the presence of a flame, means connecting said second relay and said electrical circuit to said discharge device so that said discharge device is operable to energize said second relay when flame is affecting said electrical circuit, switch means controlled by said second relay adapted to render the burner operative when said second relay is energized, safety cutout means being operable to deenergize the cathode heater of said discharge device after a predetermined time delay, further switch means controlled by either of said relays for actuating said safety cutout means when only one of said relays is energized. and switch means common to said first relay for rendering said flame sensitive circult effective only when said first relay is energized to prevent the presence of a pilot flame from maintaining said second relay energized when said first relay is deenergized.

6. A burner control apparatus for use with a fuel burner having a continuously burning pilot flame, a flame indicating apparatus having an electrical circuit adapted to render said indicating apparatus operative when exposed to a pilot flame, relay means adapted to be energized upon the need for operation of the burner, first switch means controlled by said flame indicating apparatus adapted to render the burner operative when said detection apparatus is operative, a safety cutout device for deenergizing said control apparatus after a predetermined time delay, second switch means for energizing said cutout device either when said relay means is energized and said flame indicating apparatus indicates no said cutout device when said relay means is inl0 operative and said flame indicating apparatus is not operating falsely.

7. A- burner control apparatus for use with a fuel burner having a continuously burning pilct flame, first relay means adapted to be energized by means indicative of the need for operation of the burner, a flame indicating apparatus comprising a flame rod circuit adapted when bridged by a flame to render said indicating apparatus operative, second relay means adapted when energized to initiate operation of the burner, means including said indicating apparatus for energizing said second relay means upon a pilot flame bridging said flame rod circuit, safety cutout means operable when energized for a predetermined period of time to deenergize said control apparatus, means including either but only one of said relay means for connecting said cutout means in an energizing circuit when only one of said relay means is energized, and switch means controlled by said first relay means connected in said flame rod circuit for rendering said circuit ineffective when ,said first relay means is not energized.

8. A burner control apparatus for use with a fuel burnerhaving a continuously burning pilot flame, flrst'relay means adapted to be energized by means indicative of the need for operation of the, burner, a flame indicating apparatus comprising a photocell circuit adapted when sub- Jetted to a condition of flame to render said indicating apparatus operative, second relay means adapted when energized to initiate operation of the burner, means including said indicating apparatus for energizing said second relay means upon a pilot flame light impinging on said photocell circuit, safety cutout means operable when energized for a predetermined period of time to deenergize said control apparatus, means including either but only one of said relay means for connecting said cutout means in an energizing circuit when only one of said relay means is energized, and switch means connected in said photocell circuit for rendering said circuit ineffective when said first relay means is not energized. 4

9. A fuel burner control apparatus for use with a fuel burner having a continuously burning pilot flame, electrical apparatus operating continuously adapted to operate in one manner when connected to means indicating the presence of a burner flame and in another manner when not so connected or the flame is absent, a first control relay connected to said electrical apparatus and energized thereby upon the presence of flame, a second control relay adapted to be energized by means indicative of the need for operation of the burner, means including said first relay adapted to render the burner operative when said first relay is energized and means controlledby said second control relay for rendering said electrical apparatus efiective to detect the presence of a flame only when said second control relay is energized.

DU WAYNE J. PETERSON.

REFERENCES crrap The following references are of record in the flle of this patent:

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