COMBUSTION SUPERVISION APPARATUS
United States Patent 3644748
Combustion supervision apparatus includes a flame relay responsive to a flame detector for providing an indication of flame in the supervised combustion chamber, a control relay, a magnetically operated lockout device, and a circuit for checking the continuity of the magnetically operated lockout device prior to energization of the control relay including in series with coil of the magnetically operated lockout device and the coil of the control relay.
US Patent References:
Electrical control circuitry for burners
Giuffrida et al. - April 1968 - 3376099
PROGRAMMED OIL IGNITION
Hirsch et al. - October 1970 - 3532450
Electrical control circuitry for burners
Giuffrida et al. - April 1968 - 3376099
PROGRAMMED OIL IGNITION
Hirsch et al. - October 1970 - 3532450
Application Number:
05/060229
Publication Date:
02/22/1972
Filing Date:
08/03/1970
View Patent Images:
Export Citation:
Assignee:
Electronics Corporation of America (Cambridge, MA)
Primary Class:
Other Classes:
431/26, 340/515, 340/577, 307/141
International Classes:
F23N5/22; H01H35/00
Field of Search:
431/24,26 307/117,112,141,141.4,141.8,116 340/410
Primary Examiner:
Hohauser, Herman J.
Claims:
What is claimed is
1. Combustion supervision apparatus for use in a combustion control system that includes a fuel control element; an ignition control element; a scheduler for operating components of the combustion control system to provide an initial interval, an ignition interval and a combustion interval; and a flame detector,
2. The apparatus as claimed in claim 1 wherein said lockout device includes a latch which holds said normally closed lockout contacts closed and energization of said lockout coil releases said latch and allows said normally closed lockout contacts to open instantaneously.
3. The apparatus as claimed in claim 2 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
4. The apparatus as claimed in claim 12 wherein said magnetically operated lockout device requires manually resetting after tripping thereof.
5. The apparatus as claimed in claim 1 wherein said scheduler includes a timer motor and a series of cams for operating said scheduler controlled contacts.
6. Combustion supervision apparatus including a flame relay responsive to a flame detector for providing an indication of flame in the supervised combustion chamber, a control relay, an instantaneously operative magnetically operated lockout device, and a circuit for checking the continuity of said magnetically operated lockout device prior to energization of said control relay including in series the coil of said magnetically operated lockout device and the coil of said control relay.
7. The apparatus as claimed in claim 6 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
8. The apparatus as claimed in claim 6 and further including a circuit for maintaining said control relay energized after the continuity of said lockout device has been checked including a first set of normally open control relay contacts connected in parallel with said lockout coil.
9. Combustion supervision apparatus including a flame relay responsive to a flame detector for providing an indication of flame in the supervised combustion chamber, a control relay, a magnetically operated lockout device, a circuit for checking the continuity of said magnetically operated lockout device prior to energization of said control relay including in series the coil of said magnetically operated lockout device and the coil of said control relay, a scheduler for operating components of the combustion control system to provide in sequence an ignition interval and a combustion interval, a first circuit for checking the response of said flame detector prior to commencement of said ignition interval including the series connection of normally open contacts controlled by said flame relay and a first set of scheduler controlled contacts connected in parallel with said control relay coil, and a second circuit for checking the response of said flame detector after said ignition interval including the series connection of normally closed contacts controlled by said flame relay and a second set of scheduler controlled contacts connected in parallel with the series circuit of said normally open flame relay contacts and said first set of scheduler controlled contacts.
10. Combustion supervision apparatus for use in a combustion control system that includes a fuel control element; an ignition control element; a scheduler for operating components of the combustion control system to provide an initial interval, an ignition interval and a combustion interval; and a flame detector,
11. The apparatus as claimed in claim 10 wherein said lockout device is magnetically operated and said actuator includes a coil.
12. The apparatus as claimed in claim 11 wherein said lockout device includes a latch which holds said normally closed lockout contacts closed and energization of said actuator releases said latch and allows said normally closed lockout contacts to open instantaneously.
13. The apparatus as claimed in claim 12 wherein said magnetically operated lockout device requires manually resetting after tripping thereof.
14. The apparatus as claimed in claim 13 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
1. Combustion supervision apparatus for use in a combustion control system that includes a fuel control element; an ignition control element; a scheduler for operating components of the combustion control system to provide an initial interval, an ignition interval and a combustion interval; and a flame detector,
2. The apparatus as claimed in claim 1 wherein said lockout device includes a latch which holds said normally closed lockout contacts closed and energization of said lockout coil releases said latch and allows said normally closed lockout contacts to open instantaneously.
3. The apparatus as claimed in claim 2 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
4. The apparatus as claimed in claim 12 wherein said magnetically operated lockout device requires manually resetting after tripping thereof.
5. The apparatus as claimed in claim 1 wherein said scheduler includes a timer motor and a series of cams for operating said scheduler controlled contacts.
6. Combustion supervision apparatus including a flame relay responsive to a flame detector for providing an indication of flame in the supervised combustion chamber, a control relay, an instantaneously operative magnetically operated lockout device, and a circuit for checking the continuity of said magnetically operated lockout device prior to energization of said control relay including in series the coil of said magnetically operated lockout device and the coil of said control relay.
7. The apparatus as claimed in claim 6 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
8. The apparatus as claimed in claim 6 and further including a circuit for maintaining said control relay energized after the continuity of said lockout device has been checked including a first set of normally open control relay contacts connected in parallel with said lockout coil.
9. Combustion supervision apparatus including a flame relay responsive to a flame detector for providing an indication of flame in the supervised combustion chamber, a control relay, a magnetically operated lockout device, a circuit for checking the continuity of said magnetically operated lockout device prior to energization of said control relay including in series the coil of said magnetically operated lockout device and the coil of said control relay, a scheduler for operating components of the combustion control system to provide in sequence an ignition interval and a combustion interval, a first circuit for checking the response of said flame detector prior to commencement of said ignition interval including the series connection of normally open contacts controlled by said flame relay and a first set of scheduler controlled contacts connected in parallel with said control relay coil, and a second circuit for checking the response of said flame detector after said ignition interval including the series connection of normally closed contacts controlled by said flame relay and a second set of scheduler controlled contacts connected in parallel with the series circuit of said normally open flame relay contacts and said first set of scheduler controlled contacts.
10. Combustion supervision apparatus for use in a combustion control system that includes a fuel control element; an ignition control element; a scheduler for operating components of the combustion control system to provide an initial interval, an ignition interval and a combustion interval; and a flame detector,
11. The apparatus as claimed in claim 10 wherein said lockout device is magnetically operated and said actuator includes a coil.
12. The apparatus as claimed in claim 11 wherein said lockout device includes a latch which holds said normally closed lockout contacts closed and energization of said actuator releases said latch and allows said normally closed lockout contacts to open instantaneously.
13. The apparatus as claimed in claim 12 wherein said magnetically operated lockout device requires manually resetting after tripping thereof.
14. The apparatus as claimed in claim 13 wherein the impedance of said control relay coil is at least four times the impedance of said lockout coil.
Description:
SUMMARY OF INVENTION
This invention relates to electrical control apparatus and more particularly to control apparatus particularly adapted for use in combustion supervision systems.
It is an object of this invention to provide novel and improved combustion supervision system incorporating an instantaneous type of lockout apparatus.
Another object of the invention is to provide a novel and improved circuit arrangement for use in combustion supervision systems for checking in a coordinated, reliable manner the proper operation of lockout and flame detector apparatus prior to initiation of the fuel burning sequence.
In accordance with the invention, there is provided combustion supervision apparatus for use in a combustion supervision system that includes a fuel control element, an ignition control element, a scheduler for operating components of the combustion control system to provide in sequence an initial (typically a purge) interval, an ignition interval, and a combustion interval; a flame detector; and circuitry responsive to the flame detector for providing an indication of the flame condition in the supervised combustion chamber. The apparatus further includes a circuit for checking the continuity of an instantaneous operating lockout device that includes in series the actuator of the lockout device and the coil of a control relay. In preferred embodiments, the apparatus further includes a second circuit for maintaining the control relay energized including a first set of normally open control relay contacts connected in parallel with the series circuit of the lockout coil, and a first set of scheduler controlled contacts; a third circuit for checking the response of the flame detector prior to commencement of the ignition interval including normally open contacts controlled by the flame relay, and the series connection of a second set of scheduler controlled contacts and a second set of normally open control relay contacts connected in parallel with the series circuit of the first set of scheduler controlled contacts and the control relay coil; and a fourth circuit for checking the response of the flame detector after the ignition interval including the series connection of normally closed flame relay contacts and a third set of scheduler controlled contacts connected in parallel with the series circuit of the normally closed flame relay contacts and the second scheduler controlled contacts.
In preferred embodiments, the lockout device is magnetically operated, the actuator includes a coil; the impedance of the control relay coil is at least four times the impedance of the lockout coil; the instantaneously operative lockout device requires manually resetting after tripping; and the scheduler includes a timer motor and a series of cams for operating the scheduler controlled contacts.
Apparatus in accordance with the invention provides instantaneous lockout operation; electrical continuity of the lockout actuator is checked initially; and a condition for checking that a false flame signal is not present is maintained throughout the purge cycle. During the initial interval the lockout and control relay coil circuits are connected in parallel so that failure condition which would trip the lockout device would not short out the control relay coil. A momentary flame detection signal at any time in the initial interval will cause a safety shutdown and a momentary loss of flame after the ignition interval will also cause a safety shutdown. On safety shutdown, both the lockout and control relay circuits are deenergized and the system is locked out until the lockout device is manually reset.
Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the drawing, in which:
FIG. 1 is a schematic diagram of a combustion control system constructed in accordance with the invention; and
FIG. 2 is a timing diagram indicating the operation of the scheduler employed in the system shown in FIG. 1.
DESCRIPTION OF PARTICULAR EMBODIMENT
The system shown in FIG. 1 includes terminals 10, 12 for connection to a 120 volt source of AC electrical power. Connected in series with terminal 10 is a limit control 14, such as a low water switch, an operating control 16, such as a thermostat, and a running interlock 18 that closes in response to operation of a blower 20. The circuit also includes a scheduler in the form of timer 22, an ignition control device 24, a pilot fuel control device 26, a main fuel control device 28, an alarm device 30, and a flame sensor 32. The flame sensor 32 applies signals through flame detector circuitry 34, for example of the type shown in copending application Ser. No. 60,230, entitled "Combustion Control System," filed concurrently herewith and assigned to the same assignee as this application, to operate a flame relay 36. Flame relay 36 controls contacts 36-1- 36-3 that are open when flame relay coil 36 is deenergized and contacts 36-4 that are closed when flame relay coil 36 is deenergized. The circuitry also includes a control relay coil 38 that controls normally open contacts 38-1- 38-3 and normally closed contact 38-4; and lockout coil 40 that controls normally closed contact 40-1 and normally open contact 40-2. Contacts 40-1 and 40-2 are spring loaded and when full line voltage is applied across coil 40, a lockout latch is released, immediately opening contacts 40-1 and closing contacts 40-2. This lockout device is manually reset by pushing its reset button to relatch contacts 40-1 and 40-2 in the position shown in FIG. 1.
Timer 22 controls a series of sixteen contacts that at time zero of timer 22 are in the position shown in FIG. 1. The timing diagram of FIG. 2 shows the scheduler cycle of operation, that cycle having a duration 150 seconds, and indicates the times at which the conditions of the contacts change. A low fire interlock 50 is connected across contacts 22-13 and a control circuit including resistor 52, capacitor 54, and diode 56 is connected to the flame sensor electronics 34.
In operation, in response to a request for burner operation from operating control 16, a circuit is completed from terminal 10 through interlock 14, operating control 16, lockout coil 40, normally closed flame relay contacts 36-4, timer contacts 22-9, control relay coil 38 and normally closed lockout contacts 40-1 to terminal 12. As control relay coil 38 has an impedance of 1,800 ohms, and lockout coil 40 has an impedance of 200 ohms about 12 volts appears across coil 40 and 108 volts across coil 38. This is sufficient to operate the contacts controlled by coil 38 but does not release the latch of relay 40. Continuity of the circuitry, including coil 40, however, is checked as that circuit must be complete in order for coil 38 to be energized. With the energization of coil 38, contacts 38-1 - 38-3 close and contacts 38-4 open. The closing of contacts 38-1 completes a circuit to operate the timer motor 22 through contacts 22-13, 22-14, and 22-15. After 5 seconds of operation of timer 22, contacts 22-12 close, energizing blower motor 20 to initiate a purge cycle and running interlock 18 closes as a result of airflow in the combustion chamber. After 15 seconds of operation of timer motor 22, contacts 22-9 open, interrupting the energizing circuit for control relay coil 38 through lockout coil 40 so that coil 38 can be maintained energized only through its holding contacts 38-3 and running interlock 18. Also, at time 15 seconds, slow make, quick break contacts 22-10 close, completing a circuit in parallel with quick make, slow break contacts 22-12.
The purge interval continues until timer time 90 seconds at which time contacts 22-5 (in series with pilot fuel control 26) close; damper control contacts 22-6 (not shown in FIG. 1) open; and contacts 22-16 open, removing flame relay contacts 36-1 from the circuit and terminating the check for false flame indication prior to ignition. After the control relay 38 has been energized and prior to this time, the lockout coil 40 will be energized through contacts 36-1 and produce a lockout condition immediately on any false flame signal causing even momentary pickup of flame relay 36. 6 seconds later (96 seconds into the cycle), contacts 22-4 open disconnecting capacitor 54 from a charging circuit, and contacts 22-3 close, connecting the charged capacitor 54 through resistor 52 and diode 56 to apply a pseudo flame signal to the flame electronics 34 to cause energization of flame relay 36 even though no flame is present in the combustion chamber. In this condition flame relay 36 is held in solely by the signal from capacitor 54 which is discharging. With the energization of flame relay coil 36, contacts 36-1 - 36-3 close and contacts 36-4 open.
At 95 seconds, timer contacts 22-13 open to provide a check on the position of the damper via the low fire interlock 50 which maintains timer motor 22 running if the damper is in low fire position. If the low fire interlock is not closed, the timer stops. As soon as the interlock closes the timer resumes its cycle.
At the 100 second timer, timer contacts 22-11 close and a signal is applied through the running interlock 18, contacts 38-3, flame relay contacts 36-3, timer contacts 22-11 and 22-2 to energize the ignition device 24 and through contacts 22-5 to operate the pilot fuel control 26 to admit pilot fuel to the combustion chamber. The pilot fuel must be ignited and flame sensed by detector 32 prior to 106 seconds when contacts 22--3 reopen. If the program should stop (due to timer motor failure) with contacts 22-3 closed, the pseudo flame signal will be on as long as capacitor 54 has sufficient charge, typical times being in the range of 15 to 30 seconds. If flame is not sensed, relay 36 drops out, opening contacts 36-1 - 36-3 and terminating ignition. As soon as flame is sensed, contacts 36-1 - 36-3 are held in by the energized flame relay coil 36. Pilot ignition terminates at 105 seconds with the opening of contacts 22-2, deenergizing ignition control 24. At 106 seconds contacts 22-3 open, terminating the pseudo flame signal, and contacts 22-4 close.
At 108 seconds timer contacts 22-14 open for two seconds to enable pilot flame to be checked by removing the jumper 58 across contacts 22-14. At 110 seconds, contacts 22-8 open so that the flame sensor electronics 34 remain energized only through a circuit completed by flame relay contacts 36-2; timer contacts 22-7 close completing a circuit between flame relay contacts 36-4 and control relay contacts 38-2, preparing a circuit for energization of lockout coil 40 should the flame relay become deenergized; and contacts 36-4 reclose.
At 111 seconds contacts 22-1 close, energizing the main fuel control 28 and main fuel flows in the combustion chamber for ignition by the established pilot flame. At 115 seconds contacts 22-13 close, terminating the low fire interlock check. At 121 seconds contacts 22-5 open, disconnecting the pilot solenoid 26 and terminating the flow of pilot fuel. The flame detector 32 must now be detecting the presence of main flame to keep flame relay 36 energized. Contacts 22-6 (the damper control contacts) also close at 121 seconds. At 130 seconds, contacts 22-15 open, deenergizing timer motor 22. The ignition cycle is finished and the burner system operates until a normal or safety shutdown occurs.
A normal shutdown occurs when limit control 14, operating control 16, or running interlock 18 opens, or a power interruption occurs. Any one of these events deenergizes control relay coil 38 and contacts 38-4 close starting timer motor 22. Timer contacts 22-15 close again at 135 seconds time; at 140 seconds contacts 22-1, 22-2, 22-7, 22-8, 22-11, 22-12, and 22-16 are reset preparatory for initiation of another combustion sequence; and at 150 seconds timer contacts 22-10 open deenergizing the timer motor and contacts 22-9 close. The control is ready for another ignition cycle.
A safety shutdown occurs whenever a false flame detection condition occurs during the purging cycle (actually from the time control relay 38 is energized at the start of the cycle until timer contacts 22-16 open (90 seconds into the cycle)); or when the flame detector 32 or the amplifier electronics 34 fails to indicate pilot or main burner flame after contacts 22-7 close (110 seconds into the cycle). In the first situation a continuity path is established through coil 40, flame relay contacts 36-1, timer contacts 22-16, control relay contacts 38-2, and lockout switch contacts 40-1. Should the flame relay contacts 36-1 close, full line power is immediately applied across coil 40 tripping the lockout latch and opening lockout contacts 40-1 to deenergize both lockout coil 40 and control relay coil 38. Lockout contacts 40-2 also close energizing alarm 30. If timer contacts 22-12 have closed (at timer 5 seconds), the timer motor will continue to operate until contacts 22-10 open at 150 seconds. The ignition and fuel control components 24, 26 and 28 will not be energized as control relay contacts 38-3 are open. To restart the burner, the lockout switch 40 must be manually reset by pushing its reset button.
Should the flame amplifier electronics 34 fail to provide a flame signal after contacts 22-7 close, a continuity path for lockout coil 40 is established through that coil, contacts 36-4 of the flame relay, timer contacts 22-7, control relay contacts 38-2, and lockout switch contacts 40-1. The opening of contacts 40-1 deenergizes control relay coil 38 and lockout coil 40. The opening of contacts 36-3 of the flame relay deenergize the fuel control components. Timer motor 22 continues to run through the circuit completed by control relay contacts 38-4 and timer contacts 22-10 until 150 seconds when those contacts open.
Thus it will be seen that the invention provides a combustion control system in which instantaneous lockout occurs in response to a false flame signal during the purge interval and similarly instantaneous lockout occurs in response to a flame failure signal after flame should have been established in the combustion chamber. Further, the circuitry is established through limit controls, operating controls and running controls and opening of any of those controls will cause the system to shut down in safe condition while reset of the circuitry including a delay before a further combustion request will be respected and further including a purge cycle in response to such request. While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.
This invention relates to electrical control apparatus and more particularly to control apparatus particularly adapted for use in combustion supervision systems.
It is an object of this invention to provide novel and improved combustion supervision system incorporating an instantaneous type of lockout apparatus.
Another object of the invention is to provide a novel and improved circuit arrangement for use in combustion supervision systems for checking in a coordinated, reliable manner the proper operation of lockout and flame detector apparatus prior to initiation of the fuel burning sequence.
In accordance with the invention, there is provided combustion supervision apparatus for use in a combustion supervision system that includes a fuel control element, an ignition control element, a scheduler for operating components of the combustion control system to provide in sequence an initial (typically a purge) interval, an ignition interval, and a combustion interval; a flame detector; and circuitry responsive to the flame detector for providing an indication of the flame condition in the supervised combustion chamber. The apparatus further includes a circuit for checking the continuity of an instantaneous operating lockout device that includes in series the actuator of the lockout device and the coil of a control relay. In preferred embodiments, the apparatus further includes a second circuit for maintaining the control relay energized including a first set of normally open control relay contacts connected in parallel with the series circuit of the lockout coil, and a first set of scheduler controlled contacts; a third circuit for checking the response of the flame detector prior to commencement of the ignition interval including normally open contacts controlled by the flame relay, and the series connection of a second set of scheduler controlled contacts and a second set of normally open control relay contacts connected in parallel with the series circuit of the first set of scheduler controlled contacts and the control relay coil; and a fourth circuit for checking the response of the flame detector after the ignition interval including the series connection of normally closed flame relay contacts and a third set of scheduler controlled contacts connected in parallel with the series circuit of the normally closed flame relay contacts and the second scheduler controlled contacts.
In preferred embodiments, the lockout device is magnetically operated, the actuator includes a coil; the impedance of the control relay coil is at least four times the impedance of the lockout coil; the instantaneously operative lockout device requires manually resetting after tripping; and the scheduler includes a timer motor and a series of cams for operating the scheduler controlled contacts.
Apparatus in accordance with the invention provides instantaneous lockout operation; electrical continuity of the lockout actuator is checked initially; and a condition for checking that a false flame signal is not present is maintained throughout the purge cycle. During the initial interval the lockout and control relay coil circuits are connected in parallel so that failure condition which would trip the lockout device would not short out the control relay coil. A momentary flame detection signal at any time in the initial interval will cause a safety shutdown and a momentary loss of flame after the ignition interval will also cause a safety shutdown. On safety shutdown, both the lockout and control relay circuits are deenergized and the system is locked out until the lockout device is manually reset.
Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the drawing, in which:
FIG. 1 is a schematic diagram of a combustion control system constructed in accordance with the invention; and
FIG. 2 is a timing diagram indicating the operation of the scheduler employed in the system shown in FIG. 1.
DESCRIPTION OF PARTICULAR EMBODIMENT
The system shown in FIG. 1 includes terminals 10, 12 for connection to a 120 volt source of AC electrical power. Connected in series with terminal 10 is a limit control 14, such as a low water switch, an operating control 16, such as a thermostat, and a running interlock 18 that closes in response to operation of a blower 20. The circuit also includes a scheduler in the form of timer 22, an ignition control device 24, a pilot fuel control device 26, a main fuel control device 28, an alarm device 30, and a flame sensor 32. The flame sensor 32 applies signals through flame detector circuitry 34, for example of the type shown in copending application Ser. No. 60,230, entitled "Combustion Control System," filed concurrently herewith and assigned to the same assignee as this application, to operate a flame relay 36. Flame relay 36 controls contacts 36-1- 36-3 that are open when flame relay coil 36 is deenergized and contacts 36-4 that are closed when flame relay coil 36 is deenergized. The circuitry also includes a control relay coil 38 that controls normally open contacts 38-1- 38-3 and normally closed contact 38-4; and lockout coil 40 that controls normally closed contact 40-1 and normally open contact 40-2. Contacts 40-1 and 40-2 are spring loaded and when full line voltage is applied across coil 40, a lockout latch is released, immediately opening contacts 40-1 and closing contacts 40-2. This lockout device is manually reset by pushing its reset button to relatch contacts 40-1 and 40-2 in the position shown in FIG. 1.
Timer 22 controls a series of sixteen contacts that at time zero of timer 22 are in the position shown in FIG. 1. The timing diagram of FIG. 2 shows the scheduler cycle of operation, that cycle having a duration 150 seconds, and indicates the times at which the conditions of the contacts change. A low fire interlock 50 is connected across contacts 22-13 and a control circuit including resistor 52, capacitor 54, and diode 56 is connected to the flame sensor electronics 34.
In operation, in response to a request for burner operation from operating control 16, a circuit is completed from terminal 10 through interlock 14, operating control 16, lockout coil 40, normally closed flame relay contacts 36-4, timer contacts 22-9, control relay coil 38 and normally closed lockout contacts 40-1 to terminal 12. As control relay coil 38 has an impedance of 1,800 ohms, and lockout coil 40 has an impedance of 200 ohms about 12 volts appears across coil 40 and 108 volts across coil 38. This is sufficient to operate the contacts controlled by coil 38 but does not release the latch of relay 40. Continuity of the circuitry, including coil 40, however, is checked as that circuit must be complete in order for coil 38 to be energized. With the energization of coil 38, contacts 38-1 - 38-3 close and contacts 38-4 open. The closing of contacts 38-1 completes a circuit to operate the timer motor 22 through contacts 22-13, 22-14, and 22-15. After 5 seconds of operation of timer 22, contacts 22-12 close, energizing blower motor 20 to initiate a purge cycle and running interlock 18 closes as a result of airflow in the combustion chamber. After 15 seconds of operation of timer motor 22, contacts 22-9 open, interrupting the energizing circuit for control relay coil 38 through lockout coil 40 so that coil 38 can be maintained energized only through its holding contacts 38-3 and running interlock 18. Also, at time 15 seconds, slow make, quick break contacts 22-10 close, completing a circuit in parallel with quick make, slow break contacts 22-12.
The purge interval continues until timer time 90 seconds at which time contacts 22-5 (in series with pilot fuel control 26) close; damper control contacts 22-6 (not shown in FIG. 1) open; and contacts 22-16 open, removing flame relay contacts 36-1 from the circuit and terminating the check for false flame indication prior to ignition. After the control relay 38 has been energized and prior to this time, the lockout coil 40 will be energized through contacts 36-1 and produce a lockout condition immediately on any false flame signal causing even momentary pickup of flame relay 36. 6 seconds later (96 seconds into the cycle), contacts 22-4 open disconnecting capacitor 54 from a charging circuit, and contacts 22-3 close, connecting the charged capacitor 54 through resistor 52 and diode 56 to apply a pseudo flame signal to the flame electronics 34 to cause energization of flame relay 36 even though no flame is present in the combustion chamber. In this condition flame relay 36 is held in solely by the signal from capacitor 54 which is discharging. With the energization of flame relay coil 36, contacts 36-1 - 36-3 close and contacts 36-4 open.
At 95 seconds, timer contacts 22-13 open to provide a check on the position of the damper via the low fire interlock 50 which maintains timer motor 22 running if the damper is in low fire position. If the low fire interlock is not closed, the timer stops. As soon as the interlock closes the timer resumes its cycle.
At the 100 second timer, timer contacts 22-11 close and a signal is applied through the running interlock 18, contacts 38-3, flame relay contacts 36-3, timer contacts 22-11 and 22-2 to energize the ignition device 24 and through contacts 22-5 to operate the pilot fuel control 26 to admit pilot fuel to the combustion chamber. The pilot fuel must be ignited and flame sensed by detector 32 prior to 106 seconds when contacts 22--3 reopen. If the program should stop (due to timer motor failure) with contacts 22-3 closed, the pseudo flame signal will be on as long as capacitor 54 has sufficient charge, typical times being in the range of 15 to 30 seconds. If flame is not sensed, relay 36 drops out, opening contacts 36-1 - 36-3 and terminating ignition. As soon as flame is sensed, contacts 36-1 - 36-3 are held in by the energized flame relay coil 36. Pilot ignition terminates at 105 seconds with the opening of contacts 22-2, deenergizing ignition control 24. At 106 seconds contacts 22-3 open, terminating the pseudo flame signal, and contacts 22-4 close.
At 108 seconds timer contacts 22-14 open for two seconds to enable pilot flame to be checked by removing the jumper 58 across contacts 22-14. At 110 seconds, contacts 22-8 open so that the flame sensor electronics 34 remain energized only through a circuit completed by flame relay contacts 36-2; timer contacts 22-7 close completing a circuit between flame relay contacts 36-4 and control relay contacts 38-2, preparing a circuit for energization of lockout coil 40 should the flame relay become deenergized; and contacts 36-4 reclose.
At 111 seconds contacts 22-1 close, energizing the main fuel control 28 and main fuel flows in the combustion chamber for ignition by the established pilot flame. At 115 seconds contacts 22-13 close, terminating the low fire interlock check. At 121 seconds contacts 22-5 open, disconnecting the pilot solenoid 26 and terminating the flow of pilot fuel. The flame detector 32 must now be detecting the presence of main flame to keep flame relay 36 energized. Contacts 22-6 (the damper control contacts) also close at 121 seconds. At 130 seconds, contacts 22-15 open, deenergizing timer motor 22. The ignition cycle is finished and the burner system operates until a normal or safety shutdown occurs.
A normal shutdown occurs when limit control 14, operating control 16, or running interlock 18 opens, or a power interruption occurs. Any one of these events deenergizes control relay coil 38 and contacts 38-4 close starting timer motor 22. Timer contacts 22-15 close again at 135 seconds time; at 140 seconds contacts 22-1, 22-2, 22-7, 22-8, 22-11, 22-12, and 22-16 are reset preparatory for initiation of another combustion sequence; and at 150 seconds timer contacts 22-10 open deenergizing the timer motor and contacts 22-9 close. The control is ready for another ignition cycle.
A safety shutdown occurs whenever a false flame detection condition occurs during the purging cycle (actually from the time control relay 38 is energized at the start of the cycle until timer contacts 22-16 open (90 seconds into the cycle)); or when the flame detector 32 or the amplifier electronics 34 fails to indicate pilot or main burner flame after contacts 22-7 close (110 seconds into the cycle). In the first situation a continuity path is established through coil 40, flame relay contacts 36-1, timer contacts 22-16, control relay contacts 38-2, and lockout switch contacts 40-1. Should the flame relay contacts 36-1 close, full line power is immediately applied across coil 40 tripping the lockout latch and opening lockout contacts 40-1 to deenergize both lockout coil 40 and control relay coil 38. Lockout contacts 40-2 also close energizing alarm 30. If timer contacts 22-12 have closed (at timer 5 seconds), the timer motor will continue to operate until contacts 22-10 open at 150 seconds. The ignition and fuel control components 24, 26 and 28 will not be energized as control relay contacts 38-3 are open. To restart the burner, the lockout switch 40 must be manually reset by pushing its reset button.
Should the flame amplifier electronics 34 fail to provide a flame signal after contacts 22-7 close, a continuity path for lockout coil 40 is established through that coil, contacts 36-4 of the flame relay, timer contacts 22-7, control relay contacts 38-2, and lockout switch contacts 40-1. The opening of contacts 40-1 deenergizes control relay coil 38 and lockout coil 40. The opening of contacts 36-3 of the flame relay deenergize the fuel control components. Timer motor 22 continues to run through the circuit completed by control relay contacts 38-4 and timer contacts 22-10 until 150 seconds when those contacts open.
Thus it will be seen that the invention provides a combustion control system in which instantaneous lockout occurs in response to a false flame signal during the purge interval and similarly instantaneous lockout occurs in response to a flame failure signal after flame should have been established in the combustion chamber. Further, the circuitry is established through limit controls, operating controls and running controls and opening of any of those controls will cause the system to shut down in safe condition while reset of the circuitry including a delay before a further combustion request will be respected and further including a purge cycle in response to such request. While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.