US3524717A

US3524717A - Combustion supervision system

Info

Publication number: US3524717A
Application number: US737491A
Authority: US
Inventors: Phillip J Cade
Original assignee: Electronics Corp of America
Current assignee: Electronics Corp of America
Priority date: 1968-06-17
Filing date: 1968-06-17
Publication date: 1970-08-18
Anticipated expiration: 1987-08-18
Also published as: FR2011108A1; BE734432A; DE1930750A1; GB1262947A; DE1930750B2

Description

Aug. 18, 1970 P. J. CADE coMBUsTIoN sUPERvIsoN SYSTEM Filed June 17, 1968 m @E asv Pr @N N -N H slllow @m m95@ mma hl i\/N.N u!

Nm om o. @Q vm w q, wm K v x. .h n n/f Hwom. Q -m Nm. M mqwmqq -QAM .I MDU- \NN w- 22: zoEzQ EJE mas q mma/2m ON -om @Nw/1 m -m F. Q @om Q www v o@ Niv 3% QE EMM i w United States Patent O 3 524,717 COMBUSTION SUPERVISION SYSTEM Phillip J. Cade, Winchester, Mass., assignor to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed `lune 17, 1968, Ser. No. 737,491 Int. Cl. F23n 5/ 00 U.S. Cl. 431-29 18 Claims ABSTRACT OF THE DISCLOSURE A combustion control system includes four similar adjustable electronic timers, each including a unijunction transistor, a capacitor, and a variable resistor, and each controlling a relay coil. A first timer times a purge interval, and at the end of the purge interval initiates operation of two other timers, a first of these two timers timing an ignition interval and the second of these two timers delaying application of the main fuel supply to the combustion chamber. The fourth timer times an interval at the end of the ignition interval and then releases the relay controlled by the rst timer.

SUMMARY OF INVENTION This invention relates to electrical timing and control circuitry and more particularly to timing and control circuitry particularly adapted for use in combination supervision systems.

In connection with the safe operation of combustion systems, it is desirable to sequence the fuel burner equipment automatically through a series of steps to initiate the desired combustion condition in the system and then to supervise on a continuing basis that established combustion condition in a manner to promptly shut the combustion system down in safe condition upon occurrence of flame or equipment failure. The desired operations to be performed in sequence in start up of a combustion system and the timing of those operations may differ extensively depending on the application and code specifications, for example. It is desirable that the timing of the sequence of operations be accurate and versatile and that the control be capable of providing a short time interval where desired. Accordingly it is an object of this invention to provide a simple, versatile and reliable electrical timing and control circuit for use in a combustion control system.

Another object of this invention is to provide novel and improved flame relay control apparatus for use in a combustion supervision system.

Another object of the invention is to provide a novel and improved arrangement for checking in a coordinated and reliable manner the proper operation of a flame supervision system.

Another object of the invention is to provide a novel and improved timing and control circuit particularly adapted for supervising a combustion system that does not employ motor driven timing devices.

Still another object of the invention is to provide a novel and improved control arrangement for use in a combustion control system that employs a plurality of electronic timers.

In accordance with the invention, there is provided timing and control circuitry for use in a combustion control system that includes a fuel control element; an ignition control element; a flame detector; and circuitry responsive to an operating request signal and to the llame detector for controlling the operation of the ignition and fuel control elements to provide in sequence an ignition interval, and a combustion interval. This timing and conice trol circuitry includes a plurality of adjustable electronic timers which time an ignition interval in which llame is established in the combustion chamber and initiate the application of the main fuel source after detection of establishment of flame in the combustion chamber. The timing cycles of the timers overlap so that the two timers are operating concurrently and provide a check on the proper operation of the control circuitry. In one embodiment, one timer initiates the flow of main fuel after a second timer has terminated the ignition condition. In a preferred embodiment, three timers are employed during the ignition interval, two timers commencing timing cycles simultaneously at the beginning of the ignition interval, thevtimer first ending its timing interval enabling a flame indicator and also starting a third timer; the second timer initiating the flow of main fuel at the end of its timing interval if the flame has been established; and the third timer then terminating operation of the ignition components of the combustion system. The circuitry shuts down the system in safe condition whenever an unsafe condition is detected, for example, detection of a flame indication prior to initiation of ignition, failure to detect llame Within the a predetermined period, or failure of flame after it is established. In a preferred embodiment of the invention, a fourth timer is employed which provides an initial purge interval and then initiates the ignition and fuel flow sequences. The circuitry is arranged to provide economical use of circuit components in a reliable manner.

In a preferred embodiment of the invention, each electronic timer is of similar design and includes a capacitive element. An active switch element (a unijunction transistor in a particular embodiment) is employed in conjunction with a load device such as a relay coil to provide an indication of the termination of the timing interval, the relay coil being held in by a holding contact.

A further feature of the invention is the employment of the llame relay coil as a component of an electronic timer in a manner in which the flame relay performs a checking function prior to initiation of the ignition interval, it being used as a component of a timer during the ignition interval, and then its function is returned to flame supervision. In a particular embodiment at the completion of the timing interval, the electronic timer initially energizes the flame relay coil independently of the presence of flame in the supervised combustion system and initiates a timing interval which is employed to terminate ignition. The llame relay coil is held in, however, only if flame is sensed in the supervised combustion chamber.

In the preferred embodiment of the invention, the control will shut down the system` in safe condition should any one resistor open or any transistor fail in short or open condition; as well as locking out in safe condition upon detection of any unwanted or defective condition in the supervised system or in the control equipment. The invention provides a timing and control circuit employing electronic timers that are operating simultaneously so that the failure of either one will be detected safely. An accurate, versatile and safe timing control system for use in combination supervision systems is provided in which a short timing intervals may be provided where required by particular specifications.

Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment thereof progresses, in conjunction with the drawings, in which:

FIG. l is a block diagram of components employed in the control of a combustion system in accordance with the invention;

FIG. 2 is a schematic diagram of sequencing circuitry for controlling the sequence of operation of the elements shown in FIG. l; and

3 FIG. 3 is a timing diagram indicating the sequence of operation provided by the circuitry of FIG. 2.

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to FIG. 1, line terminals and 12 are provided for connection to a suitable source of electric power. Connected in series across

terminals

10, 12 is normally closed contacts 44-1 of a magnetic lockout switch actuator 44 (FIG. 2), the normally open contacts -1 of main control relay 20, and a blower 16. Connected to the junction between contacts 44-1 and 20'-1 is line 13 which applies power to the primary winding 30 of control transformer 32 (FIG. 2). An operating control (diagrammatically indicated as switch 14) which is closed upon a request for operation of the supervised burner system is connected between terminal 10 and other control components of the system. Normally open lockout contacts 44-2 and an alarm unit 18 are connected in series between switch 14 and terminal 12. The coil 20 of the main control relay is connected across contacts 44-2 and alarm 18. Other control connected in parallel with relay coil 20 include a damper 22, a pilot fuel control 24, ignition control 26 and main fuel control 28.

These compounds are controlled by the electronic timing circuitry shown in FIG. 2. With reference to that iigure, the primary winding of stepdown transformer 32 is connected across the

terminals

10, 12 via line 13 and contact `44-1. Transformer 32 has a secondary winding 34 to which is connected a rectifier 36 and smoothing capacitor 38 so that a rectied 24 volt signal is applied across lines 40 and 42. Connected to line 40 is normally open control relay contacts 20-2, in series with air flow responsive switch 16-1 and magnetic lockout actuator 44. A iiame sensor 62 applies a signal through llame detector electronics 64 to the control electrode 66 of switch transistor 86 when ilame is detected in the supervised combustion chamber.

The circuitry also includes four electronic timing circuits, each of which includes a unijunction transistor and a timing network that includes a capacitor and a variable resistor. The first electronic timing circuit includes transistor 50, timing capacitor 52, variable timing resistor 54, and a biasing resistor 56. A relay coil is connected between the output electrode 62 of the unijunction transistor 50 and the transistor switch 120. A second timing circuit includes unijunction transistor 70, timing capacitor 72 variable timing resistor 74 and biasing resistor 76.

The output electrode 78 of the transistor 70 is connected to tap 80 of the coil 82 of the ame relay. A third timing circuit includes transistor 90, timing capacitor 92, variable timing resistor 94 and biasing resistor 96. Relay coil 98 is connected to output electrode 100 of the transistor 90. Resistor 102 provides a discharge path for

capacitors

72 and 92 when the control is in standby condition. A fourth timing circuit, which includes unijunction transistor 110, timing capacitor 112 and variable resistor 114, is connected to the control electrode 118 of switch transistor 120.

In each of these timing circuits, when a DC potential is applied to the circuit, the signal applied to the output circuit of the transistor establishes a bias potential on the emitter electrode of the transistor. The timing network of the variable resistor and the timing capacitor is also energized and the capacitor commences to charge. When the potential on the timing capacitor exceeds the bias potential on the emitter electrode, the transistor conducts and the capacitor discharges through the transistor and the relay coil to cause energization (pickup) of the relay controlled by the timer (except in the case of the fourth timer which switches off transistor 120). With the energization of its coil, the relay closes one of its contacts to complete a holding circuit to maintain it en ergized. Other contacts are operated by the energized relay to control the operation of one or more combustion control elements and/or another timer.

The sequence of operations of the components shown in FIG. 1 as controlled by the circuit shown in FIG. 2 is indicated in FIG. 3. An initial prepurge interval which may be varied from zero to ninety seconds is controlled by the rst timing network that includes unijunction transistor `50. At the end of that rst timing interval, relay 60 is energized and two other timing intervals are initiated, a second timing interval (variable from two of fifteen seconds) controlled by circuity associated with transistor 70 and a third timing interval (variable from four to twenty seconds) controlled by the circuitry associated with transistor 90. A fourth timing interval (variable from four to sixty seconds), under the control of the circuity associated With transistor 110, is initiated in respouse to the conjoint termination of the second timing interval and the detection of flame in the combustion chamber and at the end of that timing interval, the system is transferred to full operation with the de-energization of relay 60.

In response to a request for system operation, operating control 14 closes. The main control unit coil 20 is energized, closing contacts 20-1 to energize blower 16 and closing contacts 20-2 in the input to the timing circuitry. When air llow has been established in the combustion chamber, the air flow responsive switch 1641 closes and power is supplied through the lockout actuator coil 44. Should a llame signal be applied to control electrode 66 at this time, transistor 86 will conduct and energize llame relay 82, closing contacts 82-2 so that as soon as air ow is produced in response to a request for burner operation the lockout actuator 44 will open contacts 44-1, terminat ing the control sequence; and close contacts 44-2, energizing alarm 18. If a flame signal is not present, the first timing (prepurge) interval continues as power is applied via the normally closed contacts 98-1 and the normally closed contacts 60-1 to apply a bias potential, via resistor 56, to the unijunction transistor 50. This DC signal also is applied via variable resistor 54 to charge capacitor 52. When the potential on capacitor 5.2 exceeds the bias potential applied to the emitter of transistor 50, the transistor conducts and capacitor S2 discharges through the transistors output circuit to energize the relay coil 60 (the current path being completed to ground through the transistor switch 120` which conducts in response to the signal applied via resistors 122, 124). With the energization (pickup) of relay coil 60 its contacts are operated; contacts 60-1 open to interrupt a lockout actuator energizing circuit via llame relay contacts 82-2; contacts 60-2 close to complete a holding circuit; contacts 60-3 close to commence timing operation of the second and third timing circuits; normally closed contacts 60-4 open, de-energizing the damper control 22 (FIG. 1); contacts 605 close, energizing the pilot fuel control 24 and the ignition control 26 (the latter through the normally closed contacts 82-3 of the ilame relay); contacts 61)6 open disabling the circuit to the flame sensor transistor 86 so that the flame relay 82 will not be energized on detection of flame but rather by the operation of the timing circuit including transistor 70; contacts 60-7 open; and contacts 60-8 close. Thus an ignition interval is initiated at the end of the first timing interval.

During the ignition interval, pilot fuel is orwing into the supervised combustion chamber and the ignition control is operative to initiate flame. Also, the timing interrvals controlled by the second and third timers are running. With the application of power to the second timer, a bias is applied to the output circuit of transistor 70 and the timing capacitor 72 commences to charge. When that capacitor has sufficient charge to overcome the bias, that Y transistor conducts and the capacitor discharges through capacitor to pick up the relay. With the pickup of the flame relay, contacts -82-1 open, interrupting the circuit for energizing the lockout actuator; contacts 82-2 close, providing an alternate lockout actuator enabling circuit and also a circuit for the output circuit of timer transistor 1110; contacts 82-4 close, providing a holding circuit for the flame relay coil 82 if iiame is present in the combustion chamber such that transistor 86 is in conducting condition; contacts 82-3 open, terminating operation of ignition control 26 independently with the existence of ilame in combustion chamber; and contacts 82-5 close in preparation for operation of the main fuel control 28 upon the completion of the third timing interval. At this time the ignition interval has terminated and pilot flame exists in the combustion chamber.

The third timing circuit commenced operation coincidently with the second timing circuit, a bias being applied to transistor output circuit 90 via biasing resistor 96 and the capacitor 92 commenced to charge. When the charge on capacitor 92 is sucient to overcome the bias on transistor 90, that transistor conducts and capacitor 92 discharges through relay coil 98 to pick up that relay. The closing of contacts 98-2 completes a holding circuit via contacts 60-8 and resistor 126; contacts 98-1 open to interrupt one path to the lockout actuator; contacts 98-3 close to complete an alternate lockout actuator path in series with the ame relay contacts #82-1 which are now open; and contacts 98-4 close to operate the main fuel control 28 so that fuel flows into the main combustion chamber and is ignited from the pilot. llame. At this time both pilot and main flames are burning in the combustion chamber.

Operation of the fourth timing circuit -was initiated with the energization of the lllame relay coil 82 and capacitor 112 commenced to charge. When the capacitor 112 charges sufficiently to overcome the bias on transistor 110, that transistor conducts and that conduction transition is applied by capacitor 112 to cause the output circuit of transistor 120 to cease conducting so that coil 60 is de-energized. With that de-energization, contacts 60-1 reclose; contacts 60-2 open; contacts 60-3 open, de-energizing the inputs to the second and third timing circuits; contacts 60-4 close, re-energizing the damper control 22; contacts 60-5 open, de-energizing the pilot control 24; contacts 60-6 close in a resetting operation, paralleling the now-closed llame relay contacts 82-4; contacts 60-7 close, establishing a holding circuit for coil 98; and contacts 60-8 open. (Coil 98 may have a copper slug or capacitor connected to it to delay its dropout so that it is maintained in picked up condition during this transition.)

Should flame failure occur at any time after detection of flame by sensor 62, transistor 86 will cease conducting and coil 82 will be de-energized causing all of its controlled contacts to return to their normal positions. Contacts 82-1 close, and, as contacts 98-3 are closed, current Iwill flo-w through the lockout actuator 44 causing the operation of that lookout switch, opening lockout contacts 44-1 and de-energizing the primary transformer 32 and all the control circuits promptly and closing contacts 44-2 to energize the alarm 18. Also, should air flow cease for any reason, all of the relays will be de-energized, terminating the ilow of fuel to the supervised combustion chamber and shutting down the system in safe condition.

Suitable values for the components are:

Resistor:

56, 76, 96 4709 54

1M

74, 94 150K 102 l-OK 114

2M

122, 126 3009 124 10K 6 Capacitor: af. 52, 72 200 92 100 112 50 The arrangement of the circuit components in this embodiment enables provision of the interrelated timing sequence with the four relays of compact configuration, the relay 60 controlling four SPDT switches; the relay 82 having four poles, one pole being SPDT; the relay 98 having three poles, one pole being SPDT; and control relay 20 having two normally opened contacts. A wide range of timing values may be provided easily through adjustment of the

adjustable resistors

54, 74 and 94 and 114. Each timed interval may be adjusted from times as short as two seconds to times up to one minute and greater.

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 delined in the claims.

What is claimed is:

1. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to the combustion chamber and an ignition control for igniting fuel in the combustion chamber comprising:

a plurality of electronic timers, each said electronic timer being individually adjustable to vary the duration of its timing interval,

a rst of said timers being operative to initiate a timing interval for the operation of said fuel control and a second of said timers being operative to terminate operation of said ignition control at the end of its timing interval independently of the detection of ilame in the supervised combustion chamber by a flame detector, the timing intervals of said rst and second timers overlapping one another and providing a check on the proper operation of the control apparatus.

2. The burner control apparatus as claimed in claim 1 and further including a third electronic timer, the timing interval of said third timer being arranged so that at least one other timer is operating concurrently with said rst timer throughout the timing interval of said first timer.

3. The 'burner control apparatus as claimed in claim 1 wherein each said timer includes a timing network including a capacitive timing element, the rate of charge of that capacitive element determining the timing interval of said timer.

4. The control apparatus as claimed in claim 1 wherein each said timer includes an active switch element and a load device, said switch element being operative to energize said load device at the end of said timing interval.

5. The control apparatus as claimed in claim 4 wherein said load device is a relay coil and further including a circuit including a normally open contact controlled by said relay coil connected in series with said relay coil for providing a holding circuit upon energization of said relay coil.

6. The burner control apparatus as claimed in claim 1 wherein said installation further includes a blower control and further including a third electronic timer operative to initiate a timing interval at the same time said blower control is actuated and to initiate operation of said ignition control at the end of its timing interval.

7. Burner control apparatus for use with fuel burner installation having a combustion chamber, a fuel control for controlling the flow of fuel to the combustion chamber and an ignition control for igniting fuel in the combustion chamber comprising:

a plurality of electronic timers, each said electronic of flame in said combustion chamber, circuitry folrlr'eiif timer being individually adjustable to vary the duration of its timing interval,

a rst of said electronic timers being responsive to initiation of operation of said ignition control to initiate a timing interval for the operation of said fuel control; and

a second of said electronic timers being connected to terminate operation of said ignition control at the end of its timing interval independently of the detection of ame in the combustion chamber,"

the timing intervals of said rst and second timers overlapping one another and providing a check on the proper operation of the control apparatus.

8. The burner control apparatus as claimed in claim 7 wherein said installation further includes a pilot fuel control and further including a third electronic timer operative to terminate operation of said pilot fuel control, the timing interval of said third timer being arranged so that at least one other timer is operating concurrently with said iirst timer throughout the timing interval of said iirst timer. I

9. The burner control apparatus as clalmed 1n claim 8 wherein each said timer includes a timing network including a capacitive timing element and an adjustable resistive timing element, the rate of charge of that capacitive element determining the timing interval ofv s'aid timer.

10. The control apparatus as claimed in claim `9 wherein each said timer includes an active switch element and a load device, said switch element being responsive to said timing element to energize said load device at the end of said timing interval.

11. The Q control apparatus as claimed in claim 10 wherein said load device is a relay coil and further including a circuit including normally open contact controlled by said relay coil connected in series with said relay coil for providing'a holding circuit upon energization of said relay coil.

12. The burner control apparatus as claimed in claim 11 and further includinga flame detector, a iame relay responsive. to signals from said flame detector, said second electronic timer being operative to energize the cgil of said'iiame relay a predetermined interval after initiation of an ignition interval independently of the existence iblower control is actuated and to initiate operation of said 55` ignition control and said first electronic timer at the end of its timing interval.

14. In a combustion control system having an ignition control, a* main fuel control, Aand a'ame detector, a

iiame, relaylreszponsive to signals from-'saidflame detector, 60 ansle'ctronic timer responsive-toa request afoifaignit' n and operative-to' energize .the coil of said"ame .relai predetermined interval afterinitiation of said ignition rev quest independently of the existence of flame in a combustion chamber, circuitry for rendering said flame relay responsive to said iiame detector prior to said'ignition interval, and a second circuit for maintaining said iiame relay energized after said ignition interval only in response to detection of iiame by said iiame detector.

15. In a combustion control system having an ignition control and a main fuel control and a flame detector, a

llame relay responsive to signals from said iiame detector, y

a first electronic timer connected to initiate an ignition interval and to energize said iiame relay a predetermined time interval after initiation of said ignition interval i11- dependently of the existence of flame in the combustion chamber and circuitry for maintaining said llame relay energized only in response to the detection of ame by said flame detector.

16. In a combustion control system having an ignition control and a main fuel control and a flame detector, a flame relay responsive to signals from said ame detector, said flame relay including a tapped coil, and said flame detector being connected to said coil to energize said flame relay in response to detection of iiame by said flame detector, a first electronic timer including a unijunction transistor, a capacitor and a variable resistor arranged so that said transistor is switched to conducting condition in response to a predetermined charge on said capacitor, said transistor being connected to the tap of said coil to energize said coil when said transistor is switched to conducting condition, said iirst electronic timer being connected to initiate an ignition interval andV to energize said flame relay a predetermined time interval after initiation of said ignition interval independently of the existence of flame in the combustion chamber, and circuitry for maintaining said iiame relay energized only in response to the detection of flame by said iiame detector.

17. Ihe circuitry as claimed in claim 16 and further including a control relay and a second electronic timer, said second electronic timer being responsive to said first electronic timer to initiate a timing interval and being operative at the completion of said timing interval toy release said control relay.

18. The circuitry as claimed in claim 17 wherein said ame relay includes a tapped coil, said iirst and second electronic timers each include a unijunction transistor, a capacitor and a variable resistor arranged so that said transistor is switched to conducting condition in response to a predetermined charge on said capacitor, said transistor of said iirst timer being connected to the top of said coil to energize said coil when said transistor is switched to conducting condition and said flame detector is connected to said coil to energize said flame relay in response 'to the'detection of iiame by said llame detector and said secondtimer operates a transistor switch to release said control relay upon completion of its timing interval.

References Cited UNITED STATES PATENTS 3,376,099 4/1968 Giuffrida et al. 431-26 EDWARD G. FAVORS, Primary Examiner