US3376099A

US3376099A - Electrical control circuitry for burners

Info

Publication number: US3376099A
Application number: US538713A
Authority: US
Inventors: Giuffrida Philip; Phillip J Cade
Original assignee: Electronics Corp of America
Current assignee: Electronics Corp of America
Priority date: 1966-03-30
Filing date: 1966-03-30
Publication date: 1968-04-02
Anticipated expiration: 1985-04-02
Also published as: GB1175980A; CH467434A; DE1551950B2; DE1551950A1; DE1776207A1; NL6704491A; FR1515782A; BE696278A

Description

Ap 1968 P. GIUFFRIDA ETAL 3,376,099

ELECTRICAL CONTROL CIRCUITRY FOR BURNERS 5 Sheets-Sheet 1 Filed March 30, 1966 N Om A ril 2, 1968 P. GIUFFRIDA ETAL 3,376,099

ELECTRICAL CONTROL CIRCUITRY FOR BURNERS 3 Sheets-Sheet 2 Filed March 30, 1966 m m mwmm a w ..l r I ..w 5/

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I 1 a. 0 5F 6 H M April 1968 P. GIUFFRIDA ETAL' 3,376,099

ELECTRICAL CONTROL CIRCUITRY FOR BURNERS Filed March so, 1966 3 Sheets-Sheet 5 I02 I=-1 0 I04 W [F IG. 5,

United States Patent Oflice 3,376,099 Patented Apr. 2., 1968 3,376,099 ELECTRICAL CONTROL CIRCUITRY FOR BURNERS Philip Giulfrida, North Andover, and Phillip J. Cade,

Winchester, Mass, assignors to Electronics Corporation of America, Cambridge, Mass, a corporation of Massachusetts Filed Mar. 30, 1966, Ser. No. 538,713 6 Claims. (Cl. 431-26) ABSTRACT OF THE DISCLOSURE A combustion control system includes a main control relay; an ultraviolet radiation sensor andelectronic circuitry connected to the sensor for operating a flame relay; fuel control elements and an ignition transformer; a time delay relay; a safety lockout switch; and a time delay switch having a bimetallic actuator heated by a heater connected to a 0.2 volt source. When the system is energized the electronic circuitry connected to the sensor is immediately energized. A set of normally closed flame relay contacts, a set of normally closed safety lockout switch contacts, and a set of normally open time delay switch contacts are connected in the energizing circuit of the main control relay. After a short time interval the time delay switch contacts close and the main control relay is energized to start a combustion cycle. However, if the electronic circuitry causes the flame relay to be immediately energized, the control relay circuit is interrupted so that combustion cannot be initiated. In the combustion cycle the time delay relay is energized and after a predetermined interval the ignition transformer is de-energized by that relay and cannot be again re-energized until the main control relay has been de-energized.

This invention relates to electrical control circuitry and more particularly to control circuitry particularly adapted for use in combustion supervision systems and to improved components for use in such circuitry.

In conjunction with the safe operation of combustion systems it is desirable to provide a controller which automatically programs the operation of a fuel burner to initiate the desired combustion condition in the system and then to supervise on a continuing basis that established combustion condition. It is an object of this inven tion to provide novel and improved apparatus for use in such programming of fuel burners and for supervision of combustion conditions established by such fuel burners.

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 sensor prior to initiating the fuel burning sequence.

Another object of the invention is to provide a novel and improved circuit arrangement which provides protection against unwanted recycling of the fuel burner systern after occurrence of a flame failure condition.

Still another object of the invention is to provide novel and improved control components which impart a time delay in an operating sequence and which are particularly useful in combustion supervision systems.

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

FIG. 1 is a schematic diagram of a combustion control system constructed in accordance with the invention;

FIG. 2 is a side elevational view of a lock-out switch structure employed in the circuitry shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2 showing details of the lock-out switch in a first (lock-out) position;

FIG. 4 is a sectional view similar to FIG. 3 showing details of the lock-out switch in a second (normal) position;

FIG. 5 is a top elevational view of another electrical control element employed in the circuitry shown in FIG. 1; and

FIG. 6 is a front elevational view of the control circuit element shown in FIG. 5

The system shown in FIG. 1 has

terminals

10, 12 for connection to a suitable source of electric power. A transformer 14 having a primary winding 16 and a secondary winding 18 is connected directly across

terminals

10 and 12. Also connected directly across those terminals are control circuitry for an ignition control element 20, a blower control element 22, a pilot fuel control element 24 and a main fuel control element 26-. In addition the control circuitry includes a time delay element 28 that controls normally closed contacts 281.

The secondary winding 18 of the transformer has a lower terminal 36, a first tap at twelve volts to which line 32 is connected, a second tap at twenty volts to which line 34 is connected, and an upper terminal 36 which is at 580 volts. An auxiliary tap provides a potential difference of 0.2 volt and line 38 is connected to it for energizing a control element 40 that is connected across

lines

34 and 38.

Transformer secondary output voltage is connected through capacitor 42 and resistor 44 to a flame sensor 46. This flame sensor in the preferred embodiment is an ultraviolet detector of the Geiger-Mueller type. (

Elements

44 and 46 may be located at a remote location, for example in the wall of a combustion chamber that is to be supervised.) The sensor 46 is connected to inductor 50 having

output lines

52, 54 connected through diodes 56 and a tap 58 connected to the common bus 30. The diodes 56 are connected together at common junction 60 which in turn is connected through resistor 62 to an amplifier

circuit including transistors

70 and 72. Transistor 72 has coil 74 of a flame relay connected in its collector circuit. That flame relay controls contacts 74-1, 74-2, 74-3 and 744. This transistor amplifier circuit is energized by electric potential that is applied on bus 76 through diode 78 from line 34 connected to the twenty volt tap of the secondary winding 18.

Connected to the transformer secondary, in addition to the flame detector circuitry, is a main control circuit includes a main control relay 80 which controls contacts 804, 802 and 80-3. The control circuit includes, in addition, a control device such as a thermostat 82 connected in series with the control relay coil 80 and a lockout switch actuator 84 that controls contacts 841. This control circuitry is energized through a delay switch 40-1 that is physically mounted on the heater 40 (as indicated in FIGS. 5 and 6) and when that switch is closed, energization of the main control relay 80 is enabled.

When power is applied to

terminals

10, 12, the secondary of transformer 14 is energized. The flame detection circuitry is immediately energized but a delay in energizing the control circuitry is imposed by the delay control 49, 40-1. With reference to FIGS. 5 and 6, electric circuit element 40 has terminals 90, 92. Terminal 96' is securely mounted in fixed position by mounting bracket 94 and has projecting upwardly from it a bimetallic element that includes a wide main portion 96 and narrow strip 98. Strip 98 extends downwardly to flexible link 3100 on which a contact member 102 is mounted. Cooperating with contact member 102 and in juxtaposition therewith is a second contact member 104.

Electric current flows through bimetallic element 40 when the transformer is energized and narrow leg 98 flexes under the greater heating to which it is subjected and moves the contact 102 into electric circuit completing relationship to contact 104 after a short time delay. The proportioning of the wide and narrow legs 96, 98 of the bimetallic provides thermal compensation for changes in ambient temperature. It will be seen with reference to FIG. 1 that the bimetallic element 40 is continually energized as there is 0.2 volt impressed across it whenever the transformer secondary 18 is energized. Thus this simple circuit component provides an initial delay (a typical value being in the range of 3-10 seconds) in the energization of the control circuitry but subsequent to that initial delay this component continuously maintains the control circuitry in energizable condition as long as power is applied to terminals and 12. Also, should the transformer be deenergized, switch -1 resets rapidly as it is physically mounted on the bimetallic element that is directly heated by electric flow and there is no thermal mass of an auxiliary heater to delay reset.

This delay in energization of the control circuitry provides a check on the proper operability of the flame detection circuitry. It will be seen that the flame detection circuitry is energized immediately upon energization of the transformer secondary and that the control circuit is not energized until

contacts

102, 104 close. Should the flame supervision circuitry not be properly operative, for example due to a defective (e.g. continuously avalanching) sensor tube 46, contacts 74-2 will open and thus prevent energization of control relay 80 in response to a request by control element 82.

Provided the flame detection circuitry is in proper operating condition, however, contacts 74-2 remain closed at this time as there is no flame in the supervised combustion chamber and on closing of

contacts

102, 104, the control relay 80 will be energized on call for heat by the thermostat 82 or other control element. Upon energization of relay coil 80 contacts 80-2 close and completes a holding circuit for relay 80 via line 32 connected to the twelve volt tap. It will be noted that this holding circuit is independent of the heater element 84 of the safety lock out device. The heater 84 remains energized however as it is connected across eight volts between

lines

32 and 34 through contacts 40-1, the now closed flame relay contacts 74-2 and the control relay contacts 80-2. This circuit maintains the lock out switch heater 84 energized until detection of flame causes pick up of relay 74.

Also, energization of the control relay coil 80 causes contacts 80-3 to close and energizes the ignition control unit 20, the blower control unit 22 and the pilot fuel valve control unit 24. This establishes an ignition condition in the combustion chamber and fuel is supplied to that chamber through the pilot valve. As soon as ignition occurs and flame is detected in the combustion chamber by sensor 46 a signal is produced by the flame sensing circuitry to energize relay coil 74. Contacts 74-1 and 74-4 close and contacts 74-2 and 74-3 open. The Openings of contacts 74-3 deenergizes the ignition control device while the closing of contacts 74-4 energizes the main fuel control unit 26 so that fuel from the main fuel line flows into the combustion chamber to establish the main flame which is continually supervised by the sensor 46. Independently of the establishment of the main flame but normally a short time (a typical total time delay being ten seconds) subsequent thereto the timing control 28 operates to open contacts 28-1 and deenergize the pilot fuel cont-r01 element 24. (Thiscircuit arrangement thus proves main flame by shutting off the pilot flame automatically and further prevents reignition of pilot flame after flame failure except after manual restart (reset of the lockout switch 84).) The apparatus is now in operative condition with the control relay and the flame detection relay 74 in energized condition and the thermostatic device 82 indicat: ing a continued operation of the burner.

As soon as the thermostatic device 82 no longer indicates the need for operation of the burner, its circuit wall open and deenergized the control relay 80. With that occurrence, contacts 80-3 will open and the main fuel control element 26 will be deenergized. With the termination of fuel flowing into the combustion chamber flame will cease and the flame relay 74 will be deenergized so that the entire controlled apparatus will be shut down but ready for another operating cycle upon the closing of the thermostatic device 82.

Should flame failure occur during an operating cycle however, such that relay 74 is deenergized, the fuel flow is immediately interrupted by the opening of con: tacts 74-4, and the safety lock out heater 84 is energized with the closing of contact 74-2 so that after a predetermined length of time that heater will cause the contacts 84-1 to open and deenergize the main control relay coil 80, shutting down the controlled apparatus and requiring manual reset of switch contacts 84-1 before the apparatus again. Also, should the flame relay 74, after completion of an operating cycle, failto open contacts 74-1 upon termination of flame in the cumbustion chamber, the safety lock out heater will be energized by a circuit completed from line 34 through the

safe start contacts

102, 104, contacts 74-1 that remain closed and contacts 80-1 which are now closed. Heater element 84 will be heated sufliciently to cause the contacts 84-1 to open (after a delay typically in the order of 6-9 seconds) and in open condition will prevent re-energization of the relay coil 80, resulting in safe shut down of the controlled apparatus.

The structure of the lock out switch unit 84 may be seen with reference to FIGS. 2-4. That switch unit controls contacts 84-1 which includes contact elements and 112. Each contact element is mounted on a flexible, electrically conductive leaf 114 that has a

terminal element

115, 117 respectively and each leaf has an upper end 116 against which an

actuator surface

118, 120 re spectively acts. The contact elements are mounted in fixed position on the body of the lock out unit. Projecting upwardly from that body is a post member 124 and above that member an actuator element in the found plunger 126 which carries actuator surface 120. Interposed between the post member and the actuator element is a sleeve element 128 which carries the projection 118 and is disposed for sliding movement. A first biasing spring 130 acts between the unit body 122 and the sleeve 128 to urge sleeve 128 upwardly while a second biasing spring 132 acts between plunger 128 and the post 124 to urge the plunger 126 to its upper (normal) position.

The contact actuator sleeve has secured to it at its lower end a latch member l40 which cooperates with an adjustable latch member 142 mounted on a bimetallic sheet heater element 84. The configuration of the bimetallic element 84 may be best seen with reference to FIG. 2. That bimetallic element has two terminals, 146, 148 and a serpentine conductive path from terminal 146 is provided through a first set 154 of three narrow sections connected in series through an intermediate bridge portion 150 that carries a depending leg 152 to a second set .154

of three narrow sections connected in series and then to terminal 146. The depending leg 152 carries the adjustable latch member 142. A non-conductive bridging element 156 is disposed at the upper end of each set 150, 154 to assure the flexing of the sheet as a unit at those points.

In operation, the lock out switch is set into the posi tion shown in FIG. 1 by depressing the actuator 126. This compresses springs 130 and 132 moving both the

contact engaging surfaces

118, 120 downwardly and flexing the contact support structures outwardly away from the body 122 of the switch unit as the intermediate (sleeve) member 128 is moved downwardly to the latched position. Upon release of actuator 126, the actuator moves upwardly under the influence of spring 132 but the intermediate member 128 is held in latched condition in the position shown in FIG. 4 so that

contacts

110 and 112 are in circuit completing engagement. The lockout switch structure will remain in this position until the heater 84 has been subjected to sufficient electrical current flow to cause the latch member 142 to move outwardly and release the latch element 140. When that occurs spring 130 moves sleeve 126 upward and the switch components return to the position shown in FIG. 3 and remain in that position until the lock out switch is reset by manually depressing actuator 126. It will be seen that this lock out switch structure provides a compact, reliable and relatively inexpensive arrangement that includes thermal compensation provided by leg 152 for ambient temperature conditions.

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.

What is claimed is:

1. Burner control apparatus for use with a fuel burner installation having an electrically energizable main fuel control valve, an electrically energizable pilot fuel control valve, and ignition means operative when energized to ignite fuel at the burner, comprising a control relay having a plurality of normally open switches which are closed upon energization of the apparatus in response to a request for initiation of flame in the fuel burner,

flame sensing means adapted to sense the presence of flame in the fuel burner and having a normally closed switch which is opened upon the sensing of flame and a normally open switch which is closed upon the sensing of flame,

checking means having a normally closed check switch and a time delayed actuator effective after a time period of energization thereof to open said check switch,

first circuit means including one of said control relay switches and said normally closed flame sensing means switch and adapted to energize the ignition means,

second circuit means including one of said control relay switches and said check switch and adapted to energize said pilot fuel valve,

third circuit means including one of said control relay switches and said normally open flame sensing means switch and adapted to energize said main fuel control valve, fourth circuit means including one of said control relay switches and said checking means actuator and adapted to energize said checking means actuator,

said third circuit means maintaining said main fuel control valve in energized condition only in response to the continuing sensing of flame in the fuel burner,

and said checking means actuator opening said check switch and deenergizing said pilot fuel control valve after a time period of energization of said checking means actuator independently of the sensing of flame in the fuel burner and holding said check switch open and said pilot fuel control valve deenergized until said control relay is deenergized,

a fifth circuit including the coil of said control relay,

a sixth circuit including said flame sensing means,

Cir

means connecting said fifth and sixth circuits to a common electrical energy source, and means to delay energization of said fifth circuit including a circuit element arranged for movement in response to flo-w of electric current through it connected to said common electrical energy source and a circuit completing element connected in said fifth circuit and physically mounted on said circuit element for movement therewith, said circuit completing element delaying energization of said fifth circuit until said flame sensing means has been energized.

2. The apparatus as claimed in claim 1 wherein said flame sensing means includes a second normally closed switch which is opened upon the sensing of flame, said flame sensing means switch being connected in said fifth circuit so that said second flame sensing means switch prevents the energization of said control relay should said second flame sensing means switch be opened before said circuit element closes said fifth circuit.

3. The apparatus as claimed in claim 2 wherein said circuit element is a bimetallic element having one portion of said circuit completing element physically mounted on it.

4. The apparatus claimed in claim 3 and further including means to apply a fraction of a volt continuously across said circuit element.

5. The apparatus as claimed in claim 4 and further including a safety lockout switch having a pair of electric circuit completing elements forming a normally closed switch and a bimetallic time delay actuator member effective after a period of energization to open said lockout switch, a manual operator for placing said elements in a first electrical circuit control condition, means urging said elements towards a second circuit control condition, and latch means mounted on said bimetallic member for securing said circuit elements in said first condition, said latch means releasing said contact elements from said first condition upon movement of said bimetallic member.

6. A combustion control system comprising a main control relay for controlling the operation of a burner,

a flame detector circuit including a flame relay,

a circuit responsive to demand for burner operation for energizing said main control relay including a normally closed contact controlled by said flame relay,

and a voltage source for energizing said main control relay energizing circuit and said flame detector circuit,

characterized by the provision of means to delay the energization of said main control relay energizing circuit including a bimetallic circuit element connected to respond to electric current flow for energizing said flame detector circuit,

a tap connected to said voltage source for continuously applying a fraction of a volt across said bimetallic element,

and a circuit completing element physically coupled to said bimetallic circuit element for delaying the completion of said main control relay energizing circuit until after said flame detector circuit has been energized.

References Cited UNITED STATES PATENTS 2,440,700 5/ 1948 Rosche 15-8-28 2,662,591 12/1953 Hanson 158-28 2,727,568 12/1955 Smith 158-28 2,751,972 6/1956 Loeber 15828 2,989,117 6/1961 Graves 15828 JAMES W. WESTHAVER, Primary Examiner.