US2385426A - Burner control system - Google Patents

Description

Sept. 25, 1945. D, G. TAYLOR ET AL 2,385,426 BURNER CONTROL SYSTEM Filed Aug. 20, 1942 Z r M11 8 MR Wigwam A H L m .m W 0 Patented Sept. 25, 1945 UNITED STATES PATENT OFFICE BURNER CONTROL SYSTEM Daniel G. Taylor, Minneapolis, min

aldgnors ea Honeywell Regulator Company, Minneapolis,

., a corporation of Delaware Application August 20, 1942, Serial No. 455,421;

Gille, St. Paul, Minn Claims.

This invention is directed broadly to an automatlc control system for fluid fuel burners and is more particularly directed to a system which does not rely upon a thermal element responsive to combustion conditions for timing the trial ignition period and time required for the system to recycle, but provides a separate timing means for accomplishing these functions.

It is old in prior art systems to utilize a timing means such as a thermal timer for timing recycle and trial ignition periods but these systems in the past have been very complicated and cumbersome and usually require more than one relay to accomplish the necessary timing functions and to provide the required features of safety. One of the main objects of the present invention is to provide a relatively simple system of the above type which requires only one relay, one thermal timer, and the usual safety switch.

A further object of the invention is to provide a system of the above type which may be used in combination with a very sensitive and rapidly operating combustion responsive device for indicating whether combustion is present or absent at the burner, and in which the hot and cold switches of the combustion responsive device need not overlap in their operation in either direction.

A further object of the invention is to provide a control system of the above type in which a single relay cioses a maintaining circuit for itself which is independent of "the combustion responsive device while the combustion responsive device opens a cold switch and closes a hot switch, and in which a thermal timer responsive to the closure of the hot switch opens the maintaining circuit so that in running condition the relay will be held in through the hot combustion responsive switch. This invention further contemplates that the thermal timer may be utilized for terminating ignition a predetermined time after the hot switch has been closed and may also operate a switch in the initial energizing-- circuit for the relay so that the relay may not be energized until a predetermined time has elapsed from the previous burner operation and deenergization of the heater for the thermal timers An additional feature of the invention is that the safety switch heater, is maintained in operation during the time that the maintaining circuit for the relay is closed so that the safety switch is operative to shut the system down and lock it out, in the event that the cold combustion switch remains closed due to a failure of the fuel to properly ignite.

A further object of the invention is to accomplish the above results by means of a latch operated by the thermal timer so that the relay when energized will clos the switch to the maintaining circuit and the thermal timer when heated will rotate the latch and permit an arm to open the maintaining switch and also open the ignition switch.

It is further contemplated that where this system is powered from the low voltage secondary winding of a step-down transformer, the maintaining circuit which keeps the relay energized while the combustion responsive device is opening the cold switch and closing the hot switch, will be connected to a tap in the seondary winding so that the safety switch heater will remain energized as long as the cold combustion switch is closed for locking the system out in the event that combustion is not established.

These and other objects will readily become apparent as the following specification is read in the light of the accompanying drawing, in which:

Figure 1 is a schematic diagram of a control system for a fuel burner which incorporates the various features of our invention,

Figure 2 is a side elevation of the relay, thermal timer and latching mechanism, with a side cover removed to show substantially all of the elements in elevation, and

Figure 3 is a detail view of a modified form of our invention.

Referring first to Figure 2 of the drawing, the reference numeral In indicates an insulating casing in which the side cover has been removed. Within the casing I0 is a bimetallic blade ll having a relatively fixed end I! which is pivotally/mounted to a fixed portion of the casing by means of a disc element I; of a slip friction connection, element l3 being shown in elevation. The disc element I3 is rotatably mounted about a pin I 4 shown in section. The element I3 is urged by a coil spring shown in section/at II into engagement with a friction element (not shown) interposed between disc ll face in the rear of disc l3. of the bimetallic blade II is a' and a stationary sur- On the free end Ii movable contact I! upper or I in Figure 2. This spring is also invisible in I so that upon rotation of the screw the stationary contact l8 may be adjusted vertically with respect to the movable contact I].

An electric heating element 23 is carried in the casing adjacent the bimetallic blade II by means of the two brackets 24. The heater is insulated by means of the two mica sheets shown at 25. A bracket, a portion of which is shown at 21,,pivotally carries a latch member 28 which in turn carries a resilient latch blade 29, the free end being adjustable with respect to the latch member 28 by means of the adjusting screw 38. An extension 3| on the latch member 28 adjustably carries a screw 32, the head of which is adapted to be engaged by the free end 18 of the bimetallic blade I for rotating the latch 28 about its pivot 33 on the bracket 21.

A resilient contact blade 35 is suitably fixed at one end to the bracket 38 and at its free end carries a contact 31. The blade 35 carries an insulating arm 38 and forms the hinged support for this arm biasing it for movement in a downwardly direction.

The reference numeral 48 indicates the pivoted armature of an electromagnetic relay of the type shown in Patent 2,241,838, which issued May 13, 1941, to J. M. Wilson. The coil and core of this relay cannot be seen in Figure 2 because they are located directly behind the casing ii. The

armature 48 is provided with a biasing spring (not shown) which biases the armature to its unattracted position, in which it is shown this figure because it is located behind the easing Hi. The armature 48 is provided with an extension 4| which extends beneath the arm 88 and raises this arm to the position shown in Figure 2 when the armature 40 is in its unattracted position. The armature 48 carries a second projection 42 which has a conducting segment 43 which electrically bridges the contact 87 and a second contact located directly behind it. Withthe armature in the position shown in Figure 2, the electrical circuit is broken between these two contacts but when the relay is energized the conducting segment 43 electrically connects the contacts. A coil spring 45 is located between the projection 4| on the armature 48 and the latch member 28 and biases the latch member for rotation in a clockwise direction to its operative position. A contact bracket 41 is fixedly mounted in the casing i0 and carries an adjustable contact screw 48. The casing It also supports a resilient contact blade 49 having a movable contact 50. The contact blade 49 extends upwardly beyond the contact 50 and cooperates with an extension 0n the arm 38. It will be noted that with the parts in the position shown in Figure 2 there is a slight space between the extension 5| and the resilient contact blade 49. The purpose for this will appear later.

When the armature 40 moves to its attracted position the extension 4| thereof will permit the arm 38 to move downwardly as a result of the bias placed thereon by the resilient blade 35. This will cause the latching surface 53 to engage the free end of the resilient-latching blade 29 which prevents further movement of the arm 38 at this time. This movement of the arm 38 causes the extension 5| to take up the space between the extension and the resilient blade 49 but the contact 58 will remain in engagement with the stationary contact 48 as long as the arm 38 is latched upon the free end of the latching member 29. If the electric heating element 23 is energized at this time it Will heat the bimetallic blade H and cause the free end l8 to warp in an upwardly direction and therefore start to rotate the latching member 28 in a counterclockwise direction. After a predetermined period of time the latching member 28 will have rotated far enough to move the latching blade 28 from beneath the-latching surface 53 and thus permit the arm 38 to drop down further until it again engages the extension 4| on the armature 4a. This movement of the arm 38 will cause the extension 5| to move contact 5|) out of engagement with the contact 48 and will-also move the contact 31 out of engagement with the bridging member 43 on the armature 48. The bimetallic blade I! will continue to rotatethe latching member 28 until it engages the fixed stop 54, which will prevent further rotation thereof. If the temperature of the bimetallic blade H is still increasing at this time it will continue to warp and such additional warping movement will be accommodated by means of l3 which will permit an upward movement of the end l2 of the bimetallic blade i L It will be noted also that as the free end ii of bimetallic blade warps in an upwardly direction that the contacts I1 and I8 are separated. Upon deenergization of the relay, the armature 48 will return to its unattracted position as shown in Figure 2 at which time the extension 4| thereon will raise the arm 38 and return it to the position shown in which it will again permit the resilient contact blade 48 to move the contact 58 back into engagement with the stationary contact 48. If the electric heating element 23 is deenergized at this time, the bimetallic blade i! will commence to warp in the opposite direction which will cause a lowering of the free end it and will eventually cause the contact I] to reengage the stationary contact I8. As the end ll of the bimetallic blade moves downwardly, it

' permits the biasing spring to return the latch member 28 to the position shown in Figure 2 in which it will again latch the arm 38 when the armature 48 moves to its attracted position. Downward movement of the free end l6 of the bimetallic blade M will be limited by the engagement of the two contacts H and I8 and if the blade continues to cool after this engagement takes place it will continue to warp due to the slip friction connection including disc element l3. By providing this slip friction connection, the timing function of the latch 28 is facilitated due to the fact that it is not necessary to wait until the bimetallic blade heats up to its final temperature or cools to its final temperature before it performs its desired function. It will be under stood of course, that the time required for the bimetallic blade II to cause the latch 28 to release the arm 38 may be adjusted by means of the two adjustable screws 38 and 32. Also, the time required for the bimetallic blade H to reclose the contacts l1 and I8 following a deenergization of the electric heater 23 may be adjusted by rotating the screw 2| and eccentric 28 which vertically positions the contact I8 with respect,

the slip friction connection als in Figure 1 as they have in Figure 2. It will be understood that the armature 40 of the relay is adapted to actuate other switches than the one formed by th contact 31 and bridging member 49. These additional switches have been indicated schematically by the pivoted relay arms 55, 58, and 51 which engage the stationary contacts 59, 59 and 60, respectively, when the armature is in its attracted position and are in open circuit position when the armature 40 is in its unattracted position. The above switches are located in a low voltage circuit whereas the relay arm ii is adapted to engage stationary contact 62 in the high voltage circuit when the armature 40 is in its attracted position and the arm 6| is moved to open circuit position when the armature 40 is in its unattracted position. The relay coil for attracting the armature 40 has been indicated by the reference numeral 63 and dotted lines indicate the armature l diagrammatically.

This system is provided with the usual safety switch which includes a pair of contact blades 65 I be heated .by the electric heater 69 and when so heated will warp to the left and release the contact blade 99 for movement to open circuit position. The safety switch will then be locked in open position and will have to be reset by means of the manual reset button 69, which is of the trip free reset type, that is, it maintains the switch in open circuit position during the resetting operation so that the switch cannot be closed unless the bimetallic blade 91 has cooled to a point where it will relatch the switch upon release of the button 99.

This control system may obviously be placed under the control of many different types of condition responsive devices, but for the purposes of illustration it has been shown as being under the control of a thermostat which takes the form of a bimetallic blade II which is fixed at one end and which carries at its free end a pair of contact blades 12 and 13 which cooperate respectively with the two stationary contacts H and I9. These contacts are so arranged that on a decrease in temperature at the thermostat 'II it will contract and first cause the resilient contact blade 13 to engage the stationary contact I5 and then at a slightly lower temperature cause the contact blade 12 to engage the stationary contact 14,

This system is further provided with a combustion responsive device 11 which is shown as comprising a movable switch arm 19 which cooperates respectively with a cold contact 19 and a hot contact 80. This device is preferably not callbrated but is so arranged that the cold contact is closed in the absence of combustion and the hot contact is closed in the presence of combustion.

The reference numeral 83 indicates an electric motor or an electrically operated valve for controlling the fiow of fuel to a burner. Although it will be readily appreciated that various types of fuel may be controlled with this system, for the purposes of illustration, it may be assumed that the reference numeral 83 indicates the usual oil burner motor and 84 the usual spark ignition for igniting the. oil delivered to the burner. A step-down transformer is shown at 85 which comprises a primary winding 85 and a secondary winding 81. The primary winding 96 is connected to the supply lines 88 and 89 by means of the two conductors 90 and SI.

Operation The various elements are shown in Figure 1 in the position which they will occupy when the thermostat II is satisfied and has therefore moved the two contact blades 12 and II to their open circuit position. In such case the relay winding 63 will be deenergized and therefore the armature 40 will be in its unattracted position and the switch arms 55, 58, i1, and BI will be in open circuit position. The bimetallic timing blade II is cold and has closed the contacts I! and II. There is no combustion present at the burner due to the fact that the burner motor 93 and i8- nition device 04 are deenergized by the relay II which is in open circuit position. The combustion responsive device H has therefore moved the switch arm 18 into engagement with the cold contact I9.

Under such conditions the temperature at the thermostat II will begin to decrease and cause this thermostat to move the resilient contact blade 19 into engagement with its stationary contact 15. 'No circuit will be established at this time due to the fact that the switch blade 12 and the switch arm 51 are both in open circuit position. The temperature at the thermostat II will therefore continue to decrease until the switch blade 12 is moved into engagement with the stationary contact 14. This establishes an energizing circuit for the relay winding 83 which extends from one side of the secondary winding 81 through conductor 93, relay winding 53, conductor 94, safety switch blades 95 and 89, conductor 95, contact l5, switch blades 13 and I2, contact 14, conductors 96 and 91, bimetallic blade II, contacts I1 and I8, conductor 98, safety switch heater 98, conductor 99, cold contact 19, switch arm II, and conductor I00 back to the other side of the secondary winding 81. Energization of the relay winding 93 results in the movement of the armature 40 to its attracted position and the movement of the switch arms 55, 56, 51, and GI into engagement with their stationary contacts 58, 59, i0 and 62. At the same time the armature '40 causes the movement of the bridging element 43 into engagement with the contact 31 as the armature rotates about its pivot 39.

The attraction of the armature 40 sets up a holding circuit for the relay winding 63 which is independent of the switch blade I2 and contact 14. This circuit extends from one side of the secondary winding 81 through conductor 93, relay winding 53, conductor 94, safety switch blades 65 and 66, conductor 95, contact 15, switch blade 13, bimetallic element II, conductor IOI,

'contact 60, relay arm 51, conductor I02, relay arm 56, contact 59, conductors I03 and 91, bimetallic blade II, contacts I I and I8, conductor 98, safety switch heater 68, conductor 99, cold contact 19, switch arm 18, and conductor I00 back to the other side of the secondary winding 81.

At the same time a parallel circuit for the relay winding 93 is set up. This circuit extends from one side of the secondary winding 81 through conductor 93,, relay winding 63, conductor 94, safety switch blades 65 and 66, conductor 95, contact I5, switch blade 73, bimetallic element TI, conductor IOI, contact 60, relay arm 51, conductor s' I02 and I05, relay arm 55, contact 59.

conductors I06 and I01, switch blades 41 and 49,

and conductor I08 to a tap I09 in the second- I '11 leaves the cold contact and later establishes contact with the hot contact 80. The safety switch heater 68 remains energized all this time,

however, so that if combustion should not be established and the switch arm 13 should remain in engagement with'the cold contact 19, the blade 61 ofthe safety switch will be heated and will release the safety switch for movement to open position. This will, of course, shut the system down and lock it out until it is manually reset by the manual resetbutton 69.

It will be realized of course that the relay winding 63 upon being energized also causes the relay arm BI to engage the stationary contact 62. This establishes a circuit for the burner motor 83 which extends from one line wire 88 through conductor H0, burner'motor, 33, conductors III and H2, stationary contact 62, relay arm 6|, and conductor H3 to the other line wire 89. The ignition device 84 is simultaneously energized through a circuit extending from the line wire 88 through conductor I ll, ignition device 84, conductor H5, switch blade 35, contact 31, bridging member 43, conductors H6 and H2, contact 62, relay arm GI, and conductor II3 back to the line wire 89.

Normally the energization of the burner motor and ignition device will cause the establishment of combustion at the burner and the combustion responsive device 11 will cause the switch arm 18 to leave the cold contact 19 and engage the hot contact 00. It has been pointed out. above that the relay winding 63 will remain energized during this operation. Engagement of the switch arm 10 with the hot contact 80 will establish a holding circuit for the relay winding 63 which extends from one side of the secondary winding 01 through conductor 33, relay winding '63, conductor 34, safety switch blades 65 and 66, conductor 96, contact I5, switch blade 13, bimetallic element II, conductor IOI, contact 60, relay arm 61, conductors I02 and I05, relay arm 55, stationary contact 68, conductors I06 and H1, electric heating element 23, conductor us, hot contact 80, switch arm I3 and conductor I00 back to the other side of the secondary winding 81. It will be noted that this circuit extends through the electric heating element 23 for the bimetallic timer II. An additional circuit for this heating element extends from the tap I09 0! the secondary winding 11, through conductor I08, contact blades 49 and 41, conductors I01 and Ill, electric heating element 23, conductor II8, hot contact 80, switch arm 10, and conductor I00 back to the other side of the secondary winding 81.

This resultsin the heating of the bimetallic element II which causes it to warp in a direction to rotate the latch 28 in counter-clockwise direction and after a predetermined period of time this latch will release the arm 38 which will move contact 31 to open circuit position and also move contact blade 49 to open circuit position. The movement of the contact 31 to open circuit position will deenergize the circuit to the ignition device 84 and therefore terminate ignition. The moving of the contact blade 49 to open circuit position will interrupt the maintaining circuit for the relaywinding 63 with the result that this relay winding is now energized by a circuit which extends through the safety switch 85, 66, bimetal- 110 thermostat switch 13, I5 and the hot combustion responsive switch 80, 18.. This is the running condition of the circuit.

If a flame failure should occur, the combustion responsive switch arm '|8 will disengage the hot contact 80 thereby deenergizing the relay coil -63 and returning the armature 40 to its unattracted position; The circuit through the relay winding 63 cannot be reestablished for starting the system in operation until the bimetallic element II has cooled sumciently to cause engagement of the contacts I1 and I8. The same will be true if the relay winding 63 were deenergized by the thermostat II becoming satisfied. Thus the time required for the bimetallic element II to cool determines the time necessary for the system to recycle and the timerequired for this element to heat determines the time the ignition device shall be energized following the initial establishment of combustion. The trial ignition period is determined as usual by the timing of the safety switch 65, 66.

Figure 3 discloses a modified form of our invention in which an electromagnet is utilized for releasing the arm 88 to open circuit position. Specifically the latching surface 53 cooperates with the latch I30 when the armature 40 is in its attracted position. Latch I30 is pivoted at I3I and is biased to its latchingposition by the biasing spring 832. At such time the contact II carried by the latch I30 is in engagement with its stationary contact I8.

The latch I30 is made of magnetic material and an electromagnet I34 is located adjacent thereto. When combustion has been established, as explained in connection with the operation of Figure 1, the winding I35 for the electromagnet is energized and the electromagnet attracts the latch I30, which pivots to the left, separating the contacts I! and I8 and releasing the arm 38 for movement to open circuit position as in Figure l.

I It will be noted that the winding I35 is connected between the conductors Ill and H8 in place of the electric heater 23 of Figure 1.

The system utilizing the modification of Figure 3 would function the same as Figure 1 except that the ignition would terminate as soon as combustion was established and there would be no timer for timing the scavenger period. In other words the starting contacts I], I6 would be closed as soon as armature 40 dropped out and the recycle would be timed entirely by the cold combustion switch.

Many changes and modifications iii this invention will doubtless occur to those who are skilled in the art and we therefore wish to point out that we intend to be limited only by the scope of the appended claims and not by the specific embodiment of the invention which has been disclosed herein merely for the purpos of illustration.

We claim as our invention:

1. Fluid fuel burner control apparatus comprising in combination, means includingan electromagnetic relay adapted to control the flow of fuel to a burner, hot and cold switches, a combustion responsive device adapted to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion, a main switch, a circuit for energizing said electromagnetic relay including said main switch and cold switch, a maintaining switch closed by said relay, a further switch, a circuit for maintaining energization of said relay while said combustion responsive device opens said cold switch and 2,385,426 closes said hot switch, said maintaining circuit including said main switch, further switch, and maintaining switch, a thermal timer, a heatertherefor, a holding circuit for said relay including in series said relay, main switch, thermal timer heater and hot switch, and means operated by said thermal timer for opening said further switch a substantial time after the closure of said holding circuit.

2. Fluid fuel burner control apparatus comprising in combination, an electrical device adapted to control the flow of fuel to a burner, hot and cold switches, a combustion responsive device adapted to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion, a main switch, a source of power including a transformer winding, an energizing circuit for said electrical device connected across said transformer winding, said circuit including said main switch and cold switch, a maintaining switch closed as a result of the closure of said energizing circuit, a circuit for maintaining energlzation of said electrical device while said combustion responsive device opens said cold switch and closes said hot switch, said maintaining circuit extending from one side of said transformer winding to an intermediate portion thereof and includin said main switch and said maintaining switch, a holdng circuit for said electrical device connected across said transformer winding and including said main switch and hot switch, and means for opening said maintaining circuit after the closure of said holding circuit.

- 3. Fluid fuel burner control apparatus comprising in combination, an electrical device adapted to control the flow of fuel to a burner, hot and cold switches, a combustion responsive device adapted to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion, a safety switch in control of said electrical device, a thermal actuator for said safety switch, a heater for saidthermal actuator, a main switch, a source of power including a transformer winding, an enarglzing circuit connected across said transformer winding, said circuit including said main switch, heater for said thermal actuator and cold switch, a. maintaining switch closed as a result of the closure of said energizing circuit, a further switch, a circuit for maintaining the margintion of said electrical device while said combus- ;ion responsive device opens said cold switch and :loses' said hot switch, said maintaining circuit Jeing connected from one side of said transformer winding to an intermediate portion there- )i' and including said further switch, main switch ll'ld maintaining switch, a holding circuit for said :lectrical device, said holding circuit includng :aicl main switch and hot switch, and means for ipenlng said further switch followin the closure If said hot switch.

4. In a system for controlling a fluid fuel )urner and ignition means therefor; an electrical ievice adapted to control the delivery of fuel to t burner, said device comprisin an electromagietic relay having a movably mounted armature iased to its -unattracted position and adapted vhen moved to its attracted position to cause en- .-rgization of said burner, a rotatably mounted atch biased to its operative position, an arm iiased for movement into engagement with said atch but held out of engagement therewith by aid armature in its unattracted position, a first witch closed by said armature as it is pulled in by said relay upon energization thereof, said armature also providing for movement of said arm into engagement with said latch, a thermal element, an electric heater for heating said thermal element, means operated by said thermal element upon heating thereof for rotating said latch in a direction to release said arm to its tripped position, thereby opening said first switch and means operated by said armature upon deenergization of said relay for movin said arm out of engagement with said latch to permit said latch to return to its operative position under the influence of its bias; circuit connections adapted to be connected to a main-switch and a starting switch and to be effective When so connected to establish an energizing circuit for said relay including said main switch and starting switch; circuit connections adapted to be connected to an ignition means and when so connected to form an energizing circuit for said ignition means including said first switch; and circuit means adapted to be connected to a device responsive to combustion and to said main switch and effective to establish a holding circuit for said relay independent of said starting switch and includin said main switch'and electric heater.

5. In a system for controlling a fluid fuel burner; in combination, a fluid fuel burner; an ignition means therefor; an electrical device for controlling the delivery of fuel to said burner. said device comprising an electromagnetic relay having a movably-mounted armature biased to its unattracted position and effective when moved to its attracted position to cause energization of said burner, a rotatably mounted latch biased to its operative position, an arm biased for movement into engagement with said latch but held out of engagement therewith by said armature in its unattracted position, a first switch closed by said armature as it is pulled in by said relay upon energization thereof, said armature also providing for movement of said arm into engagement with. said latch, a thermal element, an electric heater for heating said thermal element, means operated by said thermal element upon heating thereof for rotating said latch in a direction to release said arm to its tripped position, thereby opening said first switch, means operated by said armature upon deenergization of said relay for moving said arm out of engagement with said latch to permit said latch to return to its operative position under the influence of its bias, and a second switch opened by said arm as it moves to its tripped position and closed by said arm as said armature returns to its unattracted position; a main switch; a combustion responsive device including hot and cold switches and operative to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion; an energizin circuit for said relay including said main switch and cold switch; an energizing circuit for said ignition means including said first switch; a. maintaining circuit for said relay independent of both said hot and cold switches and including said main switch and said second switch; and a holding circuit for said relay including said main switch, said hot switch, and said electric heater.

6. In a system for controlling a fluid fuel burner, in combination,

a. fluid fuel burner; an

ignition means therefor; an electrical device for controlling the delivery of fuel to said burner, said device comprising an electro-magnetic relay having a movably mounted armature biased to its unattracted position and effective when moved to its attracted position to cause energization of said burner, a rotatably mounted latch biasedto tis operative position, an arm biased for movement into engagement with said latch but held out of engagement therewith by said armature in its unattracted position, a first switch closed by said armature as it is pulled in by said relay upon -energization thereof, said armature also providing for movement of said arm into engagement withsaid latch, a bimetallic blade, a fixed support, slip friction means for mounting said blade at one end to said fixed support, an-electric heater for heating said bimetallic blade, means operated by the other end of said blade upon heating .for rotating said latch in a direction to release said arm to its tripped position, thereby opening said first switch, means limiting the movement of said other end of said blade in each direction, said slip friction means accommodating further warping of said blade, and means operated by said armature upon deenergization of said relay for moving said arm out of engagement with said latch to permit said latch to return to its operative position under the influence of its bias, and a second switch opened by said arm as it moves to tripped pos tion and closed by said arm as said armature returns to its unattracted position; a main switch: a combustion responsive device including hot and cold switches and operative to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion; an energizing circuit for said relay including said main switch and cold switch; an energizing circuit for said ignition means including said first switch; a maintaining circuit for said relay independent of both said hot and cold switches and including said main switch and said second switch; and a holding circuit for said relay including said main switch, said hot switch, and said electric heater.

7. In a system for controlling a fluid fuel burner, in combination, a fiuid fuel burner; an ignition means therefor; an electrical device for controlling the delivery of fuel to said burner, said device comprising an electro-magnetic relay having a movably mounted armature biased to its unattracted position and effective when moved to its attracted position to cause energization of said burner, a rotatably mounted latch biased to its operative position, an arm biased for movement into engagementwith said latch but held out of engagement therewith by said armature in its unattracted position, a first switch closed by said armature as it is pulled in by said relay upon energization thereof, said armature also providing for movement of said arm into engagement with said latch, a thermal element, an electric heater for heating said thermal element, means operated by said thermalelement upon heating thereof for rotating said latch in a direction to release said arm to its tripped position, thereby opening said first switch, means operated by said armature upon deenergization of said relay for moving said arm out of engagement with said latch to permit said latch to return to its operative position under the influence of its bias, and switch means closed by said thermal element when it is in its cold position and opened when it is in all other positions; means under the control of said last named switch means for effecting energization of said relay; means including a device responsive to combustion for establishing a holding circuit to said relay independent of said last named switch means and including said electric heater; and means including said first switch for establishing a circuit to said ignition means.

8. In a system for controlling a fiuid iuel burner, in combination, a fiuid fuel burner; an ignition means therefor; an electrical device for controlling the delivery of fuel to said burner, said device comprising an electromagnetic relay having a movably mounted armature biased to its unattracted position and effective when moved to its attracted position to cause energization of said burner, a rotatably mounted latch biased to its operative position, an arm biased for movement into engagement with said latch but held out of engagement therewith-by said armature in its unattracted position, a first switch closed by said armature as it is pulled in by said relay upon energization thereof, said armature also providing for movement of said arm into engagement with said latch, a bimetallic blade, a fixed support, slip friction means for mounting said blade at one end to said fixed support, an electric heater for heating said bimetallic blade, means operatedby the other end of said blade upon heating for rotating said latch in a direction to release said arm to its tripped position thereby opening said first switch, means limitin the movement of said other end of said blade in each direction, said slip friction means accommodating further warping of said blade, means operated by said armature upon deenergization of said relay for moving said arm out of engagement with said latch to permit said latch to return to its operative position under the influence of its bias, 9.

cold contact engaged by said other end of said blade when it is in its cold position, and means adjusting the position of said cold contact for varying the time required for said blade to engage said contact following the deenergization of the heater for said blade; mean under the control of said cold contact for effecting energization of said relay; means including a device responsive to combustion for establishing a holding circuit to said relay independent of said cold contact and including said electric heater; and means including said first switch for establishing a circuit to said ignition means.

9.'Fluid fuel burner control apparatus comprising in combination, an electrical device adapted to control the flow of fuel to a burner, an electrical ignition device, hot and cold switches, a combustion responsive device adapted to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion, a main switch, a source of power including a transformer winding, an energizing circuit for said electrical device connected across said transformer winding, said circuit including said main switch and cold switch, a maintaining switchclosed as a result of the closure of said energizing circuit, a circuit for maintaining energization of said electrical device while said combustion responsive device opens said cold switch and closes said hot switch, said maintaining circuit extending from one side of said transformer winding to an intermediate portion thereof and including said main switch and said maintaining switch, a holding circuit for said electrical device connected across said transformer winding and including said main switch and hot switch, a circuit to said ignition device controlled by said electrical device, and means for opening said ignition circuit and said maintaining circuit a predeterminedtime after the closure of said holding circuit.

10. Fluid fuel burner control apparatus comprising in combination, an electrical device adapted to control the flow of fuel to a burner, an elec irical ignition device, hot and cold switches, a combustion responsive device adapted to close said cold switch in the absence of combustion and to close said hot switch in the presence of combustion, a main switch, time switch means, a thermal actuator therefor including an electrical heater and operable when the electric heater is energized to cause said time switch means to as some an open circuit position a predetermined period of time after energization of said heater, a source of power including a transformer winding, an energizing circuit for said electrical device connected across said transformer winding, said circuit including said main switch and cold switch, a maintaining switch closed as a result of the closure of said energizing circuit, a circuit for maintaining energization of said electrical device while said combustion responsive device opens said cold switch and closes said hot switch, said maintaining circuit extending from one side of said transformer winding to an intermediate portion thereof and including said main switch, time switch means and maintaining switch, a holding circuit for said electrical device connected across said transformer winding and including said main switch, hot switch, and electrical heater, and a circuit for said ignition device controlled by said eelctrical device and by said time switch means, said time switch means being operable a predetermined period of time after energization of said holding circuit to interrupt said maintaining circuit and the circuit to said ignition device. I

DANIEL G. TAYLOR. WILLIS H. GILLE.

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