US2193516A - Burner control system - Google Patents

Description

March 12, 1940@ G, F. LAING BURNER CONTROL SYSTEM Filed Jan. 22, 1938 n. @ma 7 le uz! INVENTOR @@rdon Laing BY wfx ATTORNEY Patented Mar. i2, i194@ NETE@ STATES Zgltit cargar @trice IBTUHBINER CONTROL SYSTEM Wam@ Application `llanuary 22, 1938, Serial No. 186,367

13 Claims. (Cl. 158-28) This invention relates to a burner control system and more particularly to an improvement in the combustion responsive apparatus thereof.

In burner control systems, particularly in oil burner control systems, it is customary to employ a safety switch Which-if its operation is not interrupted opens the oil burner circuit a predetermined period lof time after the circuit has been closed. A combustion responsive apparatus is provided to prevent the operation of this safety switch from taking place in this manner if combustion occurs within the predetermined period of time. It is also quite usual to employ an electrical ignition means in conjunction with the burner, which ignition means is usually deenergized upon combustion taking place. Inasmuch Vas the mixture of fuel and air issued from the burner is highly explosive, it is necessary that only a very short period of time be allowed for combustion to take place. The combustion responsive apparatus in certain well .known oil burner control systems also operates, upon a failure of combustion, to stop the operation of the oil burner for a predetermined period of time and to thereafter turn on the oil burner again along with the ignition. Again the time interval within which these operations must take place is relatively small.

The usual Vcombustion responsive apparatus which has been employed to perform the control functions outlined above is a slip friction switch which is usually responsive to the stack temperature. A switch of this type is, by reason of.V the slip friction connection between the temperature' responsive element and `the actuated switch; responsive/ to a change of temperature. This results in a much quicker response than if the switches were set to operate at predetermined temperatures. Such stack switches in order to perform the functions previously outlined have had to be provided with contacts which overlapped in one direction and not in the other.

Such a construction is obviously somewhat com plicatd and is liable to get out of adjustment.

'I'he presence, moreover, of the slip friction connection ls a constant source of trouble inasmuch as it is necessary that this connection olers enough resistance to permit operation of the switches but not so much as to cause too great a stress on the temperature responsive element. It is obvious, of course, that with wear the friction offered by the connection is apt to change.

An object of the present construction is to provide a burner control system in which the switching action necessary for the control of the safety switch'and the ignition means is accomplished by a polarized relay whose energization is controlled by a thermo-couple placed in a region subject to the temperature of combustion.

A further object is to provide such a system in which a desired sequence of operation is provided by a new and novel arrangement of switches.

Other objects of the present invention will be apparent upon a consideration of the accompanying specification, claims, and drawing of which Figure 1 is a detailed view of the improved burner control system;

Figure 2 is a'view of the improved combustion responsive switch with a portion in sectionalong the line 2-2 of Figure 3, and

Figure 3 is an elevational end View of the switch.

Referring to the drawing, an oil burning furnace is generally designated by the reference numeral I0. This furnace is shown as being. of the hot water type having pipes II and I2 leading to and from radiators or other similar devices (not shown). Extending from the furnace I 0 is the usual stack pipe I3 .which is shown in the drawing for the purpose of better showing the combustion responsive apparatus as broken away over a portion thereof.

Associated with the furnace I0 is an oil burner l5, the nozzle I6 of which projects -into the furnace. A motor drives the fan controlling the flow of fuel to the nozzle.' Only the terminal plate of the motor is shown, being designated by the reference numeral I1. Associated with the oilburner is an ignition means designated by the 'reference numeral.l9. This ignition means may be of any conventional construction, usually consisting of a step-up transformer and electrodes positioned adjacent the oil burner nozzle.

A room-thermostat is designated by the reference numeral 22. This thermostat is `employed to control the operation of the burner in accordance with the temperature in a room or other space being heated. This thermostat comprises a bimetallic element 23 to which is'secured a contact arm 24 adapted to be engaged with a fixed contact 25 upon a suiiicient temperature drop. A magnet 26 is associated with the contact arm 24 and serves to impart a snap action to the movement of contact arm 24. This snap action both serves to prevent arcing between the contact arm 24 and the contact 25 and also serves to impart a differential to the operation of the thermostat to prevent excessive energization and deenergization of the oil burner motor resulting from a chattering of the thermostat as it approaches its contacts.

A thermal safety switch 30 is employed to interrupt the burner circuit after a predetermined period of time if combustion has not taken place. This switch may be of any suitable type, one preferable form being that shown in the Denison Patent No. 1,958,081, issued May 8, 1934. The switch is shown for purposes of illustration in the drawing as comprising a pair of switch arms 3| and 32, the latter of which is pivotally mounted. The switch arm 32 is prevented from moving away from switch arm 3| by means of a bimetallic element 33 which in its cold position extends under the arm of switch blade 32. Associated with the bimetallic element 33 is an electrical heating element 34. This heating element serves to heat the bimetallic element, warping the upper end thereof to the right. If this heating action occurs sufficiently long, the element 33 will be warped as to move from under the end of switch blade 32 allowing this blade to fall away from blade 3|. This switch thus functions as a cut-out mechanism.

A relay is generally designated by the reference numeral 35. This relay comprises a relay coil 36 with which are associated relay switch blades 31 and 38. Switch blades 31 and 38 are adapted to be moved by relay coil 36 into engagement with contacts 39 and 40. These blades are normally biased out of engagement with their respective contacts by any suitable means (not shown).

The improved combustion responsive switch of the present invention is generally indicated by the reference numeral 42. An end view of this Switch is included in Figure 1 in addition to the elevational view in order to more clearly show the electrical connections to the switch. The details of this switch are best shown in Figures 2 and 3 and reference should be made to these figures in connection with the further description of this switch. The switch consists generally of a polarized relay, the coil of which is designated by the reference numeral 44 and which is energized by a therrnopile 45. The thermopile 45 consists of elements 46, 41, 48, and 49, which elements form pairs of elements having the proper dissimilar thermo-electric characteristics, Thus elements 46 and 48 may consist of iron and elements 41 and 49 of Constantan. Constantan is an alloy consisting of approximately 50 percent nickel and 50 percent copper. The junctions between elements 46 and 41 and elements 48 and 49 are relatively small .so as to have very little thermal capacity. The junctions between elements 41 and 48, however, and the junctions between elements 46 and 49 and conductors 50 and 5| are relatively large so as `to have a considerable heat capacity. 'The first named junctions are indicated by reference numerals 53 and 54 and the last named by the reference numerals 55, 56, and 51. All of these junctions are located within the stack. The conductors 56`and 5I serve to connect the series connected thermocouples to the coil 44 of the relay. While two thermo-couples have been employed in the thermopile, it is to be understood that any number of thermo-couples may be used. In some cases, it is possible to accomplish the results with a .single thermo-couple.

The coil 44 of the relay is located on a bobbin 65 'of suitable insulating material, which bobbin is secured to U-shaped pole pieces 66 and 61. These pole pieces 66 and 61 are secured to the opposite legs of a U-shaped permanent magnet 68 by means of screws 69 and 10. Themagnet 68 is, in turn, supported upon an insulating base 1| by means of a plurality of bracket members 12. As best indicated in Figure 3, the relay is provided with three armatures 14, 15, and 16. These armatures 14, 15, and 16 constitute contact arms and are movable between contacts 18 and 19, and 8l, and 82 and 83, respectively. Only the armature 16 and its associated contacts 82 and 33 are shown in Figure 2. The arrangement of the contact structures will be described only in connection with this armature. Referring to Figure 2, terminal posts and 86 are secured to the pole pieces 66 and 61, respectively. In each case, these terminal posts are secured to the pole pieces by a screw 81 which extends through an insulating bushing 88. Insulating washers 89 and 90 are interposed between the headof screw 81 and the pole piece and the terminal post and the pole piece. The terminal posts 85 and 86 are slotted adjacent their outer ends and threaded into the slotted portions are screws 92 and 93. The contacts 82 and 83 are carried by the inner ends of these screws. Referring again to Figure 3, the various armatures 14, 15, and 16 are pivotally supported at their mid portion by a pivot pin 9|. Collars 94 and insulating washers 95 surround the pin 9| to keep the armature in properly spaced and insulated relationship.

It will be noted from Figure 2 that the armatures will normally be in either one extreme position or the other due to the fact that when in such an extreme position they are adjacent ends of the pole pieces 66 and 61 which are of. opposite polarity. Since there is considerable magnetic attraction holding the armature in its extreme position and the armature is only moved when sufcient force is built up to overcome this attraction, this force will be sufficient to move the armature over center with a snap action whereupon the armature will continue to move by reason `of the attracted force exerted by the oppo-` site ends of the two pole pieces.

The relay, as previously noted, is a polarized relay requiring a reversal of current through the winding 44. This reversal of current takes place by reason of the difference in size of the junctions 53 and 54 and junctions 55, 56, and 51 on the other. When the temperature Within the stack is rising, as occurs upon the initial of combustion, the junctions 53 and 54 will heat up more rapidly than junctions 55, 56, and 51. The result is that junctions 53 and 54 become the hot junctions and the other junctions the cold ones. Electromotive force is thus generated in one direction, which electromotive force causes a current to flow through winding 44 in one direction. The apparatus is of such design that the current flowing through coil 44 under these conditions causes the armatures 14,115, and 16 to rotate in a counter-clockwise direction as viewed from Figure 2. Upon a termination of combustion, the temperature drops and the heat ac-v quired in the meantime by junctions 55, 56, and 51 will be dissipated less rapidly than that of junctions 53 and 54. The result is that junctions 55, 56, and 51 under these conditions become the hot junctions of the thermo-couple causing a current flow in the reverse direction. When the current flows in this direction, the armatures 14, 15, and 16 are rotated in a clockwise-direction to assume the position shown in Figure 3.

It will be apparent from a reference to Figure 3 that the spacing of the various contacts is not uniform. In the illustrative embodiment shown in the drawing, contacts 80 and 8| are least widely spaced from each other and contacts 78 and 79 most widely spaced from each other. The spacing of contacts 82 and 83 is intermediate to that ofthe other two sets of contacts. Inasmuch as the spacing of the contacts limits the moving of 'the armature and hence limits the amount the armature travels past the point at which it is spaced equally from all four ends of the pole pieces, the spacing of these contacts determines the current required to move the armature from one contact to another. As will be obvious, the less Widely the contacts are spaced the less current will be required to eiect a movement of the armature from one contact to another. Thus-upon a rise in the current through coil 63 in either direction, armature 75 will be the first to move, armature 76 lthe next to move, and armature 78 the last to move.

Operation The various elements of the system are shown in the drawing in the position which they assume when the temperature in the room or other space being controlled is at or above the desired value. Let it be assumed now that the temperature begins to drop. This drop in temperature will eventually cause engagement of contact arm 2d of thermostat 22 with contact 25 whereupon the following circuit will be established to.

relay coil 36: from line wire 97, which constitutes one of two line Wires 97 and 98 leading to a suitable source of power (not shown), through conductor 99, bimetallic .element 23, contact arm 29, contact 25, conductor |00, switch blades 3| and 32, conductor armature 73. contact 78, conductor |02, heating element 38, conductors |03 and |05, relay coil 36, and conductor |06 to the other line wire 98. Energization of relay coil 36 results in contact arms 37 and 38 being moved into engagement with contacts 39 and 410.

The moving of switch blade 38 into engagement with contact 60 results in the following circuit being established: from line wire 97 through conductor |08, contact 40, switch blade 38, conductors |09 and H0, oil burner motor I7, and conductors and |05 to the other line Wire 98. At the same time, the following circuit is established to the ignition means I9: from line wire 97 through conductor |98, contact 30, switch blade 38, conductors |09 and |.|2, armature 76, contact 82, conductor ||3, ignition means i9, and conductors lll, and |06 to the other line wire 98.

The establishment of the previously traced circuits to the ignition means and to the oil burner motor results in the establishment of the conditions necessary for combustion. At the same time, the heating element 38 of the thermal safety switch is being heated by reason of the fact that the energizing circuit for relay 36 includes this heating element. Under normal conditions, combustion will take place within a very short period of time. When combustion takes place, the temperature of the stack |3 will rise rapidly causingjunctions 53 and 54 to heat up relatively rapidly. As previously explained, junctions 55, 56, and 57 are not cap-able of heating as rapidly as junctions 53 and 53. The result is that a current flow takes place through coil lli in one direction, which current flow, as previously explained, causes armatures 75, 70 and 'Hl to move out of engagement with their left-hand contacts and into engagement With their righthand contacts, in the order named. The moving of armature 'l5 into engagement with contact 8| from junctions 53 and 54.

results in the following holding circuit being established to relay coil 38: from line wire 97 through conductor 99, bimetallic element 23, contact bladeI 26, contact 25, conductor |00, switch blades 3| and 32, conductor |0|, armature 75, contact 8|, conductor l0, switch blade 37, contact 39, conductor |05, relay coil 36, and conductor |06 to the other line wire'98. It will be noted that the new holding circuit for relay coil 36 is independent of the heating element 34 and constitutes a shunt therearound. Thus as soon as armature 75 engages contact 8|, the heating of element 36 is eiectively terminated, so that there is an assurance that the oil burner will continue in operation. Shortly after armature 75 engages contact 8|, armature 76 is moved out of engagement with contact 82 and into engagement with contact member 83. The moving of armature 76 out of engagement with contact 82 interrupts the ignition circuit previously traced. This results in the deenergization of the ignition means, the energization of which is no longer" accomplished without even a momentary deenergization of relay coil 36.

Under normal conditions, the burner will continue in operation until such time as the thermo- `stat is satisfied, at which time contact arm 23 separatesfrom contact 25 to deenergize relay 35 and terminate the operation of the system. The resulting coolingof the stack temperature will cause the armatures 715, 75, and 76 to move back into engagement with contacts 76,- 00,

and 82.

The operation which has `just been described is that which occurs when combustion takes .placein a normal manner. If combustion does not take place within the time required for heating of the thermal safety switch 34 to the point where bimetallic element"33?-moves' out from under the blade 32, the 'separationA of switch blades 32 and 3| will take place. The entire system will then be deenergized and cannot be restarted until the safety switch 30 has been reclosed manually.

If combustion does take place but for some reason 'or other it is interrupted while the thermostat is stiil calling for heat, the stack will rapidly cool rdown. The cooling down of the stack causes the junctions 55, 59, and 57 to become the hot junctions sincey the heat accumulated therein is less rapidly dissipated than that Thus, a current will be generated in relay coil 44 in the opposite direction which, in turn, will cause armatures 75, 76, and 74 to move successively out of engagement with their right-,hand contacts and into again engage contactl.

continues to drop the electromotive force generated by the thermo-couple will increase with the result that after an interval of time armature 16 will be moved into engagement with contact 82. When such movement takes place, the ignition willbe reestablished. Suflicient time, however, elapses between the moving of armature 'I5 out of engagement with contact 8l and the moving of armature 'i6 into engagement with contact 82 for the ifuel accumulated within the furnace to pass up the stack I3. If it were not for this elapse of time, there would be danger of the reestablishment of the ignition causing the fuel mixture to be ignited with explosive violence. Shortly after armature 16 reengages contact 82, armature 'i4 reengages contact 18, reestablishing the originally traced energizing circuit to relay coil 36 through the heating element 34, and thus reenergizing the oil burner motor i 1. The conditions necessary for combustion are now established. If the condition causing the termination of combustion is merely a temporary one so that combustion may be reestablished, the operation which takes place will be the same as that previously described. If, however, combustion cannot be established the thermal safety switch 30 will be opened in the usual mannen It will be noted that the holding circuit to the relay coil through armature 'l5 and Contact 8l is dependent upon the closure of relay switch blade 3l with' contact 39. This insures that after the thermostat has been satisfied, causing the deenergization of the relay 35, the burner can not be started up again immediately while armature-'l5 still engages contact 8l. The result is that sufficient time must elapse for the potential of the thermo-couple to build up in the opposite direction suiciently to cause armature 14 to This both insures that a check will be made as to whether combustion takes place and that time will be allowed for any accumulated gases to pass up the stack.

It will be noted that with the improved system of the present invention, the desired functions are accomplished in a much more positive manner and with much simpler apparatus than in the prior art arrangements.. While I have shown an illustrative embodiment of my invention for purposes of illustration, it is to be understood that the invention is limited only by the p scope of the appended claims.

In my copending application Serial Number 186,368, filed of even date herewith and entitled Thermo-couple switch, the novel features of the switching mechanism broadly are claimed.

I claim as my invention:

1. In a burner control system, an electrically operated fluid fuel regulator, a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said fluid fuel regulator to cause a flow of fuel, ignition means for igniting thefuel, a cut-out mechanism automatically` operable upon the elapse of a timed period afterthe closure of said energizing circuit to interrupt said circuit, a

polarized relay comprising a plurality of switches each movable between two extreme positions including a contact making position, said switches being so designed that different amounts of current are required for actuation of said switches so that upon an increase in the current through said relay, said switches are actuated in a definite sequence, a thermo-couple connected to said .relay having one junction capable of quickly absorbing and giving up heat and another junction capable of only slowly absorbing and giving up heat, both of said junctions being located so as to be responsive to the temperature of combustion, and means including said relay switches operable upon combustion taking place to render said cut-out mechanism and said ignition means inoperative without deenergization of said fluid fuel regulator, said means further being operative vupon failure of combustion during closure of said control switch to first deenergize said regulator and subsequently to reenergize said regulator and said ignition means and to render said cut-out mechanism operative again.

2. In a burner control system, an electrically operated iiuid fuel regulator, a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said fluid fuel regulator to cause flow of fuel, ignition means for igniting the fuel, a cut-out mechanism automatically operable upon the elapse of a timed period after the closure of said energizing circuit to interrupt said circuit, a polarized relay comprising rst, second, and third switches each movable between two extremelv positions including a contact making position, said switches being so designed that different amounts of current are required for actuation of said switches and so that upon an increase in the current through said relay in a first direction, said second switch is iirst moved to its contact making position and said first and third switches are then moved from their contact making positions, and so that upon an increase in current Y through said relay in a second direction, said second switch is first moved from its contact making position and said first and third switches are then moved to their contact making positions, a thermo-couple having a first junction capable of quickly absorbing and giving up heat and a second junction capable of only slowlyabsorbing and giving up heat, both of said junctions being located so as to be responsive to the temperature. of combustion, connections between said thermo-couple and said relay operative upon the iirst junction being hotter than the second as a result of a rising temperature to cause current flow through said relay in said first direction and vice versa, circuit connections controlled by said control switch and first switch for normally causing the energization of said cut-out meansA when both switches are closed, further circuit connections controlled by said control switch and said second switch for causing the deenergization of said cut-out means when both of said switches are closed, and further circuit means controlled by said control'switch andl said third switch for causing the energization of said ignition means when both switches are closed.

3. In a burner control system, an electrically operated iiuid fuelregulator, a main control switch, first and second combustion switches` each movable with a snap action between a contact making position and a second position, said switches requiring different amounts of force to move them between their two positions, means responsive to the temperature of combustion operable upon a temperature rise to successively move said first combustion switch to its contact making position Iand said second switch away from its contact making position, a safety switch comprising an electrically operated means which upon continued energizatio-n thereof opens said switch, means controlled by said first combustion switch operative upon closure of said rst combustion switch and saidl main control switch to establish a circuit to said oil burner dependent upon the closure of said safety switch and to energize said electrically operated means of the safety switch, and means controlled by said second combustion switch and operative upon closure of said second combustion `switch and said main control switch to establish a circuit to said oil burner and to cause deenergization of said electrically operated means of said safety switch.

4. In a burner control system, an electrically operated uid fuel regulator, a main control switch, means operable upon closure' of said control switch to establish an energizing circuit to said fluid fuel regulator to cause a flow-of fuel, a cut-out mechanism automatically operable upon the elapse of a timed period after the closure of said energizing circuit to interrupt said circuit, combustion responsive apparatus comprising a pair of snap action switches requiring different amounts of force for actuation and means responsive to a change in the temperature of the combustion zone and operative upon a change to successively actuate said switches in a direction depending upon the direction of change, and means including said combustion responsive apparatus operative upon the establishment of combustion to render said cut-out mechanism inoperative without interruption in the operation .of said regulator and operative upon the failure of combustion while said control switch is closed to cause said regulator first to be deenergized for a brief time interval and thereafter to cause reenergization of said regulator and to render said cut-out mechanism operative again.

5. In a burner control system, an electrically.

operated fluid fuel regulator,` a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said fluid fuel regulator to cause a flow of fuel, a cut-out mechanism automatically operable upon the elapse of a timed period after the closure of said energizing circuit to interrupt said circuit, electrically operated ignition means, combustion responsive apparatus comprising a plurality of snap action switches requiring different amounts of force for actuation and means responsive to a change in the temperature of the combustion zone and operative upon a change to successively actuate said switches in a direction depending upon the direction of change, and means including said combustion responsive apparatus operative upon the establishment of combustion to render said ignition means and said cut-out mechanism inoperative without interruption of said regulator and operative upon the failure of combustion while said control switch is closed to cause said regulator rst to be deenergized for a lbrief time interval and thereafter to cause reenergization of said regulator and said ignition means and to. render said cut-out mechanism operative again.

6. In a burner control system, an electrically operated uid fuel regulator, a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said fluid fuel regulator to cause a flow of fuel, a cut-out mechanism automatically operable upon the elapse of a timed period after the closure of said energizing circuit to interrupt said circuit, combustion responsive apparatus comprising a pair of snap action switches requiring different amounts of force for actuation, electromagnetic operating means therefor, and means for variably energizing said operating means, the magnitude and direction of energization being dependent upon the extent and direction of the change in temperature in the combustion zone, and means including said combustion responsiveapparatus operative upon the establishment of combustion to render said cutout mechanism inoperative Without interruption in the operation of saidregulator and operative upon the failure of combustion While said control switch is closed to cause said regulator first to be deenergized for a brief time interval and thereafter to cause reenergization of said regulator and to render said cut-out mechanism operative again.

7. In a burner control system, an electrically operated fluid fuel regulator, a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said uid fuel regulator-to cause a now of fuel, a cut-o-ut mechanism automatically operable upon the elapse of a timed period after the closure of said energizing circuit to interrupt said circuit, electrically operated ignition means, combustion responsive apparatus comprising a plurality of snap action switches requiring different amounts of force for actuation, electromagnetic operating means therefor, and means for varia'bly energizing said operating means, the magnitude and direction of energization being dependent upon the extent and direction of change in temperature in the combustion zone, and means including said combustion responsive apiparatus operative upon the establishment of combustion to render said ignition means and said cut-out mechanism inoperative Without interruption of said Iregulator and operative upon the failure of combustion while said co-ntrol switch is closed to cause said regulator rst to be deenergized for a brief time interval and thereafter to cause reenergization of said regulator and ignition means and to render said cut-out mechanism operative again.

8. In a fluid fuel burner control system, a main control switch, a. burner motor, means to start the motor in response to closure' of said main switch and to stop the same in response to opening thereof, and combustion responsive means including a polarized relay having a plurality of sequentially operating snap action switches and a thermo-couple connected to said relay and having one junction capable of more quickly absorbing and giving up heat than another junction, both junctions being responsive to the temperature of combustion, said combustion responsive means being operative by reason of the sequential operation of said switches to interpose a delay between successive motor energizations when said control switch is closed. v

9. In a fluid fuel burner control system, a main control switch, a burner motor, ignition means, means to start the motor and ignition means in response to closure of said main switch and to stop the samein response to opening thereof, and

combustion responsive means including a polarinterpose a delay between successive motor energizations and to terminate operation of the ignition means upon the establishment of combustion while said control switch is closed.

10. In a uid fuel burner control system; a main control switch; a burner motor; ignition means; means to start the motor and ignition means in response to closure of said main switch and to stop the same in response to opening thereof; and combustion responsive means including relay coil means, a plurality of snap aci tion switches sequentially operated in accordance with the direction and extent of energization of the coil means, and means responsive to the direction of change in the tempeprature of the combustion zone for varably energizing said relay coil means; said combustion responsive means being operative to interpose a delay between successive motor energizations and to terminate operation of the ignition means upon the establishment of combustion while said control switch is closed.

11. In a fluid fuel burner control system, a main control switch; a burner motor; ignition means; means to start the motor and ignition means in response to closure of said said main switch and to stop the same in response to opening thereof; and combustion responsive means including relay coil means, a plurality of snap action switches sequentially operated in accordance with the direction and extent of energiza` tion of the coil means, and thermo-couple means connected to said coil means and comprising two junctions located so as to be responsive to the temperature of combustion, one of said junctions being capable of more quickly absorbing and giving up heat than the other junction; said cornbustion responsive means being operative to interpose a delay between successive motor energzations and to terminate operation of the ignition means upon the establishment of combustion while said control switch is closed.

12. In a burner control system, an electrically operatedl uid fuel regulator, a main control switch, means operable upon closure of said control switch to establish an energizing circuit to said fluid fuel regulator to cause a flow of fuel,

electrically operated ignition means, a cut-out mechanism automatically operable upon the elapse of atimed period after the closure of said energizing circuit to interrupt said circuit, a relay comprising coil means and a plurality of switches each movable between two extreme positions including a contact making position, said switches being so designed that different degrees of energization of said coil means are required for actuation of said switches so that upon a change in the current through said coil means said switches are actuated in a definite sequence, thermo-couple means connected to said coil means and comprising two junctions located so as to be responsive to the temperature of combustion, one

of said junctions being capable of more quickly absorbing and giving up heat than the other, and means including said relay switches operable upon combustion taking place to render said cutout mechanism and said ignition means inoperative without deenergization of said uid fuel regulator, said means further being operative upon failure of combustion during closure of said control switch to rst deenergize said regulator and subsequently to reenergize said regulator and said ignition means and to render said cut-out mechanism operative again.

13. In a fluid fuel burner control system; a main control switch; a burner motor; means to start the motor in response to closure of saidmain switch and to stop the same in response to opening thereof; and combustion responsive means including relay coil means, a plurality of snap action switches sequentially operated in accordance with the direction and extent of en'ergization of the coil means, and means responsive to the direction of change in the temperature of the combustion zone for variably energizing said relay means; .said combustion responsive means being operative to interpose a delay between successive motor energizations.

GORDON F. LAING.

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