US2287248A

US2287248A - Burner control system

Info

Publication number: US2287248A
Application number: US327060A
Authority: US
Inventors: Gifford I Holmes
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1940-03-30
Filing date: 1940-03-30
Publication date: 1942-06-23
Anticipated expiration: 1959-06-23

Description

June 23, 1942. L HOLMES 2,287,248

BURNER CONTROL SYSTEM -Fi1d March so, 1940 \00 A32 Ion EB M Fig 2 I finnenfor Gifforl I. Holmes GWHM Patented June 23, 1942 stares BURNER CONTROL SYSTEM 7 p v Gifford ll. Holmes, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, 'a corporation of Delaware Application March 30, 1940, Serial No. 327,060.

12 Claims.

The present invention relates to burner con-- trollers and more particularly to circuits including safety switches for an oil burner.

In systems of the class to which the instant control circuits apply, wherein a timer is adapted to trip a safety switch, dangerous conditions oft times occur when the timer fails. Timers which must be positively moved as a result of the application of heat by a heaterprove extremely hazardou for practical use because the heaters may burn out. Many systems have been proposed which operate upon the principle of heat dissipation to move a timer. element is normally heated and, upon a call for heat by the spacethermostat, the heaterwlll be deenergized to allow said element to cool to thereby start the burner.

In such systems the That is, the moving device i protected against burning out of the heater. However, if a power failure should occur, due to a burned out fuse, or a failure at the 1 source of power, the device will go out on safety.

Inasmuch as such power failures are quite frequent, it is desirable to use asafety switch which will not be placed out of operation because of such failure.

An object of this invention is to provide a simplified and eflicient burner controller which obtains a maximum of safety.

Another object of the present invention is to provide a simplified burner control system which obviates the above recited difiiculties. v A further object is to provide an improved safety switch which times the trial ignition period for an oil burner.

Another object is to provide a combustion responsive device in combination with a timer which will render a burner motor inoperative if the combustion responsive device fails to respond properly to the presence or absence ofv combus-v tion. A further object is to provide a timer'which times the trial ignition period by utilizing a heat dissipating actuating element.

, Another object is to provide a combustion controller which times the'trial ignition period by the cooling of a control element which is heated when the burner is not in operation, cooled when the, burner is placed into operation, heated if combustion is properly established, or cooled to break the burner motor circuit if combustion is not properly established.

Still another object, in connection with the last preceding object, is to provide such a controller whichwill break the burner motor circuit if a heater for the timer burns out, butwill not 3 break the burner motor circuit in the event that i tion.

Referring more in detail to the drawing a motor H1 is shown which is adapted to operate an oil burner, a gas valve, or the like. An ignition means H is adapted to ignite'the fuel which is delivered by the motor when in operation. Electrical energy is supplied from line wires I2 and I3 to the motor and to the ignition means.

The circuit to the motor I0 and theignition means II is controlled by a thermostat l5. This thermostat is suitable for location in a space in which the temperature is to be controlled. The thermostat 55 comprises a bimetal l6 which is suitably secured to some suitable mounting means (not shown) by pin IT. The bimetal I6 has an arm l8 to which a snap acting switch, such as a mercury switch I9 is secured. The mercury switch is rendered snap acting by a'suitable indentation in the center of the bottom thereof and has contacts 20 and 2| which are bridged bythemercury 23 when the bimetallic element I6 is cooled. Another pairof electrodes. 24 and metallic element It is hot.

A safety switch mechanism 30 is provided to break the circuit to the motor I0 and to' the ignition means I! in the event that an abnormal condition occurs, for example, failure of combustion or failure of the burner to start upon a callfor heat by the thermostat IS. The safety switch 30 comprises a relatively stiff contact blade 3| and a relatively flexible contact blade 32 which is normally biased away from the blade 3| so that contact 33 and 3 mounted on the blade will be held apart if blade 32 is released. A suitable heat motor is provided to maintain the

contacts

33 and 34 in engagement for normal operation of the heating system. In the present instance this heat motor comprises a bimetal 35 which engages an insulating block 32a carried upon the contact blade 32. The bimetal 35 is mounted upon a. compensating bimetal 36 by a bracket 31. The lower end of the bimetal 36is bimetal 36 and the merit which extends into or a device which is arranged so that a. tempera cold contact thermostat I is in suitably secured to a mounting bracket 39 which may be suitably secured to a switch case (not shown). The bimetals= 35 and 36 are so arranged that they will warp in opposite directions upon the application of heat to both of the bi-- metals. By so arranging the bimetals any deflection of the upper part of the bimetal 35 due to changes in ambient temperature will be compensated for by the bimetal 36.

The bimetal 36 has a heater 40 located adjacent thereto whichv is connected across the line wires i2 and i3 by electrical conductors 4| and 42. The bimetal 36 is selected so as to flex toward the right as shown in Figure 1 upon the application of heat thereto by the heater 40. In the'event of a failure in the source of electric power which supplies energy l2 and I3, the bimetallic element 36 will warp toward the left. The bimetal 35 is provided with a heater 45 which is arranged adjacent thereto and is adapted to supply heat to the bimetal 35 under control of the thermostat l5 and a combustion responsive device generally indicated at 46. The

bimetal heaters

40 and 45, is adapted to act as an ignition timing means.

The combustion responsive device 45 may be a conventional device which has a bimetallic elethe stack of a furnace,

ature responsive element will respond directly to the radiant heat of a flame present in the furnace upon the occurrence of combustion. For illustration purposes the combustion device 46 which is shown comprises a

switch arm

41, 48, and a hot contact 49. The cold contact 48 will be engaged by the contact arm 41 when there is no rlame present in the combustion chamber and the contact 49 will be engaged by the contact arm 41 when combustion is present in the combustion chamber.

An ignition controller is carried by the bimetal 35. This controller comprises a press back contact blade 53 which is adapted to engage a contact 5| when the bimetal 35 is heated up to a predetermined value. A hook 52' is adapted to engage the upper to open the contact 5| when the bimetal 35 cools off. A resistance member 53 is placed in circuit by'the combustion responsive device 46 to control the circuit to the heater 45to cause the bimetal 35 to cool off a suflicient amount to open the contact 5| in a manner more fully described.

Operation in the position shown the the satisfied, or hot, position and, the

electrodes

24 and 25 are bridged by the mercury 23. A circuit is then established for the heater 45 for the bimetal.35 as follows: From the line wire |2 to the conductor 55, switch blade 3|, contact 33, contact 34, switch blade 32, conductor 56, electrode 24, mercury 23, electrode 25, conductor 51, contact 48, contact arm 41, conductor 58, heater 45, and conductor 59 to the other line wire l3. 'Energization of t e heater will maintain the bimetal 35 in the position shown beneath the insulating piece 32a on the contact blade 32 and the contacts 50 and 5| closed.

Assuming now that the thermostat l5 cools oil to rotate the mercury switch l9 toward the right and cause the mercury 23 to pass rapidly across With the device the indentation m the bottom of the switch, toysto the line wires 35, in cooperation with the open the

contacts

24 and 25 and close the contacts 20 and 2|. A circuit for the burner motor may then be traced as follows: From the line wire |2 through conductor 55, switch blade 3|,

contacts

33 and 34, switch blade 32, conductor 56, electrodes 20 and 2| through the mercury 23, conductor 60, conductor 6|, the burner motor l0, and conductor 62 to the other line wire l3. Also a circuit for the ignition means maybe traced from the conductor 60 through the conductor as, contact 5|, contact blade 50, conductor 64, ignition means II, and the conductor 65 to the other line wire l3.

When the circuit for the burner motor and ignition is established the circuit for the heater 45 through the

hot contacts

24 and 25 on the thermostat I5 will be broken. Hence, the heater 45 will not supply heat tothe bimetal 35 to maintain the bimetalin engagement with the insulating piece'32a carried by the contact arm 32. However, if the switch arm 41 of the combustion responsive device 46 moves into engagement with the hot contact 49 in response to the establishment of the combustion, before the bimetal 35 has cooled sufiiciently to trip the

contacts

33 and 34 to open position, then a circuit for the heater 45 may be traced as follows:

- From the line wire |2 through conductor 55',

switch arm 3|,

contacts

33 and 34, switch arm 32, conductor 56, electrode 2|, mercury 23, electrode 20, resistance 53, conductor 66, contact 49, contactarm 41, conductor 58, heater and conductor 59 to the other line wire l3. If switch arm 41 should stick to cold contact 48 the above circuit will not be closed and bimetal 35 will open the

switch

33, 34. It will be noted that the resistance 53 is now in series with the heater 45. This will result in the emanation of less heat from the heater 45 and hence the bimetal 35 will cool off an amount determined by resistance 53.

It is desired that this cooling will not move the bimetal 35 out of engagement with the insulating block 32a but will be just suificient to separate the contact 5| from the contact blade to end of the contact blade 56 to be hereinafter break the ignition circuit which was energized in the ignition circuit previously pointed out. 'iIehis is the normal running condition of the sys- In the event that there is a flame failure or that combustion does not take place upona call for heat by the thermostat IS, the contact blade 41 will not engage the contact 49 and there will be no circuit to the heater-45 forthebimetal 35. When this condition occurs the bimetal 35 will cool off and the upper end thereof will warp toward the right until it moves from beneath the insulating piece 32a. thus permitting the

contacts

33 and 34 to separate and shut down the system.

After the system has been shutdown due to some undesirable condition the safety switch 30 must be manually reset. Any of several conventional reclosing means could be utilized and therefore none have been shown in the drawing.

In the event that the heater 45 should burn out it will be apparent that the bimetal 35 would move from beneath the insulating piece 32a-to permit the safety switch toopen. In the event the heater 40 for the compensating bimetal 36 should burn out the bimetal 35 would be moved in the opposite direction from beneath the insulating piece 320. by the warping of the bimetal 36 to permit opening of the safety switch. Hence it is seen that protection is given for the burning out of either of the heaters for the safety switch. After a normal burner operation the thermostat I will become satisfied and move into the positionshown in Figure 1 to set up the original heating circuit for-the bimetal 35 through the cold contact 48 of the combustion. responsive switch. If the contact 41 should stick to the hot contact 49 and not engage the contact 48 the heater 45 will not be energized and the bimetal 35 up until manual attention has been given to the system.

combustion. It is also fully anticipated that, by properly selecting the casing I 28 forthe helix I25, a differential temperature may be maintained between the two helixes whereby a small heater I35 would be suflicient to prevent opening of the safety switch even though the combustion responsive element were subjected to a wide variation of 0 temperature.

Referring now to Figure 2, burnermotor I00 and ignition means IOI are supplied with electrical energy fromline wires I02 and I03. A thermostat I05 carries a snap acting mercury switch I06 which has contacts I01 and I08 which are closed when the thermostat is in the cold position and contacts I09 and H0 which are closed by the mercury when the-thermostat is in the hot 'posi tion. A safety switch II5 has a contact arm II6 which is relatively rigid, a flexible contact arm II! which is biased so as to open the contacts I I8 and I I9 and an arm I which is moved by a combustion responsive device I2I and isadapted .to engage an insulating piece I IIa carried on the contact arm Hi to maintain the safety switch closed under normal operating conditions.

i The combustion responsive device I2I serves as a timing means and comprises a bimetallic helix I22 which is wound so as to-cause the contact arm I20 to rotate toward the left when the helix I22.

cools off and to rotate the arm I20 toward the right when the bimetallic helix I22 is heated. A

. rod I23 is secured to the left end of the helix I22 and to the arm I20. A second helix I25 is secured to the helix I22 at the point I26. The helix I25 is wound oppositely to the helix I22 so that l the two helixes will rotate in opposite directions when heated. The helix I25 is mounted at I21 to a casing I28. Therefore, because the two helixes rotate equally and oppositely, one end of the helix I25 being secured to the casing and the opposite end of the helix I22 being connected to the rod I23 the rod I23 will not be rotated due to changes in ambient temperatures which affect both of the helixes in'the same degree. A heater I30 normally supplies heat to the compensating helix I25 because it is connected across the line wires I02 and I03 by conductors I3I and I32. A heater I35 supplies heat to the helix I22 when the thermostat I05 is in the hot position as shown in the drawing. When the thermostat I05 is in the cold position no heat will be supplied to the helix I22 that by exposing the helix I22 to a lesser degree of flame, as for example through a window directed at the flame itself, rather than locating the bimetallic helix in the stack, will affect an economy in electricity supplied to the heater I35 in Operation of Figure 2 With the parts in the positionshown the thermostat I05 is satisfied and a circuit for the heater I 35 may be traced as follows: From the line wire I02 through conductor I50, switcharm H6, contacts H8 and H9, contact arm 1, conductor I5I, electrodes I09 and H0, conductor I52, heater I35 and conductor I53 to the other line wire I03. At this time heat will be supplied to the helix I22 so that the arm I20 will be maintained in engagement with the insulating piece II'Ia to prevent opening of the-contacts H8 and H9 of the safety switch I I5.

Assuming now that the thermostat I05 cools so as to cause the contacts I09 and. H0 to open and the contacts 'I 01 and I00 to close with a rapid action due to the fact that the mercury. within the switch must pass over an indentation in the bottom of the mercury switch. A circuit may now be traced for the motor and ignition means as follows: From line wire I 02, conductor I50, switch arm Il6, contacts H8 and II9, contact arm II'I, conductor I5I, electrodes I 08 and I0I, conductors I54, I55, motor I00, and conductor I56 to the other line wire I03. A circuit for the ignition may be traced from the conductor I54,

through conductor I5'I, ignition means IOI, and

conductor -I 58 to the line wire I03.

Because the electrodes I09 and H0 are unbridged when the thermostat I05 is in the cold position there will be no energy supplied to the heater I35. In the event that flame doesnot occur in the combustion chamber the helix I22 will cool off to cause the arm I20 to move out from beneath the insulating piece H111 and permit the contacts H8 and H9 of safety switch II5 to open. However, if flame occurs before this section takes place thentheheat of the fiam'e,

willaffect the helix I22 in a manner to cause the arm I20 to remain in engagement with the insulating piece IIIa to keep the contacts H8 and H0 closed. Hence, it is seen that means are provided whereby a safety switch is combined with a combustion responsive switch to effect control in response to the presence of combustion in a combustion chamber upon a call. for heat. 0

- In the event of flafiie failure when the thermostat I05 has the motorand ignition means in 0 .contacts I I8 and H9 to open there-by shutting. down the system. Any suitable means can be that the heat supplied to the helix I22 by the,

heater I35 in some installations may need to} be substantially thesame as the heat supplied by operation, the combustion responsive helix I22 will cool off to move the arm I20 out of engagement with the insulating piece I I'Ia to permit the used for manually-resetting the system once it has been opened and therefore no means have been shown. p

, If either one of the heaters I30 or I 35 should burn out of the contacts I I8 and I I9 will be permitted to open because the arm I20 can move from beneath the insulating-piece II'Ia in either direction.

In the event of power failure in either of the. systems shown in Figure 1 or Figure 2 there will be no drop out of the safety switches. When the power fails in the system shown in Figure 1 both system, in combination,

' means including a first exists.

of the

heaters

40 and 45 will be deenergized and, inasmuch as the bimetals 35 and 36 affected by the heaters warp in opposite directions they will in temperature affecting both bimetals.

While I have shown two preferred embodiments which my invention may take, it is obvious that many modifications will occur to those skilled in the art. Many modifications utilizing timing by cooling in, a combustion responsive control device while still preventing drop out on power failure will become apparent to those skilled in the art. Hence I do not wish to be limitedby those forms shown and described but by the spirit and scope of the appended claims and the status of the prior art.

I claim as my invention:

1. In a burner control system comprising an electrically operable fuel controller and a controlling circuit therefor including a normally closed safety switch, in combination, timing means including a first element movable in a first direction upon heating and in a second direction upon cooling to mechanically open said safety switch when cool and to hold said safety switch closed when hot, a continuously heated second compensating element operatively con! nected to said first element to compensate it for changes in ambient temperature, and means for causing heating of said first element when said controlling circuit is open but not when said circuit is closed, said first element being heated as a result of successful combustion.

2. In a timing device for a combustion control normally closed switch means in circuit with a fuel controller, timing element movable in a first and in a second direction said circuit when moved direction upon heating upon cooling to open beyond a predetermined range of movement, a

continuously heated second compensating element associated with said first element and movable in said second direction upon heating and in said first direction upon cooling, said second element being adapted to compensate said first element for ambient temperature variations under normal operating conditions of said combustion controller system, means for heating said first element under normal operating conditions of said combustion controller system to prevent opening of said switch means, and means associated with said timing means for causing said switch means to open when an abnormal condition 3. In a fuel burner control system, in combination, an electrically operable fuel controller, a

circuit therefor, circuit control means to open and close said circuit, a normally closed safety switch associated with said circuit in a manner to interrupt said circuit, timing means including an element movable in a first direction upon heating and in a second direction uponcooling, said element being associated with said safety switch in a manner to open said safety switch upon movement of said element beyond a predetermined range of movement, heating means to supply heat to said element, combustion responsive means movable between hot and cold opening of said safety switch under normal operating conditions of said system, an electrically operable fuel ignition circuit controlled by said element, and means for affecting the heat capacity of said heating means to effect control of said ignition circuit when said combustion responsive means moves between hot and cold posions.

4. In a. fuel burner control system, in combination, fuel burner means, an electrically operable fuel controller including ,a circuit therefor, a normally closed safety switch operable to interrupt said circuit, timing means including an element comprising means responsive to heat from the fuel burner and being movable in a first direction upon heating and in a second direction upon cooling, said element being operable to open said safety switch upon movement of said element beyond a. predetermined range of movement,

completing a circuit to said heating means andbreaking said circuit to said fuel controller.

5. In a fuel burner control system, in combination, an electrically operable fuel controller for fuel burner means and including a circuit therefor, a normally closed safety switchoperable to interrupt said circuit whenever the safety switch opens, timing means including an element comprising means responsive to heat from the fuel burner and being movable in a first direction upon heating and in a second direction u'pon cooling, said element being operable to open said safety switch upon movement of said element beyond a predetermined range of movement, heating means to supply heat to said element, condition responsive means movable between a plurality of positions, one of said positions completing a circuit to said fuel controller for initiating burner operation and breaking a circuit to said heating means to thereby render said element dependent for heat upon said fuel burner, andanother of said positions completing a circuit to said heating means and breaking said circuit to said fuelcontroller to terminate burner operation, compensating means associated with said element movable in said second direction upon heating and said first direction upon cooling to thereby compensate said element for variations in ambient temperature, and electricheating means associated with said compensating means to prevent opening of said safety switch upon power failure.

6. In a fuel burner control system, in combination, a normally closed safety switch, thermal timing meansoperable upon cooling to open said safety switch, said timing means being so located positions for controlling the supply of heat to is operating, control means to supply heat to said timing means and when said burner is not operating, and compensating means associated with said timing means -for preventing said safety switch from opening due to power failure.

8; In a burner control system comprising an electrically operable fuel controller and a controlling circuit therefor including a normally closed safety switch, in combination,-a thermal element associated with said safety switch, a heater for heating said thermal element to maintam said safety switch closed, said safety switch being opened when said thermal element is cooled, a combustion responsive device movable between hot and cold contact positions in response to combustion, and a thermostat movable between hot and cold contact-positions in re-' sponse to ambient temperature, the hot contact of said thermostat and the cold contact of said combustion responsive device'being adapted to cooperate to control said heater when said fuel controller is not in operation, the cold contact of said thermostat and the hot contactof said operatively connected at its first end with said safety switch to hold the same closed when hot and to open the same when cool, a second distortable bimetal fixed at its first end and secured at its second endto the second end ofsaid first bimetal and movable in directions opposite with ..respect thereto upon heating and cooling to combustion responsive device being adapted to when said fuel tain said safety switch closed, said safety switch being opened when said thermal element is cooled, a combustion responsive device movable between hot and cold contact positions in response to combustion, a thermostat movable between hot and cold contact positions" in response to ambient temperature, the hot contact of said thermostat and the cold contact of said combustion responsive device being adapted to cooper- .ated timing means including means for supplying ate to control said heater when said fuel contrailer is not in operation, the cold contact of said thermostat and the hot contact of said combustion responsive device being adapted to cooperate to control said heater when said 'fuel controller is in operation, ignition control means 1 associated with said thermal element, and resistance means associated in circuit with said heater and the hot contact of said combustion responsive meansfor controlling said ignition control mean by causing said thermal element to move only a predetermined amount when the resist-* ance means is placed in circuit. a

10. Ina burner control system comprising an electrically operable fuel controller and a controlling circuit therefor including a normallyclosed safety switch, a normally heated first distortable bimetal movable in a first direction upon heating and in a second direction upon cooling thereby compensate the same for fluctuations in ambient temperature, an electric heater adjacent said second bimetal for continuously heating the same, an ambient temperature responsive thermostat, means for heating said first bimetal, and switch means operable by said thermostat for controlling the supply of heat to said first bimetal.

11. A fuel burner control system comprising in combination, hot and cold switches, a heat demandresponsive device for opening the hot and closing the cold switch on a demand for heat andopening the cold and closing the hot upon becoming satisfied, an electrical fuel feeding device, a circuit therefor including'said cold switch, a safetyswitch in control of said fuel feeding device, a thermal timer which when cold opens said safety switch, means for maintaining' a supply "of heat to said thermal timer during a demand for heat by said responsive device, said last named means including saidcold switch, said supply of heat beingdependent upon the establishment of combustion, and a heating circuit for said thermal timer including saidhotswitch for maintaining said timer in .its hot position while said responsive device is satisfied.

'12. A burner control circuit in combination comprising, fuel supply means and a circuit including control means therefor, thermally oper heat thereto at a first value when the fuel supply circuit is opened by the controlmeans and to supply the timing means with heat at a second value upon the establishment of combustion, a safety switch in the fuel control circuit which is maintained in a closed position by the i said timing means when the timing means is supplied with heat within-a predetermined range including said first and second values and which is opened when the timing means is not supplied with heat sufllcie'nt to maintain it at a tempera-.

ture within said range, combustion responsive means for controlling the supply of heat to said timing means to maintain the supply at the said second value when combustion is established,

and ignition means controlled by said timing. means for operation of the igniter only when the supply of heat to the timing means is maintained'at said first value.

'cir'r'oan r. HOLMES,