US2368850A - Burner control system - Google Patents

Description

Feb. 6, 1945. F. E. LANGE 2,368,850

BURNER CONTROL SYSTEM Filed Dec. l5, '1941 ATTORNEY ...couple is employed to generate current for a Patented Feb. 6, 1945 yomni!) STATES PATENT Afir-FICE.

BURNER CONTROL ASYSTEM Frederick E. Lange, Lincoln, Nebr., vasslgnox' to j Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Y Application December 13, 1941, Serial No. 422,849

7 Claims'. (Cl. 15S-117.1)

The present invention relates to a burner contrcl system and more particularly to one employing a thermoelectric device for controlling the ow of fuel to the burner, although the present invention could well be used with other types of temperature responsive mechanisms.

In uid fuel burner control systems, particu-l larly thcse concerned with gaseous fuels, it is customary to employ a pilot burner for igniting a second burner, usually the main burner. It is the usual practice with such systems to employ some means for interrupting the flow of fuel to the main burner when the pilot burner is extin.

guished. One common ferm of such a protective means employs a therniocouple responsive to the heat ofthe pilot flame and which generates a controlling current only when the thermocouple is heated by the pilot burner. These arrangements have the serious disadvantage that the power produced by the thermocouple is necessarily extremely limited. In order to maintain the resistance as low as possible, it is necessary to use relatively short elements for the thermocouple. When this is done, the cold junction is necessarily suiliciently close to the hot junction that it is unduly influenced by the main burner. This reduces the temperature dlerence between the het and cold junctions of the thermocouple. This limitation on the amount of power generated by the thermocouple becomes extremely serious, Where, as hasbeen proposed, the thermotemperature controlling system.

An object of the present invention is to provide a safety control system for a burner employing a pilot light, which safety control system will be quick in its response and relatively unaffected by the presence or absence of a main burner flame.

Another object of the present invention is to provide a burner control. system employing thermoelectric means for detecting the condition of a pilot burner in which provision is made for increasing the output of the thermoelectric means in spite of the influence ofthe main burner.

A further object of the invention is to provide an' arrangement of the type discussed in which the normally cold junction of the controlling thermocouple is located so as to be exposed to the main burner temperature but in which an additional thermoccuple is provided which is operative upon the main burner temperature increasing to supplement the current supplied by the controlling thermocouple.,

A further object of the invention is to provide a burner control system involving a pair of burners in which there is a pair of thermocouples aiding each other, the hot junctions of .the two thermocouples being exposed to the flames of the two burners respectively and in which the cold junction of the thermocouple normally affected by the rst of the burners is exposed to the heat produced by the vsecond of the burners.

Other objects of the invention will be apparent from a consideration of the accompanying specication', claims, and drawing, of which:

The single figure is a schematic illustration of a burner'control involving my invention.

Referring to the drawing, 'a portion of a conventional gas furnace is' illustrated and is indicated by the reference numeral I0. This furnace in the usual manner comprises the furnace II and a casing or jacket I2 surrounding the furnace. Disposedwithin the furnace is a main gas burner I3, a pilot burner I4, and a bleed gas burner I5. The pilot burner I 4 is employed to ignite the main burner I3 and the bleed gas burner. The main burner- I3 has the usual spuds I1.

A pipe I8 supplies gas to the main burner and is connected by a valve I9 with a, main gas supply pipe 20. Pipe 20 leads to any suitable source of gas supply (not shown)l The pilot burner I4 at a point on the inlet side of valve I9.

The valve I9 is illustratively shown as adiaphragm gas valve. While the details of this valve do not, by themselves, form part of the present invention, they are brieyvdescribed in order to understand more fully the operation of the system. The valve comprisesY a valve casing 2| having the -usual partition Wall providing a valve seat with which cooperates `a valve disk 22. The valve stem 23 secured to valve disk 22 is connected to a diaphragm 24.` An upper casing member Y25 encloses the upper side of the.diaphragm 24 so as to form with the valve casing 2I, upper f pressure in the upper diaphragm chamber. 'I'he pressure in this chamber is controlled by a threeway pilot valve 21. This valve `is of conventional structure and the details thereof have Abeen omittedin order to simplify the drawing. Communicating with the valve chamber 21 isa pipe 28 connected to the upper diaphragm chamber, a pipe 29 connected to gas supply pipe'2, and a pipe 30 leading from pilot valve 21 to the bleed burner I5. The valve 21 is electromagnetically operated and the coil of the electromagnet has been schematically shown in the drawing in order to illustrate more fully the electric connections of the system. In general, the pilot valve 21 is so arranged that when the coil 32 is energized, the gas above the diaphragm passes out through pipes 28 and 30 to the bleed burner I5 and further gas is prevented from entering the chamber above the diaphragm. The result is that the gas pressure acting beneath the diaphragm raises the valve disk 22 and admits gas to the main burner I3. When the coil 32 is deenergized, the flow of gas from pipe 28 to pipe 30 and hence to the bleed gas burner I5 is interrupted and gas is again permitted to ow from supply pipe 20 to pipe 28 and hence to the upper chamber above the diaphragm. This permits the supply gas pressure to be applied above the diaphragm to cause the valve disk 22 to again engage its seat.

Thus, when coil 32 is energized, gas is admitted to the main burner I3 and when it is deenergized, this gas flow to the main burner is interrupted.

The energization of coil 32 is controlled in part by a room thermostat 35. This room thermostat comprises a bimetallic element 36 'to which is secured a contact arm 31 adapted to be moved into engagement with the contact 38. As indicated by the legend, the bimetallic element 36 is so arranged that upon a drop in temperature the con. tact arm 31 is moved to the left into engagement with contact member 38. Upon a rise in temperature, the contact arm 31 is moved to the right out of such engagement.

The current .for energizing coil 32 is supplied by a pair of thermopiles'4i) and 4I. As will be presently explained, these thermopiles not only supply the current for the operation of the control system but also supply this current in accordance with the presence or absence of a fiame at the pilot burner and hence act to indicate whether or not the pilot burner is ignited.

Referring specifically to thermopile 48 which may be considered to be the main control thermopile, this thermopile comprises a plurality of elements 44, 42l 48 and 43 connected alternately and in series with a pluralitv of elements 46. 45, and 41, The elements 42, 43, 44,and 48 are formed of material having thermoelectric characteristics which are differentfrom those of which elements 45 to 41 are formed. In other words. these elements form a plurality of thermocouples connected in series` with each other so as to form Junctions 50, 5I, and 52 on the one hand, and junctions 53, 54, and 55 on the other hand. The junctions 50, 5I, and 52 may for convenience be referred to as the hot junctions and the junctions 53, 54, and 55 as the cold junctions. The hot junctions 50, 5I, and 52 are exposed to the flame of the pilot burner. These junctions may be exposed to the main ame of the pilot burner or to a runner fiame 51 as illustrated in the drawing, but in any event, the hot junctions should be influenced less by the main burner than the cold junctions. The cold junctions 53, 54, and 55 are exposed to the flame of the main burner. It will be noted that these junctions are located a substantial distance above the spuds I1 so as to be exposed to a relatively hot portion of the main burner. However, the junctions 53, 54, and 55 are not located directly in the main burner flame and the thermopile 40 is preferably so located that these junctions are heated to approximately the same extent by the main burner flame as junctions 50, 5I, and 52 are heated by the pilot burner flame.

The thermopile 4I comprises a plurality of members 60, 6I and 62 and a further plurality of members 63, 64, and 65. The members 60, 6I and 62 are formed of the same material as members 45, 46, and 41 and the members 63, 64, and 65 are of the same material as members 42,143, 44 and 48. The members 6l) to 65 are connected together alternately in series so as to form junctions 68, 69, and 10 'and junctions 12 and 13. The two extreme ends of members 60 and 65 together constitute a third junction. The junctions 68, 69 and 10 may be termed the hot junctions of ther- 'mopile 4I "and the remaining junctions including junctions 12 and 13, the cold junctions.

The two thermopiles 40 and 4I are connected in series with each other to the coil 32 of control device 21 and under the control of thermostat 35. The circuit connecting these members together is as follows: through members 60, 63, 6I, 64, 62, and 65 to conductor 16, to thermocouple members 43, 41, 48, 45, 42, 46 and 44, then to conductor 11, bimetallic element 36, switch blade 31, contact 38, conductor 18, coil 32, and conductor 19 back to thermocouple member 66. It will be noted from the foregoing circuit and from a comparison of the manner in which the thermocouples are connected in the circuit that4 the thermopiles 40 and 4I are connected in series so as to aid each other. In other words, the extreme right hand hot junction of the thermopile 4I is junction 10. The next junction will of necessity be a cold junction if the thermocouples are Aconnected so as to aid each other. It will be noted that the members 43 and 65 which are of the same material are connected together by wire 16 so as to be in eect one continuous member. Thus, the first thermoelectrc junction proceeding to the right is junction 53 which is a cold junction. The next succeeding junction is junction 52 which is a hot junction. Thus, when junctions 50, 5I and 52 are considered as hot junctions, the thermopiles are connected so as to aid each other. The junctions 68, 69, and 10 are preferably located adjacent a slightly cooler portion of the main burner than the cold junctions 53, 54, vand |55. This is not absolutely essential but does oier certain advantages, as will be ex- Lplained later. The lower ends, including the cold junctions, of thermopile 4I are located in as cool a position as possible. The fact that the hot junctions 68 to 10 are located adjacent a portion of the burner ame which is not quite so hot. makes it possible to place the cold junctions of the thermopile 4I in a, lower portion of the furnace than would otherwise be possible. Inasmuch as the temperature within a furnace decreases very rapidly below the upper surface of the main burner, it is possible to place junctions 12 and 13 in a rather cool location. This tendency of the furnace temperature to decrease rapidly below the level of the main burner is due to the inflow of secondary air to support 'combustion. The temperature of this secondary air is sufficiently close to furnace room temperature that the region around cold junctions 12 and 13 tends to remain at all times at a substantially constant and relatively low temperture.

Operation Let it rst be assumed that the thermostat 35 is satisfied, as shown in the drawing, and that the pilot burner is ignited. Under these conditions, it is impossible'for current to flow to coll 32 regardless of whether energy is generated by thermopiles 40 and 4I. Consequently, as previously explained, the control device 21 is in such a position that communication is established between pipes 29 and 28 so that gas pressure exists above diaphragm 24 and valve disk 22 is maintained in closed position. Because of the valve disk 22 vbeing closed, no gas flows to the main burner and this burner is unignited.

Let it be assumed that the pilot burnerl I4 is properly ignited. Under these conditions, the junctions 50, I, and 52 are heated by the pilot burner ame 51. Due to the fact thatl the main burner is not in operation, junctions 53, 54, and

55 are relatively Acold and all of the junctions of the thermopile 4I are cold. Consequently,the action of the thermopile 40 is that of a simple thermopile in which the hot junctions are heated and the cold junctions are maintained at a relatively low temperature, while thermopile 4I acts merely as a' conductor. Under these conditions, if the room thermostat 35 now calls for heat, current is able to ilow over the circuit previously traced. The thermopile 4D is designed to operate under these conditions to generate suflcient current to energize coil 32' so as to cause the latter to change the position of the pilot valve of control device 21. When this happens, as previously explained, gas ilow between pipes 29 and 28 is interrupted and communication isestablisl1ed between pipes 28 and 30 to permit the gas above diaphragm 24 to pass to the bleed burner I4. The result of this is that the gas pressure above diaphragm y24 is relieved and valve I9 is opened to permit gas to now to the main burner.

The gas flowing to main burner I3 is ignited by the pilot burner I4 in the usual manner. As soon as it becomes ignited, the cold junctions 53 to 55 begin to 'be heated. As these junctions become heated, the electromotive force developed by thermopile 40 decreases. Eventually, the point is reached at which the hot and cold junctions of thermopile 40 vassume substantially the same temperature. If it were not for thermopile 4I the coil 32 would be deenergized and the main valve shut do-Wn. During,r this time, however, the hot junctions of thermopile 4I are also being heated by the main burner although to a slightly less extent. As previously pointed out, thermopiles 40 and 4I are connected to aid. each other. Thus. as the electromotive force generated by thermopile 45 decreases, that generated by thermopile 4I increases. Because of the fact that the cold junctions of thermopile 4I are in a relatively cool location, the electromotive force generated by this thermopile is-substantially equal to that normally generated by the thermopile 40 when the main burner is unignited. As a result, the total power supplied by the thermopiles 45 and 4I remains substantially constant, even though junctions 68to 10 are not aiected to the same degree by the main burner as junctions 53 to 55.

Let it now be assumed that the thermostat 35 becomes satisfied. The energizing circuit for coil 32 is now interrupted so that valve I9 is closed. This interrupts the ilow of 'gas to the main burner, sc that itis extinguished. The thermopiles 40 and 4I then cool down to the previous condition described in which junctions 50, 5I. and 52 are the only junctions that are heated.

The operation which has been described so far is the normal operation of the system. The various abnormal conditions for which the system is designed will now be described. The simplest abnormal condition is that of the pilot burner being extinguished along with the main burner at the time that the thermostat calls for heat. It is obvious that under these conditions, both thermocouples 40 and 4I will be unheated throughout and that there is no source of power for energization of the coil 32. Consequently, the valve I9 will not be opened. Thus a ow oi gas to the main burner is prevented because of the absence of any pilot ilame to ignite it.

Let the case now be considered in which the main burner and the pilot burner have 'both been ignited and the pilot burner is'extinguished while the main burner continues in operation. It is generally desirable under these conditions to terminate the operation of the main burner as its operation in the absence of a pilot flame may result in hazardous conditions. As soon as the pilot burner goes out, the junctions 50 to 5.2 are' no longer heated bythe pilot burner. The only heat that these junctions receive is the relatively small amount of heat they receive from the mainr vburner by convection, radiation, and conduction. In any event, the junctions 53, 54, and 55 which are heated to a relatively high degree by the main burner will be at a much higher temperature than junctions 50 to 52. As a result, an electromotive for-ce is generated which is o-pposite in polarity to that'generated by thermopile 4I. Moreover, even though the normally hot junctions (now the cold junctions) are heated to a certain extent Iby the main burner, the total electromotive force generated `by thermocouple 4I) will be very close in magnitude to that generated by thermopile 4I due to the, fact that the hot junctions 53 to 55 are adjacent a hotter part of themain 4burner flame than junctions 68 to 10. As a result, the voltage generated by thermopile 4Uv will overcome the voltage generated bv thermopile 4I so as to cause deenergization of coil 32. Thus, the coil 32 will be very quickly deenergized so as to cause closureof valve I9 upon the pilot burner being extinguished even though the main burner is in operation.

` It will be seen from the above that regardless of whether the main burner is in operation or not, the extinguishment of the pilot burner insures prompt deenergization of the coil 32. Furthermore, the total power generated by thermopiles 40 to 4I can be considerably greater than that generated by a' thermopile whose hot junctions are al1 located adjacent the pilot flame and whose cool junctions are located in as cool a location as possible'. Inevitably, in such a case, the cool junctions are affected to a considerable extent by the main burner ame. This is necessary, as previously explained, because of the fact that the thermocouples must be of .relatively short length and that in order to locate the hot junctions adjacent the pilot burner name, it is necessary to have the cold junctions at a point where the main burner will af for purposes of illustration only and that the invention is to be limited only by the scope of the appended claims.

What I claim is:

1. In combination, rst and second sources of heat, an electrically operated control device, and a plurality of thermocouples eiectively connected to said device in series with each other, the hot junction of one thermocouple being exposed to the ilrst source of heat and the cold junction to the second source of heat, and the hot junction of the other thermocouple being exposed to the second source of heat and the cold junction being located in a region having a relatively low temperature in respect to either source of heat so that said thermocouples are effective to energize said device when either the first source alone or both sources of heat are active but are ineffective to energize said device whenever said rst source of heat is inactive.

2. In a burner control system, a pair of burners, a first of said burners serving to ignite the second burner, an electrically operated device for controlling the delivery of fuel to the second burner, and a plurality of thermoelectric devices connected to said electrically operated .device and controlling the energization of said device, one of said thermoelectric devices being operative in accordance with the dierence between the temperatures adjacent the ame portions of said iirst and second burners, and the other being operative 'in accordance with the difference. between the temperature adjacent the ame portion of the second burner and a region of relatively constant temperature and hence suppleinenting the output of said rst named thermoelectric device as said output decreases dueto the operation of said second burner.

3. In a burner control system, a main burner-,

a pilot burner, an electrically operated device for controlling the supply of fuel to said main burner, and a plurality of thermocouples connected to said device in series with each other, the hot junction of one thermocouple being exposed to the heat of the pilot burner and the cold junction to the heat of the main burner, and the hot junction of the other thermocouple being exposed to the heat ofthe main burner and the cold junction being located in a region having a relatively constant temperature so that said thermocouples are effective to energize saidA device when either the pilot burner alone or both the main and pilot burners are ignited but are ineffective to energize said device whenever said pilot burner is extinguished.

4. In a burner control system, a main burner, a pilot burner, an electrically operated device for controlling the supply of fuel to said main burner, and a pair of thermocouples connected to said device in series with each other, the hot junction of one thermocouple being exposed to the heat of the pilot burner and the cold junction of said thermocouple to the heat of the main burner, and the hot junction of the other thermocouple being exposed to the heat of the main burner and the cold junction being located in a region having a, relatively constant temperature,-

-said thermocouples being so positioned with respect to the main burner that the hot junction of said last named thermocouple is heated to a lesser extent by said main burner than the cold junction of said first named thermocouple, said thermocouples being effective to energize said device when either the pilot burner alone or both the main and pilot burners are ignited but are ineffective to energize said device whenever said pilot burner is extinguished.

5. In a burner control system, a pair of burners, a rst of said burners serving to ignite the second burner, an electrically operated device for controlling the delivery of fuel to said second burner, a, thermoelectric device controlling the energization of said electrically operated device, said thermoelectric device being operative in accordance with the difference between the'temperatures adjacent two portions thereof, one of which is closer to the rst burner lthan the other and the other of which is substantially affected by the heat of said second burner, and means automatically operable upon' the second burner being ignited so as to raise the temperature of thev other portion of the thermoelectric device to apply to said electrically operated device an electromotive force of suiiicient magnitude to compensate for the decrease in magnitude .of electromotive force generated by said thermoelectric device.

6. In a burner control system, a pair of burners, a first of said burners serving to ignite the second burner, an electrically operated device for controlling the delivery of fuel to said second burner, a thermocouple controlling the energization of said electrically operated device and having its hot junction located closer to said iirst burner than its cold junction and its cold junction being heated appreciably by said second burner, and means automatically operable upon the second burner being ignited so as to raise the temperature of the cold junction of said thermocouple to apply to said electrically operated device an electromotive force of suilicient magnitude to compensate for the decrease in magnitude of electromotive force generated by said thermocouple.

7. In a burner control system, in combination, a main burner, a pilot burner for ignting the main burner, a device in control of the flow of fuel to the main burner, a, first temperature responsive means having two portions adapted to be respectively heated by the main and pilot burners and arranged to provide a force the direction and extent vof which depends upon the relative temperatures of said two portions to provide a substantially zero force when said portions are equally heated, a. force in a rst direction when the portion exposed to the pilot burner is hotter than the other portion and a `force in a second direction when the portion exposed to the pilot burner is lesshot than `said other portion, a second temperature responsive Imeans subjected to main burner heat arranged to `provide a substantially zero force when said main burner is extinguished and to provide a force in said iirst direction when said main burner is lighted, and means associating said temperature responsive means and said device whereby substantially no force is provided for said device when both burners are extinguished, a force in said rst direction is provided for said device by said second temperature responsive. means whenv both burners are ignited, a'force in said first direction is provided for said device by said first temperature responsive means when the pilot burner only is lighted, and substantially no force for said device is provided as a result of the interaction of said forces in said rst and second directions when the main burner is lighted and the pilot burner is extinguished.

FREDERICK E. LANGE`

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