US2361294A - Control system - Google Patents

Description

Oct. 24, 1944.

H. JQNES CONTROL'SYSTEM 2 Sheets-Sheet 1 Filed Aug. 22, 1941 FIG. 7

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Oct. 24, 1944. H. s. JONES 2,361,294

CONTROL SYSTEM Filed Aug. 22, 1941 2 Sheets-Sheet 2 FIG. 3.

INVENTOR. HARRY S. JONES BY 6% r I A NEY the characteristic of Patented Oct. 24, 1944 CONTROL SYSTEM Harry S. Jones, Washington,

D. 0., assignor to The Brown Instrument Company, Philadelphia, Pin, a. corporation of Pennsylvania.

Application August 22, 1941, Serial No. 407,875

9 Claims.

The present invention relates to combustion control systems for fuel burners.

It is-an object of the present invention to provide a combustion control system which operates in accordance with a characteristic'of the fuel burner flame.

Another object of the a control system for invention is to provide controlling the quality or extent of combustion in a fuel burner which relies in its operation upon the electrical conductance of th fuel burner flame.

Another object of the invention is to provide a combined combustion quality and safety control system for a fuel burner which relies it is operation upon the conductance between a pair of spaced electrodes in engagement with the fuel burner flame and otherwise insulated from each other. Another and more specific object of the invention is to provide means for indicating quality of combustion in such a combined safety control system. I

A further object of the invention is toprovide a simplified safety control system for a fuel burner whichemploys a pair of electrodes in engagement with the burner flame and which is sensitive to the presence of a flame between the electrodes but is insensitive to other conductive paths therebetween.

Various arrangements independent of safety control provisions have been proposed in the prior art for determining the quality of combustion in a fuel burner, or determining the degree of combustion of the fuel in the burner and for controlling the mixture of fuel and air to the burner tosecure optimum combustion conditions. In addition to the prior art, a copending application of Walter P. Wills, Serial No. 332,119, entitled Control appa'ratus, and filed April 27, 1940 issued into Patent 2,352,143 on June 20, 1944, discloses a combined combustion quality and safety control system for a fuel burner which relies in its operation upon a fuel burner flame of continuously fluctuating in resistance, and the further characteritsic that the amplitude of the more specifically, for.

fluctuations varies inversely with the degree of combustion of the burning fuel.

The present application discloses a combined combustion quality and safety control system of the general type disclosed in the Wills patent referred to, but relies in its operation upon the characteristic of a fuel burner flame of being lower in resistance than the surrounding medium, namely the surrounding air; and upon the further characteristic of a fuel burner flame of vary-' ing in ohmic resistance in accordance with the quality of combustion the fuel.

As is well known in the prior art all flames are the result of a chemical reaction. In the case of a gas flame, for example, the oxygen of the air combines with carbon and hydrogen of the fuel to. form carbon dioxide and water vapor. The flame is always accompanied by ionized particles which are the result of the reaction between the oxygen of the air and the carbon and hydrogen of vthe gas. These particles or ions are capable of conducting a current between the burner and an electrode inserted in the flame. With the burner as one electrode and a movable electrode inserted in the flame,- it has been determined that the conductivity of a flame is greater in the direction opposite to that of the direction of flame propagation when the movable electrode is held in the outer parts of the flame and that when the movable electrode is moved toward the burner a region is reached where the or degree of combustion of -flame conductivity becomes substantially equal in both directions of current flow between the burner and'the movable electrode. This region is near the tip of the inner cone of the flame. By the term direction of flame propagation" is meant the direction away from the burner. If the movable electrode is moved through this region toward the burner, another region is encountered where the conductivity of the flame is greater in the direction of name propagation than in the other direction. This phenomena is believed to be due to the presence of a conce tration of positive ions in the base of the flame. The negative ions or electrons of the ionized par- .ticles of the flame are much more mobile than the positive ions and tend to accumulate in the outer region of the flame while the positive ions tend to accumulate in the region closely adjacent the burner.

I have discovered that when the relation of the flame electrode and the burner is fixed, the ohmic resistance of a fuel burner flame varies inversely with the quality or extent of combustion of the fuel. Specifically, when the flame is yellow, containing a large quantity of unburned carbon, the ohmic resistance of the flame is greater than when the flame is blue, indicating more complete combustion of the fuel. Asthe quality of combustion oi the fuel is varied to gradually change the flame from yellow to blue, the ohmic resistance of the flame varies gradually in a corresponding manner.

Advantage of these characteristics of a fuel burner flame is .taken in the arrangement of my present invention, which arrangement relies in its operation on the ohmic resistance of a flame to detect the presence of a flame, and is responsive to the magnitude of the ohmic resistance of the flame to provide a measure of the quality or degree of combustion of the burning fuel.

In safety control systems for fuel burners which have been proposed in the prior art, various means havebeen employed for determining if combustion conditions are proper and whether combustion actually takes place, one such means comprising an electrode which extends into the flame of the burner and which is so connected in the system as to provide a conductive path of relatively low resistance to ground through the flame. The variation in the electrical conductivity of this path to ground when the flame is present and when a flame is not present is commonly employed to change the bias on the control grid of an electronic valve for controlling a thermal safety switch. Since there is a possibility that a low resistance path may be set up from the electrode to ground through other agencies than by means of the flame, for example, a low resistance path which may be established between the electrode and ground by reason of carbonization, by accidental touching of the electrode to ground, or other abnormal conditions simulating combustion, provisions have been made in devices of the prior art for preventing the fuel supply and ignition from being turned on when such an abnormal condition exists Since an abnormal condition of this character simulat'ng combustion may arise after the system is already in operation, it is desirable to provide means for distinguishing between such abnormal conditions and actual combustion while the system is in operaton. For example, in a thermostatically controlled house heating system if the cont ol system is insensitive to the presence of the flame after initial ignition of the flame, the fuel feeding means will be operated continuously as long as the room thermostat is closed. If the flame should then be extinguished, the furnace will be flooded with atomized fuel and a highly explosive mixture of the latter will' be permitted to accumulate.

In accordance with the teachings of the prior art of which I am aware, when the flame electrode is maintained at a negat've potential with respect to the potential of the burner, only a single electronic valve is required to control the operation of the burner in a safe manner responsively to the presence or absence of a flame at the burner. When the flame electrode is maintained at a positive potential with respect to the burner, however, at least two elcctron'c valves are necssary. Two electronic valves are necessary in the latter because if only a s ngle electronic valve is used, the output current of the valve will be a maxmum when there s no flame at the burner and will be a minimum when there s a flame at the burner. The deenerg zed conditi n of the valve a d the condition of the valve when there is a flame at t e bu ner thus are t e same. Such a condit on is obvious y not desirable in a safety control system. and accordin ly. a second electron c valve is prov ded to effect a reversal in the output current obtained upon the appearance and disap earance of a flame at the burners that is, to produce a maximum current when there is a flame at the burner. and a. min'mum current when there is no flame at the burner.

In respect to the number of electronic valves required in the safety control arrangement, therefo e. the use of a ne at ve flame electrnd is to be preferred over a positive flame electrode. The negative flame electrode arrangement, however, is subject to a disadvantage to which the positive flame electrode arrangement is not subjected, namely, that the position of the flame in which the electrode must be positioned for proper operation is critical. This critical region is within the inner cone and close to the burner. If the flame electrode is moved away from th's critical region in the flame, even though not entirely out of the flame, the system does not operate properly but operates Just as if there was no flame.

It is accordingly another object of my present invention to provide a safety control system for a fuel burner in which a negative flame electrode may be utilized thereby permitting the use of a single electronc valve and in which the relation of the flame electrode and the burner is fixed, the flame electrode and the burner being provided in the form of a unitary and mechanically rigid assembly and in this manner obviating the possibility of displacement of the flame electrode from the crit'cal region of the flame.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invent'on, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings.

F'g. 1 is a schematic diagram of an embodiment of a combined combustion quality and safety control system as applied to a fuel burner in which the flame electrode is negative in potential with respect to the burner potential;

Fig. 2 is an enlarged view in section of a portion of the arrangement of F'g. 1;

Fig. 3 is a schematic diagram of anotherembod ment of a combined combustion quality and safety control system as applied to a fuel burner in which the flame electrode is positive in potential with respect to the burner potent'al; and

Fig. 4 is an enlarged view in section of a portion of the arrangement of Fig. 3.

Fig. 1 of the drawings illustrates a gas burner l supplied with gas through aconduit 2 and the flow of gas to the burner is controlled by an electrically operated or othersuitable valve 3. Aplot burner 4 is provided which is controlled by an electrically operated or othersuitable valve 5, and means are provided for igniting the pilot flame including a pair ofelectrodes 6 which are connected to the terminals of a secondary winding 1 of anignition transformer 8 having a primary winding 9 which is adapted to be energized from the alternating current supply lines L and L2.

The fuel valve operating circuit of the control system illustrated in Fig. 1 "s controlled by means of a thermostat H) which may be located in a room or space to be heated. The thermostat It may be of any suitable construction and includes a bimetallic element I I connected by means of a conductor H to the line L and a contact blade l3 adapted to engage astationary contact 14 which is connected to line L through a thermal safety switch I5 and a secondary winding l6 of a transformer H.

The thermal safety switch i5 is preferably of the form disclosed in Patent 1,958,081 to F. S. Denison, May 8, 1934. As shown more or less diagrammatically in the drawings, this switch comprises a stationary arm. l8 and a movable arm I 9 biased for movement away from arm I8 but normally held in engagement with the latter by means of abimetallic element 20. Element is rigidly secured at one end to ablock 2| and is arranged to be heated by acoil 22 when the latter is energized through a circuit which will later be described. Upon energization ofcoil 22 for a predetermined period of time,element 20 will be warped sufl'lciently in the counter-clockwise direction to permit arm l9 acting under spring or other bias to separate from switch arm l8 thereby interrupting the circuit including the thermostat Ill. The switch |5 will remain locked in this position until manually returned to its normally closed position.

Both the main burner and thepilot burner 4 are supplied with a combustible mixture of fuel and air from a mixingchamber 23 into which v fuel is introduced through aconduit 24 and air through theconduit 25. As shown, afuel pressure regulator 24A is inserted in thefuel supply conduit 24. The amount of air passing through theconduit 25 is controlled by an electrically operated or othersuitable valve 26 which is adapted to he energized from the alternating current supply lines L1 and L2.

The transformer H which supplies power for the control system is a combination step-up, step-down transformer and comprises the primary winding I 6, low voltagesecondary windings 21, 28 and 29, and a high voltage secondary winding 30. The low voltage secondary winding 21 is connected byconductors 3| and 32 to theheater filaments 33 and 34 of anelectronic valve 35 and supplies energizing current-thereto. The 3electronic valve 35 is a twin type amplifier valve and includes two triodes, designated A and B, in one envelope. For convenience the triode designated A in the drawings will be referred to hereinbefore as the rectifier and the triode B will be referred to as the detector. The rectifier A includes theheater filament 33, acathode 36, acontrol electrode 31 and ananode 38, and the detector B includes theheater filament 34,

acathode 39, acontrol grid 40, and ananode 4|.

The rectifier A is supplied with electricai energy from the upper portion of the transformer secondary winding 30 through a circuit which may be traced from the upper terminal of winding 30 to aconductor 42,anode 38,

cathode 36, and aconductor 43, in which aresistor 44 is inserted, to the tap 45 intermediate the ends of winding 30. This circuit is conductive only during the half cycles of the alternating voltage supply source when the upper terminal of winding 30 is positive with respect to the lower terminal thereof due to the action of the rectifier A. Thus, a pulsating potential drop is produced acrossresistor 44 in the direction to renderterminal 46 ofresistor 44 positive with respect toterminal 41 thereof. Thecontrol electrode 31 of rectifier A is directly connected to thecathode 36.

The output circuit detector B is supplied with electrical energy from the lower portion to the transformer secondary winding 30 through a circuit which may be traced from the lower terminal of winding 30 through a conductor48, winding 49 of arelay 50 in shunt with acondenser 5|, winding 52 of arelay 53 in shunt with acondenser 54, anelectric meter 55,anode 4| of detector B,cathode 39 and aconductor 56,switch arm 62,contact 6| and conductor to the tap 45 on winding 30.

It will thus be noted that the output circuit of the detector B includes therelay windings 49 and 52 and theelectric meter 55 in series and that this output circuit is energized by the portion of the transformensecondary winding 36 which is below the tap 45. l

The currentfiow in the output circuit of detector B is eontrolled by an input circuit one branch of which connects thecontrol electrode 40 to thecathode 39 through a connection lndetector B connects thecontrol electrode 40,,

through aconductor 63 to anelectrode 65 which projects into the flame of thepilot burner 4.

Theconductor 63 is preferably encased within ashield 63A which, as shown is connected to the,

lower terminal 01-resistor 58. The pilot burner 4'is connected to ground and thereby to the positive terminal ofresistor 44, which terminal as shown is also grounded. In this arrangement, therefore, theflame electrode 65 is maintained at a negative potential with respect to the potential of theburner 4. As illustrated in Fig. 1 and in more detail in Fig. 2, theburner 4 andflame electrode 65 are provided in the form of a unitary mechanical assembly, the flame electrode being insulated from theburner 4 by anelectribal lnsulator 65A. Theinsulator 65A is preterably of a type capable of withstanding the high temperatures encountered near the burner Theflame electrode 65 in this arrangement is positioned close to theburner 4 and is preferably so positioned as to always be .within the region of the inner cone irrespective of the quality of combustion of the burning fuel.

A third branch of the input circuit of detector B connects thecontrol electrode 40 to thecathode 39 through a connection including theresistors 51 and 58 shunted bycondenser 59, aconductor 64, the transformer secondary winding 28, acontact 65,switch arm 62, andconductor 56 to thecathode 39.

During the normal operation of the system theresistor 58 is shunted by a connection which may be traced from the upper end ofresistor 58 through aconductor 66, aswitch arm 61, acontact 68, and aconductor 69 to the lower terminal ofresistor 58. The reason for providing theresistor 58 is'explained hereinafte The transformer secondary winding 30 is so wound on transformer |1 that the detector, B

is conductive only on the half cycles when the rectifier A is not conductive and vice versa. Thus. a pulsating direct current potential drop is produced across resistor 44' during the half cycles when the detector B is non-conductive. The phase of this pulsating potential drop is such that it will be at a maximurnwaiue when theanode 4| of detector B is negative. This pulsating potential drop produced acrossresistor 44 is applied to the input circuit of the detector B through the flame if present, and the polarity thereof is such as to cause a pulsating direct current to flow through the flame in the direction of flame propagation. The circuit through which this pulsating current flows has been described hereinbefore.

When the burner operation is first initiated and a flame is not present at the burner and no other conductive path exists from thecontrol electrode 66 to ground, no biasing potential will be applied to thecontrol electrode 40 of detector B. Thecontrol electrode 66 of detector B will be at substantially the same potential as thecathode 39 since thecontrol electrode 46 andcathode 39 are then connected byresistors 51 and 56,conductor 66,contact 6| and switcharm 62 then in engagement andconductor 56. As a result the detector B will be conductive during the time itsanode 4| is positive.

In the normal operation of the system, when a flame is present at the burner, theswitch arm 62 is actuated away fromcontact 6| and into engagement with thecontact 65 .to thereby connect the transformer secondary winding 26 in the input circuit of the detector B. The transformer secondary winding 26 is so wound on the transformer N that it tends to apply a negative potential to thecontrol electrode 46 of detector B and thereby tends to reduce the current flow in the output circuit, q the latter.

Upon the appearance of a normal flame, the bias potential produced acrossresistor 44 is applied to thecontrol electrode 46 of detector B through the resistance of the flame. The resulting flow of current through the resistance of the flame produces a potential acrossresistors 51 and 56 which is stored on thecondenser 59 and is of the proper polarity to tend to apply a positive potential to thecontrol electrode 46, and

thereby to oppose the tendency of transformer secondary winding 26 to apply a negative potential to thecontrol electrode 46. This potential is stored on thecondenser 59 during the half cycles when the rectifier A is conductive and the detector B is non-conductive, and is main-' tained on thecondenser 59 during the succeeding half cycles when theanode 4| of detector B is positive. This result is accomplished by properly proportioningcondenser 59 andresistors 51 and. 56. It is therefore seen that appreciable current flows in the output circuit of the detector B during the condition of normal flame.

If the flame electrode a path more conductive than a flame exists between the flame electrode and ground, the charge which is stored on thecondenser 59 during the half cycles when the anode ll of detector B is negative will path during the same half cycle and the initial portion of the succeeding half cycle to thereby substantially reduce the potential on thecondenser 59 during said succeeding half cycle. Consequently,electrode 66 is rendered more negative due to the action of transformer secondary winding 26 and as a result the current flow in the output circuit of detector B will be decreased.

7 It will thus be noted that current flows in the 50 output circuit of detector B when there is a flame at the burner and that little or no current flows in this output circuit when there is no flame and when theflame electrode 65 is grounded.

As illustrated in Fig. 1, therelay 50 comprises the winding 49 and switcharms 16 and 1| which are controlled by the winding 49 and which operate withfront contacts 12 and 16, respectively.Switch arms 16 and 1| also cooperate withback contacts 16 and 15, respectively, and are biased downward by gravity or spring means,

, not shown, into engagement with the latter contacts. For convenience, a contact through which a circuit is completed when a relay is operates aswitch arm 16 in addition to theswitch arm 62 previously mentioned. Theswitch arm 19 cooperates with afront contact 66. Relay 11 comprises a winding 6| which operates switcharms 62 and 66 in addition to theswitch arm 61 previously mentioned. Theswitch arms 62 and 66 cooperate withfront contacts 66 and respectively. Theswitch arms 62 and 19 ofrelay 16 and switcharms 61, 62 and 63 of relay 11 are biased downward by gravity or spring means, not shown.

When the temperature of the room or space to be heated is higher than the desired value all parts of the system are in the positions shown in'Fig; 1 and the fuel burner is then deenergized. If the temperature of the room or space to be controlled falls below the value it is desired to maintain, the thermostat l6 operates to move the switch blade |6 into engagement with the contact I. This results in closure of an energizing circuit to the transformer primary winding I6 and thereby effects energization of the transformer secondary windings. At this time theswitch arm 62 is in engagement with thecontact 6| and as a result the detector B is immediately rendered conductive as soon as thecathode 39 has been heated sufliciently and effects energization of the relay winding 49. Therelay 56 then operatesswitch arm 16 into engagement is grounded, that is, if 66 the potential applied to thecontrol 85 withfront contact 12 to complete an energizing circuit for the winding 16 ofrelay 16 in series with theheater coil 22 of the thermal safety switch i5. This circuit may be traced from the upper terminal of a secondary winding 29 through aconductor 66, winding 16, aconductor 61,heater coil 22, aconductor 66,switch arm 16,

contact 12, and aconductor 69 to the lower terminal of the winding 26.

The energization of the winding 16 causes theswitch arm 19 to close on thefront contact 66 to complete a holding circuit for the winding 16. This holding circuit may be traced from the upleak off through that conductive 50 per terminal of winding 29 throughconductor 86, winding 16,switch arm 16 andcontac 66 to ofrelay 16, when energized, also actuatesswitch arm 62 out of engagement with thecontact 6| and into engagement with contact 65' thus connecting the transformer secondary winding 26 into the input circuit of the detector B. As noted above the transformer secondary winding 26 tends to apply a negative potential to thecontrol electrode 46 of the detector B. It is noted that thecondenser 5| connected in shunt to relay winding 49 is so proportioned as to introduce a time delay in the operation ofrelay 56 as required to prevent the momentary opening of the output circuit of detector B caused by actuation of switcharm 62'from contact 6| to contact 66' from resulting in deenergization oftherelay 56.

Before the starting cycle is allowed to proceed further, however, a check is made to detect the presence of leakage resistance paths between theelectrode 65 and ground and initiation of the burner flame is prevented in a manner described hereinafter if such leakage paths exist and are of the order of a normal flame res stance or energized slightly higher as desired. This desirable fea- 58 is open at theswitch arm 61.

ture is obtained by an interlocking of therelays 59 and 16 to the end that the cycle cannot proceed further until therelay 50 has been deenergized and then reenergized. If the resistance of the path between theflame electrode 65 and ground is of the order of a normal flame, a charge is stored on thecondenser 59 which maintains the detector B conductive where therelay 50 is not deenergized.

Theresistor 59 which is connected in series with theresistor 51 is provided to accomplish this result. At this point in the starting cycle of the system the shunt circuit for the resistor Theresistor 58, therefore, is now effectively connected in the input circuit of the detector B and operates to place a, higher resistance in shunt to thecondenser 59, and as a consequence, a higher average positive potential is maintained on the control electrode 49 by thecondenser 59 than would be ma'ntained therein if theresistance 59 were shunted out. The detector B at this point in the starting cycle of the system is therefore sensitive'to conductive paths between theelectrode 65 and ground of resistance greater than that of a normal flame. If such conductive paths exist the detector B will remain conductive and the system will continue in the condition last described, namely, with therelays 50 and i9 energized. The magnitude of the resistance of such leakage paths fromelectrode 65 to ground to which the detector B is sensitive is determined by,the capacitance ofcondenser 59 and the total value ofresistors 51 and 58.

If no such leakage conductive paths exist between theflame electrode 65 and ground, however, no potential is stored on thecondenser 59,

and accordingly, detector B becomes non-conductive and therelay 50 is deenergized. This causesswitcharm 19 to close back contact H to thereby complete an energizing circuit for the winding 8| of relay IT. This energizing c rcuit may be traced from the upper terminal of transformer secondary winding 29 toconductor 96, winding 9i, aconductor 95,contact 14,switch arm 19, conductor 99,heater 22,conductor 81,

switcharm 19 and contact 99 to the lower terminal of winding 29.

.Energization of the relay 1'! causes it to close a holding circuit for itself, causes it to shunt theresistor 59, and causes it to energize the ignition transformer primary winding 9 and thepilot fuel valve 5. The'holding circuit for relay I! may be traced from the upper terminal of winding 29,conductor 95, winding 9i,switch arm 92, contact B4,conductor 88,heater 22,conductor 81, switch arm I9, and contact 90 back to winding 29. Theresistor 58 is shunted by the closure ofswitch arm 51 on the front contact 99 through theconductors 66 and 69. The energizing circuit for theignition transformer circuit 9 may be traced from the alternating supply line L through aconductor 9|, the primary winding 9,

back contact 15, switch arm H, contact 85, switch.

arm 83, and aconductor 92 to the supply line L. The energizing circuit for thepilot fuel valve 5 may be traced from the supply line L throughconductor 9|, a,conductor 93,pilot fuel valve 5, aconductor 94,front contact 85, switch arm 83, andconductor 92 to the supply line L As a result of the energization of theignition transformer 8 and the pilot fuel valve 5 a flame should appear at thepilot burner 4. If no flame appears, no further action will take place until the system is deenergized by the action of theheater coil 22 and the thermal safety switch l5. If a flame appears, however, detector B will become conductive as previously described, and consequently relay 59 will again be energized.

Reenergization ofrelay 59 causes the closure of a short circuit around theheater coil 22, opening of the energizing circuit through the ignition transformer primary winding 9, and energization of themain fuel valve 3. The burner I is then in full operation. The short circuit around theheater coil 22 may be traced from the left end thereof as seen in Fig. 1 toconductor 89,switch arm 10,front contact 72,conductor 89, front contact 80,switch arm 19, andconductor 91 to the other end ofheater coil 22. The energizing circuit of transformer primary winding 9 is opened by the movement of switch arm ll away from theback contact 15. The energizing circuit to themain fuel valve 3 may be traced from the supply line L throughconductor 9|, aconductor 94,pilot fuel 3, aconductor 95, front contact l3, switch arm H,front contact 85, switch arm 83, andconductor 92 to the supply line L.

If after the burner has been placed in full operation the flame should become extinguished or if theflame electrode 95 should be grounded, the detector B will become non-conductive andrelay 50 will be deenergized. thus causing themain burner valve 3 to close, eflecting reenergization of theignition transformer 8 and causing opening of the shunt circuit around theheater coil 22 of the thermal safety switch I5. If the flame then reappears the burner will go again into full operation. If the lime does not reappear within a predetermined time. however, the system will be deenergized by the opening of the thermal safety switch i5 due to the'action of theheater coil 22.

From the foregoing it will be seen that the system of Fig. 1 is adapted to distinguish between normal flame conditions and abnormal conditions at theburner 4 and operates to deenergize the system if an abnormal condition prevails longer than a predetermined time.

Therelay 53 comprises the winding 52 and a switch arm 99 which is adapted to cooperate with afront contact 91 and a back contact 99. Theswitch arm 95 is biased downward by gravity or spring means to close on itsback contact 98 and is adapted to be moved against that bias and against the opposing force of a compression spring 99 into engagement with thefront contact 91. If the current flow through the relay winding 52 gradually increases from zero, it first overcomes the opposing downward bias on the switch arm 99 and liftsarm 96 upward until it engages spring 99. The spring 99 then balances the attraction of the relay winding, and holds theswitch arm 96 separated from both its front and back contacts. If the current flow through winding 52 continues to increase it eventually becomes sufficient to overcome the opposing effect of the action of gravity on theswitch arm 96 and the opposing effect of spring 99 to closeswitch arm 96 on itsfront contact 91. By adjusting the force biasing theswitch arm 96 downwardly and,

the compression of spring. 99, the current levels at which these two actions ofrelay 53 take place may be adjusted as desired.

Theair controllingvalve 25 is operated by a reversible electrical motor (not shown) which is energized for rotation in one direction through a circuit which may be traced from the supply line L throughconductors 9| and 94 to thevalve 25, a conductor I00, back contact 99,switch arm 90, a conductor WI, andconductor 92 to the supply line L, and is energized for rotation in the opposite direction through a circuit which may be traced from the supply line L through conductors and 94 to thevalve 26, a conductor I02,front contact 91,switch arm 96, and conductors IM and 92 to the supply line L. The motor is adapted to open the valve when it is energized through contact 08 and conductor I00 and to close the valve when energized throughfront contact 91 and conductor I02. Thevalve 25 is provided with a limit switch (not shown) which operates to open conductor I00 and thereby to deenergize the motor when the valve has been adjusted to its fully opened position. A second limit switch (not shown) is also provided for opening the conductor I02 and thereby deenergizing the motor when thevalve 25 has been closed. The limit switch is preferably so adjusted that the valve can never be completely closed.

When the system operation is first initiated the switch arm 05 will be in the position shown, thevalve 26 will be in its open position and the fuel mixture will accordingly be lean. This will result in the establishment of a blue flame presenting relatively low resistance to the flow of current therethrough and as a result the effective current flow in the output circuit of the detector B and through relay winding 52 will be sufficient to close theswitch arm 95 againstcontact 91. This will energize the motor ofvalve 26 in the direction to close the valve. As thevalve 28 closes less air is supplied to the mixingchamber 20, Such adjustment of the valve is made until the desired mixture of fuel and air and consequently the desired quality of combustion is obtained. Specifically, as the supply of air to the mixing chamber is thus decreased, the resistance of the flame increases and the current through the relay winding 52 decreases until it reaches a value at which the switch arm 05 is biased by the action of gravity and thespring 50 out of engagement with thecontact 91 and is also held out of engagement withcontact 98. The fuel mixture will then have its proper proportions and the valve setting will remain constant until a change in fuel combustion quality caused by a change infuel 13. t. u. content, for example, causes a change in the resistance between the flame electrode 05 and ground. Upon a change in resistance of the flame between theflame electrode 65 and ground, the current flow in the output circuit of detector B is changed in the proper direction to effect actuation of thevalve 25 in the proper direction to restore the quality of combustion of the fuel to the desired value. As will be apparent to those skilled in the art themeter 55 through which the output current of detector B flows may be calibrated in terms of fuel combustion quality to thereby provide a direct indication of the quality of combustion of the fuel.

It will be clear from the foregoing explanation that the combustion control system illustrated in Fig. 1 controls a fuel burner in accordance with the presence or absence of a flame, and in addition to controlling the proportions of a fuel mixture so as to obtain efficient combustion, also provides an indication of the quality of combus tion of the fuel. Moreover, as will be apparent to those skilled in the art, either of these functions may be obtained without the other.

In Fig. 3 I have illustrated, more or less diagrammatically, a modification of the combined combustion quality and safety control system shown in Fig. 1 wherein a positive potential is impressed on the flame electrode relatively to the potential of the burner. In this modified arrangement, as shown in Fig. 3 and in more detail in Fig. 4, the flame electrode which has been designated by thereference character 65 B is positioned further away from theburner 4 than in the arrangement of Fig. 1 and preferably is at such a distance from theburner 4 as to never come in contact with the inner cone over the whole range of combustion quality variation of the flame. Theburner 4 and the flame electrode 653 in this arrangement, as in the arrangement of Fig. 1, are desirably provided in the form of a unitary mechanical assembly and are insulated from each other by means of the insulator 05A. In Fig. 3 elements corresponding to those in the Fig. 1 arrangement have been designated by the same reference numerals.

In Fig. 3 electric power is supplied to the system from a combination step-up and step-down transformer I03 which comprises a line voltage primary winding I04 and high voltage secondary windings I05, I06 and I0! and low voltage secondary windings I00, I00 and 20. The low voltage secondary winding I00 is connected by conductors H0 and III to the filament type cathode II2 of an electronic tube H3 and supplies energizing current thereto. The electronic tube H3 is a diode-triode-power amplifying pentode, for example, a type 1D8GT and includes a diode designated by the reference character C, a triode designated by the reference character D, and a pentode designated by the reference character E. The diode or rectifier C includes the filament cathode II: and an anode II4, the triode D includes the filament cathode III, a control electrode H5 and an anode H5, and the power amplifler pentode E includes the filament cathode II2, a controlelectrode H5 and an anode H0, and the power amplifler pentode E includes thefilament cathode 2, a control electrode III, a screen electrode, IIB, a suppressor electrode H0, and an anode I20. As shown the cathode H2 and the suppressor electrode II! are directly connected to each other within the tube H3.

The rectifler C is supplied with electrical en- I05 through a circuit which may be traced from the upper terminal of winding I 05 through a conductor I2I, anode II4, filament cathode III and a conductor I22 in which a resistor I23 is inserted to the lower terminal of winding I05, This circuit is conductive only during the half cycles of the alternating voltage supply source when the upper terminal of winding I05 is positive with respect to the lower terminal thereof due to the action of rectifier C. Thus, a potential drop is produced across resistor I23 in the direction to render terminal I24 positive with respect to terminal l25.

The triode D in the arrangement of Fig. 3 is utilized as a detector and is supplied with electrical energy from the transformer secondary winding I05 through an output circuit which may be traced from the lower terminal of the winding I05 through a conductor I20, anode II6, filament II2, a conductor I21, winding I09, a conductor I28 in which a resistance I29 is inserted and a conductor I30 .to the upper terminal of winding The conductivity of the output circuit of detector D is controlled by an input circuit one branch of which connects the control electrode I I5 to the grounded negative terminal I25 of the resistor I23 through a connection including a resistor I3I, a conductor I32, theswitch arm 62 of relay I6, and contact BI which is grounded. In this arrangement the contact 65' of relay I6 has been dispensed with. During the normal operation of the system, theswitch arm 62 is held away from thecontact 6| but is in engagement with the latter during the time of initiation of operation of the system in order to effect the initial energization ofrelay 50, and is moved out of engagement with thecontact 6| toeflect deenergization ofrelay 50 ii the proper conditions for operation exist between the flame electrode and ground. I

A second branch of the input circuit of the detector D connects the control electrode II5 throughconductor 63 to the electrode 653 which projects into the flame of thepilot burner 4. Thepilot burner 4 is connected to ground. As shown, theconductor 63 may desirably be provided with ashield 63A.

A third branch of the input circuit of" detector D connects the control electrode II6 to the fllament cathode II2 through a parallel connection including resistors I3I and I33 in one arm and a condenser I34 in the other arm. The resistor I33 corresponds to theresistor 58 of the Fig. 1

' arrangement and is normally shunted by a connection whiclt may be traced from the upper terminal of resistor I33 to conductor I32,switch arm 61,contact 68 andconductor 69 to the lower terminal of resistor I33. The resistor I 33 in this arrangement is provided for the same purpose for which theresistor 58 of the Fig. 1 arrangement is provided, namely, for the purpose of detecting the presence of high resistance leakage paths between the flame electrode 653 and ground. I a

The transformer secondary windings I06 and I05 are so wound on transformer I03 that the 4 detector D is conductive only on the half cycles when the rectifier C is non-conductive and vice versa. Thus, a pulsating potential dropisproduced across resistor I23 during the half cycles .when the detector D is non-conductive. The phase of this pulsating potential drop is such that it will be at a maximum value when the anode IIB of detector D is negative, and zero when the anode H6 oi! detector D is positive.

The pulsating potential drop or biasing potential produced across the resistor I23 is applied to the input circuit of the detector D through the flame, if present, and the polarity thereof is such as to cause a pulsating direct current to flow through the flame in the direction opposite to the direction of flame propagation. This input circuit may be traced from "the positive terminal I24 of resistor I23, conductor I22, resistors I 33 and HI shunted by condenser I34,

conductor 83, flame electrode 653,burner 4 to 6 ground. and through ground to the negative terminal I25 of resistor I23.

When a flame is not present at the burner and theswitch arm 62 and contact I are out of engagement and no other conductive path exists from the control electrode II5 to ground,

no bias potential will be applied to the control electrode H5 and the latter will then be at substantially the same potential as the cathode II2 since the control electrode H5 and cathode II 2 are directly connected by resistors I3I and I33. As a result, the detector D will then be conduc- \tive during the time the anode H6 is positive.

Upon the appearance of a normal flame the bias potential produced across resistor I23 is applied to the control electrode II5 through the resistance of the flame. The resulting now of current through the resistance of the flame produces a potential across resistor I 3| which is 5 storedion the condenser I34 and is of the proper polarity to apply a negative potential to the control electrode I I5 and thereby to reduce the current flow in the output circuit of the detector D. This potential is stored on the condenser I34 0 during the half cycles when the rectifier C is conductive and the detector D is non-conductive, and is maintained on the condenser I34 during the half cycles when the anode H5 is positive. This result is obtained by properly proportioning condenser I34 and resistor I3I. The result is that little or no current is conducted in the output circuit of the detector D during the condition of normal flame.

If a path more conductive than a flame exists between the flame electrode and ground, the charge which is stored on the condenser I34 during the half cycles when the anode H6 is negative will leak off through that conductive path during the same half cycles and the initial portion of the succeeding half cycles to thereby substantially reduce the potential on the condenser I34 during the same half cycle. Consequently, the potential applied to the control electrode I I5 i rendered substantially less negative and as a result current will flow in the output circuit of the detector D.

It will thus be noted that current flows in the output circuit of the detector D when there is no flame and when the flame electrode 553 is 35 grounded, and that little or no current flows in this output circuit when the normal flame is present at the burner.

The currentconducted by the detector D controls the potential difference between the termi- 0 nals of the resistor I29, which potential difference in turn is utilized to control the conductivity of the pentode power amplifier E. The output circuit of amplifier E is supplied with energyfrom the transformer secondary winding I01 through an output circuit which may be traced from the lower terminal of winding I" through a conductor I35, winding 49 ofrelay 50 which is shunted bycondenser 5|, winding 50 52 ofrelay 53 which is shunted bycondenser 54,

-meter 55, anode I20 of amplifier E, cathode III,

and a conductor I33 to the upper terminal of winding I01. As shown, the screen electrode III of amplifier E is connected by conductors I31 55 and I35 to the lower terminal of winding I01.

The conductivity 01' the amplifier E is adapted to be controlled in accordance with the potential drop across resistor I23 and thereby in accordance with the condition of the path between 0 the flame electrode 653 and ground. To this end the upp r terminal of the resistor I 28 is connected by a conductor I38 to the control electrode II! of amplifier E, and the lower terminal is connected by conductor I28 and the transformer secondary winding I09 to the filament II2. These connections including the resistance I29 are hereinafter termed the input circuit of the amplifier E and are made in such a manner that when current flows in theiresistor I29 from thedetector D, the amplifier control electrode III is biased negatively with respect to the cathode II2 by an amount determined by a difference in potential between the terminals of the resistor I29 and the potential impressed on the input circuit by the transformer secondary winding M9. The transformer secondary winding I09 tends to apply a positive potential to the control electrode ii'I relatively to the potential of the cathode H2 while the potential drop produced across the resistor I29 by the output current from detector D tends to apply a negative potential to said control electrode.

Therefore, when the detector D is conductive, the amplifier E will become non-conductive. Conversely when detector D is non-conductive, no potential difference will exist across the resistor I29 and the amplifler E will become conductive.

From the foregoing it will be seen that the arrangement of Fig. 3 is adapted to distinguish between normal flame conditions and abnormal conditions at the burner and operates to deenergize the system for an abnormal condition.

prevailing longer than a predetermined time. The further operation of the arrangement of Fig. 3 upon a call for heat by the thermostat iii and upon the appearance or disappearance of a flame at theburner 4 or upon the occurrence of an abnormal condition at the burner is substantially the same as that of thearrangement of Fig. 1 as described hereinbefore, and therefore, further description of the safety control provisions of the arrangement of Fig. 3 is believed unnecessary.

With respect to the operation of the combustion quality controlling provisions of the arrangement of Fig. 3. it is noted that when the system operation is first initiated theswitch arm 96 will be in the position shown, thevalve 26 will be in its open position and the fuel mixture accordingly will be lean, as in the arrangement of Fig.

1. This will result in the establishment of a blue flame at the burner which presents relatively low resistance to the flow of current through the flame, and accordingly, the effective current flow in the output circuit of the amplifier E and thereby to the relay winding 52 will be sufficient to close theswitch arm 98 against thecontact 91. This will effect energization of the motor valve in the proper direction to close the valve and thereby to reduce the supply of air to the mixingchamber 23. As the supply of air to the mixingchamber 23 is thus decreased, the fuel mixture is enriched, and as a result, resistance of the flame is increased and the current flow through the relay winding 52 decreases until it reaches a value at which theswitch arm 98 is biased by the action of gravity and the spring 99 out of engagement with thecontact 91, but is still held out of engagement withcontact 98. The fuel mixture will then have its proper proportions and the valve setting will remain constant until a change in fuel combustion quality produced by a change in fuel B. t. u. content for example, causes a change in the flame resistance. Upon a change in resistance of the flame, the current flow in the output circuit of the amplifier E is changed by a corresponding amount and in the proper direction to effect actuation of thevalve 26 in the proper direction to restore the quality of combustion of the fuel to the desired value.

It will be apparent from the foregoing explanation that the combustion control system described in Fig. 3 controls a fuel burner in accordance with the presence or absence of a flame at the burner and controls the proportions of a fuel mixture so as to obtain eflicient combustion. These functions, if desired, may b obtained separately. Ameter 55 calibrated in terms of fuel combustion quality may also desirably be provided in this arrangement, as in the arrangement of Fig. 1, to provide a visual indication of the quality of combustion of the burning fuel.

Subject matter disclosed in this application but not claimed herein is disclosed and is being claimed in my copending application, Serial Number 404,523, filed July 29, 1941.

While, in accordance with the provisions of the statutes, I have illustrated and described preferred embodiments of the present invention, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that some features of the present invention may sometimes be used with advantage, without a corresponding use of other features.

Havin now escribed my invention, what I claim as new and desire to secure by Letters Patent is:

1. A combined safety and quality control system for a fuel burner provided with fuel and air supply means and igniting means to establish a flame at said burner, a device to control the supply of fuel and air to said burner, a valve to control the mixture of fuel and air supplied to the burner, and a device to operate said valve, comprising in combination an electrode insulated from the burner and arranged to be connected to the burner by the flame and so positioned relatively to the burner as to contact the inner cone of the flame, a current responsive device to operate said first mentioned device, a current responsive device to operate said second mentioned device and having an operating characteristic such that when energized with current of a predetermined range it actuates said second mentioned device to open said valve and when energized with current of a different predetermined range it actuates said second mentioned means to close said valve, and means connected to said electrode and to the burner and including an energizing circuit adapted to be connected to a source of electrical energy to control the energization of said current responsive devices in accordance with the magnitude of the ohmic resistance of the path between said electrode and the burner and arranged to effect operation of said first mentioned device in the sense to prevent the supply of fuel to the burner when no flame is present at the burner and to effect operation of said second mentioned device in the sense to restore a desired quality of combustion of the flame upon variation in said quality of combustion. said last mentioned means including means to apply a potential on said electrode which is negative relative to the potential of the burner.

2. The combination of claim 1 wherein said electrode is mounted on the burner in such manner that the electrode and burner comprise a unitary mechanical assembly whereby the relation of said electrode and burner is flxed.

3. A combined safety and quality control system for a fuel burner provided with fuel and air supply means and igniting means to establish a flame at said burner, a device to control the supply of fuel and air to said burner, a valve to control the mixture of fuel and air supplied to the burner, and a device to operate said valve, comprising in combination an electrode insulated from the burner and arranged to be connected to the burner by the flame and so positioned v of a predetermined range relatively to the burner as to contact the outer cone of the flame, a. current responsive device to operate said first mentioned device, a current responsive device 'tooperate said second mentioned device and having an operating characteristic such that when energized with current it actuates said second mentioned "device to open said valve and when energized with current of a difierent predetermined range it actuates said second mentioned means to close said valve, and means connected to said electrodeand to the burner and including an energizing circuit adapted to be connected to a source of electrical energy to control the energization of said current cordance with the magnitudeof the ohmic resistance of the path between said electrode and the burner and arranged to effect operation of said first mentioned device in the sense to prevent the supply of fuel to the burner when no name is present at the burner and to effect operation of said second mentioned device in the 4. The combination ofclaim 3 wherein said electrode is mounted on the burner in such manner that the electrode and burner comprise a unitary mechanical assembly whereby the relation of said electrode and burner is fixed.

5. A combined safety and quality control system for a fuel burner provided with fuel and air supply means and igniting means to estab-,

dition and adapted when deenergized to actuate said control device toits second mentioned operating condition,a current responsive device to operate said mixture control means, and means connected to said electrode and to the burner and including an energizing circuit adapted to be connected to a source of electrical energy to control said current responsive devices in accordance withthe magnitude of the ohmic resistance of the path between said electrode and the burner. v

6. A combined safety and quality control system for a fuel burner provided with fuel and air supply means and igniting means to establish a flame at the burner, a device to control the path of the flame and arranged to be connected to the burner by the flame, a current responsive device to operate said first mentioned device, a current responsive device to operate said second mentioned device and having an operating characteristic such that when energized with a current of a predetermined range it actuates said second mentioned device to open said valve and when energized withcurrent cl 9. different predetermined range it actuates said second mentioned device to close-said valve, and means connected to said electrode and to the burner and including an energizing circuit adapted to be connected to a source of electrical energy to control the enerelectrode and the burner.

7. A combined safety and quality control system for a fuel burner provided with fuel and trol the mixture of fuel and air supplied to the burner, comprising in combination an electrode insulated from the burner and positioned in the to a source of electrical energy to control said operating devices in accordance with the magnitude of the ohmic resistance of the conductive path between said electrode and the burner.

8. A combined safety and quality control system for a fuel burner provided with fuel and air supply means and igniting flame at the burner, a device to control said fuel supply means, and means to control the mixture air supplied to the burner, comprising an electrode insulated from the burner and positioned in the path of the flame and arranged to be connected to the burner by the flame, and means connected to said electrode sistance of the burner.

at the burner, and means to control the mixture of fuel and air means and igniting means to estab- 4 means to establish a CERTIFICATE OF connze'non. 4'

' October at 19th,

Patent No. 2,561,291 7 HARRY S. JONES.

that error appears in the It is hereby certified iring correction red patent requ "it is" read ---in ite--;page 5,

first column, 111108,

of the case in the Patent Office.

th day of Ma A. D. 1915.

Signed and seated this 15 Leslie Frazer (Seal) Acting Comieaioner of 'Petent e.

printed" ete e iifieetienf as follows: Peg eiltlfi ret first cd tmiifi me' for I s Pateh't' shioflid bm g hqaac;

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