US2445051A - Electronic burner control apparatus - Google Patents

Description

July 13, 1948. J, W'LSON 2,445,051

ELECTRONIC BURNER CONTROL APPARATUS Filed 001:. 19, 1942 3nventor JOHN M. W11 50" Patented July 13, 1948 ELECTRONIC BURNER CONTROL APPARATUS John M. Wilson, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application October 19, 1942, Serial No. 462,558

Claims.

1 The present invention is concerned with burner control apparatus and more particularly with apparatus of the type employing a thermionic am plifier.

Various burner control mechanisms employing thermionic tubes have been devised. These tubes usually rely upon the change in conductivity of a flame gap or the dilference in illumination of a photoelectric cell by the burner flame to control the grid bias of the amplifier. With such thermionic amplifiers, it is undesirable to maintain the heater circuit for the amplifier energized continuously at the degree of energization which must be maintained during operation of the amplifier. Thus, it becomes necessary to increase the degree of energization of the heater circuit upon the apparatus being placed into operation. In the past, this has been accomplished by the use of switching mechanisms associated with the heater circuits. The disadvantage of such a switching mechanism is that it is very difficult to insulate it adequately from ground and often a leakage path may be established between the cathode and ground by reason of this switching mechanism in the heater circuit. Since the operation of such apparatus often requires the maintenance of a considerable potential difference between the cathode and ground, the presence of a conductive path between cathode and ground even of extremely high impedance will resultin faulty operation of the apparatus.

An object of the present invention is to provide a burner control system of the type described in which the degree of energization ofthe heater circuit of the thermionic amplifier is changed without employing a switching mechanism associated with the heater circuit.

A further object of the present invention is to provide a burner control system of the type discussed in which the heater circuit is energized by a secondary winding of a transformer which is provided with means for normally preventing the secondary from supplying suflicient power to the heater circuit to energize the same adequately and in which means operable independently oi the heater circuit is eifective to increase the power output of the secondary winding.

A still further object of the present invention is to provide such an arrangement in which a magnetic shunt is provided between the primary winding of thetransformer and the secondary winding connected to the heater circuit and in which means is provided for overcoming the effect of this magnetic shunt.

A still further object of the present invention is to provide such a burner control system in which there are two primary windings on the transformer which supplies power to the heater circuit, and in which one of these primary windings is normally energized and the other is energized only upon the burner apparatus being placed into operation.

A still further object of the present invention is to provide such an arrangement in which the transformer previously referred to is provided with additional secondary windings for supplying power to a means biasing the amplifier and for supplying power to the output circuit of the amplifler, and in which the power output of all of these secondary windings is normally maintained at a level inadequate for proper operation Of the apparatus and is increased upon the burner apparatus being placed into operation to a proper level for normal operation of the system.

A still further object of the present invention is to provide such a burner control mechanism in which the transformer is provided with a further secondary winding which supplies power for the operation of the relay, the voltage existing across this secondary winding being relatively constant regardless of whether the relay is energized or not.

It is a further object of the present invention to provide a circuit employing a thermionic amplifier in which the heater circuit is norm-ally partially energized, with provision for bringing the level or" energization to a desired value when necessary to operate the apparatus.

A still further object of the present invention is to provide a thermionic amplifier circuit in which a new and novel type of transformer is employed for supplying power to the output circuit thereof, the heater circuit thereof, and to a means for biasing the input circuit thereof, in which provision is made for changing the energization of the heater circuit, the input circuit and the output circuit without the use of switching means associated with the circuit.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims and drawing in which my improved burner control apparatus is shown connected to a burner and to a main controlling thermostat to constitute a burner control system.

Referring to the specific form of the apparatus shown in the drawing, the burner control device of the present invention is schematically indicated as enclosed within a housing Ill. Secured to this housing ID are various terminals ll, l2, l3, l4, l5, l6, l7, l8, and IS. The terminals H and I2 are power terminals and are connected by conductors 28 and H to line wires 22 and 28, respectively. leading to any suitable source of power (not shown). The terminals I3. i4 and I5 are thermostat terminals and are connected to a room thermostat 25. The terminals I8 and Il are burner terminals. The terminal I8 is an ignition terminal, and the terminal I8 is a flame electrode terminal.

The thermostat 25 is of conventional construction and comprises a bimetallic element 21 to which is secured a contact blade 28. The contact blade 28 is adapted to engage fixed contacts 28 and 80. As indicated by the legends C and H adjacent the drawing, the bimetallic element 21 is secured to the contact arm 28 in such a manner that upon a drop in temperature, the contact arm 28 is moved in the direction of the fixed contacts 28 and 80. The contact arm 28 is more widely spaced from contact 80 than from contact 28. Thus, upon a drop in temperature, the contact arm 28 moves into engagement with contact 28 first and then after a predetermined further drop in temperature moves into engagement with contact 30.

The burner control apparatus is employed to control the operation of a burner generally indicated by the reference numeral 32. This burner comprises a burner nozzle 83 through which an atomized mixture of fuel and air is forced. Associated with the burner 82 is a blower driven by a motor 34. A suitable ignition means 85 is provided with the burner 32 and serves to ignite the mixture of fuel and air forced out through the burner nozzle. I

The burner control mechanism of the present invention will now be described. This mechanism generally comprises an electronic discharge device 40, a transformer H, a first relay 42, a second relay 88, and a thermal safety switch H.

The electronic discharge device 40 is of the double triode type, having a double cathode l8 energized by a heater 50, consisting of two series connected heaters. The first triode comprises the cathode 48, a grid 52, and an anode 58. The second triode comprises the same cathode 48, a grid 88, and an anode 56. As is usual, the various elements are housed within a suitable envelope 51.

Transformer H is of novel design and is employed not only to supply power for the control mechanism but also to exert a controlling effect, as will be apparent from the subsequent description. This transformer comprises a core 88, consisting of a pair of side legs 60 and SI, 8. pair of end legs 62 and 63, and a center leg 84. Located on the end leg 82 are a primary winding 88 and a low voltage secondary winding 81. Located on the other end leg 68 is a second primary winding 68 and a further low voltage secondary winding l0. Located on the center leg 84 are a low voltage secondary winding II and a high voltage secondary winding 72. While the invention is not in any way limited to the particular number of turns of the various windings, in one particular embodiment of the invention it was found desirable to employ 1600 turns in windings 86 and 88, 400 turns in winding 81, 250 turns in winding III, 300 turns in winding ll, and 4400 turns in winding 12. The primary winding 88 is permanently connected by conductors 18, I1 and I8 to terminals II and II, which as previously explained, lead to line wires 22 and 28. Thus, the primary 86 is constantly energized.

The relay 82 comprises a relay coil 88 and a pair of cooperating switch arms II and 82. The switch arms 8| and 82 are adapted to engage contacts 88 and 84. Normally the switch arms 8I and 82 are biased away from contacts 88 and 84 but upon energization of coil 88, the switch blades are moved into engagement with these contacts.

Relay 48 comprises a relay coil 88 and a pair of switch blades 81 and I8. Cooperating with switch blade 81 are a pair of switch contacts 88 and 88. Cooperating with switch blade 88 is a fixed contact 82. When the relay coil 88 is deenergized, the switch blades 81 and 88 are moved by any suitable biasing means such as gravity into engagement with contacts 88 and 82. Upon energization of relay coil 86, the switch blades 81 and 88 are moved out of engagement with contacts and 82 and switch blade 81 is moved into engagement with contact 88. The relay coil 88,'

as will be explained in more detail later, is connected in the plate circuit of the triode including anode 88 and cathode 48. The output current flowing through this relay coil 88 will be pulsating. Accordingly, a condenser 88 is connected in parallel with this coil to filter out the alternating component of this current so as to smooth the current flowing through coil 88.

The safety switch 84 may be of any suitable type. Thus, the safety switch may take the form shown in the patent to John M. Wilson 2,290,399, granted July 21, 1942. As shown schematically in the drawing for purposes of illustration, the safety switch comprises a pair of switch blades 86 and 81 which are biased apart and are held in engagement by a bimetallic element 88. Associated with the bimetallic element is an electrical heater element 88. The bimetallic element 88 is adapted to warp to the right upon being heated. Thus, upon heater 88 being energized sufficiently long, the right-hand end of the bimetallic element 88 is moved to the right so as no longer to be underneath switch blade 81. Upon this happening, switch blade 81 is free to move away from switch blade 86. Thereafter, it is necessary to manually reset the switch before the safety switch can be reclosed.

Reference numerals I08 and I designate a pair of condensers. These condensers are charged in one direction or the other, and the charge on these condensers determines to a large extent the bias of grids 52 and 55. Resisters I05 and I08 are provided and these resisters cooperate with condenser I08 to constitute a filter network.

Reference numerals IIll, III8 and I88 are employed to designate resistors which function as protective resistances in circuits which will be referred to later.

A flame electrode III! is disclosed adjacent the burner flame in series to control the biasing grid 52 in accordance with the conductivity of the ap between electrode III and burner 88.

Operation The various elements are shown in the position which they occupy when the temperature to which thermostat 28 is exposed is at or above the desired value. The burner 32 is not in operation and the various elements of the control mechanism are in the condition which they assume when the system is shut down.

Under these conditions, the heater 58 associated with cathode I8 is slightly energized by reason of its connection through conductors I II and II! with secondary winding 18. Despite the fact that the primary 88 is permanently energized and despite the fact that secondary is constantly connected to the heater element 50, the heater is only energized partially under these conditions. This is due to the fact that the flux produced by primary winding 88 is able to fiow through both center leg 84 and end leg 83. The impedance in series with windings H and 12 on center leg 84 is considerably higher than the impedance of heater 50. As a result, less impedance is oifered to theilow of flux through leg 64 than through 7 tain the voltage of secondary 10 at a value sufficient to energize heater 50 properly.

During the shut-down period, the grid 52 is maintained at a potential considerably "below cathode 49 due to the charge on condensers I03 and I04. Referring to condenser I 04, it is possible for current to flow through condenser I04 during each half cycle that the grid is positive with respect to cathode 48, this current how being through a circuit as follows: from the lefthand terminals of secondary 1I through conductor II1, condenser I04, conductor H8, resistor I01, conductor II9, grid 55, cathode 49, and conductors I20, I2I and I22 back to the right-hand terminal of secondary 1I. During the opposite half cycle in which the grid is negative with respect to cathode 49, current cannot flow due to the fact that the grid to cathode path is conductive only when the grid is positive with respect to the cathode. During the half cycle in which grid 55 is positive with respect to cathode 49, grid 52 is also positive with respect to cathode 38. Thus, during this half cycle, current flows through condenser I04 over the following circuit: from the left-hand terminal of secondary II through conductor II1, condenser I04, conductor II8, resistor I05, conductor I25, resistor I06, conductor I21, grid 52, cathode 49, and conductors I20, Iii and I22 back to the right-hand terminal of secondary 1 I. Thus, because of the rectifying action of the grids and cathodes of both triodes, current flows through the condenser I04 in such a direction as to cause the upper terminal of the condenser I04 to become charged negatively and the lower terminal positively. Because of the fact that the upper terminal of condenser I03 is connected to the upper terminal of condenser IN, the upper terminal of condenser I03 likewise becomes charged negatively and this negative charge on condensers I04 and I03 operates to bias grid 52 negatively. The fluctuations in the value of the charge on condenser I04 are eliminated through a filter network including the resistors I05 and I06 and the condenser I03.

Because of the limited energization of heater 59 and because of the bias placed upon grid 52, it is impossible for current to flow through the output circuit of the upper triode despite the fact that this output circuit has a limited voltage applied to it constantly through the following circuit: from the right-hand terminal of secondary 12 through conductors I29 and I36, relay coil 85, conductors I3I and I32, anode 53, cathode 49, and conductors I20, I2I and I35 to the center tap of secondary I2. The fact that no current flows through this circuit is due not only to the fact that the heater 50 is not fully energized and to the fact that the grid 52 is biased negatively but also to the division of flux between the two legs 63 and 84 so that full flux does not flow through the center leg 84 on which the secondary winding 12 is located. As a result, full voltage 6 is not applied to the output circuit of the triode just traced.

both contacts 29 and 38. When this happens,

an energizing circuit is established to relay coil 80 as follows: from the left-hand terminal of secondary 81, through conductor I31, terminal I3, conductor I38, contact 29, contact blade 28,. contact 30, conductor I39, terminal I5, conductor I40, contact 90, switch blade 81, conductor I18, safety switch heater 99, conductor I42, relay coil 80, safety switch blades 96 and 91, and conductor I44 back to the right-hand terminal of secondary 61. The establishment of this circuit causes relay coil 80 to be energized with the result that switch blades 8| and 82 aremoved into engagement with contacts 83 and 84. The engagement of switch blade 8| with contact 83 results in a holding circuit being established to relay coil 80 as follows: from the left-hand terminal of secondary 81 through conductor I31, terminal I3, conductor I38, contact 29, contact blade 28, bimetallic element 21, conductor I46, terminal I4, conductor I I'I, contact 83, switch blade BI, conductor Hi8, safety switch heater 93, conductor I42, relay coil 80, safety switch blades 95 and 91, and conductor I44 to the other terminal of secondary winding 61. It is to be noted that the circuit just traced is independent of contact 30. Thus, it is assured that the circuit to relay coil 80 will not be interrupted until the temperature has risen sufficiently to cause disengagement of contact blade 28 from contact 29. In this way, it is assured that the relay will not chatter upon insecure engagernent of contact blade 28 with contact 30, due to slight fluctuations in temperature.

The engagement of switch blade 02 with contact 84 results in a circuit being established to the oil burner motor 34 as follows: from power terminal II through conductor I50, switch blade 82, contact 8 3, conductors I5I, I52 and I53, burner terminal I'I, conductor I54, burner motor 3t, conductor I55, burner terminal I6, and conductors I55, I5I and 18 back to the other power terminal I2. The establishment of this circuit causes the burner motor to be placed into operation with the result that a mixture of fuel and oil is forced out through the nozzle 33.

The closure of switch 82 with contact I I also results in the establishment of the following circuit to the ignition means 35: from power terminal II through conductor I50, switch blade 32, contact 84, conductor I5I, switch blade 88, contact 82, conductor I59, ignition terminal I8, conductor I60, the ignition means 35, conductors IGI and I55, burner terminal I8, and conductors I55, I51 and It to the other power terminal I2.

' The, establishment of this circuit to the ignition a result of the establishment of the circuit Just traced, causes the voltage of secondaries 1|, 1| and 12 to be raised to the normal values for the secondaries. Since all of the flux produced by primary 89 flows through the leg 83 on which secondary 10 is located, it will be obvious there is no opportunity for the flux generated by the primary 89 to be by-passed around secondary 10 as was the case in connection with the flux generated by primary 88. Furthermore, it is impossible for any of the flux generated by primary 88 to pass through leg 83 as was previously the case. The result is that the full output of flux of both windings 68 and 89 flows through the center leg 84 so that both windings II and 12 are fully energized. The heater 50 is now fully energized so as to raise the cathode 49 to the desired emitting temperature. The condenser I04 now has the normal voltage of secondary 1| applied to it so that the biasing effect of this condenser is at the value required for normal operation. The potential of secondary winding 12 is also at its normal value so that full voltage is applied to the anode circuits of both triodes.

As previously indicated, the establishment of circuits to the burner and to the ignition means resulted in all of the conditions being established that are necessary to the establishment of a burner flame. The function of the apparatus housed within the housing I is to detect the presence of this flame. As previously noted, the condenser I04 becomes charged in such a manner that it biases grid 52 below the cut-oif potential. When flame appears, a new energizing circuit is established to the condenser I04 and also to condenser I03. Referring to condenser I04, this circuit extends from the left-hand terminal of winding 12 through conductor I69, resistor I08, resistor I08, conductor I1I, terminal I9, conductor I13, flame electrode IIO, burner nozzle 33 to ground at I16, ground connection I18, resistor I05, conductor H8, condenser I04, conductor II1, secondary H, and conductors I22 and I85 to the center tap of secondary 12. It will be noted that in the circuit just traced, the condenser I04 is connected in series with the flame gap and that portion of secondary 12 between the center tap and the lefthand end of the secondary. The full voltage of the left-hand portion of secondary 12 is not applied to the flame gap, however, since secondary H is also included in this circuit. The voltage that is hence applied is the voltage across the left-hand portion of secondary 12 minus the voltage of secondary H. a consideration of the relative values of the various windings givenin an earlier portion of the specification, the voltage of secondary H is relativcly small as compared with that existing across the left-hand portion of secondary 12. Hence, the voltage applied to this circuit is substantially the relatively large voltage that exists across the left-hand portion of secondary 12.

In the circuit traced in the preceding paragraph, the circuit was traced from the left-hand terminal of secondary 12 through flame electrode IIO to ground and through condenser I84 in a direction opposite to which the circuit was traced in describing the biasing action of condenser I04. While a certain amount of current flows through the flame in both directions, the current flow through the flame'in the direction traced is much greater than that in the opposite direction. This is due to the rectifying property of the flame. It is well established that electrons tend to flow to a greater extent in the actual direction of propagacondenser I03 as follows: from the left-hand end As will be apparent from of secondary 12 through conductor I 89, resistor I08, resistor I09, conductor Ill, terminal I8, conductor I13, flame electrode I I0, burner 83, ground connections I15 and I16, conductor I25, condenser I03, and conductors I 2I and I88 to the mid point of secondary 12. As in the case of condenser I04, this new circuit is in the opposite direction to the circuit traced in connection with the biasing operation. Since the current flow in the direction just traced through the flame is greater than in the opposite direction, the.condenser I03 becomes either charged in the direction opposite to that previously considered for biasin purposes or at least to a considerably lesser extent in the same direction so that the grid potential is above the cut-off potential.

The result is that condensers I03 and I04 will no longer bias the grid 52 sufliciently negative to cause deenergization of relay coil 88. Thus, sufllcient current flow takes place in the output circuit of the triode including anode 53 and cathode 49 to cause relay coil 86 to be energized with the result that switch blades 81 and 88 are moved out of engagement with contacts 90 and 92 and switch blade 81 is moved into engagement with contact 89.

The movement of switch blade 81 out of engagement with contact 90 interrupts the original energizing circuit for relay coil 80. In view of the fact, however, that the holding circuit has been previously established by the engagement of switch blade 8i with contact 83, the relay coil 80 remains energized.

The engagement of switch blade 81 with contact 88 results in a new energizing circuit to relay coil 80 as follows: from the left-hand terminal of secondary 81 through conductor I31, terminal I3, conductor I38, contact 28, contact blade 28, bimetallic element 21, conductor I48, terminal I4, conductor I41, contact 83, switch blade 8I, conductors I48 and I18, switch blade 81, contact 89, conductors I19 and I42, relay coil 80, thermal switch blades 96 and 81, and conductor I44 to the other terminal of secondary 81. It is to be noted that this new circuit does not include the heater 99 and that the heater 88 is eflectively shunted out by conductor I18, switch blade 81, contact 89 and conductor I19. The result .is that heater 99 is substantially deenergized so that bimetallic element 98 is no longer heated. Because of the shunting of heater 88, switch blades 88 and 91 are allowed to remain in engagement to permit the system to continue in operation. In other words, since the flame has been properly established across the flame gap, it is desired that the burner remain in operation as long as the thermostat 25 is calling for heat and the flame persists.

The separation of switch blade 88 from contact 92 interrupts the circuit to the ignition means 35 previously traced. The result of such interruption is that the ignition means is now deenergized. The system illustrated in the drawing is of the intermittent ignition type and in such any desired value.

systems, it is customary todoenergise the ignition means as soon as. flame is established.

Assuming that the flame does not go out, the system will now continue in operation until such time as the room thermostat is completely satisfled. In other words, it will remain in operation until contact blade has separated'from both contacts 2! and III. when this happens, all of the circuits previously traced to relay coil I! are interrupted with the result that switch blade I! separates from contact it to cause deenergization of the oil burner and of primary winding I. The deenergization of primary winding 09 reduces the energization of the cathode heater '0 to a value lower than that necessary to cause operation of the cathode. The deenergization of primary winding it also reduces the voltage applied to the output circuit of the upper triode and reduces the amount of voltage applied to the biasing means. In other words, the various voltages applied to the flame detecting apparatus are substantia'ily reduced as soon as the oil burner motor is stopped and the charge on condenser I" resumes a value such as to cause the relay coil 86 to be'deenergized.

While the operation has been discussed in connection with the case where the heater l is substantially deenergized when the thermostat 2! is satisfled, it is to be understood that the energize.- tion of the heater It may be caused to assume In many cases, it may be desirable to maintain heater ll partially energized to a substantial extent when the thermostat is satisfied. The advantage of this is that the time required for the cathodes to be heated when there is a call for burner operation is relatively short. Since the only appreciable delay in the response of the apparatus to the establishment of a flame is that due to the heating of the oathode 50, any reduction in the ,heating time of cathode 50 reduces the time necessary for the apparatus to be placed in running position. Thus, in certain cases'when it is desirable to have eitremely short timing for the thermal safety switch, it is preferable to provide for a substantial partial energization of heater 5. when the thermostat is satisfied. This can be accomplished either by increasing the reluctance of center leg 64 with respect to leg 63 or by making primary winding 80 relatively large as compared with primary winding '9.

Operation if flame is extinguished or is not initially established If after normal burner operation has been established, the flame is extinguished for any reason, the path through the flame gap is interrupted so that the condensers I04 and I03 again become charged in such a manner as to bias grid 52 negatively. This results in relay coil 86 being deenergized so that switch blade 01 is moved out of engagement with contact 09 and switch blade 88 is moved into engagement with contact 92. Themovement of switch blade 81 out of engagement with contact 89 breaks the shunt circuit around the safety switch heater 99. As a result, the safety switch again starts the timing cycle at the end of which the switch blades 96 and 91 are opened if combustion has not been established. The re-engagement of switch blade 88 with contact 92 re-establishesthe circuit to the ignition means. If the conditions are still proper for initiating combustion, the re-energized ignition means will relight the burner and the cycle previously discussed will be repeated.

If, however, the interruption of the burner flame tion of proper burner operation without manu l intervention, the safety switch 44 will operate to shut down the system at the-end of a predetermined period of time.

Likewise, if flame should not be established initially upon a call for heat by the thermostat, the safety switch heater would remain energised sufliciently long to shut down the system.

Presence of other conditions than flame or normal absence of flame The electronic apparatus of the present application is able not only to diflerentiate between a normal flame and a normal absenceof a flame but is able to differentiate between flame conditions and various types of impedance conditions across the flame gap that might otherwise falsely indicate the presence of a flame. For example, if the apparatus were operated solely in accordance with the magnitude of the impedance across the flame gap, a short circuit condition would cause the system to operate as though a flame were present. This is extremely undesirable be-,

cause it may happen that the flame electrode accidentally engages the burner. Again, it often happens that after long periods of use, carbon forms around the flame electrode until a point is reached such that the flame gap is actually bridged by the carbon. Under certain conditions, the impedance of the gap to the carbon may actually be almost identical to that of the impedance when a flame is present. Again, it is necessary to distinguish between a normal flame and such a high resistance impedance.

Consider first the situation in which, due to the accumulation of carbon or for other reasons, an impedance exists across the flame gap which is substantially the same in magnitude as the impedance of a normal flame. Under these conditions, the current flow across the flame gap and through condensers I04 and I" will take place. However, the impedance of the flame gap is not rectifying so that the current flow is the same in both directions. It is essentially nothing more than alternating current and the potential impressed across the condenser I due to this current i'low therethrough has no direct current component whatsoever. Thus, the direct current potential across condensers I03 and I is exactly the same as that due to the current flow through the grid circuit. As previously pointed out, this potential causes the grid 52 to be biased to a point where relay coil 88 is deenergized.

When a short circuit condition exists between the flame electrode and ground, it is obvious that the impedance is again a non-rectifying impedance so that the direct current potential across condensers IM and I03 tends to be the same. However, certain other factors enter into the operation due to a decrease in impedance across the flame gap. It will be noted that as the impedance between flame gap H0 and ground becomes less and less, the grid 52 tends to be connected through a relatively low impedance path directly to the left-hand end of secondary I2, this circuit being as follows: from grid 52 through conductor I21, resistor I08, conductor I25, ground connection I16, ground connection I15, burner nozzle 33, flame electrode IIII, conductor Ill, terminal I9, conductor ITI, resistors I0! and I08, and conductor I69 to the left-hand end oi secondary 12. Since the anode 53 is connected to the right-hand end of secondary 12, the voltage impressed across 11 grid 52 by this connection tends to be 180 degrees out of phase with the voltage between the anode and cathode. Were it exactly 180 degrees out of phase, it would bias the grid 52 even more negatively and hence prevent the flow of current through relay coil 86. However, the condenser I64 and the flame impedance in effect form a phase shifting bridge, to one terminal of which grid 52 is connected. The cathode 46 is connected to another terminal. The result is that the increased voltage applied to the grid as a result of the decrease in impedance across the flame gap tends to be shifted in phase so that it is no longer 180 degrees out of phase with respect to the voltage applied to anode 56. Were there no complicating factors, this voltage would tend to be dis- I placed in phase to such an extent as actually to raise the potential of grid 52. However, the effect of the triode including anode 56 and cathode 49 is present to an increasing extent as the flame gap resistance is decreased. It is to be noted that any decrease in flame gap resistance tends to connect grid 55 to a point closer in potential to that of anode 56 through a circuit including conductor II9, resistors I61 and I65, ground connections I16 and I15, burner nozzle 33, flame electrode II6, conductor I13, terminal I9, conductor I'II, resistor I69 and conductor I84. Hence, the anode current of this triode is increased. This tends to produce a corrective shift in phase 50 as to bring the grid voltage more nearly 180 degrees out of phase with the potential applied to anode 53. Due to the cooperative action of anode 56, the triode including anode 53 and the cathode 49 remains sufficiently non-conductive so as to prevent energization of rela coil 86.

Summary It is to be noted that in the operation traced above the transformer 4i functions not only to supply power to the flame detecting apparatus but also to reduce the amount of power supplied to various portions thereof when the thermostat is satisfied without reducing the amount of power supplied to the relay coil 86 upon a call for heat. Since the secondary 61 is mounted on the same leg as the constantly energized primar winding 66, the full amount of magneto-motive force generated by Winding 66 is available for inducing a voltage in secondary 61. Because of this action of the transformer 4|, it is unnecessary to have any switching connections between the various control circuits and the heater circuit. If a switch blade positioned by relay coil 86 were used to change the circuit connections of either the heater circuit, the biasing circuit, or the anode circuit, there would bea danger of a high voltage leak through such switches to ground. It is very diflicult to insulate a relay blade adequately from ground where very high potentials are involved such as is employed in connection with the flame gap. Obviously, any leakage to ground at undesired points will influence the operation of the system since the proper operation of the system depends upon the existence of an impedance of the right character and magnitude between the flame electrode and ground. By utilizing the transformer itself as a switching means, this difficulty is overcome. The only switching action performed in connection with any of the windings of the transformer is in connection with primary winding 69 and the secondary winding 61. These windings are entirely separate from the windings employed for energizing the various portion O 12 the circuits directly associated with the electronic device 46.

While I have disclosed the use of a flame electrode for detecting the presence of a flame, a photoelectric cell could readily be substituted for the flame gap. Such a. cell due to its rectifying properties, when exposed to a source of light such as a burner flame, introduces a rectifying effect similar to that of the flame itself. For this reason, wherever the expression means exposed to a burner flame" or similar expression is employed in the appended claims, it is to be understood that this term is to be construed broadly enough as to be readable upon operation with either a photoelectric cell or a flame gap.

In one particular embodiment of my invention, it was found dsirable to employ a one megohm resistor for resistor I65, a flve megohm resistor for resistor I61, 8. two megohm resistor for element I68, a ten thousand ohm resistor for element I66, and a one megohm resistor for member I 69. The condenser selected for condensers I63 and I64 each had a capacity of 0.02 microfarad. A 0.5 microfarad condenser was employed for element 93. The number of turns for the various windings of transformer 58 in this particular embodiment of the invention have already been referred to. It is to be understood that the invention is in no way limited to these particulai values and that they are given merely to indicati more clearly the nature of one embodiment of thi invention.

In general, while I have disclosed a specific embodiment of my invention for purposes of illustration, it is to be understood that m invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. In burner control apparatus; a relay for controlling a burner; apparatus for detecting the presence of a burner flame; said apparatus comprising a thermionic discharge device having an anode, a control element, and a cathode and heater circuit therefor for rendering said cathode electron-emissive to a predetermined degree; a transformer having a normally energized primary winding, a second normally deenergized primary winding, and at least two secondary windings; a first of said secondary windings being connected to said heater circuit; circuit connections between a second of said windings, said cathode, and said control element, said circuit connections being effective normally to bias said control element with respect to said cathode so that said discharge device is effectively non-conductive; means adapted to be exposed to a burner flame and operative to overcome the effect of said biasing connections suflioiently to make said discharge device conductive; said flrst and second secondary windings normally being incapable of supplying sufficient power to said heater and biasing circuits to cause them to function in the manner above recited; and means controlled by said relay effective upon the latter being energized to cause the energization of said second primary winding so as to cause the power output of both secondary windings to be increased to desired values for proper operation of said apparatus as above recited.

2. In combination, an electronic amplifier having a control electrode, a relay, a plurality of sources of alternating power, biasing means adapted to maintain said control electrode at a potential such that said amplifier is effectively non-conductive, connections between a first of said sources of power and said biasing means, connections betweena second of said sources of power and the output circuit of said amplifier, a connection between said control electrode and a point on said second source such that the connection tends to aid said biasing means, said connection including a gap adapted to be bridged by an impedance, means associated with said connection and effective when said impedance is rectifying to maintain said control electrode at a different potential such that said amplifier is effectively conductive, said sources of alternating power normally being continuously operative but insufficient in power output to energize said biasing means and said output circuit to the extent necessary for operation of. said amplifier as above recited, and means controlled by said relay for increasing ,the power output of both sources of power to the extent necessary to cause operation of the amplifier in the manner above recited.

, 3. In combination, a thermionic amplifier having an anode, a control electrode, a cathode, and a heater circuit therefor for rendering said cathode electron-emissive to a predetermined degree, a relay, a plurality of sources of alternating power, connections between a first of said sources of alternating power and said heater circuit, biasing means efiective'normaliy to maintain said control electrode at a potential such that said amplifier is effectively non-conductive. connections between a second of said sources of power and said biasing means, a third of said sources of power being connected in series with the anode and cathode of said amplifier, a connection between said control electrode and a point on said second source such that the connection tends to aid said biasing means, said connection including a gap adapted to be bridged by an impedance, means associated with said connection and effective when said impedance is rectifying to maintain said control electrode at a different potential such that said amplifier is effectively conductive. said sources of alternating power normally being continuously operative but insufficient in power output to energize said heater circuit, said output circuit, and said biasing means to the extent necessary for operation of said amplifier as above recited, and means controlled by said relay for increasing the power output of all of said sources of power to the extent necessary to cause operation of the amplifier in the manner above recited.

4. In combination, a thermionic amplifier having an anode, a control electrode, a cathode, and a heater circuit therefor for rendering said cathode electron-emissive to a predetermined degree, a relay, a transformer having a normally energized primary winding and a plurality of secondary windings, one of said secondary windings being connected to said heater circuit to energize the same, biasing means adapted to maintain said control electrode at a potential such that said amplifier is effectively non-conductive, connections between a second of said secondary windings and said biasing means, connections between a third of said windings and the anode and cathode of said amplifier, a connection between said control electrode and a point on said third secondary winding such that the connection tends to aid said biasing means, said connection including a gap adapted to be bridged by an impedance, means associated with said connection and effective when said impedance is rectifying to maintain said control 14' electrode at a diflerent potential such that said amplifier is effectively conductive, said first, second and third secondary windings normally supplying insumcient power to energize said heater circuit, said output circuit, and said biasing means to the extent necessary for operation of said amplifier as above recited. and means controlled by said relay operative independently of said normally energized primary winding to increase the power output of said secondary windings to the extent necessary to cause operation of the amplifier in the manner above recited.

5. In combination, a thermionic discharge device comprising a cathode and a heater circuit therefor for rendering said cathode electronemissive to a predetermined degree, an electrically operatedrelay controlled by said discharge device, a transformer comprising a core, a secondary winding on said core and connected to said heater circuit to energize the same, a primary winding on said core, and a magnetic shunt between said primary and secondary windings effective to bypass part of the flux generated by said primary winding so that the power supplied to said heater circult by said secondary winding is, normally sufilcient to heat said cathode to a value less than that required for said cathode to be electron-emissive to said predetermined degree such as necessary to enable said discharge device to cause operative energization of said electrically operated relay, and means for forcing further flux through said secondary winding to cause adequate energization of said heater circuit to cause the cathode tolbe electronemissive to said predetermined degree.

1. In a burner control system, a burner, means for controlling the delivery of fuel to said burner, a main control'device controlling said fuel controlling means, apparatus for detecting the presence of a burner flame, said apparatus comprising a thermionic discharge device having a cathode and a heater circuit therefor, energizing means normally constantly connected to said heater circuit but incapable of adequately energizing said heater circuit, and means independent of said heater circuit operable upon said control device calling for operation of said fuel controlling means to increase the power output of said energizing means to a value such that said heatercircult is adequately energized.

'1. In combination; an electronic discharge device having input and output circuits; a transformer having a core comprising at least three portions one of which constitutes a magnetic shunt between the second and third portions, a first primary winding on the second portion, secondary windings on the third portion, and a second primary winding on the magnetic shunt portion; normally permanent connections between said first primary winding and a source of alternating power; normally permanent eonnections between said secondary windings andsaid input and output circuits; and means for selectively controlling the energization of said second primary winding by said alternating source of power to control the power supplied to said input and output circuits by said secondary windings.

4 8. In combination; an electronic discharge device having an output circuit esigned for the application of a predetermined voltage thereto; a transformer having a core comprising at least three portions one of which magnetically shunts another, a first primary winding and a first secondary winding on one portion, a further secl 15 ondary winding on another portion, and a second primary winding on a third portion; normally permanent connections between said first primary winding and a source of power; normally Dermanent connections between said secondary winding and said output circuit; relay means; a main control switch; an energizing circuit for said relay means comprising said first primary winding and said main control switch; and means controlled by said relay for energizing said second primary win-ding to increase the voltage supplied to said output circuit by said secondary winding to said predetermined value,

9. In a burner control system, a burner, means for controlling the delivery of fuel to said burner, a relay for controlling the operation of said fuel controlling means, a main controlling switch for controlling the energization of said relay, apparatus for detecting the presence of a burner flame, said apparatus comprising a thermionic discharge device having a cathode and a heater circuit therefor, a transformer having a sec ondary winding for energizing said heater circult. said transformer being normally effective to induce in said secondary winding a voltage of such magnitude that said heater circuit is inadequately energized, and means controlled by said relay and effective upon said relay being energized upon said main controlling switch being closed to cause said transformer to increase the voltage induced in said secondary winding so that said heater circuit is energized sufllciently to heat said cathode adequately.

10. In apparatus for detecting the presence of a burner flame; a thermionic discharge device having an anode, a control element, and a cathode and heater circuit therefor for rendering said cathode electron-emissive to a predetermined degree; a transformer having a constantly energized primary and at least two secondary windings; a first of said secondary windings being constantly connected to said heater circuit; circuit connections between a second of said windings, said cathode, and said control element, said circuit connections being eflective normally to bias said control element with respect to said cathode sufflciently to render said discharge device effectively non-conductive; means adapted to be exposed to a burner flame and operative to overcome the effect of said biasing connections sumciently to make Said discharge device conductive; said first and second secondary windings normally being incapable of supplying suillcient power to said heater and biasing circuits to cause them to function in the manner above recited; and means independent of said primary winding for causing said secondary windings to be subjected to an increased amount of flux so as to cause the outputs of both secondary windings to be increased simultaneously to desired values for proper operation of said apparatus as above recited.

11. In burner control apparatus; means for controlling a burner; apparatus for detecting the presence of a burner flame; said apparatus comprising a thermionic discharge device having an anode, a control element, and a cathode with a heater circuit therefor for rendering said cathode electron-emissive to a predetermined degree; a transformer having a constantly energized primary and at least two secondary windings; a first of said secondary windings being constantly connected to said heater circuit; circuit connections between a second of said windings, said cathode, and said control element, said circuit connections being eil'ective normally to bias said control element with respect to said cathode so that said discharge device is effectively non-conductive; means adapted to be exposed to a burner flame and operative to overcome the effect of said biasing connections sufllciently to make said discharge device conductive; said first and second secondary windings normally being incapable of supplying sufficient power to said heater and biasing circuits to cause them to function in the manner above recited; and means independent of said primary winding and controlled by said burner controlling means for causing said secondary windings to be subjected to an increased amount of flux upon said burner controlling means being placed into operation to cause the outputs of both secondary windings to be increased to desired values for proper operation of said apparatus as above recited.

12. In an apparatus for detecting the presence of a burner flame; said apparatus comprising a thermionic discharge device having an anode, a control element, and a cathode and heater circuit therefor for rendering said cathode electronemissive to a predetermined degree; a transformer havingi'a' constantly energized primary and at least three secondary windings; a first of said secondary windings being constantly connected to said heater circuit; circuit connections between a second of said windings, said cathode, and said control element, said circuit connections being efl'ective normally to bias said control element with respect to said cathode so that said discharge device is effectively non-conductive; connections between a third of said secondary windings, said anode, and said cathode; means adapted to be exposed to a burner flame and operative to overcome the effect of said biasing connections sufllciently to cause a current flow between said anode and said cathode as a result of the voltage applied by said third secondary winding; said secondary windings normally being incapable of supplying sumcient power to the circuit connections with which they are associated to cause them to function in the manner above recited; and means independent of said primary winding and said three secondary windings for causing all three of said secondary windings to be subjected to an increased amount of flux upon said burner controlling means being placed into operation to cause the outputs of all three of said secondary windings to be increased simultaneously to desired values for proper operation of said apparatus as above recited.

13. In burner control apparatus; means including a relay adapted to control the delivery of fuel to a burner, means for controlling the operation of said relay including apparatus for detecting the presence of a burner flame, said apparatus including a thermionic discharge device having a cathode and a heater circuit therefor. energizing means normally constantly connected to said heater circuit but incapable of adequately energizing said heater circuit, and means independent of said heater circuit operable upon said relay being energized to increase the power output of said energizing means to a value such that said heater circuit is adequately energized.

14. In combination, detecting apparatus, said apparatus including a thermionic discharge device having an energizing heater circuit therefor, a relay controlled by said discharge device, a transformer having two primary windings and at least one secondary winding, one of said primary windings being constantly energized, said one secondary winding being connected to said.

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device to cause operative energlzation of said I relay.

15. In combination, detectlon apparatus, said apparatus comprising a thermionic discharge device having an energizing heater circuit there= for, a transformer having a constantly energized primary and two secondary windings, a first oi said secondary windings being connected to said heater circuit, a main controlling switch, a con= trol relay having an energizing circuit including said other secondary winding and said main con trolling switch, a second relay controlled by said discharge device, flux controlling means forming an element of said transiormer for normally de creasing the flux to which said first secondary winding is subjected so as to render said first secondary winding incapable of energising said.

winding is subjected sumciently to enable said secondary winding to energize said heater circuit to the extent necessary to enable said discharge device tc cause operative energization oi said second reliay.

JOHN M. WILSON.

nnnnnnn'cns crrlm The following references are of record in the fiie of this patent:

UNITED STATES PATENTS Number Name Date 2923, 353 Von Weclei Dec. 10,, 1985 2,55,92il Baker Sept. 29, 1986 Kfiiiifififi Bowen Feb. 4, i941 2,238,d@2 Fanger Apr. 22, 194i. 2,289,,5il1l Schneider Oct. 20, 19 52

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