Flame Ignition And Supervision System

Abstract

Disclosed is a valve control circuit for fuel burners and the like. Energy is received by an energy storage circuit and periodically is rapidly removed therefrom and transferred to a pulse circuit. The pulse circuit, responsive only to pulses, receives the energy pulses on discharge and provides a valve activating signal in response thereto. The system is failsafe inasmuch as component failure prevents the pulses from being supplied to the pulse circuit. Furthermore, limit apparatus prevents sufficient power from being directly supplied from the power source to the valve to cause actuation. Two timers are also provided to cause system lock out in the event of failure to ignite. Either timer is sufficient by itself to cause lock out so that if one of the timers fails, lock out is still achieved.

Description

BACKGROUND OF THE INVENTION

This invention relates to burner control systems and, more particularly, to fuel valve control circuits.

Extensive efforts have been directed toward improving control systems for fuel burners such as gas and oil burners and the like. Increased system safety and reliability have been primary objectives of such efforts.

Most burner systems employ fuel supply valves that are automatically controlled by some type of flame sensing mechanism that automatically interrupts fuel flow in response to a predetermined loss of flame condition. According to one common technique, the presence of a flame is indicated by a signal current which is rectified by the flame in accordance with the well known ionization phenomena. The most serious problem caused by malfunctions in these circuits is the retention of the valve in an open position in the absence of flame. Many circuits have been developed that include numerous safeguards to insure that an unsafe condition will not result if one or more circuit components fail. However, most of these circuits have a common feature. The valve is maintained in an open position by the periodic firing of a silicon controlled rectifier that couples a power source to the valve. Unfortunately, while many circuits provide adequate "failsafe" protection to prevent unsafe operation in the event of a failure of any of the various components that cause the silicon controlled rectifier to fire, adequate protection in the event that the silicon controlled rectifier itself becomes either shorted or leaky is not provided.

Another problem associated with prior valve control circuits that caused an unsafe condition is failure of the lock out protection apparatus to cause lock out following a failure to establish flame. Conventionally, lock out is provided after a trial for ignition for a predetermined time. Consequently, it was found most convenient to design lock out systems responsive to indicia indicative of igniter operation, such as current drawn by the igniter. However, the lock out apparatus should only be activated in the event of a failure to establish flame, which is sometimes caused by a failure of the igniter. Failure of the igniter may prevent the presence of the indicia to which the lock out apparatus is sensitive thus preventing lock out. Protection was not provided when this circuit condition occurred.

An object of this invention therefore, is to provide a failsafe valve control system that will not give rise to unsafe conditions following the failure of any component, including the valve controlling silicon controlled rectifier. It is a further object that the system provide positive lock out protection in the event of a failure to establish flame.

SUMMARY OF THE INVENTION

This invention is characterized by a control circuit for controlling a fuel burner. An energy storage system receives and retains electrical energy from a source thereof and is periodically discharged by a discharge apparatus when flame is sensed by a flame detector near the burner. Discharge is rapid and therefore, provides a series of pulses, one pulse for each discharge. A pulse responsive system that responds only to pulses is coupled to a fuel controlling valve and provides a valve actuating signal in response to pulses. The pulse responsive apparatus can include, for example, a resistance or an inductance, as it will be appreciated that a surge of power through either component will create a voltage spike. Embodiments utilizing each are disclosed. To provide a continued valve actuating signal, the voltage peaks produced are passed by an isolation diode to a storage capacitor and filtered therein. The circuit is inexpensive, yet adequate failsafe protection is provided to prevent unsafe operation due to a malfunctioning circuit component. For example, the discharge apparatus includes a silicon controlled rectifier to discharge the energy storage apparatus. The SCR is periodically fired by the flame detection circuit. Failsafe protection is provided because any malfunction in the SCR or the associated circuit prevents the pulses from being delivered to the pulse responsive apparatus, and the valve remains open only in response to a series of pulses. Consequently, should the SCR become shorted or leaky the fuel valve quickly closes.

Embodiments are disclosed utilizing an inductance for the pulse response apparatus wherein the inductance comprises either the primary or a third winding of a spark transformer. These embodiments are inexpensive when utilized in conjunction with a burner employing a spark ignition apparatus, inasmuch as an inductance periodically receiving a pulse of current already is a part of the circuit. The excellent failsafe protection is provided at a minimal cost.

A feature of some of the embodiments disclosed is the division thereof into an input circuit including the energy storage apparatus and a pulse circuit including the pulse responsive apparatus. The two circuits are coupled by a transfer circuit that transfers energy from one circuit to the other. In these embodiments, a limit apparatus prevents sufficient current from passing directly from the power source to the pulse circuit to cause actuation of the valve. Sufficient energy is delivered to the pulse circuit only by proper operation of the transfer circuit. Thus short circuits or other malfunctions in the input circuit will prevent operation of the pulse responsive device rather than cause false actuation of the valve.

The inclusion of an auxiliary timer is another feature of the invention. As noted previously, conventional ignition timers are often responsive to indicia of operation of the ignition apparatus such as current drawn thereby. A common example is a circuit breaker utilized in the circuit supplying power to the ignition apparatus. For reasons which will be discussed more fully below, such a system is not completely reliable. The subject auxiliary timer is electronic and is responsive to the enabling signal delivered to the ignition apparatus when ignition is sought. The valve is opened when the ignition apparatus is enabled, but the subject auxiliary timer prevents valve actuation coupled with a defective ignition apparatus from becoming a hazard by causing lock out after the ignition apparatus has been enabled for a predetermined period of time, unless the flame responsive detector indicates flame has been established.

DESCRIPTION OF THE DRAWINGS

These and other features and objects of the present invention will become more apparent upon a perusal of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an operational diagram of a burner control system employing one embodiment of the subject valve control circuit;

FIG. 2 is a schematic diagram of a preferred system;

FIG. 3 shows various wave forms at different points within the circuit shown in FIG. 2;

FIG. 4 is a diagram of a valve control circuit in which the pulse responsive apparatus is the primary winding of a spark transformer and the valve actuating signal is generated on the flyback of the transformer;

FIG. 5 shows the control circuit depicted in FIG. 4 modified to actuate the valve on the flyforward portion of the cycle of the spark transformer; and

FIG. 6 shows another valve control circuit in which the pulse responsive apparatus includes a third winding in the spark transformer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1 there is an operational diagram of a burner control system 21. It should be understood that the diagram of FIG. 1 is not a conventional block diagram. For example, not all the blocks depicted in FIG. 1 correspond to an easily discernible portion of the circuit in FIG. 2, and lines coupling the blocks may indicate either electrical or mechanical coupling. It is however, felt that an understanding of FIG. 1 will simplify comprehension of the circuit shown in FIG. 2. The system 21 is powered by an a.c. power source (not shown). When power is applied, a delay timer 22 that is part of a first electronic switch 23 begins to time out in a predetermined delay time that is longer than one cycle of the a.c. supply current. The delay timer 22 enables a first silicon controlled rectifier 24 through a line 25. The first silicon controlled rectifier 24 fires once during each cycle of the a.c. current as long as a signal remains on the line 25. In addition the signal on the line 25 is carried to an auxiliary shut down timer 26 that begins timing out in a preselected shut down time when enabled. If the shut down timer 26 times out, a signal delivered on a line 27 to a lock out apparatus 28 causes the system 21 to lock out. Firing of the first SCR 24 produces a signal on a line 29 that performs three functions. An igniter 31 is energized in response to a signal on the line 29 and a fuel valve 32 is opened in response thereto. Thus when the first SCR 24 fires, fuel is supplied to a burner (not shown) and the igniter 31 seeks to ignite the fuel. Simultaneously, an ignition timer 33 begins running in response to the signals on the line 29. If the ignition timer 33 times out indicating that the first SCR 24 has been firing for a preselected period of time, a signal on a line 34 is delivered to the lock out apparatus 28 thus locking out the system 21. As was pointed out above, the first SCR 24 fires whenever there is a signal on the line 25. Thus the presence of a signal on the line 25 starts operation of both the shut down timer 26 and the ignition timer 33. When either timer 26 or 33 times out, the lock out apparatus 28 is activated. Thus the two timers 26 and 33 are both "ignition" timers and the provision of two separate timers is a safety feature. Disposed near the burner is a flame sensor 35 that fires a second SCR 36 through a line 37 once each cycle of a.c. power when flame is sensed. When the signal on the line 37 is deliverd to the second SCR 36, it fires producing pulses on a line 38 that maintain the valve 32 in an open position and reset the delay timer 22 through a periodic reset line 39.

During operation of the system 21 power is applied and the delay timer 22 times out in the delay time of greater than one cycle of the a.c. supply voltage. When the delay timer 22 has timed out, the first SCR 24 begins to fire and the shut down timer 26 and the ignition timer 33 begin to run. Also in response to the firing of the first SCR 24, the igniter 31 and fuel valve 32 are energized. Under normal circumstances flame will be established before either the shut down timer 26 or the ignition timer 33 has timed out. In that event, the flame sensor 35 begins firing the second SCR 36 which maintains the valve 32 in an open position and, upon firing once each cycle of the supply voltage, resets the delay timer 22 through the periodic reset line 39. Recalling that the delay time is greater than the period of the a.c. supply voltage, it is seen that the delay timer 22 is prevented from timing out while the second SCR 36 is firing. Thus it is seen that as long as flame is sensed by the flame sensor 35 the shut down timer 26 and the first SCR 24 are inoperable. If flame is lost, the second SCR 36 ceases firing and the delay timer 22 soon times out thus causing the first SCR 24 to resume firing. Consequently, the effect of a loss of flame is that the system behaves as it does when initially energized. Thus if flame is reestablished the second SCR 36 begins to fire again and the first SCR 24 is inactivated and the shut down auxiliary timer 26 is periodically reset.

If flame is not established initially, or following an effort to reignite, the system 21 is locked out upon the timing out of either the shut down timer or the ignition timer 33.

Referring now to FIG. 2 there is a schematic diagram of the burner control system 21. Portions of the circuit corresponding to the blocks in FIG. 1 have been pointed out with similar reference numerals where possible. A "hot" line 41 in a conventional 60 cycle per second a.c. power supply is connected to a buss 42 by a switch 43 such as, for example, a thermostat. A grounded line 44 is connected to a lock out thermal circuit breaker 45, that is part of a power input supply apparatus, so that the current flowing through the line 44 passes through an energy accumulating bimetalic strip member 33. A threshold member 34 in the circuit breaker 45 separates switch deactivator lock out contacts 28 in the event of a circuit breaker overload as evidenced by an excessive amount of heat building up in the bimetalic member 33. The heat energy in the bimetalic member 33 is supplied by heating caused by current flowing therethrough and the surface of the bimetalic element 33 radiates heat from the strip 33 to the atmosphere and thus comprises an energy leakage system. Because energy is radiated by the surface of the bimetalic strip 33, the circuit breaker 45 will not respond to energy supplied thereto at a low rate. The circuit breaker 45 connects the grounded line 44 to a junction 46. The power supplied on the lines 41 and 44 is alternating current and the term positive half cycle means that half of the cycle of the alternating current in which the line 44 is positive with respect to the line 41. It will be appreciated that the absolute potential on the grounded line 44 does not change and that changes in voltage refer only to relative values with respect to power line 41.

Controlled by the system is a fuel burner 47 that is grounded and is supplied with fuel through a line 48 in response to a valve control circuit 32 including a valve control relay coil 49 that is shunted by an energy storage filter capacitor 51. When the coil 49 is energized the valve is open. An isolation diode 52 couples the coil 49 and capacitor 51 combination across a pulse responsive resistor 53. One end of the coil 49 is connected to the common buss 42 along with one end of the capacitor 51 and the resistor 53. The other end of the pulse responsive resistor 53 is connected in series with an energy storage capacitor 54 and thence a limit resistor 55. At a junction 56 the resistor 55 is connected to a spark capacitor 57, the other end of which is connected to the buss 42. The junction 56 is also connected to the anode of the second SCR 36 by a diode 106 and a resistor 89. During positive half cycles of the input voltage, the capacitors 54 and 57 charge through the spark igniter apparatus 31 that includes another limit resistor 58 and diode 59 in series with a primary winding 61 of a spark transformer 62. Current flow in the above described spark circuit is prevented during negative half cycles of the supply voltage by the diode 59. Also included within the ignition apparatus 31 is a secondary winding 63 of the transformer 62 with two spark electrodes 64 and 65 connected thereto. The magnitude of the charging current is insufficient to cause sparking. Should the diode 52 become shorted, the relay coil 49 will still not be activated directly from the power supply due to the resistors 55 and 58 and the limiting, shunting effect of the resistor 53. The flame rectification flame detector apparatus 35 includes a resistor 66 connected between the electrode 65 and a falme rectification capacitor 67. The other terminal of the capacitor 67 is connected to the buss 42. Shunting the capacitor 67 is a resistor 68 and connected to a parallel combination of a capacitor 69 and complementary silicon controlled rectifier 71 by another resistor 72. Two capacitors 73 and 74 connected in series and joined at a junction 75 shunt the complementary silicon controlled rectifier 71. A resistive voltage divider including a resistor 76 and a resistor 77 spanning from the junction 46 to the buss 42 supplies current to the gate 78 of the complementary silicon controlled rectifier 71.

The first electronic switch apparatus 23 including the first SCR 24 is made to conduct by applying a voltage to a junction 81 that powers a voltage divider control circuit including two resistors 82 and 83 that supply current to the gate 84 of the SCR 24. The second electronic switch apparatus 85 including the second SCR 36 receives power from the junction 46 through a resistor 86, a diode 87, a diode 88 and another resistor 89. The preceding circuit is a cut off control circuit 90. The gate 91 of the SCR 36 is connected to the junction 75 by the line 37 and to the buss 42 by a resistor 92.

The delay timer clamping capacitor 22 connects a periodic reset line 94 to the buss 42. The cut off circuit 90 and the delay timer clamping capacitor 22 are part of an ignition interruption apparatus that deenergizes the ignition apparatus 31 upon the sensing of a flame by the flame sensor 35 as will be described more fully below.

The auxiliary shut down timer 26 includes a shut down energy accumulator capacitor 95 and a leakage resistor 96 in series and connected between the line 94 and the buss 42. A junction 97 between capacitor 95 and the resistor 96 is coupled to the gate 98 of a shut down silicon controlled rectifier 99 by a shut down threshold neon bulb 101. A capacitor 80 and a resistor 90 are connected in parallel between the gate 98 and the cathode of the SCR 99 and the anode is coupled to the line 94 by a resistor 105. Any energy absorbed by the capacitor 95 is leaked off through the leakage resistor 96 when the second SCR 36 is firing as described below. When the SCR 99 fires, it acts as a controlling apparatus for the first SCR 24 so that the SCR 24 conducts. A control circuit 102 including a capacitor 103 and a neon bulb 104 supplies current to the gate 84 of the first SCR 24 through the junction 81. The capacitor is charged through a resistor 105.

Referring now to FIG. 3(a) there are shown charging curves for the capacitors 103, 22 and 95. It is to be understood that no specific time constants are shown because the exact time constants are less important than the relationship among the three charging time constants. It should be further understood that the curves are for charging each capacitor disregarding the effect of the other. Specifically, the clamping action of the capacitor 22 is ignored in FIG. 3(a). The time t represents approximately one cycle of the alternating supply voltage. Thus it is seen by a curve 111 that in this example the capacitor 103 is nearly fully charged after only one cycle. The delay capacitor 22, as represented by a curve 112, requires several cycles to obtain a substantial charge and the capacitor 95 requires many cycles as shown by a curve 113. The capacitor 95 could take, for example, 10 seconds to charge.

During operation of the system 21 a.c. power is supplied and during the positive half cycles thereof current flows through the circuit breaker 45, the diode 59 and the primary winding 61 to charge the capacitors 54 and 57, which nearly fully charge during one half cycle. In addition, current flows through the resistor 86 to the capacitors 103, 22 and 95. During negative half cycles of power, the capacitor 103 is bypassed by a diode 100 and thus does discharge. The diode 87 prevents discharge of the capacitors 22 and 95 in the negative half cycles except through the SCR 36. Two paths of discharge are available for the capacitors 54 and 57. One path is through the primary winding 61 and then through the SCR 24. The second is through the resistor 89 and then through the second SCR 36.

To more fully understand the operation of the system 21, reference should be made to FIGS. 3(b)- (f). A sine wave form 121 shown in FIG. 3(b) represents the alternating current power supplied to the system 21 and is used to establish a time scale for FIGS. 3(c)- (f). A curve 122 in FIG. 3(c) shows the charging of the delay capacitor 22. A small amount of charge is gained during each positive half cycle of the sine wave 121 and the charge on the capacitor 22 remains constant during negative half cycles. The charge on the capacitor 103 is shown by a wave form 123 in FIG. 3(d). The capacitor 103 can substantially charge during one positive half cycle of the sine wave 121. However, during the positive half cycles the diode 87 is forward biased and thus is conductive so that the charging of the capacitor 103 is initially delayed by the clamping of the delay clamping capacitor 22 as shown in FIGS. 3(c) and (d).

After several cycles the capacitor 22 approaches its full charge and allows capacitor 103 to fire the neon bulb 104. Firing occurs at near the peak of the positive half cycle of the sine wave 121 as shown at the points 124 in FIG. 3(d). Discharge of the capacitor then proceeds through the bulb 104 and the wave shaping resistors 82 and 83 to supply current that causes the first SCR 24 to conduct. The resistor 82 lengthens the discharge period of the capacitor 103, so as to prolong current input to the gate 84 and thereby the conduction period of the SCR 24. After an initial period of discharge, the bulb 104 stops conducting and discharge proceeds as shown by the curved portion 125 of the wave form 123. Thus the first SCR 24 conducts during half of the positive half cycle as shown by a wave form 126 in FIG. 3(e). Inasmuch as the capacitors 54 and 57 absorb substantially a full charge during each positive half cycle of the wave form 121, they supply a substantial current to the primary winding 61 as they discharge through the SCR 24. This current creates sufficient power in the secondary winding 63 to cause a spark between the electrodes 64 and 65. In addition, the discharge of the capacitor 54 creates a current through the pulse responsive resistor 53 and a voltage drop thereacross as indicated in FIG. 2. This voltage drop forward biases the isolation blocking diode 52 and thus activates the relay coil 49. It should be noted that the diode 52 acts as a limit apparatus to prevent current from flowing directly from the circuit breaker 45 to the coil 49 and, furthermore, even if the diode 52 were to become shorted, the valve would not open when the capacitor 54 is charging because current flow then is too low due to the limit resistor 58. Generation of a large enough voltage across the resistor 53 requires storing a charge in the energy storage capacitor 54 and drawing it out in a rapid surge or pulse that bypasses the resistor 58. In addition, the filter capacitor 51 stores a sufficient charge to maintain the valve open until the following positive half cycle. Thus gas is released from the burner 47 and the ignition apparatus 31 sparks when the SCR 24 fires. It will be appreciated that an input circuit including the capacitor 54 is charged independently of a pulse circuit that includes the coil 49 and the capacitor 51. The pulse circuit receives power only when the first or the second SCR 24 or 36 fires and acts as a transfer apparatus to transfer energy from the input circuit. At all other times, the diode 52 isolates the input circuit from the pulse circuit. Two capacitors 54 and 57 are used because the resistor 55 is desirable to limit the surge to the capacitor 51. Obtaining an adequate spark requires that there be free flow of current from the capacitor to the primary winding 61. Thus the capacitor 57 supplies energy for sparking.

When flame is achieved at the burner 47 current is conducted between the burner and the electrode 65 in accordance with the flame rectification phenomena, thereby charging the capacitor 67 to the polarity indicated in FIG. 2. This charge is filtered and impressed across the capacitor 73 by the resistors 68 and 72 and the capacitor 69. The capacitors 73 and 74 are connected in series, and the combination is in parallel with the capacitor 69 and thus they are charged with the polarity indicated in FIG. 2. Note that the capacitor 74 is charged to a lower level than the capacitor 73 due to the drain of the resistor 92. In order for the complementary SCR 71 to conduct, the gate 78 thereof must receive current from the anode. This situation occurs during each negative half cycle of the sine wave 121 due to the resistors 76 and 77. In order for the second SCR 36 to fire, it must pass current from the gate 91 to the cathode. Under normal circumstances, precisely the opposite is true due to the charge on the capacitor 74. However, when, as a result of flame rectification, a sufficient charge has built up on the capacitor 73 the complementary SCR 71 is fired at the negative going crossovers 127 of the wave form 121. When the complementary SCR 71 fires, it effectively connects the negatively charged terminal of the capacitor 73 to the buss 42, thus discharging the capacitor 73 through the gate 91 of the second SCR 36. Consequently, when there is sufficient charge on the capacitor 73, the controlling complementary SCR 71 and the second SCR 36 both periodically fire on the negative going crossovers 127. The firing of the second SCR 36 occurs precisely at the conclusion of a conducting cycle of the first SCR 24. Thus the capacitors 54 and 57 have been previously discharged by the first SCR 24. However, as shown by FIG. 3(c), the first firing and each subsequent firing of the second SCR 36 discharges the delay capacitor 22. Inasmuch as the second SCR 36 responds to the flame detector 35 and fires every cycle if flame is sensed, the delay capacitor 22 requires several cycles before a sufficient charge can be built up to permit the first SCR 24 to fire, the first SCR 24 does not fire when the second SCR 36 is firing.

The capacitors 54 and 57 each continue to absorb a full charge during each positive half cycle of the wave form 121. However, discharge is now through the second SCR 36. Thus the voltage is still produced across the resistor 53 to maintain the valve in open position; however, the primary winding 61 of the transformer 62 is bypassed and thus the spark ignition apparatus 31 is deenergized and the spark is extinguished. This mode of operation continues as long as flame is sensed.

Note the constant time lines T.sub.1 and T.sub.2 in FIGS. 3(b) to (f). It will be observed that the values represented by the wave forms are identical at each line. Thus it will be appreciated that if the firing of the second SCR 36 indicated by a pulse 129 on the wave form 128 were not to occur, the situation would be precisely as it was at the time T.sub.1. The pulse 129 will not occur if flame is lost because the flame rectification capacitor 67 then becomes discharged. Thus it will be appreciated that if flame is lost, the system 21 automatically recycles to try for reignition.

Consider the system operation in the event of a failure to establish flame. When the delay capacitor 22 becomes charged after a few cycles, the energy absorbing capacitor 95 begins to charge. After 10 seconds the capacitor 95 has stored a sufficient charge to fire the threshold neon bulb 101 which causes the shut down SCR 99 to conduct. Conduction of the SCR 99 causes a drop across the resistor 83 and thus the SCR 24 conducts in a shut down mode. Consequently, the SCR 24 conducts at a high power shut down rate during each positive half cycle as shown by a wave form 131 shown in FIG. 3(g). Little current limitation is provided by the resistor 58. Consequently the lock out thermal circuit breaker 45 opens quickly thereby locking out the system 21.

Shown in FIG. 3(h) is a wave form 132 that represents the current passing through the lock out circuit breaker 45 when the first SCR 24 is firing normally to establish ignition. The small lobe 133 is due to the charging of the capacitors 54 and 57. The large conducting portion 134 corresponds in shape to the firing of the first SCR 24 as shown in FIG. 3(e) and indeed represents the firing of the first SCR. The first SCR 24 conducts such a large current because it fires during the positive half cycles of the supply voltage and thus a current path is established from the junction 46 through the resistor 58, the diode 59 and the SCR 24 to the buss 42. Consequently, a strain is put on the thermal lock out circuit breaker 45 during the long duty cycle of the first SCR 24. If the shut down SCR 99 fails to fire for any reason, the continued firing of the first SCR 24 at the preselected rate in an effort for ignition will cause the circuit to lock out after approximately 15 seconds. Conversely, although it is unlikely, it is possible that the first SCR 24 could begin to fire near the negative going crossover. In such an event, the valve may be held open, but the lobes 134 will not occur. Consequently, the circuit breaker 45 will not be activated. However, if no flame occurs the auxiliary shut down timer will soon cause the SCR 24 to operate in the shut down mode, causing lock out. Thus provision of two possible methods for lock out is a beneficial safety feature.

FIG. 3(j) shows a wave form indicating current passed by the lock out circuit breaker 45 when the second SCR 36 is firing. Small lobes 135 correspond to the charging of the capacitors shown by the lobes 133. There is no large current surge when the SCR fires at the negative going crossovers because no substantial power is being applied to the lines 41 and 44. Thus the only power conducted by the second SCR 36 is the discharge of the capacitors 22, 54 and 57. Consequently, continued operation of the second SCR 36 will not cause the activation of the lock out circuit breaker 45. However, should the second SCR 36 become shorted or leaky, power will pass therethrough during positive half cycles, causing overloading of the circuit breaker 45.

Referring now to FIG. 4 there is shown another valve control circuit 141 in which parts corresponding generally to those shown in the valve control circuit 32 are denoted with similar reference numerals. Alternating current power is supplied to the circuit 141 through a diode 59 and an energy storage capacitor 54 charges during positive cycles. While the capacitor 54 is charging, power also flows through a primary winding 142 of a spark transformer 143 and through an isolation diode 52 to a relay activating coil 49 and through an energy storage filter capacitor 51. During negative half cycles, the filter capacitor 51 discharges through the coil 49 but the energy storage capacitor 54 is prevented from discharging by the diode 59, unless a second discharge SCR 36 is activated. It should be noted that while current does pass through the primary winding 142 and the valve actuating coil 49 during positive cycles of the a.c. power the current levels are too low to cause actuation of the valve or sufficient energy to be transferred to the secondary winding 144 of the transformer 143 to cause sparking between spark electrodes 145.

When flame is sensed a signal appears across the flame detecting resistor 92 as was described with respect to the embodiment 21. Consequently, the charge absorbed by the capacitor 54 on each positive half cycle is discharged rapidly as a pulse through the SCR 36 on the negative going crossovers while flame is sensed. The discharge causes a pulse of current to flow in the direction of the arrow i in FIG. 4. Consequently, magnetic energy is accumulated in the transformer 143 and a voltage drop of the polarity indicated appears across the primary winding 142. It is seen that the isolation diode 52 is then back biased. However, when the pulse rapidly decays a flyback signal is developed within the transformer 143 that reverses the polarity indicated. Thus the diode 52 becomes forward biased and delivers the energy stored in the transformer 143 as a substantial voltage pulse to the capacitor 51 and coil 49. The pulse activates the relay coil 49 and charges the filter capacitor 51 sufficiently so that the coil 49 will remain activated during the following cycle of the a.c. power. It will be appreciated that the circuit 141 will not be activated if the SCR 36 becomes shorted or leaky. That is because in either of those events the required sharp pulses will not be delivered by the primary winding 142, and it is only those sharp pulses that create a sufficiently high voltage to activate the relay coil 49.

Referring now to FIG. 5 there is shown a modified valve control circuit 141a similar to the circuit 141 except that the isolation diode 52 has been reversed to render the circuit responsive to the flyforward portion of the discharge. The coil 49 and the capacitor 51 comprise a pulse responsive circuit 146 that is isolated by the isolating diode 52 from the energy storage circuit 147 including the transfer SCR 36 and the energy storage capacitor 54. It will be appreciated that the diode 59 conducts to charge the capacitor 54 on the positive half cycles. However, the isolation limiting diode 52 prevents any current from flowing through the coil 49 or the filter capacitor 51 during the positive half cycle. Consequently, power is transferred to the coil 49 and the capacitor 51 only by the firing of the transfer SCR 36. When the SCR 36 fires, a pulse is drawn from the capacitor 54 creating a voltage drop as indicated in the primary winding 142 of the transformer 143. Thus it is seen that the diode 52 is forward biased and conducts. The voltage generated across the primary winding 142 is sufficient to activate the coil 49 and charge the capacitor 51 adequately to maintain the coil in an activated state until the following cycle.

Referring now to FIG. 6 there is shown yet another valve energy storage supply capacitor 54, a primary winding 152 of a an energy responsive spark transformer 153 and the transfer SCR 36. A spark secondary winding 154 is connected to spark electrodes 155. A third winding 156 of the spark transformer 153 is part of a pulse responsive circuit including the energy storage filter capacitor 51 and the coil 49. Inasmuch as the a.c. power frequency is too low to effectively operate the limiting transformer 153, no power is passed to either secondary winding 154 or 156 during the charging of the capacitor 54 on the positive half cycle of the supplied power. Only if a sharp pulse or surge of energy with a frequency substantially greater than the power frequency is created by the discharge of the capacitor 54 through the control SCR 36 is any appreciable energy transferred through the transformer 153. Should the transfer SCR 36 become shorted or leaky, the pulse will not be supplied and thus no energy will be transferred by the transformer 153. When a pulse is impressed across the primary winding 152, a spark appears between the spark electrode 155 and the filter capacitor 51 charges through the diode 52 and activates the coil 49. The isolation diode 52 prevents the capacitor 51 from discharging through the third winding 156 between pulses. It should be appreciated that the diode 52 can be connected in either direction as sufficient energy is delivered to the third winding 156 during the flyforward and the flyback phases of the pulse.

It will be noted, as shown, that the embodiments 141, 141a, and 151 all involve simultaneous sparking and maintenance of the valve in an open position when the flame is sensed. If it is desired that the spark be extinguished after flame is detected, as in the embodiment 21, the spark electrodes 145 or 155 can be eliminated from the circuits depicted in FIGS. 4-6 and other ignition apparatus utilized. In that event, the pulse apparatus 142 or 152 can remain an inductance as shown. For example, a choke could be used in the embodiment shown in FIGS. 4 and 5 or a two winding transformer could be used in the embodiment shown in FIG. 6. Or, if it is desired, a resistance could be utilized in place of the windings 152 and 142 as the resistance 53 is utilized in the embodiment 21.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, the preignition timing may be extended to provide substantial "purge" time and the ignition timer may be adapted to closing the valve without opening the circuit breaker using conventional circuitry. It is therefore, to be understood that within the scope of the appended claims the invention can be practised otherwise than as specifically described.

Claims

What is claimed is:

1. Circuit apparatus for controlling a fuel burner and comprising:

a power source;

flame responsive means for detecting flame at the burner;

valve means for controlling the flow of fuel to the burner;

energy storage means for receiving and storing electric energy from said power source;

energy transfer means responsive to the detection of flame by said flame responsive means for transferring the energy stored in said energy storage means to said valve means for actuating said valve means to produce fuel flow to the burner; and

limit means for preventing sufficient energy from flowing from said power source directly to said valve means to provide actuation thereof at any time during normal operation of said apparatus.

2. Apparatus according to claim 1 wherein said energy transfer means comprises discharge means for rapidly removing the energy stored in said energy storage means and wherein said valve means comprises pulse responsive means for rendering said valve means responsive only to rapid surges of energy.

3. Apparatus according to claim 2 wherein said pulse responsive means comprises a resistance.

4. Apparatus according to claim 2 wherein said energy storage means comprises an inductance.

5. Apparatus according to claim 4 wherein said inductance comprises the primary winding of a spark transformer.

6. Apparatus according to claim 4 wherein said inductance comprises a third winding of a spark transformer.

7. Apparatus according to claim 2 wherein said flame responsive means comprises periodic control means for periodically activating said discharge means so as to cause the periodic removal of energy from said energy storage means.

8. Apparatus according to claim 7 wherein said pulse responsive means comprises energy storage filter means for maintaining valve actuating signals between the receipt of pulses from said discharge means.

9. Apparatus according to claim 8 wherein said energy storage filter means comprises a capacitor.

10. Apparatus according to claim 8 wherein said energy storage filter means comprises isolation means for preventing the flow of energy from said energy storage filter means to said discharge means.

11. Apparatus according to claim 10 wherein said energy storage filter means comprises a capacitor and said isolation means comprises a diode for coupling said capacitor to said discharge means.

12. Apparatus according to claim 2 comprising an input circuit including said energy storage means and further comprising a pulse circuit coupled to said input circuit by said energy transfer means and including said pulse responsive means.

13. Apparatus according to claim 12 wherein said discharge means comprises isolation means for preventing charging energy received by said input circuit from passing directly to said pulse circuit.

14. Apparatus according to claim 2 wherein said pulse responsive means comprises an inductance for receiving pulses from said discharge means and a capacitor coupled to said inductance by a diode that conducts energy to said capacitor during the flyback in said inductance induced by the pulses.

15. Apparatus according to claim 2 wherein said pulse responsive means comprises an inductance for receiving pulses from said discharge means and a capacitor coupled to said inductance by a diode that couples the voltage peaks induced by the pulses to said capacitor.

16. Apparatus according to claim 2 wherein said pulse responsive means comprises a resistance for receiving pulses from said discharge means and a capacitor coupled to said resistance by a diode that couples voltage peaks produced by the pulses to said capacitor.

17. Apparatus according to claim 2 wherein said discharge means comprises a silicon controlled rectifier.

18. Circuit apparatus for controlling a fuel burner and comprising:

flame responsive means for producing flame signals in response to detection of flame at the burner;

valve means for controlling the flow of fuel to the burner;

a power source;

energy supply means for transferring electric energy from said source to said valve means so as to produce actuation thereof and fuel flow to the burner;

control means for generating rapid surges of energy from said energy supply means in response to signals from said flame responsive means, said rapid surges of energy having a frequency substantially greater than said power source; and

energy responsive means for receiving said rapid surges of energy from said energy supply means and actuating said valve means in response thereto, and wherein said energy responsive means comprises limit means for rendering said valve means actuatable only by rapid surges of energy having a frequency substantially greater than said power source.

19. Apparatus according to claim 18 wherein said source comprises an A.C. power supply.

20. Apparatus according to claim 18 wherein said limit means comprises an inductance.

21. Apparatus according to claim 20 wherein said inductance comprises a winding of a spark transformer.

22. Apparatus according to claim 21 wherein said valve means comprises an electromagnetic valve control means coupled to said spark transformer.

23. Circuit apparatus for controlling a fuel burner and comprising:

valve means for controlling the flow of fuel to the burner;

ignition means for igniting fuel emanating from the burner;

ignition timer means for timing operation of said ignition means;

lock out means responsive to said ignition timer means for locking out said apparatus to prevent fuel flow to the burner after operation of said ignition means for a predetermined period of time;

auxiliary timer means for timing operation of said ignition means, said auxiliary timer means being coupled to said lock out means for causing lock out of said apparatus after operation of said ignition means for a second predetermined period of time; and

flame responsive means for preventing the operation of said ignition means when flame is established at the burner.

24. Apparatus according to claim 23 wherein said ignition timer means receives energy at a preselected rate during normal operation of said ignition means and comprises energy accumulation means for accumulating the energy received and threshold means for activating said lock out means for causing lock out when a predetermined amount of energy is accumulated.

25. Apparatus according to claim 24 wherein said ignition timer means further comprises leakage means for dissipating the energy accumulated and rendering said lock out means responsive to only substantially continuous operation of said ignition means.

26. Apparatus according to claim 25 wherein said lock out means comprises a thermal circuit breaker.

27. Apparatus according to claim 24 wherein said auxiliary timer means comprises shut down energy accumulation means for receiving and storing energy at a second preselected rate during normal operation of said ignition means and further comprises shut down threshold means for causing lock out after accumulation of a second predetermined amount of energy.

28. Apparatus according to claim 27 wherein said auxiliary timer means is an electronic timer and said shut down energy accumulation means comprises a capacitor.

29. Apparatus according to claim 27 comprising electronic switch means for controlling said ignition means and for supplying energy to said energy accumulation means at the preselected rate during operation of said ignition means.

30. Apparatus according to claim 29 wherein said auxiliary timer means comprises shut down means responsive to said shut down threshold means for causing said electronic switch to operate in a shut down mode after the accumulation of the second predetermined amount of energy and wherein said electronic switch means supplies energy to said energy accumulation means at a shut down rate during operation in the shut down mode and wherein the shut down rate is a higher rate than the preselected rate.

31. Apparatus according to claim 30 wherein said lock out means comprises a thermal circuit breaker.

32. Apparatus according to claim 31 wherein said electronic switch means comprises a silicon controlled rectifier.

33. Apparatus according to claim 18 wherein said rapid surges of energy have a frequency substantially greater than 60 cycles per second.

34. Apparatus according to claim 22 wherein said valve means further comprises a capacitor connected in parallel with said electromagnetic valve control means and diode means coupling said electromagnetic valve control means to said spark transformer.