U.S. patent number 3,847,533 [Application Number 05/340,448] was granted by the patent office on 1974-11-12 for flame ignition and supervision system.
This patent grant is currently assigned to Walter Kiddle & Company, Inc.. Invention is credited to William J. Riordan.
United States Patent |
3,847,533 |
Riordan |
November 12, 1974 |
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.
Inventors: |
Riordan; William J.
(Shrewsbury, MA) |
Assignee: |
Walter Kiddle & Company,
Inc. (Clifton, NJ)
|
Family
ID: |
23333399 |
Appl.
No.: |
05/340,448 |
Filed: |
March 12, 1973 |
Current U.S.
Class: |
431/78;
431/71 |
Current CPC
Class: |
F23N
5/203 (20130101); F23N 5/123 (20130101); F23N
2231/10 (20200101); F23N 2227/36 (20200101); F23N
5/20 (20130101); F23N 2227/18 (20200101); F23N
2231/12 (20200101); F23N 2229/12 (20200101) |
Current International
Class: |
F23N
5/20 (20060101); F23N 5/12 (20060101); F23n
005/12 () |
Field of
Search: |
;431/66,78,80,254,255,71 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Favors; Edward G.
Attorney, Agent or Firm: Toupal; John E.
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.
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.
* * * * *