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Патент USA US3079992

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3,079,932
: free
Patented Mar. 5, 1963
i
2
and a secondary winding '58, and power supply leads 60
3 M9332.
and 62 for connection to a suitable A.C. power source.
BURNER coisrnoi. SYSTEM
Eernardus J. §taring, Markham, @ntario, Canada, as
The oil burner it) includes the usual blower and fuel
signor, by mesne assignments, to White-Rodgers Com
pump which when driven by the motor 12 supplies ato-. -
pany, a corporation of Missouri
ized oil and combustion air to the burner nozzle where it
is ignited by spark at electrodes 52. The motor 12 is
energized through a circuit traced from power supply lead
60 through a lead 64, motor relay contacts 22, a lead 66,
Filed Dec. 14, 196i, gar. No. 159,295
10 Claims. (Ci. 158--28)
This invention relates to automatic control systems for
?uid fuel burners which include safety means operative to
permit the continued supply of fuel to the burner when
motor 12, and a lead 68 to power lead 62. The igniter
is energized through a circuit extending from the lead 64
through a lead 7t), ignition relay contacts 18, a lead 72,
the primary winding of ignition transformer 54, and a
there is combustion and to cut off the flow of fuel if corn
bustion fails to occur within a predetermined interval
lead 74- to the lead 68.
during which fuel is supplied or if combustion having
The ignition relay winding 16 is energized through a
been established subsequently fails.
15 low voltage circuit extending from one‘ side of transformer
An object of the invention is to provide a generally
secondary 53 through a lead 76, safety switch contacts 30,
new and'irnproved safety control system for fluid fuel
a lead 78, a lead 80, a lead 82, safety switch heater 32, a
burners incorporating an instantly responsive flame detec
lead 3'4, cold side contact 34 of the scavenger switch, the
tion means which is particularly economical in construc
switch blade 38, a lead 36, a lead 88, relay winding 16, a
tion and reliable in operation.
'
A further object is to provide a burner control system
employing a semiconductor-type, light-sensitive element
20 lead §ti, a lead 92, a lead 94, a lead 96, through thermo
stat 14 and a lead 98 to the other side of secondary
Winding 58.
The motor relay winding 29 is energized initially
as a combustion ?ame detector in such a manner as to re
quire only slight current ?ow through the element in per—
through a low voltage circuit starting at the right side of
formance of its function.
25 secondary Winding 58 through lead 76, safety switch
A further object is to provide a burner control system
contacts 3%, lead 78, lead 80, lead 82, safety switch heater
employing a semiconductor-type, light-sensitive element
32, lead 34, cold side contact 34 and blade 38, lead 86,
as a combustion ?ame detector in such manner that oper
a lead roe, flame detector relay contacts 28, a lead 102,
ation of the fuel supply means cannot be initiated if the
relay winding 2ft, lead 92, lead 94, lead 96, through
light sensitive element is improperly installed so as to be 30 thermostat l4, and lead 98 to the other side of trans
affected by light other than the light of combustion or if
former secondary 58.
the element is or becomes defective in a manner as to be
When the motor relay pulls in, energization of its
operatively conductive in the absence of light.
winding Ed is maintained by a branch circuit extending
A further object is to provide a burner control circuit
through its holding contacts 24. This branch circuit
having a voltage dependent resistor and a semiconductor 35 parallels the safety switch heater 32 and the ?ame detector
type, light-sensitive element in parallel connection, where
relay contacts 23, and extends from the g'unction of leads
in a predetermined voltage ‘commonly applied through
3d and
through lead 8%, through holding contacts 24-,
lead lild, scavenging switch heater 4d, a lead res, and
a ?xed resistance effects a functional conductance of the
voltage dependent resistor whenlight energy impinging
the parallel connected, light sensitive element is less than 40
that which occurs when there is burner flame and wherein
conductance of the light sensitive element when impinged
by the light of burner ?ame or its equivalent is suf?cient
to result in a drop to non-functional conductance of the
parallel connected, voltage dependent resistor.
may).
through lead
to one side of the motor relay wind~
The flame detector relay winding 26 is energized
through a circuit which may be traced from thermostat
to through the lead 96, current limiting resistor 42, a
lead res, voltage dependent resistor 44, a lead 110, the
winding 26, a lead 112, rectifier 136, a lead 114, lead
Further objects and advantages will appear from the 45 '75,
safety time switch contacts 3%, lead 7s, transformer
following description when read in connection with the
secondary
5S, and lead £98 to the thermostat. A capac
accompanying drawing.
itor 48 is connected across the flame detector relay wind
FIG. 1 of the drawing is a diagrammatic illustration of
ing to the leads lit} and 112 to prevent relay hum. The
a control system for a conventional, pressure type, oil 50 semiconductor, light sensitive element St) is connected
burner embodying a form of the present invention; and
between leads liid and lid and is therefore in parallel
FIG. 2 is a portion of a characteristic voltage/current
with the voltage dependent resistor 44 as well as with
curve of the voltage dependent resistor.
the ?ame detector relay winding and the recti?er. It is
FIG. 3 is a partially sectionalized view of a conven
to be noted that the current passing through element St)
tional pressure-type oil burner showing the mounting 55 is, therefore, alternating and not recti?ed as it is in the
. position of the light sensitive element.
network of the relay winding 26.
Referring to the drawing, the primary elements of the
The safety time switch 39 is normally closed, but
system are: an oil burner 10 having a driving motor 12,
a space thermostat 14 responsive to the temperature of a
when its bimetal blade is heated for a predetermined
period of time by resistance heater 32 when fully ener
space being heated by the burner, an ignition relay having 60 gized, it warps open and locks in an open position requir
a winding 16 and contacts 13, a motor relay having a
ing
resetting. This type of safety switch is com
monly used and its construction and operation are well
winding 29, motor contacts 22, and holding contacts 24-, a
understood in the art.
‘
?ame detector relay having a winding 26 and contacts 28,
The voltage dependent resistor lid is a commercially
va thermal safety time switch havinv contacts 3%} and a
resistance heater 32, a double-throw, scavenging time 65 available element developed and used primarily for volt
age regulation and stabilization. its structure consists of
switch having stationary contacts 34 and 36, a bimetal
blade 38 and a resistance heater ‘40, a current limiting
resistor 42, a voltage dependent resistor 44, a recti?er 46,
a capacitor 48, a light sensitive element 50, a spark type
igniter 52 and a step-up voltage transformer 54, a step
down voltage transformer having a primary winding 56
a eonglomeration of silicon carbide crystals in a ceramic
binder pressed into a desired shape and then sintered.
The voltage dependency of the element is apparently due
70 to contact resistance between carbide crystals. The char
acteristic voltage/current curve of the element is non
linear, and while at higher voltages the curve straightens
3,079,982
3
4
out, it curves sharply in the lower voltage range. FIG. 2
of the drawing illustrates the lower voltage range por
32 in series with the higher impedance ignition relay
Winding only, which considerably reduces the heat output
tion of a characteristic voltage/ current curve of one of
of the, heater 32. It is to be noted that while the
scavenger switch heater 4t} is placed in series with. the
motor relay winding 2%? when ‘holding contacts 24 close,
the pull-in circuit for the motor relay winding 20 extends,
these elements. It will be noted thatonly negligible
current. ?ows as voltage is increased from zero up toa
critical voltage range, whereafter current ?ow increases
very rapidly with slight voltage increase.
The characteristics of the particular element 44 are “
such that it has ample conductancein the circuit at the
voltage applied to energize relay winding 26 and close 10
the contacts 23 when the resistance of parallel connected,
' light sensitive cell Silis sufficiently high, but when slight
nevertheless, through the safety switch heater 32 alone,
so that the motor relay winding 2% cannot be initially
energized except through the safety switch heater.
When combustion at the burner occurs light sensitive
element 59 becomes sufficiently conductive to result in a
voltage drop across resistor 42 which effects such decrease
in the voltage applied to voltage dependent resistor 44 as
conduction occurs through parallel connected element
to render it insutliciently conductive to maintain oper
'50 due to light energy of combustion impinging thereon,
conduction through element 44.drops sharply due to the 15 ative energization of ?ame detector relay windingl26 and
therefore ?ame detector relay contacts 23 open. When
voltage drop across resistor 42v and relay contacts 23
this occurs the safety switch heater32 is placed in series
0 en.
i
pThe light sensitive element 50 is of the semiconductor
with the higher impedance, ignition relay winding 16
?ame to effect a considerable reduction in conduction
~ scavenging switch heater 40, now connected through the
through the parallel voltage dependent resistor element
motor relay winding, is heating the double-throw switch
only, and its heat output is, therefore, substantiallyre
type Which in the absence of the light of burner ?ame
has extremely high electrical resistance, but becomes suf 20 duced so that safety switch bimetal blade 30 is now
heated at a considerably slower rate. At the same time
ciently conductive when exposed to the light of burner
blade 38 of the scavenging switch at a rate which will
within the burner casing at the rear end of the blast 25 effect the movement of blade 38 so as to break its cold
44. Light sensitive element‘ 50 is preferably mounted
position with contact 34.
tube, as indicated in FIG. 3. 'It has been found that
When bimetal blade 38 of the scavenging switch breaks
ample light energy reaches the element in this position,
with cold side contact 34, safety switch heater 32' is
either directly or by re?ection, to effect its operational
completely tie-energized and ignition relay winding 16 is
conductance while, on the other hand, in the absence
of burner ?ame, it is su?iciently shielded from ambient 30 de-energized thereby rendering the igniter inoperative.
The continued heating and warping of bimetal blade 38
li ht.
by the scavenging switch heater 44) causes it to close with
gThe current limiting resistor '42 has such value as to
limit the total current through the parallel connected, volt
its hot side contact 36. When this occurs a shunting
branch through ?ame detector contacts 28is established
age dependent resistor and light sensitive element to a
range wherein the described interaction between light 35 which will effect the bypassing and ‘operative de-energiza
sensitive element 50 and voltage dependent resistor 44
tion of motor relay 20 if and when a ?ame failure results
will occur.
in the reclosing of ?ame detector contacts 28. This
branch extends from the junction of leads 92-94 to the
junction of leads 102496 and includes a lead 116,
scavenger switch blade 38 in a hot position, the lead 86,
the lead 100, ?ame detector relay contacts 28, and a lead
The ?ame detector relay is preferably a
highly sensitive, encapsulated, reed-type relay, the recti
?er 46 is preferably a semiconductor diode, and the capac
itor 48 is preferably of the electrolytic type.
Operation
Closing of thermostat 14 upon call for burner oper
118. If such ?ame failure occurs, causing de-energization
- of motor relay winding 20, its motor contacts 22 will
ation simultaneously completes the described circuit for
open rendering the burner motor inoperative to supply
energization of the ignition relay winding 16 and the 45 fuel and its holding contacts 24 will also open, thereby
described circuit for energization of the ?ame detector
rendering the scavenging switch ‘heater 4t} inoperative.
relay winding 26. Energization of relay winding 16
Under such conditions a re-start will occur only after the
elfects the closing of its contacts 18 and therefore oper
bimetal blade 38 of the scavenging switch cools and again
ation of igniter 52. Energization of ?ame detector relay
engages its cold side contact 34». In restarting, pull-in
26 effects closing of its contacts 28 and the completion 50 energization of the motor relay winding will be eifected
of the described initial energizing circuit for the motor
‘through the described starting-circuit which includes the
relay winding 20. Energization of motor relay winding
safety switch 3*!) and its heater 32.
20 effects the closing of its motor contacts 22, thereby ~
If at any time during normal operation of the burner,
energizing burner motor 12 to supply fuel and air for
a momentary power failure occurs which results in the
combustion which is ignited by igniter 52. .The ener—
dropping open of motor relay contacts 24 and 22, a
gization of motor relay winding 20 also effects the closing
re-start will occur upon resumption of power supply,
of its holding contacts~ 24,- which completes the described
but only after scavenging switch blade 38 has cooled and
branch circuit for the winding which includes the scaveng- -
again engages its cold side contact 34.
‘
_
_
ing switch heater 40, but bypasses the safety switch heater
If for any reason the light sensitive element 50 is im
60 properly installed so as to be operatively effected by light
32, and ?ame detector contacts 28.
'
‘
Under these conditions, when motor relay holding con
other than that of combustion ?ame, or'if his or becomes
tacts 24 close, the'safety switch heater 32 remains con
defective in a manner to be operatively conductive in
nected in series with the ignition relay winding 16 through
the absence of light, the motor relay'winding 210 will not
the cold contact side>34wof the scavenging switch and
be energized upon closing of the thermostat. This’is so
the scavenging switch heater 4% is now connected in 65 because if the element St) is thus defective the ?ame
series with the motor relay; but these two pairs of series
detector relay will not be energized upon closing the
thermostat to pull in its contacts 28 so as to complete
connected elements are also electrically interconnected
a pull-in circuit for the motor relay winding 20. Under
through the closed ?ame detector relay contacts 28 and
such conditions, however, the ignition relay winding will
the lead 100 which places the impedance, of the ignition
winding in parallel with the, motor relay winding with 70 be energized through the safety switch 30 and its heater
32, and the igniter will operate until the safety switch
respect to safety switch heater 32. The impedance of
opens and locks out.
i
'
ignition relay winding 16 is considerably greater than
that of the motor relay winding so that the effect of
If upon starting combustiondoes not occur within the
breaking this interconnection bythe opening of ?ame
predetermined period requiredto open safety switch 30‘
detector relay contacts 28 is to place safety switch heater 75 when safety switch heater 32 is connected through the
3,079,982
5
6
parallel ignition relay winding 16 and motor relay Wind
ing 2d, the safety switch 30 will open and lock open
requiring manual resettin".
said circuit connections including said voltage dependent
resistor, said relay winding, its parallel connected ca
pacitor, and said recti?er only, said voltage dependent
'
By balancing the ?ame detector relay winding network
resistor having su?icient conductance at the applied volt
age when said parallel connected photocond-uctive ele
ment is non-conductive in the absence of ?ame to permit
so that the voltages applied across voltage dependent
resistor 44 (when photosensitive element 50 is conductive
and when not conductive) lie in that critical range
wherein the rate of change of the voltage/current curve
is greatest, a substantial ampli?cation of any signal change
in the conductance of the photoconductive element is 10
applied voltage and said parallel connected voltage de
relay winding 26, a more inexpensive and sensitive ?ame
below that which permits operative energization of said
achieved. By rectifying the current ?owing through the
detection relay may be employed, and by connecting the
photoconductive element 59 across this recti?ed portion
of the network so that the current passing through it is
alternating, any tendency toward polarization of the semi
conductor element 5d is precluded.
in the form of the invention shown in FIG. 1, the
operative energization of said relay winding, and said
photoconductive element being sut‘dcient-ly conductive
when burner flame exists to effect a sui?cient drop in the
pendent resistor to reduce its conductance to a point
relay winding.
3. in a burner control system of the kind described,
a limiting resistor, a solid state voltage dependent resistor
in which a high rate of change in voltage/current ratio
occurs through a predetermined critical range of applied
voltages, a control relay having a winding, a solid state
igniter is operated upon starting through igniter relay
.photocouductive element shielded from ambient light
contacts 18 and continues operating untilthe scavenging 20 and arranged to see a burner ?ame when it exists, said
switch blade 33 parts with its cold side contact 34. This
element having extremely high resistance to, the ?ow of
form of operation of the ignition device is referred to
as “intermittent.” If it is desired to maintain operation
electrical current when the burner ‘?ame is non-existent
relay contacts 18 are deleted and igniter transformer leads
70 and 72 are connected at that point. In this constant
ignition arrangement the safety switch heater 32 is in
circuit connections connecting said photoconductive ele
I claim:
1. A ?ame responsive actuator for a ‘burner control
system including a voltage dependent resistor, an ac
the voltage dependent resistor is near the lower limit of
said critical voltage range and is insu?icient to e?ect a
but ‘becoming conductive when ?ame exists, a ‘source of
of the igniter constantly during operation of the burner,
power,
circuit connections connecting said limiting re
the ignition relay winding 16 and its connecting leads 25
sistor, said voltage dependent resistor, and said control
88 and 90 are deleted from the circuit. Also, the ignition
relay winding in series across said power source, and
ment in parallel with that portion of said circuit con
series with the motor relay winding 20 upon starting and 30 nections including said voltage dependent resistor and
said relay winding only, the resistance value of said limit
the scavenging switch heater 40 is placed in series with
ing resistor and the impedance of said relay winding be
the motor relay winding 29 and in parallel with the
ing such that the voltage across said voltage dependent
safety switch heater 3?. when the motor relay winding
resistor
in the absence of burner ?ame is near the upper
energizes and its holding contacts 24 close._ Also, in this
limit of said critical voltage range and is such as to cause
constant ignition arrangement when ?ame is detected and
a current ?ow through said voltage dependent resistor
?ame detector relay contacts 28 open, the safety switch
which will effect operative energization of said relay
heater 32 is completely de-energized by breaking of its
winding, and the conductivity of said parallel connected
circuit at that point instead of being reduced to partial
photoconductive element being such when there is burner
energization by being placed in series with the higher
impedance ignition relay coil only as occurs when ?ame 40 ?ame as to increase the voltage drop across said limiting
resistor to a point wherein the voltage applied across
detector contacts open in intermittent ignition operation.
tuating relay having a winding, a photoconductive ele
ment shielded from a.1 ‘bient ‘light and arranged to see
burner ?ame when it exists, a ?xed value resistor, and a
power source, circuit connections connecting said ?xed
resistor, said voltage dependent resistor, and said relay
winding in series relationship across said power source,
and circuit connections connecting said photoconductive
element in parallel with that portion of said circuit con
flow of current through said voltage dependent resistor
which will maintain operative energization of said relay
winding.
'
4. An arrangement as claimed in claim 3 which in~
eludes means for rectifying the current passing through
that portion of the circuit only which is paralleled by
said photoconductive element and its circuit connections.
5. An arrangement as claimed in claim 3 which in
cludes a recti?er in series with said voltage dependent
resistor and said relay winding, in which a capacitor is
nections including said voltage dependent resistor and
connected
across said relay winding, and in which said
said relay winding only, said voltage dependent resistor
having sufficient conductance at the applied voltage when 55 photoconductive element is connected across said volt
age dependent resistor, said relay winding, its parallel
said parallel connected photoconductive element is non
capacitor, and said recti?er.
' conductive in the absence of burner ?ame to permit opera
tive energization of said relay winding, and said photo
conductive element being sui?ciently conductive when
burner ?ame exists to effect a su?icient drop in the ap
plied vo-ltage on said parallel connected voltage dependent
resistor to reduce its conductance to the point wherein
said relay winding is no longer operatively energized.
2. A ?ame responsive actuator for a burner control
system including a voltage dependent resistor, an ac
tuating relay having a winding, a photoconductive ele
ment shielded from ambient light and arranged to see
burner flame ‘when it exists, a ?xed resistor, a recti?er, a
capacitor, and a source of AC. power, circuit connec
tions connecting said ?xed resistor, said voltage dependent
resistor, said relay winding, and said recti?er in series
relationship in that order across said power source, cir
cuit connections connecting said capacitor in parallel with
said relay winding only and circuit connections connect~
ing said photoconductive element across that portion of
6. An arrangement as claimed in claim 5 in which said
recti?er is a solid state diode.
7. in an oil burner control system, a main relay hav
60
ing a winding which when energized causes fuel to be
supplied to a burner, a starting circuit for energizing
said main relay winding including a power source, a
space thermostat, said winding, a pair of normally open
?ame detector relay contacts, a normally closed thermal
time switch and a resistance heater for operating said
time switch all in series relationship, a parallel running
circuit connected across said normally open ?ame de
tector relay contacts and said resistance heater andin
eluding in series relationship normally open main relay
holding contacts which close when said main relay wind
ing is energized and a resistor, a ?ame detector relay
including a winding which when energized effects the
closing of said ?ame detector relay contacts to complete
said starting circuit, a circuit for said ?ame detector relay
winding including in series relationship said power source,
8,079,982
.
'7
,
said thermostat, a limiting resistor, a voltage dependent
resistor, and said flame detector relay winding, said volt
age dependent resistor having a conductivity at the ap
plied voltage in series with said limiting resistor which,
permits energization of said ?ame detector relay to ef
feet the closure of said normally open ?ame detector
8
main relay Winding including a resistance heater of con
siderably greater resistance than said safety switch heater
and which is operative when energized to cause said
double-throw scavenging switch blade to move in a pre
determined time from its cold side contact to a hot side
contact, a pair of normally open main relay contacts
relay contacts in said main relay starting circuit, and
said voltage dependent resistor having a voltage/current
,ratio change in the immediate range of the applied volt
which close when said main relay winding energizes, and
circuit connections connecting said scavenging switch
?ame detector relay winding, said element being shielded
impedance main relay winding when said ?ame detector
heater and said main relay contacts in parallel with that
age which results in a substantial drop in conductivity 10 portion of said main relay circuit which includes said
?ame detector relay contacts and said safety switch
with a slight drop below the applied voltage, a solid
heater, whereby said safety switch heater is in series with
state photoconductive element connected in parallel with
‘said high impedance ignition relay winding and said scav
that portion of said ?ame detector relay winding circuit
enging switch heater is in series with said relatively low
which includes said voltage dependent resistor and said
from ambient light and arranged to ‘see ?ame at the
contacts are open, but when said contacts are closed
burner, and said element having extremely high resist
said safety switch heater and said scavenging switch
energization of said thermal time switch heater.
8. A control system as set forth in claim 7 in‘ which
burner operation the main relay winding is shorted
through this parallel.
includes said normally open ?ame detector relay con
to near the lower limit of the critical voltage range and
heater are each in series with said parallel connected
ance in the absence of burner ?ame, but becoming su?i
ignition relay and motor relay windings, thereby permit
ciently conductive in the presence of burner ?ame to effect
such drop in the applied voltage on the parallel con 20 ting relatively rapid heating of the safety'switch when
said ?ame detector contacts are closed in the absence
nected voltage dependent resistor as to reduce its con
of light and thereby immediately reducing the rate of
ductivity below that which will maintain functional en
heating of the safety switch when said ?ame detector
ergization of said ?ame detector relay winding, whereby
contacts open indicating the presence of light, and a low
it said photoconductive element defects for any reason
resistance parallel circuit connected across said motor
25
in a manner to become conductive prior to the closing
relay winding and including said ?ame detector relay
of the space thermostat said starting circuit will not be
contacts and the common blade of said double-throw
completed and said main relay winding will not be en
scavenging switch and its hot side contact, whereby if
ergized upon closure of said thermostat, and whereby
a change from a condition of light to no light with re
the appearance of burner ?ame subsequent to the closing
of said thermostat in normal operation will effect de 30 spect to said light sensitive network occurs during normal
10. A burner control circuit as set forth in claim 9 in
said ?ame detector relay winding circuit further includes
which
said light sensitive network comprises in series
va solid state diode in series with said relay Winding and
said voltage dependent resistor, in which a capacitor is 35 connect-ion a limiting resistor, a solid state voltage de
pendent resistor in which the voltage/ current ratio
connected across said ?ame detector relay winding and
changes rapidly in a critical voltage range, the ?ame de
in which said solid state photoconductive element is
tector relay winding, and a solid state diode, a capacitor
connected in parallel with said voltage dependent re
connected across said relay winding, a solid state photo
sister, said winding and said diode, whereby the cur
conductive element shielded from ambient light but ar
rent passing through said Winding is unidirectional while
ranged to see a burner ?ame, said element having an
the current passing through said photoconductive element
extremely high resistance in the absence of burner ?ame
is alternating.
but becoming conductive when ?ame exists, said ele
9. In a burner control circuit, a main relay winding
ment being connected across that portion of the series
which when energized causes fuel to be supplied to the
‘burner and an ignition relay winding having consider 45, connection which includes the voltage dependent resistor
and the ?ame detector relay winding the value of said
ably greater impedance than said main burner relay
limiting resistor being such that the'voltage applied across
winding and which when energized effects operation of
said voltage dependent resistor in the absence of burner
an ignition device, a source of power, a circuit for said
?ame is near the upper limit of said critical voltage
main relay including in series relationship a space ther
50 range and causes a current ?ow through said voltage de
mostat, said power source, a normally closed safety
pendent resistor which effects operative energization of
switch, a resistance heater for said safety switch, the
the ?ame detector relay winding, and the conductivity of
cold side contact and common bimetal blade of a double
said parallel connected photoconductive element is such
throw scavenging switch, normally open ?ame detector
relay contacts, and said main relay winding, circuit con 55 when burner ?ame exists as to increase the voltage drop
across said limiting resistor to a point wherein the volt
nection-s connecting said ignition relay Winding in paral
age
applied across said voltage dependent resistor drops
lel with that portion of said main relay circuit which
is insu?icient to e?ect a current ?ow through said volt
tacts and said main relay winding, whereby upon closure
»age dependent resistor which will maintain operative en
of said space thermostat said ignition relay winding is
60
ergization of said ?ame detector relay winding.
immediately energized, a ?ame detector relay winding
operative when energized to close said ?ame detector
References’ Cited in the ?le of this patent
relay contacts to complete a pull-in energizing circuit
UNITED STATES PATENTS
for said, m-ain relay, an energizing circuit for said ?ame
detector relay winding including said power source, said 65 2,440,700
Rosche ______________ __ May 4, 1948
space thermostat, and a light sensitive network including
2,602,847
Larew _______________ __ July 8, 1952
said relay winding and which is su?iciently conductive
2,924,754
Mead _______ __' _______ __ Feb. 9, 1960
in the absence of the light of combustion ?ame to per
2,966,619 7 Burckhardt ___________ __ Dec. 27, 1960
rnit energization of said winding but which becomes
FOREIGN PATENTS
'
, non-conductive in the presence of the light of combustion
to e?ect its de-energization, a holding circuit for said
869,876
Great Britain __________ __ June 7, 1961
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