U.S. patent number 3,766,441 [Application Number 05/035,852] was granted by the patent office on 1973-10-16 for controlling and monitoring combustible gases.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Stuart William Gray.
United States Patent |
3,766,441 |
Gray |
October 16, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
CONTROLLING AND MONITORING COMBUSTIBLE GASES
Abstract
Apparatus for monitoring and controlling the flow of a
combustible gas includes a solenoid operated gas valve to control
the gas flow. The solenoid is energized from an AC supply via a
thyristor switch. When the gas is ignited an ionization current
flows through the flame and is monitored to control the trigger
electrode of the thyristor. When the flame is out the thyristor is
not triggered so that it remains cut-off and deenergizes the
solenoid. This closes the gas valve to cut off the gas flow.
Triggering may take place through a phase advance circuit. Ignition
sparks may be provided by means of a capacitor and a step-up
transformer arrangement in which the capacitor is periodically
discharged through the thyristor to produce spark pulses via the
transformer.
Inventors: |
Gray; Stuart William (Sutton,
Surry, EN) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
|
Family
ID: |
10200929 |
Appl.
No.: |
05/035,852 |
Filed: |
May 8, 1970 |
Foreign Application Priority Data
|
|
|
|
|
May 9, 1969 [GB] |
|
|
23,763/69 |
|
Current U.S.
Class: |
361/170; 340/579;
361/198; 431/6; 431/78 |
Current CPC
Class: |
F23N
5/242 (20130101); G05B 19/00 (20130101); F23N
5/123 (20130101); F23N 2231/06 (20200101); F23N
2227/36 (20200101) |
Current International
Class: |
F23N
5/12 (20060101); F23n 005/00 () |
Field of
Search: |
;431/78,71,25,6,24
;317/148.5B,151,DIG.1 ;340/228.1 ;323/19,22SC,38,36 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Miller; J. D.
Assistant Examiner: Moose, Jr.; Harry E.
Claims
I claim:
1. Apparatus for monitoring and controlling the flow of a
combustible gas comprising, an alternating current supply, a gas
valve operated by a solenoid for controlling the flow of gas to a
burner, a semiconductor thyristor switch having a control
electrode, means connecting the switch in series circuit with the
solenoid and the AC supply so that the switch controls the flow of
current from the AC supply to the solenoid, means for monitoring
the ionization current that flows through the burner gas flame when
the gas is ignited, circuit means coupling said monitoring means to
said control electrode and responsive thereto so as to trigger the
switch into conduction when the gas is ignited and to inhibit the
triggering thereof in the absence of a flame whereby the solenoid
is operated to close the gas valve and cut off the gas flow to the
burner, and said circuit means includes a phase advance circuit
connecting said control electrode to the AC supply thereby to
trigger said thyristor switch from said AC supply.
2. Apparatus as claimed in claim 1 wherein said circuit means
further comprises a first transistor coupled to the control
electrode of said thyristor switch to inhibit the triggering
thereof when said first transistor is conductive, means for
applying to the base of said first transistor a bias voltage
derived from said AC supply and of a polarity to produce conduction
in the transistor, means for applying the flame ionisation current
to the base of said first transistor with a phase retardation
relative to the AC supply so as to render that transistor
non-conducting during at least a portion of each cycle of said
alternating supply, at least a part of said portion coinciding with
the beginning of each positive half cycle of the AC supply thereby
allowing said switch to be triggered.
3. Apparatus as claimed in claim 2 in which, in the absence of said
flame ionisation current, said first transistor is rendered
conductive by the bias voltage applied to its base thereby to
inhibit the triggering of said thyristor switch.
4. Apparatus as claimed in claim 2 wherein said circuit means
further comprises second and third transistors, means operatively
connecting said first transistor in cascade with said second and
third transistors so that said third transistor is rendered
conductive when said first transistor is conductive, and means
connecting said third transistor to the thyristor control
electrode.
5. Apparatus as claimed in claim 4 wherein said circuit means
further comprises a resistor capacitor circuit connected between
one side of said alternating supply and the collector of said third
transistor so that, with the flame ionization current present, the
thyristor switch is triggered via said RC circuit, the collector of
said third transistor also being connected to the trigger electrode
of said switch.
6. Apparatus as claimed in claim 5 in which said third transistor
is connected between the cathode and the trigger electrode of said
thyristor switch so that, in the absence of said flame ionisation
current, said third transistor is rendered conductive bypassing the
triggering current away from the trigger electrode of said
switch.
7. Apparatus for monitoring and controlling the flow of a
combustible gas comprising, an alternating current supply, a gas
valve operated by a solenoid for controlling the flow of gas to a
burner, a semiconductor switch having a control electrode, means
connecting the switch in series circuit with the solenoid and the
AC supply so that the switch controls the flow of current from the
AC supply to the solenoid, means for monitoring the ionization
current that flows through the burner gas flame when the gas is
ignited, circuit means coupling said monitoring means to said
control electrode and and responsive thereto so as to trigger the
switch into conduction when the gas is ignited and to inhibit the
triggering thereof in the absence of a flame whereby the solenoid
is operated to close the gas valve and cut off the gas flow to the
burner, a diode and a capacitor serially connected with the primary
winding of a transformer across said AC supply, and means
connecting the series circuit comprising said capacitor and primary
winding in parallel with said switch so that said capacitor is
charged from said alternating supply from the commencement of each
cycle of said AC supply for a period until said switch is triggered
and then is discharged via said switch through the primary of said
transformer to produce a train of sparks across a spark gap located
at said burner and connected across the secondary winding of said
transformer.
8. Apparatus as claimed in claim 1 further comprising a capacitor
connected in series circuit with the primary winding of an ignition
transformer across said AC supply so as to charge the capacitor at
the start of each cycle of said AC supply until the switch is
triggered into conduction, means connecting said series circuit in
parallel with said switch so that the switch provides a discharge
path for the capacitor through said primary winding, and wherein
said circuit means includes electric delay means which, during a
burner ignition period, delays the triggering of said switch to a
period between 30.degree. and 90.degree. subsequent to the start of
each cycle of said AC supply, and means connecting the secondary
winding of said transformer to an ignition electrode of the
burner.
9. Apparatus as claimed in claim 8 wherein said circuit means
further comprises a first transistor coupled to the control
electrode of said semiconductor switch so as to inhibit the
triggering thereof when said first transistor is fully conductive,
and a bias capacitor coupled to the base of the second transistor
and to said AC supply and arranged to bias said first transistor
into full conduction in the absence of said flame ionization
current.
10. Apparatus as claimed in claim 9 wherein said circuit means
includes means for coupling the flame ionization current, when
present, from said monitoring means to the base of the first
transistor so as cut-off said first transistor at the start of each
cycle of said AC supply thereby to allow said semiconductor switch
to be triggered into conduction at that time.
11. Apparatus as claimed in claim 1 wherein said circuit means
further comprises a phase delay circuit interposed between said
monitoring means and said control electrode whereby the triggering
of the switch is controlled jointly by the AC supply and the
ionisation current at a time subsequent to ignition of the gas.
12. Flow control apparatus for a combustible gas comprising, input
terminals adapted for connection to a source of AC supply current,
a solenoid operated gas valve for controlling the gas flow, a
semiconductor controlled switch connected in series circuit with
the input terminals and the solenoid so that the switch controls
the flow of current from the input terminals to the solenoid, phase
control means coupling an input terminal to a control electrode of
said switch to supply a periodic trigger signal thereto in advance
of the start of each cycle of the AC supply and independent of the
state of the gas thereby to initiate conduction through said
switch, means for monitoring the gas so as to derive an ionization
current from the gas when the gas is burning, a first current
control element with its output coupled to the control electrode of
the switch and its input coupled to said monitoring means so as to
respond to said ionization current, when present, said control
element being operative to apply a first control signal to said
control electrode that will inhibit the triggering of the switch
when said ionization current is absent at its input thereby to
operate the solenoid to close off the gas valve and being operative
when said ionization current is present at its input to apply a
second control signal thereto at or near the start of each cycle of
the AC supply that allows said trigger signal to then trigger the
switch into conduction.
13. Apparatus as claimed in claim 12 wherein the input circuit of
said control element further comprises means coupled to the input
terminals for varying the DC bias voltage applied to the control
element during an initial ignition period for the apparatus such
that, in the absence of the ionization current, said first control
signal is varied as a function of the bias voltage in a manner such
as to gradually vary the delay in the triggering of the switch
relative to the start of each cycle of the AC supply.
14. Apparatus as claimed in claim 12 further comprising a capacitor
connected in series circuit with the primary winding of an ignition
transformer, means connecting said series circuit in parallel with
said switch so that the switch provides a path for selectively
discharging the capacitor through said primary winding, a charge
circuit coupling said series circuit to the input terminals so that
the capacitor is charged from said AC supply when the switch is
cut-off, and means connecting the secondary winding of the
transformer to an ignition electrode whereby sparks are produced at
said electrode in synchronism with the discharge of the
capacitor.
15. Apparatus as claimed in claim 14 further comprising a bias
capacitor connected to the input of said first control element and
to the input terminals via a DC charge circuit and operative when
the charge thereon reaches a given level to apply a bias voltage to
said control element which, in the absence of any ionization
current, will cause said control element to derive said first
inhibit control signal to prevent the triggering of the switch and
hence prevent the generation of sparks.
16. Apparatus as claimed in claim 15 further comprising means for
retarding the phase of said AC ionization current relative to the
AC supply so as to overide said bias voltage near the start of each
cycle of the AC supply whereby said control element becomes
operative to derive and apply said second control signal to the
switch to trigger same near the start of each cycle of the AC
supply and thereby prevent the first capacitor from charging to a
level sufficient to generate sparks.
17. Apparatus as claimed in claim 16 wherein said charge circuit
includes a rectifier element, said switch comprises a thyristor,
and said phase control means includes a capacitor for advancing the
phase of the trigger signal relative to the AC supply.
18. Flow control apparatus for a combustible gas comprising, input
terminals adapted for connection to a source of AC supply current,
a solenoid operated gas valve for controlling the gas flow, a
semiconductor controlled switch connected in series circuit with
the solenoid across the input terminals to control the current flow
from said terminals to the solenoid, phase control means coupling
an input terminal to a control electrode of said switch to supply a
periodic trigger signal thereto in advance of the positive half
cycle of the AC supply voltage applied to the anode of the switch,
ignition means for igniting said gas and coupled to said switch,
means for monitoring the gas so as to derive an electric signal
therefrom when the gas is ignited, and circuit means responsive to
said signal, when present, to apply a first control signal to said
control electrode at or near the start of each positive half cycle
of the AC supply which allows said trigger signal to trigger the
switch into conduction and thereby inhibits the operation of said
ignition means, said circuit means being operative to delay the
triggering of said switch for a given ignition period when said
signal is absent thereby to operate said ignition means via said
switch and to subsequently apply a second control signal to said
control electrode that will inhibit the triggering of the switch if
the gas does not ignite during said ignition period.
19. Apparatus as claimed in claim 18 wherein said ignition means
comprises a capacitor and an ignition coil serially connected
across the switch terminals and to the input terminals in a manner
whereby said capacitor is allowed to charge up only when the switch
is cut-off, and wherein said circuit means includes an amplifier
with a control electrode coupled to said monitoring means and an
output electrode coupled to the control electrode of the
semiconductor switch.
Description
The present invention relates to a method of and apparatus for
controlling and monitoring a combustible gas. The invention also
relates to a method of and apparatus for igniting the combustible
gas.
Where it is desired to automatically ignite a conbustible gas such
as a natural or artifically produced hydrocarbon gas it is
necessary to have some means of monitoring whether or not the gas
is in fact ignited and to cut off the supply of gas if the gas is
not ignited. Such monitoring and control is necessary in gas fired
central heating appliances.
It is an object of the present invention to provide a method of and
apparatus for monitoring and controlling a combustible gas
employing electronic techniques.
The present invention provides a method of monitoring and
controlling a combustible gas, in which method a solenoid operable
gas valve is provided which, when opened, allows a stream of said
gas to pass to a burner. The solenoid is energisable by current
flowing through a semiconductor switch when in its conductive
state. An ionisation current which flows through the flame of the
gas when ignited at the burner allows the switch to be triggered to
render it conductive whereas in the absence of the flame the switch
is prevented from being triggered to hold it non-conducting thereby
closing the gas valve to cut off the gas stream to the burner.
Such a method may also incorporate a method of igniting the gas at
the burner, in which ignition method a previously charged capacitor
is periodically discharged through the switch to produce a train of
sparks at the burner. The switch at these periods is rendered
conductive thereby energising the solenoid to allow the gas stream
to pass to the burner. The train of sparks may only be produced for
a limited period, after which, if the gas is ignited, flame
ionisation current causes the switch to be triggered, or if the gas
is not ignited, the switch is prevented from being triggered.
The invention also provides apparatus for carrying out the method
of the present invention. In such apparatus the solenoid operable
gas valve may be energisable from an alternating supply. When the
gas is ignited, the switch is triggered, at or near the beginning
of each cycle of the alternating supply. Triggering takes place
through a phase advance circuit. The solenoid of the gas valve and
the switch may be connected in series across the alternating
supply. The semiconductor switch may be a thyristor and a diode may
be provided in the series connection betwen the solenoid and the
thyristor, the diode being poled for conduction in the same
direction as the thyristor. The semiconductor switch may
alternatively be a triac, i.e. a bi-directional semiconductor
switch, and a diode may be provided in the series connection
between the solenoid and the triac.
The flame ionisation current may be applied to the base of a first
transistor to render that transistor non-conducting during at least
a portion of each cycle of the alternating supply, at least a part
of this portion coinciding with the beginning of each cycle when
the switch is to be triggered. In the absence of the flame
ionisation current the first transistor is rendered conductive to
prevent the switch from being triggered when the first transistor
may be rendered conductive by a bias applied to its base derived
from the alternating supply.
The first transistor may be provided in cascade with second and
third transistors, the third transistor being rendered conductive
when the first transistor is conductive.
When the flame ionisation current is available, the switch may be
triggered from a resistor-capacitor circuit connected between one
side of the alternating supply and the collector of the third
transistor, the collector also being connected to the trigger
electrode of the switch. The emitter of the third transistor may be
connected to the other side of the alternating supply to which the
electrode of the switch remote from the solenoid also is connected.
In the absence of this flame ionisation current the third
transistor is rendered conductive bypassing the triggering current
from the trigger electrode of the switch.
The invention also provides apparatus for igniting a combustible
gas in which a capacitor is serially connected with the primary of
a transformer, the resulting series circuit being connected in
parallel with the switch. The capacitor is charged from the
alternating supply from the commencement of each cycle of the
supply for a period until the switch is triggered. The switch, when
periodically triggered, discharges the capacitor through the
primary of the transformer to produce a train of sparks across a
spark gap located at the burner and connected across the secondary
winding of the transformer. During the ignition period, the
thyristor is triggered at between 30.degree. and 90.degree. after
the commencement of each cycle.
The train of sparks may be produced during a period commencing at
or just after the energisation of the apparatus from the
alternating supply and ending when the charge on a second capacitor
in the bias circuit for the base of the first transistor has
reached a given level. After this period the switch may be
triggered at or near the commencement of each cycle if the gas has
ignited, or if the gas has not ignited, the switch may be prevented
from being triggered. If the gas has not been ignited, the train of
sparks may not be reproduced until the apparatus has been
disconnected and subsequently reconnected to the alternating
supply. Alternatively, a switch may be provided for discharging the
second capacitor. After discharging the second capacitor, a second
period maybe provided during which a further train of sparks may be
produced and the solenoid re-energised.
The above and other features of the present invention will be more
readily understood by a perusal of the following description having
reference to the accompanying drawing which shows a circuit
arrangement of apparatus for the method of the present
invention.
Referring now to the sole FIGURE of the accompanying drawing there
is shown a circuit arrangement capable of monitoring, controlling
and igniting a stream of combustible hydrocarbon gas. The circuit
is arranged to be connected between the neutral N and live L
terminals of an alternating supply such as of 240 volts 50 Hz. A
solenoid operated gas valve V is provided which, when energized,
allows a stream of the gas to pass to a gas burner B. The solenoid
of the gas valve V is provided between the neutral and live supply
lines in series with a diode D4 and a thyristor SCR, both of which
are poled for conduction in the same direction, i.e. when the
neutral line N is positive with respect to the live line L.
Thyristor SCR is shunted by a series circuit formed by a capacitor
C4 and the primary winding of a transformer T, the secondary
winding of this transformer having its terminals connected to the
gas burner B, which is at earth potential, and an ignition
electrode I which forms a spark gap. A further electrode M provided
adjacent to the burner B is returned through a resistor R3 to the
base of an npn transistor TR1 whose emitter is directly connected
to the supply line L. The base of transistor TR1 is also coupled to
the supply line L through a capacitor C2 and is additionally
connected to the junction of a resistor R1 and a capacitor C1
through a further resistor R2. The terminal of capacitor C1 remote
from this junction is connected to the supply line L while the
terminal of resistor R1 remote from the junction is connected
through a diode D1 to the junction of a pair of serially connected
resistors R6, R7. The collector of transistor TR1 is connected
through a resistor R4 to the supply line N and is directly
connected to the base of a further npn transistor TR2 and through a
diode D2 to the supply line L. The emitter electrode of transistor
TR2 is directly connected to the supply line L while its collector
electrode is connected through a resistor R5 to the junction of the
serially connected resistors R6, R7. Additionally the collector of
transistor TR2 is directly connected to the base of a npn
transistor TR3 whose emitter is directly connected to the supply
line L. The collector electrode of the latter mentioned transistor
is connected to the terminal of resistor R7 remote from its
junction with resistor R6. The terminal of resistor R6 remote from
the junction is connected through a capacitor C3 to the supply line
N, the junction being additionally connected through a diode D3 to
the supply line L. In addition the collector electrode of
transistor TR3 is directly connected to the trigger electrode of
the thyristor SCR.
In considering the operation of the circuit arrangement it is
assumed that initially the terminals L and N are disconnected from
the alternating supply in which case no part of the circuit will be
operative and gas valve V will be closed due to the solenoid being
de-energised which in turn prevents a stream of gas from being
passed to the burner B. On application of the alternating supply to
the terminals N and L, a phase advance circuit is formed by
capacitor C3 and resistors R6, R7 phase advancing the current
applied to the trigger electrode of thyristor SCR by nearly
90.degree. with respect to its anode voltage and ensuring adequate
current to trigger the thyristor at the beginning of each positive
half cycle at the supply line N. This causes the solenoid of gas
valve V to be energized thereby opening the valve and allowing a
stream of gas to be passed to the burner B. At the initial
application of the AC supply to the circuit, capacitor C1 is in a
discharged state and since its charge path includes resistor R1,
which has a high value (in the order of 1 M ohm) it takes a few
seconds for this capacitor to be charged from the direct voltage
supply produced by diode D1 from the junction of resistors R6, R7.
Thus transistor TR1 is initially cut off allowing transistor TR2 to
conduct during positive half cycles at the supply line N as this
latter transistor is biased through resistor R4. Driving negative
half cycles the base of transistor TR2 is connected to the line L
through the diode D2 cutting off transistor TR2 and additionally
preventing the collector of transistor TR1 from going negative.
During the positive half cycles transistor TR3 is non-conducting
causing the phase advanced triggering pulses to be applied to the
trigger electrode of thyristor SCR. As capacitor C1 is gradually
charged, transistor TR1 gradually turns on progressively diverting
current through resistor R4 away from the base of transistor TR2.
Due to the sinuosidal current through resistor R4 transistor TR2 is
turned on progressively later in each half cycle thus causing the
thyristor SCR to be triggered later in each half cycle, i.e.
somewhere between 30.degree. and 90.degree. after the commencement
of each positive half cycle, the solenoid of gas valve V remaining
energized if triggering takes place before 90.degree.. When the
thyristor SCR is triggered later in the cycle, say at 30.degree.,
the capacitor C4 can be charged from the alternating supply. This
capacitor is discharged through the primary of transformer T when
the thyristor SCR is triggered and rendered conductive. The
transformer T receives the energy stored in the capacitor C4 and
dissipates it across the spark gas formed between the ignition
electrode I and the burner B, these sparks providing ignition for
the gas stream. If the gas is ignited and a flame is produced at
the burner B an alternating current flows from the burner B, which
is at or near neutral potential, by way of the ionised gas in the
flame, the monitoring electrode M and resistor R3. This alternating
current is phase retarded by the capacitor C2 and applied to the
base of transistor TR1. During a portion of each alternating cycle
this alternating current opposes the bias current applied to the
base of transistor TR1 to render that transistor non-conducting.
Due to the fact that the alternating current from the monitoring
electrode M is phase retarded, transistor TR1 remains
non-conducting for a major portion of each cycle. Part of this
non-conducting portion coincides with the commencement of each
positive half cycle thereby rendering, during this time,
transistors TR2 and TR3 conducting and non-conducting,
respectively, and causing thyristor SCR to be turned on at the
beginning of each cycle when the flame is burning. With the circuit
in this condition capacitor C4 is prevented from being charged and
sparks will not occur at the spark gap.
If, however, the gas fails to ignite in the time it takes to nearly
fully charge capacitor C1, or if the flame is at any time
extinguished, transistor TR1 and hence transistor TR3 are held
conductive thereby preventing triggering pulses from being applied
to the gate electrode of the thyristor SCR. This in turn causes gas
valve V to be closed. At this time capacitor C4 is charged but as
thyristor SCR is not rendered conductive, a discharge path is not
provided for the capacitor and sparks will not be produced at the
spark gap. The circuit will then be "locked out" and in order to
return it to the igniting condition it is necessary to disconnect
the circuit arrangement from the alternating supply for a matter of
several seconds. Alternatively, a switch may be provided across
capacitor C1 capable of discharging that capacitor after which time
the charge operation will recommence and allow a train of sparks to
be produced at the burner B and the solenoid to be
re-energized.
The function of diode D3 in the circuit is to provide a reverse
current path for capacitor C3 and resistor R6, preventing the
junction of resistor R6, R7 from going negative and so preventing
the collectors of transistors TR2 and TR3 from going negative with
respect to their emitters.
In a practical arrangement of the circuit, the following components
were employed:
R1 . . 1 M ohm
R2 . . 10 M ohm
R3 . . 10 M ohm
R4 . . 10 M ohm
R5 . . 100 K ohm
R6 . . 1.2 K ohm
R7 . . 1.2 K ohm
C1 . . 1 .mu. Farad
C2 . . 3.3 n Farad
C3 . . 0.15 .mu. Farad
C4 . . 0.47 .mu. Farad
TR1 Mullard Limited Type BC 149
TR2 Mullard Limited Type BC 148
TR3 Mullard Limited Type BC 148
D1 . . Mullard Limited Type BAX 13
D2 . . Mullard Limited Type BAX 13
D3 . . Mullard Limited Type OA 91
D4 . . Mullard Limited Type BY 126
SCR . . Mullard Limited Type BT 100A
T . . Primary 25 turns, secondary 1,250 turns.
* * * * *