Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02483367 2004-09-30
TITLE
IMPROVED FLAME SENSOR FOR A BURNER
INTRODUCTION
This invention relates to a flame sensor and, more
particularly, to a flame sensor which senses the presence of a
flame within a burner and which flame sensor produces two
signals to verify the presence of the flame within the burner.
BACKGROUND OF THE INVENTION
Flame sensors are used to sense the presence or
absence of a flame in a heater or burner, for example, or
other apparatus. The heater or burner may be used to heat
water or ambient air and the fuel used may be one of several
different types.
In the event the flame is extinguished, although not
deliberately so, the sensor is adapted to sense the absence of
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the flame. The flame can be extinguished, for example, by
fuel starvation or other malfunction. After sensing the
extinguishing of the flame, the sensor or its related
circuitry will send an alarm signal to a microcontroller. The
microcontroller will take appropriate action such as shutting
down the heater or burner by terminating fuel flow. In such a
manner, serious safety problems such as continued fuel flow
into a hot burner without a flame being present for combusting
the fuel are avoided.
However, it is inconvenient to terminate the fuel
flow if the flame is present and the burner is working
properly. The termination of the fuel flow causes termination
of the operation of the burner or heater unintendedly if the
flame sensor sends an incorrect signal to the control panel.
The present invention has as an object the avoidance of
inadvertent burner shutdown and, as well, the avoidance of
burner operation when the flame is extinguished.
One reason for unintended burner shutdown is signal
contamination of the signal from the flame sensor, Since the
power of the signal previously sent to the amplifier is quite
small, in the range of 50 my to 200 mv, and since the
amplifier was located some distance from the sensor, any noise
caused by common mode radiation or other RF signals could
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disrupt the integrity of the signal being passed to the
amplifier by the sensor. This causes incorrect information to
be read by the microcontroller with the result that the heater
could be inadvertently shut down or, alternatively, the heater
may continue to run in a flame out condition. Both scenarios
are not desirable.
In our United States patent application serial no.
09/579,444 filed May 26, 2000, now United States Patent
6,652,266, there is disclosed a circuit for a flame sensor
which utilises an amplifier and rectifier circuit in which
full amplification of the pulsed signal leaving the amplifier
does not take place due to a feedback loop between the output
of the amplifier and the inverting input of the amplifier.
This leads to a decreased reading sensitivity of the pulsed
signal generated by the photodiode of the flame sensor.
To sense the presence or absence of a flame in a
burner, a photo diode is generally used. As the flame
flickers in the burner during operation, the photo diode will
sense the flickering or change of light in the flame and
generate a signal to indicate the presence of a flame. The
components of the heater, however, generates noise and this
noise can produce a signal which is similar to the
signal generated by the photo diode when a flame is present.
Thus, the flame sensor circuit may incorrectly signal that a
flame is present.
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SUMMARY OF THE INVENTION
According to one aspect of the invention there is
provided a method of sensing the presence of a flame in a
burner comprising the steps of generating a first signal from
a sensor which first signal is an intensity signal which is
proportional to the light intensity of said flame in said
burner, generating a second signal by detecting the change of
voltage in said sensor which change of voltage is caused by
the flicker of said flame in said burner, detecting whether
said first and second signals are present at a signal circuit
component and producing an output signal from said signal
circuit component if said first and second signals are both
detected at said signal circuit component.
According to a further aspect of the invention there
is provided a circuit for a flame sensor used for sensing the
presence of a flame in a burner, said circuit comprising a
sensor for sensing said flame, said sensor producing a first
intensity signal which is a voltage proportional to the light
intensity of said flame in said burner, said sensor producing
a second flickering signal sensing the flicker of said flame
in said burner, and a second output signal circuit component
for producing an output signal when said first intensity
signal and said second flickering signal are present at said
second output signal circuit component.
According to yet a further aspect of the invention
there is provided a method of sensing the presence of a flame
in a burner comprising the steps of generating a first signal
from a photo diode which first signal is an intensity signal
proportional to the light intensity of said flame in said
burner, generating a second signal by detecting the change of
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voltage in said sensor which change of voltage is caused by
the flicker of said flame in said burner, said second signal
being a flicker signal, amplifying said intensity signal,
passing said intensity signal and said flicker signal to the
collector and base of a transistor, detecting whether said
intensity and flicker signals are present at said base and
collector of said transistor and emitting an output signal
from said transistor if said intensity and flicker signals are
present at said base and collector of said transistor.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Specific embodiments of the invention will now be
described, by way of example only, with the use of drawings in
which:
Figure 1A is a diagrammatic schematic of the flame
sensor by way of photodiode which incorporates the amplifier
circuitry according to a first aspect of the invention;
Figure 1B is similar to Figure IA but illustrates
the use of a flame sensor which is a photoresistor rather that
the photodiode of Figure 1A;
Figure 2A is a diagrammatic schematic of the missing
pulses detector and sensor supervisor used for monitoring the
flame sensor signal and the integrity of the connections
between the amplifier and the microcontroller;
Figure 2B is a diagrammatic and enlarged schematic
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particularly illustrating the connections between the
amplifier and the microcontroller, the missing pulses detector
and the supervisory circuit;
Figures 3A-3F are diagrammatic schematics of the
main board which includes the missing pulses detector and the
sensor supervisor of Figures 2A and 2B;
Figures 4A and 4B are diagrammatic isometric cutaway
views of the housings used to house the flame sensor, the
amplifier, the sensor supervisor and their related circuitry;
Figure 5 is a diagrammatic isometric view of a
housing but not being illustrating in cutaway;
Figure 6 is a diagrammatic isometric view
illustrating the position of the flame sensor relative to the
flame being sensed;
Figure 7 is a diagrammatic isometric view of a
powered multifuel burner which utilises the flame sensor
according to the invention;
Figure 8 is a diagrammatic schematic illustrating a
modified circuit for the flame sensor; and
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Figure 9 is a diagrammatic schematic illustrating a
flame sensor circuit according to a further aspect of the
invention.
DESCRIPTION OF SPECIFIC EMBODIMENT
Referring now to the drawings, a powered multifuel
burner is generally illustrated at 100 in Figure 7. An
infrared type burner 101 has a flame 105 (Figure 6) generated
within the cylinder 106 of the burner 101 by way of an air
aspirated nozzle (not shown) which uses a venturi effect to
draw fuel into the nozzle. Combustion takes place outside the
nozzle but within the cylinder 106. The flame sensor 110 is
located generally at 102 as illustrated in Figure 6.
The flame sensor 110 may include either an infrared
sensor or an ultraviolet sensor or, alternatively, a
combination of an infrared and ultraviolet sensor. Each or
both of the sensors 103 are positioned in the housing 121
(Figure 4A) to sense the visible infrared and ultraviolet
radiation produced by the combustion flame. The sensors 103
selected for the particular application will depend on the
flame being produced within the burner 100. If, for example,
the flame burns with an orange patina, the primary sensor will
be infrared. Alternatively, if the flame burns primarily with
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blue radiation, an ultraviolet sensor will be utilised.
The schematic of Figure 1 discloses both infrared
and ultraviolet sensors 103, 104 and their related circuitry.
The sensors 103, 104 are photodetectors shown generally at
110. The output from the sensors 103, 104 passes to a real to
real integrator amplifier section 111. A rectifier 112
rectifies the signal passing from the amplifier section 111.
A voltage regulator 113 is used to regulate the voltage and a
read out circuit 114 is used to show the conditions of the
signal passing from the sensors 103, 104, the amplifier 111
and rectifier 112. The read our circuit is exemplified by an
LED generally shown at 120 in Figures 1 and 4A.
All of the components of the schematic of Figure 1
are included with the sensors 103, 104 and are mounted within
the housing 121 (Figures 4A, 4B and 5) associated with the
sensors 103, 104. It will thereby be seen that the components
described, particularly the amplifier circuit 111, are located
closely to the sensors 103, 104 and, indeed, are directly
connected thereto to avoid the need for cables and the like to
run from the sensors 103 to the main board 124 where further
processing is accomplished. This allows the relatively small
signal generated by the sensors 103, 104 to be amplified
without the signal picking up noise from ground terminal and
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RP radiation which may be present and picked up by the cables
if the sensors 103, 104 were separated from the amplifier 111
which otherwise would be located in the main board 124.
The missing pulse detector and the sensor supervisor
are generally illustrated at 122, 123, respectively, in Figure
2. These circuit components are located remotely from the
sensor housing 121 and on the main board illustrated generally
at 124 in Figure 3. These components 122, 123, as well as the
remaining main board circuit components which will be
described are separated from the components of Figure 1 by
cable 129 (Figure 4A) and are remote from the housing 121 of
the sensors 103, 104.
Referring to Figures 2B and 3, the missing pulses
detector 122 and the sensor supervisor 123 are shown in
greater detail and are included on the main board 124. In
addition, the burner interface circuitry :130, zone board 131,
voltage supervisor 132, computer interface 133,
microcontroller 134, filter 140, open circuit for combustion
fan supervisory 141 and relay driver 142 are further included
on the main board 124. A display unit 143 is included on the
main board 124 which shows the status of the various functions
of the burner 100.
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OPERATION
In operation, combustion of the fuel in burner 100
(Figure 5) will be initiated and, following the initiation of
the combustion, the sensors 103, 104 will be activated to
monitor the flame of the burner 100. At the beginning of the
ignition, the flame sensors 103, 104 receive power. The
sensors 103, 104 are located adjacent the flame of the burner
100 (Figure 6) and sense the infrared and ultraviolet
radiation, respectively, emanating from the flame 105. The
circuitry associated with the flame sensors 103, 104 generates
a series of pulses 115 (Figure 2B) read by the missing pulses
detector 122. In the event the flame shuts down, no pulses
will be generated with the result that the missing pulses
detector 122 will sense the missing pulses and instruct the
microcontroller 134 accordingly in order to shut down the
burner 100.
The signal from the photodetectors or sensors 103,
104 will pass to the real to real integrator amplifier 111
and, thence, to rectifier 112. Voltage regulator 113 will
regulate the voltage of the signal generated by the amplifier
111 and the signal leaving rectifier 112 will pass to the
missing pulses detector 122. The LED 120 will show the status
of the sensors 103, 104 while under operation.
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The signal from the rectifier 112 which passes to
the missing pules detector 122 will appear at "A" in Figure
4A. The remaining circuitry illustrated in Figure 3,
including the missing pules detector 122 and the sensor
supervisor 123 are located remotely from the sensors 103, 104,
by way of cables 125, 126, 127 (Figure 2B).
With reference to Figure 3, the remaining circuitry
related to the sensors 103, 104 is illustrated. Such
circuitry includes circuitry relating to the operation of the
burner 100 and the various functions that the burner 100 must
fulfil. However, the circuitry described and its position
within the housing 121 adjacent to the sensors 103, 104 allow
the signal from the sensors 103, 104 to be amplified prior to
conveying the signal to the main board 124 with the result
than any noise or other RF frequency added to the signal is
relatively much smaller than the amplified signal leaving from
"B" of Figure 1 with the result that the signal is relatively
clean and may be clearly determined by the missing pulses
detector 122 and supervisor circuit 123 so as to determine the
condition of the flame in the burner 100 without fear of
common mode RF radiation that might otherwise be gathered by
the cables 125, 126, 127 creating an erroneous signal to the
missing pulses detector 124 and sensor supervisor 123.
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If the burner 100 terminates operation, it may be
desirable to determine the reason for such shutdown. There
are several problems that may cause such shutdown as described
hereinafter.
First and most likely, the burner 100 becomes
starved for fuel because of fuel exhaustion. In this event,
the flame out condition will initiate operation of the
microcontroller 134 in an attempt to again commence operation
of the burner 100. This in intended, for example, to deal
with the problem of an air bubble in the fuel line to the
burner 100. If, following three(3) attempts to commence
operation of the burner 100, the burner 100 fails in continued
operation, the burner 100 will remain in its shutdown
condition and operator intervention will be required.
Second, it may be that the positive wires 125
(figure 2B) become disconnected between the amplifier 111 and
the microcontroller 134 of the main board 124. In this event,
the burner 100 will be in the shutdown condition and the
operator will initiate power flow to the burner 100. The LED
120 will not flash since the circuit between the amplifier 111
and the main board 124 is not complete. The operator will
then know that either the positive or ground wires 125, 126
are defective.
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If LED 120 flashes when power flow commences, the
positive and ground wires 125, 126 are not the reason for the
shutdown and the burner 100 will commence operation. If the
LED 120 is not flashing when the flame is again present, the
sensor 103 itself is at fault. If the LED 120 is flashing and
the sensor 103 is functioning, it indicates that the signal
wire 127 between the amplifier 111 and the main board is
defective.
The time of burner shutdown and the number of
attempted restarts of the burner may, of course, be clearly
changed by appropriate programming of the microcontroller 134.
The sensor 103 can operate into a range of 8-40 VDC supply
voltage. The signal and the output will be in the range of 0-
8 VDC if the output signal stays at high level (over 3.5 VDC)
for a period of time which exceeds the present time in the
sensor supervisory circuit and an alarm signal will be
generated by the sensor supervisory circuit to the
microcontroller 134 to shut down the burner.
While a photodiode and a photoresistor have been
illustrated and described, various other sensors could
likewise be used including a phototransistor and a photocell.
In a further embodiment of the invention, reference
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is now made to Figure 8 wherein a modified circuit for the
flame sensor is generally illustrated at 200. In this
circuit, the photodiode being the flame sensor 201 generates a
voltage corresponding to the brightness of the flame, mainly
in the red and near infrared regions. Its response extends
into the blue but the output is much lower. However, the
photodiode 201 is a very high speed device and its output had
a high flicker content, in step with the flicker of the flame.
The photodiode 201 is a photovoltaic device thereby generating
electricity as a result of the light it receives from the
flame. \
The signal from the photodiode 201 is passed through
C1 which blocks the actual brightness component of the flame
and leaves only the "flicker" signal. This makes the circuit
200 insensitive to ambient light which does not flicker. The
circuit 200 thereby allows for the use of different fuels
which burn at different brightnesses.
The flicker signal is amplified by amplifier U1A and
passes through C2 where the signal is moved from a biased
reference to a ground reference by R12 and D4. This flicker
signal is further amplified by amplifier UlB and detected by
U1C, a generally lossless rectifier circuit.
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It will be particularly noted that the feedback loop
between the output of U1B and the inverting input of U1B has
been eliminated with the result that there is no noise added
to the inverting input of U1B. This allows increased
amplification of the signal leaving UlB which results in the
full amplification of every pulse signal generated by the
photodiode 201 from the flicker of the flame thereby allowing
greater reading sensitivity of the pulsed signal generated by
the photodiode 201.
Yet a further embodiment of the invention is
illustrated in Figure 9which is a schematic of a further
circuit used to sense the presence of flame in a burner
according to a further aspect of the invention.
A first sensor, conveniently a photo diode 300 is
used to sense the presence or absence of a flame generally
illustrated at 301 which flame 301 is present in a burner
generally illustrated at 305 under normal operation. When a
flame 301 is present, the photo diode 300 produces a first
signal 302 due to the flicker of the flame 301 and a second
intensity signal 303 due to the light intensity of the flame
301. The first signal 302 is amplified by amplifier 304 and
then passes to the base of a transistor 311. The second
signal 303 is amplified by amplifier 310 and passes to the
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collector of transistor 311.
When both the first amplified flicker signal 302 and
the second amplified intensity signal 303 are sensed by
transistor 311, the emitter of transistor 311 produces an
output signal which indicates the presence of a flame 301
within the burner. If however, either the first amplified
flicker signal 302 or the second amplified intensity signal
303 is not present at the transistor 311, the emitter will not
produce an output signal which indicates the absence of a
flame 301 within the burner. For example, although a first
flicker signal 302 may be wrongfully present such as may be
the case when noise contaminates the amplifier 304, even
though a flame 301 may not be present, the second intensity
signal 303 will not be present in such a case which will,
therefore, result in no signal being generated by transistor
311. Thus, the control unit of the burner 305 will conclude
no flame is present and the burner 305 will terminate
operation as a safety precaution.
A voltage regulator 320 is provided to power the
circuit of the flame sensor. This voltage regulator 320 will
allow external noise generated by the various heater
components to pass into the flame sensor circuit 305 if the
level of such noise pulls the input voltage to the regulator
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320 below the minimum required voltage. For example, an
eight(8) volt regulator is required to have a minimum of 9.5
volts at the input. If the input is 10 volts and 2 volts
(peak to peak)of noise is present, then the input voltage will
go between 9 volts and 11 volts. When it drops below 9 volts,
the regulator will no longer filter the noise. By utilising a
6 volt regulator in accordance with present invention, the
minimum required voltage is 7.5 volts. So for an input
voltage of 10 volts, there will need to be 5 volts (peak to
peak) of noise to cause the voltage regulator to pass the
noise.
20
30
40
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Many modifications will readily occur to those
skilled in the art to which the invention relates. For
example, although a photo diode 300 and a transistor 311 are
useful in the flame sensor circuit according to the invention,
it seems clear they could be replaced by other suitable
components which could sense both flame flicker and flame
intensity. And although transistor 311 works appropriately
and is conveniently used, it is apparent that other components
might well be used to generate appropriate signals when flame
flicker and flame intensity signals are present at the circuit
component.
