U.S. patent number 3,909,816 [Application Number 05/465,371] was granted by the patent office on 1975-09-30 for flame and carbon monoxide sensor and alarm circuit.
Invention is credited to Lloyd L. Teeters.
United States Patent |
3,909,816 |
Teeters |
September 30, 1975 |
Flame and carbon monoxide sensor and alarm circuit
Abstract
A gas burner monitor providing a high level of protection by
virtue of its dual sensing features wherein both flame color and
combustion products are monitored by means of a simple and
inexpensive electronic circuit.
Inventors: |
Teeters; Lloyd L. (Phoenix,
AZ) |
Family
ID: |
23847544 |
Appl.
No.: |
05/465,371 |
Filed: |
April 29, 1974 |
Current U.S.
Class: |
340/578; 250/554;
340/634 |
Current CPC
Class: |
F23N
5/003 (20130101); F23N 2229/04 (20200101) |
Current International
Class: |
F23N
5/00 (20060101); G08B 017/10 () |
Field of
Search: |
;340/237R,237S,227R
;356/195 ;250/554 ;328/6 ;307/311 ;431/13-17,79 ;317/130 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Attorney, Agent or Firm: Lindsley; Warren F. B.
Claims
What is claimed is:
1. A gas burner monitor comprising in combination:
a source of electrical energy having a pair of terminals,
a carbon monoxide detection circuit,
a flame color sensing circuit,
an alarm circuit,
said carbon monoxide detection circuit comprising a gas detection
element connected to said source of electrical energy and producing
a first output signal when said detection circuit senses abnormal
amounts of carbon monoxide around it,
said gas detection element comprising a resistance means which
changes its electrical resistance when subjected to the presence of
carbon monoxide,
said color sensing circuit comprising a phototransistor having an
anode, cathode and base, said base being connected through a
variable resistance to one terminal of said source and said cathode
being connected directly to said one terminal of said source,
said emitter being connected through a resistance to the other
terminal of said source,
whereby exposure of said photo-transistor to a predetermined level
of light reduces the resistance of the phototransistor between said
anode and said cathode to change the base to emitter current flow
thereby producing a second output signal,
said variable resistance biasing said phototransistor to render it
sensitive to a desired light detection level,
an alarm activating circuit, and
means for connecting said first and second output signals to said
alarm activating circuit to actuate an alarm.
2. The gas burner monitor set forth in claim 1 wherein:
said resistance means reduces in resistance upon increase in wave
length of the hue of the light sensed.
3. The gas burner monitor set forth in claim 1 wherein:
said resistance means reduces in resistance upon increased
whiteness of the flame.
4. The gas burner monitor set forth in claim 1 wherein:
said resistance means reduces in resistance upon increase in
luminosity of the light sensed.
5. The gas burner monitor set forth in claim 1 in further
combination with:
an alarm connected to said alarm circuit, and
means connected to said alarm circuit for continuing its
energization after the undesired condition determined by said
detection circuit and said sensing circuit have ceased to exist and
until said alarm circuit is interrupted.
Description
BACKGROUND OF THE INVENTION
The number of deaths and the dollar value of property loss
resulting from faulty gas-burner operation is alarmingly high. In
most cases, the water heater or furnace has been protected by means
of a bi-metal cut-off valve which normally shuts off the gas supply
if the flame is extinguished. Nevertheless, the cut-off valve may
fail to function properly when the flame is extinguished, in which
case the gas continues to flow into the building until an occupant
is overcome or until an explosion or fire occurs. Furthermore, such
bi-metal cut-off valves are not effective in protecting against the
improper combustion of the gas due to faulty burner operation or an
inadequate supply of air, and the resulting generation of carbon
monoxide constitutes an equally hazardous and potent threat to
life.
Elaborate means have been provided for the protection of such
occurences. Light and heat-sensitive devices are widely used in
industry to detect fires and to turn on sprinkling systems to
quench the fire. Gas sensors have also been developed to detect the
presence of dangerous gases and to initiate the operation of
automatic equipment which terminates the supply of gas.
Unfortunately, such equipment is too expensive to be utilized in
the typical family dwelling, especially in the case of less
well-to-do families and in temporary or vacation homes where the
majority of such tragedies occur as the result of defective
gas-burning equipment or because of improper installations.
What is needed is a simple and inexpensive device which is capable
of detecting such malfunctions and which can respond by sounding an
alarm or by initiating the automatic cut-off of the gas supply.
DISCUSSION OF THE PRIOR ART
In U.S. Pat. No. 3,750,161 an electronic detection circuit senses
the presence of flames and reacts by cutting off the fuel supply
and initiating the operation of a sprinkling system to extinguish
the fire. The fire detector and extinguisher system described in
this patent does not, however, take action until a fire has occured
and it is not effective against the presence of dangerous gases or
in the detection of faulty burner operation.
SUMMARY OF THE INVENTION
The present invention comprises an extremely simple and inexpensive
electronic circuit which overcomes the disadvantages of the prior
art. The circuit incorporates a photo sensor and a carbon monoxide
detector which permits the reliable detection of faulty burner
operation and the sounding of an alarm before a fire, an explosion
or physical harm can occur.
It is, therefore, an object of this invention to provide an
improved means of protection against fire or asphyxiation resulting
from improper gas burner operation.
Another object of this invention is to provide as a feature of such
protective means a capability of sensing a faulty operation of the
burner through the detection of improper flame color.
A further object of this invention is to provide as another feature
of such protective means a capability to sense improper burner
operation through the detection of undesirable combustion products
such as carbon monoxide.
Still another object of this invention is to provide the improved
protective means incorporating the aforementioned dual capabilities
in the form of a simple, reliable and inexpensive electronic
circuit which may readily be applied in the most humble
circumstances where such protection is so urgently needed.
The foregoing objects are achieved in the present invention by a
simple electronic circuit which incorporates a phototransistor for
the detection of improper flame color, a carbon monoxide gas
sensing element and a solenoid actuator for the sounding of an
alarm or for the initiation of other protective action.
Further objects and advantages of the invention will become
apparent as the following description proceeds and the features of
novelty which characterize this invention will be pointed out with
particularity in the claims annexed to and forming a part of this
specification.
BRIEF DESCRIPTION OF THE DRAWING
The present invention may be more readily described by reference to
the accompanying drawing in which:
FIG. 1 is a schematic representation of the detection and alarm
circuit.
FIG. 2 is a schematic representation of a variation of the alarm
portion of the circuit of FIG. 1.
FIG. 3 is an alternate embodiment of the flame color circuit
included as a part of the circuit of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to the drawing by characters of
reference, FIGS. 1 and 2 disclose a detection and alarm circuit 10
for use in monitoring the operation of a gas burner, the circuit 10
comprising a direct current supply circuit 11, a carbon monoxide
detection circuit 12, a flame color sensing circuit 13, and an
alarm actuator circuit 14A or 14B. The circuit 10 is connected to
an alternating current power source 9.
The direct current supply circuit 11 is a conventional half wave
rectifier circuit utilizing a step down transformer 15, a
semiconductor diode 16 and a filter capacitor 17. Transformer 15
has a primary winding 18 and a secondary winding 19 with a center
tap 20. Transformer 15 provides isolation and voltage step down
between source 15 and circuit 10, the source voltage 15 typically
operating at 120 volts, 60 hertz and the desired secondary voltage
being a low value preferably on the order of 6.3 volts, each side
of the center tap. Under these conditions a d-c voltage of
approximately 15 volts is provided across filter capacitor 17 with
a polarity as indicated by the positive and negative signs.
The carbon monoxide detection circuit 12 has as a key element a gas
detection element 22 which is obtainable from Figaro Engineering,
Inc. of Toyonaka City, Osaka, Japan under the Figaro identification
code T.G.S. No. 202 or 303. Element 22 has an input resistive leg
23 and an output resistive leg 24. Leg 23 is physically separated
from leg 24 by a medium, the resistance of which is normally high.
In the presence of carbon monoxide, however, which penetrates the
medium, the resistance between legs 23 and 24 is very significantly
reduced so that current flow between legs 23 and 24 is thereby
greatly enhanced.
In addition to element 22, detection circuit 12 includes resistors
25 and 26, potentiometer 27 and semiconductor diode 28.
Input leg 23 of element 22 is serially connected with resistor 25
across the upper half of secondary winding 19. An alternating
current, i.sub.1, thus flows through leg 23 thereby heating element
22, the heat generated contributing to the operation of the
element. By virtue of resistor 25, which has a relatively large
value of resistance as compared with that of input leg 23, the
voltage potential of leg 23 is essentially that of the positive
plate of capacitor 17.
Output leg 24 of element 22 has both ends connected to a common
point 29 which is tied by means of parallelly connected resistor 26
and potentiometer 27 to the negative plate of capacitor 17. Under
normal conditions essentially no current flows from secondary leg
24 through resistor 26 and potentiometer 27. When carbon monoxide
gas penetrates element 22, however, a d-c current i.sub.2 flows
from the positive plate of capacitor 17 to input leg 23, to output
leg 24, through resistor 26 and potentiometer 27 to the negative
plate of capacitor 17. A positive voltage thus developed at movable
arm 29 of potentiometer 27 is delivered via diode 28 to output
terminal 30 of circuit 12, the positive voltage at terminal 30
being indicative of an abnormally high level of carbon monoxide gas
detected by circuit 12. Adjustment of potentiometer 27 permits
control of the detection level as appropriate for the
application.
Flame color sensing circuit 13 includes as a key element a
photo-transistor 32. Transistor 32 has the operating
characteristics of a typical transistor in the sense that a
positive current flowing from base 33 to emitter 34 reduces the
resistance of a positive current flow from collector 35 to emitter
34. In addition to such typical transistor characteristics,
however, photo-transistor 32 is fabricated in a manner which
permits exposure of the internal semiconductor element to
surrounding light. The design of transistor 32 is such that an
increasing level or whiteness of light striking the device produces
a reduced level of resistance, anode to cathode. The impinging
light 36 thus has a similar effect to or augments the effect of the
base emitter current.
The wave lengths of the hues of the flame are sensed by the
photo-transistor. For example, if the photo-transistor is set to
monitor a blue-green flame having the wave length of approximately
500 microns, any hue noted by the photo-transistor of a greater
wave length will reduce its anode to cathode resistance. Since a
white flame reflects all colors and a progressively darker flame
less color, the photo-transistor is sensitive to luminosity.
In addition to photo-transistor 32, circuit 13 includes a
potentiometer 37, resistors 38 and 39, capacitor 40 and diode 42.
Transistor 32 is serially connected, anode to cathode, with
resistor 38 across the d-c voltage appearing across filter
capacitor 17.
During normal operation of the gas burner, the light striking
photo-transistor 32 is not sufficient or of the proper wave length
to drive transistor 32 into conduction so that a very low level of
voltage exists across resistor 38. Under abnormal conditions,
however, the impinging light 36 causes transistor 32 to "turn on"
thereby allowing a relatively large value of current to flow from
collector 35 to emitter 34 and through resistor 38. The voltage
thus developed across resistor 38 is coupled by means of serially
connected resistor 39 and diode 42 to output terminal 43 and
signals an abnormal flame color condition sensed by
photo-transistor 32.
In an alternate embodiment 13A of circuit 13 as shown in FIG. 3, it
may be desired to rearrange the circuit 13 to permit thereby the
detection of a reduction in flame level as resulting from the total
or partial extinction of the flame. In this case, the positions of
the resistor 38 and the transistor 32 with potentiometer 37 still
connected between collector 35 and base 33 are reversed. Transistor
32 is in this case normally conducting in the presence of normal
burner operation and no voltage is coupled through resistor 39 and
diode 42 to output terminal 43. If the burner is totally or
partially extinguished, however, a positive current flowing from
the positive plate of capacitor 17 through resistors 38 and 39 and
diode 42 to output terminal 43 signals the failure or improper
operation of the burner.
In either embodiment of the circuits 13, 13A, the potentiometer 38
connected between collector 35 and base 33 of transistor 32
provides a means for biasing transistor 32 to render it sensitive
to a desired light-detection level, a lower value of resistance set
by potentiometer 37 causing an increased bias current to flow from
base 33 to emitter 34 and thereby rendering the transistor 32
responsive to a lower level of ambient light. Capacitor 40 in
conjunction with resistor 39 provides a time delay to prevent short
bursts of light from producing an undesired output signal at
terminal 43.
Diodes 28 and 42 of circuits 12, 13 and 13A are coupling and
blocking diodes which isolate circuit 12 from circuit 13 or 13A and
prevent interaction between these circuits.
Actuator circuit 14A includes two transistors 44 and 45 connected
in the well known Darlington configuration in series with solenoid
coil 46 across which is connected a recovery diode 47. A positive
signal at output terminal 30 or 43 of circuit 12, 13 or 13A
produces a positive base emitter current in transistor 44 which in
turn produces an amplified base emitter current in transistor 45.
As a result, transistor 45 saturates or exhibits a very low
collector to emitter resistance so that coil 46 is effectively
connected across filter capacitor 17 through transistor 45 and is
thereby energized to operate an alarm or a device for cutting of
the gas supply.
At the termination of the signal from terminal 30 or 43,
transistors 44 and 45 revert to the "off" or high impedance state.
Inductive energy stored in coil 46 tends to sustain the current in
coil 46 as transistors 44 and 45 "turn off" and except for the
presence of recovery diode 47, a high and possibly destructive
voltage would appear as a consequence across transistors 44 and 45.
Diode 47 provides a path for the sustained current to flow and
allows the stored energy to be dissipated without the generation of
such a destructive voltage.
Under certain circumstances it may be desired that the alarm should
continue to sound even after the undesired condition has ceased to
exist until the circuit is interrupted. The alternate alarm circuit
14B shown in FIG. 2 provides such a feature.
Circuit 14B incorporates a controlled rectifier 50, a transistor
51, resistors 52 and 53, a reset switch 54, a solenoid coil 55 and
a recovery diode 56. A positive signal through diode 28 or 42 from
circuit 12, 13 or 13A produces a base emitter current in transistor
51 which renders transistor 51 conductive between collector 57 and
emitter 58. A resulting current flowing through resistor 52 and
transistor 51 flows into gate 59 of controlled rectifier 50. The
gate current triggers rectifier 50 from an "off" condition to an
"on" condition in which rectifier 50 exhibits a very low value of
resistance to current flow from anode 61 to cathode 62. With
rectifier 50 in the "on" condition, coil 55 is again effectively
connected directly across capacitor 17 through rectifier 50 and
reset switch 54. By virtue of the typical operating characteristics
of controlled rectifier 50, the "on" condition of rectifier 50 is
sustained even after the disappearance of a positive signal at
diode 28 or 42 and after the termination of gate current into gate
59. The "off" condition of controlled rectifier 50 may be restored,
however, by the momentary opening of reset switch 54.
A simple and versatile circuit has thus been shown in various
embodiments which permit the detection of carbon monoxide and the
presence or absence of desired or undesired light levels as
produced by the normal or abnormal operation of a gas burner flame
or by a fire resulting from any cause. By virtue of its simplicity
and its low cost, it may readily be applied in homes of modest
means to reduce significantly the hazard of bodily injury, death or
property damage due to fire or to the improper operation of gas
burning equipment.
Although but a few embodiments of the present invention have been
illustrated and described, it will be apparent to those skilled in
the art thar various changes and modifications may be made therein
without departing from the spirit of the invention or from the
scope of the appended claims.
* * * * *