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.

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.

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.