Detector for fumes and combustion gases
United States Patent 3909815
An ionization detection means is disclosed having a housing, a reference ionization chamber and a sensing ionization chamber located in the housing. A radioactive source is also positioned in the housing and is arranged for causing ionization of particles within the chambers. A means is provided for establishing a flow path to the sensing chamber for atmospheric constituents such as fumes, vapors or aerosols. An electrical output signal is provided upon the occurrence of fumes, vapors or aerosols in the sensing chamber. A means is provided for storing information representative of the time elapsed between the initiation of the output signal and a subsequent point in time. A circuit means is also provided for indicating a defective condition in the operation of the detector. A predetermined atmosphere of pollutants is established within the reference chamber for precompensating for existing environmental pollutants.
US Patent References:
AUTOMATIC IONIC FIRE ALARM SYSTEM
Nagao Abe - March 1970 - 3500368
FIRE ALARM SYSTEMS WITH MONITORING DEVICE FOR FIRE ALARMS CONNECTED IN GROUPS TO A CENTRAL STATION
Walthard et al. - September 1970 - 3530450
IONIZING-TYPE FIRE ALARM SENSOR
Lampart et al. - October 1973 - 3767917
AUTOMATIC IONIC FIRE ALARM SYSTEM
Nagao Abe - March 1970 - 3500368
FIRE ALARM SYSTEMS WITH MONITORING DEVICE FOR FIRE ALARMS CONNECTED IN GROUPS TO A CENTRAL STATION
Walthard et al. - September 1970 - 3530450
IONIZING-TYPE FIRE ALARM SENSOR
Lampart et al. - October 1973 - 3767917
Application Number:
05/433621
Publication Date:
09/30/1975
Filing Date:
01/16/1974
View Patent Images:
Export Citation:
Assignee:
Societe Gamma Electronic (Paris, FR)
Primary Class:
Other Classes:
250/381
International Classes:
G08B17/11; G08B17/113; G08B17/10; G08B21/00; G08B17/10
Field of Search:
324/33 340/237S,408 250/381
Primary Examiner:
Smith, Alfred E.
Assistant Examiner:
Hille, Rolf
Attorney, Agent or Firm:
Kaufman & Kramer
Claims:
What is claimed is
1. An ionization detector for detecting fumes, vapors or aerosols comprising:
2. An ionization detector for detecting fumes, vapors or aerosols comprising:
3. The detection means of claim 2 wherein said electrical storage means comprises a counter.
4. The detection means of claim 3 wherein said circuit means for causing said storage means to accumulate a sum comprises a circuit arrangement for generating periodically recurring impulses.
5. The detection means of claim 4 wherein said circuit means for generating periodically recurring pulses comprises an operational amplifier having a feedback network coupled thereto for causing said amplifier to function as an integrating means.
6. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
7. The detection means of claim 6 wherein said indicating means comprises an electrically energized indicator which provides an indication which is perceptible by the human senses.
8. The detection means of claim 7 wherein said indicating means comprises a visual indicator mounted on said housing.
9. The detection means of claim 6 wherein said indicating means comprises an electrical storage means and circuit means for providing a continuous entry to said storage means when said switching means exists in said second state.
10. An ionization detector for sensing vapors, fumes and aerosols comprising:
11. The detection means of claim 10 wherein said reference chamber contains carbon monoxide at a concentration of 3 mg/m3.
12. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
13. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
1. An ionization detector for detecting fumes, vapors or aerosols comprising:
2. An ionization detector for detecting fumes, vapors or aerosols comprising:
3. The detection means of claim 2 wherein said electrical storage means comprises a counter.
4. The detection means of claim 3 wherein said circuit means for causing said storage means to accumulate a sum comprises a circuit arrangement for generating periodically recurring impulses.
5. The detection means of claim 4 wherein said circuit means for generating periodically recurring pulses comprises an operational amplifier having a feedback network coupled thereto for causing said amplifier to function as an integrating means.
6. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
7. The detection means of claim 6 wherein said indicating means comprises an electrically energized indicator which provides an indication which is perceptible by the human senses.
8. The detection means of claim 7 wherein said indicating means comprises a visual indicator mounted on said housing.
9. The detection means of claim 6 wherein said indicating means comprises an electrical storage means and circuit means for providing a continuous entry to said storage means when said switching means exists in said second state.
10. An ionization detector for sensing vapors, fumes and aerosols comprising:
11. The detection means of claim 10 wherein said reference chamber contains carbon monoxide at a concentration of 3 mg/m3.
12. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
13. An ionization detector for providing an indication of the presence of fumes, vapors or aerosols comprising:
Description:
The present invention relates to a detector for sensing the occurrence of fumes, gases or aerosols which may, for example, be indicative of the existence of a fire. The invention relates more particularly to an improved form of ionization detector for detecting fumes, gases or aerosols.
Ionization detectors adapted for sensing the occurrence of fumes, gases or aerosols which may be indicative of the existence of a fire are known. In one form of ionization detector, a reference ionization chamber and a sensing ionization chamber are electrically coupled in series. An electrode of the ionization chambers is common to each of the chambers and the potential of this common electrode will vary as gases, fumes or aerosols occur in the locale of the detector. The potential of the common electrode is applied to a circuit means which includes, for example, a vacuum tube, a gaseous tube or a transistor. This circuit means is adapted for altering the state of an electrical signaling circuit thereby providing an indication of the presence of the gaseous fumes or aerosols. Ionization detectors of this type can be used in the various locations such as factories, shops, warehouses, archives, dwellings and the like for detection and monitoring of fumes and combustion gases.
Prior ionization detectors of the type referred to exhibit several limitations. They are, for example, undesirably susceptible to external influences such as environmental pollutants and to the wind. They are also subject to defects in insulation resulting from faulty assembly or abuse of the detector; to interruption of power, etc. In addition, it is at times desirable to provide information which is indicative of the development of the emission of fumes caused by a fire for example. This indication permits tracing of the origin and progress of a fire.
Accordingly, it is an object of this invention to provide an improved form of ionization detection means which is adapted for sensing fumes, gases or aerosols.
Another object of the invention is to provide an ionization detection means for sensing fumes, gases or aerosols and having means for providing an indication of the origin and propagation of a fire or combustion.
Another object of the invention is to provide an ionization detection means for sensing fumes, gases or aerosols and which includes improved means for compensating environmental pollutants in the atmosphere.
Another object of the invention is to provide an ionization detection means which provides the indication of a defective condition existing in the detector.
A further object of the invention is to provide an ionization detector means which provides for reducing false indications caused by emissions accompanying the initiation of a fire.
Another object of the invention is to provide an improved ionization detection means which provides a quantitative and relative estimate of the magnitude of the fire or combustion.
In accordance with features of this invention, an ionization detector is provided having a housing, a reference ionization chamber and a sensing ionization chamber located in said housing, a radioactive source arranged for causing ionization of particles within said chambers, means for providing access to said sensing chamber of atmospheric constituents such as fumes, vapors or aerosols, means for providing an electrical output signal from said chamber indicative of the presence of a fume, vapor or aerosol, and means for providing and storing information representative of the time elapsed between the initiation of said output signal and a subsequent point in time. The stored information therefore provides data which, in conjunction with data from similar detection means, enables a determination of the place of initiation and progress of a fire or other occurrences creating fumes, vapors or aerosols.
In accordance with another feature of the invention, a circuit means is provided for automatically indicating a defective condition in the operation of the ionization detector chambers. The provision of means for indicating a defective condition thereby increases the realibility of a system incorporating a large number of detectors.
In accordance with further features of the invention, a predetermined atmosphere of pollutants is established within the reference chamber which pre-compensates for existing environmental pollutants. A fume detection arrangement is thereby provided which eliminates the need for electrically correcting for the alarm level of the detector.
These and other objects and features of the invention will become apparent with reference to the following specification and to the drawings wherein:
FIG. 1 is an elevation view, partly in cross section, of an embodiment of an ionization detector constructed in accordance with features of this invention; and
FIG. 2 is a circuit diagram, partly in schematic form, of a circuit arrangement employed with the detector of FIG. 1.
Referring now to FIG. 1 of the drawings, the detector is shown to include a housing comprising a rosette shaped base 1 and casing 5. The base 1 is preferably formed of a high temperature, electrical insulating material such as ceramic while the casing 5 is formed of an electrical conducting material such as aluminum, steel, etc. A plurality of bores are formed in the base 1 and there is positioned in each of the bores a female junction connector 2. An indicating means comprising a signal lamp 3 is also positioned in the base and, as indicated hereinafter, is energized when the level of fumes, vapors or aerosols in the surrounding atmosphere reach an alarm condition to provide a visible indication of the condition. Electrical leads 29, 30, 31 and 32 are provided and extend into the base through an aperture 33 formed therein and are coupled through screw terminals to the female connectors 2.
The casing 5 comprises the principal body of the detector and is threaded at one end 34 for engaging a threaded shoulder segment of the base 1. A disc shaped plate 6 is mounted to the walls of the casing 5 and supports male connectors 4 which extend from this plate and which engage the female connectors 2 in the base 1. In addition, electronic circuitry in the form of components and a printed circuit as described in greater detail hereinafter is mounted to the plate 6 as is an inner or reference ionization chamber 7.
The inner or reference ionization chamber 7 includes a positive electrode 13 which is connected to a printed circuit mounted on the plate 6 by a centrally located rod 114. A cathode electrode 15 of the reference chamber is positioned about the anode electrode 13. This cathode electrode along with a disc 16 formed of an electrically insulating material is positioned in the casing 5 in a manner for providing an enclosed chamber within the confined volume defined by the electrode 15 and the disc 16. This arrangement inhibits access of moist air to the electronic parts.
A radioactive source 17 is mounted within the reference chamber 7 and the radiation from this source causes, ionization of particles within the chamber and a resultant current flow between the electrodes 13 and 15. The radioactive source 17 is preferably an alpha emitter which does not emit radioactive gases such as plutonium-239 or americium-241 or equivalent. The electrodes 13 and 15 may be spaced relatively close to one another thereby enhancing the creation of an ionization current of significant magnitude yet requiring only a relatively small operating potential between the electrodes.
An outer or "analysis" ionization chamber 23 is provided and is defined by the electrode 15 of the inner chamber, a wall segment of the casing 5, a plurality of fins extending about the circumference and surface of the casing 5 and which provide access for fumes, aerosols and vapors to the analysis chamber through a grating 19. The grating 19 is secured in position against the fins by belts or rings 20 and 21. The electrodes of the analysis chamber include the electrode 15 which is common to both the reference and analysis chamber and which functions as a relatively positive electrode in the analysis chamber. The negative electrode comprises a disc 12 which is mounted from a surface 10 by an adjustment screw 36 and which provides for varying the spacing between the disc 12 and the electrode 15. Adjustment of the position of electrode 12 compensates for manufacturing tolerances and, in addition, provides for optimum spacing between electrodes 12 and 15; particularly when the analysis chamber is subjected to strong air currents. A radioactive ionization source 18 similar to a source 17 is also mounted in the chamber and is positioned for causing ionization of the particles and establishment of a current between the electrodes 12 and 15. The casing body 5, the fins and the grating are conductively intercoupled and are connected to a negative terminal of a source of operating potential. This results in a Faraday-cage form of protection which shields or removes the electric components and particularly field effect transistors within a device from the influence of external electric fields.
It is noted that the fin and grid structure operate to reduce the adverse effect of substantial air currents and resulting false alarms. Gases or fumes which enter the analysis chamber flow between the fins which are relatively thin and which are spaced relatively close together. These fins are shaped and sized for providing that the flow passage presented to air currents is reduced with respect to the cross section of the analysis chamber. In addition to maintaining the grid in position, the belts 20 and 21 also reduce the effective surface area of the grid which is presented to the surrounding environment. Thus, air currents, which tend to disturb the distribution of ions in the analysis chamber and to alter the potential of the common electrode is substantially neutralized.
A relatively low potential difference is applied between the electrodes 13 and 12 of the reference and measuring chambers respectively. This potential is on the order of 50 volts or less. The potential at the electrode 15, which is common to both chambers, is coupled to an electronic circuit which is provided for modifying the state of an electric or an electronic signaling circuit in accordance with changes occurring in ionization within the outer or analysis chamber.
In accordance with a feature of this invention, an atmosphere is established within the reference chamber for compensating for environmental pollutants. This is accomplished in one manner by placing a container containing a solid mixture of sodium carbonate, nickel carbonyl and an alkali sulfide in an enclosure. A partial vacuum is then produced and atmospheric pressure is then re-established. The CO level, which should correspond to 3 mg/m 3 of CO, is then measured. The finished unsealed ampoules are then stored in this enclosure for several days prior to the final assembly. This process can be shortened at times by contamination of the ampoule in situ.
Referring now to the circuit arrangement of FIG. 2, operating potential for the detector is derived from an external source 40 which may comprise a battery pack and is applied via input leads 30 and 31 to the female connectors 2 which are located in the base 1. A relatively positive potential is also coupled to the indicator lamp 3. The output potential of the source 40 which may for example comprise 25 volts is applied to the various components of the circuit arrangement through a stabilizing network comprising a resistor 42 and a zener diode 94. This stabilized positive potential is applied to the electrode 13 of the reference chamber and a negative potential to the electrode 12 of the analysis chamber. When a substantially constant potential difference is established between the positive electrode 13 of the reference chamber and the negative electrode 12 of the analysis chamber, both of which chambers are rendered conductive by the radioactive ionization means, then a small ionization current circulates and the potential of the common electrode 15 will attain an equilibrium magnitude which depends on various factors including the level of ionization created by the radiation sources, the shape of the electrodes, and the relative dimensions of the two chambers. This potential is applied to a gate electrode 44 of a junction field effect transistor 46. The positive operating potential is also applied to an electrode 48 of this transistor while the negative potential is applied to an electrode 50 of the transistor 46 through a series resistive network which includes resistors 52 and 54 and a potentiometer 56.
A control circuit is provided for causing energization of the lamp 3 when vapors, fumes or aerosols are detected or when a defective condition in the ionization chambers results in a detector fault. A lead 58 of the lamp 3 is coupled to the positive input line 30 while a lead 60 of the lamp 3 is coupled through a terminal 62 and the female and male connectors of the detector to an anode electrode 64 of a thyristor 66. A negative electrode 68 of the thyristor is connected to the negative input potential. When a trigger signal is applied to a gate electrode 70 of the thyristor 66, the thyristor is switched into a conductive state and the lamp 3 is thereby energized providing an indication of the presence of fumes, gases or aerosols of the existence of a faulty condition in the detector.
Trigger signals which are applied to the gate electrode 70 are applied through alternative circuit means, depending on whether a defect or fault in the installation or operation of the chambers occurs or whether during proper operation of the chambers a vapor, gas or aerosol is detected. In the former case, the defect is indicated by a potential at the junction of the resistors 52 and 54. This potential is applied through a resistance 72 to the base electrode 74 of an NPN transistor 76. Operating potential is applied to the transistor 76 through a resistor 78 which is coupled between the resistor 42 and a collector electrode 80 of the transistor 76 while a negative potential is applied to an emitter electrode 82 of this transistor. A diode 84 is provided for coupling a triggering signal from the transistor 76 to the gate electrode 70 of the thyristor. The diode 84, under ordinary operating conditions and in the absence of defective operation of the chamber is back-biased as a result of the potential established at this diode by a resistor 86 and by the potential of the collector electrode 80 of the transistor 76. The potential at the collector electrode 80 is established at a relatively low positive value by selecting a base resistive impedance 72 which provides for conduction of the transistor when a potential, which is indicative of proper operation of the chambers, exists at the junction of the resistors 52 and 54.
Alternatively, the thyristor 66 is triggered into conduction when vapors, gases or aerosols are detected by a signal which is derived from a wiper arm 88 of the potentiometer 56 and is applied to the gate electrode 70 through a zener diode 90.
In operation, the reference and analysis chambers under no fault, no vapor, gas or aerosol conditions provide a potential at the common electrode 15 which results in a potential at the junction of the resistors 52 and 54 having a magnitude for causing conduction of the transistor 76. The diode 84 is therefore back-biased. Similarly, the potential at the wiper arm 88 under these conditions has a magnitude insufficiently high for causing conduction of the zener diode 90. In this regard, the sensitivity of the detector to vapors, gases and aerosols is adjustable by adjustment of the wiper arm 88 of the potentiometer 56. In FIG. 1, an aperture 92 is formed in the casing 5 for providing access to the potentiometer for a sensitivity adjustment of the wiper arm 88. A defective installation or operation or abuse of the detector can result in a defect in insulation. In the analysis chamber this defect in insulation will be reflected as an abnormal drop in the equilibrium potential of the electrode 15 resulting in a decrease in the base current to the transistor 76. The collector voltage of this transistor then rises causing forward bias and conduction of the diode 84. The forward biased diode 84 provides a current passage through the resistance 78 to the gate electrode 70 of the thyristor 66, thereby switching the thyristor into a conductive condition and causing energization of the lamp 3. The lamp will then remain energized until operating potential is interrupted to the thyristor 66.
In the alternative and principal mode of operation, the entry of a vapor, gas or aerosol into the analysis chamber results in an appreciable decrease in the magnitude of the ionization current, thereby increasing the impedance of this chamber and causing an increase in the potential of the electrode 15 from its equilibrium value. The voltage at the potentiometer wiper arm 88 will accordingly increase from the corresponding equilibrium potential to a magnitude at which the zener diode 90 becomes conductive and thereby triggers the thyristor 66 into conduction. The lamp 3 is then energized and remains energized until operating potential to the thyristor 66 is interrupted.
It is beneficial at times to provide an indication of the initiation or of the progress of a fire or other disaster. In accordance with another feature of this invention, the detector includes a memory for establishing such an indication. The distribution of a number of such detectors about the site of a fire or disaster, then renders it possible to determine the initiation and duration of the fire at each detector station and to consequently trace the progress of the fire or disaster. An integrating circuit means is provided by the use of a field effect transistor 94 which is coupled to an operational amplifier 96 having a feedback loop and arranged as an integrator. In FIG. 2, the anode electrode 64 of the thyristor 66 is coupled to a gate electrode 93 of a field effect transistor 94. The field effect transistor 94 is coupled in series with an integrator 96. The integrator 96 comprises a solid state integrated circuit. One such integrated circuit suitable for the use indicated is SN521 manufactured by Texas Instruments, Inc. This integrator is thermally insulated with asbestos for example in order to protect the integrator from the effects of the fire or disaster. An output from the integrator 96 is applied via the line 29 to a remote electronic storage means 98. The storage means 98 comprises for example a totalizer counter or a binary counter. During the interval of time in which vapors, fumes or aerosols are detected or a fault condition exists, the integrator 96 provides a periodically recurring output voltage. Either the analog representation of the integrator output or the digital representation which are indicative of the total time during which the faulty condition existed can be used subsequently to determine the intensity and duration of the faulty condition. This information in turn is employed to obtain geographical indications of the origin of the faulty condition. This is accomplished for example by obtaining the different records from a number of detectors located at the fire or disaster site and correlating these records to establish a map of the location and distribution of the disaster.
A circuit arrangement comprising resistors 100 and 102 and a diode 104 are provided for generating a signal for coupling to a central location. This signaling is particularly useful when defects such as an interruption in the application of power to the unit from the source 40 occurs. This may occur for example when the casing 5 is separated from the base 1. The conduction of the thyristor 66 upon the occurrence of a defect results in a relatively low potential at the terminal 62. The resistor 102 is selected to have a relatively low resistance with respect to the resistor 100. When a relatively low potential occurs at terminal 62 and since a positive potential is applied to the resistor 100, the diode 104 will be conducting and a relatively low potential will appear on the output line 106. It is noted that other detectors sensing for similar or other conditions may be coupled to the line 106. When the supply to the unit is interrupted such as through the removal of a detector from its base, the potential at the point 106 will rise and this rise can be utilized for indicating or control purposes at a main panel.
An improved form of ionization detection means for gases, vapors or aerosols has thus been described. The detection means advantageously compensates for a level of pollution in an environment where the detector is to be utilized. In addition, the detection means provides means for recording the duration of a false alarm or of the detection of vapors, gases or aerosols and provides an indication which can be stored in a counter. The detection means further is adapted for indicating a fault condition in the detector.
While particular embodiments of the invention have been described herein, it will be apparent to those skilled in the art that variations may be made thereto without departing from the spirit of the invention and the scope of the appended claims.
Ionization detectors adapted for sensing the occurrence of fumes, gases or aerosols which may be indicative of the existence of a fire are known. In one form of ionization detector, a reference ionization chamber and a sensing ionization chamber are electrically coupled in series. An electrode of the ionization chambers is common to each of the chambers and the potential of this common electrode will vary as gases, fumes or aerosols occur in the locale of the detector. The potential of the common electrode is applied to a circuit means which includes, for example, a vacuum tube, a gaseous tube or a transistor. This circuit means is adapted for altering the state of an electrical signaling circuit thereby providing an indication of the presence of the gaseous fumes or aerosols. Ionization detectors of this type can be used in the various locations such as factories, shops, warehouses, archives, dwellings and the like for detection and monitoring of fumes and combustion gases.
Prior ionization detectors of the type referred to exhibit several limitations. They are, for example, undesirably susceptible to external influences such as environmental pollutants and to the wind. They are also subject to defects in insulation resulting from faulty assembly or abuse of the detector; to interruption of power, etc. In addition, it is at times desirable to provide information which is indicative of the development of the emission of fumes caused by a fire for example. This indication permits tracing of the origin and progress of a fire.
Accordingly, it is an object of this invention to provide an improved form of ionization detection means which is adapted for sensing fumes, gases or aerosols.
Another object of the invention is to provide an ionization detection means for sensing fumes, gases or aerosols and having means for providing an indication of the origin and propagation of a fire or combustion.
Another object of the invention is to provide an ionization detection means for sensing fumes, gases or aerosols and which includes improved means for compensating environmental pollutants in the atmosphere.
Another object of the invention is to provide an ionization detection means which provides the indication of a defective condition existing in the detector.
A further object of the invention is to provide an ionization detector means which provides for reducing false indications caused by emissions accompanying the initiation of a fire.
Another object of the invention is to provide an improved ionization detection means which provides a quantitative and relative estimate of the magnitude of the fire or combustion.
In accordance with features of this invention, an ionization detector is provided having a housing, a reference ionization chamber and a sensing ionization chamber located in said housing, a radioactive source arranged for causing ionization of particles within said chambers, means for providing access to said sensing chamber of atmospheric constituents such as fumes, vapors or aerosols, means for providing an electrical output signal from said chamber indicative of the presence of a fume, vapor or aerosol, and means for providing and storing information representative of the time elapsed between the initiation of said output signal and a subsequent point in time. The stored information therefore provides data which, in conjunction with data from similar detection means, enables a determination of the place of initiation and progress of a fire or other occurrences creating fumes, vapors or aerosols.
In accordance with another feature of the invention, a circuit means is provided for automatically indicating a defective condition in the operation of the ionization detector chambers. The provision of means for indicating a defective condition thereby increases the realibility of a system incorporating a large number of detectors.
In accordance with further features of the invention, a predetermined atmosphere of pollutants is established within the reference chamber which pre-compensates for existing environmental pollutants. A fume detection arrangement is thereby provided which eliminates the need for electrically correcting for the alarm level of the detector.
These and other objects and features of the invention will become apparent with reference to the following specification and to the drawings wherein:
FIG. 1 is an elevation view, partly in cross section, of an embodiment of an ionization detector constructed in accordance with features of this invention; and
FIG. 2 is a circuit diagram, partly in schematic form, of a circuit arrangement employed with the detector of FIG. 1.
Referring now to FIG. 1 of the drawings, the detector is shown to include a housing comprising a rosette shaped base 1 and casing 5. The base 1 is preferably formed of a high temperature, electrical insulating material such as ceramic while the casing 5 is formed of an electrical conducting material such as aluminum, steel, etc. A plurality of bores are formed in the base 1 and there is positioned in each of the bores a female junction connector 2. An indicating means comprising a signal lamp 3 is also positioned in the base and, as indicated hereinafter, is energized when the level of fumes, vapors or aerosols in the surrounding atmosphere reach an alarm condition to provide a visible indication of the condition. Electrical leads 29, 30, 31 and 32 are provided and extend into the base through an aperture 33 formed therein and are coupled through screw terminals to the female connectors 2.
The casing 5 comprises the principal body of the detector and is threaded at one end 34 for engaging a threaded shoulder segment of the base 1. A disc shaped plate 6 is mounted to the walls of the casing 5 and supports male connectors 4 which extend from this plate and which engage the female connectors 2 in the base 1. In addition, electronic circuitry in the form of components and a printed circuit as described in greater detail hereinafter is mounted to the plate 6 as is an inner or reference ionization chamber 7.
The inner or reference ionization chamber 7 includes a positive electrode 13 which is connected to a printed circuit mounted on the plate 6 by a centrally located rod 114. A cathode electrode 15 of the reference chamber is positioned about the anode electrode 13. This cathode electrode along with a disc 16 formed of an electrically insulating material is positioned in the casing 5 in a manner for providing an enclosed chamber within the confined volume defined by the electrode 15 and the disc 16. This arrangement inhibits access of moist air to the electronic parts.
A radioactive source 17 is mounted within the reference chamber 7 and the radiation from this source causes, ionization of particles within the chamber and a resultant current flow between the electrodes 13 and 15. The radioactive source 17 is preferably an alpha emitter which does not emit radioactive gases such as plutonium-239 or americium-241 or equivalent. The electrodes 13 and 15 may be spaced relatively close to one another thereby enhancing the creation of an ionization current of significant magnitude yet requiring only a relatively small operating potential between the electrodes.
An outer or "analysis" ionization chamber 23 is provided and is defined by the electrode 15 of the inner chamber, a wall segment of the casing 5, a plurality of fins extending about the circumference and surface of the casing 5 and which provide access for fumes, aerosols and vapors to the analysis chamber through a grating 19. The grating 19 is secured in position against the fins by belts or rings 20 and 21. The electrodes of the analysis chamber include the electrode 15 which is common to both the reference and analysis chamber and which functions as a relatively positive electrode in the analysis chamber. The negative electrode comprises a disc 12 which is mounted from a surface 10 by an adjustment screw 36 and which provides for varying the spacing between the disc 12 and the electrode 15. Adjustment of the position of electrode 12 compensates for manufacturing tolerances and, in addition, provides for optimum spacing between electrodes 12 and 15; particularly when the analysis chamber is subjected to strong air currents. A radioactive ionization source 18 similar to a source 17 is also mounted in the chamber and is positioned for causing ionization of the particles and establishment of a current between the electrodes 12 and 15. The casing body 5, the fins and the grating are conductively intercoupled and are connected to a negative terminal of a source of operating potential. This results in a Faraday-cage form of protection which shields or removes the electric components and particularly field effect transistors within a device from the influence of external electric fields.
It is noted that the fin and grid structure operate to reduce the adverse effect of substantial air currents and resulting false alarms. Gases or fumes which enter the analysis chamber flow between the fins which are relatively thin and which are spaced relatively close together. These fins are shaped and sized for providing that the flow passage presented to air currents is reduced with respect to the cross section of the analysis chamber. In addition to maintaining the grid in position, the belts 20 and 21 also reduce the effective surface area of the grid which is presented to the surrounding environment. Thus, air currents, which tend to disturb the distribution of ions in the analysis chamber and to alter the potential of the common electrode is substantially neutralized.
A relatively low potential difference is applied between the electrodes 13 and 12 of the reference and measuring chambers respectively. This potential is on the order of 50 volts or less. The potential at the electrode 15, which is common to both chambers, is coupled to an electronic circuit which is provided for modifying the state of an electric or an electronic signaling circuit in accordance with changes occurring in ionization within the outer or analysis chamber.
In accordance with a feature of this invention, an atmosphere is established within the reference chamber for compensating for environmental pollutants. This is accomplished in one manner by placing a container containing a solid mixture of sodium carbonate, nickel carbonyl and an alkali sulfide in an enclosure. A partial vacuum is then produced and atmospheric pressure is then re-established. The CO level, which should correspond to 3 mg/m 3 of CO, is then measured. The finished unsealed ampoules are then stored in this enclosure for several days prior to the final assembly. This process can be shortened at times by contamination of the ampoule in situ.
Referring now to the circuit arrangement of FIG. 2, operating potential for the detector is derived from an external source 40 which may comprise a battery pack and is applied via input leads 30 and 31 to the female connectors 2 which are located in the base 1. A relatively positive potential is also coupled to the indicator lamp 3. The output potential of the source 40 which may for example comprise 25 volts is applied to the various components of the circuit arrangement through a stabilizing network comprising a resistor 42 and a zener diode 94. This stabilized positive potential is applied to the electrode 13 of the reference chamber and a negative potential to the electrode 12 of the analysis chamber. When a substantially constant potential difference is established between the positive electrode 13 of the reference chamber and the negative electrode 12 of the analysis chamber, both of which chambers are rendered conductive by the radioactive ionization means, then a small ionization current circulates and the potential of the common electrode 15 will attain an equilibrium magnitude which depends on various factors including the level of ionization created by the radiation sources, the shape of the electrodes, and the relative dimensions of the two chambers. This potential is applied to a gate electrode 44 of a junction field effect transistor 46. The positive operating potential is also applied to an electrode 48 of this transistor while the negative potential is applied to an electrode 50 of the transistor 46 through a series resistive network which includes resistors 52 and 54 and a potentiometer 56.
A control circuit is provided for causing energization of the lamp 3 when vapors, fumes or aerosols are detected or when a defective condition in the ionization chambers results in a detector fault. A lead 58 of the lamp 3 is coupled to the positive input line 30 while a lead 60 of the lamp 3 is coupled through a terminal 62 and the female and male connectors of the detector to an anode electrode 64 of a thyristor 66. A negative electrode 68 of the thyristor is connected to the negative input potential. When a trigger signal is applied to a gate electrode 70 of the thyristor 66, the thyristor is switched into a conductive state and the lamp 3 is thereby energized providing an indication of the presence of fumes, gases or aerosols of the existence of a faulty condition in the detector.
Trigger signals which are applied to the gate electrode 70 are applied through alternative circuit means, depending on whether a defect or fault in the installation or operation of the chambers occurs or whether during proper operation of the chambers a vapor, gas or aerosol is detected. In the former case, the defect is indicated by a potential at the junction of the resistors 52 and 54. This potential is applied through a resistance 72 to the base electrode 74 of an NPN transistor 76. Operating potential is applied to the transistor 76 through a resistor 78 which is coupled between the resistor 42 and a collector electrode 80 of the transistor 76 while a negative potential is applied to an emitter electrode 82 of this transistor. A diode 84 is provided for coupling a triggering signal from the transistor 76 to the gate electrode 70 of the thyristor. The diode 84, under ordinary operating conditions and in the absence of defective operation of the chamber is back-biased as a result of the potential established at this diode by a resistor 86 and by the potential of the collector electrode 80 of the transistor 76. The potential at the collector electrode 80 is established at a relatively low positive value by selecting a base resistive impedance 72 which provides for conduction of the transistor when a potential, which is indicative of proper operation of the chambers, exists at the junction of the resistors 52 and 54.
Alternatively, the thyristor 66 is triggered into conduction when vapors, gases or aerosols are detected by a signal which is derived from a wiper arm 88 of the potentiometer 56 and is applied to the gate electrode 70 through a zener diode 90.
In operation, the reference and analysis chambers under no fault, no vapor, gas or aerosol conditions provide a potential at the common electrode 15 which results in a potential at the junction of the resistors 52 and 54 having a magnitude for causing conduction of the transistor 76. The diode 84 is therefore back-biased. Similarly, the potential at the wiper arm 88 under these conditions has a magnitude insufficiently high for causing conduction of the zener diode 90. In this regard, the sensitivity of the detector to vapors, gases and aerosols is adjustable by adjustment of the wiper arm 88 of the potentiometer 56. In FIG. 1, an aperture 92 is formed in the casing 5 for providing access to the potentiometer for a sensitivity adjustment of the wiper arm 88. A defective installation or operation or abuse of the detector can result in a defect in insulation. In the analysis chamber this defect in insulation will be reflected as an abnormal drop in the equilibrium potential of the electrode 15 resulting in a decrease in the base current to the transistor 76. The collector voltage of this transistor then rises causing forward bias and conduction of the diode 84. The forward biased diode 84 provides a current passage through the resistance 78 to the gate electrode 70 of the thyristor 66, thereby switching the thyristor into a conductive condition and causing energization of the lamp 3. The lamp will then remain energized until operating potential is interrupted to the thyristor 66.
In the alternative and principal mode of operation, the entry of a vapor, gas or aerosol into the analysis chamber results in an appreciable decrease in the magnitude of the ionization current, thereby increasing the impedance of this chamber and causing an increase in the potential of the electrode 15 from its equilibrium value. The voltage at the potentiometer wiper arm 88 will accordingly increase from the corresponding equilibrium potential to a magnitude at which the zener diode 90 becomes conductive and thereby triggers the thyristor 66 into conduction. The lamp 3 is then energized and remains energized until operating potential to the thyristor 66 is interrupted.
It is beneficial at times to provide an indication of the initiation or of the progress of a fire or other disaster. In accordance with another feature of this invention, the detector includes a memory for establishing such an indication. The distribution of a number of such detectors about the site of a fire or disaster, then renders it possible to determine the initiation and duration of the fire at each detector station and to consequently trace the progress of the fire or disaster. An integrating circuit means is provided by the use of a field effect transistor 94 which is coupled to an operational amplifier 96 having a feedback loop and arranged as an integrator. In FIG. 2, the anode electrode 64 of the thyristor 66 is coupled to a gate electrode 93 of a field effect transistor 94. The field effect transistor 94 is coupled in series with an integrator 96. The integrator 96 comprises a solid state integrated circuit. One such integrated circuit suitable for the use indicated is SN521 manufactured by Texas Instruments, Inc. This integrator is thermally insulated with asbestos for example in order to protect the integrator from the effects of the fire or disaster. An output from the integrator 96 is applied via the line 29 to a remote electronic storage means 98. The storage means 98 comprises for example a totalizer counter or a binary counter. During the interval of time in which vapors, fumes or aerosols are detected or a fault condition exists, the integrator 96 provides a periodically recurring output voltage. Either the analog representation of the integrator output or the digital representation which are indicative of the total time during which the faulty condition existed can be used subsequently to determine the intensity and duration of the faulty condition. This information in turn is employed to obtain geographical indications of the origin of the faulty condition. This is accomplished for example by obtaining the different records from a number of detectors located at the fire or disaster site and correlating these records to establish a map of the location and distribution of the disaster.
A circuit arrangement comprising resistors 100 and 102 and a diode 104 are provided for generating a signal for coupling to a central location. This signaling is particularly useful when defects such as an interruption in the application of power to the unit from the source 40 occurs. This may occur for example when the casing 5 is separated from the base 1. The conduction of the thyristor 66 upon the occurrence of a defect results in a relatively low potential at the terminal 62. The resistor 102 is selected to have a relatively low resistance with respect to the resistor 100. When a relatively low potential occurs at terminal 62 and since a positive potential is applied to the resistor 100, the diode 104 will be conducting and a relatively low potential will appear on the output line 106. It is noted that other detectors sensing for similar or other conditions may be coupled to the line 106. When the supply to the unit is interrupted such as through the removal of a detector from its base, the potential at the point 106 will rise and this rise can be utilized for indicating or control purposes at a main panel.
An improved form of ionization detection means for gases, vapors or aerosols has thus been described. The detection means advantageously compensates for a level of pollution in an environment where the detector is to be utilized. In addition, the detection means provides means for recording the duration of a false alarm or of the detection of vapors, gases or aerosols and provides an indication which can be stored in a counter. The detection means further is adapted for indicating a fault condition in the detector.
While particular embodiments of the invention have been described herein, it will be apparent to those skilled in the art that variations may be made thereto without departing from the spirit of the invention and the scope of the appended claims.