US3693009A - Ionization smoke detecting device - Google Patents

Ionization smoke detecting device Download PDF

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Publication number
US3693009A
US3693009A US133767A US3693009DA US3693009A US 3693009 A US3693009 A US 3693009A US 133767 A US133767 A US 133767A US 3693009D A US3693009D A US 3693009DA US 3693009 A US3693009 A US 3693009A
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United States
Prior art keywords
electrodes
ionization
voltage
smoke
potential
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Expired - Lifetime
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US133767A
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English (en)
Inventor
Koju Sasaki
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Nittan Co Ltd
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Nittan Co Ltd
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Publication date
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
    • G01N27/64—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/11—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using an ionisation chamber for detecting smoke or gas

Definitions

  • ABSTRACT An ionization smoke detector having a single ionization chamber, a pair of spaced electrodes in said chamber, a grid electrode between said spaced electrodes and a radioactive source within the chamber. A potential is applied between the spaced electrodes and means are connected between one of the spaced electrodes and the grid electrode to detect potential Int. Cl. "swig $2 in the grid produced by the presence of Field of Search ..250/43.5 D, 44, 83.6 FT;
  • This invention relates to an ionization smoke detecting device and more particularly to an ionization smoke detecting device having a single ionization chamber.
  • a prior ionization smoke detector has two ionization chambers, one of which is airtight while the other is exposed to the air. Both ionization chambers include pairs of electrodes which are mutually connected in a tivated by detecting this unbalance of the bridge circuit. Since such prior device requires two ionization chambers, it is disadvantageous in that two radioactive sources are required and the construction is complicated.
  • an object of this invention is to provide an improved ionization smoke detecting device having a single ionization chamber.
  • an ionization smoke detector is provided with a smoke sensing section composed of a single ionization chamber including a pair of facing electrodes, a grid electrode located between said facing electrodes and a single radioactive source located near one of said facing electrodes; A potential drift detected at the grid electrode due to presence of smoke is amplified to activate an alarm device.
  • FIG. 1 is a schematic diagram, partially in block form, of an ionization smoke detector according to the prior art
  • FIG. 2 is a graph explaining operation of the device of FIG. 1;
  • FIG. 3 is a schematic diagram, partially in block form, of an ionization smoke detector according to this invention.
  • FIG. 4 is a potential distribution diagram illustrating operation of the device of FIG. 3.
  • two ionization chambers l and 2 are utilized and embody radioactive sources 3 and 4.
  • the radioactive sources are each carried by one of the electrodes while a second electrode diagrammatically illustrated in a U- shaped configuration is positioned in spaced relationship to the electrode carrying the radioactive material.
  • the electrodes of the chambers are connected in series and a voltage V is applied to the series connected chambers.
  • the drain-source path of a field effect transistor 5 is connected in series with a resistor 6, and this series circuit is connected in parallel with the ionization chambers.
  • the gate electrode of the transistor 5 is connected to the junction of the two ionization chambers.
  • the ionization chamber 1 is airtight and will be referred to as the internal chamber.
  • the ionization chamber 2 is exposed to air and will be referred to as the external chamber.
  • curves A and B represent the voltage-ion current characteristics of the internal and external chambers l and 2.
  • smoke When smoke is introduced into the external chamber 2, it modifies the voltage-current characteristic and produces a curve such as illustrated at B. This is caused by the reduction of the ion current resulting from absorption of the radioactive rays by the smoke and adsorption of the ions by the fine smoke particles which are heavier than ions and electrons and therefore lack mobility.
  • the voltage-current characteristic of the external chamber 2 has been changed, the current changes from i to i.
  • the voltage across both chambers is maintained at a constant value with the result that the voltage across the external chamber changes from v, to v',.
  • the voltage change across the external chamber 2 is Av vr-v and this voltage change appears across the resistor 6. At least a portion of the voltage across the resistor 6 is fed to an amplifier 7 and actuates an alarm device 8.
  • FIG. 3 illustrates a device in accordance with the invention.
  • This device has a smoke sensing portion which comprises a pair of spaced electrodes 11 and 12 with a grid electrode 13 disposed therebetween.
  • a radioactive source 14 is positioned in the vicinity of the electrode 11.
  • the electrode 11 and the grid electrode are connected to a voltage amplifier 15 which in turn is connected through a power amplifier 16 to an alarm 17.
  • a constant voltage source 18 is connected to spaced electrodes 11 and 12.
  • the voltage source 18 produces a voltage E across the electrodes 11 and'12 and the potential distribution between the electrodes is a substantially straight line as illustrated bythe line H of FIG. 4. This occurs under a smoke free condition.
  • the potential distribution changes markedly as illustrated by the graph K in FIG. 4.
  • the grid 13 is preferably located at a position which will afford the greatest voltage change.
  • the change in the voltage is amplified by the amplifiers l5 and 16, the former having a relatively high input impedance, and the output of the amplifier 16 is fed to an alarm device 17.
  • the smoke detecting device in accordance with the invention comprises a single ionization chamber and can therefore be constructed simply and utilizes a single radioactive source. Moreover, the signal produced by the presence of smoke can be directly amplified by a conventional voltage amplifier and without the need for a complicated bridge circuit such as that shown in FIG. 1.
  • the device in accordance with this invention also provides improved operation, requires simple circuitry, and affords stable operation.
  • An ionization smoke detecting device comprising a pair of spaced electrodes having means for applying a DC potential therebetween, means supporting said electrodes to permit the movement of ambient air therebetween, a potential sensing grid disposed between said spaced electrodes, a radioactive source positioned in the vicinity of one of said electrodes, said DC potential and radioactive source producing a sub-

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  • Chemical & Material Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Emergency Management (AREA)
  • Toxicology (AREA)
  • Business, Economics & Management (AREA)
  • Electrochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US133767A 1968-12-24 1971-04-13 Ionization smoke detecting device Expired - Lifetime US3693009A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP9418168 1968-12-24

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US3693009A true US3693009A (en) 1972-09-19

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US133767A Expired - Lifetime US3693009A (en) 1968-12-24 1971-04-13 Ionization smoke detecting device

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US (1) US3693009A (enrdf_load_stackoverflow)
DE (1) DE1964669A1 (enrdf_load_stackoverflow)
GB (1) GB1275450A (enrdf_load_stackoverflow)
NL (1) NL6918515A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3926560A (en) * 1973-10-30 1975-12-16 Us Energy System for detecting gaseous contaminants in air
US4090308A (en) * 1975-08-04 1978-05-23 Aero-Dyne Manufacturing, Inc. Method and apparatus for signalling concentration of air conveyed ionizable foreign matter
FR2438841A1 (fr) * 1978-10-13 1980-05-09 Commissariat Energie Atomique Capteur ionique pour detecteur d'incendie

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3448261A (en) * 1965-03-11 1969-06-03 Boris Abel Amiragoff Signal detection and measuring circuit
US3560737A (en) * 1967-08-02 1971-02-02 Honeywell Inc Combustion products detector using a radioactive source and detector

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3448261A (en) * 1965-03-11 1969-06-03 Boris Abel Amiragoff Signal detection and measuring circuit
US3560737A (en) * 1967-08-02 1971-02-02 Honeywell Inc Combustion products detector using a radioactive source and detector

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3926560A (en) * 1973-10-30 1975-12-16 Us Energy System for detecting gaseous contaminants in air
US4090308A (en) * 1975-08-04 1978-05-23 Aero-Dyne Manufacturing, Inc. Method and apparatus for signalling concentration of air conveyed ionizable foreign matter
FR2438841A1 (fr) * 1978-10-13 1980-05-09 Commissariat Energie Atomique Capteur ionique pour detecteur d'incendie

Also Published As

Publication number Publication date
NL6918515A (enrdf_load_stackoverflow) 1970-06-26
DE1964669A1 (de) 1970-07-02
GB1275450A (en) 1972-05-24

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