US3662177A - Ionization type smoke detectors with fet protected against open circuit input - Google Patents

Ionization type smoke detectors with fet protected against open circuit input Download PDF

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Publication number
US3662177A
US3662177A US830817A US3662177DA US3662177A US 3662177 A US3662177 A US 3662177A US 830817 A US830817 A US 830817A US 3662177D A US3662177D A US 3662177DA US 3662177 A US3662177 A US 3662177A
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US
United States
Prior art keywords
electrode
ionization chamber
mesh electrode
electric contact
field effect
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Expired - Lifetime
Application number
US830817A
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English (en)
Inventor
Koju Sasaki
Akihiro Kobayashi
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Nittan Co Ltd
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Nittan Co Ltd
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Publication date
Application filed by Nittan Co Ltd filed Critical Nittan Co Ltd
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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL 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
    • G08B17/113—Constructional details
    • 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
    • G01N27/66—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 and measuring current or voltage

Definitions

  • ABSTRACT Foreign Application Priority Data In an ionization type smoke detector wherein smoke is in July 1 l [968 Japan 43/585 18 troduced in an ionization chamber through a mesh electrode and the change in the ionization current caused by the smoke is detected by the potential difference between the gate and [52] i source electrodes ofa field effect transistor, means is provided [51 1 C n to short circuit the gate and source electrodes in response to [58] Field of Search 50/44, 83.6, 83.6 FT, the removal Ofthe mesh electroda 3 Claims, 4 Drawing Figures FET 25 3* i' G 23 PATENTEUMAY 9 I972 3,662,177
  • This invention relates to an ionization type smoke detector and more particularly to the improvent of an ionization type smoke detector utilizing a field effect transistor wherein damage of the transistor caused by the removal of a mesh electrode can be prevented.
  • FIG. 1 of the accompanying drawing is a connection diagram to explain the principle of an ionization type smoke.
  • detector 1 comprising an enclosed ionization chamber 3 defined by an electroconductive isolating plate 2 and an open ended ionization chamber 5 defined by a mesh electrode 4.
  • a radioactive substance 6 is mounted on the bottom of the isolating plate 2 to irradiate ionizing chambers 3 and 5 with radiations.
  • a field effect transistor FET is provided having a gate electrode G connected to the isolating plate 2, a drain electrode D connected to an electrode 7 disposed in the enclosed ionization chamber 3 and a source electrode S connected to the mesh electrode 4.
  • the ionization current flowing through the ionization chamber 5 will be decreased by the disturbance caused by the smoke. This results in the variation of the potential between the gate electrode G and the source electrode S of the field effect transistor.
  • the potential variation is applied to the gate electrode of a silicon controlled rectifier element SCR via a Zener diode D to alarm the occurrence of the fire hazard.
  • This invention contemplates to automatically short circuit the gate electrode G and the source electrode S when the mesh electrode is removed.
  • an ionization type smoke detector comprising an enclosed ionization chamber defined by an electroconductive isolating plate and adapted to contain a radioactive substance, an open ionization chamber defined by said isolating plate and a mesh electrode, an electrode disposed in the enclosed ionization chamber, and a field effect transistor including a gate electrode connected to the isolating plate, a drain electrode connected to the electrode and a source electrode connected to the mesh electrode characterized by means interlocked with the removal of the mesh electrode to electrically short circuit the source electrode and the gate electrode.
  • FIG. 1 is a connection diagram to explain the principle of an ionization type smoke detector
  • FIG. 2 is an enlarged cross-sectional view of a portion of an ionization type smoke detector embodying this invention
  • FIG. 3 shows a portion of the detector shown in FIG. 2 when the mesh electrode is removed and
  • FIG. 4 is a view similar to FIG. 3 illustrating a modified embodiment of this invention.
  • the field effect transistor FET and the enclosed ionization chamber 3 are usually disposed in a cylindrical housing 20 and the mesh electrode 4 is secured to an annular ring 21 which is threaded into the lower end of the inner wall of the casing 20.
  • the annular ring 21 and the mesh electrode 4 are electrically connected to the source electrode S of the field effect transistor F ET.
  • the drain electrode D and the gate electrode G of the field effect transistor are connected to the electrode 7 and the isolating plate 2, respectively.
  • an electroconductive resilient piece 22 is secured to the inner wall of the casing 20 and the assembly of the mesh electrode 4 and the annular ring 21 is provided with a upright rod 23 cooperating with the resilient piece 22.
  • the upper end of a screw 25 for securing the electroconductive isolating plate 2 to a support 24 is projected upwardly for a sufficient length beyond the upper surface of the support 24.
  • rod 23 is integrally formed with the resilient piece 22 to urge the lower end of the rod 23 against the upper surface of the annular ring 21.
  • the rod 23 may be substituted by a cylindrical operating member (not shown) concentric with the casing 20.
  • Such an operating member may be slidably disposed to be pushed upwardly when the annular ring 21 is threaded into the casing 20.
  • the electrical connection between the source electrode of the field effect transistor F ET and the mesh electrode may be provided either through the engagement between the casing 20 and the annular ring 21, as shown in the drawing or through rod 23 of a conductor.
  • the upper end of the isolating plate 2 may be bent upwardly above the support 24 to establish the desired electrical connection.
  • the source electrode of the field effect transistor and the isolating plate to which the gate electrode is connected are electrically connected to short circuit the source and gate electrodes and when the mesh electrode is again mounted in position, the electroconductive resilient piece opens said short circuit, whereby damage of the field effect transistor inherent to the prior art ionization type smoke detector can be effectively prevented.
  • this invention can equally be applied to the protection of other elements having high input impedances than the field effect transistor, for example unijunction transistors and the like.
  • an ionization type smoke detector comprising an enclosed ionization chamber defined by an electroconductive isolating plate and adapted to contain a radioactive substance, an open ionization chamber defined by said isolating plate and a mesh electrode, an electrode disposed in said enclosed ionization chamber, and a field effect transistor including a gate electrode connected to said isolating plate, a drain electrode connected to said electrode disposed in said enclosed ionization chamber and a source electrode connected to said mesh electrode, the improvement which comprises switch means connected between said source and gate electrodes, and actuator means associated with said mesh electrode for open circuiting said switch means when said mesh electrode is in place on said open ionization chamber and for closing said switch means when said mesh electrode is removed to short circuit said source electrode and said gate electrode.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Elimination Of Static Electricity (AREA)
US830817A 1968-07-11 1969-06-05 Ionization type smoke detectors with fet protected against open circuit input Expired - Lifetime US3662177A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP5851868 1968-07-11

Publications (1)

Publication Number Publication Date
US3662177A true US3662177A (en) 1972-05-09

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ID=13086634

Family Applications (1)

Application Number Title Priority Date Filing Date
US830817A Expired - Lifetime US3662177A (en) 1968-07-11 1969-06-05 Ionization type smoke detectors with fet protected against open circuit input

Country Status (6)

Country Link
US (1) US3662177A (de)
BE (1) BE735386A (de)
CH (1) CH512121A (de)
DE (1) DE1933938B2 (de)
GB (1) GB1277091A (de)
NL (1) NL6910256A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3908957A (en) * 1973-04-17 1975-09-30 Cerberus Ag Ionization-type fire sensor
US3935465A (en) * 1973-04-24 1976-01-27 Geba-Gesellschaft Fuer Elektronische Brandmeldeanlagen Mbh Ionization analyzing air pollution, smoke and fire alarm device
US4041376A (en) * 1973-11-06 1977-08-09 The Furukawa Electric Co., Ltd. Detector for detecting the state of electrically non-conductive or substantially electrically non conductive fluid
US4786811A (en) * 1986-01-17 1988-11-22 Nohmi Bosai Kogyo Co., Ltd. Ionization type-smoke detector

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4245174A (en) 1978-04-24 1981-01-13 Isotec Industries Limited Dual ionization chamber

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3447137A (en) * 1965-05-13 1969-05-27 Bunker Ramo Digital memory apparatus
US3500368A (en) * 1966-03-30 1970-03-10 Nittan Co Ltd Automatic ionic fire alarm system
US3514603A (en) * 1966-12-22 1970-05-26 Johnson Service Co Ionization chamber detection apparatus having a low voltage source means

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3447137A (en) * 1965-05-13 1969-05-27 Bunker Ramo Digital memory apparatus
US3500368A (en) * 1966-03-30 1970-03-10 Nittan Co Ltd Automatic ionic fire alarm system
US3514603A (en) * 1966-12-22 1970-05-26 Johnson Service Co Ionization chamber detection apparatus having a low voltage source means

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3908957A (en) * 1973-04-17 1975-09-30 Cerberus Ag Ionization-type fire sensor
US3935465A (en) * 1973-04-24 1976-01-27 Geba-Gesellschaft Fuer Elektronische Brandmeldeanlagen Mbh Ionization analyzing air pollution, smoke and fire alarm device
US4041376A (en) * 1973-11-06 1977-08-09 The Furukawa Electric Co., Ltd. Detector for detecting the state of electrically non-conductive or substantially electrically non conductive fluid
US4786811A (en) * 1986-01-17 1988-11-22 Nohmi Bosai Kogyo Co., Ltd. Ionization type-smoke detector

Also Published As

Publication number Publication date
DE1933938B2 (de) 1971-07-22
GB1277091A (en) 1972-06-07
DE1933938A1 (de) 1970-02-05
NL6910256A (de) 1970-01-13
CH512121A (de) 1971-08-31
BE735386A (de) 1969-12-01

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