US3676678A - Single chamber ionization smoke detector - Google Patents

Single chamber ionization smoke detector Download PDF

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Publication number
US3676678A
US3676678A US10158A US3676678DA US3676678A US 3676678 A US3676678 A US 3676678A US 10158 A US10158 A US 10158A US 3676678D A US3676678D A US 3676678DA US 3676678 A US3676678 A US 3676678A
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US
United States
Prior art keywords
ionization
field effect
effect transistor
gate
smoke detector
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US10158A
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English (en)
Inventor
Naoki Takahashi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nittan Co Ltd
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Nittan Co Ltd
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Filing date
Publication date
Application filed by Nittan Co Ltd filed Critical Nittan Co Ltd
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Publication of US3676678A publication Critical patent/US3676678A/en
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    • 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
    • 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

  • This invention relates to an ionization smoke detector which utilizes a chamber including a radioactive source and wherein the saturation current flowing through the chamber is reduced by the presence of smoke.
  • Prior known smoke detectors have utilized two ionization chambers each including a radioactive source. One of the chambers are sealed while the other chamber was open for the admission of smoke. The presence of smoke was indicated by the different effective impedances of the chambers when smoke was present in one of the chambers. With prior known detectors, however, the closed ionization chamber served effectively as a high resistance with the result that the structure was not only complicated but also materially increased the cost.
  • One object of the invention resides in the provision of a novel and improved ionization chamber which overcomes the difficulties heretofore encountered with prior devices and utilizes a single open chamber for the detection of smoke.
  • a field effect transistor is utilized with the source-drain path being connected across the terminals of a power supply.
  • a single open ionization chamber including a radioactive source is connected between the gate electrode and one terminal of the power supply and the leakage resistance between the gate and drain electrodes is used as a high resistance path.
  • FIG. 1 is a circuit diagram of a conventional ionization detector using a closed chamber and an open chamber;
  • FIG. 2 is a circuit diagram of a smoke detector in accordance with one embodiment of the invention.
  • FIG. 3 is a graph showing the operation of the detector of FIG. 2.
  • HO. 4 is a circuit diagram of another embodiment of the smoke detector in accordance with the invention.
  • a typical known ionization detector utilizes a closed ionization chamber 4 having a radioactive source 2 and an open ionization chamber 8 having a radioactive source 6.
  • the two ionization chambers are connected in series between a conductor 10 attached to the positive terminal of the power supply and a conductor 12 attached to the negative terminal of the power supply.
  • a field effect transistor 14 which has a high input impedance was connected across the power supply with the drain being connected to the conductor l and the source being connected through a load resistor 20 to the conductor 12.
  • the gate 22 was connected to the junction 24 of the ionization chambers 4 and 8.
  • the current flowing through the leakage impedance 26 decreases with an increase in the voltage V at the gate electrode 22 as shown by the broken line A in FIG. 3.
  • the leakage current only varied gradually with a change in the voltage V as shown by curve B in FIG. 3.
  • the saturation current, however, flowing through the ionization chamber 8 varied linearly and approximately proportionally to the gate voltage V within the range of a low applied voltage.
  • the saturation current is relatively large and is illustrated by the line C of FIG. 3 in the absence of smoke.
  • the current through chamber 8 is represented by the line D of FIG. 3.
  • the current flowing through the leakage resistance 26 also flows through the ionization chamber 8, and the gate voltage V is V
  • the saturation current flowing through the chamber decreases so that the gate voltage of transistor 14 increases to V
  • the voltage change V -V at the gate electrode caused by presence of smoke is amplified by the transistor, and an output signal appears at the terminal 24.
  • This output signal may be utilized to drive a silicon-controlled rectifier or other device for the operation of a suitable alarm device or other indicator.
  • FIG. 4 A modified embodiment is illustrated in FIG. 4 and employs means for control of the sensitivity and also facilitates testing operations. Specifically the electrode 6 of the ionization chamber 8 is connected through a conductor 12' to the variable voltage source such as the potentiometer 28 which is connected between the conductors l0 and 12.
  • the variable voltage source such as the potentiometer 28 which is connected between the conductors l0 and 12.
  • the voltage at the electrodes 6 can be changed by adjusting the potentiometer 28, the voltage at the gate electrode 22 of the field effect transistor 14 can be changed regardless of the presence or absence of smoke.
  • the same effect is obtained as changing the bias voltage on the gate electrode 22 with the result that the sensitivity of the device can be controlled.
  • the voltage at the electrode 6 is adjusted to an extreme value by the potentiometer 28, the voltage at the gate electrode 22 will have a value corresponding to the value experienced during the presence of smoke. Accordingly it is possible to test the operation of the detector without the actual introduction of smoke.
  • An ionization smoke detector comprising a field effect transistor having the source-drain path connected between reference potential points of a power supply and a single opentype ionization chamber including a radioactive source therein connected between the gate electrode of said field effect transistor and one of said reference potential points, said ionization chamber and the gate-drain leakage path forming a voltage divider, whereby the leakage impedance existing between the gate and drain of said field effect transistor forms a substantially constant current high resistance path within a selected range of gate voltages.
  • An ionization smoke detector according to claim 1 characterized in that one terminal of the open-type ionization chamber is connected to a variable voltage source to control the sensitivity and facilitate testing operations.

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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)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US10158A 1969-04-25 1970-02-10 Single chamber ionization smoke detector Expired - Lifetime US3676678A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP44031475A JPS529998B1 (uk) 1969-04-25 1969-04-25

Publications (1)

Publication Number Publication Date
US3676678A true US3676678A (en) 1972-07-11

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Family Applications (1)

Application Number Title Priority Date Filing Date
US10158A Expired - Lifetime US3676678A (en) 1969-04-25 1970-02-10 Single chamber ionization smoke detector

Country Status (5)

Country Link
US (1) US3676678A (uk)
JP (1) JPS529998B1 (uk)
DE (1) DE2019791B2 (uk)
GB (1) GB1259437A (uk)
NL (1) NL7002577A (uk)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4423411A (en) * 1978-11-20 1983-12-27 Crucible Society Anonyme Ionization type fire detector
US5212470A (en) * 1989-09-15 1993-05-18 Cerberus Ltd. Supervised fire alarm system
US6683319B1 (en) 2001-07-17 2004-01-27 Mitec Incorporated System and method for irradiation with improved dosage uniformity

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2711457C2 (de) * 1977-03-16 1985-06-27 Siemens AG, 1000 Berlin und 8000 München Ionisationsbrandmelder
EP0011364B1 (en) * 1978-09-29 1983-05-18 Chubb Fire Limited Heat detector circuit
US5189399A (en) * 1989-02-18 1993-02-23 Hartwig Beyersdorf Method of operating an ionization smoke alarm and ionization smoke alarm
DE3904979A1 (de) * 1989-02-18 1990-08-23 Beyersdorf Hartwig Verfahren zum betrieb eines ionisationsrauchmelders und ionisationsrauchmelder

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3295121A (en) * 1961-12-30 1966-12-27 Danske Securitas As Electric alarm system, preferably for fire alarms

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3295121A (en) * 1961-12-30 1966-12-27 Danske Securitas As Electric alarm system, preferably for fire alarms

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4423411A (en) * 1978-11-20 1983-12-27 Crucible Society Anonyme Ionization type fire detector
US5212470A (en) * 1989-09-15 1993-05-18 Cerberus Ltd. Supervised fire alarm system
US6683319B1 (en) 2001-07-17 2004-01-27 Mitec Incorporated System and method for irradiation with improved dosage uniformity

Also Published As

Publication number Publication date
JPS529998B1 (uk) 1977-03-19
NL7002577A (uk) 1970-10-27
DE2019791B2 (de) 1972-03-30
DE2019791A1 (de) 1970-11-05
GB1259437A (uk) 1972-01-05

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