US3688119A - Ionization smoke detector - Google Patents

Ionization smoke detector Download PDF

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Publication number
US3688119A
US3688119A US57554A US3688119DA US3688119A US 3688119 A US3688119 A US 3688119A US 57554 A US57554 A US 57554A US 3688119D A US3688119D A US 3688119DA US 3688119 A US3688119 A US 3688119A
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United States
Prior art keywords
pair
ionization
conductors
voltage
field effect
Prior art date
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
US57554A
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English (en)
Inventor
Akihiro Kobayashi
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
Priority claimed from JP6683969A external-priority patent/JPS4819118B1/ja
Application filed by Nittan Co Ltd filed Critical Nittan Co Ltd
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Publication of US3688119A publication Critical patent/US3688119A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments
    • G01T7/12—Provision for actuation of an alarm
    • G01T7/125—Alarm- or controlling circuits using ionisation chambers, proportional counters or Geiger-Mueller tubes, also functioning as UV detectors
    • 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
    • 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
    • G08B17/113—Constructional details

Definitions

  • ABSTRACT An ionization smoke detector having open and closed ionization chambers each having at least two electrodes and a radioactive source.
  • the electrodes are connected in series across a voltage supply and the change of impedance of the open ionization chamber is detected by a field effect transistor which in turn fires a silicon controlled rectifier.
  • the silicon controlled rectifier is provided with a holding circuit so that when utilizing a pulsating voltage, the silicon controlled rectifier will be maintained in a conductive state even though the pulsating voltage periodically approaches zero.
  • the invention further contemplates means for controlling the current through the sourcedrain path of the field effect transistor so that wide voltage fluctuations will not damage the transistor or produce erroneous alarm signals.
  • This invention relates to an ionization smoke detector and more particularly to a novel and improved ionization smoke detector that will afford accurate and dependable operation when energized by an insufficiently filtered pulsating voltage as well as a filtered voltage.
  • Prior known ionization detectors comprise open and closed chambers.
  • the chambers of each detector each have a pair of electrodes and radioactive source.
  • Electrodes of the chambers are connected in series across a voltage source for producing the current flow through the chambers.
  • a field efiect transistor is connected with the chambers to detect a voltage change at the junction of the chambers which resultsfrom an increase in impedance of the open ionization chamber by reason of the entry of smoke therein.
  • a switching element such as a silicon controlled rectifier is driven into conduction by the output of the field effect transistor.
  • One object of this invention resides in the provision of an improved ionization detector which will operate dependably on an inexpensive pulsating source. This is accomplished by the use of an improved holding circuit which will maintain the silicon controlled rectifier in a conductive state once it is driven into conduction even though it is operated from a pulsating voltage.
  • An improved ionization smoke detector in accordance with the invention includes a closed ionization chamber having a pair of electrodes and a radioactive source, an open ionization chamber exposed to the ambient atmosphere and having a pair of electrodes and a radioactive source, a pair of conductors providing an operating voltage which is applied across both ionization chambers, the latter being connected in series, a field effect transistor for detecting a voltage change at the junction of the chambers which results from the admission of smoke into the open chamber, a silicon controlled rectifier connected between said conductors and controlled by the output of the field effect transistor and a holding circuit for maintaining a silicon controlled rectifier in a conductive state even when a pulsating voltage is applied to the conductors.
  • FIG. 1 is a schematic diagram illustrating one embodiment of an ionization smoke detector in accordance with the invention
  • FIGS. 2 and 3 are graphs illustrating voltage wave forms for use in explaining the operation of the detector shown in FIG. 1;
  • FIG. 4 is a schematic diagram of a modified embodiment of an ionization smoke detector in accordance with the invention.
  • the detector includes a closed ionization chamber 10 having a pair of electrodes 11 and 12 and a radioactive source 12 and an open ionization chamber 20 also including a pair of electrodes 21 and 22 and a radioactive source 23.
  • the electrodes of the chambers are connected in series across a pair of conductors 1 and 2 which are connected to a voltage source not shown.
  • the junction 5 between the ionization chambers 10 and 20 is connected to the gate electrode 31 of the field effect transistor 30, the latter having its drain electrode 32 connected to the conductor 1 and its source electrode 33 is connected through the load resistor 4 to conductor 2.
  • the anode 42 of the silicon controlled rectifier 40 is connected through a resistor 7 of relatively low value and a diode 6 to the conductor 1.
  • the cathode 43 of the silicon controlled rectifier 40 is connected directly to the conductor 2.
  • a capacitor 9 is connected between the junction 8 of the resistor 7 and the diode 6 and the conductor 2.
  • the capacitor 9 and the diode 6 form a holding circuit to maintain the silicon controlled rectifier 40 in a conducting state once it has been driven into conduction.
  • a resistor 44 and a capacitor 45 are each connected between the gate electrode 44 of the silicon controlled rectifier 40 and the conductor 2.
  • the ionization current flowing through the open ionization chamber 20 does not vary materially by a voltage change across that chamber which may be caused by an impedance change of the closed ionization chamber 10.
  • FIG. 3 illustrates the ionization current flowing through the open ionization chamber 20 in which the abscissa represents the voltage at junction 5 and the ionization current is represented by the ordinate.
  • the voltage across the closed ionization chamber 10 is high and this voltage is represented by the curve 61 when smoke does not exist in the ambient air surrounding the ionization chamber 20.
  • the volt age at junction 5 is relatively low and represented by the curve 51 of FIG. 2.
  • the ionization current across the open ionization chamber normally varies in a manner represented by the curve 71 of FIG. 3, it tends to vary in a manner represented by the curve 72 when smoke enters the open ionization chamber 20.
  • the ionization current across the open ionization chamber does not vary materially even if a pulsating voltage is applied between the conductors 1 and 2 because of the inherently large time constant of the ionization chambers.
  • the voltage at junction 5 between the two chambers varies between V and V depending on the presence or absence of smoke in the open ionization chamber 20. This voltage change is detected by the field effect transistor and produces a signal at the source electrode 33.
  • the silicon controlled rectifier 40 would normally become nonconductive when the voltage across conductors 1 and 2 becomes zero. This undesirable condition however is prevented through the utilization of a holding circuit 60. More specifically, since the capacitor 9 of the holding circuit 60 is discharged through the resistor 7 when the voltage between the conductors l and 2 becomes zero, the discharge current maintains the silicon controlled rectifier 40 in a conductive state and since the resistor 7 is of a relatively low value, the current drawn from the conductors 1 and 2 is materially increased, and this current is detected by any suitable means to produce an alarm.
  • FIG. 4 is a modified embodiment of the detector according to this invention and it can be reliably operated with a nonstabilized voltage source. This is attained by providing a protective circuit for use with the field effect transistor so that the transistor which has a low breakdown voltage is never provided with a voltage higher than a predetermined value.
  • a protective circuit for use with the field effect transistor so that the transistor which has a low breakdown voltage is never provided with a voltage higher than a predetermined value.
  • the drain 32 of the field effect transistor is connected through the collector-emitter path of transistor 15 to conductor 1.
  • the base electrode of transistor 15 is connected through resistor 16 to conductor 1 and also through a zener diode 17 to conductor 2. With this arrangement the base electrode of transistor 15 is maintained at a fixed voltage determined by the diode 17 so that the transistor 15 functions as a constant voltage protection circuit for the field effect transistor 30.
  • the embodiment shown in FIG. 4 has the further advantage that the field effect transistor which has a low breakdown voltage will not be damaged by a high transient voltage which may be produced by the relay or bell connected in series with the voltage source. Furthermore, the detector can be operated without any danger of damaging the field effect transistor by a voltage source of low quality and having relatively large fluctuations.
  • the foregoing embodiments of the invention are merely shown for illustrative purposes and various modifications and changes can be made without departing from the spirit and scope of the invention.
  • the foregoing embodiments of the invention each have a single closed ionization chamber and a single open ionization chamber each having a single pair of electrodes and a single radioactive source.
  • ionization smoke detectors according to the invention may utilize any number of closed and open ionization chambers having any number of electrodes and radioactive sources depending on the nature of the application.
  • the number of field effect transistors may also be selected in accordance with a specific application.
  • An ionization smoke detector comprising at least one closed ionization chamber including at least one pair of electrodes and a radioactive source, at least one open ionization chamber including similarly at least one pair of electrodes and a radioactive source and connected in series to said closed ionization chamber, a pair of conductors for supplying an operational voltage to a series connection consisting of said both ionization chambers, at least one field effect transistor for detecting a voltage change at the junction between said both ionization chambers caused by smoke entering into said open ionization chamber, a silicon controlled rectifier having a main conduction path connected between said pair of conductors and controlled by said field effect transistor, and a holding circuit for supplying a current for keeping said silicon controlled rectifier in conduction once it conducts, even when a pulsating voltage is applied between said pair of conductors.
  • An ionization smoke detector in accordance with claim 1, characterized in that said holding circuit includes a diode connected forwardly in series with said silicon controlled rectifier and one of said pair of conductors, and a capacitor connected between the cathode electrode of said diode and the other of said pair of conductors.
  • An ionization smoke detector comprising at least one closed ionization chamber including at least one pair of electrodes and a radioactive source, at least one open ionization chamber including similarly at least one pair of electrodes and a radioactive source and effect transistor below a breakdown voltage of said field effect transistor, a silicon controlled rectifier having a main conduction path connected between said pair of conductors and controlled by said field effect transistor, and a holding circuit for supplying a current for keeping said silicon controlled rectifier in conduction once it conducts, even when a pulsating voltage is applied between said pair of conductors.
  • said constant voltage protection circuit includes a transistor having an emittercollector path connected between the drain electrode of said field effect transistor and one of said pair of conductors, a resistor connected between the base electrode of said transistor and one of said pair of conductors, and a zener diode connected between the base electrode of said transistor and the other of said pair of conductors.

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  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • General Health & Medical Sciences (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Biochemistry (AREA)
  • Toxicology (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US57554A 1969-07-24 1970-07-23 Ionization smoke detector Expired - Lifetime US3688119A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP5797969 1969-07-24
JP6683969A JPS4819118B1 (enrdf_load_stackoverflow) 1969-08-26 1969-08-26

Publications (1)

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US3688119A true US3688119A (en) 1972-08-29

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US57554A Expired - Lifetime US3688119A (en) 1969-07-24 1970-07-23 Ionization smoke detector

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US (1) US3688119A (enrdf_load_stackoverflow)
CH (1) CH526178A (enrdf_load_stackoverflow)
DE (1) DE2036447B2 (enrdf_load_stackoverflow)
FR (1) FR2055543A5 (enrdf_load_stackoverflow)
GB (1) GB1282536A (enrdf_load_stackoverflow)
IL (1) IL35151A (enrdf_load_stackoverflow)
NL (1) NL7010779A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401979A (en) * 1981-02-11 1983-08-30 General Signal Corporation Electrical controls for ionization smoke detector

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3812362A (en) * 1973-07-02 1974-05-21 Honeywell Inc Smoke detector circuit
CH586941A5 (enrdf_load_stackoverflow) * 1975-07-25 1977-04-15 Cerberus Ag
US4228429A (en) * 1977-12-29 1980-10-14 Ricoh Company, Ltd. Alarm system having phase-sensitive bridge circuit

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3500368A (en) * 1966-03-30 1970-03-10 Nittan Co Ltd Automatic ionic fire alarm system
US3516083A (en) * 1965-12-02 1970-06-02 Denske Securitas As Electric alarm system,preferably for a fire alarm

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3516083A (en) * 1965-12-02 1970-06-02 Denske Securitas As Electric alarm system,preferably for a fire alarm
US3500368A (en) * 1966-03-30 1970-03-10 Nittan Co Ltd Automatic ionic fire alarm system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401979A (en) * 1981-02-11 1983-08-30 General Signal Corporation Electrical controls for ionization smoke detector

Also Published As

Publication number Publication date
IL35151A0 (en) 1970-10-30
IL35151A (en) 1973-08-29
DE2036447A1 (de) 1971-02-25
FR2055543A5 (enrdf_load_stackoverflow) 1971-05-07
GB1282536A (en) 1972-07-19
DE2036447B2 (de) 1972-03-02
CH526178A (de) 1972-07-31
NL7010779A (enrdf_load_stackoverflow) 1971-01-26

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