US3792279A - Ionization smoke detector - Google Patents
Ionization smoke detector Download PDFInfo
- Publication number
- US3792279A US3792279A US00193901A US3792279DA US3792279A US 3792279 A US3792279 A US 3792279A US 00193901 A US00193901 A US 00193901A US 3792279D A US3792279D A US 3792279DA US 3792279 A US3792279 A US 3792279A
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- United States
- Prior art keywords
- source
- ionization
- electrodes
- chamber
- smoke detector
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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
- 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
- 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
- An ionization smoke detector of the type concerned includes a closed ionization chamber and an open ionization chamber each having a pair of electrodes and a radioactive source and connected in series between a pair of terminals to be connected to a central unit, a field effect transistor (hereinafter referred to as FET) having a gate electrode connected to the connection point of both ionization chambers and a source-to-drain path connected between both terminals.
- FET field effect transistor
- a relay element such as silicon controlled rectifier (hereinafter referred to as SCR) has a control electrode connected to the source electrode of the FET and a main conduction path connected between both terminals. A specific operation voltage is applied between both terminals from the central unit in the normal monitoring condition.
- the ionization current flowing in the open ionization chamber is reduced and thereby the impedance of the open ionization chamber is increased to raise the potential at the junction point of both ionization chambers and, accordingly, the gate potential of the F ET.
- an object of this invention is to propose an ionization smoke detector having aninexpensive and strongly built sensitivity control which affords improved stability.
- this object is attained by inserting a series connection of a plurality of diodes in series with the source-to-drain path of the FET.
- FIG. 1 is a schematic circuit diagram representing an ionization smoke detector including a sensitivity controlaccording to prior art
- FIG. 2 is a schematic circuit diagram representing an ionization smoke detector including a sensitivity control according to this invention.
- the ionization smoke detector includes a closed ionization chamber 10 having a pair of electrodes 1 l and 12 and a radio-active source 13 and an open ionization chamber 20 having a pair of electrodes 21 and 22 and a radioactive source 23.
- Both the ionization chambers 10 and 20 are connected in series between a pair of terminals l and 2 which are to be connected to a central unit (not shown).
- the connection point 3 of both ionization chambers is connected to the gate electrode G of an FET 4 having a drain electrode D connected to the terminal 1 and a source electrode S connected through a resistive'element of a potentiometer 8 and a load resistor 5 to the terminal 2.
- the movable contact of the potentiometer 8 is connected to the control electrode of an SCR 6 whose main conduction path is connected between both terminals 1 and 2.
- the control electrode of the SCR 6 is also connected through a leakage resistor 7 to terminal 2.
- the sensitivity of the detector can be controlled by moving the movable contact'9 of the potentiometer 8 to control the voltage to be applied to the control electrode of the SCR 6.
- mechanical contact 9 is often defective or makes improper contact and, thus, reduces the reliability of the device.
- the circuit is the same as that of FIG. 1 except that a series connection of a plurality of diodes 31, 32, 33, is inserted in place of the potentiometer 8 of FIG. 1.
- Terminals 41, 42 are respectively led out from the connection points between the respective diodes and a contact 9 which is connected to the control electrode of the SCR 6 is selectively connected to one of the terminals 41, 42,
- the contact 9 may be constructed as a movable change-over contact, but it is preferable to fixedly connect it to one terminal which is previously selected in accordance with its situation, by means of screwing or soldering, in order to prevent improper'contact.
- Each of the diodes exhibits a voltage drop of about 0.5 volts, for example, and this value is maintained almost constant in spite of variations in the current flowing therethrough. Therefore, the terminals 41, 42
- An ionization smoke detector comprising at least one open ionization chamber including a pair of electrodes and a radioactive source, means for applying a voltage to said electrodes, a field effect transister having gate, drain and source electrodes, a connection between one of said chamber electrodes and said gate electrode, a plurality of series connected diodes fortrance of smoke into said chamber.
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- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Business, Economics & Management (AREA)
- Biochemistry (AREA)
- Toxicology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Electrochemistry (AREA)
- Emergency Management (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- General Health & Medical Sciences (AREA)
- Fire-Detection Mechanisms (AREA)
- Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
Abstract
An ionization smoke detector having at least one ionization chamber open to ambient air and connected to a voltage supply, a field effect transistor having a source-drain path connected to said supply and a gate interconnected with said chamber to sense the voltage across the chamber, the source-drain path having a plurality of series connected diodes in series therewith and terminals connected to the junctions between the diodes in order to obtain a desired output voltage from the transistor upon the detection of smoke.
Description
United States Patent [191 Sasaki Feb. 12, 1974 IONIZATION SMOKE DETECTOR [75] Inventor: Koju Sasaki, Tokyo, Japan [73] Assignee: Nittan Company, Limited, Tokyo,
Japan [22] Filed: Oct. 29, 1971 [2]] App]. No.: 193,901
[30] Foreign Application Priority Data Nov. 19, 1970 Japan 45-114352 [52] US. Cl 250/83.6 R, 307/251, 340/237 S [51] Int. Cl. G0lt 1/18 [58] Field of Search 340/237 S, 237 R;
[56] References Cited UNITED STATES PATENTS 3,559,196 1/1971 Scheidweiler 250/836 3,435,257 3/1969 Lawrie 307/291 3,089,968 5/1963 Dunn.... 307/230 3,395,265 7/1968 Weir 219/209 11/1970 Gilbert 307/235 OTHER PUBLICATIONS The What & Why of integrated Circuits" by Stern, Radio-Electronics, October 1963, pages 34, 35.
Primary Examiner-James W. Lawrence Assistant ExaminerHarold A. Dixon Attorney, Agent, or Firm-Eugene E. Geoffrey, Jr.
[57] ABSTRACT 1 Claim, 2 Drawing Figures PATENTEI] FEB I 21974 Or/Z FIG. I PRIOR ART INVENTOR. K6U86145Anf/ 1 IONIZATION SMOKE DETECTOR This invention relates to an ionization smoke detector and more particularly to an ionization smoke detector provided with a sensitivity control.
An ionization smoke detector of the type concerned includes a closed ionization chamber and an open ionization chamber each having a pair of electrodes and a radioactive source and connected in series between a pair of terminals to be connected to a central unit, a field effect transistor (hereinafter referred to as FET) having a gate electrode connected to the connection point of both ionization chambers and a source-to-drain path connected between both terminals. A relay element such as silicon controlled rectifier (hereinafter referred to as SCR) has a control electrode connected to the source electrode of the FET and a main conduction path connected between both terminals. A specific operation voltage is applied between both terminals from the central unit in the normal monitoring condition. When smoke enters the open ionization chamber, the ionization current flowing in the open ionization chamber is reduced and thereby the impedance of the open ionization chamber is increased to raise the potential at the junction point of both ionization chambers and, accordingly, the gate potential of the F ET. This results in an increase of the source voltage, and when the source voltage exceeds a specific value, the SCR is driven into conduction and shortcircuits both terminals to transmit a detection signal to the central unit.
It is desirable to have an ionization smoke detector whose sensitivity is controllable, since it is sometimes necessary to change the sensitivityof each ionization smoke detector to meet certain operating conditions. For this purpose it has been suggested that a potentiometer be inserted in series with the source-to-drain path of the FET to control the voltage applied to the control electrode of the SCR. However, the potentiometer is costly and delicate and, therefore, unsuitable for use as a structural element of such device. It has also been proposed to substitute a series connection of fixed resistors having tapsfor the potentiometer, but this method has the disadvantage that the tap voltages of the series resistors vary significantly with the current flowing therethrough and the sensitivity is therefore not stabilized.
Accordingly, an object of this invention is to propose an ionization smoke detector having aninexpensive and strongly built sensitivity control which affords improved stability.
According to this invention, this object is attained by inserting a series connection of a plurality of diodes in series with the source-to-drain path of the FET.
Now, the invention will be described moreclearly hereinunder with reference'to the accompanying drawings.
FIG. 1 is a schematic circuit diagram representing an ionization smoke detector including a sensitivity controlaccording to prior art, and
FIG. 2 is a schematic circuit diagram representing an ionization smoke detector including a sensitivity control according to this invention.
Throughout the drawings like reference numerals are used to denote corresponding elements.
Referring to FIG. 1 representing a prior art device, the ionization smoke detector includes a closed ionization chamber 10 having a pair of electrodes 1 l and 12 and a radio-active source 13 and an open ionization chamber 20 having a pair of electrodes 21 and 22 and a radioactive source 23. Both the ionization chambers 10 and 20 are connected in series between a pair of terminals l and 2 which are to be connected to a central unit (not shown). The connection point 3 of both ionization chambers is connected to the gate electrode G of an FET 4 having a drain electrode D connected to the terminal 1 and a source electrode S connected through a resistive'element of a potentiometer 8 and a load resistor 5 to the terminal 2. The movable contact of the potentiometer 8 is connected to the control electrode of an SCR 6 whose main conduction path is connected between both terminals 1 and 2. The control electrode of the SCR 6 is also connected through a leakage resistor 7 to terminal 2.
When smoke enters the open ionization chamber 20 as described above, the potential at the connection point 3, and accordingly the gate electrode G of the FET 4 is raised to increase the drain-to-source current, thereby increasing the source voltage and, accordingly, the voltage at the control electrode of the SCR 6. When this voltage exceeds a specific threshold value, the SCR is driven into conduction to short-circuit both' terminals 1 and 2. i
The sensitivity of the detector can be controlled by moving the movable contact'9 of the potentiometer 8 to control the voltage to be applied to the control electrode of the SCR 6. However, such mechanical contact 9 is often defective or makes improper contact and, thus, reduces the reliability of the device.
Referring next to FIG. 2 representingan embodiment of this invention, the circuit is the same as that of FIG. 1 except that a series connection of a plurality of diodes 31, 32, 33, is inserted in place of the potentiometer 8 of FIG. 1. Terminals 41, 42, are respectively led out from the connection points between the respective diodes and a contact 9 which is connected to the control electrode of the SCR 6 is selectively connected to one of the terminals 41, 42, The contact 9 may be constructed as a movable change-over contact, but it is preferable to fixedly connect it to one terminal which is previously selected in accordance with its situation, by means of screwing or soldering, in order to prevent improper'contact.
Each of the diodes exhibits a voltage drop of about 0.5 volts, for example, and this value is maintained almost constant in spite of variations in the current flowing therethrough. Therefore, the terminals 41, 42
. provide voltages which are lower than the source voltage of the FET 4;by precisely 0.5 volts and its integral multiples, respectively, regardless of the drain-tosource current. Therefore, once the terminal of the diode train is selected to set the sensitivity of the deodes may be adopted as the diodes 31, 32, 33, so as to further improve the accuracy and reliability of actuation of the device.
What is claimed is:
1. An ionization smoke detector comprising at least one open ionization chamber including a pair of electrodes and a radioactive source, means for applying a voltage to said electrodes, a field effect transister having gate, drain and source electrodes, a connection between one of said chamber electrodes and said gate electrode, a plurality of series connected diodes fortrance of smoke into said chamber.
Claims (1)
1. An ionization smoke detector comprising at least one open ionization chamber including a pair of electrodes and a radioactive source, means for applying a voltage to said electrodes, a field effect transister having gate, drain and source electrodes, a connection between one of said chamber electrodes and said gate electrode, a plurality of series connected diodes forwardly inserted in series with said source electrode, means for applying a voltage to said source and drain electrodes through said series connected diodes, a connection between the other of said chamber electrodes and said series connected diodes, an output terminal and means for connecting said output terminal to selected junctions between said series connected diodes to vary the magnitude of said output signal upon the entrance of smoke into said chamber.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP1970114352U JPS4940290Y1 (en) | 1970-11-19 | 1970-11-19 |
Publications (1)
Publication Number | Publication Date |
---|---|
US3792279A true US3792279A (en) | 1974-02-12 |
Family
ID=14635583
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US00193901A Expired - Lifetime US3792279A (en) | 1970-11-19 | 1971-10-29 | Ionization smoke detector |
Country Status (5)
Country | Link |
---|---|
US (1) | US3792279A (en) |
JP (1) | JPS4940290Y1 (en) |
DE (1) | DE2156906B1 (en) |
FR (1) | FR2116395B1 (en) |
GB (1) | GB1300909A (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4223303A (en) * | 1978-12-11 | 1980-09-16 | General Electric Company | Alarm devices for interconnected multi-device systems |
US4401979A (en) * | 1981-02-11 | 1983-08-30 | General Signal Corporation | Electrical controls for ionization smoke detector |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103680042A (en) * | 2013-11-30 | 2014-03-26 | 成都国科海博信息技术股份有限公司 | Fire warning device |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3089968A (en) * | 1961-06-22 | 1963-05-14 | Gen Precision Inc | Non-linear amplifier |
US3395265A (en) * | 1965-07-26 | 1968-07-30 | Teledyne Inc | Temperature controlled microcircuit |
US3435257A (en) * | 1965-05-17 | 1969-03-25 | Burroughs Corp | Threshold biased control circuit for trailing edge triggered flip-flops |
US3539831A (en) * | 1967-06-15 | 1970-11-10 | Tektronix Inc | Switching circuit including plural ranks of differential circuits |
US3559196A (en) * | 1966-12-29 | 1971-01-26 | Cerberus Ag | Fire alarm with bistable characteristics |
-
1970
- 1970-11-19 JP JP1970114352U patent/JPS4940290Y1/ja not_active Expired
-
1971
- 1971-10-29 US US00193901A patent/US3792279A/en not_active Expired - Lifetime
- 1971-11-09 GB GB51955/71A patent/GB1300909A/en not_active Expired
- 1971-11-15 FR FR7140733A patent/FR2116395B1/fr not_active Expired
- 1971-11-16 DE DE19712156906D patent/DE2156906B1/en active Pending
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3089968A (en) * | 1961-06-22 | 1963-05-14 | Gen Precision Inc | Non-linear amplifier |
US3435257A (en) * | 1965-05-17 | 1969-03-25 | Burroughs Corp | Threshold biased control circuit for trailing edge triggered flip-flops |
US3395265A (en) * | 1965-07-26 | 1968-07-30 | Teledyne Inc | Temperature controlled microcircuit |
US3559196A (en) * | 1966-12-29 | 1971-01-26 | Cerberus Ag | Fire alarm with bistable characteristics |
US3539831A (en) * | 1967-06-15 | 1970-11-10 | Tektronix Inc | Switching circuit including plural ranks of differential circuits |
Non-Patent Citations (1)
Title |
---|
The What & Why of Integrated Circuits by Stern, Radio Electronics, October 1963, pages 34, 35. * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4223303A (en) * | 1978-12-11 | 1980-09-16 | General Electric Company | Alarm devices for interconnected multi-device systems |
US4401979A (en) * | 1981-02-11 | 1983-08-30 | General Signal Corporation | Electrical controls for ionization smoke detector |
Also Published As
Publication number | Publication date |
---|---|
JPS4940290Y1 (en) | 1974-11-05 |
FR2116395A1 (en) | 1972-07-13 |
FR2116395B1 (en) | 1975-07-18 |
GB1300909A (en) | 1972-12-29 |
DE2156906B1 (en) | 1972-05-25 |
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