EP0015942A1 - Detecteur a chambre d'ionisation - Google Patents

Detecteur a chambre d'ionisation

Info

Publication number
EP0015942A1
EP0015942A1 EP19790900364 EP79900364A EP0015942A1 EP 0015942 A1 EP0015942 A1 EP 0015942A1 EP 19790900364 EP19790900364 EP 19790900364 EP 79900364 A EP79900364 A EP 79900364A EP 0015942 A1 EP0015942 A1 EP 0015942A1
Authority
EP
European Patent Office
Prior art keywords
electrode
detector
chamber
measuring electrode
electrodes
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.)
Withdrawn
Application number
EP19790900364
Other languages
German (de)
English (en)
Inventor
Dennis Johnson
John Brian Letts
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.)
Chloride Group Ltd
Original Assignee
Chloride Group Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Chloride Group Ltd filed Critical Chloride Group Ltd
Publication of EP0015942A1 publication Critical patent/EP0015942A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/02—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas
    • H01J41/08—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas with ionisation by means of radioactive substances, e.g. alphatrons
    • 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

Definitions

  • This invention relates to an ionisation detector chamber and is an improvement in the chamber , the subject of British Patent Specification NOs. 27668/76 and 38825/76 in which the statement of invention reads
  • a detector including an ionisation chamber has first and second electrodes, the exposed conducting area of the first of which is restricted, and a measuring electrode
  • a detector includes an ionisation chamber having first and second electrodes, and a measuring electrode disposed adjacent to the exposed area of the first electrode,
  • second electrode of the detector and that tends to eliminate the detrimental effect of the condensation while having substantially no effect on the performan of the detector if there is no condensation.
  • the conductor is conveniently in the form of a
  • sleeve surrounding all except the lower end of the insulator around the first electrode, and the conduct sleeve can itself be surrounded by an insulating sleeve.
  • the invention may be carried into practice in
  • An insulating tube 12 surrounds all of the conducting surface of the electrode 11 which is within the detector chamber except for the part closely adjacent to the measuring electrode 15, which carries an Americium foil 16 for ionising the air.
  • a conducting tube 41 which is electricall connected to the perforated wall electrode -13.
  • the conducting tube 41 is itself covered by an insulating
  • This invention relates to a detector including an ionisation chamber for example for detecting the 5. presence of smoke so as to be capable of giving a sig for giving an alarm that a fire is imminent in a building.
  • An object of the invention is to provide a sim constructed small detector which is nevertheless very 10. sensitive to the presence of smoke.
  • a detector " including an ionisation chamber has first and second electrodes, theexposed conducting area of the first of which is restricted, and a measuring electrode 15. disposed adjacent the said exposed area, together with means for ionising gas in the chamber including the space between the three electrodes.
  • the disposition of the measuring electrode in relation to the first electrode concentrates the 20. electric field, within the part of the chamber adjacent to one electrode, and ensures that the prese of smoke has a much greater ⁇ effect on the ionisation current flowing between the measuring electrode and the other electrode than on the ionisation current 25. flowing between the first electrode and the measuring electrode.
  • the first electrode preferably comprises a rod extending into the chamber, and surrounded by an insulating sleeve except for the exposed are which 30. is at its inner end.
  • the insulating sleeve is preferably around the sides of the first electrode, except for a short length of the sides of the inner end.
  • the first electrode can be positioned
  • the ionisation means is conveniently a piece of radio-active material for example, a foil of radium or Americium and that can be positioned anywhere in the •
  • ionisation chamber although a convenient position is on the measuring electrode centrally opposite the exposed part of the first electrode.
  • the chamber has an insulating base carrying the measuring electrode which
  • the ionisation chamber consists of an upstanding wall around the base J and an end wall closing the chamber, all those walls being perforated while the first electrode extends through the end wall of the ionisation chamber
  • the sensitivity of the detector may not be accurately reproducable from sample to sample if the dielectric constant of the insulation material varies
  • the critical region of the detector is the region of high electric field between the first electrode and the measuring electrode and by terminating the insulation short of the end of the elongate first electrode so that the last part of the
  • 10. is also made more sensitive as the surface area of the exposed end of the elongate first electrode is larger. This modifies the electric field pattern in the region between the first electrode and the measuring . electrode, so giving increased sensitivity.
  • the insulation must extend reasonably near to th end of the elongate electrode to prevent the lines of the electric field going directly from the positive electrode to a surrounding negative electrode rather t by way of the measuring electrode.
  • FIGURE 1 is a sectional elevation- of an ionisati
  • FIGURE 2 is an exploded view of components of t detector
  • FIGURE 3 is a circuit diagram of the detector.
  • the detector includes an ionisation chamber
  • OMPI ⁇ R NA ? electrode 15 is mounted in a central recess in the base 14 and centrally mounted on the exposed face of the measuring electrode 15 is an elongate foil 16 of Americium.
  • a cylindrical electrode 11 Closely spaced centrally from the foil 16, is the exposed end of a cylindrical electrode 11 which is a close fit within an insulating sleeve 12 which serves to mount the electrode 11 in, and insulate it from, the top wall of the chamber ' 13.
  • the insulation 12 extends down the larger part of the length of the sides of the elongate cylindrical rod electrode 11 but terminates a little short of the exposed end of that electrode. This means that the insulation is removed from the region of high intensity
  • a conducti guard ring could be fitted in an annular groove in the upper surface of the base surrounding the disc 15 and within the perforated wall 13.
  • the surface of the base 14 between the measuring 30. electrode 15 and the perforated wall 13 constituting the negative electrode is corrugated at 21 to increase the length of the creep path over insulation between those electrodes.
  • the perforated wall 13 is part of a sub-assembly
  • the perforated wall 13 is a simple mesh cup with a top having a central aperture for the insulator 12, and a frusto-conical side wall, and that fits within -.an inner moulding 22 hav
  • the measuring electrode 15 extends directly into the chamber 29, as indicated at 33, and if there is a guard ring, as described above, the connection from that also would extend through -the base 14.
  • a lamp 35 can be seen from a central hole in the top of the cover 34 for giving a visual indication of an alarm. That lamp is connected to the circuit components in the chamber 29.
  • the electrodes 11 and 13 are connected respectively to the drain and source electrode of a field effect..transistor 17, while the gate electrode of the F.E.T. is connected to the measuring electrode 15.
  • the circuit is conventional, and
  • TR4 which is a programmable unijunction transistor (PUT) .
  • TR4 will only trigger, firing the output thyristor CSR1, if the input at A on TR4 exceeds the threshold voltage
  • OMPI flows between the electrodes under the influence of the electric field in the ionisation chamber, and the voltage of the measuring electrode 15 is an intermediate voltage determined by the relationship
  • electrodes 15 and 13 will be set by the electric field concentrations in the two parts of the chamber. These concentrations are in turn determined by the sizes, shapes and spacing of the electrodes.
  • the chamber can be considered to constitute an inner part
  • electrode 11 and the measuring electrode 15, and the effect is for the impedance of the outer part of the chamber to increase so that the voltage on the measuring electrode 15 increases to the threshold value if the smoke concentration is sufficiently
  • the detector will be more immune to contamination by duct and dirt than are more conventional detectors employing two or more high impedance paths.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fire-Detection Mechanisms (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)

Abstract

Detecteur de fumee a chambre d'ionisation dans lequel une premiere electrode (11) est recouverte d'un isolant (12) sauf a une extremite ou elle est opposee a une electrode de mesure (15); la majeure partie de la surface de l'isolant (12) porte un conducteur (41) non connecte a la premiere electrode (11) pour reduire l'effet nuisible de condensation sur l'isolant (12).
EP19790900364 1978-04-11 1979-11-19 Detecteur a chambre d'ionisation Withdrawn EP0015942A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1416578A GB1603702A (en) 1978-04-11 1978-04-11 Ionisation detector chamber
GB1416578 1978-04-11

Publications (1)

Publication Number Publication Date
EP0015942A1 true EP0015942A1 (fr) 1980-10-01

Family

ID=10036185

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19790900364 Withdrawn EP0015942A1 (fr) 1978-04-11 1979-11-19 Detecteur a chambre d'ionisation

Country Status (4)

Country Link
EP (1) EP0015942A1 (fr)
CA (1) CA1143871A (fr)
GB (1) GB1603702A (fr)
WO (1) WO1979000918A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2182198B (en) * 1985-10-31 1991-05-15 Gent Ltd Ionisation detection chamber

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1422350A (fr) * 1964-11-13 1965-12-24 Commissariat A L En Atomique & Anémomètre
US3935492A (en) * 1970-11-13 1976-01-27 Nittan Company, Ltd. Ionization smoke detector
IL52357A (en) * 1976-07-02 1979-11-30 Chloride Group Ltd Ionisation detector chamber

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO7900918A1 *

Also Published As

Publication number Publication date
WO1979000918A1 (fr) 1979-11-15
GB1603702A (en) 1981-11-25
CA1143871A (fr) 1983-03-29

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Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Designated state(s): CH DE FR GB LU SE

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19801009

RIN1 Information on inventor provided before grant (corrected)

Inventor name: LETTS, JOHN BRIAN

Inventor name: JOHNSON, DENNIS