EP0221770B1 - Chambre détectrice d'ionisation - Google Patents

Chambre détectrice d'ionisation Download PDF

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Publication number
EP0221770B1
EP0221770B1 EP19860308434 EP86308434A EP0221770B1 EP 0221770 B1 EP0221770 B1 EP 0221770B1 EP 19860308434 EP19860308434 EP 19860308434 EP 86308434 A EP86308434 A EP 86308434A EP 0221770 B1 EP0221770 B1 EP 0221770B1
Authority
EP
European Patent Office
Prior art keywords
electrode
base
chamber
measuring
ionisation
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
Application number
EP19860308434
Other languages
German (de)
English (en)
Other versions
EP0221770A2 (fr
EP0221770A3 (en
Inventor
Stephen Henry Ellwood
David Appleby
Stephen Brown
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.)
Novar Systems Ltd
Original Assignee
Gent 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 Gent Ltd filed Critical Gent Ltd
Publication of EP0221770A2 publication Critical patent/EP0221770A2/fr
Publication of EP0221770A3 publication Critical patent/EP0221770A3/en
Application granted granted Critical
Publication of EP0221770B1 publication Critical patent/EP0221770B1/fr
Expired legal-status Critical Current

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Classifications

    • 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

  • This invention relates to an ionisation detection chamber for detecting the presence of small particulate solids, such as smoke particles, carried in a gaseous stream.
  • a flat negative electrode is mounted on an insulated base with a wafer-like ionisation source disposed centrally thereon.
  • a positive electrode in the form of a dome-like metal part which may be a grid or perforated sheet is disposed over the base to define the chamber and a measuring electrode in the form of an apertured disc is disposed above and nearer to the negative electrode than the grid with the aperture in the disc in register with the ionisation source.
  • the positive electrode is in the form of a rod extending through an insulated mount carried by the grid which in this case is the negative electrode.
  • a flat electrode in this case the measuring electrode, is mounted on the base and carries the wafer-like ionisation source in register with the inner end of the positive electrode.
  • an ionisation detection chamber for detecting the presence of small particulate solids, such as smoke particles, carried in a gaseous stream comprising an electrically insulating base, a first, measuring, electrode carried by the base, means for ionising gas associated with a central region of the measuring electrode, a second, negative, electrode comprising a metal grid disposed over the base and together with the base defining the chamber and a third, positive, electrode located in register with the ionisation means and nearer to the measuring electrode than to the negative electrode characterised in that the third electrode comprises at least one element extending generally parallel with the measuring electrode and carried by an electrically insulating member supported by the base.
  • an electrically insulated base 1 carries a measuring electrode indicated generally at 2, a positive electrode indicated generally at 3 and a negative electrode 4 in the form of a dome-like metal grid removably carried on the base 1 and constituting an insect screen.
  • the electrode 4, together with base 1 defines an ionisation chamber.
  • the chamber will be mounted in a casing (not shown) incorporating suitable apertures for the passage of smoke into the chamber and extra wind baffles.
  • the chamber will be mounted on a ceiling so as to be upside down relative to the disposition shown in Fig. 1.
  • the base 1 is a high density polyethylene moulding on the lower surface 5 of which is a metal cover 6 which is at the same electrical potential as the grid 4 to act as an electrical screen.
  • the cover 6 may be constituted by a conductive coating applied to the moulding.
  • the measuring electrode 2 comprises a stainless steel disc 7 fixed at 8 and 9 to the base 1 and formed with a central dished part 10 extending into a recess 11 in the base.
  • a stainless steel cover disc 12 formed with a central aperture 13 is secured to the disc 7 in good electrical contact therewith.
  • the aperture 13 is smaller than the dished part 10 and a wafer-like ionisation source comprising an Americium 241 ⁇ particle emitter 14 is trapped within the recess.
  • the disc 7 is formed with diametral apertures 15 and 16 in register with slots 17 and 18 formed in the edges of cover disc 12.
  • a connector 19 extends through an aperture 20 in the base 1 and is soldered at 21 to the disc 12.
  • the positive electrode 3 comprises an electrically insulated cylindrical mount 22 with a moulded in electrode 23 the lower part 24 of which constitutes a connection to the circuit and the upper part 25 of which is the active positive electrode.
  • This upper part 25 extends parallel with the electrode 2 diametrally in register with the emitter 14 and is nearer thereto than the nearest part of the negative electrode 4.
  • the mount 22 has a cylindrical lower part 26 extending through an aperture 27 in the base. Above the part 26 the mount has an eccentric formation 28 to ensure precise orientation relative to the base.
  • An insulating wall 29 surrounds the mount 22, which acts to increase the insulating path between the upper part 25 of the positive electrode and the measuring electrode 2. This effectively reduces the effect of contamination on the sensor.
  • the wall may be a separate PTFE or similar material ring which is moulded into the insulated base. Alternatively, it may be constituted by a raised feature on the moulding.
  • a small wall 30 surrounds the measuring electrode 2 and acts to increase the insulating path between the measuring electrode and the negative electrode 4.
  • the wall 30 is moulded as part of the insulated base 1 and may be augmented by the addition of more concentric walls (not shown).
  • a larger wall 31 also acts to increase the insulating path between the measuring electrode 2 and the negative electrode 4. Its main purpose, however, is to act as a baffle and so reduce the effect of air flow across the sensor.
  • the arrangement is "fail safe" as the shortest path from the emitter to another electrode is to the positive electrode causing an increase in signal level should the chamber become contiminated.

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  • 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)

Claims (6)

  1. Chambre détectrice d'ionisation pour détecter la présence de petites particules solides, telles que des particules de fumée, transportées dans un courant de gaz comprenant une embase électriquement isolante, une première électrode de mesure (2) portée par l'embase (1), des moyens pour ioniser du gaz associés à une région centrale de l'électrode de mesure, une seconde électrode, négative (4) comportant une grille métallique disposée sur l'embase et définissant la chambre avec l'embase et une troisième électrode, positive (3) placée en correspondance avec les moyens d'ionisation et plus près de l'électrode de mesure que de l'électrode négative, caractérisée en ce que la troisième électrode comprend au moins un élément (25) s'étendant généralement parallèlement à l'électrode de mesure et supporté par un élément électriquement isolant (22) supporté par l'embase.
  2. Chambre selon la revendication 1 dans laquelle la troisième électrode est constituée d'au moins un élément en forme de tige.
  3. Chambre selon la revendication 1 ou la revendication 2 dans laquelle l'embase isolante comporte un écran électrique (6) au même potentiel que la grille.
  4. Chambre selon l'une quelconque des revendications précédentes dans laquelle l'électrode de mesure comporte une partie emboutie (10) recouverte par un élément muni d'une ouverture correspondant à la partie emboutie, une source d'ionisation en forme de plaquette (14) étant emprisonnée à l'intérieur de l'évidement sous l'élément.
  5. Chambre selon la revendication 4 dans laquelle la source est un émetteur de particules α Americium 241.
  6. Chambre selon la revendication 4 ou la revendication 5 dans laquelle l'électrode positive s'étend parallèlement à l'électrode de mesure en correspondance avec la source et plus près de cette dernière que la partie la plus proche de l'électrode négative.
EP19860308434 1985-10-31 1986-10-29 Chambre détectrice d'ionisation Expired EP0221770B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8526892 1985-10-31
GB8526892A GB2182198B (en) 1985-10-31 1985-10-31 Ionisation detection chamber

Publications (3)

Publication Number Publication Date
EP0221770A2 EP0221770A2 (fr) 1987-05-13
EP0221770A3 EP0221770A3 (en) 1988-08-24
EP0221770B1 true EP0221770B1 (fr) 1992-02-05

Family

ID=10587558

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19860308434 Expired EP0221770B1 (fr) 1985-10-31 1986-10-29 Chambre détectrice d'ionisation

Country Status (3)

Country Link
EP (1) EP0221770B1 (fr)
DE (1) DE3683827D1 (fr)
GB (1) GB2182198B (fr)

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3560737A (en) * 1967-08-02 1971-02-02 Honeywell Inc Combustion products detector using a radioactive source and detector
GB1299234A (en) * 1970-11-06 1972-12-13 Nittan Co Ltd Ionization smoke detector
IL52357A (en) * 1976-07-02 1979-11-30 Chloride Group Ltd Ionisation detector chamber
GB1581236A (en) * 1976-07-02 1980-12-10 Chloride Group Ltd Ionisation detector chamber
GB1603702A (en) * 1978-04-11 1981-11-25 Chloride Group Ltd Ionisation detector chamber

Also Published As

Publication number Publication date
GB2182198B (en) 1991-05-15
EP0221770A2 (fr) 1987-05-13
GB2182198A (en) 1987-05-07
GB8526892D0 (en) 1985-12-04
EP0221770A3 (en) 1988-08-24
DE3683827D1 (de) 1992-03-19

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