CA1042088A - Fire detectors - Google Patents
Fire detectorsInfo
- Publication number
- CA1042088A CA1042088A CA234,041A CA234041A CA1042088A CA 1042088 A CA1042088 A CA 1042088A CA 234041 A CA234041 A CA 234041A CA 1042088 A CA1042088 A CA 1042088A
- Authority
- CA
- Canada
- Prior art keywords
- support member
- electrode
- ionization chamber
- housing
- heat
- 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
Links
Classifications
-
- 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
-
- 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
Abstract
ABSTRACT OF DISCLOSURE.
A fire detector of the kind comprosing a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic ciruit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber. In order to prevent leakage currents flowing between the electrode and the housing via the support member a heat generating component of the electronic circuit associated with the detector is mounted in a cavity in the support member to heat that part of the support member thereby to prevent the formation of moisture on that part.
A fire detector of the kind comprosing a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic ciruit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber. In order to prevent leakage currents flowing between the electrode and the housing via the support member a heat generating component of the electronic circuit associated with the detector is mounted in a cavity in the support member to heat that part of the support member thereby to prevent the formation of moisture on that part.
Description
-- ` ~
` :
` 104ZO~t~
THIS invention relates to fire detectors of the type used in mines and similar installations for detecting the out-` break of a fire.
Such detectors generally comprise a housing defining a cavity known as an ionization chamber, an electrode supported in , ~ the ionization chamber by means of a support member made of an insulating material, and an electronic curcuit to apply y a voltage between the housing and the electrode and to -~ - detect variations in the resulting electrical current flowing -, 10 through the ionization chamber. Usually, the electrical ~ current flowing through the ionization chamber is substantially -i~ constant when no combustion particles are present. On the ~-outbreak of a fire, however, the resulting combustion ;~ particles cause a decrease in the magnitude of the current.
This decrease is detected and an alarm or the like is , energised.
Under certain conditions, such as those encountered in mines, moisture and dust can accumulate on the surface of the support member. This can cause small leakage currents to flow ~ between the electrode and the housing which, in turn, can i seriously affect the operation of the detector. In this regard it should be pointed out that the current flowing through $ the ionization chamber is usually very small e.g. of the order ~ of 500 pico-amps.
~; . .
It is an nbject of the present invention to provide a fire :~ detector in which the problem of leakage currents caused by ~ the accurnulation of moisture on the support member is overcome.
''''~'~
In a fire detector according to the invention a heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between , .. ~ , , .
; .
~ - 2 -... ~
.' ~ .
,. : ~ , .',. '. . ' ' 0~
the electrode and the housing to heat that part of the support member surroundlng the component in order to prevent the formation of moisture on that part thereby to prevent leakage currents flowing between the electrode and the housing via the support member.
Further according to the invention the heat generating component ~-is an operational amplifier.
Thus, in accordance with the present teachings, a fire detector is provided of the kind which comprises a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic circuit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber. A heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between the electrode and the housing to : .
~ heat that part of the support member surrounding the component ; in order to prevent the formation of moisture on that part --, 20 thereby to prevent leakage currents flowing between the electrode and the housing by way of the support member.
To illustrate the invention an embodiment thereof is described hereunder with reference to the accompanying drawing which is a sectional side elevation of the fire detector of the invention.
' ,,~' ` 104Z ~: ~
- With reference to the drawing the fire detector comprises, in essence, a housing 10 defining an ionization chamber 12 having suitable openings therein through which smoke can ;~
pass. An electrical grid 14 is supported in the ionization chamber by means of a supporting structure 16 which is secured to one inner wall of the housing 10 at 18.
The usual electronic circuit for detecting variations in the currents flowing through the ionization chamber is located in a container 20 which is mounted in a cavity 22 in the supporting structure 16.
The supporting structure 16 includes a vertical limb 24, the ~ ~ `
electrical grid 14 being attached to the lower end of the ~ -: limb.
... .
A cavity is formed in the limb 24, and one of the heat trans~
mitting components of the electronic circuit is located in this cavity. The component in question is preferably an opera-, .~ .
tional amplifier 28 which is of course connected into the circuit : 20 .:.~ ` ' ' ' ' ' , !', ::
;
.
., .
':
:
.~, .
,': :: ' ., ~0421~
.
- located in the container 20. The heat generated by the -- operational amplifier will prevent the formation of moisture on that part of the limb 24 surrounding the operational amplifier and this, in turn, will minimize the possibility of leakage currents flowing between the grid and the housing via the supporting structure 16.
.
Experiments have shown that approximately 50 milliwatts of heat power applied to the inner surface of the limb 24 over : a length of approximately 5mm will cause a temperature rise on the outer surface of that part of the limb of about 5 degrees C, and this seems to be sufficient to keep that :~ part of the leakage current path dry under extreme humidity ~, conditions. By suitable choice of an operational amplifier `.j it is possible to obtain one with a quiescent power con-' 15 sumption (in the form of heat) of 45 milliwatts.
. '' ' .
, .
:........................................................... .
.'' :
.
.:. .
.,:
.`'" .
. .
~. .
"' .
.
:. .. . . ~
.
::
- - :
,
` :
` 104ZO~t~
THIS invention relates to fire detectors of the type used in mines and similar installations for detecting the out-` break of a fire.
Such detectors generally comprise a housing defining a cavity known as an ionization chamber, an electrode supported in , ~ the ionization chamber by means of a support member made of an insulating material, and an electronic curcuit to apply y a voltage between the housing and the electrode and to -~ - detect variations in the resulting electrical current flowing -, 10 through the ionization chamber. Usually, the electrical ~ current flowing through the ionization chamber is substantially -i~ constant when no combustion particles are present. On the ~-outbreak of a fire, however, the resulting combustion ;~ particles cause a decrease in the magnitude of the current.
This decrease is detected and an alarm or the like is , energised.
Under certain conditions, such as those encountered in mines, moisture and dust can accumulate on the surface of the support member. This can cause small leakage currents to flow ~ between the electrode and the housing which, in turn, can i seriously affect the operation of the detector. In this regard it should be pointed out that the current flowing through $ the ionization chamber is usually very small e.g. of the order ~ of 500 pico-amps.
~; . .
It is an nbject of the present invention to provide a fire :~ detector in which the problem of leakage currents caused by ~ the accurnulation of moisture on the support member is overcome.
''''~'~
In a fire detector according to the invention a heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between , .. ~ , , .
; .
~ - 2 -... ~
.' ~ .
,. : ~ , .',. '. . ' ' 0~
the electrode and the housing to heat that part of the support member surroundlng the component in order to prevent the formation of moisture on that part thereby to prevent leakage currents flowing between the electrode and the housing via the support member.
Further according to the invention the heat generating component ~-is an operational amplifier.
Thus, in accordance with the present teachings, a fire detector is provided of the kind which comprises a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic circuit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber. A heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between the electrode and the housing to : .
~ heat that part of the support member surrounding the component ; in order to prevent the formation of moisture on that part --, 20 thereby to prevent leakage currents flowing between the electrode and the housing by way of the support member.
To illustrate the invention an embodiment thereof is described hereunder with reference to the accompanying drawing which is a sectional side elevation of the fire detector of the invention.
' ,,~' ` 104Z ~: ~
- With reference to the drawing the fire detector comprises, in essence, a housing 10 defining an ionization chamber 12 having suitable openings therein through which smoke can ;~
pass. An electrical grid 14 is supported in the ionization chamber by means of a supporting structure 16 which is secured to one inner wall of the housing 10 at 18.
The usual electronic circuit for detecting variations in the currents flowing through the ionization chamber is located in a container 20 which is mounted in a cavity 22 in the supporting structure 16.
The supporting structure 16 includes a vertical limb 24, the ~ ~ `
electrical grid 14 being attached to the lower end of the ~ -: limb.
... .
A cavity is formed in the limb 24, and one of the heat trans~
mitting components of the electronic circuit is located in this cavity. The component in question is preferably an opera-, .~ .
tional amplifier 28 which is of course connected into the circuit : 20 .:.~ ` ' ' ' ' ' , !', ::
;
.
., .
':
:
.~, .
,': :: ' ., ~0421~
.
- located in the container 20. The heat generated by the -- operational amplifier will prevent the formation of moisture on that part of the limb 24 surrounding the operational amplifier and this, in turn, will minimize the possibility of leakage currents flowing between the grid and the housing via the supporting structure 16.
.
Experiments have shown that approximately 50 milliwatts of heat power applied to the inner surface of the limb 24 over : a length of approximately 5mm will cause a temperature rise on the outer surface of that part of the limb of about 5 degrees C, and this seems to be sufficient to keep that :~ part of the leakage current path dry under extreme humidity ~, conditions. By suitable choice of an operational amplifier `.j it is possible to obtain one with a quiescent power con-' 15 sumption (in the form of heat) of 45 milliwatts.
. '' ' .
, .
:........................................................... .
.'' :
.
.:. .
.,:
.`'" .
. .
~. .
"' .
.
:. .. . . ~
.
::
- - :
,
Claims
THE EMBODIMENTS OF THE INVENTION IN WHICH
AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMEDS ARE DEFINED AS FOLLOWS:
1.
A fire detector of the kind comprising a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic circuit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber characterised in that a heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between the electrode and the housing to heat that part of the support member surrounding the component in order to prevent the formation of moisture on that part thereby to prevent leakage currents flowing between the electrode and the housing via the support member.
2.
A fire detector as claimed in claim 1 characterised in that the heat generating component is an operational amplifier.
AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMEDS ARE DEFINED AS FOLLOWS:
1.
A fire detector of the kind comprising a housing defining an ionization chamber, an electrode supported in the ionization chamber by means of a support member made of an electrically insulating material, and an electronic circuit to apply a voltage between the housing and the electrode and to detect variations in the resulting electrical current flowing through the ionization chamber characterised in that a heat generating component of the electronic circuit is mounted in a suitable cavity formed in the support member between the electrode and the housing to heat that part of the support member surrounding the component in order to prevent the formation of moisture on that part thereby to prevent leakage currents flowing between the electrode and the housing via the support member.
2.
A fire detector as claimed in claim 1 characterised in that the heat generating component is an operational amplifier.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA00745453A ZA745453B (en) | 1974-08-26 | 1974-08-26 | Improvements in or relating to fire detectors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1042088A true CA1042088A (en) | 1978-11-07 |
Family
ID=25568066
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA234,041A Expired CA1042088A (en) | 1974-08-26 | 1975-08-25 | Fire detectors |
Country Status (21)
| Country | Link |
|---|---|
| JP (1) | JPS5635236B2 (en) |
| AU (1) | AU501762B2 (en) |
| BE (1) | BE832768A (en) |
| BR (1) | BR7505431A (en) |
| CA (1) | CA1042088A (en) |
| CH (1) | CH600455A5 (en) |
| DE (1) | DE2537598C3 (en) |
| DK (1) | DK136793B (en) |
| FR (1) | FR2283492A1 (en) |
| GB (1) | GB1492193A (en) |
| IE (1) | IE41452B1 (en) |
| IN (1) | IN143233B (en) |
| IT (1) | IT1042015B (en) |
| LU (1) | LU73252A1 (en) |
| NL (1) | NL167785C (en) |
| NO (1) | NO138307C (en) |
| PH (1) | PH11514A (en) |
| SE (1) | SE439209B (en) |
| SU (1) | SU703038A3 (en) |
| YU (1) | YU37410B (en) |
| ZA (1) | ZA745453B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2711457C2 (en) * | 1977-03-16 | 1985-06-27 | Siemens AG, 1000 Berlin und 8000 München | Ionization fire detector |
| CH681932A5 (en) * | 1990-12-04 | 1993-06-15 | Cerberus Ag | |
| CH682423A5 (en) * | 1991-03-13 | 1993-09-15 | Asea Brown Boveri | Method and apparatus for measuring the concentration of a gas contained in particles. |
| DE102004020489B4 (en) * | 2004-04-26 | 2007-06-28 | Minimax Gmbh & Co. Kg | Fire detector for use in outdoor atmosphere |
| CN110185461A (en) * | 2019-06-28 | 2019-08-30 | 中交路桥建设有限公司 | The shield machine of real-time detection tunnel geology condition |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2408051A (en) * | 1942-04-04 | 1946-09-24 | American District Telegraph Co | Fire and smoke detector and the like |
| DE2204930C3 (en) * | 1971-02-08 | 1974-06-20 | Veb Rft Messelektronik Otto Schoen, X 8016 Dresden | Ionization fire alarms |
| JPS485979U (en) * | 1971-06-04 | 1973-01-23 |
-
1974
- 1974-08-26 ZA ZA00745453A patent/ZA745453B/en unknown
-
1975
- 1975-08-19 IE IE1827/75A patent/IE41452B1/en unknown
- 1975-08-19 GB GB34390/75A patent/GB1492193A/en not_active Expired
- 1975-08-19 IN IN1615/CAL/75A patent/IN143233B/en unknown
- 1975-08-20 AU AU84121/75A patent/AU501762B2/en not_active Expired
- 1975-08-21 NL NL7509918A patent/NL167785C/en not_active IP Right Cessation
- 1975-08-21 CH CH1087075A patent/CH600455A5/xx not_active IP Right Cessation
- 1975-08-23 DE DE2537598A patent/DE2537598C3/en not_active Expired
- 1975-08-25 LU LU73252A patent/LU73252A1/xx unknown
- 1975-08-25 NO NO75752918A patent/NO138307C/en unknown
- 1975-08-25 PH PH17497A patent/PH11514A/en unknown
- 1975-08-25 IT IT26556/75A patent/IT1042015B/en active
- 1975-08-25 SU SU752167381A patent/SU703038A3/en active
- 1975-08-25 CA CA234,041A patent/CA1042088A/en not_active Expired
- 1975-08-25 BR BR7505431*A patent/BR7505431A/en unknown
- 1975-08-26 YU YU2167/75A patent/YU37410B/en unknown
- 1975-08-26 FR FR7526259A patent/FR2283492A1/en active Granted
- 1975-08-26 SE SE7509478A patent/SE439209B/en not_active IP Right Cessation
- 1975-08-26 JP JP10336475A patent/JPS5635236B2/ja not_active Expired
- 1975-08-26 BE BE159485A patent/BE832768A/en not_active IP Right Cessation
- 1975-08-26 DK DK384275AA patent/DK136793B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ZA745453B (en) | 1976-04-28 |
| LU73252A1 (en) | 1976-05-31 |
| SE439209B (en) | 1985-06-03 |
| CH600455A5 (en) | 1978-06-15 |
| BR7505431A (en) | 1976-08-03 |
| FR2283492B1 (en) | 1979-05-04 |
| AU8412175A (en) | 1977-02-24 |
| GB1492193A (en) | 1977-11-16 |
| YU37410B (en) | 1984-08-31 |
| NL167785B (en) | 1981-08-17 |
| NL167785C (en) | 1982-01-18 |
| DE2537598C3 (en) | 1984-12-20 |
| AU501762B2 (en) | 1979-06-28 |
| DK384275A (en) | 1976-02-27 |
| NO138307B (en) | 1978-05-02 |
| IE41452L (en) | 1976-02-26 |
| DE2537598B2 (en) | 1980-11-06 |
| IT1042015B (en) | 1980-01-30 |
| SU703038A3 (en) | 1979-12-05 |
| YU216775A (en) | 1983-04-27 |
| DK136793B (en) | 1977-11-21 |
| DK136793C (en) | 1978-04-24 |
| JPS5149784A (en) | 1976-04-30 |
| DE2537598A1 (en) | 1976-03-11 |
| NO138307C (en) | 1978-08-16 |
| BE832768A (en) | 1975-12-16 |
| IN143233B (en) | 1977-10-22 |
| SE7509478L (en) | 1976-02-27 |
| NO752918L (en) | 1976-02-27 |
| IE41452B1 (en) | 1980-01-02 |
| NL7509918A (en) | 1976-03-01 |
| JPS5635236B2 (en) | 1981-08-15 |
| FR2283492A1 (en) | 1976-03-26 |
| PH11514A (en) | 1978-02-01 |
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