CA1252172A - Smoke detection apparatus - Google Patents
Smoke detection apparatusInfo
- Publication number
- CA1252172A CA1252172A CA000460903A CA460903A CA1252172A CA 1252172 A CA1252172 A CA 1252172A CA 000460903 A CA000460903 A CA 000460903A CA 460903 A CA460903 A CA 460903A CA 1252172 A CA1252172 A CA 1252172A
- Authority
- CA
- Canada
- Prior art keywords
- photocell
- chamber
- output
- light
- stage
- 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
- 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
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/18—Prevention or correction of operating errors
- G08B29/20—Calibration, including self-calibrating arrangements
- G08B29/24—Self-calibration, e.g. compensating for environmental drift or ageing of components
-
- 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
- G08B17/103—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device
- G08B17/107—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means using a light emitting and receiving device for detecting light-scattering due to smoke
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/18—Prevention or correction of operating errors
- G08B29/185—Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system
-
- 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
A light sensing apparatus comprising a solid-state photocell responsive to low levels of light connected to an impedance matching buffer stage, a gain controlled amplifier stage and an output amplifier stage; a gain control network controlled by a temperature sensor for receiving an ampli-fied signal from said output stage the gain being adjusted to compensate for temperature dependence of the photocell signal.
A light sensing apparatus comprising a solid-state photocell responsive to low levels of light connected to an impedance matching buffer stage, a gain controlled amplifier stage and an output amplifier stage; a gain control network controlled by a temperature sensor for receiving an ampli-fied signal from said output stage the gain being adjusted to compensate for temperature dependence of the photocell signal.
Description
12S2~7;~
~ his invention relates to a device for the detection of smoke by light scatter techniques and particularly to a light scatter smoke detection means.
Devices are known for the detection of smoke by light scatter techniques. Such devices incorporate a light source configured to irradiate a volume of air provided in a sampling region in which smoke particles may be suspended.
Light scattered by said particles is collected on a light detector means. The amplitude of the signal produced from 10 said light detector is an indication of the quantity of smoke suspended in the air.
Particularly sensitive versions of such smoke detectors are also capable of monitoring air pollution.
Such hiqh sensitivity enables detection of fires at 15 the earliest possible (incipient) stage, whereby fires may be controlled with portable extinguishers by local personnel before smoke levels become dangerous to life. Such detectors require a sensitivity as high as 20 micrograms per cubic metre for woodsmoke, equivalent to a visual range of 20 40 km. To achieve such sensitivity, the light source has included a Xenon flashtube and the light detector has been a photomultiplier tube, while both devices are mounted in conjunction with a sampling chamber through which samples of airborne smoke are passed.
A prime objective of the present invention is to provide an improved smoke detector in which the disadvantages inherent with prior art devices are at least substantially overcome.
The disadvantages of the photomultiplier tubes are:
1) being vacuum-tube devices, they are prone to breakage, damage by vib~ation, loss of vacuum pres6ure or gaseous poisoning;
~ his invention relates to a device for the detection of smoke by light scatter techniques and particularly to a light scatter smoke detection means.
Devices are known for the detection of smoke by light scatter techniques. Such devices incorporate a light source configured to irradiate a volume of air provided in a sampling region in which smoke particles may be suspended.
Light scattered by said particles is collected on a light detector means. The amplitude of the signal produced from 10 said light detector is an indication of the quantity of smoke suspended in the air.
Particularly sensitive versions of such smoke detectors are also capable of monitoring air pollution.
Such hiqh sensitivity enables detection of fires at 15 the earliest possible (incipient) stage, whereby fires may be controlled with portable extinguishers by local personnel before smoke levels become dangerous to life. Such detectors require a sensitivity as high as 20 micrograms per cubic metre for woodsmoke, equivalent to a visual range of 20 40 km. To achieve such sensitivity, the light source has included a Xenon flashtube and the light detector has been a photomultiplier tube, while both devices are mounted in conjunction with a sampling chamber through which samples of airborne smoke are passed.
A prime objective of the present invention is to provide an improved smoke detector in which the disadvantages inherent with prior art devices are at least substantially overcome.
The disadvantages of the photomultiplier tubes are:
1) being vacuum-tube devices, they are prone to breakage, damage by vib~ation, loss of vacuum pres6ure or gaseous poisoning;
2) operational life is limited;
3) care must be taken to avoid exposure to bright 35 light such as sunlight;
~ ) sensitivity variation from unit to unit may be a factor of ten or more;
~25~21 7;~
~) thelr sensltlvlty ls afected by temperature;
6) they ~r~ of comp~ratively very high co~tt 7) they requlre ~ c05tly power supply~
8) th~y ar~ large ~nd un~uitable for miniaturlzatlon.
Accoeding to one a~pec~ o~ th~ prs~ant lnventlon ~t 1B proposed ~ha~ the photomultiplier tube of prlor ~rt devlce~ bC replaced by an extremely sen~itlve 301id-~tate light detector.
r~e present invontion ls dlrected to tho u~ o~
~olld-stat~ detection technology whlch w~g hithcrto con~lderQd lmpos~ible at room temp~rature Pnd ~t re~sonable co~t.
Successful colid-8tat~ 6moke detQctlon re~ult4 in a 15 more rell~ble device enabling pr4blem6 inher~nt in thermionlG valve technology (photo~ultipllers) such as an extcaordln~ry ~pread ~10 to 1) in ~en~ltivity from devlce t~
device, fr~lllty, Ageing, degradatlon when exposed to brlght llght ~nd the need for a speolal h~gh volt~qe power 20 Bupply of high ~tabllllty to be overcome.
In a ~urther aspect o~ the invrntion the 3moke detector accordlng to thc present lnventlon comprl~es a sampllng chamber which 1~ lnternally a round tub~, cont~inlng A ~erle~ of device~ to ab~orb l~ght reflected off 25 lts int~nal wall~. Alr flow through the chamber is ~chleved ~y mea~8 D tWo c~upling tubea, mounted at right-ang~e~ to the chamber. Between the coupling tubo8 1~
a sealed r~loctor and wlndow for ~ xenon tube to lrradlate th~ particle~ wlthln the ~h~mbe~. At one end of the chamber 30 18 an extr~mcly ~encitlve llght detector, whllo At the oppo~ite ond i~ an axial-llght ab~oeber. The chamber i~
airtlght e~c~pt for th~ coupllng tubes. Wlthln one coupling tube i8 an electronic air flow ~ensor, alr ~low b~lng achleved by me~n~ of an external f~n. Houced ~esida the chamber i~ tho nece~sary electronlc6 circuit b~ard~.
W;~h the need for lncreased ru~ge~ne~ ln case of rough h~ndling, lighter weight to reduce ~reight C48t8 i25217~
.~
~ ) sensitivity variation from unit to unit may be a factor of ten or more;
~25~21 7;~
~) thelr sensltlvlty ls afected by temperature;
6) they ~r~ of comp~ratively very high co~tt 7) they requlre ~ c05tly power supply~
8) th~y ar~ large ~nd un~uitable for miniaturlzatlon.
Accoeding to one a~pec~ o~ th~ prs~ant lnventlon ~t 1B proposed ~ha~ the photomultiplier tube of prlor ~rt devlce~ bC replaced by an extremely sen~itlve 301id-~tate light detector.
r~e present invontion ls dlrected to tho u~ o~
~olld-stat~ detection technology whlch w~g hithcrto con~lderQd lmpos~ible at room temp~rature Pnd ~t re~sonable co~t.
Successful colid-8tat~ 6moke detQctlon re~ult4 in a 15 more rell~ble device enabling pr4blem6 inher~nt in thermionlG valve technology (photo~ultipllers) such as an extcaordln~ry ~pread ~10 to 1) in ~en~ltivity from devlce t~
device, fr~lllty, Ageing, degradatlon when exposed to brlght llght ~nd the need for a speolal h~gh volt~qe power 20 Bupply of high ~tabllllty to be overcome.
In a ~urther aspect o~ the invrntion the 3moke detector accordlng to thc present lnventlon comprl~es a sampllng chamber which 1~ lnternally a round tub~, cont~inlng A ~erle~ of device~ to ab~orb l~ght reflected off 25 lts int~nal wall~. Alr flow through the chamber is ~chleved ~y mea~8 D tWo c~upling tubea, mounted at right-ang~e~ to the chamber. Between the coupling tubo8 1~
a sealed r~loctor and wlndow for ~ xenon tube to lrradlate th~ particle~ wlthln the ~h~mbe~. At one end of the chamber 30 18 an extr~mcly ~encitlve llght detector, whllo At the oppo~ite ond i~ an axial-llght ab~oeber. The chamber i~
airtlght e~c~pt for th~ coupllng tubes. Wlthln one coupling tube i8 an electronic air flow ~ensor, alr ~low b~lng achleved by me~n~ of an external f~n. Houced ~esida the chamber i~ tho nece~sary electronlc6 circuit b~ard~.
W;~h the need for lncreased ru~ge~ne~ ln case of rough h~ndling, lighter weight to reduce ~reight C48t8 i25217~
.~
- 4 ~
enhancQd ae~thet~c~, lower ~ost in high volume and reducQd as6embly +~me, a specl~lized aluminlum ~xtruslon 1~ used.
While retaining the ~a~lc tu~ulAr de~lgn, the ~dditlon of mounting ~crew-flute6 reduces machlning requlrement#, as dos~ the p~ovlsion of CDnVen1ent ~10tB to hold one large electronics circuit ~o~rd. Sultable wcb design allow~ for convenient heat-~inking of electronic pow~r d~vlcea.
Provislon o~ a flat 'table' ~ a part oF the ~xtruslon desi~n, 6~plifles the m~ting of coupling tubes and ~he 10 ~lash window, obvlating ~ddle-sh~pod coupllng6. ~pposlte thi~ tabl~ a ~arAllel flat ~u~fac~ i~ provld~d to ~ld clampln~ ~o~ ~achlnng operatlons.
J;g fabrlc~tion of component~ 1~ thereby di~pen~ed with lead~ng to greater dlmen~onal acc~racy ~nd 15 repeatability ln productlon re~ultlng in lmproved quality control. Furthermore ~lmple a~sembly provldes for sl~plified ~erv~clng. ~he detector of the pre~ent inventlon i6 of long lic solld-3ta~e de~ign wlth the ex~eption of the Xanon flashtub~. In my co-p~ndin~ appllc~tion concurren~ly 20 filed wltb this appllcation a novel ~ocusslng reflector deslgned to accommod~t~ the unu~ual sh~pe of the X~non flash tubo 18 dlSclo6ed. Thl~ lmprovcd light ~ource with reduced flaeh ener~y will extend the malntenance perlod beyond two year~ undar contlnuou~ apera~lon, The p~ovl~lon of a~ improvet llght abs~rber wlth sam~llng chamber as disclosed ln m~ abovementlon~d co-pcndlng appllc~tlon allow6 ~igniflcant ch~mber ~ength reduction to parmit rack mountlng of the detector in restricted s~ac~6 such ag teleph~ne ~xchan~e6 ~nd other 3D aqulpment rOo~B. Fur~he~Ore the detector of the prc6ent lnvention c~n be oper~ted from an unregulated 24 volt D~.
~upply whlch could include ~t~ndby batterle~ h~vlng a supply tolerance ~ the range of 20-2B volt~ D.C. ln confor~ity wlth mo~t ~envention~l flr~ alarm syetems.
Ac~ordlngly, the presqnt lnvontlon provlde6 in one lZS2~7~
~spect a PtN photodiode cell re~pon~lve to low l~vel5 o light conn~ctad to an lmpedsnce mAtching buffer stage, gsln controll~d amplifler 6tage snd an output ampl$~1er ~t~g~t a gain ~o~trol network cont~oll~d by ~ temperature sensor for recelvlng ~n amplified signal from sald output 6ta~e, the s~in being ad~u&table to compen~ta for te~peratur~ dependence o~ th~ photodlode ~gnal, Conveni~ntly the solld-3tate photocell i~ ~ PIN
photodlod~ cell ad~pted to be operated ln ~ zOEro bla~
10 photovoltalc mode. Thu~ extremsly high sen~ltlv~ty i~
achleved ~;th m~x~mum signal to nolge ratlo. The det~ctor i~ cou~led with ~ preampll~ler a~ deflned of ~xtremely low noieè ~nd h~gh stabllity over a w$de t~mp~r~ture range.
~ PI~ photod~ode c~l~l oper~ting ln ~ald lS zero-b~a~ photovoltalc mode, exhlblts varla~le non-line~r ~ensltlvity to low llght levels ~t ~arying temporatur~
levely. ~hus the output of the cell mu~t be ~ecurat~ly cal~b~t~d over an operatlng tem~er~tu~e r~ng~ of -20C to 50C.
COnvenlentl~ the temp~turc ~onsor ~nd photodlode are malnta~ned ~n an e~uivalent thermal ~ltuatlon OF ln thermal Co~t~ct ~uch that any ~emper~ture difference b~tween the two i4 mln~mal.
~Cco~d~ngly the output from the eombin~tion of ~Ald 25 temperAtur~ ~en~or and qaln oon~rol n~two~k 1~ non-llnear ln invec~s prDportlon to the non-lln~rity o~ the photodlode cell whareby temperature dependenco of ~ald cell 1~ ~
~ub6t~ntlally ~llmlnated.
T~ere i6 al80 provlde a ~ower 6upply ~llter network 30 to provent or reDtrlct the inject~an of nol~ into any ~ o of ~he c~Cuit. ~lectrlcal connectlon6 ~or tho ~lgnal, ~upply ~nd ground ~r~.m~d~ u~ing ~hlelded cahle.
~ inventlon wlll be de~crlbed ln gr~Ater detall havln~ r~f~ronce to the accomp~nylng drawi~g6 ln whlch r~gure 1 is a ~ectional vlew o~ an al~ ~mpling i252 chamber, ~ gure 2 1~ a block dla~ram showlng the cell and compen~at~g ampl~ier circuit, ~ gure 3 i~ A part~al viQw of ~he ~dmpling chamber showlng th~ len~ And detector a~6embly, ~igure 4 shown an lnter~erRnce ~hleldlng oontRiner.
~ Ith refe~enc~ to Flgur~ 1 the detector includes a contaln*~ or houslng 71 ~or~ng a s~mpllng chamber 70 lncluding a serles o~ iri~s 21, 22 to ~b~orb ~nd dlssip~te lO light reflQ¢~d off th~ walls. Coupllng tubo6 50 ~re provlded to circul~te amblent alr f~om ~n arca under ~lre ~ur~eillance ~nto the chdmb~r 70 acro~s reglo~ 72 which i~
sub~ected to llght from an Xsnon flqeh tu~ ln houslng 60.
Alr ~low ~g ~chleved by a ~an ~not 6hown1. ~he length of 15 the air s~llng ch~mb~r is crltlcal to prev~nt ~ncident~l ligh~ b~ing detected and the p~ovision o~ a novel llght ab40rber 10 ~nabl~d a consid~rable shortenlng of the tube.
W¦th reference to Figure 2 the ~olld-sat~ cell l i~
p~ferably a PIN photodiode responslve to low llght l~vels 20 and present~ng a cmall signal to sn imp~dance-matchlng buf~er stflg~ 2 connect~d to B g2in-controlled ampll~ier stage 3 ~nd an output ~mpli~ler stage 4.~ ~e ampl~fi~d Blgna~ hl~n fed back to z gAin-control netwDrk 5 controlled by a temperature ~ensor 6. ~he 6en~0r ~nd the 25 PIN photod~ode are malntalned ln clo6e the~l contact ~uch that temperAtur~ dlfference het~een th~ two 18 ml~lmal under varlable oper~tlng condltlon~.
T~e gain of th~ g~ln controlled ~mpllfiet 8taqe 3 i~ ad~ust~d to compen~at~ for the t~mpe~ture dependence of 30 the ~m~ll signal from P~N photodiode 1.
T~e outp~t of the t~mperature 6enso~ ~nd the galn control n~work 1B non-llne~r ln inver~e proportlon wlth the non-lin~rtty of the P~N photodiode cell such that t~mp~atu~ dependenofl o~ tlle cell signal 18 I~UblitantiAlly 35 el$~in~ted.
1 2 5'Z~ 7'~
~ e 6011d-6tate detector c~ll 1 mu~t be ~mall to mlnimlze ~he cap~cltance whlch could otherwl6e r2~ult in reduced sensltlvity to the fla6h else tlm~ of ~beut 1 mlcro-seco~d from the fla~h tube, AR a re6~1t th~ photon of llght ~eam capture ara~ mall comp~rsd wlth a conventlolal photomultlpller tube~ Th~rofore a focu~slng lens 17 $S provided wlth ~s~oclated mountlng ~ardw~re ~hown in Flgure 3.
~eferrlng to Figu~e 3 and 4 th~ preamplifier 10 clrcult 1~ encap~ulated in epoxy 15, the clrcuit belng constructed on a ~rinted crlcu~t boA~d mounted ~gain~t the ba~e ~ ~o over~ome int~rnal reflectlons, to protect the cell, ~nd ~o pravent the ingres~ of epoxy dur~n~ monu~acture ~ detector at~achmcn~ 16 16 prov~d~d. Tho Att~chment 16 i5 15 po6itionod wlth~n ~ housing 71 whlch al~o ~ou~e~ the lens aa6embly 17. Tho preamplifier, detector oell optlcs and hou~lng b~come a self contained and separately tested plug-in mo~ule connected by mean~ of ~hiolded cabl~ 1~. Ths housing 71 include~ ~ base 9 tlghtly fltted to the cyllnder 20 ~ectlon. lhe flange 11 ~u~portlng the len~ i~ a sliding ~it ln the cylLndet 6ection ~t ths other end and retained by a grub ~cre~ 12. The lens flange lncludee a mountlng 14 ~or lens asse~bly 17 ~n~ a sealing O-ring mountsd ln groova 13.
~hQ U6~ 0~ the ~ealing ~lng ~llow~ the chamber to be sealed 25 ao that it can operate ~t other ~han atmos~h~rlo pre4~ure.
Iha l~n8 mountlng arrangement ~aolll~ate~ remov~l of the leng or detecto~ assembly to allow ea~y aCCeBB to the 6smpling c~mber for servlclng purpose~.
The PIN photodllode ae11 1~ ope~ted ln a zero-~i 30 phOtovolta~c mode whloh ~uffcrs ~everal di~dv~nt~ge~ auch ~5 lower 6peed, low~r ~ta~llllty, 6mallor dynamlc rang~, hlgher te~perat~ro ~oe~ici~nt and reduced optlc~1 b~ndwldth i25Z~7~
when compared with normal photocurrent mode. However a major advantage of zero flicker noise is achievable which allows for maximum possible signal to noise ratio to be obtained. Furthermore the mentioned disadvantages can be com-
enhancQd ae~thet~c~, lower ~ost in high volume and reducQd as6embly +~me, a specl~lized aluminlum ~xtruslon 1~ used.
While retaining the ~a~lc tu~ulAr de~lgn, the ~dditlon of mounting ~crew-flute6 reduces machlning requlrement#, as dos~ the p~ovlsion of CDnVen1ent ~10tB to hold one large electronics circuit ~o~rd. Sultable wcb design allow~ for convenient heat-~inking of electronic pow~r d~vlcea.
Provislon o~ a flat 'table' ~ a part oF the ~xtruslon desi~n, 6~plifles the m~ting of coupling tubes and ~he 10 ~lash window, obvlating ~ddle-sh~pod coupllng6. ~pposlte thi~ tabl~ a ~arAllel flat ~u~fac~ i~ provld~d to ~ld clampln~ ~o~ ~achlnng operatlons.
J;g fabrlc~tion of component~ 1~ thereby di~pen~ed with lead~ng to greater dlmen~onal acc~racy ~nd 15 repeatability ln productlon re~ultlng in lmproved quality control. Furthermore ~lmple a~sembly provldes for sl~plified ~erv~clng. ~he detector of the pre~ent inventlon i6 of long lic solld-3ta~e de~ign wlth the ex~eption of the Xanon flashtub~. In my co-p~ndin~ appllc~tion concurren~ly 20 filed wltb this appllcation a novel ~ocusslng reflector deslgned to accommod~t~ the unu~ual sh~pe of the X~non flash tubo 18 dlSclo6ed. Thl~ lmprovcd light ~ource with reduced flaeh ener~y will extend the malntenance perlod beyond two year~ undar contlnuou~ apera~lon, The p~ovl~lon of a~ improvet llght abs~rber wlth sam~llng chamber as disclosed ln m~ abovementlon~d co-pcndlng appllc~tlon allow6 ~igniflcant ch~mber ~ength reduction to parmit rack mountlng of the detector in restricted s~ac~6 such ag teleph~ne ~xchan~e6 ~nd other 3D aqulpment rOo~B. Fur~he~Ore the detector of the prc6ent lnvention c~n be oper~ted from an unregulated 24 volt D~.
~upply whlch could include ~t~ndby batterle~ h~vlng a supply tolerance ~ the range of 20-2B volt~ D.C. ln confor~ity wlth mo~t ~envention~l flr~ alarm syetems.
Ac~ordlngly, the presqnt lnvontlon provlde6 in one lZS2~7~
~spect a PtN photodiode cell re~pon~lve to low l~vel5 o light conn~ctad to an lmpedsnce mAtching buffer stage, gsln controll~d amplifler 6tage snd an output ampl$~1er ~t~g~t a gain ~o~trol network cont~oll~d by ~ temperature sensor for recelvlng ~n amplified signal from sald output 6ta~e, the s~in being ad~u&table to compen~ta for te~peratur~ dependence o~ th~ photodlode ~gnal, Conveni~ntly the solld-3tate photocell i~ ~ PIN
photodlod~ cell ad~pted to be operated ln ~ zOEro bla~
10 photovoltalc mode. Thu~ extremsly high sen~ltlv~ty i~
achleved ~;th m~x~mum signal to nolge ratlo. The det~ctor i~ cou~led with ~ preampll~ler a~ deflned of ~xtremely low noieè ~nd h~gh stabllity over a w$de t~mp~r~ture range.
~ PI~ photod~ode c~l~l oper~ting ln ~ald lS zero-b~a~ photovoltalc mode, exhlblts varla~le non-line~r ~ensltlvity to low llght levels ~t ~arying temporatur~
levely. ~hus the output of the cell mu~t be ~ecurat~ly cal~b~t~d over an operatlng tem~er~tu~e r~ng~ of -20C to 50C.
COnvenlentl~ the temp~turc ~onsor ~nd photodlode are malnta~ned ~n an e~uivalent thermal ~ltuatlon OF ln thermal Co~t~ct ~uch that any ~emper~ture difference b~tween the two i4 mln~mal.
~Cco~d~ngly the output from the eombin~tion of ~Ald 25 temperAtur~ ~en~or and qaln oon~rol n~two~k 1~ non-llnear ln invec~s prDportlon to the non-lln~rity o~ the photodlode cell whareby temperature dependenco of ~ald cell 1~ ~
~ub6t~ntlally ~llmlnated.
T~ere i6 al80 provlde a ~ower 6upply ~llter network 30 to provent or reDtrlct the inject~an of nol~ into any ~ o of ~he c~Cuit. ~lectrlcal connectlon6 ~or tho ~lgnal, ~upply ~nd ground ~r~.m~d~ u~ing ~hlelded cahle.
~ inventlon wlll be de~crlbed ln gr~Ater detall havln~ r~f~ronce to the accomp~nylng drawi~g6 ln whlch r~gure 1 is a ~ectional vlew o~ an al~ ~mpling i252 chamber, ~ gure 2 1~ a block dla~ram showlng the cell and compen~at~g ampl~ier circuit, ~ gure 3 i~ A part~al viQw of ~he ~dmpling chamber showlng th~ len~ And detector a~6embly, ~igure 4 shown an lnter~erRnce ~hleldlng oontRiner.
~ Ith refe~enc~ to Flgur~ 1 the detector includes a contaln*~ or houslng 71 ~or~ng a s~mpllng chamber 70 lncluding a serles o~ iri~s 21, 22 to ~b~orb ~nd dlssip~te lO light reflQ¢~d off th~ walls. Coupllng tubo6 50 ~re provlded to circul~te amblent alr f~om ~n arca under ~lre ~ur~eillance ~nto the chdmb~r 70 acro~s reglo~ 72 which i~
sub~ected to llght from an Xsnon flqeh tu~ ln houslng 60.
Alr ~low ~g ~chleved by a ~an ~not 6hown1. ~he length of 15 the air s~llng ch~mb~r is crltlcal to prev~nt ~ncident~l ligh~ b~ing detected and the p~ovision o~ a novel llght ab40rber 10 ~nabl~d a consid~rable shortenlng of the tube.
W¦th reference to Figure 2 the ~olld-sat~ cell l i~
p~ferably a PIN photodiode responslve to low llght l~vels 20 and present~ng a cmall signal to sn imp~dance-matchlng buf~er stflg~ 2 connect~d to B g2in-controlled ampll~ier stage 3 ~nd an output ~mpli~ler stage 4.~ ~e ampl~fi~d Blgna~ hl~n fed back to z gAin-control netwDrk 5 controlled by a temperature ~ensor 6. ~he 6en~0r ~nd the 25 PIN photod~ode are malntalned ln clo6e the~l contact ~uch that temperAtur~ dlfference het~een th~ two 18 ml~lmal under varlable oper~tlng condltlon~.
T~e gain of th~ g~ln controlled ~mpllfiet 8taqe 3 i~ ad~ust~d to compen~at~ for the t~mpe~ture dependence of 30 the ~m~ll signal from P~N photodiode 1.
T~e outp~t of the t~mperature 6enso~ ~nd the galn control n~work 1B non-llne~r ln inver~e proportlon wlth the non-lin~rtty of the P~N photodiode cell such that t~mp~atu~ dependenofl o~ tlle cell signal 18 I~UblitantiAlly 35 el$~in~ted.
1 2 5'Z~ 7'~
~ e 6011d-6tate detector c~ll 1 mu~t be ~mall to mlnimlze ~he cap~cltance whlch could otherwl6e r2~ult in reduced sensltlvity to the fla6h else tlm~ of ~beut 1 mlcro-seco~d from the fla~h tube, AR a re6~1t th~ photon of llght ~eam capture ara~ mall comp~rsd wlth a conventlolal photomultlpller tube~ Th~rofore a focu~slng lens 17 $S provided wlth ~s~oclated mountlng ~ardw~re ~hown in Flgure 3.
~eferrlng to Figu~e 3 and 4 th~ preamplifier 10 clrcult 1~ encap~ulated in epoxy 15, the clrcuit belng constructed on a ~rinted crlcu~t boA~d mounted ~gain~t the ba~e ~ ~o over~ome int~rnal reflectlons, to protect the cell, ~nd ~o pravent the ingres~ of epoxy dur~n~ monu~acture ~ detector at~achmcn~ 16 16 prov~d~d. Tho Att~chment 16 i5 15 po6itionod wlth~n ~ housing 71 whlch al~o ~ou~e~ the lens aa6embly 17. Tho preamplifier, detector oell optlcs and hou~lng b~come a self contained and separately tested plug-in mo~ule connected by mean~ of ~hiolded cabl~ 1~. Ths housing 71 include~ ~ base 9 tlghtly fltted to the cyllnder 20 ~ectlon. lhe flange 11 ~u~portlng the len~ i~ a sliding ~it ln the cylLndet 6ection ~t ths other end and retained by a grub ~cre~ 12. The lens flange lncludee a mountlng 14 ~or lens asse~bly 17 ~n~ a sealing O-ring mountsd ln groova 13.
~hQ U6~ 0~ the ~ealing ~lng ~llow~ the chamber to be sealed 25 ao that it can operate ~t other ~han atmos~h~rlo pre4~ure.
Iha l~n8 mountlng arrangement ~aolll~ate~ remov~l of the leng or detecto~ assembly to allow ea~y aCCeBB to the 6smpling c~mber for servlclng purpose~.
The PIN photodllode ae11 1~ ope~ted ln a zero-~i 30 phOtovolta~c mode whloh ~uffcrs ~everal di~dv~nt~ge~ auch ~5 lower 6peed, low~r ~ta~llllty, 6mallor dynamlc rang~, hlgher te~perat~ro ~oe~ici~nt and reduced optlc~1 b~ndwldth i25Z~7~
when compared with normal photocurrent mode. However a major advantage of zero flicker noise is achievable which allows for maximum possible signal to noise ratio to be obtained. Furthermore the mentioned disadvantages can be com-
5 pensated for as described herein.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Smoke detecting apparatus comprising a light sen-sing, solid state photocell; an impedance matching buffer stage in circuit with said photocell for receiving a signal from the latter; a gain controlled amplifier stage in circuit with said buffer stage; an output amplifier stage in circuit with said gain controlled amplifier stage; a temperature sen-sor; and a gain control network in circuit with said sensor, said gain controlled amplifier stage, and said output ampli-fier stage for receiving an amplified signal from said output amplifier stage, said gain control network being adjustable to compensate for temperature dependence of the photocell signal.
2. Apparatus according to claim 1 wherein the solid-state photocell is a PIN photodiode cell adapted for opera-tion at a zero bias photovoltaic mode to achieve extremely high sensitivity at maximum signal to noise ratio.
3. Apparatus according to claim 1 wherein the tempera-ture sensor and the photocell are maintained in an equivalent thermal environment.
4. Apparatus according to claim 3 wherein said sensor and said photocell are in contact with one another.
5. Apparatus according to claim 2, 3 or 4 wherein said sensor and said gain control network produce a first non-linear output and said photocell produces a second non-linear output, the non-linearity of said first output being in in-verse proportion to the non-linearity of said second output whereby temperature dependence of said photocell is substan-tially eliminated.
6. Apparatus according to claim 1 including power supply filter means in circuit with said stages for at least restricting the injection of noise into said stages.
7. Apparatus according to claim 1, including means forming a chamber having means for admitting sample air from a remote location, said photocell being positioned in said chamber, light absorbent means accommodated in said chamber and spaced from said photocell, and a light source for emit-ting light into said chamber between said photocell and said light absorbent means.
8. Apparatus according to claim 7 including means for exhausting air from said chamber, said light source being positioned to emit light into said chamber between said air admitting means and said air exhausting means.
9. Apparatus according to claim 8 wherein said chamber is airtight except for said air admitting means and said air exhausting means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPG082083 | 1983-08-12 | ||
| AUPG0820/83 | 1983-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1252172A true CA1252172A (en) | 1989-04-04 |
Family
ID=3770281
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000460903A Expired CA1252172A (en) | 1983-08-12 | 1984-08-13 | Smoke detection apparatus |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4665311A (en) |
| EP (1) | EP0140502B1 (en) |
| JP (1) | JPS60100022A (en) |
| KR (1) | KR950002498B1 (en) |
| AT (1) | ATE48044T1 (en) |
| AU (1) | AU573243B2 (en) |
| CA (1) | CA1252172A (en) |
| DE (1) | DE3480500D1 (en) |
| NZ (1) | NZ209184A (en) |
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-
1983
- 1983-08-12 AU AU31841/84A patent/AU573243B2/en not_active Ceased
-
1984
- 1984-08-10 NZ NZ209184A patent/NZ209184A/en unknown
- 1984-08-10 JP JP59166630A patent/JPS60100022A/en active Granted
- 1984-08-11 KR KR1019840004830A patent/KR950002498B1/en not_active IP Right Cessation
- 1984-08-13 US US06/640,344 patent/US4665311A/en not_active Expired - Lifetime
- 1984-08-13 DE DE8484305512T patent/DE3480500D1/en not_active Expired
- 1984-08-13 EP EP84305512A patent/EP0140502B1/en not_active Expired
- 1984-08-13 AT AT84305512T patent/ATE48044T1/en not_active IP Right Cessation
- 1984-08-13 CA CA000460903A patent/CA1252172A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| KR950002498B1 (en) | 1995-03-20 |
| KR850001585A (en) | 1985-03-30 |
| ATE48044T1 (en) | 1989-12-15 |
| US4665311A (en) | 1987-05-12 |
| AU573243B2 (en) | 1988-06-02 |
| JPS60100022A (en) | 1985-06-03 |
| EP0140502A1 (en) | 1985-05-08 |
| DE3480500D1 (en) | 1989-12-21 |
| AU3184184A (en) | 1985-02-14 |
| EP0140502B1 (en) | 1989-11-15 |
| JPH0449645B2 (en) | 1992-08-12 |
| NZ209184A (en) | 1988-07-28 |
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