2023年全國碩士研究生考試考研英語一試題真題（含答案詳解+作文范文）_第1頁
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1、Therearetwomaintypesofsmokedetects:ionizationdetectsphotoelectricdetects.Asmokealarmusesonebothmethodssometimesplusaheatdetecttowarnofafire.Thedevicesmaybepoweredbya9voltbatterylithiumbattery120volthousewiring.Ionization

2、DetectsIonizationdetectshaveanionizationchamberasourceofionizingradiation.Thesourceofionizingradiationisaminutequantityofamericium241(perhaps15000thofagram)whichisasourceofalphaparticles(heliumnuclei).Theionizationchambe

3、rconsistsoftwoplatesseparatedbyaboutacentimeter.Thebatteryappliesavoltagetotheplatesgingoneplatepositivetheotherplatenegative.Alphaparticlesconstantlyreleasedbytheamericiumknockelectronsoffoftheatomsintheairionizingtheox

4、ygennitrogenatomsinthechamber.Thepositivelygedoxygennitrogenatomsareattractedtothenegativeplatetheelectronsareattractedtothepositiveplategeneratingasmallcontinuouselectriccurrent.Whensmokeenterstheionizationchamberthesmo

5、keparticlesattachtotheionsneutralizethemsotheydonotreachtheplate.Theincurrentbetweentheplatestriggersthealarm.PhotoelectricDetectsInonetypeofphotoelectricdevicesmokecanblockalightbeam.Inthiscasethereductioninlightreachin

6、gaphotocellsetsoffthealarm.Inthemostcommontypeofphotoelectricunithoweverlightisscatteredbysmokeparticlesontoaphotocellinitiatinganalarm.InthistypeofdetectthereisaTshapedchamberwithalightemittingdiode(LED)thatshootsabeamo

7、flightacrossthehizontalbaroftheT.AphotocellpositionedatthebottomoftheverticalbaseoftheTgeneratesacurrentwhenitisexposedtolight.UndersmokefreeconditionsthelightbeamcrossesthetopoftheTinanuninterruptedstraightlinenotstriki

8、ngthephotocellpositionedatarightanglebelowthebeam.WhensmokeispresentthelightisscatteredbysmokeparticlessomeofthelightisdirecteddowntheverticalpartoftheTtostrikethephotocell.Whensufficientlighthitsthecellthecurrenttrigger

9、sthealarm.WhichMethodisBetterBothionizationphotoelectricdetectsareeffectivesmokesenss.BothtypesofsmokedetectsmustpassthesametesttobecertifiedasULsmokedetects.Ionizationdetectsrespondmequicklytoflamingfireswithsmallercomb

10、ustionparticlesphotoelectricdetectsrespondmequicklytosmolderingfires.Ineithertypeofdetectsteamhighhuitycanleadtocondensationonthecircuitboardsenscausingthealarmtosound.Ionizationdetectsarelessexpensivethanphotoelectricde

11、tectsbutsomeuserspurposelydisablethembecausetheyaremelikelytosoundanalarmfromnmalcookingduetotheirsensitivitytominutesmokeparticles.Howeverionizationdetectshaveadegreeofbuiltinsecuritynotinherenttophotoelectricdetects.Wh

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