温度传感器中英文对照外文翻译文献.docx
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温度传感器中英文对照外文翻译文献.docx
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温度传感器中英文对照外文翻译文献
中英文资料外文翻译文献
原文:
TemperatureSensorICsSimplifyDesigns
Whenyousetouttoselectatemperaturesensor,youarenolongerlimitedtoeitherananalogoutputoradigitaloutputdevice.Thereisnowabroadselectionofsensortypes,oneofwhichshouldmatchyoursystem'sneeds.
Untilrecently,allthetemperaturesensorsonthemarketprovidedanalogoutputs.Thermistors,RTDs,andthermocoupleswerefollowedbyanotheranalog-outputdevice,thesilicontemperaturesensor.Inmostapplications,unfortunately,theseanalog-outputdevicesrequireacomparator,anADC,oranamplifierattheiroutputtomakethemuseful.
Thus,whenhigherlevelsofintegrationbecamefeasible,temperaturesensorswithdigitalinterfacesbecameavailable.TheseICsaresoldinavarietyofforms,fromsimpledevicesthatsignalwhenaspecifictemperaturehasbeenexceededtothosethatreportbothremoteandlocaltemperatureswhileprovidingwarningsatprogrammedtemperaturesettings.Thechoicenowisn'tsimplybetweenanalog-outputanddigital-outputsensors;thereisabroadrangeofsensortypesfromwhichtochoose.
ClassesofTemperatureSensors
Fourtemperature-sensortypesareillustratedinFigure1.Anidealanalogsensorprovidesanoutputvoltagethatisaperfectlylinearfunctionoftemperature(A).InthedigitalI/Oclassofsensor(B),temperaturedataintheformofmultiple1sand0sarepassedtothemicrocontroller,oftenviaaserialbus.Alongthesamebus,dataaresenttothetemperaturesensorfromthemicrocontroller,usuallytosetthetemperaturelimitatwhichthealertpin'sdigitaloutputwilltrip.Alertinterruptsthemicrocontrollerwhenthetemperaturelimithasbeenexceeded.Thistypeofdevicecanalsoprovidefancontrol.
Figure1.SensorandICmanufacturerscurrentlyofferfourclassesoftemperaturesensors.
"Analog-plus"sensors(C)areavailablewithvarioustypesofdigitaloutputs.TheVOUTversustemperaturecurveisforanICwhosedigitaloutputswitcheswhenaspecifictemperaturehasbeenexceeded.Inthiscase,the"plus"addedtotheanalogtemperaturesensorisnothingmorethanacomparatorandavoltagereference.Othertypesof"plus"partsshiptemperaturedataintheformofthedelaytimeaftertheparthasbeenstrobed,orintheformofthefrequencyortheperiodofasquarewave,whichwillbediscussedlater.
Thesystemmonitor(D)isthemostcomplexICofthefour.InadditiontothefunctionsprovidedbythedigitalI/Otype,thistypeofdevicecommonlymonitorsthesystemsupplyvoltages,providinganalarmwhenvoltagesriseaboveorsinkbelowlimitssetviatheI/Obus.Fanmonitoringand/orcontrolissometimesincludedinthistypeofIC.Insomecases,thisclassofdeviceisusedtodeterminewhetherornotafanisworking.Morecomplexversionscontrolthefanasafunctionofoneormoremeasuredtemperatures.Thesystemmonitorsensorisnotdiscussedherebutisbrieflymentionedtogiveacompletepictureofthetypesoftemperaturesensorsavailable.
Analog-OutputTemperatureSensors
Thermistorsandsilicontemperaturesensorsarewidelyusedformsofanalog-outputtemperaturesensors.Figure2clearlyshowsthatwhenalinearrelationshipbetweenvoltageandtemperatureisneeded,asilicontemperaturesensorisafarbetterchoicethanathermistor.Overanarrowtemperaturerange,however,thermistorscanprovidereasonablelinearityandgoodsensitivity.Manycircuitsoriginallyconstructedwiththermistorshaveovertimebeenupdatedusingsilicontemperaturesensors.
Figure2.Thelinearityofthermistorsandsilicontemperaturesensors,twopopularanalog-outputtemperaturedetectors,iscontrastedsharply.
Silicontemperaturesensorscomewithdifferentoutputscalesandoffsets.Some,forexample,areavailablewithoutputtransferfunctionsthatareproportionaltoK,othersto°Cor°F.Someofthe°Cpartsprovideanoffsetsothatnegativetemperaturescanbemonitoredusingasingle-endedsupply.
Inmostapplications,theoutputofthesedevicesisfedintoacomparatororanA/Dconvertertoconvertthetemperaturedataintoadigitalformat.Despitetheneedfortheseadditionaldevices,thermistorsandsilicontemperaturesensorscontinuetoenjoypopularityduetolowcostandconvenienceofuseinmanysituations.
DigitalI/OTemperatureSensors
Aboutfiveyearsago,anewtypeoftemperaturesensorwasintroduced.Thesedevicesincludeadigitalinterfacethatpermitscommunicationwithamicrocontroller.TheinterfaceisusuallyanI²CorSMBusserialbus,butotherserialinterfacessuchasSPIarecommon.Inadditiontoreportingtemperaturereadingstothemicrocontroller,theinterfacealsoreceivesinstructionsfromthemicrocontroller.Thoseinstructionsareoftentemperaturelimits,which,ifexceeded,activateadigitalsignalonthetemperaturesensorICthatinterruptsthemicrocontroller.Themicrocontrolleristhenabletoadjustfanspeedorbackoffthespeedofamicroprocessor,forexample,tokeeptemperatureundercontrol.
Thistypeofdeviceisavailablewithawidevarietyoffeatures,amongthem,remotetemperaturesensing.Toenableremotesensing,mosthigh-performanceCPUsincludeanon-chiptransistorthatprovidesavoltageanalogofthetemperature.(Onlyoneofthetransistor'stwop-njunctionsisused.)Figure3showsaremoteCPUbeingmonitoredusingthistechnique.Otherapplicationsutilizeadiscretetransistortoperformthesamefunction.
Figure3.Auser-programmabletemperaturesensormonitorsthetemperatureofaremoteCPU'son-chipp-njunction.
Anotherimportantfeaturefoundonsomeofthesetypesofsensors(includingthesensorshowninFigure3)istheabilitytointerruptamicrocontrollerwhenthemeasuredtemperaturefallsoutsidearangeboundedbyhighandlowlimits.Onothersensors,aninterruptisgeneratedwhenthemeasuredtemperatureexceedseitherahighoralowtemperaturethreshold(i.e.,notboth).ForthesensorinFigure3,thoselimitsaretransmittedtothetemperaturesensorviatheSMBusinterface.Ifthetemperaturemovesaboveorbelowthecircumscribedrange,thealertsignalinterruptstheprocessor.
PicturedinFigure4isasimilardevice.Insteadofmonitoringonep-njunction,however,itmonitorsfourjunctionsanditsowninternaltemperature.BecauseMaxim'sMAX1668consumesasmallamountofpower,itsinternaltemperatureisclosetotheambienttemperature.Measuringtheambienttemperaturegivesanindicationastowhetherornotthesystemfanisoperatingproperly.
Figure4.Auser-programmabletemperaturesensormonitorsitsownlocaltemperatureandthetemperaturesoffourremotep-njunctions.
ControllingafanwhilemonitoringremotetemperatureisthechieffunctionoftheICshowninFigure5.Usersofthispartcanchoosebetweentwodifferentmodesoffancontrol.InthePWMmode,themicrocontrollercontrolsthefanspeedasafunctionofthemeasuredtemperaturebychangingthedutycycleofthesignalsenttothefan.Thispermitsthepowerconsumptiontobefarlessthanthatofthelinearmodeofcontrolthatthispartalsoprovides.BecausesomefansemitanaudiblesoundatthefrequencyofthePWMsignalcontrollingit,thelinearmodecanbeadvantageous,butatthepriceofhigherpowerconsumptionandadditionalcircuitry.Theaddedpowerconsumptionisasmallfractionofthepowerconsumedbytheentiresystem,though.
Figure5.Afancontroller/temperaturesensorICuseseitheraPWM-orlinear-modecontrolscheme.
ThisICprovidesthealertsignalthatinterruptsthemicrocontrollerwhenthetemperatureviolatesspecifiedlimits.Asafetyfeatureintheformofthesignalcalled"overt"(anabbreviatedversionof"overtemperature")isalsoprovided.Ifthemicrocontrollerorthesoftwareweretolockupwhiletemperatureisrisingtoadangerouslevel,thealertsignalwouldnolongerbeuseful.However,overt,whichgoesactiveoncethetemperaturerisesabovealevelsetviatheSMBus,istypicallyusedtocontrolcircuitrywithouttheaidofthemicrocontroller.Thus,inthishigh-temperaturescenariowiththemicrocontrollernotfunctioning,overtcouldbeusedtoshutdownthesystempowersuppliesdirectly,withoutthemicrocontroller,andpreventapotentiallycatastrophicfailure.
ThisdigitalI/Oclassofdevicesfindswidespreaduseinservers,batterypacks,andhard-diskdrives.Temperatureismonitoredinnumerouslocationstoincreaseaserver'sreliability:
atthemotherboard(whichisessentiallytheambienttemperatureinsidethechassis),insidetheCPUdie,andatotherheat-generatingcomponentssuchasgraphicsacceleratorsandhard-diskdrives.Batterypacksincorporatetemperaturesensorsforsafetyreasonsandtooptimizechargingprofiles,whichmaximizesbatterylife.
Therearetwogoodreasonsformonitoringthetemperatureofahard-diskdrive,whichdependsprimarilyonthespeedofthespindlemotorandtheambienttemperature:
Thereaderrorsinadriveincreaseattemperatureextremes,andaharddisk'sMTBFisimprovedsignificantlythroughtemperaturecontrol.Bymeasuringthetemperaturewithinthesystem,youcancontrolmotorspeedtooptimizereliabilityandperformance.Thedrivecanalsobeshutdown.Inhigh-endsystems,alertscanbegeneratedforthesystemadministratortoindicatetemperatureextremesorsituationswheredatalossispossible.
Analog-PlusTemperatureSensors
"Analog-plus"sensorsaregenerallysuitedtosimplermeasurementapplications.TheseICsgeneratealogicoutputderivedfromthemeasuredtemperatureandaredistinguishedfromdigitalI/Osensorsprimarilybecausetheyoutputdataonasingleline,asopposedtoaserialbus.
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