08湿度传感器系统毕业论文中英文资料外文翻译文献 1.docx

08湿度传感器系统毕业论文中英文资料外文翻译文献 1.docx

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08湿度传感器系统毕业论文中英文资料外文翻译文献1

湿度传感器系统

中英文资料外文翻译文献

英文:

Therightdesignforarelativehumiditysensorsystem

Optimizingtheresponsecharacteristicsandaccuracyofahumiditysensorsystem

1Overview

Tomaketherightchoicewhenselectingarelativehumiditysensorforanapplication,itisimportanttoknowandtobeabletojudgethedecidingfactors.Inadditiontolong-termstability,whichisameasureonhowmuchasensorchangesitspropertiesovertime,thesefactorsalsoincludethemeasurementaccuracyandtheresponsecharacteristicsofthesensor.Capacitivehumiditysensorsarebasedontheprinciplethatahumidity-sensitivepolymerabsorbsorreleasesmoistureasafunctionoftherelativeambienthumidity.Becausethismethodisonlyaspotmeasurementatthesensorlocation,andusuallythehumidityofthesurroundingsisthedesiredquantity,thesensormustbebroughtintomoistureequilibriumwiththesurroundingstoobtainaprecisemeasurementvalue.Thisprocessisrealizedbyvarioustransportphenomena（cf.thesectiontitled"Thehousingeffectontheresponsetime"）,whichexhibitatimeconstant.Accuracyandresponsetimearethuscloselydependentoneachother,andthedesignofahumiditymeasurementsystembecomesachallenge.

2Measurementaccuracy

Thetermmeasurementaccuracyofahumiditysensorisunderstoodprimarilytorefertothedeviationofthevaluemeasuredbythesensorfromtheactualhumidity.Todeterminethemeasurementaccuracy,references,suchaschilledmirrorhygrometers,whoseowntolerancemustbetakenintoaccount,areused.Inadditiontothistrivialcomponent,humiditysensorsrequireagiventimeforreachingstablehumidityandtemperatureequilibrium（thehumidityisafunctionoftemperatureanddecreaseswithincreasingtemperature;adifferencebetweensensorandambienttemperatureleadstomeasurementerrors）.Thisresponsetimethushasasignificanteffectonthevaluemeasuredbythesensorandthusonthedeterminedaccuracy.Thistime-dependentcharacteristicisexplainedinmoredetailinthefollowing.

3Responsecharacteristicsandresponsetime

Theresponsecharacteristicsaredefinedbyvariousparameters.Theseare:

●Theactualresponsecharacteristicsofthehumiditysensoratconstanttemperature.

（1）Howquicklythesensitivepolymerabsorbsorreleasesmoistureuntilequilibriumisreached（intrinsicresponsetime）

（2）Howfasttheentiresystemreacheshumidityequilibrium（housingeffect）

●Thethermalresponsecharacteristicsofthehumiditysensoratanon-constanttemperature

●

（3）Thethermalmassofthesensor

（4）Thesystem'sthermalmass,whichisthermallycoupledtothesensor（e.g.printedcircuitboard）

（5）Heatsourcesinthedirectsurroundingsofthesensor（electroniccomponents）

（1）and（3）aredeterminedentirelybythesensoritself,

（1）primarilybythecharacteristicsofthesensitivepolymer.

（2）and（4）areprimarilydeterminedbytheconstructionoftheentiresystem（shapeandsizeofhousingandreadoutcircuitry）.

（5）isdeterminedbyheat-emittingelectroniccomponents.

Thesepointswillbediscussedinmoredetailinthefollowing.

Theintrinsicresponsetime

（1）

Qualitatively,theresponsecharacteristicsofcapacitivehumiditysensorslooklikethefollowing（Fig.1）.

Fig.1:

Typicalandidealizedresponsecharacteristicsofcapacitivehumiditysensors（schematic）

Becausetheseresponsecharacteristicsareespeciallypronouncedathighhumidityvalues,anisothermalhumidityjumpfrom40%to100%wasselectedhereforillustration.Thedesiredidealbehaviorofthesensorisindicatedinblue.Inpractice,however,thesensorbehavesaccordingtotheredline,approximatelyaccordingto:

Here,thetimespan1isusuallyveryshort（typ.1–30min.）,incontrast,thetimespan2isverylong（typ.Manyhourstodays）.Heretheconnectionofmeasurementaccuracyandresponsecharacteristicsbecomesclear（tuntilRH=100%isreached）.Thevalueatt4（Fig.1）isconsideredtobeanexactmeasuredvalue.However,thisassumesthatboththehumidityandalsothetemperatureremainstableduringthisentiretime,andthatthetestingwaitsuntilthisverylongmeasurementtimeiscompleted.Theseconditionsarebothveryhardtoachieveandunusualinpractice.Forthecalibration,therearethefollowingtwoapproaches,whichbothfinduseinpractice（cf.Fig.2）:

1.Themeasuredvalueatt2（Fig.1）isusedasacalibrationreference.

Advantage:

●Therequiredmeasurementtimeforreachingtheendvalue（intheexample100%）isclearlyshortened,correspondstopractice,andachievesanapparentshortresponsetimeofthesensor（cf.Fig.2）.

Disadvantage:

●Iftheconditionsaresimilarforalongtime（e.g.,wetperiodsinoutdooroperation）,thesensorsexceedthecorrectendvalue（intheexample100%）undesirablybyupto10%（cf.Fig.2）.

2.Themeasuredvalueatt4（Fig.1）isusedasacalibrationreference.

Advantage:

●Evenforsimilarconditionsoveralongtime（e.g.,wetperiodsinoutdooroperation）,anexactmeasurementresultisobtained（cf.Fig.2）.

Disadvantage:

●ForahumidityjumplikeinFig.1,thesensorsveryquicklydeliverthemeasuredvalueatt2,butreachingastableendvalue（about3-6%higher）takesalongtime（apparentlongerresponsetime）（cf.Fig.2）.

Inordertotakeintoaccountbothapproachesoptimally,themeasuredvaluesatt3（cf.Fig.1）areusedasthecalibrationreferencebySensirionAG.

Fig.2:

Responsecharacteristicsofdifferenthumiditymeasurementsystems

Thehousingeffectontheresponsetime

（2）

Here,twotypesoftransportphenomenaplayadecidingrole:

●Convection:

Forthisveryfastprocess,theair,whosehumidityistobedetermined,istransportedtothesensorbymeansofventilation.

●Diffusion:

Thisveryslowprocessisdeterminedbythethermal,molecularself-motionofthewatermolecules.Itoccursevenin"stationary"air（e.g.,withinahousing）,butleadstoalongresponsetime.

Inordertoachievefavorableresponsecharacteristicsinthehumiditymeasurementsystem,theveryfastconvectionprocessmustbesupportedbylargehousingopeningsandtheslowdiffusionprocessmustbesupportedbyasmallhousingaroundthesensor（small"deadvolume"）with"stationary"airreducedtoaminimum.Thefollowingapplies:

Thermaleffects（3）,（4）,and（5）

Becausethetotalthermalmassofthehumiditymeasurementsystem（sensor+housing）hasasignificanteffectonitsresponsetime,thetotalthermalmassmustbekeptaslowaspossible.Thegreaterthetotalthermalmass,themoreinertthemeasurementsystembecomesthermallyanditsresponsetime,whichistemperature-dependent,increases.Inordertopreventmeasurementerrors,thesensorshouldnotbemountedinthevicinityofheatgeneratingcomponents.

4Summary–whatshouldbetakenintoaccountwhendesigningahumiditymeasurementsystem

Inordertoachieveerror-freeoperationofahumidity-measurementsystemwithresponsetimesasshortaspossible,thefollowingpointsshouldbetakenintoaccountespeciallyfortheselectionofthesensorandforthedesignofthesystem.

●Theselectionofthehumiditysensorelement.Itshould

●beassmallaspossible,

●haveathermalmassthatisaslowaspossible,

●workwithapolymer,whichexhibitsminimalfluctuationsinmeasuredvaluesduringthetimespan2（cf.Fig.1）;testinggivessimpleinformationonthiscondition,

●providecalibration,whichcorrespondstotherequirements（seeabove）,e.g.,

SHT11/SHT15fromSensirion.

●Thehousingdesign（cf.Formula1）.Itshould

●haveairopeningsthatareaslargeaspossibleinthevicinityofthesensororthesensorshouldbeoperatedoutsideofthehousingàgoodconvection!

●enclosea"deadvolume"thatisassmallaspossiblearoundthesensoràlittlediffusion!

●Thesensorshouldbedecoupledthermallyasmuchaspossiblefromothercomponents,sothattheresponsecharacteristicsofthesensorarenotnegativelyaffectedbythethermalinertiaoftheentiresystem.（e.g.,itsownprintedcircuitboardforthehumiditysensor,structurallypartitioningthehousingtocreateasmallvolumeforthehumiditysensor,seeFig.3）

Fig.3:

MountingexampleforSensirionsensorsSHT11andSHT15withslitsforthermaldecoupling

●Thesensorshouldnotbemountedinthevicinityofheatsources.Ifitwas,measuredtemperaturewouldincreaseandmeasuredhumiditydecrease.

5Designproposal

Thechallengeistorealizeasystemthatoperatescleanlybyoptimallytakingintoaccountallofthepointsinsection4.ThealreadycalibratedSMDhumiditysensorsSHT11andSHT15fromSensirionaretheidealsolution.Foroptimumintegrationofthesensorsinameasurementsystem,SensirionAGhasalsodevelopedafiltercapasanadapteraid,whichtakesintoaccountasmuchaspossiblethepointsinsection4andalsoprotectsthesensoragainstcontaminantswithafiltermembrane.Fig.4showsschematicallyhowthesensorscanbeideallyintegratedintoahousingwallbymeansofthefiltercapSF1.

Fig.4:

FiltercapforSHT11andSHT15

Inadditiontotheadvantagesmentionedabove,thereisalsotheoptionofbuildinganIP67-compatiblehumiditymeasurementdevice（withO-ring,cf.Fig.4）withoptimalperformance.DetailedinformationisavailableontheSensirionWebsite.

译文：

相对湿度传感器系统的正确设计

湿度传感器系统精度及响应特性的优化

1.综述

为了在相对湿度的应用方面对传感器做出正确的选择，了解和评估那些起决定作用的因素是非常重要的。

除了衡量传感器性能随时间变化而变化的长期稳定性这个因素以外，还应考虑传感器的测量精度和响应特性这两个因素。

电容式湿度传感器工作是基于这样一个原理；其湿敏聚合体元件能吸收或释放湿气被看作是与周围环境湿度相关的一项功能，由于这种方法仅仅测量了传感器所在位置这一点的湿度，而通常是要测量其周围湿度这个数值，所以传感器必须在周围环境湿度平衡的状态下获得精确的测量值（参

照“响应时间的壳体

（1）效应”这一部分）。

这个湿度平衡过程可以通过各种用时间常数表征的传输现象得以实现。

测量精度和响应时间是如此地接近并且相互依赖，使湿度测量系统的结构设计成为一项挑战。

2.测量精度

湿度传感器的测量精度这个术语