基于S7-300PLC的煤礦井下中央泵房控制

山東科技大學(xué)學(xué)士學(xué)位論文 摘要摘要本文對煤礦井下中央泵房控制系統(tǒng)的硬件系統(tǒng)設(shè)計、軟件系統(tǒng)設(shè)計以及系統(tǒng)的抗干擾措施進(jìn)行了詳細(xì)設(shè)計。本系統(tǒng)采用SIEMENS的S7-300PLC，并結(jié)合各種傳感器（主要為水位傳感器、負(fù)壓傳感器、壓力傳感器、流量傳感器、振動傳感器、溫度傳感器等），完成系統(tǒng)中要實現(xiàn)的控制方式選擇、故障報警等功能。本系統(tǒng)采用水泵及管路的“自動輪換”工作制。采用臺達(dá)人機(jī)界面就地監(jiān)控系統(tǒng)中設(shè)備的參數(shù)，并進(jìn)行現(xiàn)場的就地手動控制，做到有故障及時發(fā)現(xiàn)并盡早處理。S7-300PLC采用RS485通信標(biāo)準(zhǔn)與地面監(jiān)控中心上位機(jī)進(jìn)行通信，對排水系統(tǒng)實施全面的監(jiān)控，并能進(jìn)行遠(yuǎn)程控制。關(guān)鍵詞：PLC傳感器排水系統(tǒng)自動控制ABSTRACTInthispaper,theselectionanddesignofdrainageequipment,thenaccordingtothedrainagecontrolrequirements,thedesignofautomaticcontrol.ThesystemusestheSIEMENSS7-300PLC,andcombinedwithavarietyofsensors(mainlyforthewaterlevelsensor,pressuresensor,pressuresensor,flowsensor,vibrationsensor,temperaturesensor),controlmodetoachievethesystemchoice,alarmandotherfunctions.Thissystemusesthewaterpumpandpipeline"turns"workingsystem.Avalley"principletodeterminethenumberoftheopening"pumpaccordingtoavoidpeak,inordertoachievethepurposeofsavingthepower.TheparametersoftheequipmentofdeltaHMImonitoringsystemofinsituPCend,andlocalmanualcontrolsite,dohavethefaulttimelydetectionandearlytreatment.S7-300PLCcommunicationusingRS485communicationstandardandthegroundcontrolcenterPC,theimplementationofacomprehensivemonitoringofthedrainagesystem,andiscapableofremotecontrol.Keywords：PLCsensordrainagesystemautomaticcontrol山東科技大學(xué)學(xué)士學(xué)位論文 目錄目錄山東科技大學(xué)學(xué)士學(xué)位論文 目錄TOC\o"1-2"\u1緒論 ②選擇滅弧性能好的低壓斷路器和交流接觸器。山東科技大學(xué)學(xué)士學(xué)位論文 總結(jié)6總結(jié)本論文針對煤礦井下主排水系統(tǒng)自動化程度不高的現(xiàn)狀，研究設(shè)計了PLC控制與PC監(jiān)視相結(jié)合的煤礦井下自動排水系統(tǒng)。本文重點介紹了以下幾點內(nèi)容:（1）進(jìn)行系統(tǒng)設(shè)計中所使用的設(shè)備的選型工作。首先是根據(jù)礦井的涌水量和井深來確定使用水泵的型號和臺數(shù)，然后確定排水管道和電動閘閥，電動球閥，根據(jù)功能要求選擇一定數(shù)量和類型的傳感器，通過了估算的輸入輸出點數(shù)和要求的PLC的存儲容量及響應(yīng)速度，確定所用PLC的型號和功能模塊。（2）設(shè)計出了系統(tǒng)控制的流程圖，使用PLC語言編寫了水泵自動控制的部分子程序。（3）利用MicrosoftVisio繪圖軟件繪制了系統(tǒng)控制的原理圖，由于是初次接觸S7-300用于礦井排水系統(tǒng)，了解甚微，所以設(shè)計中的很多細(xì)節(jié)部分考慮不周。在高正中老師的悉心指導(dǎo)下，對結(jié)構(gòu)和部分內(nèi)容進(jìn)行了修改，大體上做到了有章可尋。山東科技大學(xué)學(xué)士學(xué)位論文 致謝山東科技大學(xué)學(xué)士學(xué)位論文 參考文獻(xiàn)參考文獻(xiàn)[1]曲波.工業(yè)常用傳感器選型指南.北京：清華大學(xué)出版社,2002[2]黃海燕.PLC現(xiàn)場工程師工作指南.北京:化學(xué)工業(yè)出版社，2011[3]彭伯平.礦井排水泵工.北京：中國勞動社會保障出版社，2008[4]周美蘭.PLC電氣控制與組態(tài).北京：科學(xué)出版社，2003[5]譚國俊，韓耀飛，熊樹.基于PLC的中央泵房自動化設(shè)計.北京：工礦自動化，2006[6]張濤，王攀攀，王瑩.基于S7-300PLC的煤礦井下排水自動化控制系統(tǒng).采礦技術(shù)，2006[7]石小利，高奇峰.井下排水監(jiān)控系統(tǒng)自動化方案分析.煤礦機(jī)電，2006[8]劉敢，劉巖.礦井中央泵房水泵自動化系統(tǒng)的設(shè)計.煤礦機(jī)電,2007[9]劉凱、周海.深入淺出西門子S7-300PLC.北京：北京航空航天大學(xué)出版社,2004[10]馬寧.S7-300PLC和MM440變頻器的原理與應(yīng)用.北京：機(jī)械工業(yè)出版社，2006[11]葉湘濱.傳感器與檢測技術(shù).北京：國防工業(yè)出版社,2007[12]全國煤炭技工教材編審委員會.礦山電力拖動與控制.北京：煤炭工業(yè)出版社,2006[13]郭雨.煤礦機(jī)電設(shè)備.江蘇：中國礦業(yè)大學(xué)出版社,2005[14]SIEMENS.SIMATICS7ConfiguringHardwareandCommunicationConnectionsSTEP7V5.0Manual.[15]SIEMENS.ToolboxforDataLinkPCstoSIMATICS7.[16]AnonUnderstandingPLCnetworks,EC＆M:ElectricalConstructionandMaintenance,Jan,1996山東科技大學(xué)學(xué)士學(xué)位論文 致謝致謝本文是在導(dǎo)師高正中悉心指導(dǎo)下完成的。從論文的選題到相關(guān)材料的收集，從論文構(gòu)架的設(shè)計，到其內(nèi)容的遣詞造句，每一章節(jié)都凝聚著導(dǎo)師的心血。在此，學(xué)生表示最誠摯的謝意。高老師嚴(yán)謹(jǐn)?shù)闹螌W(xué)態(tài)度、積極的人生觀、學(xué)術(shù)上孜孜追求的精神以及對學(xué)生無微不至的關(guān)懷，都給我留下了終生難忘的印象，必然將對我以后的學(xué)習(xí)和生活產(chǎn)生重要影響。在完成整個論文期間，各位老師、同學(xué)、朋友、親人的辛勤勞動以及他們在治學(xué)和人品上給予我的深刻影響，我同樣銘記在心，并表示由衷的感謝。在此，我向所有在學(xué)業(yè)上、生活上幫助、理解、支持我的老師、同學(xué)、朋友和親人致以最真誠的謝意。最后，感謝各位專家、學(xué)者在百忙之中審閱我的論文。山東科技大學(xué)學(xué)士學(xué)位論文 附錄山東科技大學(xué)學(xué)士學(xué)位論文 附錄附錄附錄1系統(tǒng)圖紙圖9.1SM331模擬量輸入模塊1圖9.2SM331模擬量輸入模塊2圖9.3模擬量輸入模塊3圖9.4模擬量輸入模塊4圖9.5數(shù)字量輸入模塊圖9.6數(shù)字量輸出模塊附錄2外文文獻(xiàn)翻譯BasicknowledgeoftransducersAtransducerisadevicewhichconvertsthequantitybeingmeasuredintoanoptical,mechanical,or-morecommonly-electricalsignal.

Theenergy-conversionprocessthattakesplaceisreferredtoastransduction.

Transducersareclassifiedaccordingtothetransductionprincipleinvolvedandtheformofthemeasured.Thusaresistancetransducerformeasuringdisplacementisclassifiedasaresistancedisplacementtransducer.Otherclassificationexamplesarepressurebellows,forcediaphragm,pressureflapper-nozzle,andsoon.1.TransducerElements

Althoughthereareexception,mosttransducersconsistofasensingelementandaconversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.Suchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesortransducers.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicaltransducersrespectively.

2.TransducerSensitivity

TherelationshipbetweenthemeasuredandthetransduceroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthetransducersensitivityK1=output-signalincrement/measuredincrement.Inpractice,thetransducersensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=output-signalincrement/K1.

3.CharacteristicsofanIdealTransducer

Thehightransducershouldexhibitthefollowingcharacteristics

a)

highfidelity-thetransduceroutputwaveformshapebeafaithfulreproductionofthemeasured;thereshouldbeminimumdistortion.

b)

Thereshouldbeminimuminterferencewiththequantitybeingmeasured;thepresenceofthetransducershouldnotalterthemeasuredinanyway.

c)

Size.Thetransducermustbecapableofbeingplacedexactlywhereitisneeded.

d)

Thereshouldbealinearrelationshipbetweenthemeasuredandthetransducersignal.

e)

Thetransducershouldhaveminimumsensitivitytoexternaleffects,pressuretransducers,forexample,areoftensubjectedtoexternaleffectssuchvibrationandtemperature.

f)

Thenaturalfrequencyofthetransducershouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.

4.ElectricalTransducers

Electricaltransducersexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindicationormesdurement.

Electricaltransducerscanbedividedintotwodistinctgroups:

a)

variable-control-parametertypes,whichinclude:

i)resistance

ii)

capacitance

iii)

inductance

iv)

mutual-inductancetypes

Thesetransducersallrelyonexternalexcitationvoltagefortheiroperation.

b)

self-generatingtypes,whichinclude

i)

electromagnetic

ii)thermoelectric

iii)photoemissive

iv)piezo-electrictypes

Theseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinputandtheireffectsarereversible.Forexample,apiezo-electrictransducernormallyproducesanoutputvoltageinresponsetothedeformationofacrystallinematerial;however,ifanalternatingvoltageisappliedacrossthematerial,thetransducerexhibitsthereversibleeffectbydeformingorvibratingatthefrequencyofthealternatingvoltage.

5.ResistanceTransducers

Resistancetransducersmaybedividedintotwogroups,asfollows:

i)

Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.

ii)Thosewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.

5.1Potentiometers

Alinearwire-woundpotentiometerconsistsofanumberofturnsresistancewirewoundaroundanon-conductingformer,togetherwithawipingcontactwhichtravelsoverthebarwires.Theconstructionprinciplesareshowninfigurewhichindicatethatthewiperdisplacementcanberotary,translational,oracombinationofbothtogiveahelical-typemotion.Theexcitationvoltagemaybeeithera.c.or

d.c.andtheoutputvoltageisproportionaltotheinputmotion,providedthemeasuringdevicehasaresistancewhichismuchgreaterthanthepotentiometerresistance.

Suchpotentiometerssufferfromthelinkedproblemofresolutionandelectricalnoise.Resolutionisdefinedasthesmallestdetectablechangeininputandisdependentonthecross-sectionalareaofthewindingsandtheareaoftheslidingcontact.Theoutputvoltageisthusaserialsofstepsasthecontactmovesfromonewiretonext.

Electricalnoisemaybegeneratedbyvariationincontactresistance,bymechanicalwearduetocontactfriction,andbycontactvibrationtransmittedfromthesensingelement.Inaddition,themotionbeingmeasuredmayexperiencesignificantmechanicalloadingbytheinertiaandfrictionofthemovingpartsofthepotentiometer.Thewearonthecontactingsurfacelimitsthelifeofapotentiometertoafinitenumberoffullstrokesorrotationsusuallyreferredtointhemanufacture’sspecificationasthe‘numberofcyclesoflifeexpectancy’,atypicalvaluebeing20*1000000cycles.

TheoutputvoltageV0oftheunloadpotentiometercircuitisdeterminedasfollows.LetresistanceR1=xi/xt*Rtwherexi=inputdisplacement,xt=maximumpossibledisplacement,Rttotalresistanceofthepotentiometer.ThenoutputvoltageV0=V*R1/(R1+(Rt-R1))=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt.Thisshowsthatthereisastraight-linerelationshipbetweenoutputvoltageandinputdisplacementfortheunloadedpotentiometer.

ItwouldseenthathighsensitivitycouldbeachievedsimplybyincreasingtheexcitationvoltageV.however,themaximumvalueofVisdeterminedbythemaximumpowerdissipationPofthefinewiresofthepotentiometerwindingandisgivenbyV=(PRt)1/2.

5.2ResistanceStrainGauges

Resistancestraingaugesaretransducerswhichexhibitachangeinelectricalresistanceinresponsetomechanicalstrain.Theymaybeofthebondedorunbondedvariety.

a)bondedstraingauges

Usinganadhesive,thesegaugesarebonded,orcemented,directlyontothesurfaceofthebodyorstructurewhichisbeingexamined.

Examplesofbondedgaugesare

i)

finewiregaugescementedtopaperbacking

ii)

photo-etchedgridsofconductingfoilonanepoxy-resinbacking

iii)asinglesemiconductorfilamentmountedonanepoxy-resinbackingwithcopperornickelleads.

Resistancegaugescanbemadeupassingleelementstomeasuringstraininonedirectiononly,oracombinationofelementssuchasrosetteswillpermitsimultaneousmeasurementsinmorethanonedirection.

b)unbondedstraingauges

Atypicalunbonded-strain-gaugearrangementshowsfineresistancewiresstretchedaroundsupportsinsuchawaythatthedeflectionofthecantileverspringsystemchangesthetensioninthewiresandthusalterstheresistanceofwire.Suchanarrangementmaybefoundincommerciallyavailableforce,load,orpressuretransducers.

5.3ResistanceTemperatureTransducers

Thematerialsforthesecanbedividedintotwomaingroups:

a)metalssuchasplatinum,copper,tungsten,andnickelwhichexhibitandincreaseinresistanceasthetemperaturerises;theyhaveapositivetemperaturecoefficientofresistance.

b)semiconductors,suchasthermistorswhichuseoxidesofmanganese,cobalt,chromium,ornickel.Theseexhibitlargenon-linearresistancechangeswithtemperaturevariationandnormallyhaveanegativetemperaturecoefficientofresistance.

c)metalresistancetemperaturetransducers

Thesedepend,formanypracticalpurposeandwithinanarrowtemperaturerange,upontherelationshipR1=R0*[1+a*(b1-b2)]whereacoefficientofresistancein℃-1,andR0resistanceinohmsatthereferencetemperatureb0=0℃atthereferencetemperaturerange℃.

Theinternationalpracticaltemperaturescaleisbasedontheplatinumresistancethermometer,whichcoversthetemperaturerange-259.35℃to630.5℃.

d)thermistorresistancetemperaturetransducers

Thermistorsaretemperature-sensitiveresistorswhichexhibitlargenon-linerresistancechangeswithtemperaturevariation.Ingeneral,theyhaveanegativetemperaturecoefficient.

Forsmalltemperatureincrementsthevariationinresistanceisreasonablylinear;but,iflargetemperaturechangesareexperienced,speciallinearizingtechniquesareusedinthemeasuringcircuitstoproducealinearrelationshipofresistance

againsttemperature.

Thermistorsarenormallymadeintheformofsemiconductordiscsenclosedinglassvitreousenamel.Sincetheycanbemadeassmallas1mm,quiterapidresponsetimesarepossible.

5.4PhotoconductiveCells

Thephotoconductivecell,usesalight-sensitivesemiconductormaterial.Theresistancebetweenthemetalelectrodesdecreaseastheintensityofthelightstrikingthesemiconductorincreases.Commonsemiconductormaterialsusedforphoto-conductivecellsarecadmiumsulphide,lead

sulphide,andcopper-dopedgermanium.

Theusefulrangeoffrequenciesisdeterminedbymaterialused.Cadmiumsulphideismainlysuitableforvisiblelight,whereasleadsulphidehasitspeakresponseintheinfra-redregionandis,therefore,mostsuitableforflame-failuredetectionandtemperaturemeasurement.

5.5PhotoemissiveCells

Whenlightstrikesthecathodeofthephotoemissivecellaregivensufficientenergytoarrivethecathode.Thepositiveanodeattractstheseelectrons,producingacurrentwhichflowsthroughresistorRandresultinginanoutputvoltageV.

PhotoelectricallygeneratedvoltageV=Ip.Rl

WhereIp=photoelectriccurrent(A),andphotoelectriccurrentIp=Kt.B

WhereKt=sensitivity(A/im),andB=illuminationinput(lumen)

Althoughtheoutputvoltagedoesgiveagoodindicationofthemagnitudeofillumination,thecellsaremoreoftenusedforcountingorcontrolpurpose,wherethelightstrikingthecathodecanbeinterrupted.

6.CapacitiveTransducers

Thecapacitancecanthusmadetovarybychangingeithertherelativepermittivity,theeffectivearea,orthedistanceseparatingtheplates.Thecharacteristiccurvesindicatethatvariationsofareaandrelativepermittivitygivealinearrelationshiponlyoverasmallrangeofspacings.Thusthesensitivityishighforsmallvaluesofd.

Unlikethepotentionmeter,thevariable-distancecapacitivetransducerhasaninfiniteresolutionmakingitmostsuitableformeasuringsmallincrementsofdisplacementorquantitieswhichmaybechangedtoproduceadisplacement.

7.InductiveTransducers

Theinductancecanthusbemadetovarybychangingthereluctanceoftheinductivecircuit.

Measuringtechniquesusedwithcapacitiveandinductivetransducers:

a)A.C.excitedbridgesusingdifferentialcapacitorsinductors.

b)A.C.potentiometercircuitsfordynamicmeasurements.

c)

D.C.circuitstogiveavoltageproportionaltovelocityforacapacitor.

d)

Frequency-modulationmethods,wherethechangeofCorLvariesthefrequencyofanoscillationcircuit.

Importantfeaturesofcapacitiveandinductivetransducersareasfollows:

i)resolutioninfinite

ii)

accuracy+-0.1%offullscaleisquoted

iii)displacementranges25*10-6mto10-3m

iv)

risetimelessthan50uspossible

Typicalmeasurandsaredisplacement,pressure,vibration,sound,andliquidlevel.

8.LinearVariable-differentialTtransformer

9.Piezo-electricTransducersSensorbasedonpiezoelectriceffect.Isaself-generatingandelectromechanicalconversiontypesensor.Itssensitiveelementismadeofpiezoelectricmaterials.Piezoelectricmaterialsafterthestresssurfacecharge.Thischargebyachargeamplifierandmeasuringcircuitandtransformimpedancebecomesproportionaltotheexternalpoweroutput.Piezoelectricsensorformeasuringforceandcantransformintonon-electricphysicalquantity.Ithastheadvantagesofwidefrequencyband,highsensitivity,highsignal-to-noiseratio,simplestructure,reliableoperationandlightweightetc..Drawbackisthatsomepiezoelectricmaterialsneedtobemoisture-proofmeasures,andtheoutputDCresponsedifference,needtoadoptthehighinputimpedanceofthecircuitorchargeamplifiertoovercomethisdefect.

10.ElectromagneticTransducers

11.ThermoelectricTransducersThermoelectricsensorisatemperatureconversiondeviceforthepowerchange.Itisthecharacteristicperformanceusingsomematerialorcomponentthatvarieswiththetemperatureofthemeasured.Forexample,convertedtotemperaturechangeresistancechange,thermoelectric,thermalexpansion,permeabilityandsoon,throughappropriatemeasurementcircuittoachievethepurposeofthetesttemperature.Thetemperaturechangeisconvertedtothermoelectricsensorpotentialcalledthermocouple;thethermoelectricsensortemperaturechangeresistancevalueiscalledthermalresistance.

12.PhotoelectricCellsPhotoelectrictube(phototube)basicphotoelectricconverterandphotoelectriceffectbasedon.Photoelectrictubecanmaketheopticalsignalsareconvertedintoelectricsignals.Thephotoelectrictubeisdividedintovacuumphototubeandgascelltwo.Thetypicalstructureofphotoelectrictubeisthesphericalglassshellispumpedintovacuum,includingonthehemisphericalsurfacecoatedwithalayerofphotoelectricmaterialascathode,thecenterplacedsmallsphericalorringshapedmetalastheanode.Iftheballisfilledwithalowpressureinertgasasgascell.Intheprocessofphotoelectronstotheanodeandthegasmolecularcollisionandthegasionization,canincreasethesensitivityofthephotoelectrictube.Isusedasthephotoelectriccathodemetalwithanalkalimetal,mercury,gold,silver,needtobesuitablefordifferentband.Photoelectrictubelowsensitivity,largevolume,easydamage,hasbeenreplacedbysolidoptoelectronicdevices.

中文譯文：傳感器的基礎(chǔ)知識傳感器是一種把被測量轉(zhuǎn)換為光的、機(jī)械的或者更平常的電信號的裝置。能量轉(zhuǎn)換的過程稱之為換能。按照轉(zhuǎn)換原理和測量形式對傳感器進(jìn)行分類。用來測量位移的電阻式傳感器被歸為電阻式位移傳感器。分類如壓力波紋管、壓力膜和壓力閥等。1、傳感器元件除特例外，大多數(shù)的傳感器都由敏感元件、轉(zhuǎn)換元件或控制元件組成。如振動膜、波紋管、應(yīng)力管和應(yīng)力環(huán)、低音管和懸臂都是敏感元件，它們對壓力和力作出響應(yīng)把物理量轉(zhuǎn)變成位移。然后位移可以改變電參數(shù)，如電壓、電阻、電容或者感應(yīng)系數(shù)。機(jī)械式和電子式元件合并形成機(jī)電式傳感設(shè)備或傳感器。這樣的組合可用來輸入能量信號。熱的，光的，磁的和化學(xué)的相互結(jié)合產(chǎn)生的熱電式、光電式、電磁式和電化學(xué)式傳感器。2、傳感器靈敏度通過校正測量系統(tǒng)獲得的被測物理量和傳感器輸出信號的關(guān)系叫做傳感器靈敏度K1，也就是K1=輸出信號增量/測量增量。實際中，傳感器的靈敏度是已知的，并且通過測量輸出信號，輸入量由下式?jīng)Q定，輸入量=輸出信號增量/K1。3、理想傳感器的特性

a）高保真性：傳感器輸出波形應(yīng)該真實可靠地再現(xiàn)被測量，并且失真很小。b）可測量最小的干擾，任何時候傳感器的出現(xiàn)不能改變被測量。c）尺寸：傳感器必須能正確地放在所需的地方。d）被測量和傳感器信號之間應(yīng)該有一個線性關(guān)系。e）傳感器對外部影響的靈敏度應(yīng)該小，例如壓力傳感器經(jīng)常受到外部振動和溫度的響。f）傳感器的固有頻率應(yīng)該避開被測量的頻率和諧波。4、電傳感器電傳感器具有許多理想特性。它們不僅實現(xiàn)遠(yuǎn)程測量和顯示，還能提供高靈敏度。電傳感器可分為兩大類。a）變參數(shù)型，包括：i）電阻式；ii）電容式；iii）自感應(yīng)式；

iv）互感應(yīng)式；這些傳感器的工作依靠外部電壓。

b）自激型，包括：電磁式、熱電式、光柵式、壓電式。

這些傳感器根據(jù)測量輸入值產(chǎn)生輸出電壓，而且這一過程是可逆的。比如，在一般情況下，壓電式傳感器可根據(jù)晶體材料的變形產(chǎn)生一個輸出電壓；但是，如果在材料上施加一個可變電壓，傳感器可以通過變形或與變電壓同頻率的振動來體現(xiàn)可逆效應(yīng)。5、電阻式傳感器

電阻式傳感器可以分為兩大類：

i）那些表現(xiàn)為大電阻變化的物理量可通過分壓方式進(jìn)行測量，電位器就屬于此類。

ii）那些表現(xiàn)為小電阻變化的物理量可通過橋電路方式進(jìn)行測量，這一類包括應(yīng)變儀和電阻溫度計。5.1電位器繞線式電位器由許多繞在非導(dǎo)體骨架的電阻絲以及滑行在線圈上的觸頭組成。結(jié)構(gòu)原理如圖，觸頭能夠轉(zhuǎn)動、直線式運(yùn)動或者兩運(yùn)動合成的螺旋式運(yùn)動。

如果測量設(shè)備的電阻比電位器的電阻大，那么電壓既可以是交流也可以是直流，且輸出電壓與輸入運(yùn)動成正比。

這樣的電位器存在著分辨率和電子噪聲的問題。分辨率是指傳感器能檢測到的最小的輸入增量，分辨率大小取決于線圈與滑動觸頭圍成的面積。因此，輸出電壓為觸頭從一端移到另一端時一系列階躍。

電子噪聲可以通過接觸電阻的振動、觸頭摩擦形成的機(jī)械磨損以及從敏感元件傳出的觸頭振動產(chǎn)生。另外，測得的運(yùn)動量可以通過慣性和電位器中移動元件的摩擦獲得較大的機(jī)械載荷。觸頭表面的磨損將電位器的壽命限制為多少轉(zhuǎn)。通常指的是生產(chǎn)商在說明書中提及的“壽命轉(zhuǎn)數(shù)”，一個典型值為20*1000000轉(zhuǎn)。

空載電位器電路的輸出電壓V0由下式?jīng)Q定：設(shè)電阻R1=xi/xt*Rt，其中xi為輸入位移，xt為最大可能位移，Rt為電位器的電阻。那么輸入電壓V0=V*R1/(R1+(Rt-R1))=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt上式表明，對于空載電位器輸出電壓和輸入位移呈直線關(guān)系。

通過提高激勵電壓V可以獲得高的靈敏度。但是，V的最大值由電位器線圈金屬絲的功率損耗P決定，即V=(PRt)1/2。

5.2電阻應(yīng)變儀

電阻應(yīng)變儀是由機(jī)械應(yīng)變產(chǎn)生電阻變化的傳感器。它們可以是耦合的或者非耦合的

a）耦合應(yīng)變儀

運(yùn)用黏合劑可將應(yīng)變儀與