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Engineeringtestingtechnology1Thiscourseisrelativelymorepractical,wehavelearnedthegeneralformofatestsystem.itconsistedof5parts,namely,theobjectbeingtested,detectionunit,theconversioncircuit,controlunits,outputunits.(We’vemainlylearnedhowafourimportantpartsofacontrolsystem.Theyarecontroller,actuator,sensor（传感器）andtransducer.(变送器))Themostimportantpartofthissystemisthedetectionunitandwelearnsomebasicknowledgeaboutsensor.sensor:Asensorisadevicethatmeasuresaphysicalquantityandconvertsitintoasignalwhichcanbereadbyanobserverorbyaninstrument.1,温度传感器主要有两种热电阻温度传感器（热敏电阻）和热电偶温度传感器热敏电阻利用电阻随温度变化的特点制成的传感器。主要使用半导体。半导体的电阻随温度升高而下降。特点：材料成本低，加工方便，但是使用时容易受环境温度影响。应用：空调的自动调温系统，当传感器检测到房间的温度低于设定温度时，空调控制器就会发送信号启动空调压缩机，制冷；当传感器检测到房间的温度达到设定的温度时，就会想空调控制器发送一个信号，告诉控制器“环境已达到设定温度”，这个时候，控制器就会发送信号停止压缩机的运行。Engineeringtestingtechnology2电饭煲的煮饭过程也是使用了这种温度传感器。Therearetwomajorthermalresistancetemperaturesensor(thermistor)andthermocoupletemperaturesensorThermistorResistancevarieswithtemperature.ThematerialofthissensorMainlyuseofsemiconductors.Theresistanceofthesemiconductordecreaseswithincreasingtemperature.Features:Lowcostofmaterials,processingconvenience,butwhenitused,itwillbesusceptibletoenvironmentaltemperature.Applications:airconditioningthermostatsystem,whenthesensordetectstheroom’stemperaturedropsbelowthesettemperature,theairconditioningcontrollerwillsendasignaltostartairconditioningcompressorsandstartrefrigerating;whenthesensordetectstheroom’stemperaturereachesthesettemperature,thecontrollerwillsendasignaltostoptheoperationofthecompressor.Ricecookercookingprocessisalsousingthistemperaturesensor.Athermocouple热电偶convertstemperaturetoanoutputvoltage电压whichcanbereadbyavoltmeter伏特计.1,Temperaturesensor:Ptresistor,thermistor(热敏电阻)。：Athermistorisatypeofresistorwithresistanceproportionaltoitstemperature.2，压力传感器Pressuresensor:画图解释isthedevicethatisabletodetectthepressurevalue,convertstheforcetotheelectricsignal,whichcanbebyavoltmeteroranammeter.Piezoresistive压阻pressuresensorisOneofcommonlyusedpressuresensor.Principle:利用某些物质的压电效应。某些物体例如石英，在受到压力的时候，内部会形成电场。这个电场的大小反映了它所受到Engineeringtestingtechnology3外力的大小。因此，我们可以使用这种材料做成压电式传感器，通过测量材料所产生的电场来间接测量力的大小。应用：在许多大型商场的扶手电梯中，一般都会有压力传感器的。这种传感器安装在电梯的踏板下，当有客人站上电梯时候，电梯就会加速到正常速度向上；当没有人乘坐电梯时，电梯以比较低的速度运行，从而节省了能量。这个就是压力传感器应用的例子。piezoelectric[pai,i:zəui'lektrik]transducer压电传感器Principle:Usingthepiezoelectriceffectofcertainsubstances.Someobjectssuchasquartz[kwɔ:ts]石英,Whenitisunderpressure,itwillformaninternalelectricfield.Thestrengthofthefieldreflectsthestrengthoftheforce.Therefore,wecanmakeuseofthismaterialtomakeapiezoelectricsensor,bymeasuringthestrengthoftheelectricfieldtoindirectlymeasurethestrengthoftheforce.Application:Inmanylargeshoppingmalls,escalators自动扶梯,ingeneral,willhaveapressuresensor.Thesensorinstalledinthepedal踏板oftheelevator,whenacustomersetfootonthestopsofelevatorandthentheelevatorwillacceleratetonormalspeed;whennoonetaketheelevator,theelevatorisrunningarelativelylowspeed.Byusingthepressuresensorcanhelptheelevatorsavingenergy.Thisisanexampleofpressuresensorapplication.3，红外线传感器。infraredtransducer利用红外线的物理性质来进行测量的传感器。任何物质，只要它本身具有一定的温度（高于绝对零度），都能辐射红外线。红外线传感器测量时不与被测物体直接接触，因而不存在摩擦，并且有灵敏度高，响应快等优点。应用；Engineeringtestingtechnology4许多自动门就是这个原理，当有人接近的时候，传感器检测到物体发射的红外线，于是就把这个信号送到控制电路，使自动门打开。3,theinfraredsensor.Infraredtransducerthesensorusingthephysicalpropertiesoftheinfraredrays/ultraredraystomeasure.Anysubstance,aslongasititselfhasacertaintemperature(aboveabsolutezero),canemitinfraredradiation.Whentheinfraredsensorwork,itwillnotindirectcontactwiththemeasuredobject,andthereforethereisnofriction,andhashighsensitivity,fastresponse,andsoon.Application;Manyautomaticdooristhisprinciple,thetimewhensomeoneclosetothedoor,thesensordetectsinfraredraysemittedbyobjects,soitwillsendthesignaltothecontrolcircuit,theautomaticdoorsopen.4，烟雾传感器smoketransducer将空气中的烟雾浓度变量转换成有一定对应关系的输出信号的装置。这种传感器广泛应用在防火的设施中，现在的大部分建筑类都会安装这种烟雾传感器。这是非常实用的。4,smokesensor/smoketransducerrelatetotheinnerionofthematerial.TheSmokeconcentrationintheairavariable,thisdevicecanconvertthisvariableintoaelectricsignalwhichcanbereadbythecircuit.Thesensorsarewidelyusedinfirepreventionfacilities,nowmostofthebuildingswillinstallthesmokesensor.Thisisveryuseful.位移传感器：displacementsensor正电荷Positivecharge负电荷Negativecharge电动势electromotiveforce电压voltage差动式DifferentialSensor感应ElectromagneticinductionEngineeringtestingtechnology5Capacitivepressuresensor:usesthechangeofcapacitanceduetochangeofthedistancebetweentheplatesofacapacitorbecauseofchangeinpressuretocalculatethepressure.(公式推导)（4）、Controller:isadevicewhichmonitorsandaffectstheoperationalconditionsofacontrolsystemandacontrolleristhecoreinstrumentofacontrolsystem.Specifically,acontrollercanoutputacontrolsignalbycomparingthemeasuringsignalfromatransducerandthesetpoint.Therearealsoinnumerableapplicationsforsensorsofwhichmostpeopleareneveraware.Applicationsincludecars,machines,aerospace,medicine,manufacturingandrobotics.Asensorisadevicewhichreceivesandrespondstoasignal.Asensor'ssensitivityindicateshowmuchthesensor'soutputchangeswhenthem