自动化专业外文文献.docx

DevelopmentofSensorNewTechnologySensorisonekindcomponentwhichcantransformthephysicalquantity,chemistryquantityandthebiomassintoelectricalsignal.Theoutputsignalhasthedifferentformslikethevoltage,theelectriccurrent,thefrequency,thepulseandsoon,whichcansatisfythesignaltransmission,processing,recording,anddemonstrationandcontroldemands.Soitistheautomaticdetectionsystemandintheautomaticcontrolindustry.IfautomaticTechnologyisusedwider,thensensorismoreimportant.Severalkeywordsofthesensor：1 SensorElementsAlthoughthereareexception,mostsensorconsistofasensingelementandaconversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.Suchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesorsensor.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicalsensorrespectively.2 SensorSensitivityTherelationshipbetweenthemeasuredandthesensoroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthesensorsensitivityKl=output-signalincrement/measuredincrement.Inpractice,thesensorsensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=output-signalincrement/Kl.3 CharacteristicsofanIdealSensorThehighsensorshouldexhibitthefollowingcharacteristics.（八）highfidelity-thesensoroutputwaveformshapebeafaithfulreproductionofthemeasured;thereshouldbeminimumdistortion.(b)Thereshouldbeminimuminterferencewiththequantitybeingmeasured;thepresenceofthesensorshouldnotalterthemeasuredinanyway.(c)Size.Thesensormustbecapableofbeingplacedexactlywhereitisneeded.(d)Thereshouldbealinearrelationshipbetweenthemeasuredandthesensorsignal.(e)Thesensorshouldhaveminimumsensitivitytoexternaleffects,pressuresensor,forexample,areoftensubjectedtoexternaleffectssuchvibrationandtemperature.(f)Thenaturalfrequencyofthesensorshouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.Sensorscanbedividedintothefollowingcategories：1 ElectricalSensorElectricalsensorexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindicationormesdurement.Electricalsensorcanbedividedintotwodistinctgroups:（八）variable-control-parametertypes,whichinclude:(i)resistance(ii)capacitance(iii)inductance(iv)mutual-inductancetypesThesesensorallrelyonexternalexcitationvoltagefortheiroperation.(b)self-generatingtypes,whichinclude(i)electromagnetic(ii)thermoelectric(iii)photoemissive(iv)piezo-electrictypesTheseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinputandtheireffectsarereversible.Forexample,apiezo-electricsensornormallyproducesanoutputvoltageinresponsetothedeformationofacrystallinematerial;however,ifanalternatingvoltageisappliedacrossthematerial,thesensorexhibitsthereversibleeffectbydeformingorvibratingatthefrequencyofthealternatingvoltage.2 ResistanceSensorResistancesensormaybedividedintotwogroups,asfollows:(i)Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.(ii)Thosewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.3 CapacitiveSensorThecapacitancecanthusmadetovarybychangingeithertherelativepermittivity,theeffectivearea,orthedistanceseparatingtheplates.Thecharacteristiccurvesindicatethatvariationsofareaandrelativepermittivitygivealinearrelationshiponlyoverasmallrangeofspacings.Thusthesensitivityishighforsmallvaluesofd.Unlikethepotentionmeter,thevariable-distancecapacitivesensorhasaninfiniteresolutionmakingitmostsuitableformeasuringsmallincrementsofdisplacementorquantitieswhichmaybechangedtoproduceadisplacement.4 InductiveSensorTheinductancecanthusbemadetovarybychangingthereluctanceoftheinductivecircuit.Measuringtechniquesusedwithcapacitiveandinductivesensor:（八）A.C.excitedbridgesusingdifferentialcapacitorsinductors.(b)A.C.potentiometercircuitsfordynamicmeasurements.(c)D.C.circuitstogiveavoltageproportionaltovelocityforacapacitor.(d)Frequency-modulationmethods,wherethechangeofCorLvariesthefrequencyofanoscillationcircuit.Importantfeaturesofcapacitiveandinductivesensorareasfollows:(i)resolutioninfinite(ii)accuracy±0.1%offullscaleisquoted(iii)displacementranges25*104mto10-3m(iv)risetimelessthan50uspossibleTypicalmeasurandsaredisplacement,pressure,vibration,sound,andliquidlevel.5 LinearVariable-differentialTtransformer6 Piezo-electricSensor7 ElectromagneticSensor8 ThermoelectricSensor9 PhotoelectricCells10 MechanicalSensorandSensingElementsIninformationage,theinformationindustryincludesinformationgathering,transmission,processthreeparts,namelysensortechnology,co