自动化专业外文文献.docx

自动化专业外文文献.docx

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自动化专业外文文献

DevelopmentofSensorNewTechnology

Sensorisonekindcomponentwhichcantransformthephysicalquantity,chemistryquantityandthebiomassintoelectricalsignal.Theoutputsignalhasthedifferentformslikethevoltage,theelectriccurrent,thefrequency,thepulseandsoon,whichcansatisfythesignaltransmission,processing,recording,anddemonstrationandcontroldemands.Soitistheautomaticdetectionsystemandintheautomaticcontrolindustry.IfautomaticTechnologyisusedwider,thensensorismoreimportant.

Severalkeywordsofthesensor：

1SensorElements

Althoughthereareexception,mostsensorconsistofasensingelementandaconversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.Suchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesorsensor.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicalsensorrespectively.

2SensorSensitivity

TherelationshipbetweenthemeasuredandthesensoroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthesensorsensitivityK1=output-signalincrement/measuredincrement.Inpractice,thesensorsensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=output-signalincrement/K1.

3CharacteristicsofanIdealSensor

Thehighsensorshouldexhibitthefollowingcharacteristics.

（a）highfidelity-thesensoroutputwaveformshapebeafaithfulreproductionofthemeasured;thereshouldbeminimumdistortion.

（b）Thereshouldbeminimuminterferencewiththequantitybeingmeasured;thepresenceofthesensorshouldnotalterthemeasuredinanyway.

（c）Size.Thesensormustbecapableofbeingplacedexactlywhereitisneeded.

（d）Thereshouldbealinearrelationshipbetweenthemeasuredandthesensorsignal.

（e）Thesensorshouldhaveminimumsensitivitytoexternaleffects,pressuresensor,forexample,areoftensubjectedtoexternaleffectssuchvibrationandtemperature.

（f）Thenaturalfrequencyofthesensorshouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.

Sensorscanbedividedintothefollowingcategories：

1ElectricalSensor

Electricalsensorexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindicationormesdurement.

Electricalsensorcanbedividedintotwodistinctgroups:

（a）variable-control-parametertypes,whichinclude:

（i）resistance

（ii）capacitance

（iii）inductance

（iv）mutual-inductancetypes

Thesesensorallrelyonexternalexcitationvoltagefortheiroperation.

（b）self-generatingtypes,whichinclude

（i）electromagnetic

（ii）thermoelectric

（iii）photoemissive

（iv）piezo-electrictypes

Theseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinputandtheireffectsarereversible.Forexample,apiezo-electricsensornormallyproducesanoutputvoltageinresponsetothedeformationofacrystallinematerial;however,ifanalternatingvoltageisappliedacrossthematerial,thesensorexhibitsthereversibleeffectbydeformingorvibratingatthefrequencyofthealternatingvoltage.

2ResistanceSensor

Resistancesensormaybedividedintotwogroups,asfollows:

（i）Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.

（ii）Thosewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.

3CapacitiveSensor

Thecapacitancecanthusmadetovarybychangingeithertherelativepermittivity,theeffectivearea,orthedistanceseparatingtheplates.Thecharacteristiccurvesindicatethatvariationsofareaandrelativepermittivitygivealinearrelationshiponlyoverasmallrangeofspacings.Thusthesensitivityishighforsmallvaluesofd.  Unlikethepotentionmeter,thevariable-distancecapacitivesensorhasaninfiniteresolutionmakingitmostsuitableformeasuringsmallincrementsofdisplacementorquantitieswhichmaybechangedtoproduceadisplacement.

4InductiveSensor

Theinductancecanthusbemadetovarybychangingthereluctanceoftheinductivecircuit.

Measuringtechniquesusedwithcapacitiveandinductivesensor:

（a）A.C.excitedbridgesusingdifferentialcapacitorsinductors.

（b）A.C.potentiometercircuitsfordynamicmeasurements.

（c）D.C.circuitstogiveavoltageproportionaltovelocityforacapacito