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DevelopmentofSensorNewTechnologySensorisonekindcomponentwhichcantransformthephysicalquantity,chemistryquantityandthebiomassintoelectricalsignal.Theoutputsignalhasthedifferentformslikethevoltage,theelectriccurrent,thefrequency,thepulseandsoon,whichcansatisfythesignaltransmission,processing,recording,anddemonstrationandcontroldemands.Soitistheautomaticdetectionsystemandintheautomaticcontrolindustry.IfautomaticTechnologyisusedwider,thensensorismoreimportant.Severalkeywordsofthesensor：1SensorElementsAlthoughthereareexception,mostsensorconsistofasensingelementandaconversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.Suchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesorsensor.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicalsensorrespectively.2SensorSensitivityTherelationshipbetweenthemeasuredandthesensoroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthesensorsensitivityK1=output-signalincrement/measuredincrement.Inpractice,thesensorsensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=output-signalincrement/K1.3CharacteristicsofanIdealSensorThehighsensorshouldexhibitthefollowingcharacteristics.(a)highfidelity-thesensoroutputwaveformshapebeafaithfulreproductionofthemeasured;thereshouldbeminimumdistortion.(b)Thereshouldbeminimuminterferencewiththequantitybeingmeasured;thepresenceofthesensorshouldnotalterthemeasuredinanyway.(c)Size.Thesensormustbecapableofbeingplacedexactlywhereitisneeded.(d)Thereshouldbealinearrelationshipbetweenthemeasuredandthesensorsignal.(e)Thesensorshouldhaveminimumsensitivitytoexternaleffects,pressuresensor,forexample,areoftensubjectedtoexternaleffectssuchvibrationandtemperature.(f)Thenaturalfrequencyofthesensorshouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.Sensorscanbedividedintothefollowingcategories：1ElectricalSensorElectricalsensorexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindicationormesdurement.Electricalsensorcanbedividedintotwodistinctgroups:(a)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.2ResistanceSensorResistancesensormaybedividedintotwogroups,asfollows:(i)Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.(ii)Thosewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.3CapacitiveSensorThecapacitancecanthusmadetovarybychangingeithertherelativepermittivity,theeffectivearea,orthedistanceseparatingtheplates.Thecharacteristiccurvesindicatethatvariationsofareaandrelativepermittivitygivealinearrelationshiponlyoverasmallrangeofspacings.Thusthesensitivityishighforsmallvaluesofd.??Unlikethepotentionmeter,thevariable-distancecapacitivesensorhasaninfiniteresolutionmakingitmostsuitableformeasuringsmallincrementsofdisplacementorquantitieswhichmaybechangedtoproduceadisplacement.4InductiveSensorTheinductancecanthusbemadetovarybychangingthereluctanceoftheinductivecircuit.Measuringtechniquesusedwithcapacitiveandinductivesensor:(a)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*10-6mto10-3m(iv)risetimelessthan50uspossibleTypicalmeasurandsaredisplacement,pressure,vibration,sound,andliquidlevel.5LinearVariable-differentialTtransformer6Piezo-electricSensor7ElectromagneticSensor8ThermoelectricSensor9PhotoelectricCells10MechanicalSensorandSensingElementsIninformationage,theinformationindustryincludesinformationgathering,transmission,processthreeparts,namelysensortechnology,communication,computertechnology.Becauseofultralargescaleintegratedcircuit’srapiddevelopmentafterhavingbeendevel