SensortechnologyAsensorisadevicewhichproducesasignalinresponsetoitsdetectingormeasuringaproperty,suchasposition,force,torque,pressure,temperature,humidity,speed,acceleration,orvibration.Traditionally,sensors(suchasactuatorsandswitches)havebeenusedtosetlimitsontheperformanceofmachines.Commonexamplesare(a)stopsonmachinetoolstorestrictworktablemovements,(b)pressureandtemperaturegageswithautomaticsshut-offfeatures,and(c)governorsonenginestopreventexcessivespeedofoperation.Sensortechnologyhasbecomeanimportantaspectofmanufacturingprocessesandsystems.Itisessentialforproperdataacquisitionandforthemonitoring,communication,andcomputercontrolofmachinesandsystems.Becausetheyconvertonequantitytoanother,sensorsoftenarereferredtoastransducers.Analogsensorsproduceasignal,suchasvoltage,whichisproportionaltothemeasuredquantity.Digitalsensorshavenumericordigitaloutputsthatcanbetransferredtocomputersdirectly.Analog-to-coverter(ADC)isavailableforinterfacinganalogsensorswithcomputers.ClassificationsofSensorsSensorsthatareofinterestinmanufacturingmaybeclassifiedgenerallyasfollows:Machanicalsensorsmeasuresuchasquantitiesaspositions,shape,velocity,force,torque,pressure,vibration,strain,andmass.Electricalsensorsmeasurevoltage,current,charge,andconductivity.Magneticsensorsmeasuremagneticfield,flux,andpermeablity.Thermalsensorsmeasuretemperature,flux,conductivity,andspecialheat.Othertypesareacoustic,ultrasonic,chemical,optical,radiation,laser,andfiber-optic.Dependingonitsapplication,asensormayconsistofmetallic,nonmetallic,organic,orinorganicmaterials,aswellasfluids,gases,plasmas,orsemiconductors.Usingthespecialcharacteristicsofthesematerials,sensorscovertthequantityorpropertymeasuredtoanalogordigitaloutput.Theoperationofanordinarymercurythermometer,forexample,isbasedonthedifferencebetweenthethermalexpansionofmercuryandthatofglass.Similarly,amachinepart,aphysicalobstruction,orbarrierinaspacecanbedetectedbybreakingthebeamoflightwhensensedbyaphotoelectriccell.Apr