Apositionsensorisasensorthatdetectsanobject'sposition.Apositionsensormayindicatetheabsolutepositionoftheobject(itslocation)oritsrelativeposition(displacement)intermsoflineartravel,rotationalangleorthree-dimensionalspace.Differentfromthedisplacementsensor,thepositionsensorhastwotypes:contacttypeandproximitytype.Thecontactsofthecontactsensoraremovedbythecontactandextrusionoftwoobjects,andthecommononesarethetravelswitchandthetwo-dimensionalmatrixpositionsensor.Thetravelswitchhassimplestructure,reliableactionandlowprice.Whenanobjectisinmotionandencountersthetravelswitch,itsinternalcontactswillacttocompletethecontrol.Forexample,iftravelswitchesareinstalledatbothendsoftheX,Y,andZaxesofthemachiningcenter,themovementrangecanbecontrolled.Thetwo-dimensionalmatrixpositionsensorisinstalledontheinsideoftheroboticpalmtodetectthecontactpositionbetweenitselfandanobject.Proximityswitchreferstoaswitchthatcansendan"action"signalwhenanobjectisclosetoasetdistance,anditdoesnotneedtobeindirectcontactwiththeobject.Therearemanytypesofproximityswitches,mainlyelectromagnetictype,photoelectrictype,differentialtransformertype,eddycurrenttype,capacitivetype,reedswitch,Halltype,etc.TheapplicationsofproximityswitchesonCNCmachinetoolsaremainlytoolresttoolselectioncontrol,tabletravelcontrol,oilcylinderandcylinderpistontravelcontrol,etc.Also,therearepotentiometerpositionsensor,Lvdtpositionsensorandsoon.


Potentiometer,acommonelectromechanicalcomponent,iswidelyusedinvariouselectricalandelectronicequipment.Apotentiometersensorisasensorthatconvertsmechanicaldisplacementthroughapotentiometerintoaresistanceorvoltageoutputthatisafunctionofit.Accordingtotheirdifferentstructuralforms,theycanbedividedintowire-woundtype,thin-filmtypeandphotoelectrictype.Accordingtothecharacteristicsofinputandoutput,itcanbedividedintolinearpotentiometersensorandnonlinearpotentiometersensor.Mostcommonlyusedsingle-turnwire-woundpotentiometers.Potentiometer-typeresistancesensorsaregenerallycomposedofresistanceelements,skeletonsandbrushes.Themovementofthebrushesrelativetotheresistiveelementcanbelinear,rotationalorhelical.Whenthemeasuredchanges,thebrushcontactsmoveontheresistiveelement,andtheresistancevaluebetweenthecontactandtheresistiveelementwillchange,andthelinearconversionbetweenthedisplacementandtheresistancecanberealized.Theresistivesensorisakindofelectricalparametersensorthathasbeenusedearlier.Ithasawidevarietyofapplicationsandiswidelyused.Aftermeasuringthecircuit,thechangesbeingmeasuredarereflected.Thepotentiometricsensorhasasimplestructure,goodlinearityandstability,andcanformaforcemeasurement,pressuremeasurement,weighing,displacementmeasurement,accelerationmeasurement,torquemeasurement,temperaturemeasurementandotherdetectionsystemswiththecorrespondingmeasurementcircuit.Ithasbecomeoneoftheindispensablemeansofproductionprocessdetectionandrealizationofproductionautomation.


Alinearscale,alsocalledabarscale,scalebar,graphicscale,orgraphicalscale,isameansofvisuallyshowingthescaleofamap,nauticalchart,engineeringdrawing,orarchitecturaldrawing.Ascalebariscommonelementofmaplayouts.Onlargescalemapsandcharts,thosecoveringasmallarea,andengineeringandarchitecturaldrawings,thelinearscalecanbeverysimple,alinemarkedatintervalstoshowthedistanceontheearthorobjectwhichthedistanceonthescalerepresents.Apersonusingthemapcanuseapairofdividers(or,lessprecisely,twofingers)tomeasureadistancebycomparingittothelinearscale.Thelengthofthelineonthelinearscaleisequaltothedistancerepresentedontheearthmultipliedbythemaporchart'sscale.Inmostprojections,scalevarieswithlatitude,soonsmallscalemaps,coveringlargeareasandawiderangeoflatitudes,thelinearscalemustshowthescalefortherangeoflatitudescoveredbythemap.Whilelinearscalesareusedonarchitecturalandengineeringdrawings,particularlythosethataredrawnafterthesubjecthasbeenbuilt,manysuchdrawingsdonothavealinearscaleandaremarked"DoNotScaleDrawing"inrecognitionofthefactthatpapersizechangeswithenvironmentalchangesandonlydimensionsthatarespecificallyshownonthedrawingcanbeusedreliablyinprecisemanufacturing.


Athermometerisadevicethatmeasurestemperatureoratemperaturegradient(thedegreeofhotnessorcoldnessofanobject).Athermometerhastwoimportantelements:(1)atemperaturesensor(e.g.thebulbofamercury-in-glassthermometerorthepyrometricsensorinaninfraredthermometer)inwhichsomechangeoccurswithachangeintemperature;and(2)somemeansofconvertingthischangeintoanumericalvalue(e.g.thevisiblescalethatismarkedonamercury-in-glassthermometerorthedigitalreadoutonaninfraredmodel).Thermometersarewidelyusedintechnologyandindustrytomonitorprocesses,inmeteorology,inmedicine,andinscientificresearch.Thermometersutilizearangeofphysicaleffectstomeasuretemperature.Temperaturesensorsareusedinawidevarietyofscientificandengineeringapplications,especiallymeasurementsystems.Temperaturesystemsareprimarilyeitherelectricalormechanical,occasionallyinseparablefromthesystemwhichtheycontrol(asinthecaseofamercury-in-glassthermometer).Thermometersareusedinroadwaysincoldweatherclimatestohelpdetermineificingconditionsexist.Indoors,thermistorsareusedinclimatecontrolsystemssuchasairconditioners,freezers,heaters,refrigerators,andwaterheaters.Galileothermometersareusedtomeasureindoorairtemperature,duetotheirlimitedmeasurementrange.


Pressuremeasurementistheanalysisofanappliedforcebyafluid(liquidorgas)onasurface.Pressureistypicallymeasuredinunitsofforceperunitofsurfacearea.Manytechniqueshavebeendevelopedforthemeasurementofpressureandvacuum.Instrumentsusedtomeasureanddisplaypressureinanintegralunitarecalledpressuremetersorpressuregaugesorvacuumgauges.Amanometerisagoodexample,asitusesthesurfaceareaandweightofacolumnofliquidtobothmeasureandindicatepressure.Likewise,thewidelyusedBourdongaugeisamechanicaldevice,whichbothmeasuresandindicatesandisprobablythebestknowntypeofgauge.Avacuumgaugeisapressuregaugeusedtomeasurepressureslowerthantheambientatmosphericpressure,whichissetasthezeropoint,innegativevalues(forinstance,?15psigor?760mmHgequalstotalvacuum).Mostgaugesmeasurepressurerelativetoatmosphericpressureasthezeropoint,sothisformofreadingissimplyreferredtoas"gaugepressure".However,anythinggreaterthantotalvacuumistechnicallyaformofpressure.Forveryaccuratereadings,especiallyatverylowpressures,agaugethatusestotalvacuumasthezeropointmaybeused,givingpressurereadingsinanabsolutescale.


Apressuresensorisadeviceforpressuremeasurementofgasesorliquids.Pressureisanexpressionoftheforcerequiredtostopafluidfromexpanding,andisusuallystatedintermsofforceperunitarea.Apressuresensorusuallyactsasatransducer;itgeneratesasignalasafunctionofthepressureimposed.Forthepurposesofthisarticle,suchasignaliselectrical.Pressuresensorsareusedforcontrolandmonitoringinthousandsofeverydayapplications.Pressuresensorscanalsobeusedtoindirectlymeasureothervariablessuchasfluid/gasflow,speed,waterlevel,andaltitude.Pressuresensorscanalternativelybecalledpressuretransducers,pressuretransmitters,pressuresenders,pressureindicators,piezometersandmanometers,amongothernames.