Extech Instruments IRT25 - Measurement Techniques; Distance to Spot Ratio; Emissivity

EXTECHINSTRUMENTS
6IRT25‐en‐GB_V1.02/17
LocatingHotorColdSpots
Todetectahotorcoldspot,aimthethermometerataregionbeyondthetargetandthenscan
theentireregioninaslow,up/downmotion.
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DistancetoSpotRatio(FieldofView)
Themeter’s fieldof view is12:1(distance to spotratio). For example,ifthemeter is 24inches
fromthetarget(spot),thediameterofthetargetmustbeatleast2inches.Otherdistancesare
shownbelowinthefieldofviewdiagram.
Notethatmeasurementsshouldnormallybe
madecloserthan2feetfromthetarget.Themeter
canmeasurefromfurther distances but the measurementmaybeaffectedbyexternalsources
oflight.Inaddition,thespotsizemaybesolargethatitencompassessurfaceareasnotintended
tobemeasured.
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Itisnecessary to ensurethatthe size ofthe target islarger thanthespot size. Thesmaller the
target,thecloserthedistanceshouldbe.Seetheaccompanyingdiagram.
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Emissivity
Emissivityrepresents the energy reflectivity ofa material. Mostorganicmaterialsand painted
oroxidizedsurfaceshaveanemissivity ofapproximately0.95. If possible, masking tape or flat
blackpaintshouldbeappliedtocoverthemeasuredsurface.
Waitaperiodoftimetoallowthetapeorpainttoreach
thermalequilibriumwiththesurface
ofthecoveredobject.Measurethetemperatureofthesurfacecoveredwithtapeorpaintonly
afterequilibriumhasbeenachieved.