5
Infrared Thermometer
5.3 Emissivity
Depending on the nature of the material which is to be scanned, different levels
of energy will be encountered (emissivity). However, most organic and painted or
oxidised surfaces have an emissivity of 0.95. To overcome any problems with
polished or mirrored surfaces, they should be covered in masking tape or matt
black paint before scanning. Allow time for the tape or paint to attain the same
temperature as the target object before scanning.
5.4 Hot Spots
In order to locate a hot spot, aim the thermometer away from the target, before
scanning across the target in an up and down motion, keeping the trigger
depressed until the hot spot is located (See Fig. 4).
5.5 D:S Ratio (Field of View)
The D : S Ratio (Distance to Spot size) or Field Of View is 12 : 1 (See Fig. 5). This
ratio indicates that when the target object is 300mm (12") away from the
thermometer, then the target object should be at least 25mm (1"). In general, it is
good practice to ensure
that the target is larger
than the spot size. The
smaller the spot size,
t h e c l o s e r t h e
thermometer should be
to the target object. For
increased accuracy, the
target should be twice
the size of the spot size.
Fig 5.
Target Area
Keep trigger depressed
while scanning in an up
and down motion.
Fig 4.
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