Extech Instruments IR255 User Manual page 6

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.
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 600mm
from the target (spot), the diameter of the target must be at least 50mm. Other distances are
shown below in the field of view diagram.
Note that measurements should normally be made closer than 1200mm 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.
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.
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.
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EXTECH INSTRUMENTS
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