FAG Detector III User Manual page 286

Emissivity
All objects emit invisible infrared energy. The amount of energy emitted is
proportional to the object's temperature and its ability to emit IR energy. This
ability, called emissivity, is base upon the material that the object is made of and
its surface finish. Emissivity values range from 0.10 for a very refective object to
1.00 for a black body. The probe senses this energy and calculates the
temperature base on the amount of IR energy it receives and the factory set
emissivity value of 0.95, which will cover 90% of typical applications.
Measurement considerations
If the surface to measured is small [13 mm (½ in.) or less], hold the probe as
close as possible to the surface [no more than 50 mm (2 in.) away].
If the surface to be measured is covered by frost or other material, clean it to
expose the surface.
If the surface to be measured is highly refective, apply masking tape or a matte
finish black paint to the surface.
If the probe seems to be giving incorrect readings check the front of the probe.
There may be condensation or debris obstructing the sensor; clean according
to maintenance instructions.
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Fig. 6 Spot size
Fig. 7 Size of the measuring object