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Appendix
compensate for this by offering variable options for setting the emissivity factor.
(See also Fig. 5).
Fig. 5 Specific radiation at various emississivity
11.3.1 Handling the pyrometer
Distance to spot size ratio
Distance to spot ratio (or field of view) refers to the diameter of the spot that the
probe is sensing at a given distance. The closer you are to the object (or target),
the smaller the area (or spot) the probe is sensing. For example when the probe
is held at a 200 mm (8 in.) distance from the target, the spot size is approximately
50 mm (2 in.); at 100 mm (4 in.) the spot size is approximately 25 mm (1 in.), and
with the probe held at 50 mm (2 in.) distance from the target, the spot size is
approximately 13 mm (½ in.).
Hot spots can be missed if too large an area is included in the field of view, so
get as close as possible! (See Fig. 6 and Fig. 7).
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