LumaSense Technologies M67 - Manual (Page 14)

M67, M67S Manual
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6.3 Background radiation influence
It is assumed that 98% of the area seen by the INFRADUCER corresponds to the target at the stated minimum target diameter.
The remaining 2% is assumed to be background. To eliminate the possibility of any background radiation entering the
INFRADUCER, the diameter of the target should be at least 50% greater than the minimum target diameter. This requirement
may be of great significance if the background radiation is from a much hotter source than the target, so that the 2% background
area seen by the INFRADUCER produces a highly disproportionate fraction of the total energy received, and thus thoroughly
corrupts the temperature measurement.
6.4 Reflections
The 0,.521 INFRADUCER is designed to focus thermal radiation coming from the target. However, it is possible that
radiation from other hot objects located nearby may be reflected by surfaces which are at such angle that the reflected energy it
enters the instrument and reaches the infrared detector. Such reflections are obviously a source of errors in INFRADUCER
temperature readings and must be eliminated by shields.
It is easy to test whether or not the INFRADUCER is receiving reflection from nearby hot sources. This is done by shielding the
reflection path from any such objects temporarily while monitoring the indicated temperature. If shielding causes the
temperature indicated to decrease, then reflection do exist and a permanent shield must be installed. Long sight tubes are very
effective shields.
Infrared radiation shields such as sight tubes must be installed with care to ensure that the instrument's field of view is not
partially obstructed. /XPD6HQVH supplies sight tubes designed to avoid reflections effectively. See Section 14, page 43.
To explain how reflections may cause erroneous readings, and to demonstrate the methods by which such problems can be
eliminated, refer to Figure 7 through Figure 11.
Figure 5 - Example Of Infraducer Placement To Avoid Interference From Cold Objects Located In Front Of Target