RayTek 54301 - Manual (Page 88)

Appendix
12 Appendix
12.1 Determination of Emissivity
Emissivity is a measure of an object’s ability to absorb and emit
infrared energy. It can have a value between 0 and 1.0. For example a
mirror has an emissivity of < 0.1, while the so‐called “Blackbody“
reaches an emissivity value of 1.0. If a higher than actual emissivity
value is set, the output will read low, provided the target
temperature is above its ambient temperature. For example, if you
have set 0.95 and the actual emissivity is 0.9, the temperature reading
will be lower than the true temperature.
An object’s emissivity can be determined by one of the following
methods:
1. Determine the actual temperature of the material using an RTD
(PT100), a thermocouple, or any other suitable contact
temperature method. Next, measure the object’s temperature
and adjust emissivity setting until the correct temperature
value is reached. This is the correct emissivity for the measured
material.
2. If possible, apply flat black paint to a portion of the surface of
the object. The emissivity of the paint must be above 0.98. Next,
measure the temperature of the painted area using an
emissivity setting of 0.98. Finally, measure the temperature of
an adjacent area on the object and adjust the emissivity until
the same temperature is reached. This is the correct emissivity
for the measured material.
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