Appendix; Determination Of Emissivity; Typical Emissivity Values - RayTek RAYCMLTJM Operating Instructions Manual

10 Appendix

10.1 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 method. Next, measure the object's
temperature and adjust emissivity setting until the correct temperature
value is reached. This is the emissivity for the measured material.
2. For relatively low temperatures (up to 260℃, 500℉), place a plastic
sticker on the object to be measured. This sticker should be large enough
to cover the target spot. Next, measure the sticker's temperature using an
emissivity setting of 0.95. Finally, measure the temperature of an
adjacent area on the object and adjust the emissivity setting until the
same temperature is reached. This is the emissivity for the measured
material.
3. 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
emissivity for the measured material.

10.2 Typical Emissivity Values

The following table provides a brief reference guide for determining
emissivity and can be used when one of the above methods is not practical.
CM
Rev. B 06/2011
Appendix
36