LumaSense Technologies MCS640 Manual - Manual (Page 20)

16
Section 4 Principles of Thermal Imaging
Therefore, in order to perform correct measurement for true temperature, the emissivity is
determined as follows:
1. By means of a printed table
Various books and literature carry physical constants tables, but if the measuring
condition is not identical, the constants may not usable. In such cases the literature
should be used only for reference.
2. Determination by ratio — Option 1
A contact-type thermometer is used to confirm that the measured object is in
thermal equilibrium and that the blackbody-type source is at the same temperature.
The object and the blackbody-type source are then measured with the radiation
thermometer and the resulting energy ratio is then used to define the emissivity as
follows:
EK : energy of blackbody-type source
ES: energy of measured object
X: emissivity of measured object
Where, EK : ES = 1 : X
3. Determination by ratio — Option 2
An object, resembling a blackbody, is attached to a heat source to make the
temperature of the blackbody part and the measuring object the same. The ratio of
infrared radiation energies are then determined as in #2 above.
4. Comparison with blackbody surface — Option 1
A very small hole is made in the measured object to satisfy the aforementioned
blackbody conditions, and to make the temperature of the entire object uniform.
Then, using the emissivity correcting function of thermal imager, the emissivity is
reduced until the temperature of the point to be measured equals the temperature
of the small hole measured at an emissivity of 1. The emissivity setting should be
the emissivity of the object. (This applies only when the conditions are the same as
at measurement.)
5. Comparison with blackbody surface — Option 2
If a small hole cannot be made in the object, then the emissivity can be obtained
by applying black paint to the object and reaching a thermal equilibrium through
similar procedures. But since the painted object will not provide a complete
blackbody, the emissivity of the painted object needs to be set first and then the
temperature can be measured. The following figure shows examples of blackbody
paint.
examples of Blackbody paint