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MCL640 Manual Principles of Thermal Imaging
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15. 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.)
16. Comparison with blackbody surface — Option 2
17. 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.
5.6 Background Noise
When measuring the temperature of an object by a radiation thermometer, it is important to
take into consideration the above-mentioned emissivity correction as well as the environmental
conditions where the measurements will be performed.
Infrared rays enter the thermal imager from the measuring object as well as all other objects
nearby. Therefore, in order to avoid this influence, a function of environment reflection
correction, etc. is required. Also, when accurate data is required, it is necessary to minimize the
influence by shortening the transmission route of the infrared ray, for example.
Note:
For low temperatures, masking tape or cornstarch can be used.
The following methods may be useful to reduce background noise.
18. Shorten the distance between the measured object and of the thermal imager. Please
keep a safe distance to protect the operator as well as the instrument.
19. Have no high temperature object behind the measured object, such as the sun shining
on the back of the measured object.
20. Do not allow direct sunlight to strike thermal imager.
21. Do not allow obstacles such as dust or vapor (which attenuates the infrared signal)
between the measured object and the thermal imager.
5.7 Practical Measurement
There are a number of methods for correcting emissivity in order to obtain the true
temperature. The correction procedure with each method will be explained next.
Note:
If you already know the emissivity, you can make thermal imaging
measurements immediately.