LumaSense Technologies BoilerSpection-SD - Manual (Page 48)

BoilerSpection HD/SD Manual Principles of Thermal Imaging 48
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:
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.
Note: For low temperatures, masking tape or cornstarch can be used.
6.6 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.
The following methods may be useful to reduce background noise.
1. 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.
EK : energy of blackbody-type source
ES: energy of measured object
X: emissivity of measured object