6 background noise, 7 practical measurement – LumaSense Technologies MCS640 Manual User Manual
Page 21
17
Section 4
Principles of Thermal Imaging
4.6 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.
2. Have no high temperature object behind the measured object, such as the sun shin-
ing on the back of the measured object.
3. Do not allow direct sunlight to strike thermal imager.
4. Do not allow obstacles such as dust or vapor (which attenuates the infrared signal)
between the measured object and the thermal imager.
4.7 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.
1. Method of comparison or direct measurement with emissivity equal to
approximately 1.0
a) Stabilize the temperature of the measured object or similar
material.
b) Open a very small hole (hereafter called blackbody part) in the object which
the thermal imager must measure as to satisfy
blackbody conditions.
c) Then set the emissivity correcting function of thermal imager so that the
temperature of the blackbody part and the measured surface will be the
same. The obtained emissivity will be the emissivity of the measured sur-
face.
d) Thereafter when measuring the same type object, it is unnecessary to
change the emissivity setting.
2. Method of direct measurement of emissivity
If a hole cannot be made as in method 1, then apply black high emissivity paint
and carry out the same procedures to obtain the emissivity. Since the black paint
will not provide a perfect blackbody, first set the emissivity of the black paint
and then measure the
temperature.
Note:
For low tempera-
tures, masking tape
or cornstarch can be
used.
Note:
If you already know the
emissivity, you can make
thermal imaging measure-
ments immediately.