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6 background noise, 7 practical measurement – LumaSense Technologies MCS640 Manual User Manual

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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.