MCS640 Thermal Imager Manual
Principle of Thermal Imaging
•
35
1.
Method of comparison or direct measurement with emissivity equal to approximately 1.0
1. Stabilize the temperature of the measured object or similar material.
2. Open a very small hole (hereafter called blackbody part) in the object which the thermal imager
must measure as to satisfy blackbody conditions.
3. 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 surface.
4. 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.
3.
Indirect measurement
Measure a sample similar to the measured object, and place it in a condition able to be heated by a
heater, etc. Then measure the object and the sample alternately with the camera and when the
indicated values are identical, measure the sample with a contact-type thermometer. Adjust the
emissivity of the thermal imager to cause the temperature readout to match that of the contact
measurement. The resulting emissivity is that of the sample.
4.
Measuring by Wedge effect
With this method, the emissivity of the measured surface itself is enhanced through use of the wedge
or semi-wedge effect. But one must be careful about the number of reflections and/or the measuring
angle.
A small change in angle will reduce the emissivity enhancement.
Measuring by Wedge effect
