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Appendix: How Infrared Thermometry Works
A
A-2
Blackbody
When thermal radiation falls on an object, part of the energy is
transmitted through the object, part is reflected and part is
absorbed. A blackbody is defined as an ideal object that absorbs all
the radiation incident upon it. The best example of a real object that
acts like a blackbody is a small hole drilled deep into a large opaque
cavity. Thermal radiation entering the cavity is internally reflected
and has little chance of escaping the cavity before it is fully
absorbed.
Emissivity is defined as the ratio of energy radiated by an object to
that of the energy radiated by a blackbody. By definition, the
emissivity of a blackbody is 1. Most objects are considered
gray
objects
with an emissivity between 0 and 1. Various emissivities for
common materials are shown in Appendix B.
Spectral Distribution
Objects radiate energy at different wavelengths, but not with
constant intensity at each
wavelength. Figure A-2
shows the energy radiated
by a blackbody at various
temperatures as a function
of wavelength. As a body is
heated, the intensity of the
radiated energy increases
and the peak of the curve
shifts towards the shorter
wavelength end of the
spectrum. The total area
under a spectral
distribution curve is
proportional to the total
energy radiated by the
blackbody at a given
temperature.
Figure A-2. Blackbody
Spectral Distribution
Relative emission from a blackbody versus wavelength.
The area under the curve corresponds to the total ener-
gy, and is proportional to the absolute temperature to
the 4th power. The peak of the spectral distribution
curve shifts to shorter wavelengths as the temperature
increases.
Содержание OS550A
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Страница 21: ...Installing the Infrared Thermometer 2 2 8 Notes ...
Страница 46: ...3 25 Using the Infrared Thermometer Transmitter 3 Notes ...
Страница 47: ...Using the Infrared Thermometer Transmitter 3 3 26 Notes ...
Страница 51: ...Laser Sight Accessory 4 4 4 Notes ...
Страница 53: ...Maintenance 5 5 2 Notes ...
Страница 57: ...Troubleshooting Guide 6 6 4 Notes ...
Страница 63: ...1 8 2 Notes Glossary of Key Strokes 8 ...
Страница 75: ...I 3 Notes ...