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INCR 1302 San Jacinto College Physics of Instrumentation Notes

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San Jacinto College – Spring 2021 INCR 1302 – Physics of Instrumentation NOTES FOR TEST 3 (INCR 1302) 7. IR thermometers • • • • • An IR (Infrared) thermometer is a thermometer that measures IR radiation emitted by an object and based on that intensity, determines its temperature. IR thermometers are fast acting and can be used in inaccessible locations. Most references measure IR (and other wave lengths) in nanometers. As you know, IR spectrum wave length is longer than that for visible light IR is from 790 nanometer )nm)to1000,000 nm. Some of the wave lengths are absorbed by atmospheric gases such as CO2, moisture, and NO x. Thus, remaining wavelengths are useful for IR thermometers (typically 8000 nm to 14000 nm. As the wavelength become shorter, energy of a wave increases (you recall Planck’s law which says that energy of a wave is directly proportional to its frequency. In addition, higher the frequency, shorter is the wavelength. Since IR wavelength is longer than that for visible light, IR wave or waves have lower energy that visible light rays) Thus, shorter the wavelength emitted by an object, hotter its temperature. Now, let’s discuss some terms: o Blackbody: Think of it this way. When heat energy falls on an object, some is absorbed, some is reflected and some is refracted. Blackbody is such that it absorbs ALL radiation and has zero reflectivity. Blackbody emits maximum amount of energy. (the word ‘emit,” is easy to misconstrue. It is R ...
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