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Understanding Infrared Thermography Reading 3

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Characteristics of the Transmitting Medium<br />

Because lhe infrared radiation from the target passes through some<br />

transmitting medium on its way to the target, the transmission and emission<br />

characteristics of the medium in the measurement path must be considered<br />

when making non contact thermal measurement. No loss of energy or self<br />

emission (Ɛ atm ) is encountered when measuring through a vacuum. However.<br />

most measurements are made through air. For short path length (a few<br />

meters, for example), most gases (including the atmosphere) absorb and emit<br />

very little energy and can be ignored. However. when highly accurate<br />

temperature measurements are required, the effects of atmospheric<br />

absorption must be taken into account. (τ atm , Ɛ atm ).<br />

Charlie Chong/ Fion Zhang

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