Emerson Rosemount CCO 5500, Reference Manual

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However, carbon dioxide and water vapor also absorb energy within this wave band.
Fortunately, at 4.7 µm, IR absorption by each of these gases is at a minimum.
Figure A-3
demonstrates how the absorption spectra of CO
2
, CO, and water vapor affects
wavelengths between 4.5 and 4.9 µm.
Absorption spectra of CO, CO
2
, and water vapor
A narrow band pass filter only passes IR energy at wavelengths around 4.7 µm. By using
this filter, correctly designed CO analyzers are able to ignore the effects of water vapor and
CO
2
. No other flue gases absorb IR energy in the band. The filter characteristics are shown
in Figure A-3 .
Comparison of Spectra Figure A-3:
Transmissivity of CO within the 4.7 µm band
The concentration of CO affects the IR energy's transmission through the gas at about 4.7
µm.
Figure A-4 illustrates how the energy within the selected band varies with CO
concentration.
Theory of operation
110 Rosemount CCO 5500