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Non-Dispersive Infrared Detector (NDIR)
- Advantages - The best of these have sensitivities of 25-50 PPM.
- responds well to CO2
- detector lasts longer than electrochemical detectors
- Disadvantages - Typical NDIR sensors are still in the $200-$1000 range
- could also detect compounds that absorb IR light in same bands as CO2
- Examples of Instruments
TSI Web site - The intensity of 4.26 µm ( wave number = 2347) light that reaches the detector is
inversely related to the concentration of CO2 in the sensing chamber. When the concentration of
CO2 in the chamber is zero, the detector will "see" the full light
intensity. As the concentration of CO2 increases, the intensity of
light striking the detector decreases. The exact relationship between IR light intensity and
CO2 concentration is determined when the instrument is calibrated
using pure nitrogen (0 ppm CO2) and a known concentration of
CO2 such as 1000 or 5000 ppm.
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Slide 27 of 76 
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