Infrared Gas Analysis with NDIR Analyzers
What is NDIR?
The measurement principle of NDIR (Non Dispersive Infra Red) uses the absorption of infrared light by molecules. By choosing the correct wavelength from the infrared range, a specific component can be measured selectively.
The Law of Lambert Beer
The Law of Lambert Beer provides the relationship between light intensity and concentration:
Ix = I0 × e(−ε·c·x)
Construction of an NDIR Measurement Cell
Basically, an NDIR measurement cell in a gas analyzer consists of:
- An infrared source
- An optical filter
- A measurement cell
- A detector
The optical filter determines the selection of the correct wavelength at which measurement takes place. The length of the measurement cell determines the detection limit and the measurement range. By using lenses and mirrors, a compact IR bench can effectively achieve a high length of the measurement cell.
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GFC Measurement Cell for Accuracy
With a GFC (Gas Filter Correlation) measurement cell, even more accurate measurements can be made. In a GFC cell, multiple signals are compared using a disc with at least two chambers. One chamber is filled with nitrogen and the other with a known concentration of the gas to be measured. This makes it possible to practically continuously correct the signal for deviations due to contaminated optical elements or electronic drift.
Common Components
Common components from processes and in emissions can be determined with NDIR technology. Consider:
- CO (Carbon Monoxide)
- CO2 (Carbon Dioxide)
- NO (Nitric Oxide)
- N2O (Nitrous Oxide)
- CH4 (Methane)
Variants of NDIR Analyzers
- 19" rack
- Wall mount
- Tabletop version
Other measurement principles can be integrated into these analyzers. For example, an oxygen measurement can be integrated and a complete multi-gas analyzer can be assembled.