Patent ID: 7259374

Claim:
An NDIR method for detecting the concentration of a gas species X, comprising: emitting infrared radiation from a source into a sample cell comprised of a hollow waveguide with a plurality of bends that are collectively greater than 180 degrees in three dimensions, said infrared radiation being quasi-focused into a beam with an angle of incidence between greater than approximately 0° and approximately 10° relative to a longitudinal axis of a first linear segment of the sample cell proximate the source; detecting a first signal at a first detector located in a detector chamber of the waveguide: detecting a second signal at a second detector located in the detector chamber; and using the second signal to adjust the first signal for detecting the concentration of the gas species X; wherein one of the first and second signals is based upon a first absorption band for gas species X while the other of said signals is based upon a second absorption band chosen to detect water which does not coincide with any known absorption bands of gases in the sample cell.