Gas concentration measurement by spectral correlation: rejection of interferent species

Devices for continuous, in situ concentration measurements of one chemical species in a gaseous mixture rely on dispersive or nondispersive infrared (NDIR) methods. The latter are better for luminosity. NDIR spectral correlators are superior to NDIR broadband analyzers because of their selectivity. Spectral correlators include gas filter correlators and interferometric correlators. The principles of these two methods are reviewed. A synthetic analysis including both allows us to describe quantitatively their sensitivity to the wanted species and rejection of various kinds of interferent. A comparative study of these parameters is presented as an example and commented on the basis of properties in the spectral space and in the Fourier conjugate space. Interferometric correlators are shown to be better for rejection of long-term drifts affecting spectral characteristics and of similar nongaseous interferents; otherwise, either setup may be preferable depending on each particular set of experimental conditions.