Abstract: By the use of one or more beams of chopped, variable-frequency, monochromatic light to illuminate the sample chamber of at least one gas-filled cell including such sample chamber and a reference chamber joined to the sample chamber by a tunnel-like opening or orifice which permits fluid communication between the chambers and incorporating a thermal-flowmeter-type sensor element in the path of flow of the fluid between the chambers of each such cell, the compositional characteristics of one or more samples in each sample chamber can be determined accurately.

Abstract: By autocorrelating the sample photoacoustic response signal and the reference photoacoustic response signal, respectively, obtained from the sample and reference cells, of a photoacoustic spectrometer, and cross-correlating the autocorrelated signals to produce a third signal, simple mathematical operations upon the resulting three signals will produce accurate sample analysis free from the effects of the noise arising from sample illumination intensity variations and other random phenomena.

Abstract: The performance of a single light source parallel chambertype infrared gas analyzer is improved by enlarging the single inlet opening of the light divider and by positioning the light source such that the center axes of the two light passages of the light divider intersect at the light source. The assembly and alignment adjustment of the various functional components of the analyzer is also simplified.