Method and apparatus for compensating reflection losses in a path length modulated absorption-absorption trace gas detector

摘要

A method and apparatus is described for compensating for reflection losses in an optical path length modulated absorption- absorption gas analyzer used for determining the density of a reference gas in an unknown gas sample. The apparatus comprises a first chamber for containing a first gas including a reference gas at a known partial density and a second chamber for containing a second gas including a sample of the reference gas at an unknown partial density. A source of radiant energy is provided for passing radiant energy through the first and second chambers. Means are provided for modulating the path length of the radiant energy in the chambers. Additionally, a chopper wheel comprising a plurality of gas cells containing a sample of the reference gas is interspersed by a plurality of gas cells containing a gas excluding the reference gas. The chopper wheel is provided between the first and the second chambers and a radiant energy sensing means for intercepting the radiant energy emerging from the first and second chambers before it reaches the radiant energy sensing means. Signal processing means responsive to the radiant energy sensing means and the position of the chopper cells with respect to the radiant energy path provides a signal proportional to the density of the reference gas in the unknown gas sample.