Method and system for (trace) gas analysis

Claim 1

A system for monitoring exhaust gases comprising a laser unit comprising a CO 2 laser for generating a laser beam; first optical means for guiding the laser beam into a probing section containing exhaust gas to be monitored; at least one measuring unit comprising a pyroelectric detector for measuring the intensity of said laser beam and providing corresponding laser beam intensity output signals; second optical means for guiding the laser beam leaving said probing section to said measuring unit; tuning means comprising a piezoelectric drive unit for adjusting said CO 2 laser either to a first wavelength (λ1) corresponding to an absorption maximum of a gas contained in said exhaust gas or to a second wavelength (λ2) corresponding to an absorption minimum of said gas; a controller for controlling said tuning means in accordance with first control signals; a chopper for alternatively passing through or stopping down said laser beam in accordance with second control signals; sample and hold means for sampling and holding said laser beam intensity output signals of said at least one measuring unit in accordance with third control signals; a scoring circuit generating said first, second and third control signals and for correcting, processing, and displaying said laser beam intensity output signals from said measuring unit sampled and held by said sample and hold means; measuring means for measuring temperature and pressure of said exhaust gas; storage means for storing a table of correction factors as a function of gas temperature and gas pressure; means for reading said correction factors from said table of correction factors in accordance with said measured temperature and pressure and for feeding said correction factors to said scoring circuitry; wherein said first, second, and third control signals are generated and synchronized such that said piezoelectric drive unit cylically adjusts said CO 2 laser for reversing the wavelength of said laser beam between said first and said second wavelength at a first frequency in excess of 1000 cps, said chopper alternatively passes through and stops down said laser beam at a second frequency the value thereof being half of said first frequency such that one cycle of wavelength reversion occurs during passing through and one cycle of wavelength reversion occurs during stopping down of said laser beam, and during passing through of said laser beam said sample and hold means takes a sample of said laser beam intensity output signals at a defined time interval after reversing the wavelength and, during stopping down of said laser beam, takes a sample at a defined time interval after stopping down of said laser beam.

Claim 2

A system for monitoring exhaust gases comprising a laser unit comprising a CO 2 laser for generating a laser beam; first optical means for guiding the laser beam into a probing section containing exhaust gas to be monitored; at least one measuring unit comprising a pyroelectric detector for measuring the intensity of said laser beam and providing corresponding laser beam intensity output signals; second optical means for guiding the laser beam leaving said probing section to said measuring unit; tuning means comprising a piezoelectric drive unit for adjusting said CO 2 laser either to a first wavelength (λ1) corresponding to an absorption maximum of a gas contained in said exhaust gas or to a second wavelength (λ2) corresponding to an absorption minimum of said gas; a controller for controlling said tuning means in accordance with first control signals; a chopper for alternatively passing through or stopping down said laser beam in accordance with second control signals; sample and hold means for sampling and holding said laser beam intensity output signals of said at least one measuring unit in accordance with third control signals; a scoring circuit generating said first, second and third control signals and for correcting, processing, and displaying said laser beam intensity output signals from said measuring unit sampled and held by said sample and hold means; measuring means for measuring temperature and pressure of said exhaust gas; storage means for storing a table of correction factors as a function of gas temperature and gas pressure; means for reading said correction factors from said table of correction factors in accordance with said measured temperature and pressure and for feeding said correction factors to said scoring circuitry; wherein said first, second, and third control signals are generated and synchronized such that said piezoelectric drive unit cylically adjusts said CO 2 laser for reversing the wavelength of said laser beam between said first and said second wavelength at a first frequency in excess of 1000 cps, said chopper alternatively passes through and stops down said laser beam at a second frequency the value thereof being half of said first frequency such that one cycle of wavelength reversion occurs during passing through and one cycle of wavelength reversion occurs during stopping down of said laser beam, and during passing through of said laser beam said sample and hold means takes a sample of said laser beam intensity output signals at a defined time interval after reversing the wavelength and, during stopping down of said laser beam, takes a sample at a defined time interval after stopping down of said laser beam.