Patent ID: 6064488
Filing Date: 2000-05-16
Classification: G01N

Abstract:
Apparatus for measuring concentration of a gas comprising:a tunable diode laser, said laser being tuned to project a laser beam at the wavelength of a spectral feature of said gas, said laser beam being modulated;a sampling cavity having a first end and a second end, said first and second ends having opposed interior reflecting surfaces;a lens attached to said first end, said laser beam being projected onto said lens, said lens splitting said laser beam, deflecting a first surface reflection of said laser beam and projecting said laser beam into said sampling cavity;a null detector receiving said first surface reflection, said null detector measuring intensity of said first surface reflection and producing an electrical null signal proportional to said intensity;a sample detector, said laser beam being reflected a plurality of times in said sampling cavity by said first and second ends and projected back through said lens to said sample detector wherein said lens helps focus said laser beam on said sample detector, said sample detector measuring intensity of said laser beam and producing an electrical sample signal proportional to said intensity, said sample detector being located near said null detector so that the path of said laser beam to said sample detector and the path of said laser beam to said null detector differ only by the path of the laser beam inside the sampling cavity; anda microprocessor receiving and comparing said sample signal and said null signal to eliminate influence of laser beam variations and interference patterns.