Importance

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Abstract

A system (10) for detecting nitric oxide (NO) within an exhaust plume (14) includes a source (18) for generating an optical beam (20) and for directing (22, 24) the optical beam through the exhaust plume, the optical beam having wavelengths within a predetermined band of wavelengths within the infrared (IR) radiation spectrum. The system includes a sensor (32)/filter (30) assembly having a first channel for determining a measured NO transmission value for a first predetermined band of wavelengths; a second channel for determining a measured water transmission value for a second predetermined band of wavelengths; a third channel for determining a measured reference transmission value for a third predetermined band of wavelengths selected so as not to be significantly absorbed by the exhaust plume; and a fourth channel for determining a measured combustion by-product transmission value for a fourth predetermined band of wavelengths. A data processor (38) is responsive to the outputs of the channels for determining an effective NO transmission value from the measured NO transmission value that is scaled by (a) the measured water transmission value, (b) a predetermined factor that compensates for absorption by water within the first predetermined band of wavelengths, and (c) the reference transmission value. The data processor is further operable for converting the effective NO transmission value to a relative NO concentration value using a predetermined calibration factor and for converting the relative NO concentration value to an actual NO concentration value utilizing the measured combustion by-product transmission value.

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First Claim