Optical sensing apparatus for remotely measuring exhaust gas composition of moving motor vehicles

A sensing apparatus for sensing a composition of a fluid, comprising:

• a light source for radiating light including a plurality of predetermined wavelengths through said fluid;
• a chopper positioned between said source and said fluid for alternating blocking and passing said light;
• a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said light passing through said fluid;
• and
• a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.

A system for determining a concentration of nitric oxide (NO) and carbon monoxide (CO) in an exhaust plume that emits radiation, comprising:

• a source of electromagnetic radiation for directing radiation having a plurality of wavelengths along an optical path that passes through the plume;
• chopper means disposed between said source and said plume for alternately blocking and passing said radiation from said source;
• first sensor means having an output for indicating an amount of absorption of the radiation transmitted through said plume from said source and emitted by said plume, within a band of first wavelengths, that is due to the presence of NO in the plume;
• second sensor means having an output for indicating an amount of absorption of the radiation, within a band of second wavelengths, that is due to the presence of water along the optical path;
• and
• third sensor means having an output for indicating an amount of absorption of the radiation transmitted through said plume from said source and emitted by said plume, within a band of third wavelengths, that is due to the presence of CO in the plume;
• determining means, having inputs coupled to the outputs of said first, second and third sensor means, for compensating the indicated absorptions when said chopper means passes said radiation in accordance with the indicated absorptions when said chopper means blocks said radiation to produce respective normalized absorptions, and for further compensating the normalized absorption within the first band of wavelengths in accordance with the normalized absorption within the second band of wavelengths and in accordance with a predetermined NO absorption modifying factor.

A method for determining a concentration of nitric oxide (NO) and carbon monoxide (CO) in an exhaust plume that emits radiation, comprising the steps of:

• passing an optical beam through an exhaust plume, the optical beam having wavelengths within a predetermined band of wavelengths within the infrared radiation spectrum;
• alternately blocking and Unblocking said radiation from said source;
• sensing blocked and unblocked radiations levels within said predetermined band;
• determining a measured NO transmission value from said blocked and unblocked radiation levels for a first predetermined band of wavelengths;
• determining a measured water transmission value from said blocked and unblocked radiation levels for a second predetermined band of wavelengths;
• determining a measured reference transmission value from said blocked and unblocked radiation levels for a third predetermined band of wavelengths selected so as not to be significantly absorbed by the exhaust plume;
• determining a measured combustion by-product transmission value from said blocked and unblocked radiation levels for a fourth predetermined band of wavelengths;
• determining a measured CO transmission value from said blocked and unblocked radiation levels for a fifth predetermined band of wavelengths;.
• determining an effective NO transmission value from the measured NO transmission value that is scaled by the (a) 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;
• determining an effective CO transmission value from the measured CO transmission value that is scaled by the reference transmission value;
• converting the effective NO and CO transmission values to relative NO and CO concentrations using predetermined calibration factors;
• and
• converting the relative NO and CO transmission values to NO and CO concentration values utilizing the measured combustion by-product transmission value.

A sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle, comprising:

• a light source for radiating light including a plurality of predetermined wavelengths through said plume;
• a plurality of photodetectors on a substrate for simultaneously sensing radiation levels at respective ones of said predetermined wavelengths for said light passing through said plume, two of said predetermined wavelengths responding to the presence of nitric oxide and water respectively, each photodetector comprising a photosensitive element which absorbs light at one of said respective predetermined wavelengths and a reflector between said photosensitive element and said substrate for reflecting light from the light source which has propagated through said plume and the photosensitive element back through the photosensitive element;
• and
• a computer for computing transmittances of said predetermined wavelengths from said respective radiation levels and computing said composition as a predetermined function of said transmittances, said computer compensating the transmittance associated with nitric oxide in accordance with the transmittance of the water.

A sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle, comprising:

• a light source for radiating light including a plurality of predetermined wavelengths through said plume;
• at least three photodetectors for simultaneously sensing radiation levels at respective ones of said predetermined wavelengths for said light passing through said plume, two of said photodetectors responding to the presence of nitric oxide and water respectively;
• a homogenizer disposed between said plume and said photosensor for causing said light to be incident onto a continuous area of the photodetectors with substantially uniform intensity to reduce the spatial variance of said sensed radiation levels;
• and
• a computer for computing transmittances of said predetermined wavelengths from said respective radiation levels and computing said composition as a predetermined function of said transmittances said computer compensating the transmittance associated with nitric oxide in accordance with the transmittance of the water.

A sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle comprising:

• a light source for radiating light including a plurality of predetermined wavelengths through said plume as a beam;
• at least three photodetectors for simultaneously sensing radiation levels at respective ones of said predetermined wavelengths for said light passing through said plume:
• a homogenizer disposed between said plume and said photosensor for causing said light to be incident onto a continuous area of the photodetectors with substantially uniform intensity to reduce the spatial variance of said sensed radiation levels, said homogenizer comprising a multifaceted optical beam integrator that images respective segments of said beam onto a series of overlapping segments on said photodetectors;
• and
• a computer for computing transmittances of said predetermined wavelengths from said respective radiation levels and computing said composition as a predetermined function of said transmittances.