Remote emissions sensing system with improved NOxdetection
First Claim
1. A method for determining the concentration of NOx in an exhaust plume of a vehicle passing through a beam of radiation projected along an optical path between a radiation source having an initial intensity, and a detector for measuring intensities of radiation incident upon the detector over a range of wavelengths, the method comprising:
- measuring, under ambient conditions, intensities of radiation over a range of wavelengths to determine ambient NOx concentration, wherein the range of wavelengths includes at least one absorption wavelength for NOx;
measuring intensities of radiation, over the range of wavelengths, while the beam of radiation is passing through an exhaust plume of a vehicle after the vehicle passes through the optical path;
determining a baseline intensity by interpolating a substantially linear region over an absorption dip in an absorption curve generated from the intensities measured while the beam of radiation is passing through the exhaust plume of the vehicle;
calculating the concentration of NOx in the exhaust plume of the vehicle, wherein calculating the concentration of NOx includes using the baseline intensity to compensate for changes in the initial intensity; and
subtracting the ambient NOx concentration from the concentration of NOx in the exhaust plume of the vehicle.
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Accused Products
Abstract
A remote emissions sensing system is provided with NOx detection capability. First, a reading of the ambient NOx concentration is taken just prior to each vehicle passing through the system. This measurement accounts for any ambient NOx concentration that may be lingering from the exhaust of a previous vehicle. Next, the system takes a blocked reading when the vehicle is located in the path of the beam. This reading accounts for any ambient or system noise that may exist. Finally, the system takes a reading of the exhaust plume as the beam passes through the plume. A processor determines the portion of the reading due to the exhaust plume by subtracting the ambient and blocked readings from the exhaust plume reading. As a result, a more accurate exhaust concentration reading is provided. Additionally, the system may process exhaust plume readings only in a predetermined wavelength band associated with the known absorption spectrum of NOx so that data points for which there is no significant absorption of NOx may be eliminated. Thus, any noise or other interference in the non-absorptive wavelengths are minimized. Also, changes in the intensity of the radiation are compensated by subtracting a baseline intensity from each signal.
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Citations
16 Claims
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1. A method for determining the concentration of NOx in an exhaust plume of a vehicle passing through a beam of radiation projected along an optical path between a radiation source having an initial intensity, and a detector for measuring intensities of radiation incident upon the detector over a range of wavelengths, the method comprising:
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measuring, under ambient conditions, intensities of radiation over a range of wavelengths to determine ambient NOx concentration, wherein the range of wavelengths includes at least one absorption wavelength for NOx; measuring intensities of radiation, over the range of wavelengths, while the beam of radiation is passing through an exhaust plume of a vehicle after the vehicle passes through the optical path; determining a baseline intensity by interpolating a substantially linear region over an absorption dip in an absorption curve generated from the intensities measured while the beam of radiation is passing through the exhaust plume of the vehicle; calculating the concentration of NOx in the exhaust plume of the vehicle, wherein calculating the concentration of NOx includes using the baseline intensity to compensate for changes in the initial intensity; and subtracting the ambient NOx concentration from the concentration of NOx in the exhaust plume of the vehicle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for determining the concentration of NOx in an exhaust plume of a vehicle passing through a beam of radiation projected along an optical path between a radiation source having an initial intensity, and a detector for measuring intensities of radiation incident upon the detector over a range of wavelengths, the system comprising:
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means for measuring, under ambient conditions, intensities of radiation over a range of wavelengths to determine ambient NOx concentration, wherein the range of wavelengths includes at least one absorption wavelength for NOx;
.means for measuring intensities of radiation, over the range of wavelengths, while the beam of radiation is passing through an exhaust plume of a vehicle after the vehicle passes through the optical path; means for determining a baseline intensity by interpolating a substantially linear region over an absorption dip in an absorption curve generated from the intensities measured while the beam of radiation is passing through the exhaust plume of the vehicle; means for calculating the concentration of NOx in the exhaust plume of the vehicle, wherein calculating the concentration of NOx includes using the baseline intensity to compensate for changes in the initial intensity; and means for subtracting the ambient NOx concentration from the concentration of NOx in the exhaust plume of the vehicle. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification