Patent ID: 7485861

Claim:
A method of correcting for an effect of temperature and pressure on one or more exhaust gas constituents of an exhaust plume, in a measurement path, emitted from a motor vehicle during an emissions test, the method comprising: measuring ambient temperature and ambient pressure at a vehicle emissions test site; measuring, from an exhaust plume of a passing motor vehicle, an amount of a selected gas constituent present in the exhaust plume in the measurement path; generating, for the selected gas constituent, a temperature correction value based, in part, on the measured ambient temperature, wherein the temperature correction value is determined from a temperature correction proportionality coefficient that is defined by a temperature correction curve polynomial function that describes the temperature correction proportionality coefficient as a function of the measured amount of the selected gas constituent, and wherein the step of generating the temperature correction value comprises: (i) determining the temperature correction proportionality coefficient as a function of the measured amount of the selected gas constituent according to the temperature correction polynomial function; and (ii) generating the temperature correction value by multiplying the temperature correction proportionality coefficient by the temperature difference between a base temperature and the measured ambient temperature; generating, for the selected gas constituent, a pressure correction value based, in part, on the measured ambient pressure, wherein the pressure correction value is determined from a pressure correction proportionality coefficient that is defined by a pressure correction curve polynomial function that describes the pressure correction proportionality coefficient as a function of the measured amount of the selected gas constituent, and wherein the step of generating the pressure correction value comprises: (i) determining the pressure correction proportionality coefficient as a function of the measured amount of the selected gas constituent according to the pressure correction polynomial function; and (ii) generating the pressure correction value by multiplying the pressure correction proportionality coefficient by the pressure difference between a base pressure and the measured ambient pressure; applying the temperature correction value and the pressure correction value to the measured amount of the selected gas constituent to generate a corrected gas amount for the selected gas constituent; and storing the corrected gas amount generated for the selected gas constituent in a memory.