System and method for remote emissions sensing including calculation and calibration techniques compensating for temperature and pressure effects

• US 20050197794A1
• Filed: 02/09/2005
• Published: 09/08/2005
• Est. Priority Date: 02/09/2004
• Status: Active Grant

• Current Assignee: Envirotest Corp. (Opus Group AB)
• Original Assignee: Environmental Systems Products Incorporated
• Inventors: Full, Gary
• Granted Patent: US 7,485,861 B2
• Time in Patent Office: Days
• US Class Current: 702/100
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 2021/3513 Open path with an instrumental source
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A remote emissions sensing (RES) system and method for measuring the exhaust gas composition of a motor vehicle is provided, including calibration methodologies for compensating for the effects of ambient temperature and/or pressure.

Claims

1. A method of correcting for the 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;

generating, for the selected gas constituent, a pressure correction value based, in part, on the measured ambient pressure; and

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.

2. The method of claim 1, further comprising:

measuring, from the exhaust plume of the passing motor vehicle, an amount of CO₂ present in the exhaust plume;

generating, for the measured amount of CO₂, a temperature correction value based, in part, on the measured ambient temperature;

generating, for the measured amount of CO₂, a pressure correction value based, in part, on the measured ambient pressure;

applying the temperature correction value and the pressure correction value to the measured amount of CO₂ to generate a corrected amount of CO₂; and

generating a gas ratio of absorption for the corrected gas amount for the selected gas constituent to the corrected amount of CO₂.

3. The method of claim 2, wherein the selected gas constituent comprises one of CO, HC, or NO.

4. The method of claim 1, wherein the temperature correction value comprises a temperature correction curve polynomial value, and wherein the step of generating the temperature correction value comprises:

accessing a stored base curve for the selected gas constituent, wherein the stored base curve plots a number of molecules of the selected gas constituent versus transmittance of the selected gas constituent at a base temperature; and

generating the temperature correction curve polynomial value which represents a percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature for which the stored base curve was established.

5. The method of claim 4, wherein the base temperature for which the stored base curve was established is approximately 25.0 degrees Celsius.

6. The method of claim 4, wherein the selected gas constituent comprises CO, and wherein the percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature is approximately 0.05 percent per degree Celsius.

7. The method of claim 4, wherein the selected gas constituent comprises CO₂, and wherein the percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature is approximately 0.6 percent per degree Celsius.

8. The method of claim 1, wherein the pressure correction value comprises a pressure correction curve polynomial value, and wherein the step of generating the pressure correction value comprises:

accessing a stored base curve for the selected gas constituent, wherein the stored base curve plots a number of molecules of the selected gas constituent versus transmittance of the selected gas constituent at a base pressure; and

generating the pressure correction curve polynomial value which represents a percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure for which the stored base curve was established.

9. The method of claim 8, wherein the base pressure for which the stored base curve was established is approximately 13.6 psia.

10. The method of claim 8, wherein the selected gas constituent comprises CO, and wherein the percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure is approximately 2.0 percent per psi.

11. The method of claim 8, wherein the selected gas constituent comprises CO₂, and wherein the percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure is approximately 1.0 percent per psi.

12. The method of claim 1, wherein the step of measuring ambient temperature and ambient pressure at a vehicle emissions test site further comprises:

measuring ambient temperature and ambient pressure in the measurement path prior to commencing an emissions test.

13. The method of claim 1, wherein the step of measuring an amount of a selected gas constituent present in the exhaust plume in the measurement path further comprises:

emitting a radiation beam of known intensity from at least one radiation source across a vehicle travel lane and through the exhaust plume of the passing motor vehicle, the radiation beam having a wavelength corresponding to a wavelength absorbed by the selected gas constituent;

receiving the radiation beam via at least one radiation detector;

outputting a detector output voltage representing the intensity of the received radiation beam to at least one processor, the at least one processor calculating the difference between the known intensity of the radiation beam and the intensity detected by the at least one detector to measure an amount of absorption by the selected gas constituent; and

determining, based on the measured absorption, the amount of the selected gas constituent in the measurement path.

14. A system for correcting for the 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, comprising:

means for measuring ambient temperature and ambient pressure at a vehicle emissions test site;

means for 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;

means for generating, for the selected gas constituent, a temperature correction value based, in part, on the measured ambient temperature;

means for generating, for the selected gas constituent, a pressure correction value based, in part, on the measured ambient pressure; and

means for 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.

15. The system of claim 14, wherein the temperature correction value comprises a temperature correction curve polynomial value, and wherein the means for generating the temperature correction value further comprises:

means for accessing a stored base curve for the selected gas constituent, wherein the stored base curve plots a number of molecules of the selected gas constituent versus transmittance of the selected gas constituent at a base temperature; and

means for generating the temperature correction curve polynomial value which represents a percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature for which the stored base curve was established.

16. The system of claim 15, wherein the base temperature for which the stored base curve was established is approximately 25.0 degrees Celsius.

17. The system of claim 15, wherein the selected gas constituent comprises CO, and wherein the percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature is approximately 0.05 percent per degree Celsius.

18. The system of claim 15, wherein the selected gas constituent comprises CO₂, and wherein the percentage temperature correction to the stored base curve required per unit of temperature difference from the base temperature is approximately 0.6 percent per degree Celsius.

19. The system of claim 14, wherein the pressure correction value comprises a pressure correction curve polynomial value, and wherein the means for generating the pressure correction value comprises:

means for accessing a stored base curve for the selected gas constituent, wherein the stored base curve plots a number of molecules of the selected gas constituent versus transmittance of the selected gas constituent at a base pressure; and

means for generating the pressure correction curve polynomial value which represents a percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure for which the stored base curve was established.

20. The system of claim 19, wherein the base pressure for which the stored base curve was established is approximately 13.6 psia.

21. The system of claim 19, wherein the selected gas constituent comprises CO, and wherein the percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure is approximately 2.0 percent per psi.

22. The system of claim 19, wherein the selected gas constituent comprises CO₂, and wherein the percentage pressure correction to the stored base curve required per unit of pressure difference from the base pressure is approximately 1.0 percent per psi.