System and method for calibrating remote emissions sensing instruments

• US 20060047445A1
• Filed: 08/25/2005
• Published: 03/02/2006
• Est. Priority Date: 08/25/2004
• Status: Active Grant

• Current Assignee: Envirotest Corp. (Opus Group AB)
• Original Assignee: Environmental Systems Products Incorporated
• Inventors: Stedman, Donald H., Williams, Mitchell Jared
• Granted Patent: US 7,359,804 B2
• Time in Patent Office: Days
• US Class Current: 702/30
• 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 21/276 with alternation of sample and standard in optical path
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 33/0006 Calibrating gas analysers
• CPC Class Codes: G01N 33/004 CO or CO2
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y10T 436/11 Automated chemical analysis

Abstract

A system and method is provided for obtaining calibration curves for CO and CO₂ during laboratory calibration of one or more remote emissions sensing (RES) instruments, and for self-calibration of on-road RES instruments to compensate for changes in background CO and CO₂ column densities.

Claims

1. A method of calibrating of an optical absorption-based multi-gas analyzer (OABMGA), comprising:

injecting, into an optical path between an electromagnetic radiation source and a detector, a time-variable puff of gas from a cylinder, wherein the cylinder comprises a mixture of gases at known concentration ratios, and wherein the mixture of gases includes a first gas and other gases;

determining a concentration of the first gas in the puff of gas in the optical path based on a predetermined calibration curve for the first gas;

determining a concentration of one or more of the other gases in the optical path based on the determined concentration of the first gas in the optical path and the known concentration ratios for the mixture of gases; and

generating calibration curves for one or more of the other gases based on the determined concentrations of the one or more other gases.

2. The method of claim 1, wherein the first gas comprises propane, which is used as a surrogate hydrocarbon.

3. The method of claim 1, wherein the predetermined calibration curve for the first gas is obtained by inserting, into the optical path, a gas cell having a known concentration of the first gas.

4. The method of claim 1, wherein the other gases in the mixture of gases include at least CO and CO₂.

5. The method of claim 1, wherein the electromagnetic radiation source, detector, and the optical path there-between are isolated from ambient air via an enclosure, and wherein the time-variable puff of gas is injected into the optical path within the enclosure.

6. The method of claim 5, wherein the enclosure is first purged with a purge gas for a pre-determined time period to purge any gases present within the optical path prior to injecting the time-variable puff of gas into the optical path.

7. The method of claim 6, wherein the purge gas comprises N₂.

8. A system for calibrating an optical absorption-based multi-gas analyzer (OABMGA), comprising:

an optical path extending between an electromagnetic radiation source and a detector;

a cylinder that injects a time-variable puff of gas into the-optical path, wherein the cylinder comprises a mixture of gases at known concentration ratios, and wherein the mixture of gases includes a first gas and other gases; and

a processor that is configured to;

determine a concentration of the first gas in the puff of gas in the optical path based on a predetermined calibration curve for the first gas;

determine a concentration of one or more of the other gases in the optical path based on the determined concentration of the first gas in the optical path and the known concentration ratios for the mixture of gases; and

generate calibration curves for one or more of the other gases based on the determined concentrations of the one or more other gases.

9. The system of claim 8, wherein the first gas comprises propane, which is used as a surrogate hydrocarbon.

10. The system of claim 8, wherein the predetermined calibration curve for the first gas is obtained by inserting, into the optical path, a gas cell having a known concentration of the first gas.

11. The system of claim 8, wherein the other gases in the mixture of gases include at least CO and CO₂.

12. The system of claim 8, wherein the electromagnetic radiation source, detector, and the optical path there-between are isolated from ambient air via an enclosure, and wherein the time-variable puff of gas is injected into the optical path within the enclosure.

13. The system of claim 12, wherein the enclosure is first purged with a purge gas for a pre-determined time period to purge any gases present within the optical path prior to injecting the time-variable puff of gas into the optical path.

14. The system of claim 13, wherein the purge gas comprises N₂.

15. A method of calibrating an optical absorption-based multi-gas analyzer (OABMGA), comprising:

injecting, into an optical path between an electromagnetic radiation source and a detector, a puff of gas from a cylinder, wherein the cylinder comprises a first gas and a second gas at a predetermined concentration ratio, and wherein the detector generates a first signal that corresponds to the first gas and a second signal that corresponds to the second gas;

determining, based on the first signal, a change in a column density of the first gas in the optical path between a first point in time and a second point in time;

determining, based on the predetermined concentration ratio and the change in the column density of the first gas in the optical path between the first point in time and the second point in time, a change in a column density of the second gas between the first point in time and the second point in time;

determining, based on the second signal and the change in the column density of the second gas in the optical path between the first point in time and the second point in time, a calibration value that corresponds to the second gas; and

implementing the calibration value to determine the column density of the second gas in the optical path based on the second signal.

16. The method of claim 15, wherein the calibration value comprises a signal level at which the second signal is generated when substantially none of the second gas is present in the optical path.

17. The method of claim 15, wherein determining the change in the column density of the first gas in the optical path between the first point in time and the second point in time comprises determining the change in the column density of the first gas in the optical path between the first point in time and the second point in time based on the first signal and a constant slope value from a predetermined calibration curve for the first gas.

18. The method of claim 15, wherein determining the calibration value that corresponds to the second gas comprises determining the calibration value that corresponds to the second gas based on the second signal, the change in the column density of the second gas present in the optical path between the first time point and the second time point, and one or more coefficient values from a predetermined calibration curve for the second gas.

19. The method of claim 15, wherein implementing the calibration value to determine the column density of the second gas in the optical path comprises implementing the calibration value to determine a background column density of the second gas in the optical path.

20. A system for calibrating an optical absorption-based multi-gas analyzer (OABMGA), comprising:

an optical path extending between an electromagnetic radiation source and a detector;

a cylinder that injects a puff of gas into the optical path, wherein the cylinder comprises a first gas and a second gas at a predetermined concentration ratio, and wherein the detector generates a first signal that corresponds to the first gas and a second signal that corresponds to the second gas; and

a processor that is configured to;

determine a change in a column density of the first gas in the optical path between a first point in time and a second point in time based on the first signal;

determine a change in a column density of the second gas between the first point in time and the second point in time based on the predetermined concentration ratio and the change in the column density of the first gas in the optical path between the first point in time and the second point in time;

determine a calibration value that corresponds to the second gas based on the second signal and the change in the column density of the second gas in the optical path between the first point in time and the second point in time; and

implement the calibration value to determine the column density of the second gas in the optical path based on the second signal.

21. The system of claim 20, wherein the calibration value comprises a signal level at which the second signal is generated when substantially none of the second gas is present in the optical path.

22. The system of claim 20, wherein the processor is configured to determine the change in the column density of the first gas in the optical path between the first point in time and the second point in time based on the first signal and a constant slope value from a predetermined calibration curve for the first gas.

23. The system of claim 20, wherein the processor is configured to determine the calibration value that corresponds to the second gas based on the second signal, the change in the column density of the second gas present in the optical path between the first time point and the second time point, and one or more coefficient values from a predetermined calibration curve for the second gas.

24. The system of claim 20, wherein the processor is configured to implement the calibration value to determine a background column density of the second gas in the optical path.