System and method for calibrating remote emissions sensing instruments

• US 7,359,804 B2
• Filed: 08/25/2005
• Issued: 04/15/2008
• Est. Priority Date: 08/25/2004
• Status: Expired due to Fees

• Current Assignee: Envirotest Corp. (Opus Group AB)
• Original Assignee: Environmental Systems Products Incorporated
• Inventors: Williams, Mitchell Jared, Stedman, Donald H.
• Primary Examiner(s): Cosimano; Edward R
• Application Number:
  US11/210,765
• Publication Number:
  US 20060047445A1
• Time in Patent Office: 964 Days
• Field of Search: 73/10.1, 73/10.2, 73/10.3, 73/10.6, 73/10.7, 73/232, 73/232.1, 73/232.2, 73/233.1, 73/233.2, 73/233.3, 73/233.5, 73/233.6, 73/233.7, 73/233.8, 436/43, 702/22, 702/23, 702/24, 702/27, 702/28, 702/30
• US Class Current: 702/28
• 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 generating calibration curves for implementation in 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 container, wherein the container 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 measured absorption of electromagnetic radiation, from the electromagnetic radiation source, due to the presence of the first gas in the optical path and 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 generating calibration curves for implementation in an optical absorption-based multi-gas analyzer (OABMGA), comprising:

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

a container that injects a time-variable puff of gas into the optical path, wherein the container 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 measured absorption of electromagnetic radiation, from the electromagnetic radiation source, due to the presence of the first gas in the optical path and 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.