System and method for calibrating remote emissions sensing instruments
View Patent ↗A system and method is provided for obtaining calibration curves for CO and CO 2 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 CO 2 column densities.
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 CO 2 .
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 N 2 .
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 CO 2 .
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 N 2 .