INFRARED GAS ANALYZERS

• US 3,869,613 A
• Filed: 09/27/1973
• Issued: 03/04/1975
• Est. Priority Date: 02/01/1972
• Status: Expired due to Term

• Current Assignee: Edward A. Mcclatchie, William T. Link
• Original Assignee: Edward A. Mcclatchie, William T. Link
• Inventors: Link, William T., McClatchie, Edward A.
• Primary Examiner(s): Borchelt, Archie R.
• Assistant Examiner(s): Church, C. E.
• Application Number:
  US05/401,214
• Time in Patent Office: 523 Days
• Field of Search: 250/343,344,345,346,373
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques

Abstract

Infrared gas analyzers for measuring the presence of specific gas molecules in an unknown gas sample. The gas sample is illuminated by a source of infrared radiation and the radiation passing therethrough is directed to a single radiation detector. A unique absorption filter, generally comprised of a plurality of transparent chambers mounted and rotatable about an axis, is disposed so that the chambers may be caused to sequentially pass through the optical path of the infrared radiation. The plurality of chambers are adapted so as to alternately filter out the characteristic absorption bands of the specific gas molecules being tested for, and to alternately pass radiation of the same energy content which will not be substantially absorbed by the gas being tested for. By comparing the magnitude of the sequential signals derived from the detector, an accurate measure of the specific gas molecules in the unknown sample may be determined. Various embodiments of the invention are disclosed.

Claims

1. An infrared absorption gas analyzer for measuring the presence of a specific gas in an unknown gas sample comprising:

a source of infrared radiation directed along an optical path;

a rotating filter having at least first and second chambers disposed about an axis and a means for rotating said chambers about said axis so as to alternately dispose each of said chambers within said optical path, each of said chambers having at least partially infrared transparent windows therein, said first chamber containing a substantial amount of a first stable isotope of said specific gas and said second chamber containing a substantial amount of a second stable isotope of said specific gas which is less common than said first stable isotope so that the relative proportions of said first and second isotopes in said first and second chambers are substantially different, said first and second chambers being filled so to remove substantially equal amounts of infrared energy when disposed in said optical path;

means for disposing an unknown gas sample within said optical path and sensing means repetitively responsive to radiation passing through said first chamber and said gas sample to provide a first signal, and radiation passing through said second chamber and said gas sample to provide a second signal, said sensing means including a means for providing an output signal responsive to the difference in said first and second signals divided by one of said first and second signals;

said optical path being in fixed predetermined spatial relationship with respect to said source of infrared radiation, the axis of rotation of said rotating filter, said means for disposing an unknown gas sample within said optical path and said sensing means.

2. The gas analyzer of claim 1 wherein said first and second chambers containing said first and second isotopes are filled so that the amount of energy removed by said first chamber from relatively broad band infrared radiation from said infrared source is substantially the same as the amount of energy removed from the same radiation by said second chamber.

3. The gas analyzer of claim 1 wherein said rotating filter, except for said chambers, is substantially opaque to infrared light so as to terminate radiation along said optical path except when one of said chambers is aligned with said optical path.

4. The gas analyzer of claim 1 for measuring the presence of carbon monoxide wherein said first chamber is filled with 12C16O and said second chamber is filled with an isotope of carbon monoxide selected from the group consisting of 12C17O, 12C18O and 13C16O.

5. The gas analyzer of claim 1 for measuring the presence of carbon dioxide wherein said first chamber is filled with 12C16O16O and said second chamber is filled with an isotope of carbon dioxide selected from the group consisting of 12C16O17O, 12C16O18O and 13C16O16O.

6. The gas analyzer of claim 1 for measuring the presence of NO wherein said first chamber is filled with 14N16O and said second chamber is filled with an isotope of NO selected from the group consisting of 14N17O, 14N18O and 15N16O.

7. The gas analyzer of claim 1 for measuring the presence ofSO2 wherein said first chamber is filled with 32S16O16O and said second chamber is filled with an isotope of SO2 from the group consisting of 32S16O17O, 32S16O18O and 21S18O18O.

8. The gas analyzer of claim 1 for measuring the presence of NO2 wherein said first chamber is filled with 14N16O16O and said second chamber is filled with an isotope of NO2 selected from the group consisting of 14N16O17O, 14N16O18O and 15N16O16O.

9. The gas analyzer of claim 1 for measuring the presence of hydrochloric acid wherein said first chamber is filled with 1H35Cl and said second chamber is filled with 1H37Cl.

10. An infrared absorption gas analyzer for measuring the presence of a specific gas in an unknown gas sample comprising:

a source of infrared radiation directed along an optical path;

a rotating filter having at least first and second chambers disposed about an axis and a means for rotating said chambers about said axis so as to alternately dispose each of said chambers within said optical path, each of said chambers having at least partially infrared transparent windows therein, said first chamber containing at least a substantial proportion of a first stable isotope of said specific gas and said second chamber containing at least a substantial proportion of a second stable isotope of said specific gas which is less common than said first stable isotope so that the relative proportions of said first and second isotopes in said first and second chambers are substantially different, said first and second chambers being filled so to remove substantially equal amounts of infrared energy when disposed in said optical path;

a sample cell having at least partially transparent infrared windows for confining a gas sample;

an infrared detector for detecting infrared energy from said sample cell and for providing an electrical signal responsive thereto; and

electronic means coupled to said infrared detector and synchronized with respect to said rotating filter to create a first signal responsive to radiation from said infrared radiation source through said first chamber and said sample cell, and a second signal responsive to radiation from said infrared radiation source throUgh said second chamber and said sample cell, and to provide a signal responsive to the difference in said first and second signals all divided by one of said first and second signals;

said optical path being in fixed predetermined relationship with respect to said source of infrared radiation, said rotating filter, said sample cell and said infrared detector, the immediately preceding elements being arranged along said optical path in the order of recitation herein.

11. The gas analyzer of claim 10 wherein said first and second chambers containing said first and second isotopes are filled so that the amount of energy removed by said first chamber from relatively broad band infrared radiation from said infrared source is substantially the same as the amount of energy removed from the same radiation by said second chamber.

12. The gas analyzer of claim 10 wherein said rotating filter, except for said chambers, is substantially opaque to infrared light so as to terminate radiation along said optical path except when one of said chambers is aligned with said optical path.

13. The gas analyzer of claim 10 for measuring the presence of carbon monoxide wherein said first chamber is filled with 12C16O and said second chamber is filled with an isotope of carbon monoxide selected from the group consisting of 12C17O, 12C18O and 13C16O.

14. The gas analyzer of claim 10 for measuring the presence of carbon dioxide wherein said first chamber is filled with 12C16O16O and said second chamber is filled with an isotope of carbon dioxide selected from the group consisting of 12C16O17O, 12C16O18O and 13C16O16O.

15. The gas analyzer of claim 10 for measuring the presence of NO wherein said first chamber is filled with 14N16O and said second chamber is filled with an isotope of NO selected from the group consisting of 14N17O, 14N18O and 15N16O.

16. The gas analyzer of claim 10 for measuring the presence of SO2 wherein said first chamber is filled with 32S16O16O and said second chamber is filled with an isotope of SO2 selected from the group consisting of 32S16O17O, 32S16O18O and 32S18O18O.

17. The gas analyzer of claim 10 for measuring the presence of NO2 wherein said first chamber is filled with 14N16O16O and said second chamber is filled with an isotope of NO2 selected from the group consisting of 14N16O17O, 14N16O18O and 15N16O16O.

18. The gas analyzer of claim 10 for measuring the presence of hydrochloric acid wherein said first chamber is filled with 1N35Cl and said second chamber is filled with 1H37Cl.