Analysis method for gases and apparatus therefor

• US 6,040,915 A
• Filed: 12/07/1998
• Issued: 03/21/2000
• Est. Priority Date: 04/09/1997
• Status: Expired due to Fees

• Current Assignee: Nippon Sanso Corporation (Mitsubishi Chemical Group Corp.)
• Original Assignee: Nippon Sanso Corporation (Mitsubishi Chemical Group Corp.)
• Inventors: Ishihara, Yoshio, Kimijima, Tetsuya, Wu, Shang-Qian, Morishita, Jun-ichi
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US09/147,349
• Time in Patent Office: 470 Days
• Field of Search: 356/435, 356/437, 250/345
• US Class Current: 356/435
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A method for analyzing an impurity in a gas including the steps of: introducing a gas with an impurity into a first cell; introducing a gas with no impurity into a second cell; maintaining identical pressures in the first and second cells; irradiating a light from a light irradiating source; varying the frequency of the light over a frequency spectrum including an absorption frequency of the impurity; splitting the light by a splitting device in order to pass a first beam through the first cell and to pass a second beam through the second cell; measuring the intensity of the light passing through the first cell over the frequency spectrum with a first measuring device and the intensity of the light passing through the second cell over the frequency spectrum with a second measuring device; and determining an absorption spectrum of the impurity in the gas based on the difference between data measured with the first measuring device and data from measured with the second measuring device.

Claims

1. A method for analyzing an impurity in a gas, comprising the steps of

introducing a gas with an impurity into a first cell;

introducing a gas with no impurity into a second cell;

maintaining identical pressures in said first and second cells;

irradiating a light from a light irradiating source;

varying the frequency of said light over a frequency spectrum including an absorption frequency of said impurity;

splitting the light into a first beam and a second beam with a splitting device

passing said first beam through said first cell;

passing said second beam through said second cell;

measuring an intensity of light passed through said first cell over said frequency spectrum with a first measuring device;

measuring an intensity of light passed through said second cell over said frequency spectrum with a second measuring device; and

determining an absorption spectrum of the impurity in the gas with the impurity based on a difference between from measured with said first measuring device and data measured with said second measuring device.

2. A method for analyzing an impurity in a gas, according to claim 1, further comprising the step of adjusting a first light path from said splitting device via said first cell to said first measuring device and a second light path from said splitting device via said second cell to said second measuring device to have identical optical characteristics.

3. A method for analyzing an impurity in a gas, according to claim 1, further comprising the step of setting a length of a first light path from said splitting device via said first cell to said first measuring device to be equal to a length of a second light path from said splitting device via said second cell to said second measuring device.

4. A method for analyzing an impurity in a gas, according to claim 3, further comprising the step of adjusting the lengths of said first and second light paths by shifting one of said first and second measuring devices.

5. A method for analyzing an impurity in a gas, according to claim 1, wherein introducing said gases into said first and second cells is performed at identical flow rates.

6. A method for analyzing an impurity in a gas, according to claim 1, further comprising the step of converting the data measured with said first and second measuring devices into digital signals.

7. A method for analyzing an impurity in a gas, according to claim 1, further comprising the step of multiplying one of the data measured with said first and second measuring devices by a coefficient corresponding to a ratio of light powers of said first and second beams.

8. A method for analyzing an impurity in a gas, according to claim 7 further comprising the step of adjusting lengths of said first and second light paths by shifting one of said first and second measuring devices;

and

determining said coefficient based on the ratio of the light powers of said first and second beams after shifting said one of said measuring devices.

9. A method for analyzing an impurity in a gas, according to claim 1, further comprising the step of covering light paths from said light irradiating source to said first and second measuring devices with a purge device comprising a gas having no optical absorption in a range of wavelength to be measured.

10. A method for analyzing an impurity in a gas, according to claim 1, wherein varying the frequency of said light comprises varying an injection current of a laser.

11. A method for analyzing an impurity in a gas, according to claim 1, wherein:

introducing said gas with said impurity into said first cell comprises introducing a matrix gas and an impurity; and

introducing said gas with no impurity into said second cell comprises introducing said matrix gas.

15. An analysis apparatus for analyzing an impurity in a gas, according to claim 10, further comprising a shifting device configured to shift at least one of said first and second measuring devices.

12. An analysis apparatus for analyzing an impurity in a gas, comprising:

a light irradiating source;

a first cell configured to contain a gas with an impurity to be measured;

a second cell configured to contain a gas with no impurity;

a frequency varying device configured to vary the frequency of a light irradiated from said light irradiating source over a frequency spectrum including an absorption frequency of said impurity;

a splitting device configured to split the light from said light irradiating source in order to pass a first beam through said first cell and to pass a second beam through said second cell;

a first measuring device configured to measure the intensity of said first beam passing through said first cell over said frequency spectrum;

a second measuring device configured to measure the intensity of said second beam passing through said second cell over said frequency spectrum;

a gas supply mechanism configured to supply the gas with the impurity to said first cell and the gas with no impurity into said second cell while maintaining identical pressures in said first and second cells; and

a determination mechanism configured to determine an absorption spectrum of the impurity in the gas with the impurity based on a difference between data measured with said first measuring device and data measured with said second measuring device.

13. An analysis apparatus for analyzing an impurity in a gas, according to claim 12, wherein a first light path from said splitting device via said first cell to said first measuring device and a second light path from said splitting device via said second cell to said second measuring device have identical optical characteristics.

14. An analysis apparatus for analyzing an impurity in a gas, according to claim 12, wherein a length of a first light path from said splitting device via said first cell to said first measuring device is equal to a length of a second light path from said splitting device via said second cell to said second measuring device.

16. An analysis apparatus for analyzing an impurity in a gas, according to claim 12, wherein said supply mechanism is configured to supply said gases into said first and second cells at identical flow rates.

17. An analysis apparatus for analyzing an impurity in a gas, according to claim 12, further comprising a converting device for converting data measured with said first and second measuring devices into digital signals.

18. An analysts apparatus for analyzing an impurity in a gas, according to claim 12, wherein said determination mechanism multiplies data measured with one of said first and second measuring devices by a coefficient corresponding to a ratio of light powers of said first and second beams.

19. An analysis apparatus for analyzing an impurity in a gas, according to claim 18, further comprising a shifting device configured to shift at least one of said first and second measuring devices,

wherein said determination mechanism determines said coefficient based on the ratio of the light powers of said first and second beams after shifting by said shifting device.

20. An analysis apparatus for analyzing an impurity in a gas, according to claim 12, further comprising a purge device configured to cover light paths from said light irradiating source to said first and second measuring devices, said purge device comprising a gas having no optical absorption in a range of wavelength to be measured.

21. An analysts apparatus for analyzing an impurity in a gas, according to claim 12, wherein said light irradiating source comprises a semiconductor laser.

22. An analysts apparatus for analyzing an impurity in a gas, according to claim 12, wherein:

said first cell is configured to contain a matrix gas and said impurity; and

said second cell is configured to contain said matrix gas.