GAS ANALYZER

• US 3,811,776 A
• Filed: 02/26/1973
• Issued: 05/21/1974
• Est. Priority Date: 02/26/1973
• Status: Expired due to Term

• Current Assignee: ERT, Inc.
• Original Assignee: Henry H. Blau Jr
• Inventors: Blau, Henry H. Jr.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Evans, F. L.
• Application Number:
  US05/336,078
• Time in Patent Office: 449 Days
• Field of Search: 356/51,74,88,93,184-186,188,195,201,204-206 250/218,343,373
• US Class Current: 356/51
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques

Abstract

Gas in a sample region is analyzed in a nondispersive system for the presence of a particular gas of interest by cross-correlating the absorption spectra of the sample and a specimen of the gas of interest. Radiation is directed through the sample region and a filter for isolating a narrow band of frequencies within the absorption band of the gas of interest, to a radiation detector. The radiation is passed through cells that provide the total energy transmitted at the line or lines of interest and a reference energy transmitted by a region adjacent to the lines of interest and unaffected by changes in absorption in the sample region. In one embodiment this is accomplished by passing the radiation from the filter in rapid succession through three cells typically containing, respectively, an inert gas, the gas of interest at a pressure of about one atmosphere and the gas of interest at approximately two atmospheres pressure, to produce three signals which are normalized by ratioing with three comparable signals taken at the same times by transmitting part of the radiation passed by the three cells, through a reference gas cell. The normalized signals are then combined by a conventional electronic system to give the fractional absorption of the gas of interest in the sample region. An interferometer containing in one leg, a cell containing the gas of interest at a pressure of about two atmospheres, may be located in the radiation path between the cells and the detector.

Claims

1. In an optical, nondispersive absorption analyzer having a filter for passing radiation in a relatively narrow spectral band incluDing absorption lines of a material of interest, a first radiation detector sensitive in said band;

means for directing a beam of radiation, which has passed through a sample region containing material to be analyzed, through said filter to said first detector;

means for determining total energy flux transmitted to said first detector within said lines of interest; and

means for determining total energy flux transmitted to said first detector in said band immediately adjacent to said lines of interest and substantially invariant with changes in absorption at said lines of interest by said material in said sample region, the improvement comprising;

a reference cell for containing said material of interest;

means for transmitting part of said beam, after passage thereof through said sample region and filter, through said reference cell;

a second radiation detector sensitive in said band and disposed in the path of said beam transmitted through said reference cell.

2. An absorption analyzer as defined in claim 1 wherein said means for determining said energy fluxes comprises a first light-transmitting cell capable of substantially nonabsorptively transmitting radiation at said lines of interest, a second light-transmitting cell capable of substantially absorbing all of the radiation within only said lines of interest, and a third light-transmitting cell capable of substantially absorbing all of the radiation with said lines of interest and also only selected portions of said band immediately adjacent to said lines of interest.

3. An absorption analyzer as defined in claim 2 wherein said material in said sample region is a gas of interest, said first detector is adapted to provide signals corresponding to a first fixed fraction of the radiative flux transmitted by each of said light transmitting cells, and said second detector is adapted to provide signals corresponding to a second fixed fraction of the radiative flux transmitted by the combination of each of said light transmitting cells and said reference cell.

4. An absorption analyzer as defined in claim 3 including means for ratioing each signal from said first detector corresponding to transmission by each of said light transmitting cells, with the signals from said second detector corresponding to transmission by the same light transmitting cells thereby to provide normalized signals.

5. An absorption analyzer as defined in claim 4 including means for combining said normalized signals to obtain a signal which corresponds to the fractional absorption of the gas of interest in said sample region.

6. In an optical, nondispersive absorption analyzer having a filter for passing radiation from a sample region in a relatively narrow spectral band including absorption lines of a material of interest, and a radiation detector sensitive in said band, the improvement comprising;

a first light-transmitting cell capable of substantially non-absorptively transmitting radiation at said lines of interest;

a second light-transmitting cell capable of substantially absorbing all of the radiation within said lines of interest;

means for matching the transmission characteristics of said cells within said spectral band so that they can both transmit substantially the same total energy flux of a first beam of radiation of said band, which beam had not been attenuated by absorption at said lines of interest;

means for directing a second beam of radiation, which has passed through said sample region containing material to be analyzed, through said filter and thence through respective ones of said cells to said detector; and

means for determining any difference between the energy flux in said second beam as transmitted by said respective cells to said detector.

7. An analyzer as defined in claim 6 wherein said means for matching comprises means for uniformly attenuating over substantially said spectral band, radiation transmitted by said first cell, so that the combInation of said first cell and attenuating means passes the same total flux as said second cell alone when no material of interest is in said sample region.

8. An analyzer as defined in claim 7 wherein said means for attenuating can be selectively positioned so as to either attenuate radiation transmitted by said first or said second cell and;

wherein said detector is adapted to generate signals V, Y and S corresponding to the total radiation flux in said second beam transmitted to said detector respectively by a combination of said first cell and said attenuation means, said second cell without said attenuating means, and the combination of said cell and said attenuating means.

9. An analyzer as defined in claim 8 including means for so combining said signals as to obtain the fractional absorption of material of interest in said sample region as expressed by the ratio V-Y/V-S.

10. An analyzer defined in claim 6, further including;

a third light transmitting cell capable of substantially absorbing all of the radiation within said lines of interest, and wherein said means for matching comprises first means for uniformly attenuating over substantially said spectral band, radiation transmitted by said first cell, so that the combination of said first cell and first attenuating means passes the same total flux as said second cell alone when no material of interest is in said region;

second means for uniformly attenuating over substantially said spectral band, and having the same transmission characteristics as said first attenuating means, said second attenuating means being associated with said third cell so as to attenuate radiation transmitted through said third cell;

said detector being adapted to generate signals V, Y and S corresponding to the total radiation flux in said second beam transmitted to said detector respectively by the combination of said first cell and said first attenuating means, said second cell, and the combination of said third cell and second attenuating means.

11. An analyzer as defined in claim 10 including means for so combining said signals as to obtain the fractional absorption of the material of interest in said sample region as expressed by the ratio V-Y/V-S.

12. In an optical, nondispersive absorption analyzer having a filter for passing radiation from a sample region in a relatively narrow spectral band including absorption lines of a material of interest, and a first radiation detector sensitive in said region, the improvement comprising:

a first light-transmitting cell capable of substantially absorbing all of the radiation within said lines of interest;

a second light-transmitting cell capable of substantially absorbing radiation within other selected absorption lines within said band;

means for matching transmission characteristics of said cells within said spectral band so that they will each transmit substantially the same radiation intensities of unabsorbed portions of a beam of radiation in said band, and will each absorb substantially identical amounts of flux from said beam; and

means for directing said beam of radiation, after passage thereof through a sample region containing material to be analyzed, through said filter and thence through respective ones of said cells to said first detector.

13. An analyzer as defined in claim 12 including a third light-transmitting cell capable of substantially non-absorptively transmitting radiation at said lines of interest and at said other selected lines.

14. An analyzer as defined in claim 13 including means for determining a first difference (X-Z) between the energy flux in said beam as transmitted by said third cell and said second cell and detected by said first detector, a second difference (X-Y) between the energy flux in said beam as transmitted by said third cell and said second cell and detected by said first detector.

15. An analyzer as defined in claim 14 including means for determining the ratio of the difference between said first and second differences with respect to said first difference thereby to determine the fractional absorption provided by said material of interest present in said radiation from said sample region.

16. An analyzer as defined in claim 12 wherein said first cell includes a first material capable of substantially absorbing all of the radiation within said lines of interest, and said second cell includes a second material capable of absorbing radiation within said other selected absorption lines;

said analyzer further including a reference cell for containing a mixture of both said first and second materials;

a second radiation detector sensitive in said band, and means for transmitting part of said beam, after passage thereof through said sample region and said filter through a respective one of said first and second cells and thence through said reference cell to said second detector.

17. An analyzer as defined in claim 16 including means for establishing the ratio of the energy flux in said beam as transmitted by said first cell to said first detector and by said first cell and reference cell to said second detector, means for establishing the ratio of the energy flux in said beam as transmitted by said second cell to said first detector, and by said second cell and reference cell to said second detector, and means for determining any difference between said ratios.