INFRARED GAS ANALYZER

• US 3,678,262 A
• Filed: 04/30/1971
• Issued: 07/18/1972
• Est. Priority Date: 09/01/1965
• Status: Expired due to Term

• Current Assignee: Pierre Herrmann
• Original Assignee: Pierre Herrmann
• Inventors: Herrmann, Pierre
• Primary Examiner(s): Borchelt, Archie R.
• Assistant Examiner(s): Church, C. E.
• Application Number:
  US05/138,876
• Time in Patent Office: 445 Days
• Field of Search: 250/43.5R
• US Class Current: 250/339.13
• CPC Class Codes: G01N 21/3103 Atomic absorption analysis
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
• CPC Class Codes: G01N 21/37 using pneumatic detection opto-acoustic detection G01N21/1702

Abstract

The analyzer comprises, in succession, an infrared ray source, a modulator, an analysis chamber containing the mixture of gasses, and a detector together with associated electronic circuits for processing the electric signals delivered by the detector. The modulator periodically interposes in the path of the radiation of gaseous reference filter which absorbs the characteristic lines of the particular gas to be analyzed, and a measurement filter which does not absorb these lines. The filters are separated from each other by two identical base filters comprising an element permitting grey transmission slightly lower than the average transmission of the reference filter so that the detector delivers successively a measurement signal and a reference signal respectively defined with respect to a common level determined by the base filters. The electronic processing circuits comprise means for amplifying and demultiplexing the signals and means for establishing and reading out the quotient of the measurement signal and the reference signal. This quotient is representative of only the concentration sought.

Claims

1. Apparatus for obtaining By absorption of infrared rays the concentration of a given gas present in a mixture of gasses to be analyzed, comprising:

an infrared ray source, for emitting infrared radiation;

an analysis chamber adapted to contain the mixture, and disposed in the path of the radiation emitted by said source;

a modulator for periodically interposing in the path of said radiation a gaseous reference filter which absorbs the characteristic lines of the given gas and a measurement filter which does not absorb these lines;

a non-selective detection cell disposed to receive the radiation after is has been modulated and after it has passed through the analysis chamber, said detection cell delivering electric signals in response to the radiation that it receives; and

electronic circuits for processing the electric signals delivered by the cell;

wherein the said filters of the modulator are separated from one another by two identical base filters comprising an element permitting grey transmission slightly lower than the average transmission of said reference filter so that the cell delivers successively a measurement signal and a reference signal respectively defined with respect to a common level determined by said base filters; and

wherein said electronic processing circuits comprise means for amplifying and demultiplexing said signals, and means for establishing and reading out the quotient of said measurement signal and said reference signal, said quotient being representative only of the concentration sought.

2. Gas analyzer apparatus according to claim 1, wherein the base filters comprise, in addition to an element permitting grey transmission, a gaseous filter identical to said reference filter.

3. Modulator for the apparatus according to claim 1 comprises a sealed annular chamber containing the particular gas sought, this chamber being constituted between two parallel superimposed plates in an annulus of a material transparent to infred and then polished, said chamber being divided into four sectors, the first sector being occupied by a piece having polished parallel faces which is cut from the same material, this first sector constituting said measurement filter, the second and third sectors being diametrically opposed and comprising on one of the plates spots opaque to infrared, these second and third sectors constituting said base filters, and the fourth sector being free and constituting the reference filter.

4. Modulator according to claim 3, wherein the opaque spots are serigraphic.

5. Modulator according to claim 3, wherein the radial edges of the transparent pieces having parallel faces disposed in the annular chambers are perpendicular to said faces and well polished.

6. Modulator according to claim 3, wherein a small angular sector without spots is provided between each radial edge of said pieces having parallel faces and the edges of the base sectors contiguous to said edges.

7. Modulator according to claim 3, wherein each of the concentric walls of the annular chambers comprise at least one circular or helical groove occupying a width approximately equal to the height of said chambers, with a mat black coating applied to said walls.

8. Modulator according to claim 3, wherein annular plates forming the chambers bear against shoulders formed on the one hand at the exterior of a hub and/or at least of a ring engaged on said hub, and on the other hand at the interior of rims superimposed and stacked one in another, the various elements of said modulator being rigidly secured to one another by blueing.

9. Modulator according to claim 12, wherein certain chambers have a height substantially greater than the thickness of the transparent pieces disposed in said chambers.

10. Apparatus for obtaining by absorption of infrared rays the respective concentrations of a number N of given gasses present in a mixture to be analyzed, comprising, in combination:

a source of infrared rays;

an analysis chamber adapted to contain said mixture and disposed in the path of the rAys emitted by said source;

a modulator for periodically interposing in the path of the rays, a gaseous reference filter absorbing the totality of the characteristic lines of said N given gasses and N gaseous measurement filters each corresponding to a particular given gas and absorbing respectively the characteristic lines of all the given gasses other than the lines of said particular gas;

said (N +

     1) gaseous filters being separated from one another by (N +

     1) identical base filters comprising an element permitting grey transmission slightly lower than the average transmission of said reference filter;

a non-selective detection cell disposed to receive the modulated rays that have passed through the analysis chamber, said detection cell successively delivering, in response to the rays that it receives, N measurement signals and a reference signal respectively defined with respect to a common base level;

electronic circuits for processing said signals to a common base level;

electronic circuits for processing said signals comprising means for amplifying and demultiplexing said signals and means for establishing and reading out the quotients of said N measurement signals and said reference signal, said quotients being respectively representative of only the concentrations sought.

11. Gas analyzer apparatus according to claim 10, wherein the base filters comprise, in addition to an element permitting grey transmission, a gaseous filter identical to said reference filter.

12. Modulator for the device according to claim 10 comprising N sealed annular chambers adapted to contain respectively said N gasses sought, said N chambers being constituted by (N + 1) parallel superimposed plates cut in an annulus of a material transparent to infrared and then polished, the modulator being divided into 2 (N + 1) sectors which constitute respectively the N measurement filters, the reference filter and the (N + 1) base filters, said N measurement filters comprising N pieces having polished parallel faces and which are cut in the same material and are respectively disposed in said N chambers, said (N + 1) base filters comprising on a given plate (N + 1) sectors covered with spots opaque to infrared, said reference filter being constituted by the free sector.

13. Modulator according to claim 12, wherein the radial edges of the transparent pieces having parallel faces disposed in the annular chambers are perpendicular to said faces and well polished.

14. Modulator according to claim 12, wherein a small angular sector without spots is provided between each radial edge of said pieces having parallel faces and edges of the base sectors contigous to said edges.

15. Modulator according to claim 12, wherein each of the concentric walls of the annular chambers comprise at least one circular or helical groove occupying a width approximately equal to the height of said chambers, with a mat black coating applied to said walls.

16. Modulator according to claim 12, wherein the annular plates forming the chambers bear against shoulders formed on the one hand at the exterior of a hub and/or at least of a ring engaged on said hub, and on the other hand at the interior of rims superimposed and stacked one in another, the various elements of said modulator being rigidly secured to one another by glueing.

17. Apparatus according to claim 1, wherein the means for applying the measurement signal and the reference signal comprise an amplifier whose gain is variable under the action of a control voltage, and a loop for regulating the amplitude of the demultiplexed reference signal, incorporating said variable gain amplifier, is provided so that the demultiplexed measurement signal obtained is directly the quotient sought.

18. Apparatus according to claim 10, wherein the means for amplifying the measurement signals and the reference signal comprise an amplifier whose gain is Variable under the action of a control voltage, and a loop for regulating the amplitude of the demultiplexed reference signal, incorporating said variable gain amplifier, is provided so that the demultiplexed measurement signals obtained are directly the quotients sought.