Multi-component infrared analyzer

• US 3,904,880 A
• Filed: 05/10/1973
• Issued: 09/09/1975
• Est. Priority Date: 05/10/1973
• Status: Expired due to Term

• Current Assignee: Arlon D. Kompelien, Donald E. Benz, James H. Garfunkel
• Original Assignee: Arlon D. Kompelien, Donald E. Benz, James H. Garfunkel
• Inventors: Benz, Donald E., Garfunkel, James H., Kompelien, Arlon D.
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US05/359,144
• Time in Patent Office: 852 Days
• Field of Search: 250/339,343,344,345,346
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques

Abstract

A multi-component nondispersive infrared correlation spectrometer for selectively analyzing for a plurality of gases of interest in a gaseous mixture utilizes a rotating filter wheel containing filter systems corresponding to each gas of interest sought. Each filter system contains an ordered pair of filters to sequentially create filtered reference and analysis paths for each gas of interest between a source of infrared radiation and a detector. Special synchronization and signal analysis systems are provided to produce an output signal for each gas of interest. These systems are coordinated with the rotation of the filter wheel in a manner which allows a plurality of gases of interest to be analyzed with simultaneous output.

Claims

1. A multi-component gas analysis apparatus for a selective analysis for one or more gases of interest in a gaseous mixture wherein each of said gases of interest has a characteristic infrared absorption spectrum associated therewith, said apparatus comprising:

a source of infrared radiation;

a first filter system for an analysis for a first gas of interest in said gaseous mixture, said first filter system having first and second filtering means;

said first filtering means having first and second filter elements aligned to receive said infrared radiation from said source during a first time duration, said first filter element being a filter cell means containing said first gas of interest at substantially constant pressure and said second filter element being a bandpass filter having a narrow passband which contains at least in part a strong absorption line of said first gas of interest, and said second filtering means having a third filter element to receive said infrared radiation from said source during a second time duration, said third filter element being a bandpass filter having substantially said passband of said seond filter element;

detector means to receive said infrared radiation passed through both said gaseous mixture and said first filter system to provide a response in an output signal, said detector means being capable of an output signal response to received radiation in less than said first time duration and in less than said second time duration;

signal processing means to obtain from said output signal a first apparatus output indicating an analysis result as to said first gas of interest; and

synchronization means for synchronizing operation of said signal processing means to said first and second time durations.

2. The apparatus of claim 1, further comprising sample cell means for containing a sample of said gaseous mixture at substantially constant pressure.

3. The apparatus of claim 1, further comprising means for disposing said first and said second filtering means in a predetermined path including along said path said source of infrared radiation said sample cell and said detector means.

4. The apparatus of claim 3 wherein said means for disposing said first and said second filtering means in said predetermined path comprises a rotatable wheel having said first and said second filtering means fixed thereto in radial symmetry.

5. The apparatus of claim 4 further comprising means driving said wheel to dispose said first and said second filtering means repeatedly in said predetermined path.

6. The apparatus of claim 1 further comprising means for directing said infrared radiation along said predetermined path.

7. The apparatus of claim 1 wherein said second filtering means further comprises a fourth filter element aligned with said third filter element to receive said infrared radiation from said source during said second time duration, said fourth filter element being transparent to infrared radiation.

8. The apparatus of claim 7 wherein said fourth filter element comprises a filter element cell containing at substantially constant pressurre a gas transparent to infrared radiation.

9. The apparatus of claim 8, wherein said gas transparent to infrared radiation is nitrogen.

10. The apparatus of claim 8, wherein said first filtering system further comprises:

a fifth filter element aligned with said first and second filter elements to receive said infrared radiation from said source during said first time duration, said fifth filter element being a filter cell means for containing at substantially constant pressure a gas havIng an infrared absorption spectrum which overlaps that of said first gas of interest in said passband of said second filter element; and

a sixth filter element aligned with said third filter element to receive said infrared radiation from said source during said second time duration, said sixth filter element being a filter cell means for containing a substantially constant pressure a gas having an infrared absorption spectrum which overlaps that of said first gas of interest in the passband of said third filter element.

11. The apparatus of claim 1 wherein said first and said second time durations are substantially equal.

12. The apparatus of claim 1 wherein said first and second time durations are less than 10 milliseconds.

13. The apparatus of claim 1 wherein said detector means comprises a single solid state detector.

14. The apparatus of claim 12 wherein said detector means is a photoconductive detector.

15. The apparatus of claim 12 wherein said detector means is a mercury cadmium telluride detector.

16. The apparatus of claim 1 wherein said output signal has a first signal lobe in said first time duration and a second signal lobe in said second time duration and said signal processing means provides an apparatus output related to a ratio of said first and second signal lobes.

17. The apparatus of claim 1 wherein said first filtering means has a fixed relationship to said second filtering means and a reference means is provided in a fixed relationship with both said first and second filtering means, said synchronizing means deriving through said reference means a reset triggering signal such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

18. The apparatus of claim 1 wherein said first filtering means has a fixed relationship to said second filtering means and a reference means is provided with said first filtering means, said synchronizing means deriving through said reference means a reset triggering signal during said first time duration such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

19. The apparatus of claim 18 wherein said synchronizing means has no electrical switching occurring therein during said first time duration except that switching required to provide said reset triggering signal and that switching which occurs in response to provision of said reset triggering signal.

20. The apparatus of claim 1 wherein said first filtering means has a fixed relationship to said second filtering means and a reference means is provided with said second filtering means, said synchronizing means deriving through said reference means a reset triggering signal in said second time duration such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

21. The apparatus of claim 20 wherein said synchronizing means has no electrical switching occurring therein during said second time duration except that switching required to provide said reset triggering signal and that switching which occurs in response to provision of said reset triggering signal.

22. The apparatus of claim 1 further comprising:

a second filter system for an analysis for a second gas of interest in said gaseous mixture means, said second filtering system having third and fourth filtering means;

said third filtering means having fourth and fifth filter elements aligned to receive said infrared radiation from said source during a third time duration, said fourth filter element being a filter cell means containing said second gas of interest at substantially constant pressure and said fifth filter element being a bandpass filter having a narrow passband which contains at least in part a strong absorption line of said second gas of intereSt, and said fourth filtering means having a sixth filter element to receive said infrared radiation from said source during a fourth time duration, said sixth filter element being a bandpass filter having substantially said passband of said fifth filter element;

said detector means to also receive said infrared radiation passed through both said gaseous mixture and said second filter system to provide response in said output signal, said detector means being capable of an output signal response to received radiation in less than said third time duration and in less than said fourth time duration;

said signal processing means to also obtain from said output signal a second apparatus output indicating an analysis result as to said second gas of interest; and

said synchronization means to also synchronize operation of said signal processing means to said third and fourth time durations.

23. The apparatus of claim 22 further comprising sample cell means for containing a sample of said gaseous mixture at substantially constant pressure.

24. The apparatus of claim 22 further comprising;

a rotatable filter wheel having said first through said fourth filtering means fixed thereto in radial symmetry and wherein the rotation of said filter wheel sequentially disposes said first through said fourth filtering means in a predetermined path including along said path said source of infrared radiation and said detector means.

25. The apparatus of claim 22 wherein said first through said fourth time durations are substantially equal.

26. The apparatus of claim 22 wherein first through said fourth time durations are less then 10 milliseconds.

27. The apparatus of claim 22 wherein said detector means is a single solid state detector.

28. The apparatus of claim 27 wherein said detector means is a photoconductive detector.

29. The apparatus of claim 27 wherein said detector means is a mercury cadmium telluride detector.

30. The apparatus of claim 22 wherein said output signal has a first signal lobe in said first time duration, a second signal lobe in said second time duration, a third signal lobe in said third time duration and a fourth signal lobe in said fourth time duration;

and said first apparatus output is related to a ratio of said first and second signal lobes and said second apparatus output is related to a ratio of said third and fourth signal lobes.

31. The apparatus of claim 22 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided in a fixed relationship with both said first and second filter systems, said synchronizing means deriving through said reference means a reset triggering signal such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

32. The apparatus of claim 22 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided with said first filter system through which said synchronizing means derives a reset triggering signal during one of said first and second time durations, said reset triggering signal causing, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

33. The apparatus of claim 32 wherein said synchronizing means has no electrical switching occurring therein during said one of said first and second time durations in which said reset triggering signal is derived except that switching required to provide said reset triggering signal and that switching which occurs in response to provision of said reset triggering signal.

34. The apparatus of claim 22 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided in a fixed relationship with both said first and second filter systems, said synchronizing means deriving through said reference means a reset tRiggering signal such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

35. The apparatus of claim 22 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided with said first filter system through which said synchronizing means derives a reset triggering signal during one of said first and second time durations, said reset triggering signal causing, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

36. The apparatus of claim 35 wherein said synchronizing means has no electrical switching occurring therein during said one of said first and second time durations in which said reset triggering signal is derived except that switching required to provide said reset triggering signal and that switching which occurs in response to provision of said reset triggering signal.

37. The apparatus of claim 22 wherein said signal processing means has a channel demultiplexing switching means contained therein, said channel demultiplexing switching means, as controlled by said synchronizing means, to direct first and second channel signals, as derived from said first and second signal lobes, to a first subchannel electronic system and to direct third and fourth channel signals, as derived from said third and fourth signal lobes, to a second subchannel electronic system.

38. The apparatus of claim 37 wherein said signal processing means has a subchannel demultiplexing switching means provided in said first subchannel electronic system, said subchannel demultiplexing switching means, as controlled by said synchronizing means, to direct a first subchannel signal, as derived from a first channel signal, to a first averaging means having a first averaging means output signal and to direct a second subchannel signal, as derived from said second channel signal, to a second averaging means having a second averaging means output signal.

39. The apparatus of claim 38 wherein said first and second subchannel signals are derived from said first and second channel signals through a controlled gain element, said controlled gain element having its gain controlled by one of said first and second averaging means output signals through an electronic feedback loop.

40. The apparatus of claim 39 wherein said electronic feedback loop acts to hold substantially constant said one of said first and second averaging means output signals used to control said controlled gain element.

41. The apparatus of claim 40 wherein said first apparatus output is obtained from an output signal of an output amplifier which has as said output signal a signal proportional to a difference between said first and second averaging means output signals.

42. The apparatus of claim 41 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided in a fixed relationship with both said first and second filter systems, said synchronizing means deriving through said reference means a reset triggering signal such that said reset triggering signal causes, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

43. The apparatus of claim 42 wherein said first filter system has a fixed relationship to said second filter system and a reference means is provided with said first filter system through which said synchronizing means derives a reset triggering signal during one of said first and second time durations, said reset triggering signal causing, upon its occurrence, electronic systems in said synchronizing means to be reset to a preselected electronic state.

44. The apparatus of claim 42 wherein said signal processing means provides for a transmission of at least one of said signal lobes, said channel signals and said subchannel signals between two points by use of a capaciTor means, said capacitor means being discharged to some voltage level after said transmission by having a switch close to provide a discharge path.

45. The apparatus of claim 44 wherein said synchronizing means has no electrical switching occurring therein during said one of said first and second time durations in which said reset triggering signal is derived except that switching required to provide said reset triggering signal and that switching which occurs in response to provision of said reset triggering signal.

46. A multi-component gas analysis apparatus for a selective analysis for a plurality of gases of interest in a gas sample wherein each of said gasses of interest has a characteristic infrared absorption spectrum associated therewith, said apparatus comprising:

a source of infrared radiation;

a sample cell means to contain said gas sample to be analyzed at substantially constant pressure;

a plurality of filter systems each of which is associated with an analysis for a corresponding one of said plurality of gases of interest, each of said filter systems having first and second filtering means;

said first filtering means having first and second filter elements aligned to receive said infrared radiation from said source during a time duration which forms part of a corresponding one of a plurality of periodic subsequences of a sequence of time durations, said first filter element being a filter cell means containing said corresponding gas of interest at substantially constant pressure and said second filter element being a bandpass filter having a narrow passband which contains at least in part a strong absorption line of said corresponding gas of interest, and said second filtering means having a third filter element to receive said infrared radiation from said source during another time duration which forms part of another corresponding one of said plurality of periodic subsequences being a bandpass filter, said third filter element having substantially said pass-band of said second filter element;

detector means to receive said infrared radiation passed through both said sample means and said plurality of filter systems to provide responses in an output signal, said detector means being capable of output signal responses to received radiation in less than each of said time durations;

signal processing means to obtain from said output signal an apparatus output indicating an analysis result as to each of said gases of interest; and

synchronization means for synchronizing operation of said signal processing means to said periodic subsequences of saaid durations.