METHOD AND SYSTEM FOR THE INFRARED ANALYSIS OF GASES

• US 3,790,797 A
• Filed: 09/07/1971
• Issued: 02/05/1974
• Est. Priority Date: 09/07/1971
• Status: Expired due to Term

• Current Assignee: James E. Young, John W. Lennington, Stanley R. Sternberg
• Original Assignee: James E. Young, John W. Lennington, Stanley R. Sternberg
• Inventors: Young, James E., Lennington, John W., Sternberg, Stanley R.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Nelms, D. C.
• Application Number:
  US05/178,260
• Time in Patent Office: 882 Days
• Field of Search: 250/43.5,83,83.3H 356/78,82,156,181,96,97
• US Class Current: 250/345
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 2201/1215 for interfering gases

Abstract

A dual path analyzer and a single path analyzer are disclosed, each for determining the concentration of one or more gaseous components in a mixture of gases. The preferred analyzer is a single path instrument which includes a source of infrared energy, a detector for the energy, a sample cell for the gas mixture positioned between the source and detector, and a filter wheel having a plurality of filters and a source blocking device positioned between the sample cell and detector for sequentially interposing the filters and the source blocking device between the source and the detector. Means are provided for amplifying the output signal of the detector and for processing the signal to provide a direct readout display which indicates the concentration of the gaseous components being analyzed. The processing electronics preferably include provision for calibrating the analyzer with clean ambient air, for compensating for background levels of radiation, and for correcting the displayed output signal for the effects of absorption band interferences between two or more gases in the gas mixture. The structure of the dual path analyzer includes a source of infrared energy, a detector for the energy, a sample cell for the gas mixture, a cell for a reference gas, and optical path means between the source and detector for sequentially directing the source energy through the sample cell, the reference cell, and through neither cell. Processing electronics similar to the single path instrument can be incorporated to compensate for background radiation and absorption band interferences.

Claims

1. A spectrophotometer for analyzing fluids through which energy is transmitted to determine the concentration of a component therein comprising:

detecting means for receiving said energy after transmission through said fluid and for providing an output signal representative of the intensity of the received energy;

first component filter means having a predetermined bandpass at which a first component has a predetermined low transmissivity of said energy, said first component filter means being adapted for transmission of said energy therethrough to said detecting means;

second component filter means having a predetermined bandpass at which a second component has a predetermined low transmissivity of said energy, said second component filter means being adapted for transmission of said energy therethrough to said detecting means;

reference filter means having a predetermined bandpass at which said first component and all other components of said fluids have a predetermined high transmissivity of said energy, said reference filter means being adapted for transmission of said energy therethrough to said detecting means;

means for interrupting the transmission of said energy to said detecting means;

means for receiving the output signal of said detector and for providing a reference signal representative of the intensity of energy transmitted through said fluid and said reference filter means, a first component signal representative of the intensity of said energy transmitted through said fluid and said first component filter means, a second component signal representative of the intensity of said energy transmitted through said fluid and said second component filter means, and at least one background signal representative of the detector output signal with the transmission of said energy interrupted by said interrupting means, said detector output signal receiving means further including means for compensating said reference signal, said first component signal and said second component signal in accordance with said background signal; and

spectrum interference compensating means for adjusting said first component signal for a contribution thereto due to a concentration of said second component in said analyzed fluid.

2. A spectrophotometer according to claim 1 wherein said spectrum interference compensating means adjusts said second component signal for a contribution thereto due to a concentration of said first component in said analyzed fluid.

3. A spectrophotometer according to claim 1 wherein said spectrum interference compensating means receives said second component signal for adjusting said first component signal for said contribution thereto due to a concentration of said component in said analyzed fluid in accordance with said second component signal.

4. A spectrophotometer according to claim 3 wherein said spectrum interference compensating means receives said first component signal for adjusting said second component signal for a contribution thereto due to a concentration Of said first component in said analyzed fluid in accordance with said first component signal.

5. A spectrophotometer according to claim 3 wherein said first and second component signals have values representative of the respective transmitted energies, said sprectrum interference compensating means adjusts the value of said received second component signal in accordance with said contribution of said second component to said first component signal and adjusts the value of said first component signal in accordance with said adjusted-value second component signal.

6. A spectrophotometer according to claim 5 wherein said spectrum interference compensating means linearly adjusts the value of said second component signal.

7. A spectrophotometer according to claim 6 wherein said spectrum interference compensating means includes resistive means for linearly adjusting the value of said second component signal.

8. A spectrophotometer according to claim 1 wherein said second component is water vapor.

9. A spectrophotometer according to claim 1 wherein said detector output signal receiving means provides one background signal for compensating said reference and said first component signals.

10. A spectrophotometer according to claim 1 wherein said detector output signal provides a first component background signal being representative at least in part of the background provided by said first component filter means for compensating said first component signal, and provides a reference background signal being representative at least in part of the background provided by said first reference filter means for compensating said reference signal.

11. A spectrophotometer according to claim 1 wherein said first and second component filter is a single variable-bandpass filter.

12. A spectrophotometer for analyzing a fluid having first and second components therein for determining the concentration of said first component comprising:

means for providing a first component electrical signal having a value which is related at least to the concentrations of said first and second components of said fluid, with said concentration of said second component contributing to said value of said first component electrical signal to a first degree;

means for providing a second component electrical signal having a value which is related at least to the concentration of said second component of said fluid, with said concentration of said second component contributing to said value of said second component electrical signal to a second degree which differs from said first degree; and

means for adjusting the value of said first component electrical signal in accordance with the value of said second component electrical signal and in accordance with the difference between said first and second degrees of contribution of said concentration of said second component of said fluid to the values of said first and second component electrical signals to provide a compensated first component electrical signal having a value representative of the concentration of said first component of said fluid.

13. A spectrophotometer according to claim 12 wherein the value of said first component electrical signal is adjusted in accordance with a linear function of the value of said second component electrical signal.

14. A spectrophotometer according to claim 12 further including:

means for providing a third component electrical signal having a value which is related at least to the concentration of a third component of said fluid;

said means for adjusting the value of said first component electrical signal additionally adjusts the value of said first component electrical signal in accordance with the value of said third component electrical signal.

15. A spectrophotometer according to claim 12 further including means for adjusting the value of said second component electrical signal in accordance with the value of said first component electrical signal.

16. A spectrophotometer according to claim 14 further including means for adjusting the value of said second component electrical signal in accordance with the value of said third component electrical signal.

17. A spectrophotometer according to claim 16 wherein said means for adjusting the value of said second component electrical signal additionally adjusts the value of said second component electrical signal in accordance with said first component electrical signal.

18. A spectrophotometer according to claim 12 wherein said adjusting means adjusts the value of said first component electrical signal in accordance with a linear relationship with the value of said second component electrical signal.

19. A spectrophotometer according to claim 18 wherein said first component electrical signal is linearly related to the concentrations of said first and second components of said fluid and said second component electrical signal is linearly related to the concentration of said second component of said fluid.

20. A spectrophotometer according to claim 12 wherein said adjusting means adjusts the value of said first component electrical signal by adding at least a portion of said second component electrical signal to said first component electrical signal.

21. A spectrophotometer according to claim 12 wherein said first component electrical signal has a value which is representative of the absorption of energy within a first band of wave lengths by said fluid and said second component electrical signal has a value which is representative of the absorption of energy within a second band of wave lengths by said fluid.

22. A spectrophotometer according to claim 21 wherein said first band of wave lengths is selected so that at least said first and second components of said fluid contribute to the absorption of energy within said first band of wave lengths and said second band is selected so that at least said second component of said fluid contributes to the absorption of energy within said second band of wave lengths.

23. A spectrophotometer for analyzing a fluid having first and second components therein for determining the concentration of said first component comprising:

means for providing a first component electrical signal having a value which is related at least to the concentrations of said first and second components of said fluid, with said concentration of said second component contributing to said value of said first component electrical signal to a first degree;

means for providing a second component electrical signal having a value which is related at least to the concentration of said second component of said fluid, with said concentration of said second component contributing to said value of said second component electrical signal to a second degree which differs from said first degree;

transfer means receiving said second component electrical signal for adjusting the value of said second component electrical signal in accordance with the difference between said first and second degrees of contribution of said concentration of said second component to the values of said first and second component electrical signals to provide an adjusted second component signal having said adjusted value; and

means for receiving said first component electrical signal and said second component electrical signal for adjusting the value of said first component signal in accordance with the value of said adjusted second component electrical signal to provide a compensated first component electrical signal having a value representative of the concentration of said first component of said fluid.

24. A spectrophotometer according to claim 23 wherein said last means adjusts the value of said first component electrical signal in accordance with a linear relationship with the value of said second component electrical signal.

25. A spectrophotometer according to claim 24 wherein said first component electrical signal is linearly related to the concentratIons of said first and second components of said fluid and said second component electrical signal is linearly related to the concentration of said second component of said fluid.

26. A spectrophotometer according to claim 23 wherein said last means adjusts the value of said first component electrical signal by adding said adjusted second component electrical signal to said first component electrical signal.

27. A spectrophotometer according to claim 23 wherein said first component electrical signal has a value which is representative of the absorption of energy within a first band of wave lengths by said fluid and said second component electrical signal has a value which is representative of the absorption of energy within a second band of wave lengths by said fluid.

28. A spectrophotometer according to claim 27 wherein said first band of wave lengths is selected so that at least said first and second components of said fluid contribute to the absorption of energy within said first band of wave lengths and said second band is selected so that at least said second component of said fluid contributes to the absorption of energy within said second band of wave lengths.

29. A spectrophotometer according to claim 23 wherein said transfer means includes resistor means for reducing the value of said second component electrical signal, said resistor means having a resistive value which is selected in accordance with the difference between said first and second degrees of contribution of said concentration of said second component to the values of said first and second component electrical signals to provide an adjusted second component electrical signal having said reduced value.

30. A spectrophotometer according to claim 29 wherein said last means adjusts the value of said first component electrical signal by adding said adjusted second component electrical signal to said first component electrical signal.

31. A spectrophotometer for analyzing a fluid having first and second components therein for determining the concentration of said first and second components comprising:

means for providing a first component signal having a value which is related at least to the concentrations of said first and second components of said fluid;

means for providing a second component signal having a value which is related at least to the concentrations of said first and second components of said fluid; and

means for linearly adjusting the value of said first component signal in accordance with the value of said second component signal an amount in accordance with the contribution of said concentration of said second component of said fluid to the value of said first component signal to provide a compensated first component signal having a value representative of the concentration of said first component of said fluid, and for linearly adjusting the value of said second component signal in accordance with the value of said first component signal an amount in accordance with the contribution of said concentration of said first component of said fluid to the value of said second component signal to provide a compensated second component signal having a value representative of the concentration of said second component of said fluid.

32. A spectrophotometer according to claim 31 wherein said adjusting means adjusts the value of each of said first and second component electrical signals in accordance with a linear relationship with the value of the other of said first and second component electrical signals.

33. A spectrophotometer according to claim 32 wherein said first component electrical signal is linearly related to the concentrations of said first and second components of said fluid and said second component electrical signal is linearly related to the concentration of said second component of said fluid.

34. A spectrophotometer according to claim 31 wherein said adjusting means adjusts the value of each of said first and second component electrical sigNals by adding thereto at least a portion of the other of said first and second component electrical signals.

35. A spectrophotometer according to claim 31 wherein said first component electrical signal has a value which is representative of the absorption of energy within a first band of wave lengths by said fluid and said second component electrical signal has a value which is representative of the absorption of energy within a second band of wave lengths by said fluid.

36. A spectrophotometer according to claim 35 wherein said first band of wave lengths is selected so that at least said first and second components of said fluid contribute to the absorption of energy within said first band of wave lengths and said second band is selected so that at least said second component of said fluid contributes to the absorption of energy within said second band of wave lengths.

37. A spectrophotometer for analyzing a fluid having first and second components therein for determining the concentration of said first component comprising:

means for providing a first component signal having a value which is representative of the absorption of energy within a first band of wave lengths by said fluid and providing a second component signal having a value which is representative of the absorption of energy within a second band of wave lengths by said fluid;

first amplifying means receiving said first component signal at an input thereof and for providing an amplified first component output signal at an output thereof;

second amplifying means receiving said second component signal at an input thereof and for providing an amplified second component output signal at an output thereof; and

transfer means connecting the output of said second amplifying means to the input of said first amplifying means for combining said first component signal and and second component signal in accordance with the contribution of the concentration of said second component of said fluid to the absorption of energy within said first band so that the value of said first component signal is adjusted in accordance with the concentration of said second component of said fluid to provide a first component output signal having a value which is substantially compensated for said concentration of said second component of said fluid.