Method and system for the infrared analysis of gases

• US 3,887,473 A
• Filed: 11/29/1973
• Issued: 06/03/1975
• Est. Priority Date: 09/07/1971
• Status: Expired due to Term

• Current Assignee: James E. Young, John W. Lennington, Stanley P. Sternberg
• Original Assignee: James E. Young, John W. Lennington, Stanley P. Sternberg
• Inventors: Sternberg, Stanley P., Young, James E., Lennington, John W.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Nelms, D. C.
• Application Number:
  US05/420,305
• Time in Patent Office: 551 Days
• Field of Search: 250/345,564,565,252 356/81,82,97,204,205
• 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 a fluid to determine the concentration of a component therein comprising:

means providing a component signal which is related to the concentration of a component of said fluid;

means providing a reference signal;

means for determining a ratio of said component signal with respect to said reference signal including amplifying means having an input terminal for sequentially receiving said component signal and said reference signal, and an output terminal providing a component ratio signal representative of said ratio of said component signal with respect to said reference signal, variable transfer means connected between said input terminal and said output terminal to provide a feedback signal at said input terminal, means for providing a standard signal means for determining the difference between said standard signal and said signal at said output terminal and for providing a difference signal representative thereof, and means for adjusting said variable transfer means in accordance with said difference signal when said reference signal is received at said input terminal so that said signal at said output terminal is adjusted by said feedback signal to approach said standard signal in value when said reference signal is received at said input terminal, said feedback signal remaining substantially constant when said component signal is received by said input terminal, whereby said component ratio signal is provided at said output terminal; and

means for subtracting said standard signal from said component ratio signal to provide a component concentration signal having a magnitude of zero when there is no concentration of said component and having a magnitude greater than zEro representing the concentration of said component when there is a concentration of said component.

2. A spectrophotometer according to claim 1 wherein said variable transfer means is an electrically-variable resistor.

3. A spectrophotometer according to claim 2 wherein said electrically variable resistor is a photocell, and said means for adjusting said variable transfer means is a radiant source in operative relationship with said photocell which is intensity-varied in accordance with said difference signal.

4. A spectrophotometer according to claim 1 wherein said means for determining the difference between said standard signal and said signal at said output terminal is a differential operational amplifier having a subtractive input terminal, an additive input terminal, and an output terminal with said reference signal and said component signal being received at one of said input terminals, said standard signal being received at the other of said input terminals, and said difference signal being provided at said other output terminal.

5. A spectrophotometer according to claim 1 wherein said means for providing said component signal includes detector means for providing a signal representing the absorption of said fluid at a predetermined wave length, means for determining the background radiation at said detector means, and means for subtracting said background radiation from said detector means signal to provide said component signal.