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Optical instrument for measuring concentrations of polluting gases on long and short geometrical paths

  • US 4,060,326 A
  • Filed: 07/03/1975
  • Issued: 11/29/1977
  • Est. Priority Date: 07/04/1974
  • Status: Expired due to Term
First Claim
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1. An optical instrument for measuring concentrations of polluting gases on long and short geometrical paths, characterized in that it comprises a spectrometer;

  • a telescope focussing a light beam coming from a source located at a predetermined distance, into a slit of said spectrometer;

    at least a cell, containing a known concentration of the polluting gas under examination, brought by first control means along the path of the light beam between said telescope and said slit;

    said spectrometer dispersing and focussing said light beam on its own outlet focal plane;

    a mask provided with movable slits, moved by second control means and located on the outlet focal plane of said spectrometer, said mask provided with movable slits that are adapted to effect the sampling of said dispersed light beam in at least four series of wave length ranges;

    a photodetector giving at the outlet electrical signals when receiving at the inlet light signals caused by said sampling;

    an electronic apparatus, located at the outlet of said photodetector, including means to elaborate at least four numerical values, of which;

    a first numerical value relating to the ratio between two electrical signals referring respectively to the sampling of a first and second of said series of wave length ranges of the dispersed light beam, a second numerical value referring to the ratio between two electrical signals referring respectively to the sampling of a third and fourth of said series of wave length ranges of the dispersed light beam, a third numerical value referring to the ratio between two electrical signals referring respectively to the sampling of said first and second series of wave length ranges of the dispersed light beam when said cell is interlocated along the light beam, and a fourth numerical value relating to the ratio between two electrical signals referring respectively to the sampling of said third and fourth series of wave length ranges of the dispersed light beam when said cell is interlocated along the path of the light beam;

    said elaboration of the numerical data being such to give at the outlet a numerical value given by the value of the known concentration of the polluting gas contained in said cell multiplied by the length of the cell and by a ratio having as numerator the difference between said first and second numerical value and as denominator the product of the distance between said source and the measuring device by the value obtained substracting from the difference between said third and fourth numerical value the said difference between the first and second numerical value.

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