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Periodically alternating path and alternating wavelength bridges for quantitative and ultrasensitive measurement of vapor concentration

  • US 5,381,010 A
  • Filed: 12/03/1993
  • Issued: 01/10/1995
  • Est. Priority Date: 12/03/1993
  • Status: Expired due to Fees
First Claim
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1. An apparatus for measuring optical absorption by a constituent gas in a measurement cell, said apparatus comprising:

  • radiation means for emitting broad band infrared radiation along one of a measurement lightpath and a reference lightpath, the measurement cell being positioned in said measurement lightpath so that said radiation passes therethrough;

    alternating means for alternately and periodically directing said radiation along one of said lightpaths at a first frequency;

    attenuating means for balancing the relative power of said radiation in each of said lightpaths in the absence of optical absorption of the constituent in the measurement cell;

    sensor means for sensing radiation from each of said lightpaths and for producing a sensed signal, said sensed signal exhibiting modulation thereupon at said first frequency only when there is optical absorption of the constituent in the measurement cell; and

    synchronous detection means for demodulating said first frequency from said sensed signal so as to extract a DC signal, said DC signal being proportional to the optical absorption of the constituent in the measurement cell.

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