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Method of using an opto-acoustic apparatus for measuring concentration of gas

  • US 4,817,413 A
  • Filed: 03/11/1986
  • Issued: 04/04/1989
  • Est. Priority Date: 01/08/1983
  • Status: Expired due to Fees
First Claim
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1. A method of using an opto-acoustic apparatus for measuring, an environment containing extraneous noise, the concentration of a gas in a mixture of gases or of particulates in a gas, comprising:

  • providing a measuring opto-acoustic cell having gas inlet and gas outlet means for receiving and discharging a gas containing particulates or a mixture of gases containing a gas the concentration of which is to be measured;

    placing said cell in an environment containing extraneous or unwanted noise signals;

    directing laser rays from a laser ray generating device into said opto-acoustic cell;

    placing a chopper in the path of the laser rays between said device and said cell and operating said chopper for chopping the laser rays at a frequency corresponding to the resonant frequency of said cell;

    providing a narrow band microphone having a resonator with a narrow resonance frequency range including the resonant frequency of said cell and sufficiently narrow to exclude the extraneous or unwanted noise signals from the environment in which said cell is located;

    placing said microphone on said cell for detecting the sound signal generated by changes in the internal pressure of said cell; and

    determining from said sound signal the concentration of the gas in the mixture of gases or the concentration of the particulates in the gas.

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