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Capnometer

  • US 6,267,928 B1
  • Filed: 07/09/1998
  • Issued: 07/31/2001
  • Est. Priority Date: 02/24/1995
  • Status: Expired due to Term
First Claim
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1. A capnometer comprising:

  • a radiation source for irradiating infrared radiation to a respiratory gas;

    a thermal detector for sensing a transmission of said infrared radiation and for outputting a detection signal;

    means for turning said radiation source on and off at predetermined intervals;

    a memory for storing an output from said thermal detector;

    maximum value detecting means for detecting a maximum value of said detection signal output from said thermal detector for the present inspiration phase;

    minimum value detecting means for detecting a minimum output value, corresponding to an offset value, of said detection signal output from said thermal detector when said radiation source is turned off momentarily;

    corrected value determining means for determining a corrected value based upon said maximum value for the present inspiration phase, means for determining a density signal by calculating the difference between a subsequent detection signal, output from said thermal detector, and said corrected value;

    means for determining a reference value by calculating the difference between said corrected value and said minimum value for the present inspiration phase;

    means for determining the concentration of carbon dioxide by calculating a ratio of said density signal to said reference value.

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