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Humidity measuring apparatus

  • US 5,027,077 A
  • Filed: 08/22/1989
  • Issued: 06/25/1991
  • Est. Priority Date: 08/22/1988
  • Status: Expired due to Term
First Claim
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1. A humidity measuring apparatus comprising:

  • humidity sensor means for sensing humidity as a function of resistance;

    a reference resistor having a predetermined resistance value;

    a reference capacitor having a predetermined capacitance;

    charge switching means for selectively coupling one of said reference resistor or said humidity sensor means in series to said reference capacitor to charge said reference capacitor;

    voltage judging means for determining whether the terminal voltage of the reference capacitor is at about a predetermined high voltage (H) or at about a predetermined low voltage (L);

    charge/discharge switching means for selectively charging and discharging said reference capacitor in accordance with the output of said voltage judging means producing an oscillating charge/discharge cycle in response to the output of the voltage judging means;

    sensor direction switching means coupled to said charge/discharge switching means for inverting the direction of current flowing through said humidity sensor means during at least a portion of the period said reference capacitor is charged through said humidity sensor means in response to the output of the charge/discharge switching means;

    determining means coupled to said voltage judging means for determining the resistive value of said humidity sensor means and said humidity as a function of the charge/discharge cycle.

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