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Oxygen concentration sensing apparatus

  • US 4,804,454 A
  • Filed: 03/19/1987
  • Issued: 02/14/1989
  • Est. Priority Date: 03/19/1986
  • Status: Expired due to Term
First Claim
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1. An oxygen concentration sensing apparatus comprising:

  • oxygen sensing means, responsive to oxygen in a gas under measurement, for producing an output signal having a magnitude proportional to the concentration of oxygen in the gas under measurement when contacted by a stream of the gas, said oxygen sensing means having,a sensor cell element made of a first active plate of an oxygen ion conductive solid electrolyte and a first pair of electrodes sandwiching said first active plate,an oxygen pump element made of a second active plate of an oxygen-ion conductive solid electrolyte and a second pair of electrodes sandwiching said second active plate,said first and second active plates defining a restricted region into which said gas under measurement is introduced;

    command generating means for generating a voltage value command representing a voltage to be generated across said first pair of electrodes of said sensor cell element;

    delay means for gradually supplying said voltage value command supplied by said command generating means;

    current supply means, responsive to said gradually supplied voltage value command received from said delay means, for supplying a pump current across said second pair of electrodes of said oxygen pump element so that a voltage generated across said electrodes of said sensor cell element equals said voltage represented by said voltage value command, said current supply means further developing a current value of said pump current supplied to said oxygen pump element as said output signal indicating the measured oxygen concentration; and

    limit means for stopping the supply of an excess current to said electrodes of said oxygen pump element by said current supply means, said limit means including,first switch means for stopping the supply of said voltage value command from said command generating means to said delay means when said voltage generated across said electrodes of said sensor cell element exceeds a first predetermined voltage, andsecond switch means for immediately reducing said pump current across said electrodes of said oxygen pump element when said voltage generated across said electrodes of said sensor cell element exceeds a second predetermined voltage which is higher than said first predetermined voltage.

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