Patent ID: 6242928
Filing Date: 2001-06-05
Classification: G01N

Abstract:
Apparatus for detecting the resistance of an oxygen concentration sensor, said apparatus comprising:voltage applying means for applying a voltage to the oxygen concentration sensor for the purpose of generating a sensor current related to oxygen concentration of a gas;applied-voltage changing means for changing the voltage applied to the oxygen concentration sensor for the purpose of detecting its resistance;first current detecting means for detecting the sensor current before the voltage is changed by said applied-voltage changing means;second current detecting means for detecting the sensor current when a predetermined period elapses after the voltage to the oxygen sensor is changed by said applied-voltage changing means; andelement-resistance-component calculating means for calculating resistance of the oxygen concentration sensor based on a difference between the sensor current detected by said first current detecting means and the sensor current detected by said second current detecting means;wherein said voltage applying means further includes:an output circuit for applying a voltage to the oxygen concentration sensor;a constant-voltage circuit for inputting a first predetermined constant voltage to an input terminal of said output circuit through an output resistor; anda first voltage switching circuit including a first voltage dividing resistor and a first switching device, which are connected in series between a signal line from said output resistor to said input terminal of said output circuit and a first terminal having a second predetermined voltage; andwherein said applied-voltage changing means changes the voltage applied to the oxygen concentration sensor by said voltage applying means by switching said first switching device.