Method for accurately detecting sensor element resistance

A method for detecting element resistance of an oxygen sensor which is used for determining oxygen concentration of a gas sample, said method comprising the step of:

• selectively executing at least one of:
• a first detection method which includes the steps of
• setting a time constant corresponding to a frequency at which impedance characteristics of an oxygen sensor are stable,
• applying a changing voltage having said time constant to said oxygen sensor,
• determining a current change in electric current flowing in said oxygen sensor due to said changing voltage, and
• determining element resistance of said oxygen sensor based on said changing voltage and said current change;
• and
• a second detection method which includes the steps of
• deactuating said oxygen sensor,
• detecting a voltage change in voltage of said oxygen sensor after deactuating said oxygen sensor,
• detecting a current change in said electric current of said oxygen sensor due to said voltage change, and
• determining said element resistance based on said voltage change and said current change.

A method for detecting element resistance of an oxygen sensor which produces a current corresponding to oxygen concentration of a gas sample in response to a voltage applied thereto, said method comprising the steps of:

• switching, at a predetermined time constant, a magnitude of said voltage applied to said sensor for oxygen concentration detection to a magnitude for element resistance detection;
• maintaining said magnitude of said voltage for said element resistance detection for more than a time period in which said current attains a peak magnitude;
• and
• determining an element resistance of said sensor based on a change in said magnitudes of said voltage and a change in magnitudes of said current.

A method for detecting element resistance of an oxygen sensor which produces a current corresponding to oxygen concentration of a gas sample in response to a voltage applied thereto, said method comprising the steps of:

• switching, at a predetermined time constant, a magnitude of said voltage applied to said sensor for oxygen concentration detection to a magnitude for element resistance detection;
• maintaining a magnitude of said voltage existing when said current attains a maximum magnitude for a time period after a maximum current magnitude attainment;
• and
• determining an element resistance of said sensor based on a change in said magnitudes of said voltage and a change in magnitudes of said current.