Patent ID: 7938944

Claim:
A gas concentration measurement apparatus comprising: a cell that comprises a solid electrolyte and a pair of electrodes on the surface of said solid electrolyte with one of the electrodes facing a measurement target gas chamber and causes, upon receipt of an applied voltage, a current to flow in accordance with the amount of oxygen discharge while discharging oxygen from said measurement target gas chamber; a power supply for applying a voltage to said cell; voltage variation means for varying the voltage by sweeping from a reference level to a predetermined level to be applied to said cell; current measurement means for measuring the current caused by said cell; and fault detection means for detecting an open-circuit in said cell in accordance with a change in the current caused by said cell during a sweep of the voltage, wherein the cell has a gas concentration measurement mode and an open-circuit detection mode, and the open-circuit detection mode is activated only periodically at appropriate time intervals, the sweep of the voltage is accomplished by superposing an AC voltage component over the applied voltage, only in the open-circuit detection mode is the sweep of the voltage applied, and an open-circuit is detected when a magnitude of a change in cell current is less than a predetermined amount when the sweep of the voltage is applied, and remains less than the predetermined amount for a predetermined number of applications of the sweep of the voltage.