Abstract: For achieving a highest possible measuring accuracy of a circuit for measuring the internal resistance of an exhaust-gas sensor, a method and a circuit for measuring the internal resistance R1 (10) of an electrochemical cell (12) are provided for determining the temperature of an exhaust-gas sensor, especially of a motor vehicle. The circuit is provided with the objective to improve the control to a constant temperature to therefore also improve the performance of the exhaust-gas sensor. A measurement current I_Mess (20) is applied to the internal resistance R1 (10) of the electrochemical cell (12) and a resulting first voltage is detected. A switchover to a reference resistor R2 takes place from time to time or at regular time intervals. With a switchover to the reference resistor R2, the resulting second voltage is stored and thereafter is applied as a reference value for the measurement of the internal resistance R1 (10).

Abstract: For achieving a highest possible measuring accuracy of a circuit for measuring the internal resistance of an exhaust-gas sensor, a method and a circuit for measuring the internal resistance R1 (10) of an electrochemical cell (12) are provided for determining the temperature of an exhaust-gas sensor, especially of a motor vehicle. The circuit is provided with the objective to improve the control to a constant temperature to therefore also improve the performance of the exhaust-gas sensor. A measurement current I_Mess (20) is applied to the internal resistance R1 (10) of the electrochemical cell (12) and a resulting first voltage is detected. A switchover to a reference resistor R2 takes place from time to time or at regular time intervals. With a switchover to the reference resistor R2, the resulting second voltage is stored and thereafter is applied as a reference value for the measurement of the internal resistance R1 (10).

Abstract: A method is distinguished in that outside of the analog/digital converter, on the basis of an analog signal (UA) to be digitized by the analog/digital converter, a sequence of digital pulses (P2) is generated, of which at least the width or the repetition frequency is analog signal-dependent, and that a digital result determined based on the pulse sequence and the digital value generated on the basis of the same analog signal by the analog to digital converter are checked for conformance with one another. As such, in a simple manner, a continuous monitoring of the A/D converter to be monitored is rendered possible during its "normal" operation.