Patent ID: 6939037

Claim:
A method of measuring th internal resistance (R 1 ) of an electrochemical cell for determining the temperature of an exhaust-gas sensor including the electrochemical cell, the method comprising the steps of: applying a measurement current (I_Mess) to the internal resistance (R 1 ) of the electrochemical cell and detecting a resulting first voltage in the form of a voltage signal; switching over to a reference resistor (R 2 ) from time to time or at regular time intervals to obtain a second voltage which results from the measurement current (I_Mess); storing the second voltage and thereafter applying the second voltage as reference value for the measurement of the internal resistance (R 1 ); and, wherein said voltage signal, which results at internal resistance (R 1 ), is amplified and/or processed by means of a measurement signal evaluation unit; and, wherein the measurement current (I_Mess) is switched to said internal resistance (R 1 ) and reference resistor (R 2 ) by means of force switches (S 1 , S 2 ) and that the in-coupling of said first and second voltages into the measurement signal evaluation unit takes place via sense switches (S 3 , S 4 ).