METHOD FOR OPERATING A LAMBDA PROBE

The invention relates to a method for operating a broadband lambda probe which has a measuring space which communicates with a measuring gas and which has an electrochemical pump cell with which oxygen can be transported into the measuring space and out of the measuring space according to the total pump voltage (Up) which is present at said pump cell and according to a pump current (Ip) which results therefrom, and which has an electrochemical Nernst cell at which the Nernst voltage (Un) is formed according to the ratio of the oxygen content in the measuring space relative to the oxygen content in a reference space of the broadband probe, wherein the method provides a control loop whose actual value is the Nernst voltage (Un), whose setpoint value is a predefined value (UnSet) and whose manipulated variable is the pump current (Ip), wherein in order to protect the pump cell the manipulated variable of the pump current (Ip) is subjected to limitation by another limiting value (LL) and/or by a lower limiting value(LR) by means of a further effective loop, wherein the upper limiting value (LL) and/or the lower limiting value (LR) are each determined in a variable fashion in accordance with the pump current (Ip), the pump voltage (Up) and the internal resistance (R) of the pump cell.