A first condition, which is met when a measuring signal (V_SENS) of a sensor exceeds a first threshold value (V_SW), is checked. A second condition, which is met when a gradient (GRD_V_SENS) of a measuring signal (V_SENS) is greater than a predefined second threshold (GRD_V_SW), is checked. If the first and second conditions are met, this is recognized on a sensor with a signal evaluation area multiplex output for the measuring signal. If at least one of the conditions is not met, this is recognized on a sensor without a signal evaluation area-multiplex output for the measuring signal.