Abstract: A method is provided for the monitoring of a moving medium (1), in particular the measurement of the filling level in a container or the distance signal of an object (1) to be detected where a sensor (2) is employed. The sensor (2) is subjected at its input to a supply voltage source (Ubs) or a supply current source. In order to suppress relatively slowly changing interfering values, the output signal (Uas) of the sensor (2) is fed back in a feedback loop to the input of the sensor (2) or, respectively, to the supply voltage of the sensor (2). The feedback loop is formed such that the input supply voltage source (Ubs) of the sensor, which is changeable for adjustment of the sensitivity, changes in dependence on the output signal (Uas) of the sensor (2) such that a constant sensitivity is present at all times. In case of an occurrence of a sufficiently fast or, respectively, sufficiently jumpy change larger than 0.01 V/sec.