Patent ID: 8044671

Claim:
A method for servicing, especially for checking, an apparatus for capacitive ascertaining or monitoring of the fill level of a medium in a container, wherein the apparatus includes at least one probe unit comprising a probe electrode serving for actual measurement, an auxiliary electrode and an insulation that is located between said probe electrode and said auxiliary electrode, wherein said auxiliary electrode surrounds the probe electrode and serves as a guard during measurement by being supplied with the same signal as the probe electrode, the method comprising the steps of: supplying the probe electrode with a test signal, and connecting the auxiliary electrode with ground tapping a first response signal; disconnecting the auxiliary electrode from ground; supplying the probe electrode with a second test signal; supplying the auxiliary electrode with the second test signal or with a signal phase-shifted by 180° with respect to the test signal, wherein the signal supplied to the auxiliary electrode has essentially the same frequency and the same amplitude as the second test signal; tapping a second response signal; evaluating the first response signal and the second response signal as to whether they differ from one another by an offset; and obtaining information concerning a deterioration of the probe unit at least from said offset and predetermined, desired value.