Patent ID: 8096178

Claim:
An apparatus for capacitive ascertaining and/or monitoring of fill level of a medium in a container, comprising: at least one probe unit, which is electrically insulated relative to the medium by an insulating layer surrounding said at least one probe unit; and at least one electronics unit, which supplies said at least one probe unit with at least one electrical, actuating signal, receives an electrical measurement signal from said probe unit, and evaluates the measurement signal with respect to the fill level, wherein: the actuating signal is an electrical, alternating voltage signal; and said electronics unit is embodied in such a manner that it supplies said at least one probe unit, in a measuring phase, with the actuating signal, that it supplies said at least one probe unit, in a test phase, with a test signal; wherein the test signal is embodied in such a manner that it has at least one section with an essentially constant voltage value, that it receives a test measurement signal from said at least one probe unit in the test phase and that it infers from the test measurement signal whether the insulating layer has been compromised.