Apparatus for monitoring a predetermined fill level

An apparatus for monitoring a predetermined fill, level of a medium in a container, comprising:

• a mechanically oscillatable unit;
• a driving/receiving unit for exciting said mechanically oscillatable unit to execute mechanical oscillations and for receiving the oscillations of said mechanically oscillatable unit;
• and
• an electronics unit for producing an electrical exciter signal and for evaluating an electrical, received signal, wherein:
• said electronics unit is embodied to excite the mechanically oscillatable unit by means of said driving/receiving unit to execute mechanical oscillations within a fixedly predetermined, narrow frequency band with discrete, sequentially following, exciter frequencies;
• the frequency band contains the resonant frequency of said mechanically oscillatable unit in the case of an oscillation under standard conditions;
• said electronics unit is embodied to detect whether, within the predetermined frequency band an oscillation of said mechanically oscillatable unit occurs, whose amplitude exceeds a predetermined threshold value;
• and
• said electronics unit is embodied to excite said mechanically oscillatable unit with frequencies within a second predetermined frequency band;
• and
• the frequencies of the second frequency band lie above the frequencies of the first frequency band, and to detect an oscillation within the second frequency band, whose amplitude exceeds the threshold value, said electronics unit produces an alarm signal.