Device for determining and/or monitoring a predetermined material level in a container

A device for determining and/or monitoring a predetermined material level in a container, comprising:

• a material level sensor which contains a mechanical oscillatory structure, an electromechanical excitation transducer and at least one electromechanical reception transducer, the mechanical oscillatory structure being secured at the height of the predetermined material level for permitting it to come into contact with the material when said material reaches the predetermined material level;
• a first and a second circuit channel, each of which contains an amplifier circuit whose input is connected to said reception transducer and whose output is connected to said excitation transducer, said amplifier circuit being designed so that the mechanical oscillatory structure is excited to oscillations with its natural resonance frequency, and each of which circuit channels further contains a measuring signal transducer which receives the output signal of the amplifier circuit of the respective circuit channel and produces a measuring signal containing information about the frequency of said output signal, the measuring signal transducer of each circuit channel being designed for adding to the measuring signal an identifier which is assigned to the respective circuit channel and which is different from the identifier assigned to the other circuit channel;
• a control circuit for activating the two circuit channels alternately;
• and
• an evaluation device which receives the output signals of the measuring signal transducers of said two circuit channels for initiating at least one of a display and a switching operation in accordance with the frequency of the output signal of the amplifier circuit of said circuit channel and for detecting faults in the operation of the device with the help of the identifiers contained in said output signals.