Patent ID: 7723898

Claim:
A device for the vibrational detection of a fill-level limit state, the device comprising: a vibrational resonator; at least one piezoelement that is loaded with a piezo-capacitance in order to induce a vibration in the vibrating resonator by providing a drive frequency, and in order to detect a vibration in the vibrating resonator; first and second connecting conductors for the piezoelement; circuit components for evaluating a vibration in the vibrating resonator detected by the piezoelement; a frequency divider circuit receiving an output voltage from the circuit components for evaluating the vibration detected by the piezoelement and providing a capacitance measuring voltage; a circuit capable of superimposing the output voltage from the circuit components for evaluating the vibration detected by the piezoelement with the capacitance measuring voltage; an inverter providing an output corresponding to an inverted voltage obtained by superimposing the output voltage from the circuit components for evaluating the vibration detected by the piezoelement with the capacitance measuring voltage; and a synchronous rectifier controlled by the capacitance measuring voltage and providing a control signal for amplitude adjustment, wherein a branch with a compensating capacitor is connected in parallel to a branch with the piezoelement in order to compensate a recharging current belonging to the piezoelement and dependent on the piezo-capacitance, a first lead of the compensating capacitor is connected to the piezoelement via the second connecting conductor for the piezoelement, a second lead of the compensating capacitor is connected to the inverter, the inverter supplies the second lead of the compensating capacitor with a signal which is inverted with respect to a signal on the first connecting conductor for the piezoelement, and the synchronous rectifier provides evaluation of a fault voltage by rectifying, at a frequency corresponding to an output of the frequency divider circuit, a signal corresponding to an output of the piezoelement to cause a voltage after rectification to depend on capacitance of the piezoelement and capacitance of the compensating capacitor.