| 摘要 |
An apparatus for establishing and/or monitoring a predetermined filling level in a container is provided, in which a reception signal (E) is equal to the measurement signal, and in which a fixed phase difference ( DELTA phi R), which is independent of the oscillation quality of the apparatus, exists between a first transmission signal (S1), and a reception signal (E) at a resonant frequency (fr). The apparatus comprises a mechanical oscillatory structure (1) and a piezoelectric element (2), which has a first region (I) having a reception electrode (21), a second region (II) having a first transmission electrode (22) and a third region (III) having a second transmission electrode (23), the two transmission electrodes (22, 23) having an identical form and being arranged symmetrically with respect to one another and to the reception electrode (21), in the first and in the second region (I, II), the piezoelectric element having a polarization which is in the opposite direction to a polarization of the third region (III), and a first transmission signal (S1) being applied to the first transmission electrode (22), which first transmission signal has the same amplitude as and is in antiphase with a second transmission signal (S2), which is applied to the second transmission electrode (23).
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