| 摘要 |
An apparatus for establishing and/or monitoring a predetermined filling level in a container is provided, in which the reception signal (E) corresponds to the desired measurement signal and in which a fixed phase difference (OAR), which is independent of the oscillation quality of the apparatus, exists between the transmission signal and the reception signal (E) at the resonant frequency (f r) of the mechanical oscillatory structure (1). The apparatus comprises a mechanical oscillatory structure (1) and a piezoelectric element (2), which has at least three regions, a first region (I) having a transmission electrode (21), a second region (II) having a first reception electrode (22) and a third region (III) having a second reception electrode (23), the two reception electrodes (22, 23) having an identical form and being arranged symmetrically with respect to one another and to the transmission electrode (21), and in the first and in the second region (I, II), the piezoelectric element (2) having a polarization which is in the opposite direction to a polarization of the third region (III). The reception signal (E) is equal to the difference between a first signal (E1), which is present at the first reception electrode (22), and a second signal (E2), which is present at the second reception electrode (23).
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