| 摘要 |
PCT No. PCT/DE93/00917 Sec. 371 Date Jun. 1, 1994 Sec. 102(e) Date Jun. 1, 1994 PCT Filed Sep. 25, 1993 PCT Pub. No. WO94/08214 PCT Pub. Date Apr. 14, 1994In devices for determining and/or monitoring a predetermined level with a sensor that is excited to perform mechanical oscillations at its self-resonant frequency by means of an electronic excitation circuit which is excited via a piezoelectric excitation and a reception transducer and an evaluation circuit for triggering display and/or switching processes, there exists the difficulty that the natural frequencies of the sensors are different due to the manufacturing conditions, and that the operating frequency must be adjusted individually for each sensor. This disadvantage makes repair and maintenance procedures quite difficult. The invention thus suggests arranging a plug connection between the electronic excitation circuit on one hand and the piezoelectric transducer on the other hand, whereby said plug connection encloses a characteristic impedance which is selected as a function of the measured, individual self-resonant frequency of the sensor, and whereby the characteristic impedance is connected electrically to the evaluation circuit in addition to producing the electrical connection between the excitation circuit and the piezoelectric transducer when the plug connection is closed electrically.
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