System for determining and monitoring preset filling level in container - has piezoelectric vibration system with sensor for contacting filling medium in container if preset level is exceeded and evaluation circuit producing signal depending upon amplifier output frequency.

摘要

The excitation system produces a mechanical vibration. The system includes a piezoelectric converter (65) excited by an AC voltage and a piezoelectric receiver converter (66), which converts the vibration in to an electrical output signal. This signal is fed to an amplifier circuit. The output of this circuit is supplied to the excitation converter (65), to produce vibrations with its characteristic resonance frequency. An evaluation circuit (73) is connected to the output of the amplifier circuit (70, 71, 72) so that its output signal assumes one or another of two conditions, depending on whether the frequency of the amplifier circuit output signal exceeds or undershoots an adjusted reference frequency. A voltage lowering circuit controlled by the output signal of the evaluation circuit, lowers the AC voltage applied at the excitation converter (65) from the amplifier circuit, if the output signal of the evaluation circuit has the condition, which corresponds to the exceeding of the set reference frequency. ADVANTAGE - System has reduced noise level with good signal-noise ratio.