Vorrichtung zur Feststellung und/oder Überwachung eines vorbestimmten Füllstandes

摘要

Known devices for determining and/or monitoring a predetermined filling level have a sensor excited by an electronic exciting circuit over a piezoelectric exciting and receiving transducer to produce mechanical vibrations at its self-resonant frequency, and an evaluation circuit for triggering display and/or switching processes. An inconvenient of the state of the art devices is that because of manufacturing conditions, the resonant frequency differs from sensor to sensor and the switching frequency must be individually set for each sensor. This inconvenient makes repair and servicing more difficult. It is therefore proposed to arrange between the electronic exciting circuit and the piezoelectric transducer a plugging device which comprises a characteristic resistance selected according to the individual self-resonant frequency measured at each sensor. When the plug connecting is electrically closed, not only an electric connection is established between the exciting circuit and the piezoelectric transducer, but also the characteristic resistance is put in electric contact with the evaluation circuit.