Patent ID: 6138507
Filing Date: 2000-10-31
Classification: G01F

Abstract:
An apparatus for establishing and/or monitoring a predetermined filling level in a container, which apparatus comprises:a mechanical oscillatory structure (1), which is fitted at the level of the predetermined filling level,an electromechanical transducer (2),which has at least one transmitter (23),to which an electrical transmission signal is applied andwhich excites the mechanical oscillatory structure (1) to produce oscillations, andwhich has a receiver (24),which picks up the mechanical oscillations of the oscillating structure (1) and converts them into an electrical reception signal (E),an evaluation unit (9),which picks up the reception signal (E) and determines its frequency, compares said frequency with a reference frequency (f.sub.R) and generates an output signal which indicates that the mechanical oscillatory structure (1) is covered by a charge material if the frequency has a value which is less than the reference frequency (f.sub.R), and that is not covered if the value is greater, anda control loop, which regulates a phase difference existing between the electrical transmission signal and the electrical reception signal (E) to a specific, constant value (.DELTA..phi..sub.R) at which the oscillatory structure (1) oscillates at a resonant frequency (f.sub.r),whereina reception signal line (6), which transmits the reception signal (E), is connected via an electrical impedance (Z) to a transmission signal line (5), which transmits the transmission signal, the impedance being set to compensate for additional signals caused by mechanical and/or electrical coupling between the at least one transmitter and the receiver.