Endress U. Hauser Gmbh U. Co.

Jurgen Lau

Wolfram Berger

Bernhard Michalski

The filling level meter for measuring the filling level in a container includes a transmitting and a receiving arrangement which directs sonic or ultrasonic pulses onto the filling material surface and receives the backscattered pulses reflected by the filling material surface and converts them to electrical reception signals. Connected to the transmitting and receiving arrangement is an evaluating circuit which in a signal processing path generates an envelope signal corresponding to the envelope of the reception signals, digitizes sampled values of the envelope signal, stores in a memory the digitized sampled values for creating a distance-dependent or travel-time-dependent amplitude profile of the measurement distance and evaluates the amplitude profile for determining the travel time of the most probable useful echo signal. Parallel to the signal processing path for generating the envelope signal, in the evaluating circuit a frequency detection of the echo signals is carried out by which echo signals having the transmission frequency of the sonic or ultrasonic pulses are determined. In dependence upon the result of the frequency detection the signal processing path is opened only for the echo signals having a frequency corresponding to the transmission frequency. As a result all the reception signals having a frequency not corresponding to the transmission frequency are excluded from the digitizing and further processing. Due to the Doppler frequency shift these include all the reception signals which are caused by reflections at moving obstacles. On the other hand, all reception signals having a frequency identical to the transmission frequency are passed on unchanged for the digitizing and further signal processing.

Filling level meter

An ultrasonic echo sounding apparatus disposed at a measuring location transmits ultrasonic pulses in successive transmission periods. The echo pulses received after reflection at a target are converted to electrical envelope signals which represent the envelope curves of the echo pulses. The envelope signals are transmitted via a connecting line to an evaluation apparatus disposed at an evaluation station remote from the measuring location. In the evaluation apparatus the envelope signals are evaluated for determining the target distance from the travel time of the ultrasonic pulses. The transmission of envelope signals results in the advantage that the information contained in the pulse shape of the echo pulses is available in the evaluation station, although it is not necessary to transmit signals having the high frequency of the ultrasonic pulses via the connecting line. Preferably, the envelope signals are transmitted in a first section of each transmission period, and low-frequency signals which are generated at the measuring location and are characteristic of parameters necessary for the evaluation of the envelope signals are transmitted in a second section of each transmission period. It is also possible to transmit control signals from the evaluation station to the measuring location during the second section of every transmission period.

Method and arrangement for signal transmission in ultrasonic echo

The sonic or ultrasonic distance measuring device used for example to measure the filling level in a container comprises an electroacoustic transducer which operates alternately as transmission transducer for the transmission of sonic or ultrasonic pulses and as reception transducer for the reception of the reflected echo pulses. Connected to the transducer is a signal processing circuit which includes an amplifier with controllable gain and a threshold value discriminator. A gain control circuit controls the gain of the amplifier during a predetermined period after the start of each transmission pulse in accordance with a stored function which is fixed in accordance with the dying-down behaviour of the transducer so that the electrical signals originating from the dying-down of the transducer after amplification are smaller than the threshold value of the threshold value discriminator but are as close as possible to said threshold value. As a result the evaluation of echo pulses which occur during the dying-down of the transducer is possible.

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Weil am Rhein, Germany

Jurgen Lau