A transmitting and receiving circuit for an ultrasonic flowmeter. In such circuits,
an ultrasonic transducer is typically used as both transmitter and receiver. This
is obtained by using switching means, for example in the form of CMOS switches.
However, problems arise with ringings of a transducer when having acted as a transmitter.
This unwanted ringing makes the crystal of the transducer act as an additional
signal generator, and the signal is coupled via parasitic capacitances in a switching
means to the receiving ultrasonic transducer. This problem is solved by connecting
one pole of a short circuit switch (S3, S4) to the ultrasonic transducer
(TR1, TR2) or to the switching means (S1, S2) and the
other pole of the short circuit switch to ground. Keeping the short circuit switch
closed when the switching means is open, and open when the switching means is closed,
creates a decoupling path for the unwanted signal, thereby improving the accuracy
of the transmitting and receiving circuit.