Echo tracking system for apparatus for ultrasonic measurement of the position of a mobile wall

Echo tracking system for an apparatus for ultrasonic measurement of the position of a mobile wall, comprising an input to receive a digital echo signal produced by reflection from a mobile wall of an interrogating ultrasonic pulse the transmission of which is controlled by a control pulse (A) transmitted at a given repetition rate (F.sub.r), said echo tracking system comprising:

• clock means for delivering a clock signal (CLK);
• enabling means for delivering, on reception of a validation signal (VAL), an enabling signal (AUT) which defines a time-window during which the echo signal is expected;
• and
• logic circuit means for receiving said digital echo signal and for delivering, at said repetition rate, a recenter position value (POSREC) which is a function of a received echo position value (POSECH) and which represents the time-position of the digital echo signal in said window;
• said echo tracking system further comprising:
• depth counter means for counting at the frequency of said clock signal (CLK) between said recentered position value (POSREC) and a first given value, wherein the beginning of the counting is triggered by said control pulse (A), and said depth counter means emits said validation signal when it reaches said first given value;
• and
• position detector means for determining the position of the echo in said time-window, said position detector means counting at the frequency of the clock signal (CLK) from a second given value, wherein the beginning of counting is triggered by said validation signal, and said position detector means delivers said echo position value (POSECH) to said logic circuit means.