Method of processing echo pulses, and pulse-echo ranging system using the method
Error correction in an echo pulse is performed by periodically (for example, every 100th pulse) generating a parabola derived from a selected part of the pulse leading edge. An error value is generated from the distance from a leading edge reference point to the peak of the generated parabola or to the echo peak, whichever is less. In this way an error correction is dynamically re-learned.
1. A method of processing echo pulses in a pulse-echo measurement system, comprising:
providing and using a tank containing a material, wherein the tank comprises an ultrasonic transducer;
providing and using a microprocessor which is coupled to the ultrasonic transducer via a transmitter;
generating ultrasonic pulses using the ultrasonic transducer, wherein the ultrasonic pulses are reflected by a top surface of the material in the tank;
receiving reflected pulses by the transducer and converting the reflected pulses into electrical signals;
generating a digital echo profile based on the electrical signals, wherein the digital echo profile is processed by the microprocessor, comprising:
identifying a rising edge of an echo;
defining a rising edge reference point;
fitting a parabolic curve to the rising edge;
calculating an error correction as being the lesser of
a distance from the rising edge reference point to a peak of the parabolic curve, or
a distance from the rising edge reference point to a peak amplitude of an echo profile; and
adding the calculated error correction to a previous error correction using a first order filter to provide an updated error correction value.
2. The method according to claim 1 , wherein the microprocessor processes every n-th received echo, where n>1.
3. The method according to claim 2 , wherein n is about 100.
4. The method according to claim 2 , wherein the method is performed for each received echo during a start-up phase.
5. The method according to claim 3 , wherein the method is performed for each received echo during a start-up phase.
6. The method according to claim 1 , wherein the rising edge reference point is defined as a predetermined percentage of the rising edge between the leading valley and the peak amplitude.
7. The method according to claim 1 , wherein the updated error correction value is used to modify a time reference provided by the rising edge reference point.
8. The method according to claim 6 , wherein the updated error correction value is used to modify the percentage of the rising edge between the leading valley and the peak amplitude.
9. The method according to claim 1 , wherein a plurality of error buckets are maintained, each error bucket corresponding to a given part of the measurement range, each error correction calculated being assigned to an appropriate error correction bucket and with the first order filter being performed on the contents of that bucket.
10. The method according to claim 1 , wherein the first order filter provides 10% of the new correction plus 90% of the existing correction.
11. A method of processing echo pulses in a pulse-echo measurement system, comprising:
providing and using a tank containing a material, wherein the tank comprises an ultrasonic transducer;
providing and using a microprocessor which is coupled to the ultrasonic transducer via a transmitter;
generating ultrasonic pulses using the ultrasonic transducer, wherein the ultrasonic pulses are reflected by a top surface of the material in the tank;
receiving reflected pulses by the transducer and converting the reflected pulses into electrical signals;
generating a digital echo profile based on the electrical signals, wherein the digital echo profile is processed by the microprocessor, comprising:
periodically calculating an error correction;
maintaining a plurality of error buckets, each error bucket corresponding to a given part of a measurement range, each error correction calculated being assigned to an appropriate error correction bucket; and
adding the calculated error correction to a previous error correction in that bucket using a first order filter.
12. The method according to claim 11 , wherein contents for the error buckets are defined by a user.
13. The method according to claim 11 , wherein a smoothing curve is fitted through the error bucket values, and an error correction value is obtained by interpolation of the smoothing curve.
14. The method according to claim 12 , wherein a smoothing curve is fitted through the error bucket values, and an error correction value is obtained by interpolation of the smoothing curve.
15. The method according to claim 13 , wherein the smoothing curve is a cubic spline or a least squares fit.
16. The method according to claim 14 , wherein the smoothing curve is a cubic spline or a least squares fit.