Paired ZF Sampling for Pulse Running Time Filling Level Sensor

Abstract

A pulse running time filling level sensor includes a sampling device for sampling an IF signal at discrete instants and for converting the sampling values into digital sampling values, and a digital signal processing device for subsequent processing of the digital sampling values by calculating at least one new value characterizing the IF curve from respectively exactly two digital sampling values.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a functional diagram of a radar filling level sensor.

FIG. 2 shows a signal processing flow-chart of a signal processing with a quadrature demodulator for evaluating envelope and phase.

FIG. 3 shows a functional diagram of a radar filling level sensor for carrying out the inventive method.

FIG. 4 a and b show a signal processing flow-chart of the signal processing according to various embodiments of the invention.

FIG. 5 shows an ideal IF signal.

FIG. 6 shows a detail of the IF signal of FIG. 5 with marking of IF samplings according to the state of the art.

FIG. 7 shows a detail of the IF signal of FIG. 5 with marking of IF samplings according to an exemplary embodiment of the inventive method.

FIG. 8 shows errors in the envelope calculation according to an exemplary embodiment of the inventive method before and after application of the improved calculation method.

FIG. 9 shows a signal processing graph of analog and digital signal processing according to an exemplary embodiment of the invention.

FIG. 10 shows a sample illustration of an IF signal, sampling points, envelope, and phase angle when applying an exemplary embodiment of the inventive method.

Claims

1. A method for level measuring of a pulse running time filling level sensor, comprising: sampling an IF signal at discrete points in time;converting the sampled IF signal into digital sampling values; andcalculating at least one new value characterizing the IF curve as a function of respectively exactly two digital sampling values.

2. The method according to claim 1, wherein the characterizing value is an envelope value.

3. The method according to claim 2, wherein the calculation of the envelope value is performed according to

4. The method according to claim 1, wherein the characterizing value is a phase value.

5. The method according to claim 1, wherein the two digital sampling values are adjacent in time.

6. The method according to claim 5, wherein the time interval of the two digital sampling values is one quarter of an IF frequency period.

7. The method according to claim 6, wherein an envelope is formed as the root of a sum of squares of the two digital sampling values.

8. The method according to claim 5, wherein the time interval of the two digital sampling values is one eighth of an IF frequency period.

9. The method according to claim 1, wherein the digital sampling values are assigned alternately to one of two groups.

10. The method according to claim 9, wherein the characteristic value is calculated from respectively one value of each group.

11. The method according to claim 9, further comprising: before the calculating step, digital filtering each group.

12. The method according to claim 9, further comprising: before the calculating step, coherent system averaging each group.

13. The method according to claim 9, wherein time intervals of the digital sampling values of each group are smaller than the reciprocal value of a double bandwidth.

14. The method according to claim 13, wherein the time intervals of the digital sampling values of each group do not satisfy the sampling theorem so that the time intervals are larger than the reciprocal value of twice the IF frequency.

15. The method according to claim 13, wherein for the time intervals of the digital sampling values of each group the following holds true:

16. The method according to claim 15, wherein the time intervals of the digital sampling values of each group are situated half-way between two stop bands.

17. The method according to claim 16, wherein digital band filtering of each group with a center frequency of about one quarter of the sampling frequency is performed.

18. The method according to claim 9, wherein the time intervals of the digital sampling values of each group correspond to the IF frequency period or a multiple thereof.

19. The method according to claim 18, further comprising: digital low-pass filtering each group.

20. The method according to claim 2, further comprising: iteratively improving the envelope value based on an approximation method according to

21. The method according to claim 2, further comprising: calculating a phase value from sampling values and envelope values.

22. The method according to claim 1, wherein the time interval between two consecutive sampling pairs and is greater than half the period of the IF signal.

23. The method according to claim 22, wherein the time interval between two consecutive sampling pairs does not match exactly one period.

24. The method according to claim 22, wherein for the time interval between two consecutive sampling pairs the following holds true furthermore:

25. A pulse running time filling level sensor for determining a filling level in a tank, comprising: a sampling device sampling an IF signal at discrete points in time, the sampling device converting sampling values into digital sampling values; anda digital signal processing device subsequently processing of the digital sampling values through calculation of at least one new value characterizing the IF curve from respectively exactly two digital sampling values.

26. The pulse running time filling level sensor according to claim 25, wherein the characterizing value is one of an envelope value and a phase value.

27. The pulse running time filling level sensor according to claim 25, further comprising: a dividing device assigning the digital sampling values alternately to one of two groups.