Method and apparatus for radar-based level gauging

• US 6,759,977 B1
• Filed: 12/20/2002
• Issued: 07/06/2004
• Est. Priority Date: 12/20/2002
• Status: Expired due to Term

• Current Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Original Assignee: Saab Marine Electronics Aktiebolag (Emerson Electric Company)
• Inventors: Westerling, Jan, Edvardsson, Kurt Olov
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/327,815
• Publication Number:
  US 20040119636A1
• Time in Patent Office: 564 Days
• Field of Search: 342/27, 342/28, 342/73, 342/74, 342/75, 342/81, 342/82, 342/89, 342/118, 342/119-133, 342/159-175, 342/192-197, 342/134-145, 342/22, 732/90.R, 732/91, 733/04.R, 733/04.C, 733/05--225
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/103 particularities of the measurement of the distance G01S13/12, G01S13/14, G01S13/16, G01S13/18 and G01S13/20 take precedence
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: H01Q 1/225 used in level-measurement devices, e.g. for level gauge measurement
• CPC Class Codes: H01Q 25/00 Antennas or antenna systems providing at least two radiating patterns arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00

Abstract

A method for radar-based gauging of the level of a substance in a tank (13) having at least one interfering structure (16a-c), comprises the steps of: (i) transmitting a microwave signal in a plurality of radiation lobes (15a-b; 15a-d), each of which being individually directed towards the substance and at least one of which being directed towards the interfering structure; (ii) for each of the radiation lobes detecting temporally resolved the microwave signal as reflected against the substance, and for at least one of the lobes detecting the microwave signal as reflected against the interfering structure; (iii) based on signal strengths of the detected microwave signals, distinguishing the detected microwave signals, which have been reflected against the substance; and (iv) based on a propagation time of at least one of the microwave signals distinguished as those, which have been reflected against the substance, calculating the level of the substance.

Claims

1. A method for radar-based gauging of the level of a substance in a tank having at least one interfering structure, comprising the steps of:

transmitting a microwave signal in a plurality of differently directed radiation lobes, each of which being directed towards a surface of said substance and at least one of which being directed towards said at least one interfering structure;

detecting temporally resolved, for each of said plurality of differently directed radiation lobes, the microwave signal as reflected against the surface of said substance, and, for at least one of said plurality of differently directed radiation lobes, the microwave signal as reflected against said at least one interfering structure;

distinguishing based on signal strengths of said detected microwave signals, the detected microwave signals, which have been reflected against the surface of said substance; and

calculating based on a propagation time of at least one of the microwave signals distinguished as those, which have been reflected against the surface of said substance, the level of said substance in said tank.

2. The method of claim 1 wherein the detected microwave signals, which have been reflected against the surface of said substance, are distinguished by means of their similar signal strengths.

3. The method of claim 2 wherein the detected microwave signals, which have been reflected against the surface of said substance, are distinguished by means of their similar signal strengths after correction for inclination angles of said plurality of differently directed radiation lobes.

4. The method of claim 1 wherein the signal strengths of the detected microwave signals, which have been reflected against the surface of said substance, are weaker than the signal strength of the detected microwave signal, which has been reflected against said at least one interfering structure.

5. The method of claim 1 wherein the microwave signal is transmitted in at least four differently directed radiation lobes.

6. The method of claim 1 wherein at least one of said plurality of differently directed radiation lobes is essentially vertical.

7. The method of claim 1 wherein at least one of said plurality of differently directed radiation lobes has a symmetry axis, which deviates from a vertical direction by an angle large enough so the microwave signal in said radiation lobe as reflected against the surface of said substance, becomes significantly stronger for a turbulent surface of said substance than for a calm surface of said substance.

8. The method of claim 1 wherein the directions of said plurality of differently directed radiation lobes are only slightly different.

9. The method of claim 1 wherein the directions of said plurality of differently directed radiation lobes are separated by about 0.5-1 times a radiation lobe width of any of said plurality of differently directed radiation lobes.

10. The method of claim 1 wherein said substance is a liquid.

11. The method of claim 1 wherein said substance is a granular solid.

12. The method of claim 1 wherein said at least one interfering structure is any of a beam, an agitator, or a tank side wall.

13. The method of claim 1 wherein

a signal strength as a function of propagation time for each reflected microwave signal in each of said plurality of differently directed radiation lobes is deduced; and

the detected microwave signals, which have been reflected against the surface of said substance, are distinguished by means of comparing said functions.

14. The method of claim 13 wherein said at least one of the distinguished microwave signals is selected by means of comparing said functions.

15. The method of claim 1 wherein the signal strength of each detected microwave signal is stored in a database.

16. The method of claims 1 wherein said at least one of the distinguished microwave signals is selected depending on the level of said substance.

17. The method of claim 1 wherein said at least one interfering structure is localized based on said step of detecting.

18. The method of claim 1 wherein

said steps of transmitting and detecting are repeated;

and

said step of distinguishing is based also on the variation in signal strengths of the repeatedly detected microwave signals.

19. The method of claim 1 wherein said steps of transmitting and detecting are performed by a device including any of a reflector antenna;

a parabolic antenna;

a lens antenna;

or a planar antenna.

20. The method of claim 19 wherein said any of a reflector antenna;

a parabolic antenna;

a lens antenna;

or a planar antenna is fed by a Butler matrix.

21. The method of claims 1 wherein the phase of each of said detected microwave signals is measured.

22. An apparatus for radar-based gauging of the level of a substance in a tank having at least one interfering structure, comprising:

a transmitter for transmitting a microwave signal in a plurality of differently directed radiation lobes, each of which being directed towards a surface of said substance and at least one of which being directed towards said at least one interfering structure;

a detector adapted to detect temporally resolved, for each of said plurality of differently directed radiation lobes, the microwave signal as reflected against the surface of said substance, and, for at least one of said plurality of differently directed radiation lobes, the microwave signal as reflected against said at least one interfering structure; and

a processing device adapted to distinguish, based on signal strengths of the detected microwave signals, the detected microwave signals, which have been reflected against the surface of said substance; and

to calculate, based on a propagation time of at least one of the microwave signals distinguished as those, which have been reflected against the surface of said substance, the level of said substance in said tank.

23. The apparatus of claim 22 wherein said processing device is adapted to distinguish the detected microwave signals, which have been reflected against the surface of said substance, by means of their similar signal strengths, optionally after correction for inclination angles of said plurality of differently directed radiation lobes.

24. The apparatus of claim 22 wherein said transmitter is adapted to transmit the microwave signal in at least four differently directed radiation lobes.

25. The apparatus of claim 22 wherein at least one of said plurality of differently directed radiation lobes is essentially vertical.

26. The apparatus of claim 22 wherein the directions of said plurality of differently directed radiation lobes are separated by about 0.5-1 times the radiation lobe width of any of said plurality of differently directed radiation lobes.

27. The apparatus of claim 22 wherein said at least one interfering structure is any of a beam;

an agitator or a tank side wall.

28. The apparatus of claim 22 wherein

said transmitter and said detector are adapted to repeatedly transmit and detect; and

said processing device is adapted to distinguish the detected microwave signals, which have been reflected against the surface of said substance, depending on the variation in signal strengths of the repeatedly detected microwave signals.

29. The apparatus of claims 22 wherein said transmitter and said detector include any of a reflector antenna;

a parabolic antenna;

a lens antenna;

or a planar antenna.

30. The apparatus of claim 29 wherein said any of a reflector antenna;

a parabolic antenna;

a lens antenna;

or a planar antenna is fed by a Butler matrix.