Radar level gauge and methods of testing radar level gauge and system

Patent metadata

Field	Value
Publication number	US-9322699-B2
Application number	US-201313934969-A
Country	US
Kind code	B2
Filing date	Jul 3, 2013
Priority date	Jul 3, 2013
Publication date	Apr 26, 2016
Grant date	Apr 26, 2016

Abstract

The present invention relates to a radar level gauge comprising a reference reflector arranged at a known reference reflector level in a tank. The radar level gauge is controllable between a filling level measuring state and a proof test state. In the proof test state, the radar level gauge is configured to determine a first verification level based on a reference reflector echo resulting from reflection of an electromagnetic transmit signal at the reference reflector; determine a second verification level based on a surface echo resulting from reflection of an electromagnetic transmit signal at the surface of the product; and provide the first verification level and the second verification level to allow determination of a proof test result based on at least the first verification level, the known reference reflector level and the second verification level.

First claim

What is claimed is:

1. A method for testing a radar level gauge arranged at a tank containing a product, said radar level gauge comprising a reference reflector, the reference reflector being arranged at a known reference reflector level, wherein the method comprises the steps of:
transmitting a plurality of electromagnetic transmit signals towards a surface of said product in the tank;
receiving a plurality of electromagnetic reflection signals, each including several echoes resulting from reflection of a corresponding one of said electromagnetic transmit signals at impedance discontinuities encountered by the electromagnetic transmit signal;
determining a first verification level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals at said reference reflector;
determining a second verification level based on a surface echo resulting from reflection of one of said electromagnetic transmit signals at said surface of the product; and
determining a test result based on a relation between said first verification level and said known reference reflector level, and on said second verification level;
wherein said test result is determined to be positive only if:
a difference between said first verification level and said known reference reflector level is less than a first threshold value.

2. The method according to claim 1 , wherein said step of determining said first verification level further comprises the steps of:
identifying said reference reflector echo; and
temporarily assigning said reference reflector echo as said surface echo.

3. The method according to claim 1 , wherein said step of determining said second verification level further comprises the steps of:
identifying said reference reflector echo;
determining a set of surface echo candidates excluding said reference reflector echo; and
assigning one surface echo candidate in said set of surface echo candidates as said surface echo.

4. The method according to claim 3 , wherein said step of determining said second verification level further comprises the steps of:
permanently arranging said reference reflector in a reference reflector position.

5. The method according to claim 1 , wherein said test result is determined to be positive only if:
said second verification level meets a predetermined level criterion based on prior surface echo measurements.

6. The method according to claim 1 , wherein said test result is determined externally of said radar level gauge.

7. The method according to claim 1 , further comprising the step of:
determining a filling level of said product in the tank without using said radar level gauge,
wherein said test result is additionally based on a relation between second verification level and said filling level.

8. The method according to claim 1 , further comprising the step of:
determining a filling level of said product in the tank by means selected from a set including:
a second radar level gauge functionally independent of said radar level gauge, an ultrasonic level gauge, a float level gauge, a level measurement based on flow of said product, a level measurement based on pressure of said product, a level measurement based on capacitance of said product, a manual level measuring procedure such as hand-dipping;
wherein said test result is additionally based on a relation between second verification level and said filling level.

9. The method according to claim 8 , wherein said test result is determined based on a first difference between said first verification level and said known reference reflector level and a second difference between said second verification level and said filling level.

10. The method according to claim 9 , wherein said test result is determined to be positive only if:
said first difference is less than a first threshold value; and
said second difference is less than a second threshold value.

11. The method according to claim 10 , wherein said test result is determined to be positive only if:
a ratio between said first difference and said first verification level is less than a third threshold value; and
a ratio between said second difference and said second verification level is less than a fourth threshold value.

12. The method according to claim 10 , wherein said first threshold value is less than said second threshold value.

13. The method according to claim 12 , wherein said first threshold value is less than one half of said second threshold value.

14. The method according to claim 1 , further comprising the steps of:
when said tank is filled with said product to a first level above said reference reflector level:
determining, using said radar level gauge, a first filling level;
determining, without using said radar level gauge, a first reference filling level;
when said tank is filled with said product to a second level below said reference reflector level:
determining, using said radar level gauge, a second filling level;
determining, without using said radar level gauge, a second reference filling level; and
determining a test result based on a relation between said first filling level and said first reference filling level, and on a relation between said second filling level and said second reference filling level.

15. The method according to claim 1 , further comprising the steps of:
determining an amplitude of said reference reflector echo; and
determining an amplitude of said surface echo.

16. The method according to claim 15 , wherein said test result is determined to be positive only if:
said amplitude of the reference reflector echo is in a predetermined first amplitude range.

17. The method according to claim 15 , wherein said test result is determined to be positive only if:
said amplitude of the surface echo is greater than said amplitude of the reference reflector echo.

18. The method according the claim 1 , wherein said first verification level and said second verification level are determined based on reflections of the same electromagnetic transmit signal.

19. The method according the claim 1 , wherein said first verification level and said second verification level are determined based on reflections of different electromagnetic transmit signals.

20. The method according to claim 1 , wherein said known reference reflector level is stored in memory comprised in said radar level gauge.

21. The method according to claim 1 , wherein said reference reflector is arranged at or above a high level alarm limit for said tank, and wherein said method further comprises the steps of:
determining a proof test filling level based on a reference reflector echo resulting from reflection of one of said electromagnetic transmit signals at the reference reflector; and
providing, to a host system externally of said radar level gauge, a signal indicative of the proof test filling level.

22. The method according to claim 21 , wherein said radar level gauge is further controllable to operate in a filling level measuring state or a system proof test state, said method further comprising the steps of:
determining in said radar level gauge a filling level of said product based on said surface echo;
providing from said radar level gauge a signal indicative of said filling level to said host system;
receiving, as an input to said radar level gauge, a system proof test start command;
controlling, in response to said system proof test start command,

Assignees

• Rosemount Tank Radar Ab

Inventors

• Korsbo Thense
• Skaug Christian
• Wennerberg Tomas
• Larsson Michael

Classifications

• G01F25/0061 Primary

  Physics · mapped topic

• G01F23/284 Primary

  Electromagnetic waves · CPC title

• G01F25/00 Primary

  Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume · CPC title

• G01F25/20 Primary

  of apparatus for measuring liquid level · CPC title