Radar level gauge system using a waveguiding structure with periodically arranged reference impedance transitions
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
G01S-013/08
G01S-013/00
출원번호
UP-0122016
(2008-05-16)
등록번호
US-7586435
(2009-09-22)
발명자
/ 주소
Edvardsson, Olov
출원인 / 주소
Rosemount Tank Radar AB
대리인 / 주소
Westman, Champlin & Kelly, P.A.
인용정보
피인용 횟수 :
17인용 특허 :
5
초록▼
A radar level gauge system, for determining a filling level of a product contained in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals within a frequency range; a waveguiding structure arranged to extend into said p
A radar level gauge system, for determining a filling level of a product contained in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals within a frequency range; a waveguiding structure arranged to extend into said product contained in the tank and to guide a transmitted signal from said transceiver towards a surface of said product and to guide echo signals resulting from reflections at impedance transitions encountered by the transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface, back to said transceiver; a plurality of reference impedance transitions provided substantially periodically along said waveguiding structure with a distance between adjacent reference impedance transitions that is selected such that signals resulting from reflection of said transmitted signal at each of said reference impedance transitions combine to form a reference signal having a frequency within said frequency range; and processing circuitry connected to said transceiver for determining a propagation velocity of said electromagnetic signals in a medium inside the tank above said surface of the product based on said frequency of said reference signal and said distance between adjacent reference impedance transitions, and determining said filling level based on said surface echo signal and said propagation velocity.
대표청구항▼
What is claimed is: 1. A radar level gauge system, for determining a filling level of a product contained in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals within a frequency range; a waveguiding structure arranged
What is claimed is: 1. A radar level gauge system, for determining a filling level of a product contained in a tank, said radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals within a frequency range; a waveguiding structure arranged to extend into said product contained in the tank and to guide a transmitted signal from said transceiver towards a surface of said product and to guide echo signals resulting from reflections at impedance transitions encountered by the transmitted electromagnetic signals, including a surface echo signal resulting from reflection at said surface, back to said transceiver; a plurality of reference impedance transitions provided substantially periodically along said waveguiding structure with a distance between adjacent reference impedance transitions that is selected such that signals resulting from reflection of said transmitted signal at each of said reference impedance transitions combine to form a reference signal having a frequency within said frequency range; and processing circuitry connected to said transceiver for determining a propagation velocity of said electromagnetic signals in a medium inside the tank above said surface of the product based on said frequency of said reference signal and said distance between adjacent reference impedance transitions, and determining said filling level based on said surface echo signal and said propagation velocity. 2. The radar level gauge system according to claim 1, wherein each reference impedance transition is configured to reflect an echo signal having a power that is lower than-20 dB in relation to a power of said transmitted signal. 3. The radar level gauge system according to claim 1, wherein, for each reference impedance transition, said distance between adjacent reference impedance transitions is smaller than 1 meter. 4. The radar level gauge system according to claim 1, wherein, for said plurality of reference impedance transitions, a standard deviation of said distance between adjacent reference impedance transitions is below 1 percent of an average of said distance. 5. The radar level gauge system according to claim 1, wherein at least 10 reference impedance transitions are provided along said waveguiding structure. 6. The radar level gauge system according to claim 1, wherein said waveguiding structure is single line probe. 7. The radar level gauge system according to claim 6, wherein each of said reference impedance transitions is formed by a reflecting structure attached to said single-line probe. 8. The radar level gauge system according to claim 1, wherein said waveguiding structure is a coaxial waveguide having an inner conductor and an outer conductor. 9. The radar level gauge system according to claim 8, wherein each of said reference impedance transitions is formed by a spacing structure arranged to space apart said inner and outer conductors. 10. The radar level gauge system according to claim 1, wherein said waveguiding structure is a twin-line probe comprising a pair of conductors. 11. The radar level gauge system according to claim 10, wherein each of said reference impedance transitions is formed by a spacer element for spacing apart said conductors. 12. The radar level gauge system according to claim 1, wherein said waveguiding structure is a still pipe for guiding signals emitted by an antenna. 13. The radar level gauge system according to claim 12, wherein each of said reference impedance transitions is formed by at least one recess formed in a wall of said still pipe. 14. A waveguiding structure for use in a radar level gauge system for guiding transmitted electromagnetic signals within a frequency range towards and into a material comprised in a tank and for guiding echo signals resulting from reflections at impedance transitions encountered by the transmitted electromagnetic signals back along said waveguiding structure, the waveguiding structure comprising a plurality of reference impedance transitions provided substantially periodically along said waveguiding structure with a distance between adjacent reference impedance transitions that is selected such that signals resulting from reflection of a transmitted signal at each of said reference impedance transitions combine to form a reference signal having a frequency within said frequency range, thereby enabling determination of a propagation velocity of said electromagnetic signals in a medium inside the tank based on said frequency of said reference signal and said distance between adjacent reference impedance transitions. 15. The waveguiding structure according to claim 14, wherein each reference impedance transition is configured to reflect an echo signal having a power that is lower than-20 dB in relation to a power of said transmitted signal. 16. The waveguiding structure according to claim 14, wherein, for each reference impedance transition, said distance between adjacent reference impedance transitions is smaller than 1 meter. 17. The waveguiding structure according to claim 14, wherein, for said plurality of reference impedance transitions, a standard deviation of said distance between adjacent reference impedance transitions is below 1 percent of an average of said distance. 18. The waveguiding structure according to claim 14, wherein at least 10 reference impedance transitions are provided along said waveguiding structure. 19. The waveguiding structure according to claim 14, wherein said waveguiding structure is single line probe. 20. The waveguiding structure according to claim 19, wherein each of said reference impedance transitions is formed by a reflecting structure attached to said single-line probe. 21. The waveguiding structure according to claim 14, wherein said waveguiding structure is a coaxial waveguide having an inner conductor and an outer conductor. 22. The waveguiding structure according to claim 21, wherein each of said reference impedance transitions is formed by a spacing structure arranged to space apart said inner and outer conductors. 23. The waveguiding structure according to claim 14, wherein said waveguiding structure is a twin-line probe comprising a pair of conductors. 24. The waveguiding structure according to claim 23, wherein each of said reference impedance transitions is formed by a spacer element for spacing apart said conductors. 25. The waveguiding structure according to claim 14, wherein said waveguiding structure is a still pipe for guiding signals emitted by an antenna. 26. The waveguiding structure according to claim 25, wherein each of said reference impedance transitions is formed by at least one recess formed in a wall of said still pipe. 27. A method for determining a filling level of a product contained in a tank, said method comprising: generating and transmitting electromagnetic signals within a frequency range; propagating transmitted electromagnetic signals along a waveguiding structure extending towards and into said product contained in the tank, the waveguiding structure comprising a plurality of reference impedance transitions provided substantially periodically along said waveguiding structure with a distance between adjacent reference impedance transitions that is selected such that signals resulting from reflection of a transmitted electromagnetic signal at each of said reference impedance transitions combine to form a reference signal having a frequency within said frequency range; receiving echo signals resulting from reflections at impedance transitions encountered by said transmitted electromagnetic signals, including said reference signal and a surface echo signal resulting from reflection at said surface of the product; determining a propagation velocity of said electromagnetic signals in a medium inside the tank above said surface of the product based on said frequency of said reference signal and said distance between adjacent reference impedance transitions; and determining said filling level based on said surface echo signal and said propagation velocity. 28. The method according to claim 27, wherein generating and transmitting electromagnetic signals comprises: frequency modulating said electromagnetic signals. 29. The method according to claim 28, wherein frequency modulating said electromagnetic signals comprises: in a first frequency sweep, sweeping a frequency of said electromagnetic signals across a first frequency range, excluding said frequency of the reference signal, at a first sweep rate; and in a second frequency sweep, sweeping a frequency of said electromagnetic signals across a second frequency range, including said frequency of the reference signal, at a second sweep rate lower than said first sweep rate. 30. The method according to claim 29, wherein said second sweep rate is lower than 50 percent of said first sweep rate. 31. The method according to claim 29, wherein said second frequency range is smaller than said first frequency range. 32. The method according to claim 31, wherein said second frequency range is smaller than 50 percent of said first frequency range. 33. The method according to claim 29, further comprising determining intermediate frequency signals by combining said echo signals and a signal indicative of said transmitted electromagnetic signal; analyzing intermediate frequency signals corresponding to said second frequency sweep to determine said frequency of the reference signal; and analyzing intermediate frequency signals corresponding to said first frequency sweep to determine a frequency shift indicative of said filling level. 34. The method according to claim 33, wherein: said intermediate frequency signals corresponding to said second frequency sweep are analyzed in a time domain; and said intermediate frequency signals corresponding to said first frequency sweep are analyzed in a frequency domain.
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이 특허에 인용된 특허 (5)
Berry, James M.; Gard, Alan M., Guided wave radar level transmitter with automatic velocity compensation.
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