초록 ▼

A guided wave radar level gauge system, comprising a transmission line probe configured to support a first propagation mode such that it travels along the transmission line probe with a first propagation velocity exhibiting a first dependence on a dielectric constant of the surrounding medium, and s

A guided wave radar level gauge system, comprising a transmission line probe configured to support a first propagation mode such that it travels along the transmission line probe with a first propagation velocity exhibiting a first dependence on a dielectric constant of the surrounding medium, and support a second propagation mode such that it travels along the transmission line probe with a second propagation velocity exhibiting a second dependence, different from the first dependence, on the dielectric constant of the surrounding medium. The guided wave radar level gauge system further comprises processing circuitry connected to the transceiver for determining the filling level based on the reflected electromagnetic signal in the first propagation mode and the second propagation mode, and a known relation between the first dependence and the second dependence on the dielectric constant of the surrounding medium. Hereby, a filling level determination that is independent of the dielectric constant of the medium surrounding the transmission line probe can be achieved.

대표청구항 ▼

1. A guided wave radar level gauge system, for determination of a filling level of a product contained in a tank, said guided wave radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals;a transmission line probe comprising at least two p

1. A guided wave radar level gauge system, for determination of a filling level of a product contained in a tank, said guided wave radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals;a transmission line probe comprising at least two probe conductors extending from a ceiling of the tank towards and into the product in the tank, said transmission line probe being arranged and configured to guide a transmitted electromagnetic signal from said transceiver in at least a first propagation mode and a second propagation mode through a surrounding medium towards and into said product inside the tank, and to return a reflected electromagnetic signal resulting from reflection of said electromagnetic signal by a surface of said product back towards said transceiver in said first propagation mode and said second propagation mode,the transmission line probe being configured to support said first propagation mode such that it travels along the transmission line probe with a first propagation velocity exhibiting a first dependence on a dielectric constant of the surrounding medium, and support said second propagation mode such that it travels along the transmission line probe with a second propagation velocity exhibiting a second dependence, different from the first dependence, on said dielectric constant of the surrounding medium; andprocessing circuitry connected to the transceiver for determining the filling level based on said reflected electromagnetic signal in said first propagation mode and said second propagation mode, and a known relation between said first dependence and said second dependence on said dielectric constant of the surrounding medium. 2. The guided wave radar level gauge system according to claim 1, wherein said transmission line probe further comprises a dielectric enclosing structure at least partly enclosing at least one of said probe conductors. 3. The guided wave radar level gauge system according to claim 2, wherein said dielectric enclosing structure is arranged symmetrically with respect to said at least two probe conductors. 4. The guided wave radar level gauge system according to claim 2, wherein said dielectric enclosing structure is arranged non-symmetrically with respect to said at least two probe conductors. 5. The guided wave radar level gauge system according to claim 1, wherein at least one of said first and second propagation modes is a surface waveguide (SWG) mode. 6. The guided wave radar level gauge system according to claim 1, wherein at least one of said first and second propagation modes is a transversal electromagnetic wave (TEM) mode. 7. The guided wave radar level gauge system according to claim 1, wherein said transmission line probe comprises a first supporting probe conductor and a second probe conductor wound around the first supporting probe conductor. 8. The guided wave radar level gauge system according to claim 1, further comprising a feeding arrangement connected between said transceiver and said transmission line probe and configured to create the first propagation mode and the second propagation mode, and to feed the first propagation mode and the second propagation mode to the transmission line probe. 9. The guided wave radar level gauge system according to claim 8, wherein said feeding arrangement comprises: a first input for receiving the transmitted electromagnetic signal from the transceiver;a second input for receiving the transmitted electromagnetic signal from the transceiver; andfeeder circuitry connected to the first and second input and to the transmission line probe, said feeder circuitry being configured to:provide a first connection between the first input and the transmission line probe resulting in the first propagation mode; andprovide a second connection between the second input and the transmission line probe resulting in the second propagation mode. 10. The guided wave radar level gauge system according to claim 9, wherein said transmission line probe comprises at least two probe conductors, and wherein said feeder circuitry is configured in such a way that: said first connection results in that the transmitted electromagnetic signal is provided to said at least two probe conductors in antiphase; andsaid second connection results in that the transmitted electromagnetic signal is provided to said at least two probe conductors in phase. 11. The guided wave radar level gauge system according to claim 9, wherein said feeder circuitry comprises a transformer having a primary winding and a secondary winding. 12. The guided wave radar level gauge system according to claim 11, wherein said first input is provided across said primary winding, and said second input is provided between a reference voltage and a mid-point of said secondary winding. 13. The guided wave radar level gauge system according to claim 9, wherein said feeder circuitry comprises a microwave circuit configured in such a way that: there is a first difference in propagation distance for said transmitted electromagnetic signal from the first input to the a first one of said probe conductors and a second one of said probe conductors; andthere is a second difference in propagation distance, different from said first difference, for said transmitted electromagnetic signal from the second input to the a first one of said probe conductors and a second one of said probe conductors. 14. The guided wave radar level gauge system according to claim 13, wherein said first difference is approximately a half center wavelength of the transmitted electromagnetic signal, and the second difference is approximately zero. 15. A method of determining a filling level of a product contained in a tank using a guided wave radar level gauge system comprising a transceiver, a transmission line probe comprising at least two probe conductors extending from a ceiling of the tank towards and into the product in the tank, and processing circuitry, said method, comprising the steps of: feeding a transmitted electromagnetic signal generated by said transceiver to the transmission line probe such that said transmitted electromagnetic signal is guided by the transmission line probe towards a surface of the product in the tank in a first propagation mode having a first propagation velocity and a second propagation mode having a second propagation velocity;receiving by said transceiver a reflected electromagnetic signal in said first propagation mode and said second propagation mode, said reflected electromagnetic signal resulting from reflection of said transmitted electromagnetic signal at said surface of the product in the tank; anddetermining, using said processing circuitry, said filling level based on a time-of-flight of said first propagation mode of the reflected electromagnetic signal and a difference in time-of-flight of said first propagation mode and said second propagation mode of the reflected electromagnetic signal.