A method and a system for radar-based gauging of a filling level of a filling material is disclosed, wherein the tank has at least one interfering structure. The method comprises: transmitting at a first time moment a microwave signal towards the surface of the filling material; receiving microwave
A method and a system for radar-based gauging of a filling level of a filling material is disclosed, wherein the tank has at least one interfering structure. The method comprises: transmitting at a first time moment a microwave signal towards the surface of the filling material; receiving microwave signals as reflected against the surface of the filling material and as reflected against said at least one interfering structure; calculating based on propagation times of the transmitted and reflected microwave signals at least two distances to reflective surfaces in the tank; and repeating at a second time moment the transmitting, the detecting and the calculating, wherein said first time moment is timely separated from said second time moment. Based on the several repeated measurements, the distance to the surface of the filling material is determined as the calculated distance that exhibits the greatest change between said first and second time moments. Based on this time difference analysis, it is possible to discinguish moving surfaces very easy and acurate. The method is specifically advantageous in overfill or high level alarm systems.
대표청구항▼
What is claimed is: 1. A method for microwave signal based gauging of a distance to a surface with reflective properties at a filling level of a filling material in a tank having at least one interfering structure having a surface with reflective properties, comprising: transmitting at a first time
What is claimed is: 1. A method for microwave signal based gauging of a distance to a surface with reflective properties at a filling level of a filling material in a tank having at least one interfering structure having a surface with reflective properties, comprising: transmitting at a first time first transmit signals towards the surfaces; receiving at essentially said first time first receive signals including a first surface echo; recording first propagation properties of the first transmit and receive signals associated with the first surface echo; transmitting at a second time second transmit signals towards the surfaces; receiving at essentially said second time second receive signals including a second surface echo; recording second propagation properties of the second transmit and receive signals associated with the second surface echo; wherein the first time and the second time are temporally separated by a first separation time; calculating a first difference between the first and second propagation properties; transmitting at a third time third transmit signals towards the surfaces; receiving at essentially said third time third receive signals including a third surface echo; recording third propagation properties of the third transmit and receive signals associated with the third surface echo; transmitting at a fourth time fourth transmit signals towards the surfaces; receiving at essentially said fourth time fourth receive signals including a fourth surface echo; recording fourth propagation properties of the fourth transmit and receive signals associated with the fourth surface echo; wherein the third time and the fourth time are temporally separated by a second separation time; calculating a second difference between the third and fourth propagation properties; comparing the first and second differences; selecting the greatest of said first and second differences as the difference associated with the surface of the filling material; and determining said distance to said surface of the filling material based on propagation properties of said transmit and receive signals. 2. The method of claim 1, wherein the first and third times occur essentially simultaneously. 3. The method of claim 2, wherein the second and fourth times occur essentially simultaneously, and wherein the second transmit signals are identical to the fourth transmit signals. 4. The method of claim 1, wherein the first transmit signals are identical to the third transmit signals. 5. The method of claim 1, wherein the second transmit signals are identical to the fourth transmit signals. 6. The method of claim 1, further comprising the steps of calculating, based on the recorded propagation properties, distances to reflective surfaces in the tank, and wherein the difference between the propagation properties are calculated as the difference between said calculated distances. 7. The method of claim 1, wherein the recorded propagation properties comprise at least one of phase information and amplitude information from the transmitted and received signals. 8. The method of claim 1, wherein the calculation of a difference between the recorded propagation properties involves identification of at least one of a phase difference or an amplitude difference between the recorded propagation properties. 9. The method of claim 1, wherein the determined distance to the surface of the filling material is used for a high-level or overfill alarm functionality. 10. The method of claim 9, wherein the high-level or overfill alarm functionality involves comparing the determined distance to the surface of the filling material to at least one predetermined level threshold value. 11. The method of claim 10, wherein high-level or overfill alarm functionality involves identifying if a difference above a certain level between the first and second propagation properties or the third and fourth propagation properties occurs within a predetermined high level zone. 12. The method of claim 9, wherein the high-level or overfill alarm functionality involves identifying if a difference above a certain level between the first and second propagation properties or the third and fourth propagation properties occurs within a predetermined high level zone. 13. The method of claim 1, wherein continuous signals are emitted, and wherein distances are calculated based on a phase difference between the received echo signal and a reference signal. 14. The method of claim 1, wherein emit pulsed signals are emitted, and wherein distances are calculated based on the time between the emission of a pulsed signal and the reception of the echo of said signal. 15. The method of claim 1, wherein the received signals are filtered for reducing noise related changes before recording of the propagation properties, or before using said recorded propagation properties for calculating a difference. 16. The method of claim 1, wherein only primary echo signals are considered for recording of propagation properties, whereas secondary double-bounce echoes are disregarded. 17. The method of claim 1, further comprising the step of initially assuming that the first and second surface echoes or the third and fourth surface echoes are reflected from the surface of the filling material, whereby if the step of selecting the greatest of said first and second differences associates a different surface echo with the surface of the filling material, the assumption is thereafter changed to the now selected surface echoes. 18. The method of claim 17, wherein in use, the initial assumption is always tested and if necessary corrected within a limited time period, said time period being at least one of: less than one hour, less than one minute and less than 10 seconds. 19. The method of claim 1, wherein the surface of the filling material having reflective properties and the surface of the interfering structure having reflective properties are so much separated that the echo signals originating from said surfaces are distinguishable from each other. 20. The method of claim 1, wherein the temporal separation between at least one of the first and second times and the third and fourth times is less than a maximum separation time, said maximum separation time being one of one hour, one minute and 10 seconds. 21. The method of claim 1, wherein the determining of said distance to the selected surface of the filling material is based on at least one of the recorded propagation properties. 22. A method for microwave signal based gauging of a distance to a surface with reflective properties at a filling level of a filling material in a tank having at least one interfering structure, comprising: transmitting at least two temporally separated times transmit signals into the tank, and subsequently receiving receive signals including surface echoes; recording propagation properties of the transmit and receive signals in association with at least two distinguishable reflective surfaces; calculating for each distinguishable reflective surface a difference in the recorded propagation properties between the at least two temporally separated times; comparing the calculated differences for the at least two distinguishable reflective surfaces; selecting the greatest of said differences as the difference associated with the surface of the filling material; and determining said distance to said surface of the filling material based on propagation properties of transmitted and received signals. 23. The method of claim 22, further comprising the step of calculating, based on the recorded propagation properties, distances to reflective surfaces in the tank, and wherein the difference between the propagation properties is calculated as the difference between said calculated distances. 24. The method of claim 22, wherein the recorded propagation properties comprises at least one of phase information and amplitude information from the transmitted and received signals. 25. The method of claim 22, wherein the calculation of a difference between the recorded propagation properties involves identification of at least one of a phase difference or an amplitude difference between the recorded propagation properties. 26. The method of claim 22, wherein the determined distance to the filling material is used for a high-level or overfill alarm functionality. 27. The method of claim 22, wherein continuous signals are emitted, and wherein distances are calculated based on a phase difference between the received echo signal and a reference signal. 28. The method of claim 22, wherein emit pulsed signals are emitted, and wherein distances are calculated based on the time between the emission of a pulsed signal and the reception of the echo of said signal. 29. The method of claim 22, wherein the received signals are filtered for reducing noise related changes before recording of the propagation properties, or before using said recorded propagation properties for calculating a difference. 30. The method of claim 22, wherein the transmitting and receiving are repeated at least three temporally separated times, wherein a trend value or average value based on said recorded propagation properties is used for calculation of the differences in the recorded propagation properties between the at least two temporally separated times. 31. The method of claim 22, wherein only primary echo signals are considered for recording of propagation properties, whereas secondary double-bounce echoes are disregarded. 32. The method of claim 22, wherein the determining of said distance to the selected surface of the filling material is based on at least one of the recorded propagation properties. 33. A radar level gauge system for determining a distance to a surface with reflective properties at a filling level of a filling material in a tank having at least one interfering structure, comprising: a transmitter for transmitting measuring signals towards the surface of the filling material; a receiver for receiving echo signals from the tank; a storage for recording propagation properties of the transmitted and received signals in association with at least two distinguishable reflective surfaces; processing circuitry for calculating for each distinguishable reflective surface a difference in the recorded propagation properties between at least two temporally separated times, and selecting the greatest of the calculated differences for the at least two distinguishable reflective surfaces as the difference associated with the surface of the filling material, and determining said distance to the selected surface of the filling material based on propagation properties of transmitted and received signals. 34. The radar level gauge system of claim 33, wherein the storage is adapted to record propagation properties comprising at least one of phase information and amplitude information from the transmitted and received signals. 35. The radar level gauge system of claim 33, wherein the processing circuitry is adapted to calculate a difference between the recorded propagation properties based on at least one of a phase difference or an amplitude difference between the recorded propagation properties. 36. The radar level gauge system of claim 33, wherein it is usable as a high-level or overfill alarm. 37. The radar level gauge system of claim 33, wherein the transmitter is adapted to emit continuous signals, and wherein the processing circuitry is adapted to calculate the distances based on a phase difference between the received echo signal and a reference signal. 38. The radar level gauge system of claim 33, wherein the transmitter is adapted to emit pulsed signals, and wherein the processing circuitry is adapted to calculate distances based on the time between the emission of a pulsed signal and the reception of the echo of said signal. 39. The radar level gauge system of claim 33, further comprising filtering means for filtering the received signals for reducing noise related changes before recording of the propagation properties, or before using said recorded propagation properties for calculating a difference. 40. A method for microwave signal based determination of a high-level or overfill situation for the filling level of a filling material in a tank having a surface with reflective properties, comprising: transmitting at a first time first transmit signals towards the surfaces; receiving at essentially said first time first receive signals including a first surface echo; recording first propagation properties of the first transmit and receive signals associated with the first surface echo; transmitting at a second time second transmit signals towards the surfaces; receiving at essentially said second time second receive signals including a second surface echo; recording second propagation properties of the second transmit and receive signals associated with the second surface echo; wherein the first time and the second time are temporally separated by a first separation time; calculating a first difference between the first and second propagation properties; determining a distance to the surface of the filling material based on propagation properties of transmitted and received signals; identifying if the difference exceeds a predetermined difference level and if the determined distance is within a predetermined high level zone, and if so setting the alarm.
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