DE112005003220T5 - Radar Level Measurement System - Google Patents

Abstract

A method for microwave signal-based measuring a distance to a surface having reflective properties at a fill level of a fill material in a container having at least one interfering structure with a surface having reflective properties, comprising:
Transmitting at a first time first transmission signals towards the surfaces;
Receiving, substantially at the first time, first received signals including a first surface echo;
- recording first propagation characteristics of the first transmit and receive signals associated with the first surface echo;
Transmitting at a second time second transmission signals towards the surfaces;
Receiving at substantially the second time second received signals including a second surface echo;
- receiving second propagation conditions of the second transmit and receive signals associated with the second surface echo;
- wherein the first time and the second time are separated in time by a first separation time;
- Calculate a first difference between the first ...

Description

Field of the invention

The The present invention relates to a radar level measuring system / radar level measuring system for determining the fill level a filling material in a container, comprising a transmitter for emitting measurement signals in the direction the surface of the filling material; a receiver for receiving echo signals from the container; and a processing circuit for determining the filling level of the container based on the echo signal. More specifically, the invention relates to a Radar level measuring system in containers with at least one disturbing structure is to be used, which reflects the emitted measurement signals. Furthermore, the invention relates to a corresponding method for Determine the filling level a filling material in a container.

Background of the invention

• • Suchen: Finden des korrekten Oberflächenechos unter möglichen Störechos.
• • Verfolgen: Folgen des gefundenen Oberflächenechos während verschiedener sich ändernden Bedingungen.
• • Genauigkeit: Anforderungen an die Genauigkeit während üblicher Behälterzustände, die üblicherweise sehr viel diversifizierter sind als die allgemein genannte "Instrumentengenauigkeit".

Radar level gauging (RLG), for measuring the level of a filling material, such as a liquid or a solid, such as granules, is an increasingly important method of filling level measurement in tanks, containers, etc. The method of radar level measurement can be very general be divided into three steps:

• • Find: Find the correct surface echo under possible clutter.
• • Track: Follow the surface echo found during various changing conditions.
• Accuracy: Accuracy requirements during common container conditions, which are usually much more diversified than the commonly-called "instrument accuracy".

to Radar level measurements are the conditions for various applications very different. For example, mm accuracy in CTS applications (custody Transfer system) a very precise control of the installation conditions. A Such accuracy is now practical in marine and refinery facilities achievable, but it is common in common process applications not easy to reach due to the amount of false echoes. More or less, however, all existing RLGs are on the market optimized under the assumption of a simple echo situation where the surface echo generally by its strength can be distinguished. This is based on a natural evolution from the oldest RLG applications, such as marine uses, where installation conditions in a sense controllable, and the CTS application in huge Refinery tanks, where the distance to disturbing Objects usually as big as required is. At usual process vessels is the distance to the walls much smaller and a turbulent surface is a normal situation. Accordingly, the task of finding and tracking the correct surface is very much much more difficult in a process vessel than for example in a refinery container. In front This background can be questioned if an echo retrieval logic based on an Echologik for relatively simple conditions, improved by a number of more or less usual Improvements, really can be enough compared to one Lo gik directly for the actual Situation is developed.

today RLGs usually use the information of an FFT spectrum to distinguish which one Echo of the surface to be measured equivalent. The FFT spectrum gives the reflected energy at different intervals again. Accordingly, the FFT spectrum is usually one more inaccurate means for distinguishing between, for example, one stationary Object, a turbulent Füllmaterialoberfläche and a moving agitator structure, in the container is arranged. Furthermore, it is usually difficult to distinguish the filler surface, if the container is essentially empty and started to fill it. To At this time, the filler surface is too rather turbulent. Furthermore would strong echoes from stationary Objects and structures in the container interfere with the measurement and the tracking functionality could simply be misdirected to be arrested an erroneous echo too stay or could the filler surface echo lose when it is close to an annoying echo.

In existing RLG systems, various hardware-related means have been proposed to accomplish and maintain the selection of the correct surface echo. For example, narrow antenna lobes have been used which reduce the amplitude of spurious echoes, such as structural steel beams. Unfortunately, a narrower antenna lobe requires a larger antenna diameter, which may be incompatible with existing mounting holes. Accordingly, in conventional process vessels, the number of spurious echoes that occur in the raw signal is usually greater than desired. Furthermore, often a domain restriction function is usually implemented in the software. Regardless of whether the system is of the FMWC type or pulsed type, a "bin spectrum" can be used as a tool to select the most probable echo. The container spectrum is a detected container signal, the amplitude being used only in combination with appropriate logical decisions. In addition, usually becomes a function to measure the amplitude and related threshold needed to distinguish noise or irrelevant echoes from the most likely surface echo. This is also primarily a software function, but it requires a certain calibration of gains, etc., to tell the system what a "normal" echo should be. A more or less complex echologic can also be used in processing the echoes which have passed the test with sufficient amplitude and sufficient similarity to already reflected echoes. However, there is still a need for improved radar level measurement, particularly for containers having interfering structures that produce reflective signals.

To improve the situation, various solutions have been proposed. Receiving the echo in two polarizations (with a slightly more complicated antenna / microwave module) and comparing the received signal is a method to increase the possibilities of distinguishing a surface echo from less symmetric spurious echoes. In this regard, see for example the US 6,759,976 , The time variation of the echo amplitude is another possibility that can be combined with the polarization and which is helpful for a turbulent surface. A third method is to use an even more complicated antenna to create a few different antenna lobes (or a slightly non-vertical lobe that rotates about the vertical) all in the ideal case of producing the same surface echo, but very different echoes disturbing structures, which are usually not arranged symmetrically. In this regard, see for example the US 6,759,977 , Unfortunately, these methods can be efficient, but unfortunately they require extra hardware and are therefore usually more expensive and difficult to produce and install. Furthermore, such systems will normally require more time and development resources.

Furthermore, it is known, for example from the EP 1 128 169 to use different signals to improve the resolution or accuracy of RLG systems. However, these known methods are proposed for other reasons and not as a remedy for the systems described above.

Accordingly there is still a need for a improved RLG system that solve the above problems can.

Summary of the invention

It It is therefore an object of the present invention to provide a radar level measuring system and a method for determining the filling level of a filling material which at least partially addresses the abovementioned problems of Fix the state of the art.

These Task becomes with a Radarlevelmesssystem and a procedure according to the attached claims solved.

In accordance with a first aspect of the invention, there is provided a method of measuring a distance to a surface having reflective properties at a filling level of a filling material in a container having at least one perturbing structure having a surface having reflective properties, comprising:
Transmitting at a first time of first transmit signals toward the surfaces;
Receiving substantially at the first time first receive signals including a first surface echo;
Receiving first propagation characteristics of the first transmit and receive signals associated with the first surface echo;
Transmitting at a second time second transmission signals towards the surfaces;
Receiving at substantially the second time second received signals including a second surface echo;
Taking in second propagation conditions of the second transmit and receive signals associated with the second surface echo;
wherein the first time and the second time are separated in time by a first separation time;
Calculating a first difference between the first and second propagation conditions;
Transmitting at a third time third transmission signals toward the surfaces;
Receiving at substantially the third time third received signals including a third surface echo;
Recording third propagation characteristics of the third transmit and receive signals associated with the third surface echo;
Transmitting at a fourth time of fourth transmission signals toward the surfaces;
Receiving at substantially the fourth time fourth received signals including a fourth surface echo;
Receiving fourth propagation conditions of the fourth transmit and receive signals associated with the fourth surface echo;
wherein the third time and the fourth time are separated in time by a second separation time;
Calculating a second difference between the third and fourth propagation conditions;
Comparing the first and second differences;
Select the largest of the first and the second Difference as the difference associated with the surface of the filler; and
Determining the distance to the selected surface of the filler based on propagation characteristics of transmitted and received signals.

The Determining the distance to the selected surface of the filler is preferably based on at least one of the recorded Propagation properties made. Additionally or alternatively but it is also possible for others Propagation properties, for example, of a different Set of transmitted and received signals to use.

It is worth mentioning, that the first and the third time occur substantially simultaneously can. In this case, you can the first transmission signals identical to the third transmission signals although it is possible is, separate transmission signals, for example, with different Polarization, to use. Furthermore, the second and the fourth Time substantially occur simultaneously, the second transmission signals may be identical to the fourth transmission signals. But times can be too be separated in time. Optional measurements can be made to one or more added later become more reliable, producing a set of measurements conclusions allows, if For example, the level and amplitude values due to turbulence fluctuate, etc.

The temporal separation between the first and the second time and / or the third and the fourth time is less than a maximum separation time. Preferably the time separation is less than one hour and preferably less than a minute, and most preferably less than 10 Seconds.

The New methods of microwave signal or radar level measurement are particular suitable for process applications with complicated container situations. Compared to conventional Radar level gauges The invention includes means for enabling even small ones Movements of the liquid surface used be to the surface echo unwanted echoes generated by disturbing objects, to distinguish.

It is worth noting that the present invention uses a difference based on the same measurement but at different times to distinguish events and changes that have occurred. Previously known difference signals, such as that in the EP 1 128 169 are usually aligned to the difference between different measurement situations, such as the difference between measurements made in different media, etc.

The Differential analysis of the present invention provides a number of Advantages because the echoes corresponding to the Füllmaterialoberfläche easier and can be detected more accurately. Accordingly, the present invention is considered as an addition to usual RLG logic systems can be used to control the surface during a start-up, during the Situation where the container empty state is left and is started to fill the container when the filling level reflecting structures in the container happens to identify, etc. Difference analysis is also helpful in distinguishing echoes moving objects, such as agitators, to stationary objects, such as partitions and striving.

The The method may further comprise the steps of: calculating, based on the recorded propagation conditions, from distances to reflective surfaces in the container, wherein the difference between the propagation conditions is preferable as the difference between calculated distances is calculated.

It is further preferred that the recorded propagation properties at least one of a phase information and an amplitude information from the transmitted and received signals. alternative or additionally It is also preferred that the calculation of a difference between the recorded propagation characteristics an identification of at least one phase difference or amplitude difference between the recorded propagation characteristics.

The Using the phase information in the signals has proven to be very efficient and accurate. The use of amplitude information although not as extensive as the phase information, for the most situations and applications completely adequate. Amplitude may be in the context This application is generally understood as a signal strength.

The method of searching for the echoes showing the greatest change over time may alternatively be described in the following manner, particularly suitable for the case where measurements of more than two times are used. It is possible to infer from the gradual time change of the level or the phase of two echoes, whether the two echoes will coincide in the future or whether they have been at the same level before, both ending Conclusions were made from a linear extrapolation of the change based on two or more times. The event of a predicted or past coincidence is called an intersection, and in the case of an intersection below the current average level of two surfaces, the upper level is the liquid surface, while an intersection above the average current level indicates that the lower level is the liquid surface.

Preferably the method comprises repeating at least three times separate times of transmission, acquisition and calculation; being the distance to the surface of the filling material is determined as the calculated distance, which is the biggest change between the different times. Such a difference analysis with several previous times allows both slow as well as to distinguish faster movements and changes. Furthermore, this will be the possibility exclude, that is the surface by exactly a multiple of λ / 2 has moved between two events, and this is even a moving echo disappears. Here λ is the Wavelength of Radar waves and for a 5.8 GHz frequency becomes λ 52 mm, etc.

The Method is particularly useful for high level or overfill alarm systems, since the new method is especially helpful for identifying moving surfaces and because only moving surfaces are interesting for trapping considerations. Such Systems can for this single use may be determined or may be a function that installed in a general RLG system. The high level or trapping alarm functionality may be a comparison the certain distance to the filler with at least a predetermined threshold level value. In used as a high-level or trapping alarm, the calculation is based a difference between the propagation characteristics preferably on a comparison between distances resulting from these propagation properties were calculated. Here the distances become the surface levels continuously monitored and that's the fastest way the time changing surface level is automatically called the surface level considered the filling material. Alternatively or in addition is it possible the Set alarm when a surface movement within a predetermined Nahzone occurs. This situation can be noticed if a difference between the first and second propagation characteristics or the third and fourth propagation properties as within a predetermined high-level zone occurring is identified. A threshold for the differences to be considered can also be set to noise-related To avoid false alarms. Here it is possible to prioritize signals, which occur within the near zone when the difference determined for the signals is high.

The Method is usable, both when emitting continuous signals where the distances are based on a phase difference between the received echo signal and a reference signal, such as in FMCW systems, as well as when pulsed signals be emitted, with the distances based on the time between the emission of a pulsed signal and the reception of the echo of the signal.

It it is preferred that the received signals be filtered to changes due to noise reduction before the propagation conditions be included or before the propagation conditions are included used to calculate a difference.

Preferably become only primary echo signals considered for recording the propagation conditions while secondary twofold reflected echoes are discarded.

The The method may further comprise the step initially assumed is that certain of the surface echoes received from the surface of the filler originate, i.e. that the first and the second surface echo or the third and the fourth surface echo from the surface of the filling material be reflected. In this case, if the step of selecting the largest one of first and second difference another surface echo with the surface of the filling material connected, the assumption is then preferably on the now selected surface echoes changed. The initial one Acceptance will as well preferably tested regularly and if necessary corrected within a limited time period, with the time span less than one hour and preferably less than half an hour Hour. Even more preferably, the time span is less than one Minute and most preferably less than 10 seconds.

The Link of echo signals from separately received signals with the assumption that they originate from the same reflective surface can performed in different ways which are known per se from the prior art. These shortcut between echo signals can be directly upon receipt of the signals or subsequently based on the recorded propagation characteristics become.

In accordance with another aspect of the present invention, there is provided a method of measuring, by microwave signal, a distance to a surface having reflective properties at a fill level of a fill material in a container having at least one interfering structure, comprising:
Transmitting at least two time-separated times of transmission signals into the container and subsequently receiving signals including surface echoes;
Recording propagation characteristics 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 characteristics between the at least two time-separated times;
Comparing the calculated differences for the at least two distinguishable reflective surfaces;
Selecting the largest of the differences as the difference associated with the surface of the filler material; and
Determining the distance to the selected surface of the filler based on propagation conditions of transmitted and received signals.

In accordance with this aspect are similar Advantages and preferred features obtainable, as already related were described on the first aspect.

In accordance with yet another aspect of the present invention, a radar level measurement system is provided for determining a distance to a surface having reflective properties at a fill level of a filler material in a container having at least one perturbing structure, comprising:
a transmitter for sending measurement signals toward the surface of the filler material;
a receiver for receiving echo signals from the container;
a memory for receiving propagation characteristics of the transmit and receive signals in association with at least two distinguishable reflective surfaces;
a processing circuit for calculating, for each distinguishable reflective surface, a difference in the recorded propagation characteristics between at least two time-separated times, and selecting the largest of the calculated differences for the at least two distinguishable reflective surfaces as the difference associated with the surface of the fill material, and determining the distance to the selected surface of the filler based on propagation characteristics of transmitted and received signals.

In accordance with this aspect can be similar Benefits and preferred features are obtained as they already are in relation to the first aspect.

The The present invention is useful for level measuring in containers a filling material with a surface with re inflecting properties, as well as with at least one disturbing structure with a surface with reflective properties. In particular, the invention usable when the reflective surfaces are separated, i. Not at the substantially same level, and accordingly independently distinguishable are in the reflected echo signals. The ability to access the surfaces may depend on various parameters, such as one or more of the separation distance, the level resolution, the measuring equipment, the signal strength Etc.

In accordance with yet another aspect of the present invention, there is provided a method for microwave signal based determination of a high level or fill situation for the fill level of a fill material in a container having a surface having reflective properties, comprising:
Transmitting at a first time transmission signals towards the surfaces;
Receiving at substantially the first time first receive signals having a first surface echo;
Receiving first propagation characteristics for the transmit and receive signals associated with the first surface echo;
Transmitting at a second time second transmission signals towards the surfaces;
Receiving at substantially the second time second received signals having a second surface echo;
Taking in second propagation conditions of the second transmit and receive signals associated with the second surface echo;
wherein the first time and the second time are separated in time by a first separation time;
Calculating a first difference between the first and second propagation conditions;
Determining a distance to the surface of the filler material;
Identifying whether the difference exceeds a predetermined difference level and whether the determined distance is within a predetermined high-level zone and if so, setting the alarm.

It should be noted that the invention according to this aspect also in containers without ir which disruptive structures are usable and helpful. However, as will be appreciated by those skilled in the art, this aspect of the invention uses the same basic principles as described in connection with the other aspects of the invention, and it should also be noted that all features of the other aspects are also described in conjunction with the latter Aspect of the invention can be used.

These and other aspects of the invention will become apparent from the following described embodiments clear and with reference to these embodiments clearly.

Brief description of the drawings

To For exemplary purposes, the invention will be discussed in more detail below Reference to its embodiments described in the accompanying drawings, wherein:

1 Fig. 12 is a schematic side sectional view of a container in which an antenna device according to the embodiment is arranged;

2 FIG. 12 is a schematic block diagram illustrating the radar level measurement system of FIG 1 shows;

3 Figure 12 are some schematic diagrams depicting various signal spectra for an exemplary container situation; and

4 shows a possible signal processing for use in this invention.

Description of preferred embodiments

The 1 schematically shows a Radarlevelmesssystem 1 in which the invention can be implemented advantageously. In short, the system in the 1 an electronic unit 3 for transmitting and receiving radar signals and for processing the received signals to determine the level in the container, an antenna 4 disposed within the container for transmitting and receiving radar waves in the container, and a radar waveguide assembly 5 for conducting signals between the electronic unit 3 and the antenna 4 , The same antenna may preferably be used as a transmitter for emitting the transmitted radiation and as a receiver for receiving the reflected echo signal, although it is also possible to use separate antennas for these functions. The exemplary embodiments of the invention use radar antennas that provide a free radar beam, in which case spurious echoes are particularly frequent, but it is also possible to use the invention in guided radar systems, wherein a waveguiding structure for propagating the emitted radar beam to and / or used by the container.

During operation, the radar level gauge transmits 2 Radar energy along the waveguide 5 through the tank ceiling port and receives from the fluid surface 8th reflected energy from the liquid surface 8th to provide an indication of the level of liquid within the container. The radar level gauge 2 may be connected to a remote location (eg, a control room) via a signal line or the like.

The System can use pulsed or continuously emitted radiation. If pulsed signals are used, the signals may be DC pulses with a length of about 2 ns or less, with a frequency of the order of MHz with average power levels in the nW or μW range. Alternatively, the pulses are on a carrier wave with a GHz frequency modulated. If necessary, is the container equipped with a seal, which is arranged to allow the electromagnetic signals to pass through the wall of the container to happen while one airtight seal is maintained, so the container contents to prevent it from leaving the container to escape.

In the general embodiment shown in the 2 is shown, the circuit comprises 20 a signal processor 21 , a transmitter 23 , a receiver 28 and signal processing circuitry 29 indicating the received signals to the processor 21 Recycle. The circuit further comprises a transmit / receive (TR) coupler 25 which the transmitter 23 and the receiver 28 with the antenna 4 connects the signals towards the surface 28 of the material whose level is to be measured. The TR coupler 25 may be a directional coupler, a ferrite circulator, a switch, or any other conventional component. The circuit comprises at least power circuits 22 and communication circuits 24 which can be both of many types.

The signal processor 21 is preferably a microprocessor-based circuit adapted to receive the incoming signal, as described above, and provides as an output a signal or information indicating the level of the material 8th reproduces. The through the signal processor 110 Implemented functions and algorithms, some of which may be implemented in hardware and some of which may be implemented as software, are well known in the art Technically known and will not be further described in this application.

After reflection on the surface 2 The electromagnetic signals are transmitted through the antenna 12 receive and return to the transceiver 10 where they are sampled and digitized in a process controlled by a processing circuit, such as a processor 11 , The processor is equipped with software for analyzing the signal to a level in the container, ie the level of the surface 2 to determine. The processor 11 is preferably a microprocessor based circuit adapted to receive the incoming signal as described above and which as an output provides a signal or information indicating the level of the material 3 reproduces. The through the signal processor 11 implemented functions and algorithms, some of which may be implemented as hardware and some of which may be implemented as software, are known per se from the prior art and will not be further described in this application. In particular, the method preferably includes the well-known functionality of searching to identify surface echoes among possible spurious echoes and tracking to follow the found surface echo during various changing conditions. Various reflective signal-generating surfaces can be monitored simultaneously, and typically the processing circuitry is arranged to simultaneously manage monitoring of 5-10 such surface echoes.

For radar systems, where there are two or more echoes, usually one limited resolution be present when these echoes are close to each other. Two reasonably close echoes lying together will generally appear as two echoes, whereas, if these are very close to each other, so it is not to be possible is to distinguish them, as a single echo in one Average distance will appear, and between these two make is a transitional area, in which the accuracy can be low. The border is through the Pulse time or the inverted bandwidth and fixed at about 150 mm for a system with a bandwidth of 1000 MHz or a pulse time of 1 ns, this being reasonably independently of the type of system. The embodiments to be described solve the echo situation at distances outside this zone, where there is less accuracy.

Farther a means is provided for assisting the selection, if different reflective surfaces in the container exist, which part of the received signal and which calculated Distance the surface of the filling material. This functionality is preferably mainly software related and can in many cases be based on existing (or slight extended) hardware and is used at FMWC like also work with pulsed systems. She can be alone, but also in combination with the above methods or with many other methods are used.

In a first embodiment the phase information is used in the received signals. In this embodiment a memory function is provided, from which the unprocessed Container signal stored with the phase information at appropriate times becomes. In a typical system, the information is in a "snapshot" (one sample in an FMWC system or the corresponding interval at a pulsed system) a few kilobytes in size, allowing storage from some "snapshots" even with one modest but modern processor is compatible with its RAM. Between the last "snapshots" and one of the older one becomes a difference is formed and it becomes a substantially normal one Signal processing performed on the difference. Assuming that the surface has moved a bit between the two "snapshots" will the different phase of surface echoes are very likely generate a nonzero difference if all echoes are above the surface be extinguished. The optimal change in the level is λ / 4 (7 mm at 10 GHz), this being an opposite phase for the surface echo gives, but a constant phase for disturbing echoes above the surface. however already gives λ / 12 (2.5 mm at 10GHz) the original amplitude when the difference is formed becomes. With a typical surface speed a few cm per minute will only be a short time interval needed (5-10 s) and in the very usual Fall of a turbulent surface even if the surface does not move steadily. Some different "snapshots" are preferred saved and the interval for Storage is estimated matched with the movement so that the best comparison can be done can. The sampling is preferably performed before any detection is performed (which usually is used in today's pulsed systems). For the described function it is preferred that the signal is treated linearly and that the Phase is maintained. A standard way to do this is off, two signals 90 ° off store the phase rotated, commonly referred to as I and Q channel.

• – Schnitt-Level unter dem Durchschnitt zwischen den beiden gemessenen Levels bedeutet, dass das höchste Level das richtige ist.
• – Schnitt-Level über dem Durchschnittslevel, jedoch unter dem höchsten der zwei (mit einer bestimmten Bandbreite) bedeutet, dass das unterste Level verwendet werden soll te.
• – Schnitt-Level über dem höchsten Level zeigt an, dass das höchste Level verwendet werden sollte aufgrund der auf gedeckten Existenz eines mehrfachen (mehrfach reflektierten) Echos.

In many cases it is sufficient to make a comparison between two moments or times as described above and the final result struggling to pull out of the difference. In many practical cases, however, there are variations in both the measured level and the amplitude which depend on small movements in the surface or on a third interfering echo, both of which cause a fairly rapid variation of the measured level or amplitude. Such variations can easily make a comparison ambiguous to determine the "biggest change". By including more than two moments with their own measured values, this ambiguity can be resolved by flipping the trends over a few different times instead of the difference between two times. This is through the 4 shown in the three different cases, each with a comparison between two echoes. In the 4a For example, a sequence of four levels (or phases) is plotted on a time-lapse graph and estimated linear trends are represented by lines. In the 4a For example, the upper echo is an interfering echo (eg, a tank structure) with a dotted trend line, and the lower echo of the changing liquid surface is represented by a solid trend curve. The intersection between the two trend lines (assuming a constant velocity) gives the level at which the two echoes will coincide (in the future) or where they were at the same level (in the past). The "cut level" is now close to the upper end of the level interval between the two echoes and the significance thereof will be further described below. In the 4b if the spurious echo is below the surface and the corresponding set of levels measured at four different times will have a slightly different appearance. The spurious echo is now measured by a variable thickness of an at least partially radar-transparent liquid and both levels will have a variation, but in opposite directions. The cut level can still be defined, but it is below the average of the two measured levels. This will be true at both rising and falling levels, but the hypothetical moment of cutting will be different. In the third case, shown in the 4c , a multiple echo from the tank roof (ie, twice the distance) is compared with the normal surface echo in the same way. In this case, the level of the intersection will be higher than the two measured levels, and the multiple echo will become apparent. It is obvious that for very clear signals, the result of this simple trend analysis in the 4a and 4b the same result as in a larger change study, however, in a noise like disturbance the trend analysis will provide a safer result. The position of the cutting level can be used in the following way:

• - Cut level below the average between the two measured levels means that the highest level is the right one.
• - Cut level above the average level, but below the highest of the two (with a certain bandwidth) means that the lowest level should be used.
• - Intersection level above the highest level indicates that the highest level should be used due to the existence of a multiple (multi-reflected) echo.

Preferably For example, in the software, a suitable analysis of the degree of scattering provided for determining how many points are needed to include the trend analysis. From the above description, it will be apparent to those skilled in the art, that the conclusions are independent of the direction of the movements are valid.

at In many applications, the system must be able to operate even with one non-moving surface to measure and then the container signal on a conventional Be used way. However, this only applies if the surface is neither moving nor turbulent and then the amplitude the echo at least 10-20 dB stronger is as in turbulent conditions. Accordingly, the standard procedure only during the best Conditions used. Alternatively, a combination of these Procedure possible. For example can the procedures for a more accurate determination of the surface continuously and in parallel be operated, the information extracted from both and can be compared. If there is no turbulence or movement is, the result of the standard procedure is used as it is and when movements occur, the standard method can be used as a check. Furthermore possible the procedure that the disturbing Echoes are saved with their phase, making the particular strong echoes from the container signal even for a steady surface echo can be deducted. The difference-forming from the two echo signals, at two pretty much However, it is more efficient because the false echoes are "fresh" and there are these the same influence of sediments, temperature and variations etc. exhibit.

The method described above can be applied to various types of RLG systems, including the conventionally used pulsed systems and FMWC systems. With a pulsed system, short pulses are sent, each of which may be a 1 ns pulse of some 6 GHz periods. After reflection at the Surface, the pulses are received and mixed with a similar pulse train with a slightly different PRF (eg 1.00000 MHz as opposed to 1.00001 MHz) and then, after a low-pass filtering, the received pulses (repeating for a fairly long time) in the Time "stretched" for easier processing. The mixing is linear so that phase, amplitude and mixed signals are preserved, with the pulses being output at a much slower rate (10 ^-5 in the example). One period of this stretched signal (100 ms in this example) is referred to herein as a "snapshot" of the bin signal. Ideally, for an FMCW signal, the IF signal is a sum of sine signals, one for each retained phase and amplitude echo and of length equal to the length of a sweep (eg, 100 ms). Signal processing in a modern system can be thought of as including one or more FFTs, and at this stage, it can be assumed that the difference in signal processing between a pulsed and an FMCW system is reduced to whether an even or an odd number of FFTs be applied. The term "generic IF signals" is used for both pulsed systems and FMCW systems or other radar systems that output a linear combination of echoes from possible multiple retained amplitude, phase, etc., echoes.

The snapshots of the generic IF signals at one or more times preferably stored in a memory in the described system. With usual Parameters is a snapshot by recording about 1000 samples with 8 to 16 bit amplitude resolution well kept. Accordingly, some or up to 10 kilobytes of space for every snapshot needed, whereby the storage of some snapshots is easy to achieve, even with a limited space in a modern digital Processor. Existing systems today have 1000 samples a usual amount, so that the hardware requirements with today's RLG industry standard are compatible.

The Forming the difference between any two snapshots of different times is easy to execute. An important observation is that a static echo in the difference essentially disappears, while a moving echo generally contributes to a non-zero contribution will make the difference. The storage of several different snapshots becomes the possibility exclude, that the surface by exactly a multiple of λ / 2 between two times, with even a moving echo would disappear. A pretty small movement is needed to distinguish the difference not equaling zero and, for example, a change around λ / 12 of the level will have a phase difference of 60 ° and the same amplitude in the differential Snapshot compared to the originals revealed. in case we assume a signal reduction of 10 dB before processing should be acceptable, then even a change of 1 mm in a 10 GHz system is sufficient, around the true surface to distinguish.

For an FMCW system is the difference signal for a moving echo obviously similar to the original echo be, but with a different amplitude and different phase, where this has no effect on the normal type of signal processing on the calculated distance will have. For a pulsed signal is the difference be very similar, assuming that the time difference is small in comparison at the pulse time (which corresponds to a distance of the order of 100 mm). Even in one impulse, most of the information is in phase. For the Impulse case is preferred that the signal before video capture is used (where the two pulses have different phases), because the two detected signals from slightly different points in time very similar are and will not make any usable difference.

One becomes any echo of any structure above the liquid surface virtually disappear while the surface echo with an expected change in amplitude, the chosen can be left by using a limited selection of snapshots. Accordingly, the surface echo becomes very much be much cleaner and more importantly, it will be the closest one Echo may not be zero, even in situations where many strong false echoes available.

in the Case of a smooth surface container structure over the surface can this through a reflection in the surface (double mirroring) be reflected and can appear as echoes that are farther away than the surface and themselves move at twice the speed as the surface moves. For a more complex bill the phases of all echoes that look more like them the calculated surface are, in accordance with the change the calculated surface. A Number of trial calculations will produce the correct assumption.

Some liquids are transparent to radar waves and in this case echoes will be visible below the surface and they will appear as if they are moving, but they act as if they are moving in the opposite direction and slower. A particular type of algorithm for echoes above the surface will make it possible to remove these echoes as well, before the last accurate calculation takes place.

One Radar Level Meter can have various uses and an important use is as a trapping alert. The method described is well suited for this task since it the capture of even weak, but somehow moving Enable echoes in a well defined vicinity of the radar level gauge becomes. The echo situation in the nearer Environment of the measuring device is quite static, making the instrument sensitive to any change which is most likely in this part of the container caused by the rising liquid surface becomes.

In the embodiment described above the phase information was used in the received signals, around a moving surface to distinguish from a non-moving surface and thereby the reflective signals from the surface of the filler against interfering echoes to identify. However, it is also possible signals without phase information for im To use essentially the same purpose. Such an embodiment will now be described in more detail.

at this embodiment becomes a difference spectrum for the amplitude is formed in each position and it becomes different Times received signals from which the echo characteristics are determinable.

The difference in amplitude for a position n at a time t can be determined as: AmplDiff (n) t = Ampl (n) t - Ampl (n) t-1

Alternatively, the difference can be determined as: AmplDiff (n) t = Abs (Ampl (n) t - Ampl (n) t-1 )

The amplitude difference is further preferably filtered to avoid noises due to noise, for example in the following way:
FiltFactor = 90% FiltAmplDiff (n) t = FiltFactor × FiltAmplDiff (n) t-1 + (1 - FiltFactor) × AmplDiff (n) t

through the comparison between signals of different times, becomes the difference analysis will produce a clear indication of moving surfaces, such as a turbulent surface, a surface that is raised or lowered or by a moving agitator. A stationary one surface however, will not be substantially visible, such as bars, sheets etc. The same applies to a completely calm filling material surface.

If a movement in the container occurs, the signal-to-noise ratio in the difference spectrum be bigger than that in the standard "container spectrum". Likewise, As previously mentioned, static echoes will not be present in the difference spectrum. Accordingly makes a turbulence, a cooking product or a moving one surface actually make it easier to use compared to using the more traditional echologics, the correct surface echo using the new method to determine even under quiet conditions.

The information obtainable from the difference signal will now be described in detail with reference to an example. In the diagram in the 3a For example, an exemplary bin spectrum is shown where the y-axis represents the amplitude on a linear scale and the x-axis represents the distance (0.0-9.0 m), also on a linear scale. In this spectrum, the maximum representing the surface at 3.7 m is clearly visible, but others are also visible, in particular a strong false echo at 0.5 m. Judging by this information alone, it is difficult to say which of the maxima represents the surface echo.

In the 3b a difference spectrum for the same container situation is shown. In this diagram, it is easy to determine where movement is taking place in the container. Up to 3.0 m is no movement and the strong false echo at 0.5 m can therefore be neglected. The S-shaped curve from 3.0 m to 4.0 m also indicates which direction the echo is moving. In this case, the surface is lowered.

Preferably, the difference analysis uses received signals of at least two and preferably different previous times, and preferably with different temporal separation. This makes it possible to detect both slow movements, such as a slowly raised or abge lowered level, as well as faster movements, such as turbulence on the surface, and to differentiate between them. Furthermore, this extended analysis makes it possible to avoid the situation where the difference between two received signals is exactly a multiple of λ / 2, and even a moving echo could disappear SSE. For example, the difference analysis for signals received at a time t may be performed based on measurements at, for example, t-1, t-10, and t-100.

• – OFA LowLimit, das eine untere Grenze für den zu überwachenden Bereich ist,
• – OFA HighLimit, das die obere Grenze für den Bereich ist,
• – OFA AmpThreshold, welcher ein Schwellenwert für eine Amplitude ist, die den Alarm innerhalb dieses Bereichs erzeugen kann.

The method and system described above are particularly useful for overfill applications. In such a congestion application, the determined surface level may be compared to one or more thresholds and, for example, a set of the following three thresholds:

• - OFA LowLimit, which is a lower limit for the area to be monitored,
• - OFA HighLimit, which is the upper limit for the range,
• - OFA AmpThreshold, which is a threshold for an amplitude that can generate the alarm within this range.

It is natural important that the thresholds are chosen appropriately so that no surface echoes are overlooked but at the same time false alarms due to other reflections, noise etc. as much as possible be avoided. Accordingly, the trap alarm functionality was previous difficult to implement in practice and normally required a fundamental and cumbersome Configuration for every single use situation. With the time differential described above Spectrum, capable is, changes and events that over however, the time to capture can be much higher which makes it easier to produce trapping alerts and install. A threshold for the amplitude would normally be needed even if the differential analysis described above is used. In this case, however, the threshold may be considered a general parameter independent from the filling material, the container environment etc. are set. Accordingly, a constant threshold be used independently where and how the system is installed.

The Measurement system may further include an alarm (not shown), which is activated by the alarm signal. The alarm can for example in a control unit for the system can be arranged. The alarm system can be distributed wherein the alarm is located at a distance from the measuring system. Alternatively, the alarm signal may be sent to a separate system such as a general control system. Of the Alarm can be next to the measuring equipment be arranged or at a remote location (for example, in a control room), the alarm signals being through a signal line or the like can be. The alarm unit can be constructed in various ways to an operator over to inform the current situation. Some examples: an acoustic one Signal can be activated, alarm lamps can start to light up or to blink or it may be some kind of signaling on a control panel be activated, alarms on a computer screen or a remote unit (telephone, mini-cell, radio, etc.) can be activated be, etc.

specific embodiments The invention has now been described. Different alternatives are possible, however as for the skilled person will be clear. For example, many different components to perform the various functions of the level measuring system and the processing circuit as will be readily apparent to those skilled in the art. Furthermore, different Types of thresholds and alarm parameters within the above sketched system can be used, the system can be pulsed or use continuously transmitted measurement signals, the system can a dedicated alarm system or in a conventional one Integrated measuring system, etc. Such and other obvious Modifications need as within the scope of the present invention as defined by the attached claims is defined lying down.

SUMMARY

One Method and device for radar-based measurement of a filling level of a filling material is disclosed, wherein the container at least one annoying Structure has. The method includes: at a first time Sending a microwave signal towards the surface of the filling material; Receiving microwave signals as from the surface of the filler reflected and as reflected by the at least one disturbing structure; Calculate based on transit times of the sent and reflected To reflect microwave signals of at least two distances surfaces in the container; and repeating at a second time of transmission, detection and calculating, wherein the first time in time of the second Time is separated. Based on the different repeated Measurements will be the distance to the surface of the filler material as the calculated Distance determines which is the biggest change between the first and second times. Based on this time difference analysis, moving surfaces are very much possible easy and precise to determine. The method is particularly advantageous in case of overcrowding or high-level alarm systems.

Claims (39)

Method for microwave signal-based measuring a distance to a surface with reflek at a filling level of a filling material in a container having at least one interfering structure with a surface having reflective properties, comprising: transmitting at a first time first transmission signals towards the surfaces; Receiving, substantially at the first time, first received signals including a first surface echo; - recording first propagation characteristics of the first transmit and receive signals associated with the first surface echo; Transmitting at a second time second transmission signals towards the surfaces; Receiving at substantially the second time second received signals including a second surface echo; - receiving second propagation conditions of the second transmit and receive signals associated with the second surface echo; - wherein the first time and the second time are separated in time by a first separation time; Calculating a first difference between the first and second propagation conditions; Transmitting at a third time third transmission signals towards the surfaces; Receiving at substantially the third time third received signals including a third surface echo; - recording third propagation characteristics of the third transmit and receive signals associated with the third surface echo; Transmitting at a fourth time of fourth transmission signals toward the surfaces; Receiving at substantially the fourth time fourth received signals including a fourth surface echo; - recording fourth propagation conditions of the fourth transmit and receive signals associated with the fourth surface echo; - wherein the third time and the fourth time are separated in time by a second separation time; Calculating a second difference between the third and the fourth propagation conditions; Comparing the first and the second difference; Selecting the largest of the first and second differences as the difference associated with the surface of the filler material; and determining the distance to the selected surface of the filler based on propagation characteristics of transmitted and received signals. The method of claim 1, wherein the first and the third time essentially occur simultaneously. The method of claim 1 or 2, wherein the second and the fourth time occur substantially simultaneously and where the second transmission signals identical to the fourth transmission signals are. Method according to one of the preceding claims, wherein the first transmission signals identical to the third transmission signals are. Method according to one of the preceding claims, wherein the second transmission signals identical to the fourth transmission signals are. A method according to any one of the preceding claims, further comprising the steps of calculating based on the recorded ones Propagation properties, from distances to reflective surfaces in the container, the difference between the propagation characteristics being the Difference between the calculated distances is calculated. Method according to one of the preceding claims, wherein the propagation characteristics recorded phase information and / or an amplitude information of the transmitted and received signals include. Method according to one of the preceding claims, wherein the calculation of a difference between the propagation characteristics recorded an identification of a phase difference and / or an amplitude difference between the recorded propagation properties. Method according to one of the preceding claims, wherein the certain distance to the filler for one High level or trapping alarm functionality used becomes. The method of claim 9, wherein the high-level or trapping alarm functionality comparing the determined distances to the filler with at least one includes a predetermined level threshold. The method of claim 9 or 10, wherein the high level or trapping alarm functionality includes identifying if one Difference over a certain level between the first and the second propagation conditions or the third and fourth propagation conditions within a predetermined high-level zone occurs. Method according to one of the preceding claims, wherein continuous signals are emitted and where distances are based on a phase difference between the received echo signal and be calculated a reference signal. Method according to one of the preceding Claims, wherein pulsed signals are emitted and wherein distances are calculated based on the time between the emission of a pulsed signal and the receipt of the echo of the signal. Method according to one of the preceding claims, wherein the received signals are filtered to reduce noise induced changes before picking up the spreading characteristics or before using the propagation characteristics recorded for the calculation of a Difference. Method according to one of the preceding claims, wherein only primary Echo signals are taken into account for recording the propagation properties while secondary doubly reflected echoes are discarded. A method according to any one of the preceding claims, further comprising the step of the initial one Assume that the first and the second surface echo or the third and the fourth surface echo from the surface of the filling material if the step of selecting the largest of the first and second difference another surface echo with the surface the filling material linked, the Assumption is then changed to the now selected surface echoes. The method of claim 16, wherein during the Operating the initial Assumption always checked and if necessary within a limited amount of time is corrected, the time span less than an hour or less than a minute or less than 10 seconds. Method according to one of the preceding claims, wherein the surface of the reflective material having filling material and the surface of the reflecting structure having disturbing structure are so widely spaced, that of these surfaces originating echo signals are distinguishable from each other. Method according to one of the preceding claims, wherein the temporal separation between the first and the second time and / or the third and the fourth time is less than a maximum separation time, where the maximum separation time is one hour, one minute or 10 seconds is. Method according to one of the preceding claims, wherein the determination of the distance to the selected surface of the filler on at least one of the recorded propagation properties based. Method for microwave signal-based measurement a distance to a surface with reflective properties at a fill level of a filler in a container with at least one annoying one Structure comprising: - Send at least two temporally separate times of transmission signals in the container and subsequently receiving received signals including surface echoes; - Take up propagation characteristics of the transmit and receive signals in shortcut at least two distinguishable reflective surfaces; - To calculate for every distinguishable reflective surface of a difference of the recorded Propagation properties between the at least two time-separated times; - To compare the calculated differences for the at least two distinguishable reflective surfaces; - Select the largest of the Differences as the difference with the surface of the Filling material is linked; and - Determine the distance to the selected surface of the filler based on propagation conditions of sent and received Signals. The method of claim 21, further comprising the step of calculating based on the recorded propagation characteristics of Distances to reflective surfaces in the container and the difference between the propagation characteristics being the Difference between calculated distances is calculated. The method of claim 21 or 22, wherein the recorded Propagation properties a phase information and / or amplitude information of the transmitted and received signals. Method according to one of claims 21 to 23, wherein the calculation a difference between the propagation characteristics recorded an identification of a phase difference and / or an amplitude difference between the recorded propagation properties. The method of any one of claims 21 to 24, wherein the particular Distance to the filler used for high-level or trapping alarm functionality becomes. Method according to one of claims 21 to 25, wherein continuous Signals are emitted and distances are based on a Phase difference between the received echo signal and a reference signal be calculated. Method according to one of claims 21 to 26, wherein pulsed signals are emitted and wherein distances are calculated based on the time between the emission of a pulsed signal and the receipt of the echo of the signal. Method according to one of claims 21 to 27, wherein the received Signals are filtered to reduce noise-induced changes picking up the propagation characteristics or before using the propagation characteristics recorded for the calculation of a Difference. A method according to any one of claims 21 to 28, wherein the sending and repeating the reception at at least three time-separated times is a trend value or an average based on the recorded propagation conditions for the calculation of the differences the recorded propagation conditions between the at least two separate times is used. Method according to one of claims 21 to 29, wherein only primary Echo signals are taken into account for recording the propagation characteristics, whereas secondary doubly reflected echoes are discarded. The method of any one of claims 21 to 30, wherein said determining the distance to the selected one surface of the filling material on at least one of the recorded propagation properties based. Radar level measuring system for determining a distance to a surface with reflective properties at a filling level of a filling material in a container with at least one disturbing structure, full: - one Transmitter for sending measurement signals towards the surface of the filling material; - one receiver for receiving echo signals from the container; - a memory for recording propagation characteristics of the transmit and receive signals in association with at least two distinguishable reflective surfaces; - one Processing circuit for calculating for each distinguishable reflective surface a difference in the recorded propagation characteristics between at least two time-separated times, and selecting the largest of the calculated differences for the at least two distinguishable reflective surfaces as those with the surface of the filling material linked Difference, and determining the distance to the selected surface of the filler based on propagation characteristics of sent and received Signals. Radar level measuring system according to claim 32, wherein the Memory is adapted to accommodate propagation characteristics, the one phase information and / or an amplitude information of the include transmitted and received signals. Radar level measuring system according to claim 32 or 33, wherein the processing circuit is arranged to make a difference between the recorded propagation properties based on a phase difference or an amplitude difference between the to calculate absorbed propagation properties. Radar level measuring system according to one of claims 32 to 34, being usable as a high level or overfill alarm. Radar level measuring system according to one of claims 32 to 35, wherein the transmitter is adapted to continuous signals to emit, and wherein the processing circuitry is adapted to the distances based on a phase difference between the received Echo signal and a reference signal to calculate. Radar level measuring system according to one of claims 32 to 36, wherein the transmitter is adapted to pulsed signals and wherein the processing circuitry is set up is, distances based on the time between the emission of a pulsed signal and the reception of the echo of this signal. Radar level measuring system according to one of claims 32 to 37, further comprising a filtering means for filtering the received Signals to reduce noise changes before recording the propagation characteristics or before using the recorded Propagation properties to calculate a difference. A method for microwave-based determination of a high-level or trapping situation for the fill level of a filler having a surface with reflective properties in a container, comprising: transmitting at a first time transmission signals towards the surfaces; Receiving, at substantially the first time, first receive signals having a first surface echo; - recording first propagation characteristics for the transmit and receive signals associated with the first surface echo; Transmitting at a second time second transmission signals towards the surfaces; Receiving at substantially the second time second received signals with a second one Surface echo; - receiving second propagation conditions of the second transmit and receive signals associated with the second surface echo; - wherein the first time and the second time are separated in time by a first separation time; Calculating a first difference between the first and second propagation conditions; Determining a distance to the surface of the filling material; Identifying whether the difference exceeds a predetermined difference level and whether the determined distance is within a predetermined high-level zone and if so, setting the alarm.