KR100891694B1 - Apparatus And Method For Radar-Based Level Gauging - Google Patents

Abstract

The present invention is a liquid level measurement device having a liquid in a container and a gas having a dielectric constant above the liquid level within a predetermined dielectric constant range, and transmitting a micro signal in a propagation mode to the tube through the gas toward the liquid surface. A transmitter for; A receiver for receiving the microwave signal reflected against the liquid surface and propagating back through the tube; And a signal processing device for calculating the liquid level in the tube from the propagation time of the transmitted and received microwave signal. In order to essentially avoid the influence of the calculated water level by the dielectric constant of the gas on the liquid, the transmitter is characterized in that the group velocity of the microwave signal of the in-tube propagation mode is essentially independent of the dielectric constant within the predetermined dielectric constant range. One is adapted to transmit the microwave signal in the frequency band.

Radar-based water level measurement device, microwave signal, dipole antenna

Description

Radar-based level measuring device and method {Apparatus And Method For Radar-Based Level Gauging}

FIELD OF THE INVENTION The present invention generally relates to radar-based level measurements, and more particularly, the present invention relates to radar-based levels for liquid levels through waveguides with high accuracy without prior knowledge of the exact gas composition and / or pressure on the liquid surface. It relates to a measuring device and a method.

An apparatus for measuring the level of a liquid in a container includes a transmitter for transmitting a microwave signal to a liquid surface, a receiver for receiving the microwave signal reflected against the liquid surface, and a propagation time of the transmitted and received microwave signal. And a signal processing device for calculating the liquid level in the body.

Such devices have become even more important especially for petroleum products such as crude oil and products made from crude oil. By container is meant herein a large container, which constitutes part of the total load capacity of a tanker, or a larger container, such as a circulating cylindrical ground-based tank having a capacity of mainly tens or thousands of cubic meters.

In one particular method of radar based devices for measuring liquid levels in a container, microwave signals are transmitted, reflected and received through vertical steel tubes mounted in a container that acts as a waveguide for the microwaves. Examples of level measurements based on such tubes are disclosed in US Pat. No. 5,136,299 to Edvardsson. Although the speed of microwaves in waveguides is slower than the speed of free wave propagation, in calculating liquid levels in a container from propagation time, this can be considered by calculations or measurement procedures based on knowledge of waveguide dimensions. .

In addition, the gas on the liquid surface reduces the speed of the microwaves. This slowdown can be accurately measured only if the gas component, temperature and pressure are known, but this is rarely the case.

When conventional petroleum products are used, ie when used to make them fluid at ordinary temperatures, the gas in the tube is generally air. The nominal dielectric constant of air typically varies from 1.0006 to ± 0.0001. However, the tank capacity increases the dielectric constant above the dielectric constant of air in the case of steam such as hydrocarbons. This increase can be significant.

In addition, when measuring the level in a container containing liquefied gas under excessive pressure, the change in speed can be very significant. Among the typical gases, propane has the largest dielectric constant (corresponding to [epsilon] = 1.02) which causes a speed reduction of about 1% at a pressure of 10 bar. Many applications, such as custody transfer applications, have this large discrepancy, which cannot be tolerated.

Therefore, greater accuracy, often defined as storage transport accuracy, is often required. Expressly speaking, custody accuracy refers to an accuracy that is fully acceptable for custody transfer, which is a formal requirement for many commercial uses of level measurement herein. For propagation speed, storage transport accuracy may mean an accuracy in the range of about 0.005-0.05% in determining the level. However, while the requirements for custody vary greatly from country to country and from institution to institution, the examples above clearly do not depend on any custody accuracy.

Accordingly, it is a primary object of the present invention to provide a radar based level measurement apparatus and method for measuring liquid level passing through a tube with a high degree of accuracy without prior knowledge of the exact gas component and / or pressure on the liquid surface.

A particular object of the invention is better than 0.4%, preferably better than 0.1%, and most preferably 0.01% for gases or gas mixtures on liquid surfaces having a dielectric constant in any of the intervals 1 ≦ ε ≦ 1.03. It is an object of the present invention to provide a level measuring device and method that provides better measurement level accuracy. This section is chosen to include propane, butane, methane and other conventional gases with certain limits.

In this regard, it is a specific object of the present invention to provide a level measuring apparatus and method capable of measuring liquid level with storage transportation accuracy.

It is yet another object of the present invention to provide a level measuring device and method for measuring the liquid level passing through a tube, which is provided for accurate measurement of the internal dimension of the tube.

Another object of the present invention is to provide one or more properties of a tube or environment in a container, such as the cross sectional dimension of the tube, the change in the cross sectional dimension along the length of the tube, the measurement of the concentricity of the tube, It is to provide a leveling device and method provided for reducing errors by measuring the presence, in particular the presence of mists, especially oil mists, in solid or liquid hydrocarbons, or gases in the inner wall of the tube.

These objects are achieved, in particular, by an apparatus and a method as claimed in the claims.

Radar level gauges use a fairly wide bandwidth (the width can be 10-15% of the center frequency) and the propagation is characterized by group speed in the middle of the band. According to the present invention, by appropriate selection of the frequency band and mode propagation of the transmitted and received microwave signals, and the inner diameter of the tube, it is possible to obtain a group speed of the microwave signal which is quite constant over the dielectric constant value target range, preferably between 1 and 1.03. According to the analysis, the group velocities rarely change as much as ± 0.005% over the 1 to 1.03 interval with respect to the dielectric constant, whereas with conventional devices, for example using free space propagation, the change of ± 0.75% Obtained.

The center frequency of the frequency band of the microwave signal is preferably about (2 / ε) ^1/2 times or close to the cutoff frequency in vacuum for the mode and the selected inner tube, where ε is the target range of the dielectric constant value. Center dielectric constant, for example 1.015 in the above preferred range. Thus, the optimum center frequency is about 2 ^1/2 times the actual cutoff frequency for the gas having the dielectric constant in the center of the target range of dielectric constant values.

The present invention provides for frequencies at which the microwave signal _deviates from less than 7%, preferably less than 5%, more preferably less than 3%, even more preferably less than 2%, and most preferably less than 1% from the optimum frequency f _opt . Can be quantitatively specified to be transmitted in the including frequency band, and the optimum frequency is

Where f _co is the cutoff frequency of the propagation mode in the tube and ε is the central dielectric constant in the target dielectric constant range. These frequencies are higher than those used when single-mode propagation should be guaranteed, as described in two US patents 4,641,139 and 5,136,299 to Evason, but are generally used when overdraft tube and mode suppression is applied. Much lower than the frequency used. Thus, the frequency used in the present invention is at least partially outside the frequency range used in the prior art for both tube and level measurements.

However, most advantageously, the frequency band has an optimal frequency f _opt or a center frequency that deviates by less than 1-7% of the optimal frequency f _opt .

Preferably, a round tube and H ₁₁ mode are used for the measurement. Frequency selection of about (2 / ε) ^1/2 times the H ₁₁ mode in vacuum also causes the microwave signal to propagate in E ₀₁ mode. The microwave signal can be measured in these two modes that are distinct from each other, and the measurement of the E ₀₁ mode microwave signal infers information about the dimensions of the tube and / or the dielectric properties of the gas or gas mixture on the liquefied gas surface. Can be used.

More generally, the microwave signal is measured in at least two different modes that are separate from each other. This dual mode measurement infers information about the condition of the pipe, for example the pipe dimension, the presence of an oil layer on the inner wall of the pipe, or the atmosphere of the pipe, for example the presence of fog, and uses this information to make measurements. It can be used to reduce any error introduced by the state at the specified level.

The main advantage of the present invention is that the level measurement through the tube with a high degree of accuracy can be carried out without prior knowledge of the composition and pressure of the gas on the surface being measured.

Another advantage of the present invention is that the error introduced by the state of the tube can be reduced by the bimodal measurement.

Another advantage of the present invention is the effect due to a change in the amount of hydrocarbon droplets in the tube and a thin hydrocarbon layer whose thickness on the inner wall of the tube changes by selecting a frequency close to the optimum frequency as defined above for a dielectric constant range of 1-1.03. Is to be minimized.

Further features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention and the accompanying drawings of FIGS. 1 to 12, which are given by way of example only and thus limit the present invention. It is not.

In this description, the waveguide markings H ₁₁ , E ₀₁ , H ₀₁ , and the like are used as being similar and fully equivalent systems for the markings TE ₁₁ , TM ₀₁ , TE _01, and the like.

1 is a perspective view schematically showing a radar based level measuring apparatus according to a preferred embodiment of the present invention;

2 is a schematic of group velocity as a function of dielectric constant for H ₁₁ mode of microwave radiation in a waveguide at optimum frequency;

3 shows microwave radiation in a waveguide at three different frequencies representing the principles of the present invention, one of which is an optimum frequency, one of which is a frequency substantially lower than the optimum frequency, and one of which is a frequency substantially higher than the optimum frequency. Is a schematic diagram of group velocities as a function of dielectric constant for H ₁₁ mode of;

4 is a schematic diagram of group velocity as a function of dielectric constant for H ₁₁ mode of microwave radiation in a waveguide at optimum frequency for different waveguide diameters;

5 is a schematic diagram of group velocity as a function of wave number for H ₁₁ mode of microwave radiation in a waveguide filled with gases having different dielectric constants;

6 is a schematic diagram of group velocities normalized to group velocities in vacuum as a function of wavenumber for H ₁₁ mode of microwave radiation in a waveguide filled with gases having different dielectric constants;

7A and 7B schematically show cross-sectional and base views, respectively, of a waveguide feeding device in H ₁₁ mode, E ₀₁ mode, or both modes separately using separate feeding points;

FIG. 8A schematically illustrates a cross-sectional view of a waveguide power feeding device in H ₀₁ mode and E ₀₁ mode having separate feed points, and FIG. 8B schematically illustrates an antenna device included in the device of FIG. 8A.

9A schematically illustrates a cross-sectional view of a waveguide power feeding device of H ₁₁ mode and H ₀₁ mode having separate feed points, and FIG. 9B schematically illustrates an antenna device included in the device of FIG. 9A, and FIG. 9C A schematic illustration of a connection network for powering the antenna device of FIG. 9B; And

10-12 show the group velocity in vacuum as a function of the wavenumber for each of the H ₁₁ mode, E ₀₁ mode, and H ₀₁ mode of microwave radiation in a gas filled waveguide with dielectric layers having different dielectric constants and different inner wall thicknesses. Schematic of inverted military velocity normalized to.

A preferred embodiment of the present invention is described with reference to FIG. 1, which schematically shows a radar based level measuring device in a perspective view. The device may be a frequency modulated continuous wave (FMCW) radar device or a pulse radar device or any other type of ranging radar, but is preferably a frequency modulated continuous wave transmitting radar device. The radar device may have the ability to transmit microwave signals at variable frequencies that can be adjusted.

In FIG. 1, 1 represents a vertical tube or tube substantially fixedly mounted to a container, and 3 represents an upper limit or a roof of the tube. Containers contain liquids, which may be petroleum products, such as crude oil or products made from crude oil, or liquefied gases stored in overcompressed and / or cooled containers.

The tube 1 is preferably made of a metallic material capable of acting as a waveguide for microwaves, and may have any cross-sectional shape. However, circular, rectangular or super-elliptical cross sections are preferred. The tube is shown only at the top and bottom, not at full length. The tube is formed with a relatively large number of small openings 2 in the tube wall, which allows for fluid communication from the container to the inside of the tube, with the same level of liquid in the tube as in the container. It has been shown that the size and location of the holes can be selected so that the holes do not interfere with the propagation of the wave and also the internal and external liquid levels are equally fast enough.

The device 4 is fixedly mounted. The apparatus 4 comprises a transmitter for providing a microwave signal which is not clearly shown, a receiver for receiving the reflected microwave signal and a signal processing device for determining the reflection position of the reflected microwave signal.

The transmitter has a waveguide, denoted 5 in FIG. 1, which is surrounded by a protective tube 8. The waveguide 5 passes through the conical intermediate piece 9 to the tube 1.

In operation, the transmitter generates a microwave signal, which is provided to the tube 1 through the waveguide 5 and the conical intermediate piece 9. The microwave signal propagates in the tube 1 towards the surface to be measured, reflected by the surface and propagated back towards the receiver. The reflected signal is received at the receiver via the conical intermediate piece 9 and the waveguide 5. The signal processing apparatus calculates the liquid level from the round trip time of the microwave signal.

According to the invention, the transmitter is adapted to transmit a microwave signal in a frequency band comprising a frequency which is outside the optimum frequency f _opt by less than 7%, the optimum frequency being

Where f _co is the cutoff frequency of the propagation mode in the tube (1) in vacuum and ε is preferably the central dielectric constant in the target dielectric constant range, which is not limited to, but is in the range of 1 to 1.03 or less. to be.

By the selection of this frequency, the change in the group velocity of microwaves becomes very small when the dielectric constant of the gas in the tube 1 changes from 1 to 1.03 over the liquid surface, even if the composition and pressure of the gas are not known over the liquid surface. Accurate measurements of the liquid level can be performed.

Preferably, the frequency _deviates by less than 5% of the optimum frequency f _opt , more preferably less than 3%, more preferably less than 2%, even more preferably less than 1%, and most preferably the optimal frequency f _opt Same as Optionally, the frequency band has a center frequency that deviates from the optimum frequency f _opt by less than 7%, 5%, 3%, 2% or 1%.

These numbers give a slightly larger rate change than the number obtained using the optimum frequency, but the variation is much smaller than the change obtained using the frequency used in prior art devices.

Prior to the present invention, a theoretical explanation and such a deviation of the optimum frequency are given.

The propagation in any uniform (ie, filled with one material with dielectric constant ε) is explained by the change in phase constant β that provides a phase change in radians per meter:

Where k is the wave number (k = 2πf / c, f is the frequency, c is the speed of light in a vacuum), and k _c0 is the cutoff frequency in vacuum (k = 2πf _c0 , the lower limit for propagation in a waveguide). / c, f _c0 is the cutoff frequency in vacuum). Equation 1 is valid for any single propagation mode independent of the cross section of the waveguide.

The cutoff frequency k _c0 is related to the geometric shape of the waveguide cross section. For a circular cross section with radius a,

, Wherein X is a muscle that can be applied for the Bessel function _{(J 0 (x), J} 1 (x) , and so on), in k _c0 0 is inserted to stress that is applied to the _c0 k vacuum. A few lowest modes in a circular waveguide (diameter D = 2a) are shown in Table 1 below.

As a comparison, the cutoff frequency in a rectangular waveguide with a cross-sectional size of b (a> b) times

Where n and m are non-negative integers with optional constraints of nm> 0 (E mode) or n + m> 0 (H mode).

With reference to the propagation constant β, it is noted that there is at least some nonlinear frequency dependency compared to the propagation constant for free traveling waves. Typically, the propagation of a band-limited signal is described as the group speed v _g and is calculated as follows:

Where c is the light velocity in vacuum (299792458 m / s) and the quotient c / v _g is slightly greater than at least one. For waveguides with very large cross sections (approximately in the case of free space), k _c0 can be ignored, and the quotient simply becomes the square root of the dielectric constant ε.

Mode in a circular waveguide. The common notation, X, λ _co / D, where λ _co is the cutoff wavelength in vacuum and D is the diameter, and D = 2a is given for each propagation mode. Mark X nm λ _co / D Remarks H ₁₁ or TE ₁₁ 1.841 (primary max of J ₁ ) 1.706 Lowest mode E ₀₁ or TM ₀₁ 2.405 (primary zero of J ₀ ) 1.306 H ₂₁ or TE ₂₁ 3.054 (1st maximum of J2) 1.029 H ₀₁ or TE ₀₁ 3.832 (maximum nonzero primary of | J ₀ |) 0.820 Low loss mode E ₁₁ or TM ₁₁ 3.832 (secondary zero of J ₁ ) 0.820 X same as H ₀₁ H ₃₁ or TE ₃₁ 4.201 (primary maximum of J ₃ ) 0.748

Closure testing of equation (4) revealed that the dielectric constant ε always has a minimum value when allowed to change for all positive values. This can be easily seen by noting that if ε is slightly above the denominator of 0, c / v _g will be very large and obviously the same for very large ε. This minimum may appear when ε has a physically unrealistic value, but for any waveguide diameter 2a (since k _c0 is related to diameter 2a according to FIG. 2) this minimum may occur for possible values of ε Even if the frequency (or frequency k) can be presented.

This minimum may appear when ε has a physically unrealistic value, but for any tube diameter 2a the frequency (or wave number k) may be given even if this minimum can occur for a possible value of ε. To find the minimum of c / v _g , the second derivative is made:

The minimum value of c / v _g is found where this derivative is zero. Therefore, the frequency indicated by the optimal frequency k _opt that satisfies

to be. By this selection, small changes in ε (around the middle of the assumed ε interval, which may be 1-1.03) can be expected to provide very small changes in v _g , where the numerical mean is quantified below. This phenomenon can be explained by a combination of two factors contributing to v _g : An increase in ε reduces the speed of the microwave, but can also cause the waveguide to appear larger, thus increasing the waveguide propagation speed. The differential expression indicates that these two reaction effects can be canceled out.

To illustrate the behavior, the case of a waveguide where a small change in v _{g with} a diameter of 2a = 100 mm and an ε interval in the range of 1 to 1.03 is to be obtained is given (i.e. the optimum wavenumber k _opt is found for ε = 1.015). ). If the lowest mode H ₁₁ of propagation is used, the optimum wavenumber k _opt of 51.5 m ⁻¹ is obtained using equations 2 and 6. This optimum frequency corresponds to an optimal frequency f _opt of 2.46 GHz.

FIG. 2 shows a plot of group velocities normalized to luminous flux in vacuum as a function of dielectric constant for H ₁₁ mode of microwave radiation in a 100 mm waveguide at an optimum frequency, 2.46 GHz.

The group velocity change is within ± 0.005% when the dielectric constant epsilon varies over 1-1.03 (± 1.5%) or contains propane (ε = 1.03) in air (ε = 1.0006). The improvement in speed change is 150 times and is greater when the interval of dielectric constant values is limited to intervals smaller than 1-1.03.

FIG. 3 shows a plot of group velocities normalized to luminous flux in vacuum as a function of dielectric constant for H ₁₁ mode of microwave radiation in 100 mm waveguides at 2.46 GHz, 10 GHz and 2 GHz for comparison. Note that the vertical scale is magnified 200 times with respect to FIG. The curve for the optimal frequency is a horizontal straight line, i.e. no ε dependence on the group speed appears, whereas the group speed at 2 and 10 GHz respectively depends heavily on ε in the illustrated intervals.

Figure 4 shows the effect of the waveguide diameter on the obtained group speed. The figure shows the group velocities normalized to the luminous flux in vacuum as a function of the dielectric constant for H ₁₁ mode of microwave radiation in waveguides 100 mm, 100 mm + 0.005% and 100 mm-0.005% in diameter.

The maximum position of the group speed does not change significantly even if the diameter is slightly different. However, the group velocity is highly dependent on the diameter, so the diameter of the waveguide must be measured or measured very carefully. More are described below. First, however, another example of the inventive concept is shown in FIGS. 5 and 6.

FIG. 5 shows the H ₁₁ mode in a 100 mm waveguide for various values of dielectric constant ε, ie ε = 1.0006 (air) and ε = 1.03 (1.02 corresponds to propane at 10 atm, estimated to be the worst case). Normalized group velocities versus luminous flux in vacuum as a function of wavenumber for. Note that the two curves actually intersect at a particular frequency, which is the optimal frequency k _opt .

FIG. 6 shows a plot of group velocities normalized to luminous flux in vacuum as a function of wavenumber for H ₁₁ mode of microwave radiation in a 100 mm waveguide for various values of the dielectric constant ε clearly indicated. Velocity is shown for ε: 1.03, 1.02, 1.01 and 1.0006. The intersection is found at the optimum wave number k = 51.5m ⁻¹ as indicated above.

Many methods are available for measuring or measuring the diameter of a waveguide that must be performed more carefully than when using overdimensioned waveguides and mode suppression as disclosed in US Pat. No. 4,641,139 to Edvardson. have.

One method is to determine the effective diameter for one or several levels by field measurements for one or several known heights. In Fig. 1, a relatively thin metal pin 10 is mounted radially in the lower part of the tube 1 perpendicular to the longitudinal direction. This metal pin 10 consists of a reactance which causes a defined reflection of the emitted microwave signal, which is received by the receiver in the device 4 and the measurement of the gauge function via the electronics is made. to provide. Such field measurements are further described in US Pat. No. 5,136,299 to Edvardson, which is incorporated herein by reference. The same measurement is, of course, preferred and can be done several times using an accurate measurement of the actual liquid surface.

Another method is, by means of a feeder, to transmit a microwave signal through the gas in the secondary propagation mode in the tube 1 towards the surface of the liquid, reflected off the liquid surface and back to the secondary propagation mode through the tube. Receiving a propagated microwave signal and identifying the portion of the microwave signal received in a different mode than the first and second propagation modes.

7A and 7B illustrate one embodiment of waveguide feeding for two modes. The tube 1 is closed with a cover 10 sealed by sealings 11 and 12. Down sealing λ / 2 dipole (dipole), (13) a tube feeding the H ₁₁ mode (1), and the H ₁₁ mode is a power supply through two wires (15). Below the dipole 13, a member 14, which is given in a form suitable for feeding the E ₀₁ mode to the tube 1, is mounted symmetrically. The member 14 is fed by the line 16. Lines 15 and 16 are connected to cables (not shown) of the circuit and measuring device via pressure seals 12. The two lines 15 are fed to the balun so that the lines are fed in the opposite phase, so that the signal lines 16 which are supplied like a coaxial line with a part of the cover 10 as a part different from the line 15 are supplied. Automatically insulate between. Since it has a formation suitable for matching, etc., it is obvious that basically the same output line will work for both of the two modes (H ₁₁ and E ₀₁ ) as well as any of these two modes. Antennas and feeds 13-16 may be fabricated on a printed circuit board, indicated by dashed lines 17.

Thus, two separate measurements can be performed and the level as well as the diameter of the tube 1, for example the effective or average diameter, can be deduced from the measurement with reference to FIG. 4. One way to achieve this is to use a waveguide connection that provides two modes, and if the modes are very different, the group velocities for the two modes are echoes in time for the pulse system or the FMCW system. This is to take advantage of the fact that it can vary sufficiently to separate the echo at frequencies.

The receiver of the apparatus 4 of FIG. 1 can be adapted to identify parts of the microwave signal received in a mode different from the first and second propagation modes based on the parts where the times of arrival at the receiver are different. The waveguide feed then has two (or more) connections connected to different modes, and the RF switch connects the modes sequentially, or the receiver or transmitter chain portions have two (or two) Above) are paired to allow measurement of the mode.

The microwave signal portion may have very different propagation time to allow sequential detection. Otherwise, the transmitter of the apparatus 4 may be adapted to sequentially transmit micro signals in the first and second propagation modes.

Alternatively, the transmitter of the apparatus 4 can be adapted to transmit spectrally separated first and second propagation modes. Thus, waveguide feeding has a different function for different frequencies providing one mode at one frequency interval and another mode at another frequency interval.

The signal processing device is alternatively adapted to calculate the dielectric constant of the gas above the liquid level based on the received and identified portion of the microwave signal received in a mode different from the first and second propagation modes (if the diameter is known). Can be.

8A and 8B illustrate another waveguide feeding suitable for feeding a microwave signal in mode H ₀₁ or E ₀₁ . The tube 1, the cover 10 and the sealing 11 are similar to the embodiment of FIG. 7. In general, the antenna device formed by the printed circuit board 20 is a very important part of feeding. The printed circuit board 20 is powered by a coaxial line shown at 21 on the outside. The printed circuit board 20 carries four λ / 2 dipoles 25 which are fed in phase (efficiently connected in parallel by radial wires not shown) providing the electric field direction as indicated by the arrows, thus The dipole can be efficiently connected to the H ₀₁ waveguide propagation mode. The distance from the printed circuit board 20 to the cover 10 is about λ / 4. The outside of the feed coaxial line 21 is also inside another coaxial line with insulation 23 and shield 24. This coaxial line feeds the E ₀₁ mode generated by the member 24 and a portion of the pattern on the printed circuit board 20. Mechanical attachment of 22 and 23 is not shown.

9A-9C illustrate another method of arranging waveguide feeds for generating microwave signals in H ₀₁ and H ₁₁ modes. For example, in the form of a printed circuit board, the antenna element 30 has four dipoles 33 fed by four coaxial cables 32 through the seal 31. Outside the container, four cables are fed through a connecting network, indicated at 34 in FIG. 9C, which is located outside the container or possibly on the antenna element 30. The feed network consists of four standard hybrid circuits 34 which may involve three different waveguide modes. The top input provides, with reference to FIG. 9B, a H ₀₁ mode with four dipoles oriented as continuous arrows. The other two inputs provide an H ₁₁ mode that is fed with right circular polarization and left circular polarization, and the polarization modes are used to transmit and receive the H ₁₁ mode.

Each feeder as illustrated in FIGS. 7 to 9 has a funnel (not shown) in the tube 1 to match the diameter of the tube 1. The funnel can be hung in the tube 1 as mentioned in US Pat. No. 4,641,139, which is incorporated herein by reference.

In Table 2 below, attenuations are found for certain preferred combinations of center frequency and tube diameter for the four waveguide modes H ₁₁ / E ₀₁ / H ₀₁ / H ₀₂ . Attenuation (ie 2 × 25m transmission) for a 25m tube is given for these four modes in the given order and the given dB separated by diagonal lines.

Note that the numbers in Table 2 merely indicate other embodiments. Any mode can theoretically be used as the main propagation mode. Other modes are given in Equations 2 and 3 and Table 1. However, the two combinations in Table 2 seem to have particularly desirable properties.

Using a frequency of about 10 GHz, the H ₀₂ / E ₀₁ combination in a 100 mm tube is used as two rotationally symmetric modes, when the H ₀₂ mode is clearly independent of the condition of the tube wall, and E ₀₁ is far from the cutoff. This is useful when having a propagation similar to conventional radar level measurement through a tube.

Using a frequency range around 2.5 Hz (for example within the ISM-band 2.4-2.5 GHz), the H ₁₁ / E ₀₁ combination in a 100 mm tube produces lower frequencies that are less sensitive to mechanical details such as holes, joints, etc. One way to use it.

Finally, the table below shows that use of shorter tubes (many LPG spheres are only 10-15 m in height) can use smaller tubes and other modes without very large damping (proportional to tube length). have.

Attenuation over 2 x 25 m stainless steel pipe for four waveguide modes H ₁₁ / E ₀₁ / H ₀₁ / H ₀₂ for different frequency selections and tube diameters (0.5 Ω / m 2 at 10 GHz). NP indicates no propagation (cutoff), NA indicates that no mode can propagate, the mode where the 1.41 condition is met is underlined, and the combination of the two most preferred modes indicates a mode that meets the 1.41 condition. Represents one of the combinations underlined to represent. The frequencies shown are only display and must be slightly different to meet the 1.41 requirement. frequency 2.5 GHz 5 GHz 10 GHz Pipe diameter attenuation down dB attenuation down dB attenuation down dB 100 mm 7/15 / NP / NP H 11 / E 01 5/9/6 / NP H 01 / E 01 5/12/2/7 H 02 / H 11 50 mm NA 21/41 / NP / NP 13/26/18 / NP H 01 / H 11 25 mm NA NA (59/115 / NP / NP )

In these embodiments, the same frequency is generally assumed to be used for both modes, which means separation by switches, separate transmitter and receiver channels, and the like. Obviously other frequencies can also be used to make the system into two or more separate microwave devices (or devices that can be broadly tuned) connected to the same conduit and commonly connected to signal processing parts. In this case the filtering function can be used to separate the signals and the mode generator can be adapted to generate different modes for different frequencies.

By measuring microwave signals in two propagation modes that are independent of each other, the properties of the tube or environment within the container can be detected and compensated for. To obtain good results, the modes can be selected such that the microwave signal of one mode is greatly disturbed while the microwave signal of another mode is very little disturbed.

The signal processing device of the device 4 calculates the liquid level in the container from the propagation time of the transmitted and reflected microwave signal in each propagation mode, and based on the liquid level calculated in the container, one or more properties of the tube or environment in the container. It is preferred to be adapted to measure.

Alternatively, the signal processing device of the apparatus 4 calculates the attenuation of the identified portion of the microwave signal received in a mode different from the first and second propagation modes, and calculates the calculated attenuation of the identified portion of the microwave signal. It is adapted to measure one or more properties of a tube or environment in a container based on.

One or more properties of the tube or environment within the container may include the cross section of the tube, the change in cross-sectional dimension along the length of the tube, the measurement of the co-centre of the tube, the presence of impurities, in particular the solid or liquid hydrocarbons in the inner wall of the tube, and In may include any of the presence of fog. Modes with different properties can be used to represent different parameters.

10-12 show H ₁₁ mode (FIG. 10), E ₀₁ mode (FIG. 11), and H ₀₁ of microwave radiation in a waveguide filled with a gas having a dielectric layer of different thickness t on the inner wall with different dielectric constants epsilon. 12 is a schematic of the inverted group velocity normalized to the group velocity in vacuum as a function of wavenumber for each mode. The dielectric constant of the dielectric layer is set to 2.5, which is representative of the oil layer.

Note that the behavior is similar for gas filling and dielectric layers (gases with ε = 1.03 give roughly similar curves, such as oil layers approximately 1 mm thick). For the H ₁₁ mode, the thin dielectric layer behaves very similar to gas, but the thicker layer moves across zero for lower frequencies. For the E ₀₁ mode, the sensitivity to the dielectric layer is slightly larger, while for the H ₀₁ mode, the dielectric layer has a very small impact.

Thus, the difference in sensitivity to the dielectric layer offers the possibility of measuring the oil layer (eg average thickness or dielectric constant) and possibly correcting for the oil layer.

Finally, the reflective reactance 10 arranged in the tube 1 can be designed to provide substantially stronger reflection of the microwave signal in one of the propagation modes than in the other of the propagation modes. Reflective reactance 10 may be embodied as a short metal pin, which is a thin PTFE (could not be reflected about H ₁₁ ) supported coaxially to tube 10. This can be used to obtain a reference reflection at a mechanically known position for the E ₀₁ mode but very weak reflection for the H ₀₁ mode.

Claims (49)

There is a liquid in a container and a gas having a dielectric constant above the liquid level so long as it is within a predetermined dielectric constant range A transmitter (4, 5, 9) for transmitting a micro signal in a first propagation mode in a tube (1) past the gas and towards the liquid surface; A receiver (4, 5, 9) for receiving said microwave signal reflected against said liquid surface and propagating back through said tube; And A signal processing device for calculating the liquid level in the container from the propagation time of the transmitted and received microwave signal, A liquid level measurement device in a high accuracy container in which there are many holes in the pipe wall such that the liquid in the container can flow in and out of the pipe to the side and out of the pipe to maintain one level for the liquid. The transmitter is configured to transmit the microwave signal in a “frequency band” that includes a frequency that is less than 7% from the optimum frequency f _opt , wherein the optimum frequency is

Where f _co is the cutoff frequency of the first propagation mode in the tube and ε is the center dielectric constant of the dielectric constant range. delete The method of claim 1, And said frequency is less than 5% from the optimum frequency f _opt . The method of claim 3, wherein And said frequency is equal to said optimum frequency f _opt . The method according to any one of claims 1, 3 and 4, And said frequency band has a center frequency deviating less than 7% from said optimum frequency f _opt . The method of claim 5, wherein And said center frequency deviates less than 5% from said optimum frequency f _opt . The method of claim 1, And said predetermined dielectric constant range is 1 to 1.03. The method of claim 1, And said liquid is comprised of liquefied gas, said gas is comprised of said gaseous liquefied gas, and said liquefied gas is stored in said container at an overpressure. delete The method of claim 1, The pipe (1) is a liquid level measuring device in a container for high accuracy having a rectangular cross section. The method of claim 1, The pipe (1) is a liquid level measuring device in a container for high accuracy having a circular cross section. The method of claim 11, Apparatus for level measurement in a high accuracy container in which the first propagation mode in which the transmitters 4, 5, 9 are adapted to transmit the microwave signal to the tube 1 is any one of H ₁₁ , H ₀₁ and H ₀₂ . . The method of claim 12, The tube is 100 mm in diameter and the transmitter measures liquid level in a high accuracy container adapted to transmit the microwave signal in any one of H ₁₁ mode at 2.5 GHz, H ₀₁ mode at 5 GHz, and H ₀₂ mode at 10 GHz. Device. The method of claim 12, And said tube is 50 mm in diameter, and said transmitter is configured to transmit said microwave signal in H ₀₁ mode of 10 GHz. The method of claim 1, The transmitter is configured to transmit a micro signal of a second propagation mode to the tube 1 through the gas and towards the liquid surface, The receiver (4,5,9) receives the microwave signal reflected against the liquid surface and propagated back through the tube to the second propagation mode; And a liquid level measuring device in a container of high accuracy, configured to identify a portion of the microwave signal received in a mode different from the first and second propagation modes. The method of claim 15, The pipe (1) has a circular cross section, and the second propagation mode is either E ₀₁ or H ₁₁ , the liquid level measuring device in the container for high accuracy. The method of claim 15, And the receiver is configured to identify a portion of the microwave signal received in a mode different from the first and second propagation modes based on different portions of the time arriving at the receiver. The method of claim 17, And the transmitter is subsequently configured to transmit the microwave signals in the first and second propagation modes. The method of claim 15, And said transmitter is configured to transmit said microwave signals in said first and second propagation modes spectrally separated. The method according to any one of claims 15 to 19, The signal processing device is configured to calculate a dielectric constant of the gas above the liquid level based on the received and identified portion of the microwave signal received in a mode different from the first and second propagation modes. Liquid level measuring device in container. The method according to any one of claims 15 to 19, The signal processing apparatus is configured to calculate a cross-sectional dimension of the tube on the basis of the received and identified portion of the microwave signal received in a different mode than the first and second propagation modes. Measuring device. The method of claim 21, The tube has a circular cross section and the calculated cross sectional dimension is an average diameter of the tube according to the distance at which the microwave signal propagates before being reflected against the liquid surface. The method of claim 15, The signal processing apparatus is configured to calculate the liquid level in the container from the propagation time of the transmitted and reflected microwave signal in the second propagation mode; The signal processing apparatus further comprises one or more properties based on the calculated liquid level in the container, wherein the cross-sectional dimension of the tube, the change in cross-sectional dimension along the length of the tube, the measurement of the concentricity of the tube, impurities Measuring one or more properties of the tube or environment in the container, including the presence of, in particular, the presence of solid or liquid hydrocarbons in the inner wall of the tube or of fog in the gas, and using the measurement for the one or more properties And an apparatus for measuring liquid level in a container of high accuracy, configured to calculate a modified level of the liquid in the liquid. The method of claim 15, The signal processing apparatus is configured to calculate attenuation of the identified portion of the microwave signal received in a mode different from the first and second propagation modes, The signal processing apparatus further comprises one or more properties based on the calculated attenuation of the identified portion of the microwave signal, the cross sectional dimension of the tube, the change in the cross sectional dimension along the length of the tube, the co-center of the tube. measuring one or more properties of the tube or environment in the container, including the measurement of concentricity, the presence of impurities, in particular the presence of solid or liquid hydrocarbons in the inner wall of the tube or of fog in the gas, A liquid level measurement apparatus in a high accuracy container adapted to calculate a modified level of the liquid in the container using the measurement. delete The method of claim 23 or 24, A liquid level measuring device in a container for high accuracy, wherein a reflective reactance is arranged in the tube to provide stronger reflection of a microwave signal in any one of the propagation modes than in any of the propagation modes. The method of claim 1, And said microwave signal is a frequency modulated continuous wave (FMCW) signal. The method of claim 1, And said microwave signal is a pulse radar signal. The method of claim 1, And said transmitter is configured to transmit said microwave signal in an adjustable frequency band. There is a liquid in a container and a gas having a dielectric constant above the liquid level, which is within a predetermined dielectric constant range, in which the container is arranged a tube with many side holes, so that the liquid in the container is one of the liquid into and out of the tube. A liquid level measurement method in a container for high accuracy that can flow in and out of the tube to maintain the water level, Determining a first amount representing an internal dimension of the tube; Determining a frequency band comprising a frequency that is less than 7% from an optimal frequency f _opt based on the first amount; Tuning a transmitter to operate in the frequency band; Transmitting in said frequency band a micro signal of a first propagation mode in said tube past said gas and towards said liquid surface; Receiving in the frequency band the microwave signal reflected against the liquid surface and propagating back through the tube; Determining a second amount representing a propagation time of the transmitted and received microwave signal; And Calculating the liquid level in the container based on the first and second amounts, The optimum frequency is

Wherein f _co is the cutoff frequency of the first propagation mode in the tube, and ε is the central dielectric constant of the dielectric constant range. delete The method of claim 30, Said frequency being less than 5% from the optimum frequency f _opt . 33. The method of claim 30 or 32, Said frequency band having a center frequency deviating less than 7% from the optimum frequency f _opt . The method of claim 30, And said predetermined dielectric constant range is 1 to 1.03. The method of claim 30, And said liquid is composed of liquefied gas, said gas is composed of said gaseous liquefied gas, and said liquefied gas is stored in said container at an overpressure. The method of claim 30, The transmitter (4, 5, 9) is formed to transmit the microwave signal in the tube (1) and the first propagation mode is a liquid level measuring method in a container for high accuracy, any one of H ₁₁ , H ₀₁ and H ₀₂ . The method of claim 30, The microwave signal is transmitted in the second propagation mode in the tube (1) through the gas and toward the surface of the liquid, Receiving the microwave signal reflected against the liquid surface and propagating back through the tube in the second propagation mode, And a portion of the microwave signal received in a mode different from the first and second propagation modes is identified. delete delete delete delete delete delete The method of claim 1, And said frequency is less than 3% from the optimum frequency f _opt . The method of claim 1, And said frequency is less than 2% from the optimum frequency f _opt . The method of claim 1, And said frequency is less than 1% from the optimum frequency f _opt . The method of claim 5, wherein And said center frequency deviates less than 3% from said optimum frequency f _opt . The method of claim 5, wherein And said center frequency is less than 2% from said optimum frequency f _opt . The method of claim 5, wherein And said center frequency is less than 1% from said optimum frequency f _opt .

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