Method for determining and displaying the optimal material thickness for level measurement using radar sensors

Abstract

Method for reducing the electromagnetic radiation reflected back from the surfaces of a wall (10) and from the surfaces of an adapter (14) adhering to the surface of the wall (10) and / or glued to the surface of the wall (10) of a measuring arrangement (1), wherein the measuring arrangement (1) comprises the following: - a container (4) whose interior (2) can be filled with a filling material (6), - a radar level measuring device (12) arranged outside the container (4) and directed towards the interior (2) of the container (4), which is designed as a radar level measuring device and which can emit electromagnetic waves of at least one wavelength and detect the course of the reflected electromagnetic radiation of at least one wavelength as an echo curve, - the wall (10) arranged between the interior (2) of the container (4) and the radar measuring device (12), which is at least partially transparent to electromagnetic radiation of at least one wavelength, - a recording unit (30) for recording the echo curve, - the adaptation (14) for reducing the electromagnetic radiation reflected back from the surfaces of the wall (10), wherein the adaptation (14) comprises at least one self-adhesive, and / or wall-adherent, and / or wall-lying plastic film (16) and / or plastic plate at least partially transparent to electromagnetic radiation of at least one wavelength, which adheres to the wall (10) and / or is affixed to the wall (10) in such a way that the electromagnetic radiation pulses emitted by the radar level gauge (12) penetrate the at least one plastic film (16), wherein the method is characterized in that the following steps are carried out successively: a) Applying and / or sticking the plastic film (16) to the wall (10), b) Irradiating the interior of the container (4), preferably made of plastic, through the plastic film (16) with the electromagnetic radiation pulse emitted by the radar level gauge (12) and recording the intensity of the electromagnetic radiation reflected back into the radar level gauge (12) as an echo curve (20) over time. c) Determining a time period (26) of the echo curve (20) in which the echo curve (20) exhibits at least a part of the electromagnetic radiation reflected back from the surfaces of the wall (10) and the plastic film (16) and determining the energy value of the radiation pulse detected in the time period (26) from the intensity of the reflected electromagnetic radiation recorded in the time period (26), d) Applying and / or adhering another plastic film (16) to the plastic film (16) already applied and / or adhering to it, e) Irradiating the interior (2) of the container (4) again through the plastic film (16) with an electromagnetic radiation pulse emitted by the radar level gauge (12), recording the echo curve (20) and determining the energy value of the radiation pulse detected in the period (26), f) Applying and / or adhering another plastic film (16) to the applied and / or adhering plastic film and then performing step e), if the last determined energy value is less than the previously determined energy value, (g) Storing the last determined energy value in a memory (34) if the last determined energy value is greater than or equal to the previously determined energy value.

Description

[0001] The present invention relates to methods for reducing the electromagnetic radiation reflected back from the surfaces of a wall, preferably a plastic wall, of a measuring arrangement according to the preamble of claims 1 and 4.

[0002] A measuring arrangement for measuring a fill level in a container with a radar level gauge is described, which includes an adaptation for reducing the electromagnetic radiation reflected back from the surfaces of a wall of the container, as well as methods for optimizing the adaptation and reducing the interference radiation, for example the radiation reflected back from the container walls, wherein display devices indicate whether interference radiation is sufficiently reduced.

[0003] Level measurement devices for determining and / or monitoring the fill level in a container are known in various designs. Radar level measurement devices, for example, level gauges operating on the time-of-flight principle, emit electromagnetic radiation pulses of a specific wavelength and then detect the temporal evolution of the reflected electromagnetic radiation as an echo curve. This detects not only reflections from the surface of the liquid being measured, but also a multitude of interfering reflections, such as reflections from the container walls, the container bottom, or the container lid. The sum of these reflections produces a signal that is measured as a function of time and is detected and displayed as a time-dependent echo curve, usually with several maxima.The fill level of the liquid in the container is then to be determined from the course of this echo curve.

[0004] In FMCW (Frequency Modulated Continuous Wave) radar, a high-frequency signal is used in which the transmission frequency is changed during the measurement, for example, increasing linearly. The frequency change is typically up to about 10 percent of the transmission frequency of the high-frequency signal. The signal is transmitted, reflected off the surface of the product, and received with a time delay. For further signal processing, the difference Δf is calculated from the current transmission and reception frequencies. This difference is directly proportional to the distance; that is, a large measured frequency difference indicates a large distance, and vice versa. This frequency difference is then converted into a frequency spectrum using a Fourier transform, and the product distance is then calculated. The fill level is determined by the difference between the fill level and the distance.

[0005] Reflections from the container lid are often particularly problematic with radar level measuring devices. If the lid is positioned between the level measuring device and the contents, it must be penetrable by the incoming electromagnetic radiation and therefore must be made of a material permeable to the incoming electromagnetic radiation pulse, such as a plastic material, or at least have a window through which the electromagnetic radiation pulse emitted by the radar level measuring device can penetrate into the interior of the container.

[0006] Interfering reflections, especially those from the container lid, result in an inaccurate measurement of the fill level of the liquid or bulk material inside the container, leading to measurement errors caused by these reflections. Therefore, these interfering reflections must be minimized.

[0007] The state of the art is known from "Level Gauges with Radar - Guide for the Process Industry" by Peter Devine, published by VEGA Grieshaber KG, 2002, ISBN 3-00-008216-6; Chapter 6, pp. 135 and 137f, as well as DE 10 2012 003 948 A1.

[0008] The object of the present invention is therefore to provide a method for reducing the electromagnetic radiation reflected back from the surfaces of the container lid and / or the wall, so that the fill level of the liquid or bulk material in the container can be determined more accurately.

[0009] The problem is solved by a method according to claim 1. Advantageous embodiments are disclosed in the dependent claims.

[0010] A measuring arrangement according to the present application comprises a container whose interior can be filled with a material, a radar level measuring device arranged outside the container and directed towards the interior of the container, preferably designed according to the time-of-flight principle, which can emit electromagnetic radiation pulses and / or electromagnetic waves of at least one wavelength and can detect the, preferably temporal, course of the reflected electromagnetic radiation of at least one wavelength as an echo curve, a wall arranged between the interior of the container and the radar level measuring device, for example in the form of a plastic lid, which is at least partially transparent to electromagnetic radiation of at least one wavelength, and a detection unit for detecting the echo curve, preferably in a time-dependent manner.as well as an adaptation for reducing the electromagnetic radiation reflected back from the wall surfaces. The adaptation comprises at least one, preferably self-adhesive and / or wall-mounted, plastic film or plastic sheet, at least partially transparent to electromagnetic radiation of at least one wavelength, which adheres to the wall and / or is affixed to the wall and / or rests on the wall in such a way that the electromagnetic radiation pulses emitted by the radar level gauge penetrate the at least one plastic film or plastic sheet. The plastic film or plastic sheet can also simply rest on the wall. The wall is preferably a plastic wall. In this application, plastic sheets will also be referred to as plastic films.

[0011] By having the adaptation comprise at least a self-adhesive and / or wall-adherent plastic film that is at least partially transparent to electromagnetic radiation of at least one wavelength, it is possible, with a suitable thickness and an adapted dielectric constant of the at least one plastic film, to achieve that the interference reflections at the surfaces of the wall or the plastic films are at least partially compensated so that the interference reflections are reduced.

[0012] The adaptation can also include several, preferably two, three, four or five layers of plastic film glued and / or adhering to each other.

[0013] In a preferred embodiment, the plastic films have approximately the same thickness. They can be made of the same material, for example, the same material as the wall. This material is preferably matched to the dielectric constant of the wall. By using several plastic films of the same thickness and dielectric constant glued and / or bonded together, it is easier to achieve an optimal layer thickness in a stepwise process, minimizing the electromagnetic radiation reflected back from the surfaces of the plastic films and the surfaces of the wall.

[0014] The container is preferably made of plastic and / or it has at least one container lid made of plastic, through which the fill level in the container is determined.

[0015] Interference reflections from the surfaces of the container lid's window materials, or from the surfaces of the container lid penetrated by the electromagnetic radiation emitted by the radar measuring device, or from plastic containers in which a radar sensor is used for level measurement, are thus reduced by reflection-reducing layers whose thickness can be varied continuously or in specific steps. The layers are preferably made of the same material as the medium being irradiated and / or have a similar dielectric constant. A total thickness corresponding to half the wavelength or a multiple thereof in the material being irradiated achieves destructive interference, i.e., cancellation of the reflections from both the signal input and output.Although in practice the thickness can only be adjusted approximately, since a certain bandwidth of the transmission frequency is required for measurement, reflection can nevertheless be significantly reduced by this type of adjustment.

[0016] An important feature is the ability to visualize these interfering reflections via a display, preferably integrated into the sensor. This visualization can be achieved either through a graphical representation of the echo curve and its visual assessment, or through analog or digital information about the reflection intensity of the interfering reflection. Based on this display, the reflection-reducing layer can then be adjusted. For example, an analog or digital display can be used to show the reflection intensity of the interfering reflection. However, it is also possible to visualize the effectiveness of the adjustment using a simple traffic light indicator. For instance, a red light could indicate poor adjustment, a yellow light moderate adjustment, and a green light good adjustment.

[0017] The detection unit can, for example, have a memory in which at least the part of the echo curve that contains the electromagnetic radiation reflected from the surfaces of the adapter and the wall is stored in a time-dependent manner.

[0018] In order to determine the interfering reflections to be minimized, a period of time is preferably determined in which the echo curve exhibits at least a part of the electromagnetic radiation reflected back from the surfaces of the wall.

[0019] The acquisition unit can include a comparator that compares the measured values ​​of the echo curve within a specific time period with corresponding values ​​of a predefined reference curve. If, for example, all measured values ​​of the echo curve within this specific time period are below the corresponding values ​​of the predefined reference curve, the comparator can, for instance, send an OK signal to a display device. The display device then indicates that the interfering reflections have been sufficiently minimized.

[0020] The detection unit can also include an evaluation unit that determines an energy value from the echo curve over a specific period, for example by summing the individual values ​​detected during that period, and feeds this value to a comparator that compares it to a predefined reference value. In this case, too, the comparator can, for example, send an OK signal to a display device if the reference value is greater than or equal to the value determined by the evaluation unit.

[0021] The display device can be an optical and / or an acoustic display element, wherein the display device is preferably designed as an LED or as an electronic display.

[0022] With such a measuring arrangement, a method according to the invention for reducing the electromagnetic radiation reflected back from the surfaces of a wall and from the surfaces of an adaptation adhering and / or glued to a surface of this wall can be carried out.

[0023] In this process, a plastic film is first placed and / or adhered to the wall, towards which the radar level gauge is pointed. Then, the interior of the container is irradiated through the plastic film and this wall with an electromagnetic radiation pulse emitted by the radar level gauge, and the intensity of the electromagnetic radiation reflected back to the radar level gauge is recorded as an echo curve.

[0024] A period of the echo curve is then determined in which the echo curve exhibits at least a portion of the electromagnetic radiation reflected back from the surfaces of the wall and the plastic film, and the energy value of the radiation pulse detected in this period is determined from the intensity of the reflected electromagnetic radiation recorded during this period. This energy value is preferably stored.

[0025] Subsequently, another plastic film is placed and / or adhered to the already applied and / or adhered plastic film, and the interior of the container is again irradiated through the plastic film with an electromagnetic radiation pulse emitted by the radar level gauge. The resulting echo curve from this radiation pulse is also detected and recorded. Then, the energy value of the radiation pulse detected again within the previously determined time period is calculated and preferably also stored.

[0026] If the last determined energy value is lower than the previously determined energy value, another plastic film is placed and / or glued onto the surface of the top plastic film, and after irradiating the interior of the container again through the further plastic film with an electromagnetic radiation pulse emitted by the radar level gauge, the echo curve is recorded and the energy value of the radiation pulse detected in the specified period is determined.

[0027] If, however, the last measured energy value is greater than or equal to the previously measured energy value, the user can be notified, for example via a display device, that the last measured energy value is greater than or equal to the previously measured energy value, thus indicating to the user that the optimal number of overlapping and / or bonded plastic films has now been reached or exceeded. The last measured energy value is stored in a memory.

[0028] Using this method, it is possible to gradually minimize interference reflections and to gradually optimize the adaptation of the measuring arrangement to a wall, whether it is adhered and / or glued.

[0029] For comparison purposes, a reference value higher than the smallest determined energy value can be determined and stored in a further memory of the measuring arrangement, wherein the reference value is preferably chosen between the smallest determined energy value and the second smallest determined energy value, so that a comparator can compare the energy value determined in the specified period with the specified reference value and can transmit an OK signal to a display device if the specified reference value is higher than the energy value determined in the specified period.

[0030] In this way, the fill level of a bulk material or liquid in the interior of the container can be determined more accurately, since the maximum value corresponding to the fill level in the echo curve is shifted less in the case of lower interfering reflections at the container lid, which also form maxima in the echo curve adjacent to the fill level maximum.

[0031] In a preferred embodiment of the method, the last applied and / or glued plastic film is removed after the last process step.

[0032] The described measuring arrangement can be used to determine the fill level of a substance in a container. The arrangement preferably comprises so many superimposed plastic films of the same thickness and material properties that the energy reflected back from the surfaces of the wall and the plastic films is minimized.

[0033] Of course, it is also possible to modify the described procedure accordingly and, instead of determining energy values ​​from the echo curve within the specified period, to take the echo curve values ​​directly and compare them individually with the values ​​of a corresponding reference curve. If, in this case, the last recorded intensity values ​​of the echo curve within the specified period are less than or equal to the intensity values ​​of a corresponding reference curve, an OK signal can be transmitted to a display device.

[0034] A preferred method for reducing the electromagnetic radiation reflected back from a measuring arrangement by the surfaces of a wall and by the surfaces of an adaptation that is adhered and / or glued to a surface of the wall provides that the following steps are carried out successively: First, a plastic film is placed and / or glued to the wall. Then, the interior of the container is irradiated through the plastic film with an electromagnetic radiation pulse emitted by the radar level gauge.

[0035] The intensity of the electromagnetic radiation reflected back into the radar level gauge is recorded as a time-dependent echo curve, and a period of the echo curve is determined in which the echo curve shows at least a part of the electromagnetic radiation reflected back from the surfaces of the wall and the plastic film.

[0036] Subsequently, the energy value of the radiation pulse detected in the specified period is determined from the intensity of the back-reflected electromagnetic radiation recorded in this period, and this energy value is compared with a predetermined reference value.

[0037] If the last determined energy value is greater than the reference value, another plastic film is placed and / or glued onto the plastic film and the energy value of the radiation pulse detected in the specified period is determined again from the intensity of the back-reflected electromagnetic radiation recorded in the period and compared again with the specified reference value.

[0038] If, however, the specified reference value is higher than the energy value determined in the specified period, an OK signal is transmitted to a display device, indicating that the measuring arrangement can now be used to determine the fill level of a product in a container.

[0039] The terms used in the following description, such as "top", "bottom", "left" and "right" and similar terms, refer to exemplary embodiments and are not intended to be restrictive in any way, even when referring to preferred embodiments.

[0040] The invention is explained in more detail below with reference to the drawings. These show: Fig. 1 A schematic representation of a measuring setup, Fig. 2 echo curves without and with optimized adjustment, Fig. 3 a first example of a detection unit of the measuring arrangement, Fig. 4 a second example of a detection unit of the measuring arrangement.

[0041] Fig. Figure 1 shows the schematic setup of the measuring arrangement 1. The interior 2 of a container 4 is filled with a substance 6 up to a level 8. A wall 10 is arranged on the container 4 as a lid, through which the level 8 of the substance 6 is measured by a radar level gauge 12. An adapter 14 is bonded to the outer surface of the wall 10. This adapter consists of several layers of superimposed plastic films 16, which are at least partially transparent to the wavelengths of the radiation pulses emitted by the radar level gauge 12. A portion of the pulsed radiation emitted by the radar level gauge 12, which penetrates the interior 2 of the container 4 through the adapter 14 and the wall 10, is reflected back to the radar level gauge 12 from the surface 8 of the substance 6.Part of the electromagnetic radiation reflected back from the surfaces of the wall 10 and the surfaces of the adaptation 14 also hits the radar measuring device 12 and is detected there as interference reflection 18.

[0042] Fig. Figure 2 shows the echo curves 20 detected by the radar level gauge 12 on a time axis 22 as a function of intensity on an intensity axis 24. In the Fig. Figure 2 shows two echo curves 20, where the dashed curve shows the echo curve 20 without adjustment, i.e., without plastic films 16, and the solid curve shows the echo curve 20 with adjustment. The interference reflections 18 of the echo curves 20 are formed as maxima within a time window 26. Another maximum 28 indicates the fill level 8 of the material 6.

[0043] Fig. Figure 3 shows a first example of a detection unit 30, which processes the radiation signal detected by a detector 32 of the radar level gauge 12. The signal detected by the detector 32 is stored in a memory 34 as an echo curve 20, depending on the time. In another memory 36 of the detection unit 30, a corresponding reference curve is stored, the values ​​of which are individually compared with the corresponding values ​​of the echo curve in memory 34 by means of a comparator 38.

[0044] If the values ​​of the echo curve 20 in memory 34 are below the corresponding values ​​of the reference curve in memory 36 in the time window 26, the comparator 38 transmits an OK signal 40 to a display device 42, so that the user of the measuring arrangement 1 knows that the interference reflections 18 are now sufficiently reduced and the measuring arrangement 1 can be used to measure the fill level 8 in the container 4.

[0045] If at least some of the values ​​of the echo curve 20 in the selected time window 26 are above the corresponding values ​​of the reference curve, no OK signal 40 is transmitted to the display device 42, and the user knows that the interference reflections 18 of the measuring arrangement 1 have not yet been sufficiently minimized, and can further optimize the measuring arrangement by placing or sticking on additional plastic films 16.

[0046] A second embodiment of a detection unit of the measuring arrangement 1 is shown in Fig. Figure 4 illustrates this. The reflected values ​​of the electromagnetic radiation determined by the detector 32 are stored as an echo curve 20 in the memory 34. From the values ​​of the echo curve 20 measured in the time window 26, an energy value 44 is determined in an evaluation unit 46, for example by summing the measured values ​​of the echo curve 20 determined in the specified period 26, and compared with a reference value 48 in the comparator 38.

[0047] If the reference value 48 is less than the energy value 44, the comparator 38 transmits an OK signal 40 to the display unit 42, so that the user of the measuring arrangement 1 knows that the interference reflections 18 are now sufficiently reduced and the measuring arrangement 1 can be used to measure the fill level 8 with sufficient accuracy. If no OK signal 40 is transmitted to the display unit 42 when measuring the fill level 8, the operator of the measuring arrangement 1 knows that the adaptation 14 is not yet optimized and can thus further optimize the measuring arrangement, for example by applying additional plastic films 16 to the adaptation 14.

[0048] The invention has been explained with reference to preferred embodiments, without being limited to these embodiments. The features of the individual embodiments can be freely combined or interchanged with functionally equivalent features of other embodiments, provided that the inventive concept is retained. For example, elements of the first embodiment can be taken from Fig. 3 with elements of the second embodiment from Fig.4 can be combined such that the comparator 38 only sends an OK signal 40 to the display unit 42 if both the evaluated energy values ​​are below the reference value and the values ​​of the echo curve 34 determined in the time window 26 are below the corresponding values ​​of the reference curve stored in the memory 36. It is also possible to use a first display unit to indicate that the evaluated energy values ​​are below a reference value and a second display unit to indicate that at least some of the values ​​of the echo curve 20 in the selected time window 26 are below the corresponding values ​​of the reference curve. Another display unit could, for example, indicate that all values ​​of the echo curve 20 in the selected time window 26 are below the corresponding values ​​of the reference curve. The quality of the matching can be visualized, for example, by a simple traffic light display, where...B. a red light indicates that few or none of the criteria for a good match are met, a yellow light indicates that at least some of the criteria for a good match are met, and a green light indicates that all or almost all criteria for a good match are met, where criteria may be, for example, the energy value 44 determined in time window 26 or the individual values ​​of the intensities detected in time window 26, compared with the corresponding intensities of a reference curve. Reference symbol list 1 Measuring setup 2 Interior 4 containers 6 Filling material 8 Fill level 10 Wall, container lid, plastic window, plastic wall 12 radar measuring device, radar level measuring device 14. Adjustment 16 plastic film 18 Interference reflection 20 Echo curve 22 Timeline 24 Intensity axis 26 time windows, specific period 28 Reflection maximum Fill level 30 recording units 32 Detector 34 Memory Echo Curve 36 Memory Reference Curve 38 Comparator 40 OK signal 42 Display unit 44 Energy value 46 evaluation units 48 Reference value

Claims

[1] Method for reducing the electromagnetic radiation of a measuring arrangement (1) reflected from the surfaces of a wall (10) and from the surfaces of an adaptation (14) adhering to the surface of the wall (10) and / or glued to the surface of the wall (10), wherein the measuring arrangement (1) comprises the following: - a container (4) whose interior (2) can be filled with a filling material (6), - a radar level measuring device (12) arranged outside the container (4) and directed towards the interior (2) of the container (4), which is designed as a radar level measuring device and which can emit electromagnetic waves of at least one wavelength and detect the course of the reflected electromagnetic radiation of at least one wavelength as an echo curve, - the wall (10) arranged between the interior (2) of the container (4) and the radar measuring device (12), which is at least partially transparent to electromagnetic radiation of at least one wavelength, - a recording unit (30) for recording the echo curve, - the adaptation (14) for reducing the electromagnetic radiation reflected back from the surfaces of the wall (10), wherein the adaptation (14) comprises at least one self-adhesive, and / or wall-adherent, and / or wall-lying plastic film (16) and / or plastic plate at least partially transparent to electromagnetic radiation of at least one wavelength, which adheres to the wall (10) and / or is affixed to the wall (10) in such a way that the electromagnetic radiation pulses emitted by the radar level gauge (12) penetrate the at least one plastic film (16), wherein the method characterized byThe following steps are carried out sequentially: a) Applying and / or sticking the plastic film (16) to the wall (10), b) Irradiating the interior of the container (4), preferably made of plastic, through the plastic film (16) with the electromagnetic radiation pulse emitted by the radar level gauge (12) and recording the intensity of the electromagnetic radiation reflected back into the radar level gauge (12) as an echo curve (20) over time. c) Determining a time period (26) of the echo curve (20) in which the echo curve (20) exhibits at least a part of the electromagnetic radiation reflected back from the surfaces of the wall (10) and the plastic film (16) and determining the energy value of the radiation pulse detected in the time period (26) from the intensity of the reflected electromagnetic radiation recorded in the time period (26), d) Applying and / or adhering another plastic film (16) to the plastic film (16) already applied and / or adhering to it, e) Irradiating the interior (2) of the container (4) again through the plastic film (16) with an electromagnetic radiation pulse emitted by the radar level gauge (12), recording the echo curve (20) and determining the energy value of the radiation pulse detected in the period (26), f) Applying and / or adhering another plastic film (16) to the applied and / or adhering plastic film and then performing step e), if the last determined energy value is less than the previously determined energy value, (g) Storing the last determined energy value in a memory (34) if the last determined energy value is greater than or equal to the previously determined energy value. [2] Method according to claim 1, characterized by, that a reference value (48) above the smallest determined energy value is determined and stored in a further memory (36) of the measuring arrangement (1), wherein the reference value (48) is preferably chosen between the smallest determined energy value and the second smallest determined energy value. [3] Method according to claim 1 or 2, characterized by , that after step g) the last applied and / or glued plastic film (16) is removed again. [4] Method for reducing the electromagnetic radiation of a measuring arrangement (1) reflected back from the surfaces of a wall (10) and from the surfaces of an adaptation (14) adhering to the surface of the wall (10) and / or glued to the surface of the wall (10) according to the preamble of claim 1, characterized by that the following steps are carried out sequentially: a) Applying and / or sticking a plastic film (16) to the wall (10), b) Irradiating the interior (2) of the container (4) through the plastic film (16) with an electromagnetic radiation pulse emitted by the radar level gauge (12) c) Time-dependent recording of the intensity of the electromagnetic radiation reflected back into the radar level gauge (12) as an echo curve (20), d) Determining a time period (26) of the echo curve (20) in which the echo curve (20) exhibits at least some of the electromagnetic radiation reflected back from the surfaces of the wall (10) and the plastic film (16), e) Determining the energy value of the radiation pulse detected in the period (26) from the intensity of the back-reflected electromagnetic radiation recorded in the period (26) and comparing the determined energy value with a given reference value (48), f) Applying and / or adhering another plastic film (16) to the applied and / or adhering plastic film and then carrying out step e) if the last determined energy value is greater than the reference value, g) Transmitting an OK signal to a display device (42) when the specified reference value (48) is higher than the energy value determined in the specified period (26).

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