Radiometric measuring arrangement comprising a displaceable radiation source

Abstract

The invention relates to a radiometric measuring arrangement (10) comprising at least one radiation source (12) and at least one detector (14), wherein the radiation source (12) can be displaced relative to the detector (14) in such a manner that the radiation source (12) and the detector (14) can be positioned relative to one another in at least three different measurement positions (A, B, C). The invention also relates to a method for carrying out a radiometric measurement.

Description

[0001] Radiometric measuring setup with movable radiation source

[0002] The invention relates to a radiometric measuring arrangement, in particular for detecting a separating layer or for subtracting extraneous radiation according to claim 1. Furthermore, the invention relates to a method for carrying out a radiometric measurement using a radiometric measuring arrangement according to claim 8.

[0003] Various radiometric measuring arrangements for determining the density of media in containers and, in particular, for determining density profiles or for determining interfaces between different media are known from the prior art.

[0004] Radiometric measurement is characterized in particular by the fact that the density or stratification of media is measured without contact. The measurement is independent of process conditions within a tank and independent of the specific chemical composition of the material being measured. In particular, any corrosive properties are irrelevant, as the necessary measuring instruments can be positioned outside the material and, in some cases, even outside the tank.

[0005] The underlying measurement principle utilizes the density-dependent absorption of gamma quanta in different media. For this purpose, gamma quanta are emitted from one or more radiation sources through the material to be measured towards a measuring device to detect the arriving radiation intensity. Depending on the density of the material between the radiation source and the measuring device, more or fewer gamma quanta are absorbed by the material, so that the radiation intensity at the measuring device represents a measure of the material's density.

[0006] Radiation intensity is typically detected using a scintillation counter, which essentially consists of a scintillator to convert gamma radiation into light pulses and a downstream photomultiplier to generate electrical pulses from these light pulses. The electrical pulses are then processed in downstream measuring electronics, for example, amplified and counted. The number of detected pulses is representative of the radiation intensity and thus also of the density of the material. The fewer pulses detected, the higher the density of the material.

[0007] A radiometric measuring setup can be used to detect, in particular, whether a separation layer is present. A separation layer occurs when two media with different densities, for example, water and oil, are contained within a volume bounded by a container. The liquid components, which are immiscible in themselves, can form an emulsion. To separate the two liquid components, it is necessary to determine when the individual components separated and where the interface between them is located. In addition to the overall fill level, it is particularly advantageous for efficient further processing to measure both the individual fill levels of the components and the location of the separation layer. After the emulsion has separated, it is then possible, for example, to selectively pump out the separated components.

[0008] The underlying object of the invention is to provide a radiometric measuring arrangement and a method for carrying out a radiometric measurement, which require few components and function simply.

[0009] The problem is solved according to the invention by the features of the independent claims. Further practical embodiments and advantages are described in connection with the dependent claims.

[0010] A radiometric measuring arrangement according to the invention comprises at least one radiation source. The radiation source emits, in particular, radioactive radiation, and especially gamma radiation. Furthermore, the radiometric measuring arrangement comprises at least one detector associated with the radiation source, which generates an electrical signal in a known manner, depending on the intensity of the radiation arriving at the detector. The radiation source and the detector are typically arranged on a container such that the radiation source and the detector are located on opposite sides of the container and the radiation penetrates the entire container. Alternatively, the radiation source can also be arranged in a tube within the container and the medium to be measured.

[0011] According to the invention, the radiation source is movable relative to the detector. That is, the radiation source and / or the detector are arranged to be movable. With respect to a stationary container, the radiation source and / or the detector are particularly movable in the vertical direction. The radiometric measuring arrangement includes, in particular, means for moving the radiation source relative to the detector.

[0012] The radiation source and the detector can be arranged in at least three different measurement positions relative to each other. "Measurement position" here means that the radiation intensity is measured in that position. In particular, the at least three measurement positions lie on a vertical line. Specifically, the detector has a fixed position, and the radiation source can be arranged relative to the detector in a first, in particular upper, measurement position, in a second, in particular middle, measurement position, and in a third, in particular lower, measurement position. The middle measurement position is selected such that the radiation source and the detector are arranged exactly opposite each other and the radiation travels the shortest path.The first measurement position is shifted upwards relative to the second measurement position, so that the path of the radiation from the radiation source to the detector is longer in the first measurement position than the path from the radiation source to the detector in the second measurement position. The third measurement position is shifted downwards relative to the second measurement position, so that the path of the radiation from the radiation source to the detector is longer in the third measurement position than the path from the radiation source to the detector in the second measurement position.

[0013] It is also conceivable that the radiation source and the detector occupy more than three discrete measurement positions at which the intensity is determined. In particular, the radiation source and the detector are continuously movable relative to each other over a measurement range, and multiple measurements are performed within this range. This movable relative arrangement allows at least three different measured values ​​to be determined: the intensity of the radiation arriving at the detector for each measurement position. The arriving intensity is related to the path length of the radiation from the radiation source to the detector and to the density of the medium through which it travels. The path length between the radiation source and the detector in the individual measurement positions is known.can be determined in advance by measurements at known densities, so that the measured intensity can be assumed to be in relation to the density of the respective medium lying in the path traveled by the radiation.

[0014] A difference between the intensities at different measurement positions can then be determined. In particular, a difference in intensity between the first and second measurement positions, and a difference in intensity between the second and third measurement positions, is determined.

[0015] The difference in measured intensity between the first (outermost) measurement position A and the second (middle) measurement position B of the radiation source has a logarithmic ratio to the density p of the medium between the radiation source at the first measurement position A and the second measurement position B:

[0016] IB-IA ~ pB,A

[0017] Similarly, the difference in measured intensity between the third (outermost) measurement position C and the second (middle) measurement position B of the radiation source is in a logarithmic ratio to the density p between the third measurement position C and the second measurement position B:

[0018] Iß-Ic ~ pB,C,

[0019] It should be mentioned that the measured intensity is related to the number of pulses or electrical signals at the detector.

[0020] A comparison of pB,A and pB,C allows conclusions to be drawn about the presence of a boundary layer. If pB,A and pB,C are identical, then no boundary layer exists in the region between the measurement positions, and the density of the medium can be determined in the usual way. Specifically, the density is determined by measuring the intensity of the radiation at the second measurement position, directly opposite the detector. If pB,A and pB,C are not identical, then the presence of a boundary layer in the region between the three measurement positions can be inferred.

[0021] A plausibility check can also be performed here. If the quotient pB,A / pB,C is calculated and is less than 1, then a separation layer is present. If the quotient is greater than 1, this indicates a measurement error, since the density of the upper layer cannot be greater than the density of the lower layer.

[0022] In summary, the presence of a separating layer can be determined by recording at least three measurements and calculating their differences. An advantage of the invention is that only one radiation source and one detector are required to obtain the three measurements.

[0023] The constant values, such as distance, shielding thickness, and output intensity, are determined in particular through calibration and can be stored in a look-up table.

[0024] A further advantage of the invention is that any existing extraneous radiation is factored out by calculating the difference in intensity. It is common practice, particularly with containers and media where radiometric measuring systems are used, to perform material testing with highly radioactive sources, whereby this radioactivity can sometimes influence measurements at distances of several hundred meters. This extraneous radiation, which is present suddenly but for a certain period of time, can affect the actual measurement of density or interface. Further measurements with radioactive sources in the vicinity can also influence the current measurement. However, by calculating the difference, this component of the intensity attributable to the extraneous radiation is eliminated.

[0025] In the following, an upper measuring position and a lower measuring position will also be referred to as an outer measuring position.

[0026] In a practical embodiment of the radiometric measuring system, a shield for attenuating the radiation is arranged in at least one measuring position between the radiation source and the detector. In particular, a shield is arranged between the first, upper measuring position and the detector and / or the second, lower measuring position and the detector. The shield is preferably a lead plate, which is arranged in the direct radiation path between the radiation source in the first measuring position and / or the third measuring position. In particular, the shield is designed as a ring and surrounds the radiation source in a ring-like manner. Particularly if the radiation source is arranged in a tube, the shield can be arranged in a ring-like manner surrounding the tube.

[0027] In particular, no shielding is provided in the second, middle measurement position. As described above, a first shield is provided in the first, upper measurement position, and a second shield is provided in a third, lower measurement position. By providing shielding in the area of ​​the first and third measurement positions, the difference in the measured intensity compared to the measured intensity in the second position is increased beyond the extended path length. This enables more robust measurement results.

[0028] In particular, the two outer measurement positions exhibit essentially identical conditions. That is, the distance between the first, upper measurement position and the third, lower measurement position relative to the second, middle measurement position can be identical, as can the thickness of the shielding. The only difference in intensity would then be due to the medium being measured. Alternatively, different conditions, such as different distances of the outer measurement positions relative to the middle measurement position, can be chosen, and these differences can then be taken into account when determining the interface.

[0029] In another practical embodiment, the shield is designed to taper in a wedge shape towards the second, central measurement position. This gradient formed by the wedge is particularly advantageous in continuous measurements, as it allows for differences in intensity beyond the change in path length, since the shield thickness and thus the intensity at the detector vary depending on the measurement position. To eliminate only the extraneous radiation, instead of moving the radiation source and the detector relative to each other, only the shield can be moved at a measurement position, generating different intensities with different thicknesses at that same position of the radiation source. With the shield thickness known, the density can then be determined.

[0030] In particular, the radiometric measuring arrangement includes means for moving the radiation source and / or the detector. Specifically, the movement is achieved by means of a cable from which the radiation source and / or the detector is suspended and which can be moved up or down by a motor. If several radiation sources and / or detectors are present, each radiation source or detector can be arranged on a separate cable.

[0031] The radiation source and / or the detector can alternatively or additionally be guided on rails.

[0032] In particular, the shielding can also be suspended from a rope in order to mount the shielding at the desired measurement position, corresponding to the measurement positions of the radiation source.

[0033] In another practical embodiment of the radiometric measuring arrangement, several radiation sources and their corresponding detectors are distributed along a height. In particular, several corresponding shields can also be distributed along this height. The radiation sources can be arranged at different heights within a tube. Specifically, the radiation sources are then located at different radial measuring positions within the tube. Multiple radiation sources can be used to create either multiple separation layers or separation layers at different heights.

[0034] In particular, the invention also relates to a system with a radiometric measuring device as described above, mounted on a container for filling with one or more media. The radiation source is arranged, in particular, on one side of the container or inside the container, especially in a tube. The detector is arranged outside the container. The invention also relates to a method for performing a radiometric measurement using a radiometric measuring arrangement, in particular with a radiometric measuring arrangement as described above. For this purpose, a radiation source is moved relative to a detector in at least three measuring positions, and a radiation intensity is determined in each measuring position. Subsequently, a difference between the first and second measuring positions and between the second and third measuring positions is calculated with respect to the determined radiation intensities.

[0035] According to variant a), the presence of a separating layer can be inferred, and the density of at least one medium can be determined depending on the presence of such a layer. If the calculated differences are equal, no separating layer is present. If the calculated differences are different, the presence of a separating layer can be inferred.

[0036] According to variant b), any extraneous radiation that may be present can also be factored out and the measurement result can be corrected for the extraneous radiation.

[0037] For the advantages and further features of the process, please refer to the description above.

[0038] Before recording the measurements of the individual intensities, a calibration is performed. This involves determining, in particular, the initial intensity of the radiation source at the various measurement positions as a function of the radiation path length, and the influence of the container wall and the thickness of the shielding.

[0039] In particular, the intensity is not only measured at three discrete measurement positions, but continuously between two outermost positions across a measurement range.

[0040] In particular, the radiation source is moved relative to the detector using means for moving the radiation source. The radiation source can be raised and lowered on ropes to move it into the different measurement positions.

[0041] In particular, the radiation source is moved behind a shield in the outer measurement positions. As described above, the shield can be, in particular, a lead plate or a lead ring, which reduces the intensity in the corresponding measurement position.

[0042] Further practical embodiments and advantages are described below in conjunction with the figures. They show:

[0043] Fig. 1 shows a radiometric measuring arrangement according to a first embodiment in a schematic cross-sectional representation,

[0044] Fig. 2 shows a part of the radiometric measuring arrangement from Fig. 1 in a top view,

[0045] Fig. 3 shows a schematic view of a radiometric measuring arrangement of a radiation source according to a second embodiment from a first side.

[0046] Fig. 4 shows the arrangement according to Fig. 3 from the other side,

[0047] Fig. 5 shows a system consisting of a radiometric measuring arrangement and a container in a schematic cross-sectional view and

[0048] Fig. 6 shows a flowchart of a process.

[0049] Figures 1 and 2 show a radiometric measuring arrangement 10 according to a first embodiment.

[0050] The radiometric measuring arrangement 10 according to the first embodiment comprises three radiation sources 12a, 12b, 12c for the emission of gamma radiation and detectors 14 assigned to each of the radiation sources 12a, 12b, 12c. The radiation sources 12a, 12b, 12c are arranged in a tube 16 inside a container 18. The radiation sources 12a, 12b, 12c are arranged one above the other in the tube 16. As can also be clearly seen in the top view in Fig. 2, the radiation sources 12a, 12b, 12c are arranged at different radial positions in the tube 16.

[0051] The radiation sources 12a, 12b, 12c are arranged in a movable manner in the vertical direction (z-direction) and can thus be arranged in different measuring positions relative to the detector 14 corresponding to the radiation source 12a, 12b, 12c.

[0052] To move the radiation sources 12a, 12b, 12c upwards, the radiation sources 12a, 12b, 12c are each attached to ropes 20. The ropes 20 are connected to a drive 22 (see Fig. 2) and the radiation sources 12a, 12b, 12c can be raised and lowered on the ropes 20 by means of the drive 22.

[0053] For the medium radiation source 12b, three measurement positions A, B, C are shown here as examples: a first, upper measurement position A, a second, middle measurement position B, and a third, lower measurement position C. The measurement range 36 extends between the first measurement position A and the third measurement position C.

[0054] The radiometric measuring arrangement 10 also includes shields 24. In this arrangement, two shields 24 in the form of lead rings are provided for each radiation source 12a, 12b, 12c. The shields 24 are also arranged on cables 26 and are movable in the vertical direction.

[0055] The shields 24 are arranged at the level of the first, upper measuring position A and the third, lower measuring position C. The shields 24 have a wedge-shaped geometry, with the wedge tapering towards the middle measuring position B.

[0056] The second, middle measurement position B is chosen such that the radiation source 12a, 12b, 12c is directly opposite the detector 14 and the radiation from the radiation source 12a, 12b, 12c takes the shortest path to the detector 14 in the second measurement position B. In the second, middle measurement position B, the radiation passes through the tube 16 and the wall of the container 18, but not through the shielding 24.

[0057] The first measurement position A and the third measurement position C are chosen such that they are equidistant above and below the second measurement position B. In both the first measurement position A and the second measurement position B, the radiation sources 12a, 12b, 12c are arranged such that the radiation propagates through the shielding 24 on its way to the detector 14, thereby attenuating the intensity of the radiation arriving at the detector 14 more strongly than at the second measurement position B, in addition to the longer path distance.

[0058] Figures 3 and 4 show radiation sources 12 belonging to a further embodiment of a radiometric measuring arrangement 10. In contrast to the first embodiment, the radiation source 12 is not arranged in a tube 16, but is guided on a rail 28. The radiation source 12 is moved up and down on the rail by a cable 20. Two shields 24 are arranged around the rail 28. As can be seen in a combined view of Figures 3 and 4, the shields 24 are ring-shaped and have a wedge-shaped geometry in one direction.

[0059] With reference to Fig. 5, a method for detecting a separation layer 34 using the radiometric measuring arrangement 10 is now explained. Only a radiation source 12 and a corresponding detector 14 are shown here.

[0060] Container 18 contains a first medium 30 and a second medium 32, the first medium 30 and the second medium 32 having different densities, with a separating layer 34 formed between them. The separating layer 34 is located between the first measuring position A and the second measuring position B.

[0061] The radiation source 12 is moved here by means of the rope 20 (not shown in Fig. 5) to the three measuring positions A, B and C, and three intensities are determined by the detector 14: an intensity IA in the first, upper measuring position A, an intensity IB in the second, middle measuring position B, and an intensity Ic in the third, lower measuring position C. Given the known path length of the individual beam paths from the measuring positions A, B, C to the detector 12, as well as the known thickness of the shielding 24 in the respective beam path and the thickness of the wall of the container 18, a corresponding density can be calculated for each measuring position A, B, and C.

[0062] A difference is calculated between the intensities I and IB, and another difference is calculated between the intensities IB and Ic. In the example shown, the intensity IB-IC is logarithmically related to the density of the lower medium 30, which has a higher density. The intensity IB-IA is related to the superimposed density of the two media 30 and 32. Therefore, the two differences are distinct, and it can be concluded that the interface 34 is present in a measurement area 36 between the first measurement position A and the third measurement position C. Based on the measured intensities, the density of the first medium 30 and the second medium 32 can also be determined, in addition to confirming its presence.

[0063] Another side effect resulting from the calculation of the difference is that the influence of extraneous radiation 38, which is present in all three measurements and at all measurement positions, is factored out.

[0064] Figure 6 shows a flowchart of a method for detecting a separating layer 34.

[0065] The process starts in step S1.

[0066] In step S2, the radiation source 12 is moved to a first measurement position, e.g. measurement position A; subsequently, in step S3, the intensity is measured and determined, e.g. I A for the first measuring position A.

[0067] In step S4, it is checked whether the last measurement position, e.g., measurement position C, has been reached. If no (n), the procedure continues in step S2, and the radiation source 12 is moved to a second measurement position, e.g., measurement position B, where a second intensity is measured and determined, e.g., IB for the second measurement position B. In step S4, it is checked again whether the last measurement position has been reached. If no (n), the procedure continues again in step S2, and the radiation source 12 is moved to a third measurement position, e.g., measurement position C, where a third intensity is measured and determined, e.g., Ic for the third measurement position C.

[0068] If in step S4 it is determined that all measurement positions have been reached by the radiation source 12 (y), then in step S5 the differences are calculated from the measured intensities, I B -IA and IB-IC are determined and in step S6 the quotient thereof: IB-IA / IB-IC.

[0069] If, in step S7, the quotient is found to be equal to 1 (y), it can be concluded that no interface 34 is present in the measuring area 36. The density of the medium located in the measuring area 36 is then determined in step S8.

[0070] If step S7 determines that the quotient is not equal to 1 (n), step S9 determines whether the quotient is greater than 1, and if so (y), it can be concluded that a separation layer is present in measuring area 36. Subsequently, in step S10, the densities of the first medium 30 and the second medium 32 located in measuring area 36 are calculated.

[0071] If the quotient in step S9 is less than 1, a measurement error has occurred and the procedure ends in step Sil with the output of a warning.

[0072] Reference symbol list

[0073] 10 radiometric measuring arrangements

[0074] 12. Radiation source

[0075] 12a-c radiation source

[0076] 14 Detector

[0077] 16 pipe

[0078] 18 containers

[0079] 20 rope

[0080] 22 Drive

[0081] 24 Shielding

[0082] 26 rope

[0083] 28 rail

[0084] 30 first medium

[0085] 32 second medium

[0086] 34 Separation layer

[0087] 36 measuring range

[0088] 38 External radiation

[0089] A first, upper measuring position

[0090] B second, middle measuring position

[0091] C third, lower measuring position

Claims

Patent claims 1. Radiometric measuring arrangement with at least one radiation source (12) and with at least one detector (14), wherein the radiation source (12) can be moved relative to the detector (14) in such a way that the radiation source (12) and the detector (14) can be arranged in at least three different measurement positions (A, B, C) relative to each other.

2. Radiometric measuring arrangement according to the preceding claim, characterized in that in at least one measuring position (A, B, C) a shield (24) for attenuating the radioactive radiation is arranged between the radiation source (12) and the detector (14).

3. Radiometric measuring arrangement according to the preceding claim, characterized in that no shielding (24) is arranged in a middle measuring position (B).

4. Radiometric measuring arrangement according to one of the two preceding claims, characterized in that a first shield (24) is arranged in at least one first outer measuring position (A) and / or a second shield (24) is arranged in at least one second outer measuring position (C).

5. Radiometric measuring arrangement according to one of the preceding claims 2 to 4, characterized in that the shielding (24) tapers in a wedge shape towards a central measuring position (B).

6. Radiometric measuring arrangement according to one of the preceding claims, characterized in that the movement of the radiation source (12) and / or the detector (14) is effected by means of a rope (20) and / or the radiation source (12) and / or the detector (14) is guided on rails (28).

7. Radiometric measuring arrangement according to one of the preceding claims, characterized in that several radiation sources (12a, 12b, 12c) and corresponding detectors (14) are arranged distributed over a height.

8. Method for performing a radiometric measurement using a radiometric measuring arrangement (10), wherein a radiation source (12) is moved relative to a detector (14) in at least three measuring positions (A, B, C) and a radiation intensity is determined in each measuring position (A, B, C) and subsequently a difference between the first measuring position (A) and the second measuring position (B) and between the second measuring position (B) and the third measuring position (C) is calculated with respect to the determined radiation intensities and a) the presence of a separating layer (24) is inferred from this and, depending on the presence of a separating layer (24), the density of a medium (30, 32) is determined and / or b) any extraneous radiation present is subtracted and the measurement result is corrected for the extraneous radiation.

9. Method according to the preceding claim, characterized in that the radiation source (12) is moved.

10. Method according to one of the preceding claims, characterized in that the radiation source (12) is moved behind a shield (24) in outer measuring positions (A, C).

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