Radiometric fill level measurement

Abstract

The invention relates to a structurally simplified detector (1) for a radiometric measuring system, said measuring system being used to determine the density or the fill level (L) of contents (2) in a container (2). The detector (1) comprises the following components: a scintillator (11) and a photomultiplier (12) which is optically connected to the scintillator (11) in order to generate an electric analysis signal (sa) on the basis of a radioactive radiation intensity entering the scintillator (11). An analysis unit (13) of the detector (1), said analysis unit being connected to the photomultiplier (12), determines the density or the fill level (L) of the contents (1) using the analysis signal (sa). According to the invention, the detector (1) is characterized by an optically and magnetically shielding housing (14) which shields at least the scintillator (11) and the photomultiplier (12). By virtue of the housing (14) design according to the invention, a separate magnetic shielding of the photomultiplier (12) is superfluous. The number of components, and thus the manufacturing complexity of the detector (1), is therefore reduced.

Description

[0001] Radiometric level measurement

[0002] The invention relates to a simply constructed detector for radiometric level or density measurement.

[0003] In automation technology, particularly in process automation, measuring devices and measuring systems are often used to record and / or influence process variables. Process variables include, among others, fill level, flow, pressure, temperature, pH value, redox potential, or conductivity. Depending on the process variable, different measuring principles are implemented in the measuring device or measuring system. Actuators such as valves or pumps are used to influence process variables; these can be used to change the flow of a liquid in a pipe section or the fill level in a container. A wide variety of such measuring devices and measuring systems are manufactured and distributed by the Endress + Hauser Group.

[0004] Radiometric-based measuring systems are used for level measurement, primarily in applications where other measuring principles such as radar fail due to harsh operating conditions. According to the radiometric measuring principle, radioactive radiation (for example gamma radiation from a cesium or cobalt source) is emitted by a radioactive radiation source in the measuring system and passed through the container containing the relevant filling material. After passing through the container, the transmitted radiation intensity is recorded by a corresponding detector in the measuring system. For this purpose, the detector is arranged on the container approximately opposite the radiation source. By determining the intensity or power of the signal arriving at the detector, the transmitted portion of the radiation emitted by the radiation source is determined.The transmitted portion, in turn, is used to determine the fill level of the contents in the container. However, the transmitted portion of the radioactive radiation cannot be directly detected after passing through the container. For this purpose, the radioactive radiation must first be converted into electromagnetic radiation in the optical spectral range by a suitable material in the detector. Only then can the radiation output within the detector be detected by a photomultiplier.

[0005] Materials that exhibit such scintillating properties are referred to as scintillating materials. Among others, polystyrene, polyvinyl toluene, and thallium-doped sodium iodide all exhibit this scintillating property. In addition to the fill level, measuring systems based on this radiometric measuring principle can, after appropriate calibration, also determine the density of the product. Radiometric fill level or density measuring systems are already known from the prior art. The basic operating principle is described, for example, in patent EP 2 208 031 B1.

[0006] In contrast to the scintillator and the evaluation unit, the photomultiplier is particularly sensitive to magnetic fields, which is why the photomultiplier in the detector must be separately shielded against such interference. This involves additional effort in terms of design, materials, and manufacturing.

[0007] The invention is therefore based on the object of providing a detector for a radiometric measuring system which has a simplified structure under these aspects.

[0008] The invention solves this problem by a detector for a radiometric measuring system, wherein the detector comprises the following components:

[0009] - A scintillator,

[0010] - a photomultiplier which is optically connected to the scintillator in such a way as to generate an electrical evaluation signal depending on the radioactive radiation intensity arriving at the scintillator, and

[0011] - an evaluation unit connected to the photomultiplier, which is designed to determine the density or fill level of the filling material based on the evaluation signal. The detector is characterized by an optically and magnetically shielding housing, which shields or completely encloses at least the scintillator and the photomultiplier and, if necessary, also the evaluation unit. For this purpose, the housing can be made of any magnetizable material, such as nickel, copper, iron, or in particular black steel. The inventive design of the housing eliminates the need for separate, magnetic shielding of the photomultiplier. This reduces the number of components and thus the manufacturing effort of the detector. To protect the magnetizable material from the effects of the weather, it is advantageous if the housing includes corrosion protection, in particular a coating and / or galvanization.

[0012] The term "unit" in the context of the invention essentially refers to any electronic circuits that are intended for a specific application, such as for measurement signal processing or as an interface. Depending on the application, the respective unit can therefore comprise corresponding analog circuits for generating or processing analog signals. However, the unit can also comprise digital circuits, such as FPGAs, microcontrollers or storage media in conjunction with corresponding programs. The program is designed to carry out the necessary method steps or apply the necessary arithmetic operations. In this context, different units within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit.On the other hand, it is not relevant whether different electronic circuits within a unit are arranged on a common circuit board or on several interconnected circuit boards.

[0013] A corresponding radiometric measuring system, which is used to measure the fill level or density of filling materials in containers, comprises, in addition to the detector according to the invention, a radioactive radiation source that can be mounted relative to the container in such a way that radioactive radiation is emitted toward the container within a defined beam cone. The detector is to be mounted on the container opposite the radiation source in such a way that the detector's scintillator is at least partially located within the beam cone of the radiation source.

[0014] The invention is explained in more detail using the following figure. It shows:

[0015] Fig. 1 : a radiometric measuring system according to the invention on a container.

[0016] To understand the invention, Fig. 1 shows a radiometric measuring system for industrial fill level measurement, which is based on a detector 1 according to the invention. Accordingly, Fig. 1 shows a container 3 of an industrial process plant. The container 3 can contain, for example, crude oil as fill material 2, which undergoes a refractionation process there. To control the process, the fill level L and / or a density profile of the fill material 2 must be determined, whereby the radiometric measuring principle is used due to the harsh process conditions. For this purpose, a radioactive radiation source 5 of the measuring system is arranged and aligned on the container 3 such that radioactive radiation emerges towards the container 3 within a defined beam cone. In the embodiment shown in Fig. 1, the radiation source 5 is arranged at an upper end region of the container 3 and inclined downwards by approximately 45°.This ensures that the beam cone a penetrates the measuring range I of the container interior, which is essential for level or density profile measurement. Depending on the height of the container 3 or the process in progress, this measuring range I can vary, which is why the measuring system must, in principle, be individually adaptable.

[0017] The detector 1 is arranged opposite the radiation source 5 on the container 3 in the beam cone a of the radiation source 5.

[0018] The detector 1 comprises all the components required in terms of the functional principle to generate an electrical evaluation signal s based on incident radioactive radiation ato generate a signal that represents the power or intensity of the incident radiation: A scintillator 11 of the detector 1 serves to convert the radioactive radiation incoming from the radiation source 5 into optical or spectrally adjacent radiation. For this purpose, the scintillator 11c can be based on an organic-based scintillating material, such as polystyrene or polyvinyl toluene. Alternatively, inorganic materials with corresponding scintillating properties, such as thallium-doped sodium iodide or gadolinium aluminum gallium gamete, can be used.

[0019] The radiation converted into optical by the scintillator 11 is then converted into an evaluation signal s by a photomultiplier 12 a which thereby represents the power or intensity of the radiation incident on the scintillator 11.

[0020] Due to the vertical alignment of the scintillator 11 toward the beam cone a of the radiation source 5, the scintillator 11 receives the radioactive radiation after passing through the filling material 2 or through the gas phase located above it in the container interior. Thus, the intensity of the received radiation - in relation to the initial intensity at the radiation source 5 - depends essentially on the fill level L of the filling material 1 and its density: If, depending on the fill level L, the filling material 2 is located in the beam path between the radiation source 5 and the scintillator 11, the intensity of the incident radioactive radiation decreases significantly or measurably. The evaluation signal s thus represents a ,of the photomultiplier 12, the radiation intensity incident on the scintillator 11.

[0021] To determine the density or the level L based on the evaluation signal s aA correspondingly designed evaluation unit 13 of detector 1 serves this purpose. As shown in Fig. 1, the photomultiplier 12 and the evaluation unit 13 are electrically connected for this purpose. At the same time, the power supply of the photomultiplier 12 is ensured by the evaluation unit 13 via this contact.

[0022] Overall, the radiation source 5 and the detector 1 can be mounted either directly on the container 3 or indirectly on appropriate free-standing stands. As shown in Fig. 1, the evaluation unit 13 of the measuring system for controlling the process can also be connected to a higher-level unit 4, such as a local process control system or a decentralized server system, via a separate interface unit, such as "4-20 mA", "PROFIBUS", "HÄRT", or "Ethernet". This can be used to transmit the measured density or fill level value L, for example, to control heating elements or any supply lines on the container 3. However, other information about the general operating status of the measuring system can also be communicated.

[0023] In the embodiment of the detector 1 according to the invention shown in Fig. 1, the evaluation unit 12 is structurally arranged in a separate housing part. This housing part, in turn, adjoins the lower end region of a housing 14 in which the scintillator 11 and the photomultiplier 12 are arranged. In contrast to the illustration shown, it is also conceivable for the housing part of the evaluation unit 12 to adjoin the upper end region of the housing 14. Furthermore, in contrast to the illustration in Fig. 1, it is also conceivable for the evaluation unit 13 to be arranged in the same housing 14 in which the scintillator 11 and the photomultiplier 12 are located.

[0024] So that the evaluation signal s arepresents exclusively the power or intensity of the radioactive radiation incident on the scintillator 11, it is necessary that the photomultiplier 12 is shielded from possible magnetic interference fields. At the same time, the photomultiplier 12 and the scintillator 11 must not be influenced by ambient light. Therefore, the housing 14, in which the scintillator 11 and the photomultiplier 12 are arranged together, is designed to shield the scintillator 11 and the photomultiplier 12 both from optical radiation and magnetically. For this purpose, the housing 14 can in principle be made of any magnetizable metal, such as iron, cobalt, or nickel. This eliminates the need for separate magnetic shielding of the photomultiplier 12, in contrast to the prior art. Black steel is particularly advantageous as a housing material in this context due to its mechanical robustness.This protects the housing 14 not only optically and magnetically, but also in terms of mechanical impact resistance. Particularly when using easily rusting black steel, it is conceivable to provide the housing 14 with an external coating or a sacrificial anode to protect the housing from further weather influences, such as moisture. With regard to weather influences, the housing section of the evaluation unit 12 illustrated in Fig. 1, as well as any other covers or closures, should also preferably be designed such that the housing 14 seals the scintillator 11 and the photomultiplier 12 from the outside in a media-tight manner. This housing section, any covers, closures, or corresponding sections of the housing 14 that are not located at the level of the photomultiplier 12 can be made of a non-magnetically shielding material, as long as magnetic shielding is ensured.

[0025] List of reference symbols

[0026] 1 detector

[0027] 2 Filling material 3 Container

[0028] 4 Superior unit

[0029] 5 Radioactive source

[0030] 11 Scintillator

[0031] 12 Photomultiplier 13 Evaluation unit

[0032] 14 Optically and magnetically shielding housing a beam cone

[0033] L Fill level

[0034] L Measuring range Sa Evaluation signal

Claims

Patent claims 1 . Detector (1 ) for a radiometric measuring system used to determine a density or a level (L) of a filling material (2) in a container (2), comprising the following components: - A scintillator (11 ), - a photomultiplier (12) which is optically connected to the scintillator (11 ) is connected to generate an electrical evaluation signal (s a ) to generate - an evaluation unit (13) connected to the photomultiplier (12), which is designed to use the evaluation signal (s a ) to determine the density or the level (L) of the filling material (1 ), and - an optically and magnetically shielding housing (14) which shields at least the scintillator (11) and the photomultiplier (12).

2. Detector according to claim 1, wherein the housing (14) additionally shields the evaluation unit (13).

3. Detector according to one of the preceding claims, wherein the housing (14) is made of a magnetizable material, in particular black steel.

4. Detector according to one of the preceding claims, wherein the housing (14) comprises a corrosion protection, in particular a paint coating and / or a galvanization.

5. Radiometric measuring system used to determine the fill level (L) of a filling material (2) in a container (3), comprising the following components: - A radioactive radiation source (5) which can be mounted in relation to the container (3) in such a way that radioactive radiation is emitted towards the container (3) within a defined beam cone (a), and - a detector (1) according to one of the preceding claims, which can be mounted on the container (3) opposite the radiation source (5) in such a way that the scintillator (11) is at least partially located in the beam cone (a).

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