Radiometric detector

Abstract

The invention relates to a reliable detector (1) for radiometric measuring systems, said measuring systems being used to determine the density and / or the fill level (L) of contents (2) in containers (3). The detector (1) comprises the following components: a scintillator (11) and a photo-receiver unit (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 (4, 14) can determine the density or the fill level (L) using the analysis signal (sa). According to the invention, the detector (1) is characterized by a reference photo-receiver unit (13) which is likewise optically connected to the scintillator (11) in order to generate an electric reference signal (sr) on the basis of the radioactive radiation intensity entering the scintillator (11). In this manner, the analysis unit (4, 14) can check whether the analysis signal (sa) and the reference signal (sr) match. If not, the detector (1) is classified as not being functional. By virtue of the aforementioned redundant design, the detector (1) according to the invention satisfies corresponding SIL specifications and thus becomes correspondingly more reliable or maintenance-friendly.

Description

[0001] Radiometric detector

[0002] The invention relates to a safe detector for radiometric density or level 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 device and passed through the container containing the relevant filling material. After passing through the container, the transmitted radiation intensity is recorded by a detector in the measuring device. For this purpose, the detector is positioned on the container approximately opposite the radiation source. By determining the intensity or power of the signal received by the detector, the transmitted portion of the radiation emitted by the detector is determined. Based on this, the fill level of the filling material in the container is determined.The transmitted portion of the radioactive radiation cannot be directly detected after passing through the container. For this to happen, 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 power be detected within the detector by a photoreceiver unit. For this purpose, the photoreceiver unit and the reference photoreceiver unit can comprise, for example, one or more photomultipliers and / or photodiodes, such as an avalanche photodiode or a silicon photomultiplier. Materials that convert radiometric radiation into optical radiation are called scintillating materials. Polystyrene, polyvinyl toluene, and thallium-doped sodium iodide, among others, all exhibit this scintillating property.Radiometric level or density measurement systems are already known from the state of the art. The basic operating principle is described, for example, in patent EP 2 208 031 B1.

[0005] Regardless of the measurement principle implemented, safety-relevant measuring systems must be able to monitor the various functional units of the device in such a way that any malfunction of any unit can be detected with sufficient reliability. Corresponding safety specifications are defined, for example, as "Safety Integrity Level x (SILx)" according to the IEC 61508 series of standards. If the measuring system cannot comply with such safety specifications or can only partially comply with them, it is considered unsafe and may only be operated with correspondingly shorter test cycles, if at all. However, such test cycles are complex and therefore undesirable in ongoing production processes. With regard to the photoreceiver unit, however, verifying correct function is difficult because failures there may not be clearly identified as defects.The invention is therefore based on the object of providing a radiometric measuring system which is improved in this regard.

[0006] The invention solves this problem by a detector for a radiometric measuring system which serves to determine a density and / or a filling level of a filling material in a container, comprising the following components:

[0007] - a scintillator,

[0008] - a photoreceiver unit 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

[0009] - a reference photoreceiver unit, which is in particular not identical in construction to the photoreceiver unit and is optically connected to the scintillator in such a way as to generate an electrical reference signal depending on the radioactive radiation intensity arriving at the scintillator, and

[0010] - an evaluation unit which is designed o to check whether the evaluation signal and the reference signal match, and o to determine the density and / or the fill level of the filling material at least on the basis of the evaluation signal or the reference signal, o to classify the detector as not functioning if the evaluation signal and the reference signal do not match.

[0011] If the evaluation unit digitizes the evaluation signal and the reference signal, it is of course conceivable that the evaluation unit checks the already digitized signals for consistency.

[0012] The inventive redundant design of the detector with an additional reference photoreceiver unit allows the evaluation unit, with appropriate design, to generate a SIL-compliant error signal if the evaluation unit classifies the detector as non-functional or if the evaluation signal and the reference signal do not match. Overall, this makes the detector more reliable and easier to maintain with regard to test cycles.

[0013] If the evaluation unit is designed to determine the density or fill level based on both the evaluation signal and the reference signal, the measured value can also be determined with greater accuracy using the detector according to the invention.

[0014] The invention can be implemented independently of the photoreceiver design. For example, the photoreceiver unit and the reference photoreceiver unit of the detector can each be based on one or more photomultipliers, or on photodiodes, such as an array of avalanche photodiodes or an array of silicon photomultipliers. From a safety perspective, it is advantageous not to design the reference photoreceiver unit of the detector according to the invention with the same construction as its photoreceiver unit, in order to reduce the risk that both photoreceiver units are subject to a type-related failure mechanism. For this purpose, the reference photoreceiver unit can be designed, for example, as a GaAs-based avalanche photodiode, while the actual photoreceiver unit is designed as a silicon photomultiplier.

[0015] It is not absolutely necessary for the photoreceiver unit and the reference photoreceiver unit to optically couple to the same, first end region of the scintillator. In principle, it is also conceivable for the first photoreceiver unit to optically couple to the first end region of the scintillator, while the reference photoreceiver unit to optically couple to a second, opposite end region of the scintillator. In this case, however, to achieve signal coherence, it may be necessary for the evaluation unit to include a signal delay component by means of which the evaluation signal and / or the reference signal can be delayed. In the case of digitized signals, this can be a shift register, for example.

[0016] A corresponding radiometric measuring device used to measure the density or fill level 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 mounted on the container opposite the radiation source in such a way that the scintillator is at least partially located within the beam cone.

[0017] The term “unity 1In the context of the invention, "electronic circuits" are understood to mean, in principle, any electronic circuits that are intended for a specific application, e.g., for processing measurement signals 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 required method steps or apply the necessary computing 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.It is not relevant whether different electronic circuits within a unit are arranged on a common circuit board or on several interconnected circuit boards.

[0018] The invention is explained in more detail using the following figure. It shows:

[0019] Fig. 1 : A radiometric measuring system on a container.

[0020] 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.

[0021] The detector 1 is arranged opposite the radiation source 5 on the container 3 in the beam cone a of the radiation source 5.

[0022] 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 11 can be based on organic scintillator materials, such as polystyrene or polyvinyl toluene. Alternatively, crystalline or inorganic materials with corresponding scintillating properties, such as thallium-doped sodium iodide or gadolinium aluminum gallium gamete, can be used.

[0023] The radiation converted into optical by the scintillator 11 is then converted into an evaluation signal s by a photoreceiver unit 12 a, which thereby represents the power or intensity of the radiation incident on the scintillator 11. The photoreceiver unit 12 can be implemented as a photomultiplier or as a photodiode, such as a GaAs-based avalanche photodiode or a so-called silicon photomultiplier. In the illustrated embodiment, the photoreceiver unit 12 is arranged at a lower end region of the scintillator 11.

[0024] 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 ,the photoreceiver unit 12 the radiation intensity incident on the scintillator 11, provided that the photoreceiver unit 12 is fully functional.

[0025] To determine the density or the level L based on the evaluation signal sa A correspondingly designed evaluation unit 14 of the detector 1 serves for this purpose. As shown in Fig. 1, the photoreceiver unit 12 and the evaluation unit 14 are electrically connected to each other for this purpose. At the same time, the power supply to the photoreceiver unit 12 is ensured by the evaluation unit 14 via this contact.

[0026] Overall, the radiation source 5 and the detector 1 can be mounted either directly on the container 3 or indirectly on appropriate freestanding stands. As shown in Fig. 1, the evaluation unit 14 of the measuring system for controlling the process can also be connected via a separate interface unit, such as "4-20 mA", "PROFIBUS", "HART" 1, or "Ethernet with a higher-level unit 4, such as a local process control system or a decentralized server system. The measured density or fill level value L can be transmitted via this, 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. If the functional scope of the evaluation unit 14 is limited to the transmission of the evaluation signal s a to the higher-level unit and the power supply of the photo-receiver unit 12 is limited, the determination of the density or level measurement value L can be carried out using the evaluation signal s a in this case also be taken over by the higher-level unit 4.

[0027] Various mechanisms, such as aging or mechanical vibrations, can lead to the evaluation unit 14 or the higher-level unit 4 determining an incorrect level or density measurement during operation, which can lead to faulty control of the process taking place in the container 3. It is not apparent from the outside that the measured value is incorrect or that the detector 1 is not functioning.

[0028] To prevent this, the detector 1 according to the invention comprises, in addition to the actual photoreceiver unit 12, a reference photoreceiver unit 13, which in turn optically couples to the scintillator 11. In the illustrated embodiment, the reference photoreceiver unit 13 is not structurally identical to the photoreceiver unit 12. This means that the reference photoreceiver unit 13 can be designed, for example, as a photomultiplier, while the actual photoreceiver unit 12 is designed, for example, based on GaAs-based avalanche photodiodes.

[0029] In the embodiment shown in Fig. 1, the reference photoreceiver unit 13 is arranged at the same lower end region of the scintillator 11 as the actual photoreceiver unit 12. With such a design, it is advantageously ensured that these signals s a , s rthe photoreceiver units 12, 13 are not offset in time. In contrast, it is also possible within the scope of the invention for the reference photoreceiver unit 13, in contrast to the actual photoreceiver unit 12, to be arranged at the upper end region of the scintillator. This design offers the advantage that, due to the potentially larger contact area toward the scintillator 11, an overall higher radiation power can be received. This, in turn, fundamentally increases the measurement resolution.

[0030] The reference photoreceiver unit 13 generates, analogously to the evaluation signal s a the photoreceiver unit 12 an electrical reference signal s r which also represents the radioactive radiation intensity arriving at the scintillator 11, provided the reference photoreceiver unit 13 is fully functional. According to the invention, this can be used to check whether the evaluation signal s a and the reference signal sr within a permitted or previously defined tolerance. This test can be performed by the evaluation unit 14. Alternatively, this test can also be performed by the higher-level unit 4, provided that the evaluation unit 14 is only used for digitizing and / or transmitting the signals s a , s r to the higher-level unit 4.

[0031] If the check shows that the evaluation signal s a and the reference signal s r match, the Based on the evaluation signal Sa or the reference signal s rdetermined density or level measurement value can be considered valid. In the event that the density or level measurement value is determined in the evaluation unit 14, this can generate a corresponding error signal in addition to the measured value or transmit it to the higher-level unit 4 if the detector 1 has been classified as non-functional or if the evaluation signal s a and the reference signal s r do not match.

[0032] Through this redundant design and the comparison of the signals s a , s r Detector 1 fulfills the corresponding "S / / _" specifications and is therefore correspondingly safer and easier to maintain. In addition, the redundant design also offers the advantage that the level or density measurement value can be determined with greater accuracy, provided that this is based on both the evaluation signal s a , as well as the reference signal s ris determined, since in this case the evaluation unit 14 has an overall higher signal strength available for evaluation and the signal-to-noise ratio is significantly increased.

[0033] In the embodiment of the detector 1 according to the invention shown in Fig. 1, the evaluation unit 14 is structurally arranged in a separate housing part. This housing part in turn adjoins the lower end region of a housing 15 in which the scintillator 11 and the photoreceiver unit 12 are arranged. In contrast to the illustration shown, it is also conceivable for the housing part of the evaluation unit 14 to adjoin the upper end region of the housing 15. Furthermore, in contrast to the illustration in Fig. 1, it is conceivable for the evaluation unit 14 to be arranged in the same housing 14 in which the scintillator 11 and the photoreceiver unit 12 are located. For interference-free measurement, it is essential that the housing 15 is designed to be opaque to protect the photoreceiver units 12, 13 from extraneous light and the resulting falsification of the measured values.

[0034] List of reference symbols

[0035] 1 detector

[0036] 2 Filling material 3 Container

[0037] 4 Superior unit

[0038] 5 Radioactive source

[0039] 11 Scintillator

[0040] 12 Photoreceiver unit 13 Reference photoreceiver unit

[0041] 14 Evaluation unit

[0042] 15 Housing a beam cone

[0043] L Fill level Sa Evaluation signal s r Reference signal

Claims

Patent claims 1 . Detector (1) for a radiometric measuring system used to determine a density and / or a fill level (L) of a filling material (2) in a container (3), comprising the following components: - A scintillator (11 ), - a photoreceiver unit (12) which is optically connected to the scintillator (11) in such a way as to generate an electrical evaluation signal (s a ) and - a reference photoreceiver unit (13) which is optically connected to the scintillator (11) in such a way as to generate an electrical reference signal (s r ) and - an evaluation unit (4, 14) which is designed, o at least based on the evaluation signal (s a ) or using the reference signal (s r) to determine the density and / or the level (L) of the filling material (1 ), o to check whether the evaluation signal (s a ) and the reference signal (s r ) and o classify the detector (1 ) as not functioning if the evaluation signal (s a ) and the reference signal (s r ) do not match.

2. Detector according to claim 1, wherein the evaluation unit (14) is designed to determine the density or the fill level (L) based on the evaluation signal (s a ) and based on the reference signal (s r ) to determine.

3. Detector according to claim 1 or 2, wherein the photoreceiver unit (12) and the reference photoreceiver unit (13) are optically coupled to a first end region of the scintillator (11).

4. Detector according to claim 1 or 2, wherein the first photoreceiver unit (12) is optically coupled to the first end region of the scintillator (11), and wherein the reference photoreceiver unit (13) is optically coupled to a second End region of the scintillator (11 ) which is opposite the first end region.

5. Detector according to one of the preceding claims, wherein the evaluation unit (14) is designed to evaluate the evaluation signal (s a ) and the reference signal (s r ), and wherein the evaluation unit (14) transmits the digitized signals (s a , s r ) checks for consistency.

6. Detector according to one of the preceding claims, wherein the photoreceiver unit (12) and the reference photoreceiver unit (13) comprise at least one photomultiplier and / or at least one photodiode, in particular an avalanche photodiode or a silicon photomultiplier.

7. Detector according to one of the preceding claims, wherein the photoreceiver unit (12) and the reference photoreceiver unit (13) are not of identical construction.

8. Detector according to one of the preceding claims, wherein the evaluation unit (14) is designed to generate an error signal if the evaluation unit (14) classifies the detector (1) as not functioning or if the evaluation signal (s a ) and the reference signal (s r ) do not match.

9. 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) of the radiation source (5).

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