Radiance detector

Abstract

The invention relates to a reliable detector (1) for a radiometric measurement system for determining the density and / or filling level (L) of a content (2) in a container (3). The detector (1) comprises the following components: a scintillator (11) and a photoelectric receiver unit (12) optically connected to the scintillator (11) in order to generate an electrical analysis signal (sa) based on the radioactive radiation intensity entering the scintillator (11). The analysis unit (4, 14) can determine the density or filling level (L) using the analysis signal (sa). According to the invention, the detector (1) is characterized by a reference photoelectric receiver unit (13) which is likewise optically connected to the scintillator (11) in order to generate an electrical reference signal (sr) on the basis of the radioactive radiation intensity entering the scintillator (11). In this way, the evaluation unit (4, 14) can check whether the evaluation signal (sa) and the reference signal (sr) match. If not matching, the detector (1) is classified as a fault. By means of the above redundant design, the detector (1) according to the invention meets the corresponding SIL specification and thus becomes more reliable or maintenance-friendly accordingly.

Description

Field of the Invention

[0001] The present invention relates to a reliable detector for radiometric density or fill level measurement. Background Art

[0002] In automation technology - especially in process automation - measuring devices or measuring systems are used to record and / or influence process variables. The determined process variables include fill level, volume 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 each time. Actuators, such as valves or pumps, by means of which the flow rate of the liquid in a pipeline section or the fill level in a container can be changed, are used to influence the process variable. A plurality of such measuring devices are manufactured and sold by the Endress+Hauser group.

[0003] Measuring systems based on radiation measurement are especially used for fill level measurement in applications where other measuring principles, such as radar, fail due to adverse operating conditions. According to the radiometric measurement principle, radioactive radiation (e.g., γ-radiation from a cesium or cobalt source) is used, which is emitted by a radioactive radiation source of the measuring device and guided through a container containing the relevant contents. After passing through the container, the intensity of the transmitted radiation is recorded by a detector of the measuring device. For this purpose, the detector is arranged on the container so as to be approximately opposite the radiation source. By determining the intensity or power of the signal entering at the detector, the transmitted part of the radiation emitted by the detector is determined. This is used to infer the fill level of the contents in the container. The transmitted part of the radioactive radiation power cannot be directly detected after it has passed through the container. For this purpose, the radioactive radiation in the detector must first be converted into electromagnetic radiation in the spectral range by a suitable material. Only then can the radiation power in the detector be detected by a photoelectric receiver unit. For this purpose, the photoelectric receiver unit and the reference photoelectric receiver unit can include, for example, one or more photomultiplier tubes and / or photodiodes, such as avalanche photodiodes or silicon photomultipliers. The material that converts the radiometric rays into light radiation is called a scintillation material. Polystyrene, polyethylene toluene, and sodium iodide doped with thallium each exhibit such scintillation properties. Radiometric fill level or density measurement systems are already known from the prior art. For example, the basic operating principle is described in the patent specification EP2208031B1.

[0004] Regardless of the measurement principle implemented, safety-related measurement systems are required to monitor different functional units of a device such that any faults in each unit can be detected with a sufficient degree of safety. Corresponding safety specifications are defined, for example, according to the IEC 61508 standard series as "Safety Integrity Level x (SILx)". If a measurement system does not comply with such safety specifications or only complies with some of them, it is considered unsafe and can only be operated with an appropriately shorter test cycle (if any). However, such a test cycle is complex and thus undesirable during an ongoing production process. However, it is difficult to check the correct functionality of a photoelectric receiver unit because faults in the unit may not be clearly identified as defects. Therefore, it is an object of the present invention to provide an improved radiometric measurement system in this regard. Summary of the Invention

[0005] The present invention solves this problem by means of a detector of a radiometric measurement system for determining the density and / or filling level of the contents in a container, the detector comprising the following components:

[0006] - A scintillator,

[0007] - A photoelectric receiver unit, which is optically connected to the scintillator so as to generate an electrical analysis signal based on the intensity of the radioactive radiation entering the scintillator, and

[0008] - A reference photoelectric receiver unit, which is in particular different from the photoelectric receiver unit and is optically connected to the scintillator so as to generate an electrical reference signal based on the intensity of the radioactive radiation entering the scintillator, and

[0009] - An analysis unit, which is designed to

[0010] ○ Check whether the analysis signal matches the reference signal, and

[0011] ○ Determine the density and / or filling level of the contents based at least on the analysis signal or based on the reference signal,

[0012] ○ Classify the detector as faulty if the analysis signal does not match the reference signal.

[0013] If the analysis unit digitizes the analysis signal and the reference signal, it is of course conceivable for the analysis unit to check whether the digitized signals match.

[0014] Due to the redundant design of the detector according to the present invention including an additional reference photoelectric receiver unit, if the analysis unit classifies the detector as faulty or if the analysis signal does not match the reference signal, the analysis unit can generate an SIL-compliant error signal in the case of an appropriate design. In summary, this makes the detector more reliable and easier to maintain in terms of the test cycle.

[0015] If the analysis unit is designed to determine the density or the filling level based on both the analysis signal and the reference signal, the measured value can also be determined with higher accuracy by means of the detector according to the invention.

[0016] The invention can be implemented independently of the implementation of the optoelectronic receiver. For example, the optoelectronic receiver unit and the reference optoelectronic receiver unit of the detector can each be based on one or more photomultiplier tubes or on photodiodes, such as an avalanche photodiode array or a silicon photomultiplier array. From a safety point of view, it is advantageous not to design the reference optoelectronic receiver unit of the detector according to the invention to be the same as its optoelectronic receiver unit in order to reduce the risk that the two optoelectronic receiver units are subject to type-related failure mechanisms. For this purpose, the reference optoelectronic receiver unit can be designed, for example, as a GaAs-based avalanche photodiode, while the actual optoelectronic receiver unit is designed as a silicon photomultiplier.

[0017] The optoelectronic receiver unit and the reference optoelectronic receiver unit do not absolutely have to be optically coupled to the same first end region of the scintillator. In principle, it is also conceivable that the first optoelectronic receiver unit is optically coupled to the first end region of the scintillator, while the reference optoelectronic receiver unit is optically coupled to the second opposite end region of the scintillator. However, in this case, in order to achieve signal coherence, it may be necessary for the analysis unit to include a signal delay component for delaying the analysis signal and / or the reference signal in time. In the case of digitized signals, this can be, for example, a shift register.

[0018] In addition to the detector according to the invention, a corresponding radiometric measuring device for measuring the density or the filling level of the contents in a container also includes a radioactive radiation source, which can be mounted relative to the container such that the radioactive radiation is emitted towards the container within a defined beam cone. In this case, the detector must be mounted on the container opposite the radiation source such that the scintillator is at least partially located within the beam cone.

[0019] In the context of the present invention, the term "unit" is in principle understood to mean any electronic circuit provided for a specific application - for example for processing measurement signals or as an interface. Depending on the application, each unit can thus include corresponding analog circuits for generating or processing analog signals. However, the unit can also include digital circuits, such as an FPGA, a microcontroller or a storage medium combined with an appropriate program. The program is designed to perform the required method steps or to apply the necessary computational operations. In this case, different units in the sense of the present invention can also potentially access a common physical memory or operate by means of the same physical digital circuit. In this case, it does not matter whether the different electronic circuits within the unit are arranged on a common printed circuit board or on a plurality of interconnected printed circuit boards. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be explained in more detail with reference to the following drawings, in which:

[0021] Figure 1 : shows a radiometric measurement system on a container, DETAILED DESCRIPTION OF THE INVENTION

[0022] For the purpose of understanding the present invention, Figure 1 a radiometric measurement system intended for industrial fill level measurement is shown, which is based on a detector 1 according to the present invention. Thus, Figure 1 a container 3 of an industrial process plant is shown. The container 3 can contain, for example, crude oil as the content 2, which undergoes a re-fractionation process in the container 3. To control this process, the fill level L and / or the density distribution of the content 2 must be determined, where the radiometric measurement principle is used due to the harsh process conditions. For this purpose, the radioactive radiation source 5 of the measurement system is arranged and aligned on the container 3 such that the radioactive radiation is emitted towards the container 3 within a defined beam cone a. In Figure 1 the shown variant, the radiation source 5 is arranged in the upper end region of the container 3 and is inclined downwards by approximately 45°. This ensures that the beam cone a radiates through the measurement region l inside the container, which is necessary for measuring the fill level or the density distribution. Depending on the height of the container 3 or the ongoing process, the height of this measurement region l can vary, which is why the measurement system must in principle be adapted to it individually.

[0023] The detector 1 is arranged on the container 3 opposite to the radiation source 5 so as to be located within the beam cone a of the radiation source 5.

[0024] In each case, the detector 1 includes all components required for the functional principle of generating an electrical analysis signal s a based on the incident radioactive radiation, which signal represents the power or intensity of the incident radiation: the scintillator 11 of the detector 1 serves to convert the radioactive radiation arriving from the radiation source 5 into light radiation in the spectrum or radiation adjacent thereto. For this purpose, the scintillator 11 can be based on an organic scintillator material such as polystyrene or polyvinyltoluene. Instead, a crystal or an inorganic material with corresponding scintillation properties such as sodium iodide doped with thallium or gadolinium-aluminum-gallium garnet can be used.

[0025] The radiation converted into light radiation by the scintillator 11 is then converted into an analysis signal s a by the photoelectric receiver unit 12, which thereby represents the power or intensity of the radiation entering the scintillator 11. The photoelectric receiver unit 12 can be implemented as a photomultiplier or a photodiode, such as an avalanche photodiode based on GaAs or a so-called silicon photomultiplier. In the shown exemplary embodiment, for this purpose, the photoelectric receiver unit 12 is arranged in the lower end region of the scintillator 11.

[0026] Due to the -vertical- alignment of the scintillator 11 towards the beam cone a of the radiation source 5, the scintillator 11 receives the radioactive radiation after the radioactive radiation has passed through the contents 2 inside the container or through the gas phase located thereon. Thus, the intensity of the received radiation, which is related to the initial intensity at the radiation source 5, essentially depends on the filling level L of the contents 1 and its density: If, depending on the filling level L, the contents 2 are located in the beam path between the radiation source 5 and the scintillator 11, the intensity of the incident radioactive radiation is correspondingly significantly or measurably reduced. Thus, if the photoelectric receiver unit 12 is fully functional, the analysis signal s from the photoelectric receiver unit 12 a represents the radiation intensity entering the scintillator 11.

[0027] In order to determine the density or the filling level L based on the analysis signal s a a correspondingly designed analysis unit 14 of the detector 1 is used. As Figure 1 shown, for this purpose, the photoelectric receiver unit 12 and the analysis unit 14 are electrically contacted with each other correspondingly. At the same time, the analysis unit 14 ensures the power supply to the photoelectric receiver unit 12 via this contact.

[0028] Overall, the radiation source 5 and the detector unit 1 can be mounted directly on the container 3 or indirectly on a correspondingly freestanding support. As Figure 1 shown, in order to control the process using closed-loop control, the analysis unit 14 of the measurement system can also be connected to a main unit 4, such as a local process control system or a distributed server system, via a separate interface unit, such as "4 - 20 mA", "PROFIBUS", "HART" or "Ethernet". The measured density or filling level value L can thereby be transmitted, for example, to control a heating element or any supply line on the container 3 using open-loop control. However, other information about the overall operating state of the measurement system 1 can also be transmitted. If the functional range of the analysis unit 14 is restricted to transmitting the analysis signal s a to the main unit and the power supply to the photoelectric receiver unit 12 is restricted, the main unit 4 can in this case also determine the measured density or filling level value L based on the analysis signal s a

[0029] During operation, various mechanisms, such as aging or mechanical vibrations, can cause the analysis unit 14 or the main unit 4 to determine incorrect measured filling levels or density values, which can lead to incorrect closed-loop control of the process occurring in the container 3. It is not obvious from the outside that the determined measured values are incorrect or that the detector 1 is faulty.

[0030] ​To prevent this, in addition to the actual photoelectric receiver unit 12, the detector 1 according to the invention further comprises a reference photoelectric receiver unit 13, which in turn is optically coupled to the scintillator 11. In the illustrated variant, the reference photoelectric receiver unit 13 is different from the photoelectric receiver unit 12. This means that the reference photoelectric receiver unit 13 can be designed, for example, as a photomultiplier tube, while the actual photoelectric receiver unit 12 is designed, for example, based on a GaAs-based avalanche photodiode.

[0031] In Figure 1 the illustrated variant, the reference photoelectric receiver unit 13 is arranged in the same lower end region of the scintillator 11 as the actual photoelectric receiver unit 12. This design advantageously ensures that these signals s a , s r from the photoelectric receiver unit 12 and the photoelectric receiver unit 13 do not have different delay times. Instead, within the scope of the present invention, it is also possible that the reference photoelectric receiver unit 13 is actually arranged in the upper end region of the scintillator compared to the photoelectric receiver unit 12. This design offers the advantage that overall, due to the possibly larger area in contact with the scintillator 11, a higher radiation power can be received. This in turn increases the measurement resolution in principle.

[0032] Similar to the analysis signal s a from the photoelectric receiver unit 12, the reference photoelectric receiver unit 13 generates an electrical reference signal s r , which, if the reference photoelectric receiver unit 13 is fully functional, also represents the intensity of the radioactive radiation entering the scintillator 11. According to the invention, this can be used to check whether the analysis signal s a and the reference signal s r match within a permitted or previously defined tolerance. This test can be performed by the analysis unit 14. However, alternatively, this test can also be performed by the main unit 4, provided that the analysis unit 14 is only used to digitize and / or transmit the signals s a , s r to the main unit 4.

[0033] If the check shows that the analysis signal s a matches the reference signal s r , then the measurement density or fill level value determined based on the analysis signal s a or the reference signal s r can be considered valid. In the case where the measurement density or fill level value of the measurement is determined in the analysis unit 14, if necessary, if the detector 1 has been classified as faulty, or if the analysis signal s a the reference signal s rIf there is a mismatch, the unit is able to generate a corresponding error signal in addition to the measured value, or transmit the error signal to the main unit 4.

[0034] Through this redundancy design and the comparison of the signals s a 、s r The detector 1 meets the corresponding SIL specifications and is thus more reliable and easier to maintain. In addition, this redundancy design also has the following advantages: If it is determined based on both the analysis signal s a and the reference signal s r Then the filling level or density value of the measurement can be determined with higher accuracy, because in this case, the analysis unit 14 as a whole has a higher signal strength available for analysis and the signal-to-noise ratio increases significantly.

[0035] In Figure 1 In the shown variant of the detector 1 according to the invention, the analysis unit 14 is structurally arranged in a separate housing part. This housing part is in turn connected to the lower end region of the housing 15 in which the scintillator 11 and the photoelectric receiver unit 12 are arranged. Contrary to the shown illustration, it is also conceivable that the housing part of the analysis unit 14 is connected to the upper end region of the housing 15. In addition, contrary to Figure 1 the illustration in

[0036] List of reference numerals

[0037] 1 Detector

[0038] 2 Contents

[0039] 3 Container

[0040] 4 Main unit

[0041] 5 Radioactive radiation source

[0042] 11 Scintillator

[0043] 12 Photoelectric receiver unit

[0044] 13 Reference photoelectric receiver unit

[0045] 14 Analysis unit

[0046] 15 Housing

[0047] a Beam cone

[0048] L Filling level

[0049] sa Analyze the signal

[0050] s r Reference signal

Claims

1. A detector (1) of a radiometric measurement system for determining the density and / or the filling level (L) of the contents (2) in a container (3), said detector comprising the following components: - A scintillator (11), - A photoelectric receiver unit (12), the photoelectric receiver unit being optically connected to the scintillator (11) so as to generate an electrical analysis signal (s) based on the intensity of radioactive radiation entering the scintillator (11) a ) and - Refer to the reference photodetector unit (13), which is optically connected to the scintillator (11) to generate an electrical reference signal (s based on the intensity of the radioactive radiation entering the scintillator (11) r ), and - An analysis unit (4, 14), said analysis unit being designed to ○ Determine the density and / or the filling level (L) of the content (1) at least based on the analysis signal (s a ), or based on the reference signal (s r ). ○ Check the analysis signal (s a ) and the reference signal (s r ) for matching, and ○ If the analysis signal (s a ) does not match the reference signal (s r ), the detector (1) is classified as faulty.

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

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

4. The detector according to claim 1 or claim 2, wherein, The first photoelectric receiver unit (12) is optically coupled to the first end region of the scintillator (11), and wherein the reference photoelectric receiver unit (13) is optically coupled to a second end region of the scintillator (11) opposite to the first end region.

5. The detector according to any one of the preceding claims, wherein, The analysis unit (14) is designed to digitize the analysis signal (s a ) and the reference signal (s r ), and wherein the analysis unit (14) checks the matching of the digitized signals (s a , s r ).

6. The detector according to any one of the preceding claims, wherein, The photoelectric receiver unit (12) and the reference photoelectric receiver unit (13) comprise at least one photomultiplier tube and / or at least one photodiode, in particular an avalanche photodiode or a silicon photomultiplier.

7. The detector according to any one of the preceding claims, wherein, The photoelectric receiver unit (12) and the reference photoelectric receiver unit (13) are not identical.

8. The detector according to any one of the preceding claims, wherein, The analysis unit (14) is designed such that if the analysis unit (14) classifies the detector (1) as faulty or if the analysis signal (s a ) does not match the reference signal (s r ), an error signal is generated.

9. A radiometric measurement system for determining the filling level (L) of the contents (2) in a container (3), comprising the following components: - A radioactive radiation source (5), said radioactive radiation source being mountable relative to the container (3) such that radioactive radiation is emitted towards the container (3) within a defined beam cone (a), and - A detector (1) according to any one of the preceding claims, said detector being mountable relative to the radiation source (5) to the container (3) such that the scintillator (11) is at least partially located within the beam cone (a) of the radiation source (5).

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