Radiometric detector

Abstract

The invention relates to a detector (1) for radiometric measuring systems, of which the scintillator (11) and photodiode (12) are dimensioned compactly and optically coupled such that they can be encased by means of microelectronic assembly and connection techniques so as to be optically shielded. A corresponding common casing (13) for the scintillator (11) and the semiconductor component comprising the at least one photodiode (12) can thus be designed according to any IC package type, such as through-hole or surface mount. Accordingly, the evaluation signal (sa), which the photodiode (12) generates on the basis of the incoming radioactive radiation intensity at the scintillator (11), can be tapped, for example via an output pin (131) of the casing (13). The advantage of the detector (1) according to the invention is its manageability as a conventionally mountable electronic component. This makes it possible to design radioactive measuring systems on a modular basis or to individually adapt them to a particular field of application with little design complexity.

Description

[0001] Radiometric detector

[0002] The invention relates to a detector for radiometric measuring systems.

[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 (e.g. 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 positioned 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. 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 power within the detector be detected by a photoreceptor, such as a photomultiplier or a photodiode, in particular an avalanche photodiode or a silicon photomultiplier.

[0005] Materials that exhibit such scintillating properties are referred to as scintillating materials. Among others, organic scintillator materials such as polystyrene, polyvinyl toluene, or inorganic or crystalline forms such as thallium-doped sodium iodide and gadolinium aluminum gallium garnet (Gd3Al2Ga30i2) each 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 as an alternative to the fill level. 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] Each radiometric measurement system must be individually adapted to the process or container being observed. This particularly applies to the detector, since the vertically observed area of ​​the container, whether for level or density measurement, must be completely covered by the detector's scintillator. However, depending on the process and container size, the area to be covered can vary greatly. The invention is therefore based on the object of providing an individually adaptable measurement system in this regard.

[0007] The invention solves this problem by a radiometric detector for radiometric measuring systems, which comprises the following components:

[0008] A scintillator and one or more photodiodes optically connected to the scintillator to generate an electrical evaluation signal depending on the radioactive radiation intensity entering the scintillator. In the case of multiple photodiodes, these can be arranged, for example, as an array, in particular on a common semiconductor component. The photodiode(s) can be designed, for example, as a GaAs-based avalanche photodiode or as a silicon photomultiplier ("S / P / W"). Within the scope of the invention, the term "photodiode" therefore explicitly includes silicon photomultipliers.

[0009] According to the invention, the at least one photodiode and the scintillator are so compactly dimensioned and coupled to one another that they can be encapsulated using microelectronic assembly and connection techniques. A corresponding joint encapsulation of the detector can, if appropriately designed, also protect the scintillator and the photodiode from optical interference. The detector's evaluation signal can be tapped via an electrical output of the encapsulation. The encapsulation or the output can be designed according to any type of IC package, such as, for example,

[0010] 'Through-Hole'

[0011] 'Surface-Mounted'

[0012] “Chip Carrier” “Pin Grid Array”

[0013] “Flat Package”

[0014] “Small Outline Integrated Circuit”

[0015] “Chip-Scale Package”

[0016] “Ball Grid Array”

[0017] - “Multi-chip package” with encapsulated circuit board.

[0018] An advantage of the detector according to the invention is its manageability as a conventionally assembled electronic component. This allows radioactive measurement systems to be designed modularly or individually adapted to the respective application area with minimal design effort.

[0019] The design of the detector according to the invention can be further simplified if the encapsulation is formed by the scintillator, or vice versa. This is feasible, for example, with organic scintillator materials, which are cast as an encapsulation, for example, by injection molding. To protect the at least one photodiode from light influences that could distort the radiometric measurement, the scintillator-based encapsulation must be coated with an optically opaque coating in this design variant.

[0020] The detector according to the invention can also be expanded by connecting a signal processing unit downstream of the at least one photodiode within the encapsulation, which can amplify, filter, and / or digitize the evaluation signal. Since, depending on the photodiode type, a DC voltage supply between 20 V and 95 V is required, a high-voltage converter can also be integrated within the encapsulation to supply voltage to the photodiode. In this case, it makes sense to also integrate a temperature sensor within the encapsulation so that the high-voltage source can be controlled accordingly depending on the temperature. This makes it possible to compensate for the temperature dependence of the photodiode through control technology.

[0021] The detector according to the invention can be encapsulated in a particularly compact manner - for example on the basis of a "chip-scale package" - provided that the signal processing unit, the high-voltage source, or the temperature sensor are / are designed as an integral part of the semiconductor component which also comprises the photodiode(s).

[0022] The detector according to the invention can be used, for example, in computer tomography scanners or in radiometric measuring systems in industrial process measurement technology, for example to determine a density, a density profile, and / or a fill level of a filling material in a container. Measuring systems that can be used in this way are constructed as follows: A radioactive radiation source is mounted relative to the container such that radioactive radiation is emitted toward the container within a defined beam cone. At least one detector according to the invention according to one of the previously described embodiments is mounted on the container opposite the radiation source such that the scintillator of the respective detector is at least partially located within the beam cone.

[0023] An evaluation unit connected to at least one detector determines the density, density profile or fill level of the filling material in the container based on the evaluation signal(s), depending on the design of the measuring system.

[0024] In general, the term "unit" within the scope of the invention refers to any electronic circuits intended for a specific application, e.g., for measurement signal processing or as an interface. Depending on the application, the respective unit may therefore comprise corresponding analog circuits for generating or processing analog signals. However, the unit may 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 may 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.

[0025] Especially for level and density profile measurements, it is advantageous if the measuring system comprises several cascaded detectors, which are arranged vertically in a row on the container. The detectors can either be mounted on a common circuit board or each detector can be arranged on a separate circuit board and housed in a separate housing, allowing them to individually complement the measuring system as a standalone module. In the case of a computer tomography scanner, the detectors according to the invention are arranged as an array according to the functional principle of tomography.

[0026] The invention is explained in more detail with reference to the following figures. Shown are:

[0027] Fig. 1: A cross-sectional view of a detector according to the invention Fig. 2: a cross-sectional view of the detector in a preferred embodiment,

[0028] Fig. 3: a block diagram of a variant of the detector, and

[0029] Fig. 4: a radiometric measuring system based on detectors according to the invention on a container.

[0030] Fig. 1 shows the structural design of a detector 1 according to the invention for radiometric measuring systems, which can be used, for example, for level measurement or in computer tomography. In terms of its functional principle, the detector 1 comprises all the necessary components to generate an electrical evaluation signal s based on incident radioactive radiation. awhich represents the power or intensity of the incident radiation. This allows conclusions to be drawn about further physical quantities that are correspondingly meaningful within the framework of various measurement principles, such as computer tomography. A scintillator 11 of the detector 1 accordingly serves to convert incident radioactive radiation 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, inorganic scintillator materials with corresponding scintillating properties, such as thallium-doped sodium iodide or gadolinium aluminum gallium garnet, can be used.The radiation converted into optical radiation by the scintillator 11 is subsequently converted into an electrical current by a single photodiode 12 or an array of photodiodes 12, which produces the electrical evaluation signal s. a at least in its raw form. The photodiode 12 is to be designed such that its band gap corresponds to the scintillator material or the wavelength of the radiation converted into optical signals.

[0031] The detector 1 according to the invention is characterized by being encapsulated using assembly and connection techniques known from semiconductor technology. This allows the detector 1 to be mounted on circuit boards or deployed as a separate module, allowing corresponding radiometric measurement systems to be designed compactly and modularly. In principle, any type of IC encapsulation is suitable, such as THP ("Through Hole Package") or SMD ("Surface Mount Device").

[0032] As shown in the embodiment in Fig. 1, for IC-compliant encapsulation, the dimensions of the scintillator 11 are selected on the order of magnitude of the semiconductor component that comprises the photodiode 12 or the array of photodiodes 12. This means that at a defined contact surface to the semiconductor component, the relevant edge lengths of the approximately cuboid-shaped scintillator 11 correspond at most to the edge length of the semiconductor component, as shown schematically in Fig. 1. It is essential in this embodiment that the scintillator 12 covers the area on the semiconductor surface that is formed by the photodiode(s) 12. In this case, the scintillator 11 can be attached to the photodiode(s) 12, for example by means of optically transparent adhesive, in the case of both organic and inorganic materials, so that they are optically coupled to one another.

[0033] On the other hand, in the embodiment shown in Fig. 1, the height of the scintillator 11 protruding from the photodiode 12 is dimensioned such that it is no greater than the longest edge length of the semiconductor chip. This allows the detector 1 to be encapsulated using conventional assembly and connection techniques. Accordingly, the encapsulation 14 of the detector 1 according to the invention can be designed as any type of IC package. The only essential requirement here is that the encapsulation material has an optically shielding effect and completely encloses the scintillator 11 and the semiconductor component so that the photodiode 12 is protected from extraneous light. In principle, any mold encapsulation known in the art can be used for this purpose, with black-colored plastics being particularly advantageous for protection against extraneous light. However, it is also conceivable to design the encapsulation 13 on a ceramic basis or as a metal housing (“metal can package”).

[0034] In the embodiments shown in Fig. 1 and Fig. 2, the detector 1 is encapsulated according to the THP (through-hole package) type. Accordingly, the semiconductor component, which includes the photodiodes 12, is arranged on a leadframe 133 and connected via bond wires. One of the pins 131 of the THP encapsulation functions as an electrical output for the evaluation signal s. a .

[0035] Fig. 2 shows a further embodiment of the detector 1 according to the invention, which corresponds to the embodiment shown in Fig. 1 with the exception of the encapsulation 13 and the scintillator 11. However, the encapsulation 13 is formed by the scintillator 11, or vice versa. For this purpose, the photodiode(s) 12 are encapsulated with scintillator material, for example by injection molding or a comparable manufacturing process. In this case, a suitable plastic, such as polystyrene or polyvinyl toluene, is to be used as the scintillator material. One advantage of this is that, from a manufacturing perspective, the dedicated assembly of the scintillator 12 is eliminated. On the other hand, by encapsulating the scintillator material around the semiconductor component, an optical coupling automatically results between the scintillating encapsulation 11, 13 and the semiconductor component on which the photodiode(s) 12 is / are arranged.To protect the photodiode 12 from light, however, the scintillator 11 or the encapsulation 13 in this embodiment must include an optically opaque coating 132, e.g., in the form of a suitable coating. Fig. 3 shows a possible block diagram of the semiconductor component that monolithically encloses the photodiode(s) 12. On the one hand, an analog low-pass filter 121 is connected downstream of the photodiode(s) 12 within the semiconductor component to remove high-frequency interference components from the evaluation signal s. a before it is sent to the signal output 131. In this context, it is also conceivable to filter the evaluation signal s aFurthermore, a high-voltage source 123 is monolithically integrated into the semiconductor component, the block diagram of which is shown in Fig. 4, to supply the photodiodes 12 with the required DC voltage of 20-95 V. For this purpose, the high-voltage source 123 can be based, for example, on the "switched capacitor" principle.

[0036] In the embodiment of the semiconductor component shown in Fig. 3, this also includes a chip-integrated temperature sensor 122. The temperature value measured by the temperature sensor 122 can be tapped via a separate electrical output 136 on the semiconductor chip or at a corresponding connection of the detector 1 in order to supply the temperature value, for example, to the evaluation unit 6. With appropriate design, the evaluation unit 6 can thereby regulate the high-voltage source 123 such that the temperature dependence of the output signal s a the photodiode 12 is compensated. For this purpose, the detector 1 includes, for example, an electrical input 135 on a corresponding pin for controlling the high-voltage source 123, which in turn is controlled, for example, by the evaluation unit 6.

[0037] The power supply for the high-voltage source 123, the temperature sensor 122, and the low-pass filter 121 is provided internally via a common power supply connection on the semiconductor chip or on the detector 1. As an alternative to a monolithic integration of the high-voltage source 123, the temperature sensor 121, the low-pass filter 121, and the photodiodes 12 as a common semiconductor component, the block diagram shown in Fig. 4 can also be realized using hybrid components on a common printed circuit board. In this case, to implement the inventive idea, the entire printed circuit board must be encapsulated according to the "System in Package" principle, according to which the printed circuit board, including the components 12, 121, 122, 133 located thereon, is potted.

[0038] Fig. 4 illustrates a radiometric measuring system for industrial fill level measurement as a possible application of the detector 1 according to the invention. Accordingly, Fig. 4 shows a container s 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 of the fill material 2 is to be determined, with radiometric fill level measurement being used due to the harsh process conditions. For this purpose, a radiation source 5 of the measuring system is arranged and aligned such that radioactive radiation emerges towards the container 3 within a defined beam cone a. In the embodiment shown in Fig. 4, the radiation source 5 is arranged at an upper end region of the container 3 and is inclined downwards by approximately 45°. This ensures that the beam cone a forms the angle required for level or fill level measurement.Density profile measurement penetrates the significant height range of the vessel's interior. Depending on the height of the vessel 3 or the process in progress, this height range can vary, which is why the measurement system must, in principle, be individually adaptable.

[0039] Eleven detectors 11 are arranged opposite each other on the container 3 in relation to the radiation source 5, each with its scintillator 11 aligned toward the container 3, so that the detectors 1 are distributed vertically at equal distances within the beam cone a of the radiation source 5 or in the relevant height range for level measurement. In the embodiment shown in Fig. 4, the detectors 1 are enclosed by a common housing 14, which protects against environmental influences such as optical radiation. In this case, the detectors 1 can be arranged or electrically contacted within the housing 14, for example, on a common circuit board.

[0040] In relation to the measuring system, the detectors 1 designed according to the invention enable a structurally simple adaptation of the measuring system to different container sizes, since the number of detectors 1 can be expanded modularly. A further degree of freedom is the vertical distance between the detectors 1 on the container 3. Due to the vertical arrangement of the detectors 1 in the beam cone a of the radiation source 5, each detector 1 receives the radioactive radiation after it has passed through the filling material 2 or through the gas phase located above it in the container interior. As a result, the respective 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 respective detector 1, the intensity of the incident radiation decreases significantly accordingly.The radiation intensity is determined by the evaluation signal s. a of the associated detector 1. The reason for this is that the incoming radioactive radiation within the detectors 1 is converted by means of the scintillators 11 into optical radiation in the visible or adjacent UV / IR range, and that the radiation converted into optical radiation by the respective scintillator 11 is converted by the photodiode 12 into the electrical evaluation signal s a This allows the evaluation signals to be used to determine a of the detectors 1, for example, quasi-digitally (each detector 1 c corresponds to one digit), it can be determined from which detector 1 the incoming radiation intensity increases significantly in relation to the container height in order to determine the filling level L. Alternatively, the filling level L can also be calculated, for example, in the form of an analogue or relative value by evaluating the evaluation signals s aare added in terms of signal technology, whereby the added value can be assigned to an absolute or relative level value L, e.g. on the basis of a calibration.

[0041] Based on the evaluation signals s a With the arrangement of the detectors 1 shown in Fig. 4, it is also possible to determine a height-dependent density profile of the filling material 2. In this case, each evaluation signal s represents a (e.g. based on a calibration) a density value of the filling material 2. The evaluation signal s a Each detector 1 is assigned a corresponding height on the container s (or at least a number in a height-dependent sequence 1-11), resulting in the height-dependent density profile. If only a single density value is to be determined, the measuring system, in contrast to the embodiment shown in Fig. 4, only needs to comprise a single detector 1.

[0042] To determine the density, the density profile or the fill level L based on the evaluation signals s a The measuring system shown in Fig. 4 comprises a correspondingly designed evaluation unit 6, which is mechanically connected in a separate housing part to the lowest detector 1 or to the corresponding end area of ​​the housing 14. The detectors 1 can be coupled to the evaluation unit 6, for example, serially or via a bus system, in order to each receive the evaluation signal s ato transmit, or to supply the detectors 1 with power. In this context, the evaluation unit 6 can be functionally designed to, on the one hand, record the number of currently connected detectors 1 or their sequence (on the container 3). On the other hand, it is advantageous in this case if the evaluation unit 6 automatically sets or adjusts the height range over which the density profile is created or the fill level L is measured, depending on the number of currently connected detectors 1.

[0043] Overall, the radiation source 5 and the detectors 1 or the housing 14 can be mounted either directly on the container 3 or indirectly on corresponding free-standing stands. As shown in Fig. 1, the evaluation unit 6 of the measuring system for controlling the process can 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", "HART", or "Ethernet". The measured density or fill level value L can be transmitted via this interface, for example, to control heating elements or any supply lines on the container s. However, other information about the general operating status of the measuring system can also be communicated.

[0044] List of reference symbols

[0045] 1 detector

[0046] 2 Filling material

[0047] 3 containers

[0048] 4 Superior unit

[0049] 5 Radioactive source

[0050] 6 Evaluation unit

[0051] 11 Scintillator

[0052] 12 photodiodes

[0053] 13 Encapsulation

[0054] 14 housings

[0055] 121 Analog low-pass filter

[0056] 122 Temperature sensor

[0057] 123 High-voltage source

[0058] 131 Electrical output for the evaluation signal

[0059] 132 Optically opaque coating

[0060] 133 Leadframe

[0061] 134 Power supply connection

[0062] 135 Electrical input for controlling the high-voltage source

[0063] 136 Electrical output for the value of the temperature sensor a Beam cone L Level Sa Evaluation signal

Claims

Patent claims 1 . Radiometric detector (1) for a radiometric measuring system, comprising the following components: A scintillator (11), At least one photodiode (12) which is optically connected to the scintillator (11) in such a way as to generate an electrical evaluation signal (s a ), and an optically shielding encapsulation (13) which shields the scintillator (11) and the photodiode (12), with at least one electrical output (131) for the evaluation signal (Sa).

2. Detector according to claim 1, wherein the encapsulation (14) or the output (131) is designed as an IC package.

3. Detector according to claim 1 or 2, comprising: A plurality of photodiodes (12), which are arranged in particular as an array.

4. Detector according to one of the preceding claims, wherein the encapsulation (13) is formed by the scintillator (11), and wherein the encapsulation (13) has an optically non-transparent coating (132).

5. Detector according to one of the preceding claims, wherein the photodiode (12) is designed as an avalanche photodiode or as a silicon photomultiplier.

6. Detector according to one of the preceding claims, wherein the at least one photodiode (12) within the encapsulation (13) is followed by a signal processing unit (121) which is designed to process the evaluation signal (s a ) to amplify, filter and / or digitize.

7. Detector according to one of the preceding claims, wherein a high-voltage converter (123) for supplying voltage to the photodiode (12) is arranged within the encapsulation (13).

8. Detector according to one of the preceding claims, wherein a temperature sensor (122), in particular for controlling the high-voltage source (123), is arranged within the encapsulation (13).

9. Detector according to claim 6, 7 or 8, wherein the signal processing unit (121), the high voltage source (123), and / or the temperature sensor (122) are / is an integral part of the photodiode semiconductor chip (12).

10. 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 radioactive radiation source (5) which can be mounted in relation to the container (3) in such a way that radioactive radiation is emitted within a defined beam cone (a) of the container (3), at least one 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), and an evaluation unit (6) connected to the at least one detector (1) which is designed to use the evaluation signal (s a ) to determine a density, a density profile or a fill level (L) of the filling material (2).

11. Measuring system according to claim 10, comprising: A plurality of detectors (1) according to one of claims 1 to 8, which are arranged in particular vertically in a row on the container (3).

12. Computer tomography, including: An array of detectors (1) according to any one of claims 1-9.

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