DE102022133800A1 - Radiometric detector - Google Patents

Abstract

The invention relates to a detector (1) for radiometric measuring systems, the scintillator (11) and photodiode (12) of which are so compactly dimensioned and optically coupled that they can be encapsulated in an optically shielding manner using microelectronic assembly and connection techniques. A corresponding, common encapsulation (13) for the scintillator (11) and the semiconductor component which comprises 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 (s _a ) which the photodiode (12) generates as a function of the radioactive radiation intensity entering the scintillator (11) can be tapped, for example, via an output pin (131) of the encapsulation (13). An advantage of the detector (1) according to the invention is that it can be handled as an electronic component which can be fitted in a conventional manner. This makes it possible to design radioactive measuring systems in a modular manner or to adapt them individually to the respective application area with little construction effort.

Description

The invention relates to a detector for radiometric measuring systems.

In automation technology, particularly in process automation, measuring devices or measuring systems are often used to record and/or influence process variables. The process variables determined include the 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, which can be used to change the flow of a liquid in a pipe section or the fill level in a container. A large number of such measuring devices and measuring systems are manufactured and sold by the Endress + Hauser group of companies.

Radiometric-based measuring systems are used to measure fill levels, especially 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 used, which is emitted by a radioactive radiation source in the measuring system and passed through the container with 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 received by the detector, the transmitted portion of the radiation emitted by the radiation source is determined. The fill level of the filling material in the container is in turn determined on the basis of the transmitted portion. The transmitted portion of the radioactive radiation power cannot be directly detected after passing through the container. For this purpose, the radioactive radiation in the detector must first be converted into electromagnetic radiation in the optical spectral range by a suitable material. Only then can the radiation power within the detector be detected by a photoreceiver, such as a photomultiplier or a photodiode, in particular an avalanche photodiode or a silicon photomultiplier.

Materials that have such scintillating properties are referred to as scintillating materials. Organic scintillator materials such as polystyrene, polyvinyl toluene, or inorganic or crystalline forms such as thallium-doped sodium iodide and gadolinium aluminum gallium garnet (Gd ₃ Al ₂ Ga ₃ O ₁₂ ) all have this scintillating property. In addition to the fill level, measuring systems based on this radiometric measuring principle can also determine the density of the filling material as an alternative to the fill level after appropriate calibration. Radiometric fill level or density measuring systems are already known from the state of the art. The basic functional principle is described, for example, in the patent specification EP 2 208 031 B1 described.

Each radiometric measuring system must be individually adapted to the process or container to be observed. This applies in particular to the detector, since the vertical area of the container to be observed, 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 measuring system in this regard.

• - Einen Szintillator, und
• - eine oder eine Mehrzahl an Photodioden, welche optisch mit dem Szintillator verbunden ist, um in Abhängigkeit einer am Szintillator eingehenden, radioaktiven Strahlungs-Intensität ein elektrisches Auswerte-Signal zu generieren. Im Falle mehrerer Photodioden können diese beispielsweise als Array, insbesondere auf einem gemeinsamen Halbleiterbauteil angeordnet sein. Dabei können/kann die Photodiode(n) zum Beispiel als GaAs-basierte Avalanche-Photodiode oder als Silicon Photomultiplier („SiPM“) ausgelegt werden. Im Rahmen der Erfindung werden unter dem Begriff „Photodiode“ also auch explizit Silicon Photomultiplier verstanden.

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

• - A scintillator, and
• - one or a plurality of photodiodes which are optically connected to the scintillator in order to generate an electrical evaluation signal depending on the intensity of radioactive radiation entering the scintillator. In the case of several 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 (“SiPM”). In the context of the invention, the term “photodiode” is therefore also explicitly understood to mean silicon photomultipliers.

• - „Through-Hole“
• - „Surface-Mounted“
• - „Chip Carrier“
• - „Pin Grid Array“
• - „Flat Package“
• - „Small Outline Integrated Circuit“
• - „Chip-Scale Package“
• - „Ball Grid Array“
• - „Multi-Chip Package“ mit vergossener Leiterplatte.

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 construction and connection techniques. A corresponding joint encapsulation of the detector can also protect the scintillator and the photodiode from optical interference radiation if designed accordingly. The evaluation signal of the detector 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

• - “Through hole”
• - “Surface Mounted”
• - “Chip Carriers”
• - “Pin Grid Array”
• - “Flat Package”
• - “Small Outline Integrated Circuit”
• - “Chip-Scale Package”
• - “Ball Grid Array”
• - “Multi-chip package” with encapsulated circuit board.

The advantage of the detector according to the invention is that it can be handled as a conventionally assembled electronic component. This makes it possible to design radioactive measuring systems in a modular manner or to adapt them individually to the respective application area with little construction effort.

The structure of the detector according to the invention can be further simplified if the encapsulation is formed by the scintillator or vice versa. This can be achieved, for example, with organic scintillator materials that are cast as encapsulation by means of injection molding, for example. In order to protect the at least one photodiode from light influences that distort the radiometric measurement, the scintillator-based encapsulation in this design variant must be coated in an optically non-transparent manner.

The detector according to the invention can also be expanded in such a way that a signal processing unit is connected downstream of the at least one photodiode within the encapsulation, which can amplify, filter and/or digitize the evaluation signal. Since, depending on the type of photodiode, a DC voltage supply of 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 using control technology.

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 designed as an integral part of the semiconductor component which also comprises the photodiode(s).

• - Eine radioaktive Strahlenquelle ist derart in Bezug zum Behälter angebracht, so dass radioaktive Strahlung innerhalb eines definierten Strahl-Kegels gen Behälter ausgesendet wird,
• - zumindest ein erfindungsgemäßer Detektor gemäß einem der vorhergehend beschriebenen Ausführungsvarianten ist der Strahlenquelle derart gegenüberliegend am Behälter angeracht, dass sich der Szintillator des jeweiligen Detektors zumindest teilweise im Strahl-Kegel befindet.
• - Eine an den zumindest einen Detektor angeschlossene Auswerte-Einheit bestimmt anhand des Auswerte-Signals bzw. der Auswerte-Signale je nach Auslegung des Mess-Systems die Dichte, das Dichte-Profil oder den Füllstand des Füllgutes im Behälter.

The detector according to the invention can be used, for example, in computer tomographs 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 in relation to the container in such a way that radioactive radiation is emitted towards the container within a defined beam cone,
• - at least one detector according to the invention according to one of the previously described embodiments is attached to the container opposite the radiation source in such a way that the scintillator of the respective detector is at least partially located in the beam cone.
• - 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 or signals, depending on the design of the measuring system.

In general, the term "unit" in the context of the invention refers in principle to any electronic circuits that are intended for the specific purpose, e.g. for measuring signal processing or as an interface. Depending on the purpose, 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 process steps or to 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. 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.

It is particularly advantageous for level and density profile measurement if the measuring system comprises several cascaded detectors, which are arranged vertically next to one another on the container. The detectors can either be mounted on a common circuit board Or the detectors can be arranged on a separate circuit board and housed in a separate housing so that they can be used as an independent module to supplement the measuring system individually. In the case of a computer tomograph, the detectors according to the invention are to be arranged as an array in accordance with the functional principle of tomography.

• 1: Eine Querschnittansicht eines erfindungsgemäßen Detektors
• 2: eine Querschnittansicht des Detektors in einer bevorzugten Ausführungsvariante,
• 3: ein Blockschaltbild einer Ausführungsvariante des Detektors, und
• 4: ein radiometrisches Mess-System, das auf erfindungsgemäßen Detektoren basiert, an einem Behälter.

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

• 1 : A cross-sectional view of a detector according to the invention
• 2 : a cross-sectional view of the detector in a preferred embodiment,
• 3 : a block diagram of a variant of the detector, and
• 4 : a radiometric measuring system based on detectors according to the invention on a container.

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 the functional principle, the detector 1 comprises all the components required to generate an electrical evaluation signal s _a based on incident radioactive radiation, which represents the power or intensity of the incident radiation. This allows conclusions to be drawn about other physical quantities which are correspondingly meaningful in the context of various measuring principles, such as computer tomography, among others. A scintillator 11 of the detector 1 accordingly serves to convert incident radioactive radiation into optical radiation or radiation which is spectrally adjacent thereto. For this purpose, the scintillator 11 can be based on organic scintillator materials such as polystyrene or polyvinyl toluene. On the other hand, inorganic scintillator materials can be used that have corresponding scintillating properties, such as thallium-doped sodium iodide or gadolinium aluminum gallium garnet. 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 represents the electrical evaluation signal s _a at least in raw form. The photodiode 12 is to be designed so that its band gap corresponds to the scintillator material or to the wavelength of the radiation converted into optical radiation.

The detector 1 according to the invention is characterized in that it is encapsulated using construction and connection techniques known from semiconductor technology. This means that the detector 1 can be fitted onto circuit boards or laid out as a separate module, so that corresponding radiometric measuring systems can be designed to be compact and modular. In principle, any type of IC encapsulation is suitable, such as THP ("Through Hole Package" or SMD ("Surface Mount Device").

As with the version in 1 As shown, for IC-compliant encapsulation, the dimensions of the scintillator 11 are selected in the order of magnitude of the semiconductor component which 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 in 1 is shown schematically. It is essential in this embodiment that the scintillator 12 covers the area on the semiconductor surface which is formed by the photodiode/photodiodes 12. In the case of both organic and inorganic materials, the scintillator 11 can be attached to the photodiode(s) 12, for example by means of optically transparent adhesive, so that they are optically coupled to one another.

On the other hand, the height of the scintillator 11 protruding from the photodiode 12 is 1 shown embodiment is dimensioned such that it is not larger 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 important thing here is that the encapsulation material has an optical shielding effect and completely encloses the scintillator 11 and the semiconductor component so that the photodiode 12 is protected from external light. In principle, for example, any mold encapsulation known from the prior art can be used for this purpose, with black-colored plastics being particularly advantageous for protection against external light. However, it is also conceivable to design the encapsulation 13 on a ceramic basis or as a metal housing (“metal can package”).

In the 1 and 2 In the embodiments shown, the detector 1 is encapsulated according to the THP type (“Through Hole Package”). Accordingly, the semiconductor component, which includes the photodiodes 12, is arranged on a lead frame 133 and connected accordingly using bonding wires. One of the pins 131 of the THP encapsulation functions as an electrical output for the evaluation signal s _a .

In 2 a further embodiment of the detector 1 according to the invention is shown, which, with the exception of the encapsulation 13 and the scintillator 11 of the 1 shown embodiment variant. However, the encapsulation 13 is formed there by the scintillator 11, or vice versa. For this purpose, the photodiode/photodiodes 12 is/are cast with scintillator material, for example by means of 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. The advantage of this is, on the one hand, that in terms of manufacturing technology, the dedicated assembly of the scintillator 12 is no longer necessary. On the other hand, by casting 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/photodiodes 12 is/are arranged. In order to protect the photodiode 12 from light, the scintillator 11 or the encapsulation 13 in this embodiment must comprise an optically non-transparent coating 132, for example in the form of a corresponding coating.

In 3 a possible block diagram of the semiconductor component is shown which monolithically comprises the photodiode/photodiodes 12. On the one hand, an analog low-pass filter 121 is connected downstream of the photodiode(s) 12 within the semiconductor component in order to filter high-frequency interference components from the evaluation signal s _a before it is passed to the signal output 131. In this context, it is also conceivable to directly amplify or digitize the evaluation signal s _a within the semiconductor component. On the other hand, in the semiconductor component, the block diagram of which is shown in 4 As shown, a high-voltage source 123 is also monolithically integrated in order to supply the photodiodes 12 with the required direct voltage of 20-95 V. For this purpose, the high-voltage source 123 can be based on the "switched capacitor" principle, for example.

At the 3 In the embodiment variant of the semiconductor component shown, it also comprises 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. As a result, the evaluation unit 6 can, with appropriate design, regulate the high-voltage source 123 in such a way that the temperature dependence of the output signal s _{a of} the photodiode 12 is compensated. For this purpose, the detector 1 comprises, for example, on a corresponding pin, an electrical input 135 for controlling the high-voltage source 123, which in turn is controlled, for example, by the evaluation unit 6.

The power supply of the high-voltage source 123, the temperature sensor 122 and the low-pass filter 121 takes place chip-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 4 The block diagram shown can also be implemented using hybrid components on a common circuit board. In this case, in order to implement the inventive idea, the entire circuit board must be encapsulated according to the "System In Package" principle, after which the circuit board is encapsulated together with the components 12, 121, 122, 133 located on it.

4 illustrates a possible application of the detector 1 according to the invention in a radiometric measuring system for industrial level measurement. Accordingly, 4 a container 3 of an industrial process plant is shown. The container 3 can contain, for example, crude oil as the filling material 2, which undergoes a refraction process there. To control the process, the filling level L of the filling material 2 is to be determined, whereby radiometric filling level measurement is used due to the harsh process conditions. For this purpose, a radiation source 5 of the measuring system is arranged and aligned in such a way that radioactive radiation emerges from the container 3 within a defined beam cone. The radiation source 5 is in the 4 In the embodiment shown, the beam cone a is arranged at an upper end area of the container 3 and is inclined downwards by approximately 45°. This ensures that the beam cone a radiates through the height range of the container interior that is essential for the fill level or density profile measurement. Depending on the height of the container 3 or the process being carried out, this height range can vary, which is why the measuring system must in principle be individually adaptable to this.

In relation to the radiation source 5, eleven detectors 11 are arranged opposite each other on the container 3 and are each aligned with their scintillator 11 towards the container 3, so that the detectors 1 are distributed vertically at the same distance in the beam cone a of the radiation source 5 or in the relevant height range for level measurement. 4 In the embodiment shown, the detectors 1 are surrounded by a common housing 14, which is protected from environmental influences, such as opti radiation. In this case, the detectors 1 can be arranged or electrically contacted within the housing 14, for example on a common circuit board.

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. Another 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 interior of the container. As a result, the respective intensity of the radiation received - in relation to the initial intensity at the radiation source 5 - depends essentially on the fill level L of the filling material 1 and on its density: If, depending on the fill level L, filling material 2 is in the beam path between the radiation source 5 and the respective detector 1, the intensity of the incident radiation is reduced significantly accordingly. The radiation intensity is represented 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 makes it possible to determine, based on the evaluation signals s _a of the detectors 1, for example in a quasi-digital manner (each detector 1c corresponds to one digit), from which detector 1 the incoming radiation intensity increases significantly in relation to the container height in order to determine the fill level L from this. Alternatively, the fill level L can also be calculated, for example, in the form of an analogue or relative value by adding the evaluation signals s _a together, whereby the added value can be assigned to an absolute or relative fill level value L, for example on the basis of a calibration.

Based on the evaluation signals s _a it is possible to 4 In addition, the arrangement of the detectors 1 shown also makes it possible to determine a height-dependent density profile of the filling material 2. In this case, each evaluation signal s _a (e.g. based on a calibration) represents a density value of the filling material 2. The evaluation signal s _{a of} each detector 1 can be assigned a corresponding height on the container 3 (or at least a number of a height-dependent sequence 1 - 11), from which the height-dependent density profile results. If only a single density value is to be determined, the measuring system must, in contrast to the arrangement shown in 4 The embodiment shown may comprise only a single detector 1.

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

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 in 1 As shown, 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, 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.

List of reference symbols

1

detector

2

Filling material

3

container

4

Superior unit

5

Radioactive radiation source

6

Evaluation unit

11

Scintillator

12

Photodiode

13

Encapsulation

14

Housing

121

Analog low-pass filter

122

Temperature sensor

123

High voltage source

131

Electrical output for the evaluation signal

132

Optically non-transparent coating

133

Lead frame

134

Power supply connection

135

Electrical input for controlling the high voltage source

136

Electrical output for the value of the temperature sensor

a

Beam cone

L

Fill level

sa

Evaluation signal

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely to provide the reader with better information. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP 2208031 B1 [0004]

Claims (12)

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 ) depending on a radioactive radiation intensity arriving at the scintillator (11), 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 (s _a ). Detector after Claim 1 , wherein the encapsulation (14) or the output (131) is designed as an IC package. Detector after Claim 1 or 2 , comprising: - a plurality of photodiodes (12), which are arranged in particular as an array. 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). Detector according to one of the preceding claims, wherein the photodiode (12) is designed as an avalanche photodiode or as a silicon photomultiplier. 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 amplify, filter and/or digitize the evaluation signal (s _a ). 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). 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). Detector after Claim 6 , 7 or 8th , 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). Radiometric measuring system which is 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 attached in relation to the container (3) such that radioactive radiation is emitted towards the container (3) within a defined beam cone (a), - at least one detector (1) according to one of the preceding claims, which can be attached to the container (3) opposite the radiation source (5) such 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 determine a density, a density profile or a fill level (L) of the filling material (2) based on the evaluation signal (s _a ). Measuring system according to Claim 10 , comprising: - A plurality of detectors (1) according to one of the Claims 1 until 8th which are arranged in particular vertically next to one another on the container (3). Computer tomograph, comprising: - an array of detectors (1) according to one of the Claims 1 - 9 .

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