Capacitive sensor assembly for field device and field device

Abstract

The invention relates to a capacitive sensor arrangement (100) for a field device belonging to automation technology. The circuit carrier (3) has a gap section (31) which protrudes into a gap (4) between the two housing elements (1, 2) and which has a circuit arrangement (5) which has at least one electrically conductive conductor element (6a, 6b), an electrically insulating layer (7a, 7b) covering the conductor element (6a, 6b). At least one first electrode of the capacitor unit (8) is formed by at least one electrically conductive conductor element (6a, 6b,...) of the circuit arrangement (5), and one or more second electrodes of the capacitor unit (8) are formed by electrically conductive walls (11, 21) facing the gap section (31), namely an inner wall (21) of the second housing element (2) and / or an outer wall (11) of the first housing element (1). The invention also relates to a field device belonging to automation technology.

Description

Field of the Invention

[0001] The present invention relates to a capacitive sensor assembly for field devices used in automation technology and a field device used in automation technology. Background Art

[0002] In principle, in the context of the present application, all measuring devices for determining and / or monitoring process variables used for processes and information related to supply or processing processes close to the process are referred to as field devices. These are, for example, level measuring devices, flow meters, pressure and temperature measuring devices, pH-redox potentiometers, conductivity meters, etc., which are used to record corresponding process variables such as level, flow rate, pressure, temperature, pH level, and conductivity of the process medium. Such field devices are manufactured and distributed by Endress+Hauser in a wide range of designs.

[0003] Capacitive sensor assemblies are used, for example, in capacitive level measuring devices, pressure measuring devices, and eddy current flow meters.

[0004] The latter are used, for example, to measure the flow rate of a fluid flowing in a pipe, particularly for fast-flowing and / or hot gases (>100 °C) and / or fluid flows with a high Reynolds number (Re>10,000), or the volumetric or mass flow rate corresponding to a specific flow rate. Examples of such eddy current flow meters are known in particular from US-A4716770, US-A6003384, US-B6910387, US-B6938496, US-B9719819, US-B10845222, or US-B10948321, and are also provided in particular by the applicant, for example, under the trade names "PROWIRL D 200", "PROWIRL F 200", "PROWIRL O 200", "PROWIRL R 200".

[0005] Such an eddy current flow meter has a non-streamlined body against which the fluid flows, and this non-streamlined body is used to create a so-called Kármán vortex street consisting of vortices arranged in sequence within a fluid sub-volume flowing directly downstream of the non-streamlined body. The known vortices have a shedding rate depending on the flow rate ( )(Generated at the non-streamlined body. The eddy current flowmeter also has an (eddy current) sensor, which is integrated into the non-streamlined body, or connected to the non-streamlined body, or arranged downstream of the non-streamlined body in the flow, specifically, in the region of the Karman vortex street. The sensor is used to detect the pressure fluctuations in the Karman vortex street formed in the flowing fluid and convert these pressure fluctuations into a measurement signal representing the pressure fluctuations, especially a capacitance measurement signal. The measurement signal corresponds to the dominant pressure in the fluid, which undergoes periodic fluctuations due to the counter-rotating eddies downstream of the non-streamlined body, and has a signal frequency corresponding to the shedding rate of the eddies ( ).

[0006] For this purpose, the sensor has a thin deformable body made of metal (measurement membrane) and a (mechanical) sensor assembly formed by sensor vanes (referred to as "paddles") mainly in the shape of rods, planes, wedges or paddles, which extend from the substantially flat surface of the deformable body. The mechanical sensor assembly is designed to detect the pressure fluctuations in the Karman vortex street and convert them into the movement of the deformable body corresponding to the pressure fluctuations.

[0007] To generate the measurement signal, the sensor includes a transducer element, which is directly arranged on the aforementioned surface of the deformable body, away from and / or near the surface carrying the sensor vanes. The transducer element is formed by a capacitor unit with a variable measurement capacitance, which is mechanically coupled to the deformable body and is configured to detect the movement of the deformable body or the compensating body (if any), i.e., via the corresponding change in the measurement capacitance of the capacitor unit, so that the measurement signal can be generated by the capacitance sensor assembly.

[0008] The capacitor units used in the prior art and based on electrodes to be sealed in glass have the disadvantages of low robustness and complex manufacturing. This is also the case, for example, because the dielectric between the electrodes is usually evacuated and / or filled with a protective gas. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a capacitive sensor assembly for a field device used in automation technology, which is easy to manufacture and as robust as possible.

[0010] This object is achieved by a capacitive sensor assembly for a field device used in automation technology and a field device used in automation technology.

[0011] Regarding the sensor assembly, this object is achieved by a capacitive sensor assembly for a field device used in automation technology, the sensor assembly comprising:

[0012] A first housing element and a second housing element; and

[0013] Circuit carrier;

[0014] wherein a second housing element surrounds the first housing element spatially at least in sections such that a gap exists between the inner wall of the second housing element and the outer wall of the first housing element;

[0015] wherein the inner wall of the second housing element and / or the outer wall of the first housing element is / are conductive, in particular metallic; and

[0016] wherein the circuit carrier has at least one gap section protruding into the gap, which has a circuit arrangement;

[0017] wherein the circuit device has at least one conductive conductor element, and an electrically insulating layer covers the conductor element;

[0018] wherein the gap section protrudes into the gap such that a first surface of the gap section faces the outer wall of the first housing element and a second surface of the gap section faces the inner wall of the second housing element;

[0019] wherein in particular, the second surface of the gap section is opposite to the first surface of the gap section;

[0020] wherein the gap section has an electrically insulating layer on at least one of the first surface and the second surface facing a conductive wall, i.e., the inner wall of the second housing element and / or the outer wall of the first housing element;

[0021] such that

[0022] at least one first electrode of the capacitor unit is formed by at least one conductive conductor element of the circuit arrangement of the gap section;

[0023] one or more second electrodes of the capacitor unit are formed by the conductive wall facing the gap section, i.e., the inner wall of the second housing element and / or the outer wall of the first housing element;

[0024] and

[0025] the dielectric of the capacitor unit is formed by the volume occupied in the gap between the gap section and the conductive wall facing the gap section, i.e., the inner wall of the second housing element and / or the outer wall of the first housing element, and the electrically insulating part of the gap section.

[0026] In particular, the gap section is adapted to the shape of the first housing element and the second housing element. Thus, the circuit carrier is at least in sections, in particular formable, in particular flexible, or shape-adaptable (also freely formable in its form).

[0027] Advantages of the invention are as follows:

[0028] - The capacitor unit is very simply formed by at least one conductive wall and a circuit carrier arranged in a gap between two housing elements.

[0029] - The layer of the circuit carrier that insulates the conductor elements directly provides insulation between the housing elements and the conductive walls of the conductor elements. Thus, the two housing elements are at least directly electrically connected to each other without passing through the conductor elements. However, they can be electrically connected to each other in other ways, for example, by being part of a common structural unit.

[0030] - The glass sealing of the electrodes in the capacitor unit used in the prior art is no longer required. On the one hand, this results in a significant reduction in manufacturing costs. On the other hand, even in the case of overload and / or severe asymmetric deformation of the deformable body, short - circuiting is impossible. This also applies if a conductive liquid and / or conductive particles such as metal chips enter the gap.

[0031] - Even under overload conditions, evacuation of the gap or introduction of a protective gas into the gap is not required to ensure sufficient insulation.

[0032] - The circuit carrier can be inserted from the outside, especially pushed into the gap. Thus, it can be inserted very easily and, in particular, can also be replaced directly during the process.

[0033] - Using the circuit carrier introduced into the gap enables very simple connection of direct integration and / or a connection cable for transmitting the capacitance measurement signal generated by the capacitor unit. The connection cable can be directly integrated into the circuit carrier or connected to the conductor elements of the gap section to detect and transmit the capacitance of the capacitor unit used as a measurement signal.

[0034] In one embodiment of the sensor assembly, the inner wall of the second housing element and the outer wall of the first housing element are both conductive, especially metallic.

[0035] In particular, the first housing element and the second housing element are both conductive, especially metallic.

[0036] In this case, the capacitive sensor assembly thus has a capacitor unit that has two capacitors - namely, electrodes formed by two conductive walls (i.e., the outer wall and the inner wall) and the conductor elements. As a result, for example, in the case of the above - mentioned eddy current flowmeter, compared with their conventional design, the sensitivity of the capacitor unit is doubled.

[0037] In one embodiment of the sensor assembly, the first housing element and the second housing element are at least partially cylindrical and especially concentric.

[0038] In this case, the gap is especially annular. In particular, it is a circular gap.

[0039] In one embodiment of the sensor assembly, the gap section is curved, in particular having a curvature that conforms to the contour of a cylindrical section of the first and second housing elements. In the case of at least a partially cylindrical housing element opposite the cylindrical part of the housing element of the gap section, at least a partially formable or shape-adaptable circuit carrier is curved such that in its inserted state into the gap, the gap section is not flat and in particular follows the curvature of the cylindrical part.

[0040] In a preferred embodiment of the sensor assembly, the circuit carrier is at least a partially flexible printed circuit board,

[0041] wherein at least the gap section is designed as at least one flexible printed circuit board section.

[0042] Fully flexible or only partially flexible printed circuit boards and their use as circuit carriers are known from the prior art, the latter also being referred to as semi-flexible or semi-rigid printed circuit boards. Designing the gap section as a flexible printed circuit board section allows it to easily adapt to the shape of the two housing elements. For example, in the case of the above-mentioned partially annular or circular gap, the gap section is curved such that it substantially follows the curvature of the partially annular gap.

[0043] In one embodiment of the sensor assembly, the gap section includes a first flexible printed circuit board section and a second flexible printed circuit board section,

[0044] wherein the first flexible printed circuit board section and the second flexible printed circuit board section are arranged in different regions of the gap.

[0045] Preferably, the two flexible printed circuit board sections are arranged in different, in particular opposite, regions of a particularly annular gap.

[0046] For this purpose, for example, the first flexible printed circuit board section is connected to the second flexible printed circuit board section by a flexible connection section protruding from the gap.

[0047] In one embodiment of the sensor assembly, the circuit carrier is a circuit carrier produced using a method for producing a three-dimensional injection-molded circuit carrier.

[0048] This circuit carrier is an injection-molded plastic part (molded interconnect device, MID) into which a metallic structure is introduced, where the metallic structure serves as at least one first electrode of at least one conductor element or capacitor unit. In fact, there are no constraints on the geometry of the plastic part or on the spatial arrangement of the metallic structure within the plastic part. For example, an overview of the common manufacturing process of MIDs was published by the "Research Association for Mechatronic Integrated Devices 3-D MID e.V." Similar to the aforementioned variant of the flexible circuit board, the advantage of the circuit carrier formed as an MID is the almost completely free geometric design of the circuit carrier, such that the shape of the circuit carrier can optimally adapt to the shape of the housing element and / or the shape of the gap.

[0049] In one embodiment of the sensor assembly, the gap section is mechanically connected to the first housing element and the second housing element, in particular in a force-fitting manner, preferably only in a force-fitting manner, since the gap section is clamped between the first housing element and the second housing element in the gap.

[0050] Particularly advantageously, no additional connecting elements and / or additional process steps (such as gluing, potting, etc.) are required to connect the housing element to the circuit carrier. Thus, the gap has no additional potting, adhesive, or any other connecting means commonly used in assembly and interconnection technology (AVT) for mechanically connecting the circuit carrier and the housing element, such as a mechanical plug connection for additional form-fitting connection, such as a rivet. As a result, the circuit carrier can be replaced particularly easily by pulling out the circuit carrier to be replaced and clamping in a new circuit carrier.

[0051] Furthermore, the sensor assembly also has high vibration resistance due to the clamping. This also applies to the connection section mentioned below, which adjoins the gap section and protrudes from the gap.

[0052] In one embodiment of the sensor assembly, the gap section has no electronic components, and the circuit arrangement particularly essentially exclusively has conductor tracks as conductor elements.

[0053] In one embodiment of the sensor assembly, the gap has a gap width of less than 2 mm, where the gap width is particularly between 0.1 mm and 0.5 mm. The gap width is particularly defined as the maximum distance between the outer wall of the first housing element and the inner wall of the second housing element.

[0054] In one embodiment of the sensor assembly, the electrical insulation layer of the gap section comprises polyimide and is particularly formed as an electrical insulation film made of polyimide.

[0055] Polyimide is characterized by extremely high heat resistance, especially at temperatures up to and exceeding about 300 °C, and high mechanical stability.

[0056] Such polyimide films are sold under, for example, the following trade names or by the following manufacturers:

[0057] APICAL - Kaneka Americas Holding, Inc.

[0058] KAPTON or VESPEL - DuPont

[0059] KINEL - Vyncolit N.V.

[0060] MELDIN - Saint Gobain

[0061] P 84 - Evonik Industries

[0062] UPILEX - Ube Industries, Ltd.

[0063] In one embodiment of the sensor assembly, the circuit carrier is a semi-flexible or fully flexible circuit board, wherein the circuit carrier has a connection section that abuts a gap section and protrudes from the gap.

[0064] In one embodiment of the sensor assembly, at least one electrically insulating layer of the circuit arrangement in the gap section and at least one conductor element of the circuit arrangement in the gap section extend into the connection section.

[0065] In one embodiment of the sensor assembly, the semi-flexible or fully flexible circuit board has a shielding element in the connection section for shielding electromagnetic interference fields.

[0066] In one embodiment of the sensor assembly, the shielding element includes:

[0067] - a conductive surface layer that covers the electrically insulating layer, especially over the entire area;

[0068] - an electrically insulating layer that covers the conductive surface layer, especially over the entire area,

[0069] wherein the conductive surface layer and the insulating layer are formed as layers of the semi-flexible or fully flexible circuit board.

[0070] Preferably, the insulating layer is formed similarly to the electrical insulating layer described above and particularly also comprises polyimide.

[0071] In one embodiment of the sensor assembly, the circuit carrier is a flexible printed circuit board, in particular a fully flexible printed circuit board, wherein connecting elements, in particular plug-in connector elements, are arranged on the connecting section,

[0072] and wherein in particular the connecting elements can be in electrical contact with a rigid printed circuit board via electrical feedthroughs.

[0073] In one embodiment of the sensor assembly, the circuit carrier is a semi-flexible printed circuit board, wherein the semi-flexible printed circuit board comprises a rigid section, and wherein the rigid section comprises a connecting section and / or wherein the rigid section adjoins the connecting section.

[0074] Advantageously, additional components can be arranged on the rigid part or the rigid printed circuit board, such as vibration sensors, in particular acceleration sensors or temperature sensors.

[0075] In one embodiment of the sensor assembly, the gap is formed as a gas gap. This is a particularly simple variant in terms of manufacturing technology, wherein the gap does not need to be evacuated or filled with a protective gas.

[0076] Regarding the field device, this object is achieved by a field device used in automation technology for detecting a process variable of a medium, wherein the field device has a capacitive sensor assembly according to the invention.

[0077] In one embodiment of the field device, the capacitor unit serves as a signal generation unit of the field device for generating at least one capacitance measurement signal based on the process variable, and the field device has a measurement electronics unit connected to the signal generation unit, which is used for processing and / or forwarding the capacitance measurement signal generated by the signal generation unit.

[0078] In one embodiment of the field device, the field device comprises a rigid printed circuit board, which is in electrical contact with the connecting elements via electrical feedthroughs, and wherein the rigid printed circuit board is part of the measurement electronics unit.

[0079] In an alternative embodiment of the last-mentioned embodiment, the rigid section of the semi-flexible printed circuit board forms part of the measurement electronics unit.

[0080] In one embodiment of the field device, the field device comprises a medium contact section, wherein the measurement electronics unit is arranged at a distance of at least 50 mm from the medium contact section.

[0081] In one embodiment of the field device, the medium is a flowing fluid, wherein the sensor assembly serves as a sensor element for capacitively detecting the pressure fluctuations of a Karman vortex street formed in the flowing fluid.

[0082] The present invention also includes a use of a field device according to the present invention for detecting flow parameters of a fluid, in particular steam, flowing in a pipeline at a temperature greater than 400 °C and / or a pressure greater than 250 bar, in particular flow velocity and / or volume and / or mass flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The present invention will be further explained with reference to the drawings which are not drawn to scale, in which the same reference numerals denote the same features. For reasons of clarity, or if it seems reasonable for other reasons, the reference numerals previously indicated will not be repeated in the subsequent drawings.

[0084] Shown are:

[0085] Figure 1a , Figure 1b various views of an embodiment of a capacitive sensor assembly 100 according to the present invention;

[0086] Figure 2a , Figure 2b various views of an embodiment of a capacitive sensor assembly 100 incorporating field device components according to the present invention;

[0087] Figure 3 a view of an embodiment of a field device 200 having a sensor assembly 100 according to the present invention; and

[0088] Figure 4 a view of an embodiment of a field device 200 having a sensor assembly 100 with a shielding element according to the present invention. DETAILED DESCRIPTION

[0089] Figure 1a A perspective view of a part of a sensor assembly 100 according to the present invention is shown. A metallic, cylindrical first housing element 1 is surrounded by a second metallic housing element 2 such that there is a gap 4 with a gap width SB between the two housing elements 1, 2. The gap width SB is between 0.1 mm and 0.5 mm.

[0090] In this exemplary embodiment, for the sake of clarity, both the housing element 1 and the housing element 2 are metallic and thus conductive, but this is of course not necessary for the present invention; it is sufficient if at least the inner wall 21 of the second housing element 2 or the outer wall 11 of the first housing element 1 is conductive. The circuit carrier 3 is arranged relative to the housing elements 1, 2 such that it projects into the gap 4 with a gap section 31. The circuit carrier 3 also has a connection part 32 located outside the gap 4 and adjacent to the gap section 31 (also refer to FIGS. 2 to Figure 3). In the gap section 31, the circuit carrier 3 has a circuit arrangement 5 with at least one conductor element 6a; 6b. Thus, the gap section 31, in combination with the housing element 1 and the housing element 2, forms a capacitor unit 8.

[0091] This is shown in Figure 1b and is shown in more detail in the Figure 1b dashed - circle area of Figure 1a . For the sake of clarity, the connection section 32 is not shown here. The circuit arrangement 5 of the circuit carrier 3 includes a central carrier element 19, on both sides of which the conductor elements 6a; 6b are arranged, and each conductor element is covered by an electrical insulation layer 7a; 7b. The carrier element 19 is not essential for the present invention either; as long as the circuit carrier 3 is stable enough, it is also entirely possible to provide only one or more central conductor elements 6a; 6b, which are covered by electrical insulation layers 7a, 7b on both sides and are thus encapsulated between them.

[0092] The outer wall 11 of the first housing element 1 is opposite the first surface 31a of the gap section 31 and is insulated from the first conductor element 6a due to the electrical insulation layer 7a and the free volume in the gap 4. Thus, the conductor element 6a forms the first electrode of the capacitor unit 8, and the outer wall 11 forms the second electrode of the capacitor unit 8. The inner wall 21 of the second housing element 2 is opposite the second surface 31a of the gap section 31 and is insulated from the second conductor element 6b due to the electrical insulation layer 7b and the free volume in the gap 4. Thus, the second conductor element 6b forms the other first electrode of the capacitor unit 8, and the inner wall 21 of the second housing element 21 forms the other second electrode of the capacitor unit 8.

[0093] The housing elements 1 and 2 are mounted so that they can move relative to each other. During the relative movement of the housing elements 1 and 2 and the circuit carrier 3 relative to each other, the distance between the electrodes of the capacitor unit 8 changes, thereby changing the capacitance of the capacitor unit 8, which is used as a measurement signal MS. Due to the use of two conductive walls 11, 21, two capacitance measurement signals MS can be detected with the capacitor unit 8.

[0094] Figure 2aA top view of another embodiment of a capacitive sensor assembly 100 is shown. In this embodiment, the second housing element 2 substantially completely surrounds the inner first housing element 1. The gap section 31 of the circuit carrier 3 is designed as a curved flexible circuit board, wherein the curvature of the flexible circuit board 31 is adapted to the shape of the circular gap 4. The flexible circuit board is characterized by high stability and flexibility of shape. Although the exemplary embodiments described here and below are explained in conjunction with a flexible circuit board, the solution according to the invention includes all other formable or shape-adaptable (also: freely formable in its form) circuit carriers 3, such as the injection-molded circuit carriers or MIDs mentioned above.

[0095] The flexible printed circuit board 31 is clamped from above into the gap 4 so that a force-fit connection is established between the circuit carrier 3 and the housing elements 1, 2. This makes it easy to insert the circuit carrier 3 into the gap 4 and, in the event of a fault, to replace the circuit carrier 3 in the process.

[0096] 2, the gap segment 31 includes an opposing first gap segment 311 and a second gap segment 312. The two gap segments 311, 312 are positioned in different regions of the gap 4. As a result, the number of electrodes used as the measurement signal MS and the detectable measurement capacitance increase, thereby further enhancing the sensitivity of the capacitor unit 8 of the capacitive sensor assembly 100.

[0097] The first gap section 311 is connected to the second gap section 312 via a bent connecting section 320 made of a flexible circuit board material. Figure 2b In Figure 2a 90° rotation of the arrangement already shown in FIG. 1 is shown - here, in a transverse section. The connecting section 320 connects the two gap sections 311, 312 outside the gap 4 to each other by connecting to the flexible connecting section 32 which adjoins the first gap section 311 and protrudes from the gap 4. A connecting element 17, for example a plug-in connector element, is provided on the connecting section 32, which is used to connect the connecting cable 10 (see Figure 3 ). Where applicable, the circuit carrier 3 may further include a rigid section 33 adjacent to the flexible connecting section 32; the circuit carrier 3 may of course also be designed as a fully flexible circuit board.

[0098] The second housing element 2 transitions into the sensor blade 9 at the end facing away from the first housing element 1 , so that the sensor assembly 100 serves as a sensor element for capacitively detecting pressure fluctuations of a Karman vortex street formed in a flowing fluid and can be used in the above-mentioned vortex flowmeter 200 .

[0099] This is Figure 3 It is shown in Figure 3Schematically illustrates such a field device 200. The capacitive sensor assembly 100 basically corresponds to the embodiment already shown in Figure 2b , except that here the connection section 32 is designed to be completely flexible. Thus, the capacitor unit 8 of the sensor assembly 100 is used here as a signal generation unit of the field device 200 for generating at least one capacitance measurement signal MS based on the process variable. In addition, the field device 200 has a measurement electronics unit ME connected to the signal generation unit via a connection cable 10. The measurement electronics unit ME is used to process and / or forward the capacitance measurement signal MS generated by the signal generation unit. For this purpose, it naturally includes additional electronic components and / or circuit arrangements, such as those used in a measurement electronics unit ME (also a transmitter unit) known in the prior art, which will not be discussed in detail here for the sake of clarity. The same applies to further details regarding the design of the eddy current flowmeter; in this regard, the applicant refers to the above-mentioned prior art.

[0100] The plate-shaped sensor vane 9 is in contact with the fluid during operation of the field device 200. Thus, for high-temperature applications, it is advantageous if the circuit carrier 3 is sufficiently heat-resistant at its end facing the medium (especially at the gap section 31). This is achieved here by means of a flexible circuit board 31 having polyimide as the electrical insulation layers 7a; 7b (and possibly also as the carrier element 19, if present), which is characterized by excellent heat resistance in the operating range from -196 °C to over 300 °C. This makes the sensor assembly 100 suitable for direct processes in the above-mentioned hot gas applications of eddy current flowmeters. Since only the end of the sensor assembly 100 facing away from the circuit carrier 3 (i.e., the sensor vane 9) is in contact with the medium and is arranged at a slight distance from the circuit carrier 3, it is entirely possible to use it at fluid temperatures above 400 °C (e.g., up to 450 °C) without causing a short circuit between the electrodes of the capacitor unit 8, which would be caused, for example, by the complete melting of the electrical insulation layers 7a; 7b.

[0101] The gap 4 is further formed as an air gap here, through which ambient air can flow in and out unobstructed, so that in the context of the present invention, the usually complex venting gap 4 of eddy current flowmeters is no longer required in other ways.

[0102] The components of the measurement electronics unit ME can have a lower temperature resistance than the gap section 31 of the circuit carrier 3. Thus, the measurement electronics unit ME is further sufficiently far away from the gap section 31.

[0103] The use of the connection cable 10 is not necessary; according to the design, the conductor elements 6a; 6b can extend to the measurement electronics unit ME in order to detect the measurement signal MS.

[0104] This is in Figure 4is shown in more detail, showing a circuit carrier 3 inserted into the gap 4 between the housing elements 1 and 2. The circuit carrier 3 here includes the aforementioned gap section 31 and transitions outside the gap 4 into a connection section 32. The connection section 32 can be rigid-flexible or fully flexible. The conductor elements 6a; 6b and the layers 7a; 7b that electrically insulate the conductor elements 6a; 6b extend into the connection section 32 outside the gap 4. The extended conductor elements 6a; 6b here perform the function of forwarding the measurement signal MS to Figure 3 the measurement electronics unit ME of the connection cable 10 shown.

[0105] Outside the gap 4, an electromagnetic interference field can have a destructive effect on the conductor elements 6a, 6b, which distorts the measurement signal MS detected and / or transmitted by the capacitor unit 8. To reduce the influence of the electromagnetic interference field, the circuit carrier 3 includes a shielding element in the connection section 32. For this purpose, the circuit carrier 3 includes inner conductive surface layers 15a, 15b in the connection part 32, which cover the electrically insulating layers 7a, 7b to shield possible interference fields. This full-area coverage is particularly suitable for the entire surface of the corresponding electrically insulating layers 7a, 7b. The conductive surface layers 15a, 15b are in turn each covered by a further - in particular full-area - insulating layer 16a, 16b. This applies to each conductor element 6a; 6b extending into the connection part 32 and each electrically insulating layer 7a, 7b extending into the connection section 32. The insulating layers 16a, 16B are particularly made of polyimide. Thus, the shielding element is advantageously directly formed by the layers 15a, 15b, 16a, 16B of the circuit carrier 3 designed as a semi-flexible or fully flexible circuit board.

[0106] Reference Signs and Symbols

[0107] 100 Capacitive Sensor Assembly

[0108] 1 First Housing Element

[0109] 11 Outer Wall

[0110] 2 Second Housing Element

[0111] 21 Inner Wall

[0112] 3 Circuit Carrier

[0113] 31 Gap Section

[0114] 31a, 31b First and Second Surfaces

[0115] 311, 312 First Gap Section, Second Gap Section

[0116] 32 Connection Section

[0117] 320 Connection Segment

[0118] 33 rigid section

[0119] 4 gap

[0120] 5 circuit arrangement

[0121] 6a conductor element

[0122] 7a electrical insulation layer

[0123] 8 capacitor unit

[0124] 9 sensor vane

[0125] 10 connection cable

[0126] 15a, 15b conductive surface layer

[0127] 16a, 16b insulation layer

[0128] 17 connection element

[0129] 18 rigid circuit board

[0130] 19 support element

[0131] 200 field device

[0132] SB gap width

[0133] MS measurement signal

[0134] ME measurement electronic unit

Claims

1. A capacitive sensor assembly (100) for a field device used in automation technology, the sensor assembly comprising: A first housing element (1) and a second housing element (2); And A circuit carrier (3); Wherein, the second housing element (2) spatially surrounds the first housing element (1) at least in sections, such that a gap (4) exists between the inner wall (21) of the second housing element (2) and the outer wall (11) of the first housing element (1), Wherein, the inner wall (21) of the second housing element (2) and / or the outer wall (11) of the first housing element (2) is conductive, in particular metallic; and Wherein, the circuit carrier (3) has at least one gap section (31) with a circuit arrangement (5) protruding into the gap (4), Wherein, the circuit arrangement (5) has at least one conductive conductor element (6a; 6b), and an electrically insulating layer (7a; 7b) covers the conductor element (6a; 6b), Wherein, the gap section (31) protrudes into the gap (4), such that a first surface (31a) of the gap section (31) faces the outer wall (11) of the first housing part (1), and a second surface (31a) of the gap section (31) faces the inner wall (21) of the second housing part (2); Wherein, in particular, the second surface (31b) of the gap section (31) is opposite to the first surface (31a) of the gap section (31); Wherein, the gap section (31) facing the conductive wall (11; 21), that is, the inner wall (21) of the second housing element (2) and / or the outer wall (11) of the first housing element (1), has the electrically insulating layer (7a; 7b), such that At least one first electrode of the capacitor unit (8) is formed by the at least one conductive conductor element (6a; 6b,...) of the circuit arrangement (5) of the gap section (31), One or more second electrodes of the capacitor unit (8) are formed by the conductive walls (11, 21) facing the gap section (31), that is, the inner wall (21) of the second housing element (2) and / or the outer wall (11) of the first housing element (1), And The dielectric of the capacitor unit (8) is formed by the volume occupied in the gap (4) between the gap section (31) and the conductive wall facing the gap section (31), that is, the inner wall (21) of the second housing element (2) and / or the outer wall (11) of the first housing element (1), and by the electrically insulating part (7,...) of the gap section (31).

2. The capacitive sensor assembly (100) according to claim 1, wherein, Both the inner wall (21) of the second housing element (2) and the outer wall (11) of the first housing element (1) are conductive, in particular metallic, And wherein, in particular, both the first housing element (1) and the second housing element (2) are conductive, in particular metallic.

3. The capacitive sensor assembly (100) according to claim 1 or 2, Among them, wherein the first housing element (1) and the second housing element (2) are at least partially cylindrical and, in particular, concentric.

4. The capacitive sensor assembly (100) according to claim 3, wherein, The gap section (31) is curved and, in particular, has a curvature adapted to the contour of the cylindrical portions of the first housing element (1) and the second housing element (2).

5. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the circuit carrier (3) is at least partially flexible printed circuit board, and wherein the gap section (31) is formed as at least one flexible printed circuit board section.

6. The capacitive sensor assembly (100) according to claim 5, Among them, wherein the gap section (31) comprises a first flexible printed circuit board section (311) and a second flexible printed circuit board section (312), and wherein the first flexible printed circuit board section (311) and the second flexible printed circuit board section (312) are arranged in different regions of the gap (4).

7. The capacitive sensor assembly (100) according to any one of the preceding claims 1 to 4, Among them, wherein the circuit carrier (3) is a circuit carrier produced by a method for producing a three-dimensional injection molded circuit carrier.

8. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the gap section (31) is mechanically connected to the first housing element (1) and the second housing element (2), in particular in a force-fitting manner, preferably only in a force-fitting manner, such that the gap section (31) is clamped between the first housing element (1) and the second housing element (2) in the gap (4).

9. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the gap section (31) has no electronic components and the circuit arrangement (5) particularly essentially exclusively has conductor tracks as conductor elements (6a; 6b,...).

10. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the gap (4) has a gap width (SB) of less than 2 mm, the gap width (SB) particularly being between 0.1 and 0.5 mm.

11. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the electrical insulating layer (7a; 7b) of the gap section (31) comprises polyimide and is particularly formed as an electrical insulating film made of polyimide.

12. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, wherein the circuit carrier (3) is a semi-flexible or fully flexible printed circuit board, and wherein the circuit carrier (3) has a connecting section (32) adjacent to the gap section (31), the connecting section (32) protruding from the gap (4).

13. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, At least one electrically insulating layer (7a; 7b) of the circuit arrangement (5) and at least one conductor element (6a; 6b) of the circuit arrangement (5) extend into the connection section (32).

14. The capacitive sensor assembly (100) according to at least one of the preceding claims 12 to 13, Among them, The semi-flexible or fully flexible circuit board has a shielding element in the connection section (32), and the shielding element is used to shield the electromagnetic interference field.

15. The capacitive sensor assembly (100) according to claim 14, Among them, The shielding element includes: - A conductive surface layer (15a; 15b) that covers the electrically insulating layer (7a; 7b), especially over the entire area; - An electrically insulating layer (16) that covers the conductive surface layer (15), especially over the entire area, wherein the conductive surface layer (15a, 15b) and the insulating layer (16a; 16B) are formed as layers of the semi-flexible or fully flexible circuit board.

16. The capacitive sensor assembly (100) according to at least one of the preceding claims, Among them, The circuit carrier (3) is a flexible circuit board, especially a fully flexible circuit board, wherein a connection element (17), especially a plug-in connector element, is arranged on the connection section (32), wherein, in particular, the connection element (17) can be in electrical contact with a rigid circuit board via an electrical feedthrough.

17. The capacitive sensor assembly (100) according to at least one of the preceding claims 1 to 16, Among them, The circuit carrier (3) is a semi-flexible circuit board, and wherein the semi-flexible circuit board includes a rigid section (33), and wherein the rigid section (33) includes the connection section (32) and / or wherein the rigid section (33) abuts the connection section (32).

18. The capacitive sensor assembly (100) according to any one of the preceding claims, Among them, The gap (4) is formed as an air gap.

19. A field device (200) in an automation technology for detecting a process variable of a medium, wherein, The field device (200) has a capacitive sensor assembly (100) according to at least one of claims 1 to 18.

20. The field device (200) according to claim 19, wherein, The capacitor unit (8) serves as a signal generation unit of the field device (200) for generating at least one capacitance measurement signal (MS) according to a process variable, and wherein the field device (200) has a measurement electronics unit (ME) connected to the signal generation unit, and the measurement electronics unit is used to process and / or forward the capacitive measurement signal (MS) generated by the signal generation unit.

21. The field device (200) according to claim 20, Among them, The field device (200) includes a rigid circuit board (18), the rigid circuit board (18) is in electrical contact with the connection element (17) via an electrical feedthrough (19), and wherein the rigid circuit board (18) is part of the measurement electronics unit (ME).

22. The field device (200) according to claim 20, wherein, The rigid section (33) of the semi-flexible circuit board is part of the measurement electronics unit (ME).

23. The field device (200) according to claim 21 or 22, comprising a media contact section, Among them, wherein the measurement electronics unit (ME) is arranged at a distance of at least 50 mm from the media contact section.

24. The field device (200) according to at least one of claims 20 to 23, Among them, wherein the medium is a flowing fluid. and wherein the sensor assembly (100) serves as a sensor element for capacitively detecting pressure fluctuations of a Karman vortex street formed in the flowing fluid.

25. Use of a field device (200) according to any one of the preceding claims 19 to 24 for detecting flow parameters, in particular flow velocity and / or volume and / or mass flow rate, of a fluid, in particular steam, flowing in a pipe at a fluid temperature of greater than 400 °C and / or a pressure of greater than 250 bar.

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