Device for determining and / or monitoring a process variable

Abstract

Device for determining and / or monitoring the flow of a medium through a pipe, with the pipe designed to carry the medium, with ultrasonic sensors, with at least one first chamber (1) arranged laterally on the tube, and a second chamber (2), wherein the first chamber (1) is designed as a sensor connection chamber and for receiving the ultrasonic sensors, wherein the second chamber (2) is designed to accommodate electronic units, wherein at least one passage (3) is located between the first chamber (1) and the second chamber (2), wherein at least one printed circuit board (4) is provided, and wherein the passage (3) and the circuit board (4) are designed and arranged in such a way that the circuit board (4) completely closes the passage (3).

Description

[0001] The invention relates to a device for determining and / or monitoring at least one process variable of a medium. The process variable is, for example, the flow rate, fill level, viscosity, density, electrical conductivity, or pH value of the medium.

[0002] Measuring devices for determining and / or monitoring a process variable generally consist of at least two separate chambers or rooms or room- and / or chamber-like units: a measuring chamber or measuring room and an electronics chamber or electronics room. This separation serves the purpose of isolating the potentially sensitive evaluation and control electronics from the conditions prevailing in the process, i.e. the medium (e.g. high temperatures or high pressures). Since the electronics unit is usually also connected to a higher-level control room or a display unit, this separation creates an additional barrier for the medium. This is particularly important when the medium must not be released into the outside world due to its properties. Examples of such measuring devices are described in DE 43 35 732 A1 or DE 101 14 648 C2.

[0003] However, a connection must generally exist between the two chambers / spaces, for example, to transmit electrical power to the measurement chamber for the measurement or to retrieve corresponding measurement signals from the measurement chamber. This usually involves a feedthrough, which, in the current state of the art, is sealed tightly with various designs, again taking into account the power / signal connection. These designs are sometimes cost-intensive.

[0004] The object of the invention is to propose a cost-effective and easy-to-install closure between two chambers / spaces of a measuring device. A further object is to enable the transmission of energy and signals via the closure.

[0005] The invention thus relates to a device according to independent claim 1 for determining and / or monitoring at least one process variable of a medium, comprising at least a first chamber and a second chamber, wherein at least one passage is located between the first chamber and the second chamber. Each chamber or each space or each chamber- and / or space-like unit is thus a section or area of ​​the measuring device.

[0006] The invention achieves this object in that at least one printed circuit board is provided, and in that the passage and the printed circuit board are designed and arranged in relation to one another in such a way that the printed circuit board essentially completely closes the passage. The invention therefore consists in using a printed circuit board, which is usually used for connecting cables or other electrical connections, to seal the passage. The printed circuit board is preferably an essentially rigid printed circuit board. The chambers or spaces or chamber- and / or space-like units do not have to be completely closed, but can also have further openings or passages, recesses, etc. In the following, chamber is used generally for chamber- and / or space-like units or structures.

[0007] One embodiment provides that at least one electrical connection for transmitting electrical signals and / or electrical energy between the first chamber and the second chamber exists through the circuit board. In this embodiment, the circuit board also fulfils its usual functions, such as that of an electrical connection or attachment element. In one embodiment, both the design of the circuit board and the attachment of the circuit board are such that the passage between the two chambers is gas-tight. The design is such, for example, that penetration of the medium from the chamber in which the medium is located or which is closer to the medium into the chamber in which, for example, the electronics of the measuring device are located or which represents the contact to a control room is prevented. Preferably, the penetration of, for example,gases generated during the process or by the medium.

[0008] One embodiment involves arranging the circuit board outside the passage. The circuit board is thus located in a chamber above the passage, thus sealing it. In this embodiment, the circuit board can have a larger diameter than the passage, allowing more space for, for example, the installation of seals or fasteners.

[0009] One embodiment provides that at least the first chamber and / or the second chamber has at least one wall, and that the circuit board is fastened to the wall with at least one fastening element. The two chambers / spaces are preferably each surrounded by a corresponding housing or are only formed by the respective housing. In one embodiment, at least one wall is assigned to both chambers together and thus preferably forms the wall which separates the two chambers from one another or in which the passage is arranged. If the circuit board is located outside the passage according to the previous embodiment and thus lies on it, in this embodiment the circuit board is fastened by at least one fastening element, e.g. a screw, being connected through the circuit board to the wall, i.e. the circuit board is screwed tight.Alternatively, the fastening element can be a bolt, an adhesive joint, or a solder joint.

[0010] One embodiment includes at least one recess in the wall for accommodating at least one sealing element. The sealing element can be, for example, an O-ring or a seal of any shape, or possibly a sealing compound or potting compound.

[0011] One embodiment provides for at least one detection unit to be provided, which is designed such that it at least registers and / or indicates a change in at least one physical and / or chemical process condition that occurs on at least one side of the circuit board. Such a detection unit can, for example, be a strain gauge that indicates that the circuit board is expanding due to increased pressure. Or it can be a temperature sensor that indicates a temperature change. The detection unit can be a standalone unit, which is possibly connected to a component of the circuit board, or the detection unit can be an integral part of the circuit board itself, so that the circuit board or a component thereof becomes the detection unit. The following embodiment is associated with this.

[0012] One embodiment includes the circuit board being designed in such a way that it at least registers and / or displays a change in at least one physical and / or chemical process condition that occurs on at least one side of the circuit board. This means that the circuit board itself takes on the function of the detection unit. This and the previous embodiment have the advantage that the circuit board not only serves to seal, but is also used to display or detect a change, e.g. in the measuring chamber. The purely passive seal thus becomes an active display or monitoring element. The circuit board therefore not only prevents the medium or substance from the process from penetrating into, for example, the electronics compartment, but also displays or monitors how the medium or process behaves in the first (process) chamber.The circuit board thus provides additional monitoring of the process or medium.

[0013] One embodiment provides that the circuit board is designed in such a way that it reacts essentially reversibly to a change in at least one physical and / or chemical process condition that occurs on at least one side of the circuit board. Rupture discs, for example, are known in the prior art, which indicate an increase in pressure above a certain value by bursting. However, it is more advantageous if the circuit board reacts reversibly to the changed conditions, thus indicating them while also remaining functional.

[0014] One embodiment includes at least one electrical cable unit and / or a flexible printed circuit board, which is / are electrically and / or mechanically connected to the printed circuit board. Cables are typically used to transmit electrical energy and electrical signals. One embodiment for attaching a cable—for example, a coaxial cable—to a printed circuit board can be found in the applicant's pending and not yet published patent application at the German Patent and Trademark Office (the file number is: DE 10 2004 060 416). The connection provides for a gradation of depressions to be created in the printed circuit board. In the case of a coaxial cable, this means, for example, that there is a deeper depression for the shielding and a depression arranged above it for the core in the printed circuit board.These two recesses are each metallized to create the electrical connection between the coaxial cable and the circuit board. A flexible circuit board allows for optimal adaptation to the available space and optimal utilization of this space.

[0015] One embodiment provides for the flexible circuit board to be designed such that at least one electrical conductor is surrounded by a shield. This design allows signals to be routed within the flexible circuit board like a coaxial cable, while still offering the space-saving option of a flexible circuit board. Furthermore, multiple signals can be routed within the flexible circuit board.

[0016] The invention is explained in more detail with reference to the following drawings. It shows: Fig. 1: a schematic representation of the device according to the invention, Fig. 2: a representation of a flow meter according to the invention, Fig. 2a and Fig. 2b: an enlarged view of a connecting element for a coaxial cable from the Fig. 2, Fig. 3: a section of a flow meter according to the invention, Fig. 4: a section through a flexible printed circuit board used in the measuring device according to the invention, Fig. 5a, Fig. 5b and Fig. 6: schematic representations of different variants of the detection unit used in the measuring device according to the invention.

[0017] Fig. 1 shows the two chambers or the two spaces of a measuring device according to the invention. In this embodiment, the first chamber 1 is the chamber that represents the sensor connection space. The measurement signals are transmitted from the corresponding sensors (not shown here) via the cable unit 9 - alternatively, in one embodiment, the connection of a flexible printed circuit board 10 is provided (in one embodiment, a cable unit 9 or a cable harness is provided). The passage 3 between the two chambers is closed by the printed circuit board 4. For this purpose, the printed circuit board 4 is fastened by two screws 8 to the wall 7 of the first chamber 1, which is simultaneously a wall of the second chamber 2. In the second chamber 2, the signal from the cable unit 9 is routed via a flexible printed circuit board 10.To seal between the two chambers 1, 2, a recess 5 is provided in the wall 7, into which a sealing element 6 is inserted for sealing. This can be an O-ring, which is arranged in a recess 5 radially surrounding the passage 3. On the circuit board 4, in the second chamber 2, which in this case is the electronics compartment, for example, there is a strain gauge 11 which acts as a detection unit. If the pressure in the first chamber 1 increases, the pressure acts against the circuit board 4 and presses it into the second chamber 2. This pressing in of the circuit board 4 is indicated by the strain gauge 11 or can be read from it. The circuit board 4 thus fulfills a dual function: on the one hand, it closes the passage 3 and, on the other hand, it allows a chamber - in this case the first 1 - to be monitored.Furthermore, as an electrical circuit board, it also provides the electrical connection between the first chamber 1 and the second chamber 2.

[0018] In the Fig. 2 shows a flow meter as the measuring device. The pipe through which the medium flows can be seen below. The sensor connection spaces are arranged on the sides and thus represent the first chamber 1, in which the corresponding sensors are also mounted. These are ultrasonic sensors that generate and receive ultrasonic waves. Coaxial cables are used to transmit signals and energy to and from the sensors. These are attached to the circuit board 4. For this purpose, recesses of varying depths are provided in the circuit board 4 specifically for the coaxial cables, so that the shielding is deeper than the core of the cable. Metallizations are also applied in the recesses for electrical contact. In the upper second chamber 2, further signal or energy transmission is handled by the flexible circuit board 10, which is constructed similarly to a cable strip.The circuit board 4 also serves to separate the first chamber 1, which houses the sensors and, in the event of a leak, the medium, from the second chamber 2, which houses additional electronic units or provides the connection to a higher-level control center. An additional separation from the medium can also be provided in the second chamber, for example, to comply with the dual seal. In the measuring tube, i.e., in the first chamber 1, the coaxial cables are attached to the housing of the measuring device via special cable connectors 26 and are also routed through these.

[0019] In the Fig. 2a and Fig. Figure 2b shows such a connector 26 enlarged from two different perspectives. This is, for example, a stamped piece that grounds the shielding 31 of the coaxial cable 27, attaches the cable 27 to the sensor, and guides the core 30 of the coaxial cable 27. For attachment, the shielding 31 and the plastic sheath are first removed from the coaxial cable 27 over a corresponding length, so that from a certain point onward, only the core 30 with its special plastic seal remains. This core 30 is guided towards the sensor (not shown here) through the cable guide 29, a type of eyelet at one end of the cable connector 26. The cable connector 26 has a press-in tongue 28, which is inserted into a suitable recess in the housing of the measuring device. The tongue 28 is a component of the connector 26.In an alternative embodiment, the connector 26 is riveted to the housing in the area of ​​the center piece, which is widened here. The tongue 28 is preferably designed such that a slight spring effect is created at the edges of the tongue 28, so that the tongue 28 essentially snaps into the recess in the housing. A crimp sleeve 32 is provided for attaching the coaxial cable 27 to the connector 26; this crimp sleeve is pushed over the coaxial cable 27 up to a stop 33. This area is better visible in the magnification X: At the connection point, the end portion of the connector 26, which serves as the grounding contact 34, is inserted between the core 30 and the shielding 31 of the coaxial cable 27. In particular, the shielding 31 is connected to this sleeve- or cannula-like end section 34, whereby the earthing of the shielding is relatively easy to realize, since only the connection 26 still has to be earthed.The sleeve 32 is then pressed tight and thus also creates a certain strain relief for the coaxial cable 27.

[0020] In the Fig. 3 is a section of the design of a variant of a Fig. 2, in which the device neck can be welded on. The transition between the neck of the first chamber 1 and the second chamber 2 above it can be seen. The cables 9, which lead to the sensors of the measuring device (not shown here), are connected to the printed circuit board 4, which simultaneously closes the passage 3 in the wall 7. This wall 7 here is both the end of the first chamber 1 and part of the enclosure of the second chamber 2. The signals from the cables 9 are transmitted via the printed circuit board 4 to the flexible printed circuit board 10. The fastening and sealing of the printed circuit board 4 is shown in the enlarged view X.

[0021] In section X it can be seen that the circuit board 4 is connected to the wall 7 via a screw as fastening element 8. For this purpose, a fastening ring 12 is located above the circuit board 4, which presses evenly on the edge of the circuit board 4 and thus allows sufficient play in the interior of the circuit board 4 so that the circuit board 4 can react reversibly, for example, to an increase in pressure in the first chamber 1. Below the circuit board 4 there is a recess 5 in the wall, in which a sealing element 6 is inserted. Furthermore, there is also an additional sealing element 6 on the side of the circuit board 4. The sealing elements 6 are, for example, O-rings. These prevent the medium or moisture from penetrating the second chamber 2.

[0022] In the Fig. Figure 4 is a section through a flexible printed circuit board 10 as in the Fig. 3. The actual signal or power conductor 13 is located as part of a layer of the flexible circuit board 10 within the flexible circuit board 10. The conductor 13 is surrounded by a shield 14, comparable to that of a coaxial cable. The special feature is that it combines the advantages of a coaxial cable with those of a flexible circuit board. Additional conductors 13 can be accommodated accordingly within the width of the flexible circuit board 10.

[0023] In the Fig. 5 a) and b) each show a specific embodiment of the invention with respect to the detection unit. The sizes and proportions are not shown to scale here. The first chamber 1 is shown above the circuit board 4 in the drawing, and the second chamber 2 is shown below it (the orientation of the chambers relative to the circuit board, however, has no effect on the embodiments described here). The circuit board 4 is designed here such that it has a transparent window 20, which is attached with solder 3 or, if necessary, an adhesive. Alternatively, the window 20 can be created directly during the manufacture of the circuit board 4, or the circuit board 4 can even be designed to be completely transparent. A measuring sensor 19—this is essentially the control and evaluation unit of the detection unit—is connected here via two electrical connections, e.g., electrical cables 25, to the optical sensor 18 below the window 20.The optical sensor 18 has a transmitting and receiving unit. The light beams 21 generated by this sensor 18 pass through the window 20 and are reflected by the indicator 17. The indicator 17 and the optical sensor 18 are designed in relation to one another in such a way that a change in the process conditions such as temperature, pressure or humidity or e.g. the penetration of the medium via the indicator 17 and the optical sensor 18 is recognized and detected by the measuring sensor 19. The indicator 17, the optical sensor 18 and the measuring sensor 19 thus form an embodiment of the detection unit 11. If, for example, the pressure in the first chamber 1 increases to such an extent that the circuit board 4 here in . Fig. 5a and Fig. 5b is pressed downward, the travel time of the light beams between emission and reflection changes, for example. This is measured by the measuring sensor 19, evaluated, and displayed accordingly, or transmitted to a higher-level control center, or possibly stored in a data storage device.

[0024] The difference between the designs in the Fig. 5a) and Fig. 5b) is that in the Fig. 5a) the indicator 17 is attached to a bracket and in the Fig. 5b) is mounted directly on the circuit board 4.

[0025] In a further embodiment, both the indicator 17 and the optical sensor 18 are arranged together in a chamber. The implementations of the detection unit 11 are therefore not limited to the examples shown here.

[0026] In the Fig.Figure 6 shows a further schematic embodiment of the measuring device according to the invention, with particular attention to the detection unit 11. Here, the measuring sensor 19 is a resistance measuring device. In this embodiment, the measuring sensor 19 is connected, on the one hand, to a conductor track 24 on the side of the circuit board 4 opposite the sensor 19 via the electrical connection 25 and, on the other hand, to a holding bracket 16 made of an electrically conductive material, likewise via an electrical connection, e.g., an electrical cable 25. Located above the conductor track 24 is a detachable connecting element 23, which in turn establishes contact with an electrically conductive spring element 22. The spring element 22 is fastened to the said holding bracket 16.Under normal conditions—the associated parameters are to be determined depending on requirements—a closed electrical circuit is formed, which has a specific electrical resistance, which is measured by the measuring sensor 19. The detachable connecting element 23 is designed such that, upon a change in pressure, temperature, or similar, it breaks the connection between the circuit board 4 and the spring element 22. One implementation is that it is a connection that melts at a specific temperature. If the connecting element 23 breaks the connection, the spring element 22 springs back. This interrupts the electrical circuit, and the significant change in resistance can be interpreted by the measuring sensor 19 as an indicator of a change in a process condition.In a similar embodiment, the circuit board 4 is designed such that, upon a change in pressure, a displacement of the circuit board 4 results in the disruption of an electrical contact—e.g., a conductor track—on the circuit board 4. Alternatively, the circuit board 4 has a metallic coating, which, upon a pressure increase, is pressed against a corresponding metallization in the housing, thus establishing an electrical connection upon the pressure increase. Further embodiments are at the discretion of the person skilled in the art.

Claims

[1] Device for determining and / or monitoring the flow of a medium through a pipe, with the pipe designed to carry the medium, with ultrasonic sensors, with at least a first chamber (1) arranged laterally on the tube and a second chamber (2), wherein the first chamber (1) is designed as a sensor connection space and for accommodating the ultrasonic sensors, wherein the second chamber (2) is designed to accommodate electronic units, wherein at least one passage (3) is located between the first chamber (1) and the second chamber (2), wherein at least one printed circuit board (4) is provided, and wherein the passage (3) and the circuit board (4) are designed and arranged relative to one another in such a way that the circuit board (4) completely closes the passage (3). [2] Device according to claim 1, characterized bythat at least one electrical connection for transmitting electrical signals and / or electrical energy between the first chamber (1) and the second chamber (2) exists through the circuit board (4). [3] Device according to claim 1, characterized by , that at least the first chamber (1) and / or the second chamber (2) has at least one wall (7), and that the circuit board (4) is fastened to the wall (7) with at least one fastening element (8). [4] Device according to claim 3, characterized by that at least one recess (5) for receiving at least one sealing element (6) is provided in the wall (7). [5] Device according to claim 1, characterized bythat at least one detection unit (11) is provided which is designed such that it at least registers and / or displays a change in at least one physical and / or chemical process condition which occurs on at least one side of the printed circuit board (4). [6] Device according to claim 1 or 5, characterized by that the printed circuit board (4) is designed in such a way that it at least registers and / or displays a change in at least one physical and / or chemical process condition which occurs on at least one side of the printed circuit board (4). [7] Device according to claim 1, characterized by that at least one electrical cable unit (9) and / or a flexible printed circuit board (10) is provided, which are / is electrically and / or mechanically connected to the printed circuit board (4). [8] Device according to claim 7, characterized bythat the flexible printed circuit board (10) is designed in such a way that at least one electrical conductor (13) is present therein, which is surrounded by a shield (14).

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