Field device for process automation and method for producing a field device

Abstract

The invention relates to a field device (1) for process automation, comprising: - at least one electronics and / or sensor component (20, 30); and - a metal housing (10) for accommodating the at least one electronics and / or sensor component (20, 30), the housing (10) having a housing body (11), which has a housing wall (12), and a housing chamber (13), which is delimited by the housing wall (12). The at least one electronics and / or sensor component (20, 30) is at least partly provided in the housing chamber (13); the housing wall (12) is equipped with an opening (41), through which a metal sub-unit (40), in particular a metal connection sleeve (16, 50) or a measuring tube (60) extends; the sub-unit (40) is welded to the housing wall (12) by means of a laser beam welding method; the sub-unit (40) has a first end face (SF1) in an outer edge region; the housing wall (12) has a second end face (SF2) in a wall region around the opening (41); and the first end face (SF1) is offset relative to the second end face (SF2) of the housing wall (12) in the longitudinal direction of the sub-unit (40) such that there is a minimum offset of 0.3 mm between the second end face (SF2) and the first end face (SF1).

Description

[0001] Field device for process automation and method for manufacturing a field device

[0002] The invention relates to a field device for process automation and a method for manufacturing a field device.

[0003] Field devices typically have a housing with a metallic wall that defines a housing chamber. The sensor and / or electronic component(s) required to determine a monitored parameter are / are located, at least partially, within this housing chamber. To enable communication between the electronic component and an external monitoring and / or display unit, the electronic component typically has a connector located in an opening in the housing wall. Connectors are known that have a metallic sleeve with a receptacle for a plastic connector. There are applications in which the field device, particularly the sensor and / or electronic component, must be connected to an electrical reference potential. For this purpose, a metallic connection sleeve can be provided in the housing wall, into which a plug electrically connected to a reference potential can be inserted.Especially for applications where a flowing medium needs to be monitored, the sensor component of the field device features a metallic measuring tube for guiding the flowing medium. This tube can extend through an opening in the housing wall and be fixed in place there.

[0004] The attachment of the partially metallic subunit mentioned in the previous examples to the metallic housing wall can be achieved using a laser beam welding process. However, it has been found that the laser beam welding process can lead to strong local heat generation. This can cause damage to plastic components that are part of the subunit.

[0005] The invention is based on the objective of providing a remedy.

[0006] The problem is solved by the field device according to claim 1 and the method according to claim 11.

[0007] The field device for process automation according to the invention, comprising:

[0008] - at least one electronic and / or sensor component;

[0009] - a metallic housing for accommodating the at least one electronic and / or sensor component, wherein the housing comprises a housing body with a housing wall, wherein the housing has a housing chamber which is bounded by the housing wall, wherein the at least one electronic and / or sensor component is arranged at least partially in the housing chamber, wherein there is an opening in the housing wall through which a metallic subunit, in particular a metallic connecting sleeve or a measuring tube, extends, wherein the subunit is welded to the housing wall by means of a laser beam welding process, wherein the subunit has a first end face in an outer edge region, wherein the housing wall has a second end face in a wall region around the opening, wherein the first end face is offset in the longitudinal direction of the subunit to the second end face of the housing wall,so that there is a minimum offset of 0.3 millimeters between the second end face and the first end face.

[0010] Advantageous embodiments of the invention are the subject of the dependent claims.

[0011] One embodiment provides for a maximum offset of 10 millimeters between the second end face and the first end face.

[0012] One embodiment provides that the subunit is a, in particular hollow cylindrical, metallic connection sleeve with a receptacle for a (grounding) connector for connecting the housing to a reference potential.

[0013] One embodiment provides that the subunit is a, in particular hollow cylindrical, metallic connection sleeve with a receptacle in which a connector, at least partially made of plastic, is arranged for connecting the field device to a control unit, a voltage source and / or a parameterization device, wherein the connector is electrically connected to the electronic component, and wherein the metallic connection sleeve is connected to a reference potential.

[0014] One embodiment provides that the subunit, in particular the metallic connecting sleeve, has a circumferential annular groove in an edge area (RB) that touches the housing wall.

[0015] One embodiment provides that the annular groove has a depth of at least 1 millimeter, in particular at least 2 millimeters and preferably 3 millimeters, and / or wherein the annular groove has a maximum depth of 4 millimeters.

[0016] One embodiment provides that the ring groove has a minimum width of 1 millimeter, in particular

[0017] 2 millimeters, and / or wherein the annular groove has a maximum width of 3 millimeters. One embodiment provides that the housing wall comprises a housing frame and a housing shell, wherein the housing shell is connected to the housing frame by means of a welded joint, in particular a welded joint produced by a laser beam welding process, wherein the opening is located in the housing frame, wherein a minimum distance between the welded joint and the subunit is less than 8 millimeters, in particular less than 7 and preferably less than 6 millimeters.

[0018] One embodiment provides that the subunit is a metallic measuring tube for guiding a medium.

[0019] One embodiment provides that the field device is a flow meter, in particular a magnetic-inductive flow meter.

[0020] The inventive method for manufacturing a field device according to one of the preceding claims comprises the following process steps:

[0021] - Providing a housing comprising a housing frame and at least one housing shell, wherein the housing frame has an opening in which a sub-unit is arranged, wherein the housing frame has an outer contour having a minimum distance x to an edge of the opening which is between 2 millimeters and 8, in particular 7 and preferably e millimeters;

[0022] - Welding the housing frame to the at least one housing shell along the outer contour of the housing frame using a laser beam welding process, preferably with a power of maximum 1900W / cm² 2, in particular a maximum of 700 W / cm² 2 , is used, wherein a starting point at which the welding begins has a minimum distance y to the edge of the opening of 5 millimeters, in particular 7 millimeters.

[0023] The invention is explained in more detail with reference to the following figures. They show:

[0024] Fig. 1 : an embodiment of a field device according to the invention;

[0025] Fig. 2: a close-up view of a cross-section through a terminal sleeve and a connector;

[0026] Fig. 3: a perspective view of a partially cutaway representation of a connection sleeve for a reference potential;

[0027] Fig. 4: a cross-section through a measuring tube; and Fig. 5: a block diagram of an embodiment of the method according to the invention.

[0028] Fig. 1 shows an embodiment of a field device 1 according to the invention for process engineering. In automation technology, particularly in process automation technology, field devices are frequently used to detect and / or influence process variables. Sensors, such as those integrated into level gauges, flow meters, pressure and temperature gauges, pH / ORP meters, conductivity meters, etc., are used to detect process variables. These sensors detect the corresponding process variables such as level, flow rate, pressure, temperature, pH value, and conductivity. Actuators, such as valves or pumps, are used to influence process variables. These devices can change the flow rate of a liquid in a section of a pipeline or the fill level in a container.Field devices are, in principle, all devices that are used close to the process and that provide or process process-relevant information. In the context of the invention, field devices also include remote I / Os, radio adapters, and, more generally, electronic measuring components that are arranged at the field level. A field device can be selected, in particular, from a group consisting of flow meters, level meters, pressure gauges, temperature meters, limit level gauges, and / or analytical instruments. Flow meters include, in particular, Coriolis, ultrasonic, vortex, thermal, and / or magnetic-inductive flow meters.Level measuring devices include, in particular, radar-based level measuring devices, microwave level measuring devices, ultrasonic level measuring devices, time-domain reflectometric level measuring devices, radiometric level measuring devices, capacitive level measuring devices, inductive level measuring devices, and / or temperature-sensitive level measuring devices. Pressure measuring devices include, in particular, absolute, gauge, or differential pressure devices. Temperature measuring devices include, in particular, devices with thermocouples and / or temperature-dependent resistors. Limit level measuring devices include, in particular, vibronic limit level measuring devices, ultrasonic limit level measuring devices, and / or capacitive limit level measuring devices. Analytical measuring devices include, in particular, pH sensors, conductivity sensors, oxygen and active oxygen sensors, (spectro)photometric sensors, and / or ion-selective electrodes.

[0029] The field device 1 comprises at least one electronic component 20 and / or at least one sensor component 30. The electronic component 20 is part of an electronic unit EE, which is configured to operate the field device 1. The electronic unit EE can be a measuring, operating, and / or evaluation circuit. Furthermore, the electronic unit EE can include a display and a display circuit. The electronic unit EE can include a microprocessor or a microcontroller. The sensor component 30 is a subunit of a sensor. Thus, the sensor component 30 can be a measuring tube 60 for guiding a medium, a container for receiving a medium, a transducer, and / or a transmitter, or a subunit of a transducer and / or a transmitter.

[0030] The field device 1 according to the invention further comprises a housing 10 for accommodating the at least one electronic and / or sensor component 20, 30. The housing 10 comprises a metallic housing body 11 with a housing wall 12 that delimits a housing chamber 13. The housing body 11 can be made of stainless steel, preferably 1.4301 or 1.4404, or alternatively of thermoplastic material. The housing chamber 13 defines a volume in which the at least one electronic and / or sensor component 20, 30 is arranged, at least partially. The housing chamber 13 can be partially or completely encapsulated. Furthermore, the housing chamber 13 is delimited by the housing wall 12. The housing chamber 13 can comprise several individual chambers separated from one another by partitions.

[0031] According to the invention, the housing wall 12 has at least one opening 41 through which a metallic subunit 40, in particular a metallic connecting sleeve 16, 50 or a measuring tube 60 with a metallic support tube, extends. The subunit 40 is welded to the housing wall 12 by means of a laser beam welding process. A laser beam is directed onto the outer surface of the housing wall in order to weld the housing wall to the subunit 40 along a weld seam to be formed by creating a weld pool that spans the entire component.

[0032] In the illustrated embodiment, the housing wall has three openings 41, each containing a subunit 40. These three subunits 40 are a measuring tube 60, a connecting sleeve 16 for connecting the housing to an electrical reference potential, and a connecting sleeve 50 for connecting the field device 1 to an external unit. However, the invention is not limited to a solution with the three subunits 40 shown. It is also possible to provide only one subunit 40, two subunits 40, or more than four subunits.

[0033] The subunit 40 according to the invention has a first end face SF1 in an outer edge region. Furthermore, the housing wall 12 has a second end face SF2 in a wall region around the opening 41. The subunit 40 is positioned in the opening such that the first end face SF1 is offset in the longitudinal direction of the subunit 40 relative to the second end face SF2 of the housing wall 12, resulting in a minimum offset of 0.3 millimeters between the second end face SF2 and the first end face SF1. This creates an offset whose geometric properties are selected such that a large proportion of the incoming laser beam is not reflected onto or away from the subunit 40. The subunit 40 can be positioned in the opening 41 such that a maximum offset of 10 millimeters is formed between the second end face SF2 and the first end face SF1.

[0034] As already described, the subunit 40 can be a metallic connection sleeve 50, in particular a hollow cylindrical one (see Fig. 2), which has a receptacle 51 in which a connector 52, at least partially made of plastic, is arranged for connecting the field device 1 to a control unit 160, a power supply, and / or a parameterization device. The connector 52 is electrically connected to the electronic component 20, in particular to the measuring electronics. The metallic connection sleeve 50 is connected to an electrical reference potential, for example, via the housing wall 12. The connector 52 can, for example, be an M12x1 connector that is pressed into the metallic connection sleeve 50. Conventional connection sleeves with M12x1 threads are welded to the housing wall 12 without an internal plastic connector.The connector is retrofitted and secured against axial rotation. This securing can be achieved through form-fit or material-fit connections.

[0035] Alternatively, the subunit 40 can be a, in particular hollow cylindrical, metallic connecting sleeve 16 with a receptacle 19 for a (grounding) connector 17 for connecting the housing 10 to an electrical reference potential (see Fig. 3).

[0036] Alternatively, the subunit 40 can be a metallic measuring tube 60 for guiding a medium, which extends through the opening 41. The metallic measuring tube 60 is not necessarily entirely metallic. For example, the measuring tube 60 can comprise a metallic support tube whose inner surface is at least partially, and in particular completely, lined with an electrically insulating liner. The liner can be a plastic and / or ceramic coating. The liner itself can also be a plastic or ceramic tube or a hose that is inserted into the support tube. In this case, the coupling between the measuring tube 60 and the housing wall 12 is via the metallic support tube.

[0037] The subunit 40, in particular the metallic connecting sleeve 50, can have a circumferential annular groove 61 in an edge region RB contacting the housing wall 12 (see also Figs. 2 and 4). The annular groove 61 can preferably have a depth of at least 1 millimeter, in particular at least 2 millimeters and preferably 3 millimeters, and / or a maximum depth of 4 millimeters. Furthermore, the annular groove 61 can have a minimum width of 1 millimeter, in particular 2 millimeters, and / or a maximum width of 3 millimeters. The annular groove 61 is a circumferential recess in the metallic body of the subunit 40. The recess extends in the direction of a longitudinal axis of the subunit 40. The subunit 40 and the annular groove 61 can be designed such that a closed volume is formed in the annular groove 61 by the body of the subunit 40 itself and the housing wall 12.

[0038] The embodiment shown in Fig. 1 depicts a housing 10 with a housing wall 12 comprising a housing frame 70 and a housing shell 71. The housing shell 71 is a sheet metal part, in particular a metal sheet with a thickness of less than 5 millimeters, and more specifically less than 3 millimeters. The housing frame 70 itself is U-shaped, with two legs running substantially parallel to each other and a base. The housing frame 70 can be formed in one piece or in multiple parts. If the housing frame 70 is formed in one piece as shown, the two legs and the base are produced by bending an originally planar sheet metal part. The thickness of the housing frame 70 is greater than the sheet metal thickness of the housing shell 71. Thus, the thickness of the housing frame 70 can be between 5 and 8 millimeters. The opening 41 can be located in the housing frame 70 as shown in the embodiment.Alternatively, the opening 41 can also be located in the housing shell 71.

[0039] The housing shell 70 is metallurgically bonded to the housing frame 71 by means of a weld, in particular by means of a weld produced by a laser beam welding process. The minimum distance between the weld and the subunit 40, which is arranged in the opening 41, is less than 8 millimeters, in particular less than 7 millimeters, and preferably less than 6 millimeters. This results in the subunit 40 being heated along with the housing shell 70 when it is welded to the housing frame 71. This can lead to damage to the subunit 40 itself or to a component of the subunit 40 made of a plastic.

[0040] The field device 1 can be a flow meter configured to measure and / or monitor a flow velocity-dependent quantity. This flow velocity-dependent quantity can be a mass flow rate, a volumetric flow rate, or a flow velocity. The embodiment shown in Fig. 1 is a magnetic-inductive flow meter 2 for determining a flow velocity-dependent quantity of a flowable medium. Alternatively, the flow meter can also be a vortex, Coriolis, ultrasonic, or thermal mass flow meter. The magnetic-inductive flow meter can be an inline flow meter with a measuring tube inserted between two ends of a pipeline.Alternatively, the magnetic-inductive flowmeter can be an insertion flowmeter, which is to be arranged in a lateral opening in the outer surface of the pipeline and is at least partially surrounded by the medium during operation. The insertion flowmeter is a plug-in probe designed to determine a flow-velocity-dependent measurement parameter, e.g., the flow velocity. The connecting sleeve 16, in particular the through-hole 19, is further sealed with a sealing plug 80, in particular a (pull) expander, preferably made of metal. The sealing plug 80 can be made of a non-corrosive material. However, this requirement is not necessary if the sealing plug 80 is positioned and covered by the connecting element 17 in such a way that it does not come into contact with splashing water.For this purpose, the connecting element 17 must close the through-opening 19 in such a way that no splash water reaches the sealing plug 80.

[0041] Furthermore, the illustrated feedthrough 18 has a shoulder 90 that reduces the cross-sectional area of ​​the through-opening 19 in the direction of the housing chamber 13 and in the longitudinal direction of the through-opening 19. The sealing plug 80, in particular the (pull) expander, rests against the shoulder. The shoulder limits the insertion depth of the sealing plug 80 and thus prevents the sealing plug 80 from falling into the housing chamber 13 when inserted.

[0042] Fig. 2 shows a close-up view of a cross-section through a metallic terminal sleeve 50, which is at least partially hollow-cylindrical, and a connector 52, which is at least partially made of plastic. The terminal sleeve 50 has a receptacle 51 in the form of a through-hole, into which the connector 52 is arranged for connecting the field device 1 to a control unit (see Fig. 1), a power source, and / or a parameterization device. The connector 52 comprises a plastic body in which connection pins are arranged, in particular pressed in. The connector 52 is electrically connected to the electronic component 20 via the connection pins and electrical connectors (connecting cables). The metallic terminal sleeve 50 itself is electrically connected to an electrical reference potential via the metallic housing wall 12.

[0043] In the illustrated embodiment, the connecting sleeve 50 has a substantially planar first end face SF1 in an outer edge region. The housing wall 12 has a substantially planar second end face SF2 in a wall region around the opening 41 and the connecting sleeve 50. The first end face SF1 is offset longitudinally along the connecting sleeve 50 relative to the second end face SF2 of the housing wall 12, such that a step with a minimum offset of 0.3 millimeters exists between the second end face SF2 and the first end face SF1. Furthermore, the step can be configured such that there is a maximum offset of 10 millimeters between the second end face SF2 and the first end face SF1.

[0044] The metallic connecting sleeve 50 has a circumferential annular groove 61 in an edge region RB that contacts the housing wall 12. The annular groove 61 has a depth t of at least 1 millimeter, in particular at least 2 millimeters, and preferably 3 millimeters. The depth t of the annular groove 61 is a maximum of 4 millimeters. Furthermore, the annular groove 61 has a minimum width b of 1 millimeter, in particular 2 millimeters, and a maximum width b of 3 millimeters. The annular groove 61 serves to minimize heat transfer from the housing wall 12 to the connecting sleeve 50 during the laser beam welding process, so that the connecting sleeve 50 does not melt due to the heat.

[0045] Fig. 3 shows a perspective view of a partially cutaway representation of a metallic connection sleeve 16, which is in particular partially hollow-cylindrical, for connecting an electrical reference potential. The connection sleeve 16 has a receptacle 19, which can be configured as a through-hole, into which a (grounding) connector 17 for connecting the housing 10 to an electrical reference potential can be inserted. The metallic connection sleeve 16 is metallurgically bonded to the housing wall 12 by a laser beam welding process. A sealing plug 80, in particular a metallic one, is also arranged in the receptacle 19, which is configured as a through-hole, for closing the connection sleeve 16.

[0046] The connecting sleeve 16 has a first end face SF1 in an outer edge region. Additionally, the housing wall 12 has a second end face SF2 in a wall region around the opening 41. The connecting sleeve 16 is positioned in the opening 41 such that the first end face SF1 is offset longitudinally from the second end face SF2 of the housing wall 12, creating a step between the second end face SF2 and the first end face SF1 with a minimum offset of 0.3 millimeters. This creates an offset whose geometric properties are selected such that a large portion of the incoming laser beam is not reflected onto or away from the connecting sleeve 16. The connecting sleeve 16 can be positioned in the opening 41 such that a maximum offset of 10 millimeters is formed between the second end face SF2 and the first end face SF1.

[0047] Fig. 4 shows a section of a cross-section through a measuring tube 60 and a housing wall 12. The housing wall 12 has an opening 41 through which the measuring tube 60 extends. The measuring tube 60 comprises a metallic support tube 81, which is provided on its inner surface with a liner 82, in particular a plastic coating. The liner 82 can also be a drawn-in plastic tube. The measuring tube 60, in particular the support tube 81, is metallurgically bonded to the metallic housing wall 12 by means of a laser beam welding process.

[0048] The measuring tube 60 has a first end face SF1 in an outer edge region. Additionally, the housing wall 12 has a second end face SF2 in a wall region around the opening 41. The measuring tube 60 is positioned in the opening 41 such that the first end face SF1 is offset longitudinally from the second end face SF2 of the housing wall 12, creating a step between the second end face SF2 and the first end face SF1 with a minimum offset of 0.3 millimeters. This creates an offset whose geometric properties are selected such that a large portion of the incoming laser beam is not reflected onto or away from the measuring tube 60. The measuring tube 60 can be positioned in the opening 41 such that a maximum offset of 10 millimeters is formed between the second end face SF2 and the first end face SF1.

[0049] The support tube 81 itself has a circumferential annular groove 61 in an edge region RB that contacts the housing wall 12. The advantageous dimensioning described above also applies to the embodiment shown in Fig. 4.

[0050] Fig. 5 shows a block diagram for a process for manufacturing a field device. The process comprises the following steps:

[0051] I. Providing a housing comprising a housing frame and at least one housing shell. The housing shell may, for example, be made of sheet metal. The housing frame has a through opening for a subunit. The subunit may be a measuring tube with a metallic support tube or a metallic connecting sleeve.

[0052] II. Positioning the subunit in the opening. The housing frame has an outer contour that maintains a minimum distance (x, see Fig. 1) from an edge of the opening (42, see Figs. 1 to 3), which minimum distance is between 2 mm and 8 mm, in particular 7 mm and preferably 6 mm. The outer contour describes the contact line between the housing shell and the housing frame. The small minimum distance allows for a more compact field device. However, using a laser welding process to join the housing frame to the housing shell can lead to increased heating of the subunit and thus to damage to it.

[0053] III. Welding the housing frame to the at least one housing shell along the outer contour of the housing frame using a laser beam welding process, preferably with a power of maximum 1900W / cm² 2 , in particular a maximum of 700 W / cm² 2The starting point (SP, see Fig. 1), where the laser beam is applied and welding begins, has a minimum distance (y, see Fig. 1) of 5 millimeters, particularly 7 millimeters, from the edge of the opening. The subunit can only be exposed to the power generated by the laser beam up to a critical power level before damage occurs. Selecting this minimum distance ensures that when the laser beam is applied to the starting point, no increased power is introduced into the subunit that exceeds the critical power level. This protects the subunit without compromising the compactness of the housing. The starting point is often also the endpoint of the welding process, where the laser beam remains for a longer period before being switched off. Therefore, there is also a risk when the laser beam is applied that the power generated by the laser beam in the housing will exceed the critical power level.The method according to the invention also ensures that the data transferred to the subunit.

[0054] Power remains below the critical power level.

Claims

PATENT CLAIMS 1. Field device (1) for process automation, comprising: - at least one electronic and / or sensor component (20, 30); - a metallic housing (10) for accommodating the at least one electronic and / or sensor component (20, 30), wherein the housing (10) comprises a housing body (11) with a housing wall (12), wherein the housing (10) comprises a housing chamber (13) which is bounded by the housing wall (12), wherein the at least one electronic and / or sensor component (20, 30) is arranged at least partially in the housing chamber (13), wherein an opening (41) is provided in the housing wall (12) through which a metallic subunit (40), in particular a metallic connecting sleeve (16, 50) or a measuring tube (60), extends, wherein the subunit (40) is welded to the housing wall (12) by means of a laser beam welding process, wherein the subunit (40) has a first end face (SF1) in an outer edge region, wherein the housing wall (12) is formed in a wall region around the opening (41) around which it has a second end face (SF2),wherein the first end face (SF1) is offset in the longitudinal direction of the subunit (40) to the second end face (SF2) of the housing wall (12), such that there is a minimum offset of 0.3 millimeters between the second end face (SF2) and the first end face (SF1).

2. Field device according to claim 1, wherein there is a maximum offset of 10 millimeters between the second end face (SF2) and the first end face (SF1).

3. Field device according to claim 1 or 2, wherein the subunit (40) is a, in particular hollow cylindrical, metallic connection sleeve (16) with a receptacle (19) for a (grounding) connector plug (17) for connecting the housing (10) to a reference potential.

4. Field device according to claim 1 or 2, wherein the subunit (40) is a, in particular hollow cylindrical, metallic connection sleeve (50) with a receptacle (51) in which a connector (52) formed at least partially from a plastic for connecting the field device (1) to a control unit (160), a voltage source and / or a parameterization device is arranged, wherein the connector (52) is electrically connected to the electronic component (20), and wherein the metallic connection sleeve (50) is connected to a reference potential.

5. Field device according to claim 3 or 4, wherein the subunit (40), in particular the metallic connecting sleeve (50), has a circumferential annular groove (61) in an edge region (RB) contacting the housing wall (12).

6. Field device according to claim 5, wherein the annular groove (61) has a depth of at least 1 millimeter, in particular at least 2 millimeters and preferably 3 millimeters, and / or wherein the annular groove (61) has a depth of a maximum of 4 millimeters.

7. Field device according to claim 5 or 6, wherein the annular groove (61) has a minimum width of 1 millimeter, in particular 2 millimeters, and / or wherein the annular groove (61) has a maximum width of 3 millimeters.

8. Field device according to one of claims 5 to 7, wherein the housing wall (12) comprises a housing frame (70) and a housing shell (71), wherein the housing shell (70) is connected to the housing frame (71) by means of a welded connection, in particular a welded connection produced by means of a laser beam welding process, wherein the opening (41) is located in the housing frame (70), wherein a minimum distance between the welded connection and the subunit (40) is less than 8 millimeters, in particular less than 7 and preferably less than 6 millimeters.

9. Field device according to claim 1 or 2, wherein the subunit (40) is a metallic measuring tube (60) for guiding a medium.

10. Field device according to one of the preceding claims, wherein the field device (1) is a flow meter, in particular a magnetic-inductive flow meter (2).

11. Method for manufacturing a field device (1) according to one of the preceding claims, comprising the method steps: - Providing a housing (10) comprising a housing frame (70) and at least one housing shell (71), wherein the housing frame (70) has an opening (41) in which a sub-unit (40) is arranged, wherein the housing frame (70) has an outer contour (72) which has a minimum distance x to an edge (42) of the opening (41) which is between 2 millimeters and 8, in particular 7 and preferably 6 millimeters; - Welding the housing frame (70) to the at least one housing shell (71) along the outer contour (72) of the housing frame (70) by means of a laser beam welding process, which preferably has a power of a maximum of 1900W / cm² 2 , in particular a maximum of 700 W / cm² 2, is used, wherein a starting point (SP) at which the welding begins has a minimum distance y to the edge (42) of the opening (41) of 5 millimeters, in particular 7 millimeters.

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