Housing for a process automation field device, and field device

Abstract

The invention relates to a housing. A cover (1) has a base (10) with a cutout (11), a viewing panel (2) lies on the base (10), and a pre-tensioning element (3) is partly mounted in a circumferential groove (13) in an inner wall (11) of the cover (1) and partly protrudes therefrom. The viewing panel (2) is in direct contact with the pre-tensioning element (3) and is under axial pre-tension. The invention further relates to a field device.

Description

[0001] Housing for a field device for process automation and field device

[0002] The invention relates to a housing for a field device for process automation. The invention further relates to a field device. The field device serves, for example, to determine and / or monitor process variables such as fill level, flow rate, mass flow rate, pressure, temperature, or pH value.

[0003] In modern technology, it is common practice to monitor and control processes in process plants using field devices. These field devices are therefore designed as either sensors or actuators. The sensors typically have a housing containing electronics coupled to a measuring unit. The measuring unit usually detects a process variable or a related measurement variable. The housing is generally multi-part and can be opened multiple times. Access is usually provided via a cover (see, for example, DE 102012 102948 A1 or DE 102015223362 A1).

[0004] Such housings, or at least their covers, are made, for example, partially or entirely of sheet metal. Covers that allow a view of, for example, a display unit located inside the housing are also known in the prior art. For this purpose, the so-called viewing cover has a recess under which a viewing window made of glass or translucent plastic is positioned. A spring element and a retaining ring are typically used to secure the viewing window, with the spring element (e.g., a wave spring) bearing against the retaining ring. Thus, several components are required, and manufacturing is correspondingly complex.

[0005] The invention is based on the objective of proposing a housing with a viewing window that is characterized by reduced costs and the easiest possible assembly.

[0006] The invention solves the problem by providing a housing for a field device for process automation, comprising a cover, a viewing window, and a preloading element, wherein the cover has a base with a recess, the viewing window rests on the base of the cover, the cover has a circumferential groove in an inner wall, the outer diameter of the groove being larger than the inner diameter of the inner wall, the preloading element and the groove being designed and aligned such that the preloading element is partially arranged in the groove of the cover and partially protrudes from the groove, and the groove, the viewing window, and the preloading element being designed and aligned such that the viewing window is in direct contact with the preloading element and is under axial preload.

[0007] The lid of the housing according to the invention is a so-called viewing lid, insofar as it has a recess and a viewing window located beneath it. The inner diameter of the lid is dimensioned such that the viewing window can be inserted. Thus, preferably the outer diameter of the viewing window is less than or equal to the inner dimensions of the lid. The viewing window is axially fixed to the base of the lid by a preload element, which is partially located in a groove in the inner wall and partially protrudes from it. The projection of the preload element provides the support surface for the viewing window in the axial direction.By matching the dimensions of the preload element and the viewing window, and by positioning the groove relative to the ground, the design of the preload element ensures that the viewing window and the preload element are in direct contact and that the viewing window is under axial preload. Because the viewing window and the preload element are in direct contact, a spring element, as required in prior art, is not necessary. The preload element thus combines the functions of a spring element and a snap ring in a single component. This not only simplifies manufacturing but also contributes to cost reduction.

[0008] One embodiment provides that the prestressing element is essentially ring-shaped and made of an elastomer. Elastomers are elastically deformable plastics. They can be elastically deformed under tensile or compressive stress and subsequently return to their original shape. Such an elastomer-based prestressing element is therefore suitable for assembly. The prestressing element is first deformed, particularly in terms of its external dimensions, which is also simplified by its ring shape. The deformed prestressing element is then inserted into the groove, where it relaxes and returns to its original shape.

[0009] According to one embodiment, the groove and the prestressing element are designed and aligned such that an outer surface of the prestressing element is adapted to an inner surface of the groove. In this embodiment, the prestressing element rests fully against the inner surface of the groove with its outer surface.

[0010] In one embodiment, the prestressing element has a substantially rectangular cross-section.

[0011] In one embodiment, the elastomer has a hardness between 60 Shore and 80 Shore, preferably 70 Shore.

[0012] In one embodiment, the material, and preferably the elastomer, from which the prestressing element is made belongs to the group of materials that exhibit a low to very low compression set. Compression set describes how much an elastomer fails to regain its original shape after a specific compressive load. This is expressed as a percentage of the material's original cross-sectional area. The lower the percentage, the better the material's ability to regain its shape, and the more effective the compressive force remains. Examples of materials used in this embodiment include ethylene propylene diene monomer (EPDM) rubbers, hydrogenated acrylonitrile butadiene rubbers (HNBR), and fluorocarbon rubbers (FKM). Preferably, the material used has a compression set of less than 35%.

[0013] In one embodiment, the prestressing element consists at least partially of silicone. Alternatively or additionally, the material from which the prestressing element is made is characterized by a good elongation value (keyword:

[0014] “elongation test”).

[0015] One embodiment involves a groove height greater than the height of the prestressing element. In this embodiment, due to the lower height of the prestressing element, the viewing window projects axially into the area of ​​the groove.

[0016] One embodiment provides that the inner wall of the lid has a constricted section, that the constricted section has a decreasing inner radius towards the bottom, and that the groove is located downstream of the constricted section towards the bottom. In this embodiment, the insertion of the preloading element into the groove is facilitated by the smaller inner diameter of the constricted section upstream of the groove, thus guiding the preloading element. In one embodiment, the constricted section adjoins a section that has an internal thread for fastening the lid.

[0017] One embodiment includes a recess in the base of the lid that extends around the opening, a sealing element in the lid, and the sealing element being positioned within this recess. In this embodiment, the transition between the viewing window and the base of the lid is sealed by a sealing element. This sealing element is partially located within a recess that preferably surrounds the opening in the base radially.

[0018] One design provides for the sealing element to be an O-ring.

[0019] One design includes the lid being made at least partially of metal.

[0020] One design provides for the viewing window to be made of glass.

[0021] Furthermore, the invention relates to a field device with a housing according to one of the preceding or following embodiments. The explanations apply accordingly to the field device, so repetition is omitted. The field device serves, for example, to measure or monitor fill level, temperature, pressure, flow rate, or pH value.

[0022] The invention is explained in more detail with reference to the following figures. They show:

[0023] Fig. 1: a spatial representation of the housing of a field device and

[0024] Fig. 2: a section through part of the lid of the housing.

[0025] Fig. 1 shows a housing of a field device with a lower component that supports the housing neck 100 and a cover 1. The cover 1 has an opening 11 through which a display unit (not shown) located under the viewing window 2 can be viewed. The cover 1 and its components are preferably rotationally symmetrical about the longitudinal axis.

[0026] Fig. 2 shows part of a section through a design of a lid 1.

[0027] The cup-shaped housing 1 has an inner wall 12 and an opening 11 in its base 10. The opening 11 is closed by the viewing window 2. In the illustrated embodiment, a sealing element 4 is located between the viewing window 2 and the opening 11, partially situated in a recess 15 in the base 10. The recess 15 radially encompasses the opening 11. In the illustrated embodiment, the sealing element 4 is an O-ring.

[0028] The viewing window 2 is radially fixed by resting against the inner wall 12.

[0029] The axial fixation, by which the viewing window 2 is pressed against the base 10, is described below.

[0030] Above the area where the viewing window 2 is located, the inner wall 10 has a circumferential groove 13. The groove 13 has an outer surface with a constant diameter. A prestressing element 3 is located partially inside and partially outside the groove 13. The portion of the prestressing element 3 that extends beyond the groove 13 creates a constriction in the interior of the cover 1. Therefore, if the viewing window 2 is inserted into the cover 1 before the prestressing element 3 is installed during manufacturing, the viewing window 2 cannot fall out.

[0031] The preload force results from the interplay of the heights of the viewing window 2 and the preload element 3, the position of the groove 13, and the material of the preload element 3. The heights of the viewing window 2 and the preload element 3, and the position of the groove 13, are coordinated such that the viewing window 2 rests precisely on the preload element 3 and is therefore pressed between the preload element 3 and the base 10 of the cover 1. The material of the preload element 3 is selected to be sufficiently elastically deformable to be inserted into the groove 13 and to return to its original shape there.

[0032] As can be seen, the prestressing element 3 rests completely against the wall of the groove 13 with its outer surface. The cross-section of the prestressing element 3 is rectangular. Furthermore, the prestressing element 3 has a lower height than the groove 13, so that the viewing window 2 projects axially into the area of ​​the groove 13.

[0033] In the illustrated embodiment, the insertion of the preload element 3 into the groove 13 is simplified by the narrowing section 14, which is located axially – starting from the base 10 – in front of the groove 13. The narrowing section 13 has an inner diameter that tapers conically towards the base 10. Therefore, when the preload element 3 is inserted, it is compressed until it reaches the groove 13 and can expand and relax within it. Reference symbol

[0034] Cover, viewing window, pre-tensioning element, sealing element, base

[0035] Recess in inner wall

[0036] Groove narrowing section recess

[0037] case neck

Claims

Patent claims 1. Housing for a field device for process automation, with a lid (1), with a viewing window (2), and with a pre-tensioning element (3), wherein the lid (1) has a base (10) with a recess (11), wherein the viewing window (2) rests on the base (10) of the lid (1), wherein the lid (1) has a circumferential groove (13) in an inner wall (12), wherein an outer diameter of the groove (13) is larger than an inner diameter of the inner wall (12), wherein the prestressing element (3) and the groove (13) are designed and coordinated such that the prestressing element (3) is partially arranged in the groove (13) of the cover (1) and partially protrudes from the groove (13), and wherein the groove (13), the viewing window (2) and the prestressing element (3) are designed and coordinated such that the viewing window (2) is in direct contact with the prestressing element (3) and is under axial prestress.

2. Housing according to claim 1 , wherein the prestressing element (3) is essentially ring-shaped, and wherein the prestressing element (3) consists of an elastomer.

3. Housing according to claim 1 or 2, where the height of the groove (13) is greater than the height of the prestressing element (3).

4. Housing according to one of claims 1 to 3, wherein the inner wall (12) of the lid (1) has a narrowing section (14), wherein the constriction section (14) has a decreasing inner radius in the direction of the bottom (10), and wherein the groove (13) is located downstream of the narrowing section (14) in the direction of the bottom (10).

5. Housing according to one of claims 1 to 4, wherein the base (10) of the lid (1 ) has a depression (15) running around the recess (11 ), wherein the lid (1) further comprises a sealing element (4), and wherein the sealing element (4) is arranged in the recess (15).

6. Housing according to claim 5, wherein the sealing element (4) is an O-ring.

7. Housing according to one of claims 1 to 6, wherein the lid (1) is at least partially made of a metal, and / or wherein the viewing window (2) is made of glass.

8. Housing according to one of claims 1 to 7, wherein the prestressing element (3) consists at least partially of a material with a low to very low compression set - preferably with a compression set of less than 35%.

9. Field device for determining and / or monitoring at least one process variable with a housing according to one of claims 1 to 8.

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