Pressure gauge, especially differential pressure gauge

Abstract

Pressure gauge, comprehensive: a metallic housing that is at least partially cylindrical or conical (20; 520); a pressure measuring cell (590); and at least one first side flange (40; 540); wherein the housing (20; 520) has a measuring cell chamber, a first end-face flange connection surface (22; 522) and a second end-face flange connection surface, wherein a first pressure channel (592) extends from the first flange connection surface (22; 522) into the measuring cell chamber, wherein a second pressure channel (594) extends from the second flange connection surface to the measuring cell chamber, wherein the pressure measuring cell (590) is arranged in the measuring cell chamber communicating with at least one of the two pressure channels (592, 594), wherein the pressure measuring cell (590) has a transducer to provide a signal which depends on a difference between pressures in the first pressure channel (592) and the second pressure channel (594), wherein at least the first side flange (40; 540) – with respect to a longitudinal axis of the housing (20; 520) – has at least a first process connection surface (42; 542) in a radial direction, which projects radially with respect to a shell surface section of the housing (20; 520) adjacent to the side flange (40; 540), wherein the first process connection surface (42; 542) has a first pressure inlet opening (44; 544) from which a first flange pressure channel extends through the first side flange (40; 540) to a first pressure outlet opening (46; 546) in a first end-face housing connection surface (48; 548) of the first side flange (40; 540), wherein the first housing connection surface (48; 548) faces the first flange connection surface (22; 522), characterized in that the housing (20; 520) is welded to at least the first side flange (40; 540) along an annular circumferential weld seam (250; 750) forming a first pressure-tight connection chamber (252; 752) between the first housing connection surface (48; 548) and the first flange connection surface (22; 522), so that a pressure present at the first pressure inlet opening can be transmitted through the first flange pressure channel, the first connection chamber (252; 752) and the first pressure channel (592) to the pressure measuring cell (590), wherein the first housing connection surface (48) of the first side flange (40) has a first annular connecting surface (482) with a concave basic structure, wherein the first connecting surface (482) radially limits the first housing connection surface (48), wherein the first flange connection surface (22) of the housing (20) has a second annular connecting surface (222) with a convex base structure, wherein the second connecting surface (222) radially limits the first flange connection surface (22), wherein the weld seam (250) is formed between the first connecting surface (482) and the second connecting surface (222).

Description

[0001] The present invention relates to a pressure measuring device, in particular a differential pressure measuring device.

[0002] In pressure measurement technology, absolute, relative, and differential pressure gauges are used. Absolute pressure gauges measure the pressure of a medium as an absolute value, i.e., as a pressure difference relative to a vacuum. Relative pressure gauges measure the pressure of a medium as a pressure difference relative to a reference pressure, such as atmospheric pressure at the location of the gauge. Differential pressure gauges measure the difference between a first and a second pressure applied to the gauge.

[0003] Typical differential pressure gauges feature a pressure measuring cell enclosed in a cylindrical housing, the housing being axially clamped between two side flanges. The side flanges seal the two end faces of the housing in a pressure-tight manner, with sealing rings clamped between the end faces and the side flanges for this purpose. The flanges are clamped against each other by several, in particular four, bolts running parallel to the axis of the housing. The flanges have process connection surfaces extending radially in the direction of the longitudinal axis of the housing. Each process connection surface has a pressure inlet opening from which a pressure channel extends through the flange to a pressure outlet opening in an end face of the housing connection surface. The pressure outlet opening is located in the area of ​​the housing connection surface bounded by one of the sealing rings.

[0004] Corresponding differential pressure measuring devices are disclosed, for example, in EP 0 370 013 B1 and DE 10 2008 054 991 A1.

[0005] The aforementioned sealing rings are critical components, as differential pressure gauges are often exposed to high static pressures, for example, several hundred bar. In many cases, elastomer seals are sufficient, but these cannot be used with all media. In such cases, thermoplastic seals, such as those made of PTFE or PFA, are used. However, thermoplastic seals do not possess sufficient elasticity to withstand media under high pressure or the clamping forces required for high pressures, especially under temperature fluctuations. To address this issue, German patent application DE 10 2012 102 834 A1, for example, discloses a sealing ring with an elastic, metallic ring body that has a thermoplastic coating on its sealing surfaces.

[0006] The sealing ring concept described in patent EP 0 370 013 B1 is also based on polymer seals, each of which is elastically supported by a metallic ring structure.

[0007] Although elastically supported thermoplastic seals can be used reliably over a wide pressure range, their application area is not unlimited, since, for example, sealing surfaces of the side flanges are elastically deformed above a limit value for static pressure due to deflection of the side flanges to such an extent that this can no longer be compensated for by the sealing rings.

[0008] Differential pressure measuring devices have become known, among others, from DE 196 08 321 A1, US 7 841 240 B2, US 5 375 473 A and US 5 959 213 A.

[0009] It is therefore the object of the present invention to remedy this situation and to provide a pressure measuring device, in particular a differential pressure measuring device, which is sealed to be resistant to the medium and can be used under temperature changes.

[0010] The problem is solved according to the invention by the pressure measuring device according to independent claim 1.

[0011] The pressure measuring device according to the invention comprises a metallic housing that is at least partially cylindrical or conical; a pressure measuring cell and at least one first side flange; wherein the housing has a measuring cell chamber inside it, a first end-face flange connection surface and a second end-face flange connection surface, wherein a first pressure channel extends from the first flange connection surface into the measuring cell chamber, wherein a second pressure channel extends from the second flange connection surface to the measuring cell chamber, wherein the pressure measuring cell is arranged in the measuring cell chamber communicating with at least one of the two pressure channels, wherein the pressure measuring cell has a transducer to provide a signal which depends on a difference between the pressures in the first pressure channel and the second pressure channel.wherein at least the first side flange – with respect to a longitudinal axis of the housing – has at least a first process connection surface in the radial direction, which projects radially with respect to a shell surface section of the housing adjacent to the side flange, wherein the first process connection surface has a first pressure inlet opening, from which a first flange pressure channel extends through the first side flange to a first pressure outlet opening in a first end-face housing connection surface of the first side flange, wherein the first housing connection surface faces the first flange connection surface, , wherein according to the invention the housing is welded to the first side flange along an annular circumferential weld seam forming a first pressure-tight connection chamber between the first housing connection surface and the first flange connection surface, so that a pressure present at the first pressure inlet opening can be transmitted through the first flange pressure channel, the first connection chamber and the first pressure channel to the pressure measuring cell.

[0012] The welding between the side flange and the housing makes the pressure gauge suitable for use in high-pressure applications, especially at pressures above 150 bar, or even above 300 bar or above 350 bar.

[0013] According to the invention, the first housing connection surface of the first side flange has a first annular connecting surface with a concave base structure, wherein the first connecting surface radially limits the first housing connection surface, and wherein the first flange connection surface of the housing has a second annular connecting surface with a convex base structure, wherein the second connecting surface radially limits the first flange connection surface, wherein the weld seam is formed between the first connecting surface and the second connecting surface.

[0014] The concave basic structure means that the first connecting surface is inclined radially inwards, i.e., that a surface normal vector of the first connecting surface averaged along a radial direction between the inner radius and the outer radius of the first connecting surface is directed radially inwards.

[0015] The convex basic structure means that the second connecting surface is inclined radially outwards, i.e., that a surface normal vector of the second connecting surface averaged along a radial direction between the inner radius and the outer radius of the second connecting surface is directed radially outwards.

[0016] In a further development of the invention, the concave basic structure of the first connecting surface and the convex basic structure of the second connecting surface have mutually complementary conical surface sections whose conical axis is aligned with the longitudinal axis of the housing, wherein in particular the opening angle of the conical surface to the conical axis is not less than 45°, preferably not less than 55° and particularly preferably not less than 58°, and wherein the opening angle of the conical surface to the conical axis is not more than 75°, preferably not more than 65°, and particularly preferably not more than 62°.

[0017] The definition of the shape of the basic structures of the connecting surfaces does not preclude the connecting surfaces from having additional structural elements. For example, an annular groove may be formed in a conical surface, the radial extent of which is no more than 20%, preferably no more than 15%, and particularly preferably no more than 10% of the radial extent of the connecting surface.

[0018] The design of the mutually complementary connecting surfaces with a concave basic structure on the side flange and a convex basic structure on the housing, in particular as sections of conical shell surfaces, enables the preparation of a deep weld seam between the housing and the side flange, even if parts of the side flange protrude radially from the housing.

[0019] Thus, the described convex and concave basic structures ensure that tangents to the connecting surfaces, which define, for example, the direction of incidence of an electron beam in electron beam welding, are not blocked by radially protruding parts of the side flange.

[0020] A sufficient weld depth is particularly advantageous when the pressure gauge is to withstand high pressures, because due to the depth of the weld, it can have a sufficiently large, pressure-bearing ring area.

[0021] In a further development of the invention, a projection of the weld seam onto a plane perpendicular to the longitudinal axis of the housing has an area that is not less than 50%, in particular not less than 60%, and preferably not less than 70% of the area enclosed in a ring shape by an inner radius of the weld seam.

[0022] Due to the surface area of ​​the weld seam within the defined size range, it can withstand pressures of several hundred bar.

[0023] In a further development of the invention, the flange connection surface of the housing in the connection chamber, adjacent to the weld seam, has an axial projection, wherein the housing connection surface of the side flange has an axial recess complementary to the axial projection, into which the axial projection extends, so that an annular gap is formed in the connection chamber adjacent to the weld seam between the housing and the side flange, which has a gap width of not less than 0.3 mm, preferably not less than 0.5 mm, and particularly preferably not less than 0.6 mm, especially adjacent to the weld seam.

[0024] In a further development of the invention, the axial projection of the flange connection surface has an annular radial projection on its end face facing the side flange, so that the gap width of the annular gap is reduced in the area of ​​the radial projection, wherein the minimum gap width in the area of ​​the radial projection is no more than 50%, in particular no more than 25%, of the maximum gap width or the mean gap width of the annular gap.

[0025] In a further development of the invention, the annular gap has a depth that is not less than three times, in particular not less than four times and preferably about four and a half to five and a half times the maximum gap width.

[0026] The axial projection ensures that a central area of ​​the end face, the flange connection surface, encompassed by the end face of the axial projection, is set back from the weld seam and thus protected from the thermal effects of the welding process. This is advantageous because a first pressure channel extends from the central area of ​​the end face to the measuring cell chamber, and the opening of the pressure channel is usually covered by a thin, metallic separating membrane. This metallic separating membrane, which has an embossed pattern, could be destroyed or at least have its mechanical properties altered by direct exposure to a weld front.

[0027] The annular gap between the axial projection and the corresponding recess in the side flange prevents undefined connections or stresses from forming between the housing and the side flange. Furthermore, the narrowing of the annular gap at its opening facing away from the weld seam provides improved protection for the central area of ​​the end face and any separating membrane that may be located thereon, from damage during the welding process.

[0028] In a further development of the invention, the housing connection surface of the side flange in the connection chamber has a circumferential annular groove, wherein in particular the outer radius of the annular groove is not less than 5% of the inner radius of the weld, preferably not more than 2%, and particularly preferably not less than 5% of the inner radius of the weld.

[0029] In a further development of the invention, the annular groove has a concave curvature adjacent to its outer radius in an axial longitudinal section, with a radius of curvature that is not less than 5%, preferably not less than 10% and particularly preferably not less than 12.5% ​​of the inner radius of the weld, wherein the radius of curvature increases, in particular monotonically, up to an inflection point, from which the curvature becomes convex up to an inner radius of the annular groove, and wherein, in particular, a substantially planar circular surface adjoins the inner radius of the annular groove.

[0030] The annular groove serves primarily to relieve stresses that arise during welding. Since these stresses also affect the weld seam, the reduction of these stresses by the annular groove allows the weld seam to be designed with a weaker profile while maintaining the desired compressive strength. This, in turn, reduces the mechanical stresses in and between the joining partners during the welding process itself. Furthermore, because such mechanical stresses can impair measurement accuracy through feedback to the pressure sensor, the annular groove ultimately contributes to improved measurement accuracy.

[0031] In a further development of the invention, at least the first flange connection surface has a first separating membrane which covers the first pressure channel.

[0032] In a further development of the invention, the housing comprises a base body and a closure body, wherein one of the flange connection surfaces includes an end face of the closure body facing away from the base body, and wherein the weld seam between the side flange and the housing is formed both between the base body and the side flange and between the closure body and the side flange. In a further embodiment of this further development of the invention, an overload diaphragm is arranged between the base body and the closure body.

[0033] Such overload membranes serve to protect the pressure measuring cell in the event of one-sided overloads. Differential pressure gauges with such overload membranes are marketed, for example, by the applicant under the designations Deltabar S PMD 75, FMD 77 and FMD 78, and the principle of overload protection by means of an overload membrane is described in German patent applications DE 10 2006 057 828 A1 and DE 10 2006 040 325 A1 as well as in patent EP 1 299 701 B1.

[0034] In a further development of the invention, the weld seam is formed by means of electron beam welding and has in particular a depth of not less than 6 mm, preferably not less than 8 mm.

[0035] In a further development of the invention, the connection chamber contains a filling element to reduce the free volume available to a fluid, in particular a transmission fluid, in the connection chamber.

[0036] This further development of the invention relates in particular to pressure measuring devices which have a pressure transmitter, i.e., a hydraulic path connected to the pressure inlet opening of the side flange in order to introduce a pressure to be measured into the connection chamber, wherein the hydraulic path comprises a pressure line filled with a transfer fluid and a pressure transmitter diaphragm, wherein the pressure transmitter diaphragm closes an opening of the pressure line facing away from the side flange, and wherein the pressure transmitter diaphragm can be pressurized with a medium whose pressure is to be measured in order to transmit the pressure into the pressure line. The pressure line usually comprises a capillary tube or a bore, in particular a capillary bore through a solid.

[0037] The packing material reduces pressure measurement errors caused by temperature-dependent volume expansion of the transmission fluid, as the packing material reduces the total amount of transmission fluid trapped between the connecting chamber and the pressure transmitter diaphragm.

[0038] In a further development of the invention, the pressure measuring device is designed as a differential pressure measuring device, wherein a second side flange has a second housing connection surface which is essentially designed like the first housing connection surface of the first side flange, and wherein the housing has a second flange connection surface, wherein the housing is welded to the second side flange along a second annular circumferential weld seam forming a second pressure-tight connection chamber between the second housing connection surface and the second flange connection surface, so that a pressure present at a second pressure inlet opening of the second side flange can be transmitted to the pressure measuring cell through a second flange pressure channel extending through the second side flange, the second connection chamber and the second pressure channel.

[0039] As previously discussed, according to a further development of the invention, the housing can have a base body and a closure body, wherein one of the flange connection surfaces comprises an end face of the closure body facing away from the base body, and wherein the weld seam between the side flange and the housing is formed both between the base body and the side flange and between the closure body and the side flange. Apart from this feature, which only concerns one of the flange connection surfaces, the first flange connection surface and the second flange connection surface are essentially identical in design.

[0040] The described pressure gauge is primarily designed for use as a differential pressure gauge, but it can also be operated as a relative pressure gauge or an absolute pressure gauge. For the latter, a medium pressure is applied to one side of the pressure cell via a first side flange, while the other side of the pressure cell is exposed to the ambient air pressure or a vacuum. In this case, the second side flange may be omitted.

[0041] The invention will now be explained with reference to the exemplary embodiments shown in the drawings. These show: Fig. 1a a simplified cross-section through a first embodiment of a pressure measuring device according to the invention; Fig. 1b a simplified longitudinal section through the first embodiment of a pressure measuring device according to the invention Fig. 1a; Fig. 1c a detail (A) from the simplified longitudinal section through the first embodiment of a pressure measuring device according to the invention Fig. 1b; Fig. 2a a longitudinal section through a second embodiment of a pressure measuring device according to the invention; and Fig. 2b a cross-section through the second embodiment of a pressure measuring device according to the invention Fig. 2a.

[0042] The in Fig. 1a, Fig. 1b and Fig. The simplified pressure gauge shown in Figure 1c is a differential pressure gauge comprising a substantially cylindrical housing 20 with two end faces, each having a flange connection surface 22. Side flanges 40 are connected to each of these two flange connection surfaces 22. Each side flange 40 has a housing connection surface 48 facing the housing 20. This housing connection surface 48 is welded along a circumferential, pressure-bearing weld 250 to the edge of the flange connection surface 22 facing it, forming a connection chamber 252 between the flange connection surface 22 and the housing connection surface 48. Each side flange 40 has at least one process connection surface 42 with a pressure inlet opening 44. A flange pressure channel extends from this inlet through the side flange 40 to a pressure outlet opening 46, which opens into the connection chamber 252.

[0043] The side flange 40 also has openings 49 which lead into the connection chamber 48, and which are closed during operation of the sensor by blind plugs, drainage plugs or vent plugs.

[0044] The cylindrical housing comprises a base body 202 and a closure body 204, which is pressure-tightly connected to the base body, in particular by welding. The closure body 204 closes, in particular, a measuring cell chamber (not shown) arranged in the base body 202. Furthermore, an overload chamber may be formed between the base body 202 and the closure body 204, which is divided by an overload diaphragm 206. Since these components are of secondary importance in connection with the present invention and are familiar to a person skilled in the art of differential pressure measurement, their illustration in the drawings and a detailed explanation thereof are unnecessary.

[0045] The flange connection surfaces 22 of the housing 20 and the housing connection surfaces 48 of the side flanges 40 have contours which are now defined in particular by reference to Fig. 1c will be explained in more detail.

[0046] To connect the side flanges 40 to the housing 20 with sufficient pressure resistance for high-pressure applications at static pressures of several hundred bar by welding, the weld seam 250 must have a depth t of, for example, 7 mm to 10 mm. This can be achieved in particular by electron beam welding, for which the electron beam must be able to pass unhindered from the outer surface of the housing 20 between the surfaces to be welded. This is made more difficult by the fact that the side flanges 40 protrude radially from the housing 20, at least in the direction of the process connection surfaces 44. In order to nevertheless allow the electron beam to pass between the surfaces to be welded, the flange connection surface 22 of the housing 20 has an annularly circumferential connection surface 222 with a convex basic structure, which here is designed as a conical surface segment.The connecting surface 222 of the base body has three sub-regions: an outer conical surface section 222a, an inner conical surface section 222c (where the inner conical surface 222c is a section of the same reference conical surface as the outer conical surface section 222a), and an annular decoupling groove 222b, which separates the two conical surface sections and extends between the inner and outer conical surface sections. The boundary between the base body 202 and the closure body 204 runs in the region of this decoupling groove 222b, such that the inner conical surface section 222c is exclusively a surface section of the closure body 204, and the outer conical surface section 222a is exclusively a surface section of the housing body 202.

[0047] In this case, the reference cone shell has an angle of approximately 60° to the cone axis.

[0048] The decoupling groove 222b is specifically designed to prevent a direct connection of three or four joining partners when connecting the side flange to the housing. Without the decoupling groove 222b, the base body 202 and the closure body 204, and possibly the intermediate overload membrane 206, would abut the connecting surface 482 of the side flange at the transition. This would cause them to melt and re-weld both to the flange and to each other in the edge region. This could potentially create undefined stress states, which are prevented by the decoupling groove 222b.

[0049] If, when joining the side flange and housing, only two monolithic joining partners in the area of ​​the weld are to be connected, for example when joining a second side flange 40 to the housing 20, the decoupling groove 222 can be omitted.

[0050] The housing connection surface 48 has a concave connecting surface 482 in its edge region, which is designed as a concave conical shell section of the reference conical shell. The concave connecting surface 482 of the side flange 40 essentially completely covers the connecting surface 222 of the housing 20 and is welded to it by electron beam welding with a weld depth t of approximately 9 mm.

[0051] The housing 20 has a separating membrane 208 at its end face, the outer surface of which faces the connection chamber 252 in order to transmit pressure prevailing in the connection chamber to the pressure measuring cell by means of a transmission fluid. The separating membrane is pressure-tightly connected along its edge to the end face 225 of an axial projection of the flange connection surface 22 by a circumferential joint – in particular a weld seam. The separating membrane 208 typically comprises a metal foil with a thickness between, for example, 30 µm and 300 µm, the foil being embossed with a ring pattern to allow for a sufficiently large volume stroke.

[0052] Deformations of the end face 225 of an axial projection of the flange connection surface 22 in the area of ​​the joining point of the separating membrane alter the stiffness or the rest position of the separating membrane 208 and should therefore be avoided or minimized. Furthermore, it is advantageous if the separating membrane 208 is not directly exposed to the heat or welding fumes generated during the welding process when the side flange 40 is welded to the housing 20.

[0053] The axial projection contributes to the protection of the separating membrane 208, because the axial projection axially distances the separating membrane 208 from the inner edge of the weld 250 between the housing and the side flange and protects it from direct thermal radiation and welding fumes by an edge area of ​​the axial projection.

[0054] For thermal and mechanical decoupling of the axial projection from the side flange, the axial projection has a substantially cylindrical outer surface 223 downstream of the weld 250. This outer surface is radially spaced from an opposing, concave, cylindrical outer surface section 484 of the housing connection surface, so that an annular gap 254 with a width b1 of approximately 600 µm is formed between the axial projection and the side flange. The annular gap 254 has a height h of approximately 3 to 4 mm in the axial direction between the inner edge of the weld and the end face 225 of the axial projection. Furthermore, the end face 225 of the axial projection has a radial projection of approximately 450 µm, so that the annular gap 254 narrows in an upper end section to a gap width b2 of approximately 150 µm. This narrowing provides additional heat protection for the separating membrane 208 during the preparation of the weld seam 250.As a result, the annular gap 254 makes a considerable contribution to the thermal and mechanical decoupling of the separating membrane from the side flange 40, especially when it is attached by welding.

[0055] To mechanically relieve the weld joint 250 between the side flange 40 and the housing 20, the housing connection surface 48 of the side flange 40 has an annular relief groove 486 within the connection chamber 252, which adjoins the concave cylindrical outer surface section 484 of the housing connection surface, wherein the relief groove has a concave curvature 486a with a minimum radius of curvature of, for example, about 3 mm to 4 mm in an axial section plane following the concave cylindrical outer surface section 484, wherein the radius of curvature increases up to an inflection point after the relief groove has a convex curvature 486b with a radius of curvature of about 7 mm, wherein the convex curvature extends to an inner radius of the relief groove 486.A substantially planar surface adjoins the relief groove 486 radially inwards, which has a distance of, for example, 500 µm to the separating membrane 208 in order not to impede sufficient deflection of the separating membrane.

[0056] The statements regarding the connection between the first side flange 40 and the housing 20 also apply accordingly to the connection between the second side flange 40 and the housing 20 at its other end face.

[0057] Fig. 2a and Fig. Figure 2b shows sectional views of a second embodiment, which has essentially the same structure as the first embodiment. A substantially cylindrical housing 520 is arranged between two side flanges 540 and welded to each of them along an annular, circumferential, pressure-bearing weld 750. The housing 520 has end-face flange connection surfaces 522 facing the side flanges 540, which are designed according to the flange connection surfaces of the first embodiment. The side flanges 540 have housing connection surfaces 548 that are complementary to the flange connection surfaces 522 and are designed according to the housing connection surfaces of the first embodiment.

[0058] The side flanges 540 have - with reference to the axis of the cylindrical housing - at least one connection surface 542 with a pressure inlet opening 544 in the radial direction, from which a flange pressure channel extends through the side flange, which opens into a connection chamber 752 between the side flange 540 and the housing 520, in order to transmit the pressure through a pressure channel 592, 594 to a pressure measuring cell 590 in a measuring cell chamber inside the housing 520.

[0059] The pressure inlet openings 544 are designed here as connections for capillary lines, as used in hydraulic pressure transmitters, which transmit the pressure to the pressure gauge via a transmission fluid. In the two connection chambers 752 between the side flanges 540 and the housing 520, annular packing elements 570 are arranged, which in particular fill the volume of the relief grooves 586 in the housing connection surfaces of the side flanges in order to minimize the volume of the transmission fluid. For the sake of clarity, the packing elements are shown only in Fig. 2a shown, although existing filler material is actually also shown in the representation of Fig. 2b should be recognizable.

[0060] In Fig. 2a and Fig.Figure 2b shows how the pressure measuring cell 590 is connected via a glass feedthrough 596 and lines 598 to an electronic circuit 600 for operating an electrical transducer of the pressure measuring cell 590. The pressure measuring cell can, in particular, have a capacitive or (piezo-)resistive transducer, as is common in pressure measurement technology.

Claims

[1] Pressure gauge comprising: a metallic housing that is at least partially cylindrical or conical (20; 520); a pressure measuring cell (590); and at least one first side flange (40; 540); wherein the housing (20; 520) has a measuring cell chamber, a first end-face flange connection surface (22; 522) and a second end-face flange connection surface, wherein a first pressure channel (592) extends from the first flange connection surface (22; 522) into the measuring cell chamber, wherein a second pressure channel (594) extends from the second flange connection surface to the measuring cell chamber, wherein the pressure measuring cell (590) is arranged in the measuring cell chamber communicating with at least one of the two pressure channels (592, 594), wherein the pressure measuring cell (590) has a transducer to provide a signal which depends on a difference between pressures in the first pressure channel (592) and the second pressure channel (594), wherein at least the first side flange (40; 540) – with respect to a longitudinal axis of the housing (20; 520) – has at least a first process connection surface (42; 542) in a radial direction, which projects radially with respect to a shell surface section of the housing (20; 520) adjacent to the side flange (40; 540), wherein the first process connection surface (42; 542) has a first pressure inlet opening (44; 544) from which a first flange pressure channel extends through the first side flange (40; 540) to a first pressure outlet opening (46; 546) in a first end-face housing connection surface (48; 548) of the first side flange (40; 540), wherein the first housing connection surface (48; 548) faces the first flange connection surface (22; 522), characterized by, that the housing (20; 520) is welded at least to the first side flange (40; 540) along an annular circumferential weld seam (250; 750) forming a first pressure-tight connection chamber (252; 752) between the first housing connection surface (48; 548) and the first flange connection surface (22; 522), so that a pressure present at the first pressure inlet opening can be transmitted through the first flange pressure channel, the first connection chamber (252; 752) and the first pressure channel (592) to the pressure measuring cell (590), wherein the first housing connection surface (48) of the first side flange (40) has a first annular connecting surface (482) with a concave basic structure, wherein the first connecting surface (482) radially limits the first housing connection surface (48), wherein the first flange connection surface (22) of the housing (20) has a second annular connecting surface (222) with a convex base structure, wherein the second connecting surface (222) radially limits the first flange connection surface (22), wherein the weld seam (250) is formed between the first connecting surface (482) and the second connecting surface (222). [2] Pressure gauge according to claim 1, wherein the convex basic structure of the first connecting surface (482) and the concave basic structure of the second connecting surface (222) have mutually complementary conical surface sections whose conical axis is aligned with the longitudinal axis of the housing, wherein in particular the opening angle of the conical surface to the conical axis is not less than 45°, preferably not less than 55° and particularly preferably not less than 58°, and wherein the opening angle of the conical surface to the conical axis is no more than 75°, preferably no more than 65°, and particularly preferably no more than 62°. [3] Pressure gauge according to one of the preceding claims wherein a projection of the weld (250) onto a plane perpendicular to the longitudinal axis of the housing (20) has an area which is not less than 50%, in particular not less than 60%, and preferably not less than 70% of the area enclosed in an annular manner by an inner edge of the weld (250). [4] Pressure gauge according to any one of the preceding claims, wherein the flange connection surface (22) of the housing (20) has an axial projection in the connection chamber (252) adjacent to the weld seam (250), wherein the housing connection surface (48) of the side flange (40) has an axial recess complementary to the axial projection into which the axial projection extends, so that an annular gap (254) is formed in the connection chamber (252) adjacent to the weld seam (250) between the housing (20) and the side flange (40), which in particular has a gap width (b1) of not less than 0.3 mm, preferably not less than 0.5 mm, and particularly preferably not less than 0.6 mm, especially adjacent to the weld seam (250). [5] Pressure gauge according to claim 4, wherein the axial projection of the flange connection surface (22) has an annular radial projection on its end face (225) facing the side flange (40), such that the gap width of the annular gap (254) is reduced in the area of ​​the radial projection, wherein the minimum gap width (b2) in the area of ​​the radial projection is not more than 50%, in particular not more than 25%, of the maximum gap width or the mean gap width (b2) of the annular gap (254). [6] Pressure measuring device according to claim 4 or 5, wherein the axial projection of the annular gap (254) has a depth (h) that is not less than three times, in particular not less than four times and most preferably about four and a half to five and a half times the maximum gap width (b1). [7] Pressure gauge according to one of the preceding claims, wherein the housing connection surface (48; 548) of the side flange (40, 540) in the connection chamber (252; 752) has a circumferential annular groove (486; 586), wherein in particular an outer radius of the annular groove (486; 586) is not less than the inner radius of the weld (250; 750) by more than 5% of the inner radius of the weld (250; 750), preferably by no more than 2%, and particularly preferably not less than the inner radius of the weld (250; 750). [8] Pressure gauge according to claim 7, wherein the annular groove (486; 586) has a concave curvature adjacent to its outer radius in an axial longitudinal section with a radius of curvature which is not less than 5%, preferably not less than 10% and particularly preferably not less than 12.5% ​​of the inner radius of the weld (250; 750), wherein the radius of curvature increases in a particularly monotonous manner up to an inflection point from which the curvature is convex up to the inner radius of the groove, and where a substantially planar circular surface adjoins the inner radius of the ring groove (486; 586). [9] Pressure gauge according to one of the preceding claims, wherein at least the first flange connection surface (22) has a first separating membrane (208) which covers the first pressure channel (592). [10] Pressure gauge according to one of the preceding claims, wherein the housing (20) comprises a base body (202) and a closure body (204), wherein one of the flange connection surfaces (22) comprises an end face of the closure body (204) facing away from the base body (202), wherein the weld seam (250) between the side flange (40) and the housing (20) is formed both between the base body (202) and the side flange (40) and between the closure body (204) and the side flange (40). [11] Pressure measuring device according to claim 10, wherein an overload diaphragm (206) is arranged between the base body (202) and the closure body (204). [12] Pressure gauge according to one of the preceding claims wherein the weld (250; 750) is formed by electron beam welding and in particular has a depth of not less than 6 mm preferably not less than 8 mm. [13] Pressure measuring device according to one of the preceding claims wherein the connection chamber (752) contains a filling element (570) to reduce the free volume available to a fluid, in particular a transmission fluid, in the connection chamber (752). [14] Pressure gauge according to any one of the preceding claims, the pressure gauge is designed as a differential pressure gauge, wherein a second side flange has a second housing connection surface designed like the first housing connection surface (48; 548) of the first side flange (40; 540), wherein the housing (20; 520) is welded to the second side flange along a second annular circumferential weld seam forming a second pressure-tight connection chamber between the second housing connection surface and the second flange connection surface, so that a pressure present at a second pressure inlet opening of the second side flange can be transmitted through a second flange pressure channel extending through the second side flange, the second connection chamber and the second pressure channel (594) to the pressure measuring cell (590).

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