WO2010094293A1

WO2010094293A1 - Electromagnetic flowmeter and method of manufacture thereof

Info

Publication number: WO2010094293A1
Application number: PCT/EP2009/001105
Authority: WO
Inventors: Claus Vilesen Christensen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2009-02-17
Filing date: 2009-02-17
Publication date: 2010-08-26

Abstract

The present invention provides an electromagnetic flowmeter (10) that is interposable between flanged ends (18,20) of upstream and downstream pipes (14,16) and carrying a fluid whose flow rate is to be measured. The proposed flowmeter (10) comprises a measurement tube (12) having an inner surface (46) defining a passage for carrying said fluid along a longitudinal axis (15). A liner (40) is disposed on said inner surface (46) of said measurement tube (12) along a portion of the length of said measurement tube (12) and ending short of upstream and downstream ends (17,19) of said measurement tube (12). A pair of flanged members (22,24) is provided for coupling said measurement tube (12) with respective flanged ends (18,20) of upstream and downstream pipes (14,16). Each of said pair of flanged members (22,24) has an inside surface (52,54) that interfaces with a corresponding end face (48,50) of said liner (40).

Description

Electromagnetic flowmeter and method of manufacture thereof

The present invention relates to electromagnetic flowmeters with liners, particularly those used in the food processing industry.

Electromagnetic flowmeters utilize the principle of electrodynamic induction for flow rate measurement of a fluid medium. In an electromagnetic flowmeter, a magnetic field is generated across a measuring section of the flowmeter pipe through which the medium flows, which, by operation of

Faraday's law, generates a voltage perpendicular to both the flow of the medium and the magnetic field. The induced voltage is measured by a pair of electrodes on opposite sides of the measuring section. This induced voltage measured by these electrodes is proportional to the flow velocity of the medium to be measured averaged over the cross section of the pipe.

Electromagnetic flowmeters find application in the food processing industry. Such flowmeters are also referred to as food sensors. Such flowmeters have a flow measurement tube, also known as a support tube, that is usually interposed between upstream and downstream process connections carrying the fluid whose flow rate is to be measured. The flow measurement tube has a liner, usually made of an electrically non-conductive material, disposed on its inner surface, to protect the tube' s inner surface from being corroded by the fluid. Electromagnetic flowmeters of the above type thus require such liners to ensure accurate flow measurement. Further, in the food processing industry, it is a requirement that the liner meets the hygiene requirements as specified by bodies such as European Hygienic Engineering and Design Group (EHEDG) . For this purpose, the liner is generally made of a plastic material. However using a liner made of a plastic material presents some disadvantages as mentioned below. It is known that the interface between the support tube and the process connection is sealed, most commonly using a rubber seal. However, this means that at this interface, there are three different materials leaning up against each other, namely, the process connection (which is metallic) , the seal (made of rubber) and the liner (made of plastic) . The expansive properties are different with each material, which causes edges and sharp corners at high operating temperatures. However, the presence of edges and sharp corners present a difficulty in getting sanitary approvals from bodies such as EHEDG as these edges and sharp corners decrease the level of cleanability of the sensor, which is a criterion in getting a sanitary approval.

The second issue with this is that machining metal is relatively easy, but in case of a plastic liner and especially a rubber seal, it is difficult to obtain precise tolerances, which causes more sharp edges and corners. Moreover, in the given arrangement, a standard seal cannot be used and the seal needs to be specially designed for this purpose, for which it is hard to get an approval from bodies such as EHEDG.

The object of the present invention is to overcome the aforementioned problems and to provide an improved electromagnetic flowmeter.

The above object is achieved by an electromagnetic flowmeter in accordance with claim 1 and a method for manufacturing an electromagnetic flowmeter in accordance with claim 9.

The underlying idea of the present invention is to provide a connection between the flowmeter and the process connection pipes which ensures that there is a metal-to-metal contact, the process connection pipes being made of metal. This is achieved by finishing the liner before the ends of the measurement tube. This allows an optimal design for a hygienic seal between the flowmeter and the process connection. Indeed, using the proposed design for the flowmeter, it is possible to use a standard and already approved design of the seal. The proposed design has an additional advantage of relieving fluid pressure due to the accumulation of gas on the backside of the liner (that takes place in certain food processing applications), by allowing the gas to evaporate. This is possible because since the liner ends before the ends of the measurement tube, it is not compressed by the tension between the process connection pipes and the measurement tube as in the case of the conventional (existing) design. This reduces the liner end pressure and allows the gas to evaporate, thereby releasing the tension from the back side of the liner.

In one embodiment, the liner is made of a fluor plastic material. Using a fluor plastic liner protects the inner surface of the measurement tube from corrosion as well as meets the hygiene requirements of bodies such as EHEDG. Further, fluor plastics show favorable thermal expansivity and can be used for high operating temperatures around 150⁰C.

In a further embodiment, the flowmeter comprises an annular seal interposed between a flanged member, of said pair of flanged members, and the respective flanged end. The seal ensures a tight connection between the flowmeter and the upstream and downstream pipes of the process connection during temperature fluctuations, which may range from -20⁰C to 180⁰C in food processing industry application. The seal can be a standard seal already approved by EHEDG. In a preferred embodiment, the seal is made of nitrile butadiene rubber (NBR) , or hydrogenated nitrile butadiene rubber (HNBR), or ethylene propylene diene M-class (EPDM) rubber.

In one embodiment, the flanged members are made of a metallic material. This is advantageous because metallic parts can be machined easily to provide better tolerances. In a further embodiment, the metallic flanged members are welded to the measurement tube. This obviates the need to have 0-ring seals as is used in present day food sensors to ensure tight connection of the flanged member ring.

In a preferred embodiment of the present invention, the flowmeter further comprises a mesh structure disposed within said liner. The mesh ensures that the liner does not collapse under high temperatures.

In a still preferred embodiment, the liner has a reduced thickness towards the end faces. This makes a smooth transition between the liner and measurement tube that is not affected by unequal expansion due to heat.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

FIG 1 is a sectional view of an electromagnetic flowmeter,

FIG 2 is a schematic sectional view of an end face of a liner according to one embodiment of the present invention,

FIG 3 is a schematic sectional view of an end face of a liner according to another embodiment of the present invention, and

FIG 4 is a schematic diagram illustrating how the end face of the proposed liner is advantageous in reducing fluid pressure on the backside of the liner.

The embodiments described below relate to a food sensor. However, the general principle of the present invention may be applicable to any kind of electromagnetic flowmeters.

FIG 1 is a longitudinal sectional view of a flowmeter 10 in accordance with one embodiment of the present invention. The flowmeter 10 includes a measurement tube 12, also referred to as a support tube that is interposed between flanged ends 18 and 20 of upstream and downstream pipes 14 and 16. In this example, the upstream and downstream pipes 14 and 16 belong to the process connection of a food processing industry application. The measurement tube is generally metallic and has an inner surface 46 that defines a passage for the fluid 11, whose flow rate is to be measured, along a longitudinal axis 15. A liner 40 is disposed on the inner surface 46 of the measurement tube 12 inner surface 46 from being corroded by the fluid 11. The liner 40 is typically made of an electrically non-conductive material. The liner 40 may be molded through one or more electrode holes 44 provided on the measurement tube 12. In a preferred embodiment, the liner 40 is made of a fluor plastic material such as PFA

(perfluoroalkoxy plastic) , which is advantageous since fluor plastic materials show favorable thermal expansivity and can be used for high operating temperatures around 150⁰C and further meets the hygiene requirement for EHEDG approval. To ensure that the liner 40 does not collapse at high temperatures, a mesh structure 42 is disposed within the liner 40. So that the mesh structure 42 is visible, the liner 40 is marked transparently.

However, unlike in the conventional design, according to the present invention, the liner does not extend along the full length of the measurement tube to the face ends of the flowmeter. Instead, as illustrated, the liner 40 extends along a portion of the length of the measurement tube 12, but ends short of the upstream and downstream ends 17 and 19 of the measurement tube. This excludes the contact of the liner material (fluor plastic in this example) at the interface of the flowmeter and the process connection, which is not the case in conventional design. The advantages of this feature will be explained with respect to the embodiment illustrated herein.

A pair of flanged members 22 and 24 is provided for coupling the measurement tube 12 to the flanged ends 18 and 20 of the process connection pipes 14 and 16. For this purpose, bolts 26, 28, 30, 32 are provided for rigidly fixing the flanged members 22 and 24 to the flanged ends 18 and 20. In the illustrated example, the flanged members 22 and 24 are gasket rings. The inventive feature is implemented by providing an interface of the inside surfaces 52 and 54 of the flanged members 22 and 24 with corresponding end faces 48 and 50 of the liner 40. This ensures that the liner material does not come into contact with the interface between the flowmeter 10 and the process connection pipes 14 and 16. In the illustrated example, the flanged members 22 and 24 are metallic, since it is much easier to machine metallic parts and thus obtain a better tolerance at the interface of the flowmeter with the process connection. Still advantageously, this design ensures that the metallic flanged members 22 and 24 can be welded to the measurement tube 12. The conventional design does not permit such a welding and instead uses of O- ring seals for providing a tight connection of the flanged members 22 and 24. The above welding thus obviates the need for such O-ring seals.

At the interface of the flowmeter 10 with the process connection pipes 14 and 16, annular seals 36 and 38 are respectively provided for ensuring a tight connection between the flowmeter and the process connection. The seals 36 and 38 are generally made of rubber. Examples include nitrile butadiene rubber (NBR) , hydrogenated nitrile butadiene rubber

(HNBR) , ethylene propylene diene M-class (EPDM) rubber, or even synthetic rubber, such as Viton™ (registered trademark of DuPont Performance Elastomers L. L. C) . However, unlike in the conventional design, where the seal needed to be specially designed to take into account the expansion of the liner that is in contact with the seal, the design in the illustrated embodiment permits the use of a standard seal that is already approved by EHEDG. Such a seal can be available from any supplier of sanitary pipe equipment and does not need any special design or modification. As can be appreciated, the present invention solves the problems with the conventional (existing) design. In the existing design there are three materials leaning up against each other at the interface of the flowmeter and the process connection, namely the liner (made of PFA) , the process connection pipe (made of metal) and the seal (made of NBR) . There are two major problems with this existing design that causes many edges and sharp corners. Firstly, the expansive properties are different with each material, which means that there will be more edges and sharp corners at high temperatures. Secondly, machining metal is quite easy, but in case of the fluor plastic liner and especially the rubber seal, it is difficult obtain precise tolerances, whereby it is prone to have more sharp edges and corners. Moreover, in the existing design, a standard seal cannot be used and the seal needs to be specially designed for this purpose, for which it is hard to get an approval from bodies such as EHEDG. As can be seen, in the present invention, the liner 40 is designed to end before the ends of the measurement tube 12 and instead interface with the inside surfaces 52 and 54 of the flanged members 22 and 24 respectively. This allows the use of a standard seal at the interface of the flowmeter and the process connection pipes due to the fact that design provides a metal-to-metal connection as the interface of the flowmeter and the process connection pipes. Advantageously, such a seal is already approved under EHEDG. Because the seal is already approved according to the EHEDG, this connection does not have to be approved by the EHEDG again, and it is only required to test the connection between the fluor plastic liner and metallic flow measurement tube. At this connection (fluor plastic against metal) it is much easier to get good tolerances, and both these materials are easier to machine than rubber. Thereby the number and size of the edges and corners are reduced.

Further advantages of the present invention are that less material (fluor plastic) is required for making the liner and that it can be implemented with a standard support tube (measurement tube) with no modification in the tube. In a preferred embodiment the transition between the liner and the measurement tube is a slide with a high angle. There may be several ways of implementing such a design. Exemplary embodiments are illustrated in FIGS 2 and 3, which show an enlarged cross-sectional view of the region 60 in FIG 1. The idea of this design is to have a reduced thickness of the liner layer in the region where the liner 40 meets the metal

(flange member 24), i.e. towards the end face 50 (and 48) of the liner 40. This provides a smooth transition between the liner and measurement tube that is not affected by unequal expansion due to heat. It should be noted that FIGS 2 and 3 are merely exemplary embodiments and several other designs of the liner end face are possible while not deviating from the inventive features mentioned above.

Referring to FIG 4, a further advantage of the present invention is now described. In certain applications, such as in the beverage industry, there exists problem of accumulation of gas (typically CO₂) on the back side of the liner which destroys the liner some time after installation. This is because there is no possibility for the gas to evaporate from the back side of the liner. The reason is that, in the existing design, the liner end face is made of PFA and when the flowmeter is mounted between the process connection pipes, the PFA liner is compressed by the tension of the support tube (measurement tube) and process connection pipes. This excluded any possibility of the gas accumulated on the back side of the liner to evaporate. In the design according to the present invention, as shown in FIG 4, the fluid pressure F of the gas leads to accumulation of gas forming gas pockets 64 on the back side of the liner 40. However, since the liner 40 of the present invention ends before the process connection, the liner end pressure P is significantly lower than in the existing design. This allows the gas to evaporate along a short distance from the center of the liner end face 50 (indicated by 62), thereby releasing the tension from the back side of the liner 40. This results in lower strength in the design of the liner and a longer life of the liner.

Summarizing, the present invention provides an electromagnetic flowmeter that is interposable between flanged ends of upstream and downstream pipes and carrying a fluid whose flow rate is to be measured. The proposed flowmeter comprises a measurement tube having an inner surface defining a passage for carrying said fluid along a longitudinal axis. A liner is disposed on said inner surface of said measurement tube along a portion of the length of said measurement tube and ending at a short distance of upstream and downstream ends of said measurement tube. A pair of flanged members is provided for coupling said measurement tube with respective flanged ends. Each of said pair of flanged members has an inside surface that interfaces with a corresponding end face of said liner.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined by the below-mentioned patent claims.

Claims

Patent claims

1. An electromagnetic flowmeter (10) interposable between flanged ends (18,20) of upstream and downstream pipes (14,16) and carrying a fluid whose flow rate is to be measured, said flowmeter (10) comprising: - a measurement tube (12) having an inner surface (46) defining a passage for carrying said fluid along a longitudinal axis (15), - a liner (40) disposed on said inner surface (46) of said measurement tube (12) along a portion of the length of said measurement tube (12) and ending short of upstream and downstream ends (17, 19) of said measurement tube (12), and - a pair of flanged members (22,24) for coupling said measurement tube (12) with respective flanged ends

(18,20) of upstream and downstream pipes (14,16), each of said pair of flanged members (22,24) having an inside surface (52,54) that interfaces with a corresponding end face (48, 50) of said liner (40) .

2. The flowmeter (10) according to claim 1, wherein said liner (40) is made of a fluor plastic material.

3. The flowmeter (10) according to any of the preceding claims, further comprising an annular seal (36,38) interposed between a flanged member (22,24), of said pair of flanged members (22,24), and the respective flanged end (18, 20) .

4. The flowmeter (10) according claim 3, wherein said seal

(36,38) is made of nitrile butadiene rubber (NBR) or hydrogenated nitrile butadiene rubber (HNBR) or ethylene propylene diene M-class (EPDM) rubber.

5. The flowmeter (10) according to any of the preceding claims, wherein said flanged members (22,24) are made of a metallic material.

6. The flowmeter (10) according to claim 5, wherein said flanged members (22,24) are welded to said measurement tube (12) .

7. The flowmeter (10) according to any of the preceding claims, further comprising a mesh structure (42) disposed within said liner (40) .

8. The flowmeter (10) according to any of the preceding claims, wherein said liner (40) has a reduced thickness towards said end face (48,50) .

9. A method of manufacturing an electromagnetic flowmeter (10), comprising: - making a measurement tube (12) having an inner surface (46) defining a passage for carrying a fluid whose flow rate is to be measured,

- disposing a liner (40) on said inner surface (46) of said measurement tube (12) along a portion of the length of said measurement tube (12) such that said liner (40) ends short of upstream and downstream ends (17,19) of said measurement tube (12), and

- disposing a pair of flanged members (22,24) on said measurement tube (14), said pair of flanged members (22,24) adapted for coupling said measurement tube

(12) with respective flanged ends (18,20) of upstream and downstream pipes (14,16), each of said pair of flanged members (22,24) being provided with an inside surface (52,54) that interfaces with a corresponding end face (48,50) of said liner (40) .

10. The method according to claim 9, wherein disposing said liner (40) on said inner surface (46) of said measurement tube (12) comprises molding of said liner (40) through an electrode hole (44) provided on said measurement tube (12) .

11. The method according to any of claims 9 and 10, wherein said liner (40) is made of a fluor plastic material.

12. The method according to any of claims 9 to 11, wherein disposing said flanged members (22,24) on said measurement tube (12) comprises welding said flanged members (22,24) to said measurement tube (12) .

13. The method according to any of claims 9 to 12, further comprising disposing a mesh structure (42) within said liner (40) .

14. The method according to any of claims 9 to 13, comprising providing a reduced thickness to said liner (40) towards said end face (48,50) .

15. The method according to any of claims 9 to 14, further comprising interposing said flowmeter (10) between said flanged ends (18,20) of said upstream and downstream pipes (14,16) .

16. The method according to claim 15, further comprising interposing an annular seal (36,38) between a flanged member (22,24), of said pair of flanged members (22,24), and the respective flanged end (18,20) .

17. The method according to claim 16, wherein said seal (36,38) is made of nitrile butadiene rubber (NBR) or hydrogenated nitrile butadiene rubber (HNBR) or ethylene propylene diene M-class (EPDM) rubber.