GB2402219A

GB2402219A - Electromagnetic flow meter

Info

Publication number: GB2402219A
Application number: GB0312404A
Authority: GB
Inventors: Philip Stafford
Original assignee: ABB Ltd Great Britain
Current assignee: ABB Ltd Great Britain
Priority date: 2003-05-29
Filing date: 2003-05-29
Publication date: 2004-12-01
Anticipated expiration: 2023-05-29
Also published as: GB2402219B; GB0312404D0

Abstract

An electromagnetic flow meter for measuring flow rate of a fluid passing therethrough comprises a polymeric conduit (12) defining a fluid inlet (16), a fluid outlet (18) and a central bore (14) for passage of the fluid. The flow meter also comprises coil means for generating a magnetic field in the bore and electrode means for detecting induced electrical potential due to the fluid passage. A non-magnetic metal reinforcing, preferably holed, element (34) surrounds the bore to reinforce the polymeric conduit to prevent it from deforming due to pressure of the fluid. The element (34) may be moulded into the conduit. The use of such a polymer material is cheaper and lighter than conventional materials.

Description

ELECTROMAGNETIC FLOW METER

The present invention relates to flow meters and in particular to electromagnetic flow meters and the manufacture thereof. However, it will be appreciated that the invention is not limited to this particular field of use.

Electromagnetic flow meters, and their modes of operation, are well known.

In use, an electromagnetic field is generated whose lines of flux are mutually to perpendicular to the longitudinal axis of the flow tube through which the fluid to be metered is conducted and to the transverse axis along which the electrodes are located at diametrically-opposed positions with respect to the tube. The operating principles are based on Faraday's law of induction, which states that the voltage induced across any conductor as it moves at right angles through a magnetic field is will be proportional to the velocity of that conductor. The metered fluid effectively constitutes a series of fluid conductors moving through the magnetic field; the more rapid the rate of flow, the greater the instantaneous values of the voltage established at the electrodes.

Electromagnetic flow metering is a mature and robust technology and works to reliably once installed into a pipeline or the like. The cost of electromagnetic flow meters is relatively high, however, mainly due to the type of materials used in their construction and necessarily high labour costs.

Materials for construction for electromagnetic flow meters must be robust enough to withstand pressures applied by the fluids that flow therethrough without deformation. Steel is typically used. Polymers are not normally suitable as they may not be sufficiently dimensionally stable under pressure to ensure accurate readings and are prone to plastic deformation under high pressure.

An example of an electromagnetic flow meter is provided in US Patent Number 5458003.

It is an object of at least the preferred embodiment of the present invention to provide at least a useful alternative to the electromagnetic flow meters of the prior art.

According to the invention there is provided an electromagnetic flow meterfor measuring flow rate of a fluid passing therethrough, the electromagnetic flow meter comprising: a polymeric conduit defining a fluid inlet, a fluid outlet and a central bore therethrough for passage of the fluid;

means for generating a magnetic field in the bore;

means for detecting electrical potential of the fluid passing through the bore; and a reinforcing, non-magnetic, metal element substantially surrounding the to bore.

An advantage of the present invention is that the presence of the reinforcing metal element allows the conduit of the electromagnetic flow meter to be manufactured predominantly from a material which may not otherwise sufficiently resist deformation. It also preferably provides electrical screening which helps in measuring the small electrical potential in the presence of electrical noise. The total mass of the assembly may be less than a conventional solid metal meter, however.

Advantageously the metal element substantially prevents the conduit from deformation by the fluid acting on the conduit, and, having a low magnetic susceptibility, does not substantially affect the measurement of electrical potential so (references to "non-magnetic" includes that the material is not "ferro-magnetic").

Preferably, the metal element is holed. Preferably the metal element comprises a perforated sidewall. Alternatively the metal element is a mesh. The metal element being perforated, or at least mesh, means that the resulting electromagnetic flow meter is lighter and cheaper to manufacture than if a solid walled cylindrical metal element were employed.

Preferably the reinforcing metal element is substantially cylindrical. Also preferably, the reinforcing metal element is substantially circular in cross section.

Preferably, the metal element comprises stainless steel. Stainless steel has a low magnetic susceptibility and so would not affect the electrical potential so measurement of the flow meter. Also, stainless steel is highly resistant to corrosion in most applications. Therefore, if exposed in any part in the bore (or more typically - 3 outside the bore), the stainless steel reinforcing metal element would resist corrosion by the fluid passing therethrough. Also, stainless steel mesh or cylinders are readily obtainable to various specifications. In alternative embodiments, the metal element comprises aluminium.

s Preferably the metal element is moulded wholly within the conduit. Such a configuration of the flow electrode would ensure the metal element would not come into contact with the fluid flowing through the flow meter or the exterior.

Alternatively, the metal element may be partially exposed (at the exterior of the conduit) or partially embedded in the conduit.

to Preferably the conduit is moulded from any one of polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene (ETFE), polypropylene (PP), polyvinylchloride (PVC), polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS), polyethylene (PE), polybutylene terephtalate (PBT), polyoxymethylene (POM), polyphenylene sulphide (PPS) polyetherether ketone (PEEK), high density Is polyethylene (HOPE) or polyvinilidene difluoride (PVDF).

Preferably the detecting means includes electrodes moulded in the conduit.

In the specification and claims, the term "holed" is to mean having "holes", the holes being formed by the following non-limiting examples: perforating; moulding; stamping; drilling; piercing; pitting; etc. and are not limited to being circular to or regular in shape. Alternatively, the "holes" may be defined by spaces surrounded by interlaced or interwoven wires, such as mesh, for example. A plurality of the "holes" may be of different respective dimensions, and in a regular or irregular array.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings where like numerals as denote like parts, in which: Figure 1 is a plan view an electromagnetic flow meter in accordance with the present invention; Figure 2 is a cross-sectional side elevation of the meter illustrated in Figure 1, taken on line A-A; so Figure 3 is a cross-sectional end elevation of the electrode illustrated in Figure 1, taken on line B-B; and - 4 Figure 4 is a perspective view of an embodiment of a reinforcing metal holed element for use with the present invention.

Referring to Figures 1 to 3 a preferred embodiment of the present invention is an electromagnetic flow meter 10 for measuring flow rate of a fluid passing therethrough. The flow meter 10 has a conduit 12 formed from a polymer such as PTFE, ETFE, PP, PVC, PET, ABS, HOPE, PE, PBT, POM, PPS, PEEK, PVDF, or other appropriate polymers. The type of polymer used will depend on the application. For example, PP would not be used in applications where chlorine is present, since chlorine chemically attacks polypropylene.

to The conduit 12 has a passage therethrough in the form of a central bore 14 for the passing of the fluid. The central bore 14 defines a fluid inlet end 16 and a fluid outlet end 18 and is itself defined by an inner wall 19 of the conduit 12. Means in the form of electrodes 20 for detecting electrical potential of the fluid passing through the central bore 14, using known methods, are located in the conduit 12. As illustrated in Figure 3, there are also earthing electrodes 21 in the presently described embodiment of the invention, though more or larger electrodes 20 may be used depending on the application of the electromagnetic flow meter, or the diameterof its bore 14. For example, if the bore 14 is relatively large orthe fluid has relatively low conductivity, additional or larger electrodes may be employed.

so At either end 16 and 18 of the conduit 12, mounting plates 22 and end pieces 24 are mounted to enable the meter 10 to be mounted between flanges of an existing pipe (not shown) in the usual manner. End pieces 24 are usually formed from the same material as the conduit 12, but may be formed from a different material, e.g. ABS, and bonded onto the conduit 12 by adhesives or by welding.

The mounting plates 22 are then held captively on the outside of the conduit 12 between respective end piece flanges 26 and coil assembly flanges 28. The coil assembly flanges 28 define a coil volume 30 for housing coils 31 for generating a magnetic field across the bore as described above. An outer cover 32 is fixably mounted to the coil assembly flanges 28 to seal the coil volume 30.

In an alternative embodiment, rather than using end pieces 24 and mounting plates 22, socket type joints are formed in respective ends 16 and 18 of the body to - 5 mount the meter 10 to existing pipes. Depending on material used, the socket type joints are either electro fusion bonded, bonded with adhesives or clamped as with a rubber ring joint (RRJ).

A reinforcing, non-magnetic, metal element in the form of a metal perforate cylinder 34 is moulded in this embodiment wholly within the conduit 12 and substantially prevents the conduit 12 from deforming when acted upon by the fluid passing through the bore 14. In this embodiment, the metal perforate cylinder 34, as illustrated in Figure 4, is made from stainless steel and thus has a low magnetic susceptibility such that it does not substantially affect the generation of the field in JO the bore but serves to screen the electrodes 20 from external electrical noise.

The cylinder 34 having a cylindrical wall is a further advantage of the embodiment. Pressure of the fluid passing through the bore 14 is substantially evenly applied to the inner wall 19 of the conduit 12. Therefore, the cylinder's 34 cylindrical form ensures even reinforcing pressure is applied by the cylinder on the is conduit 12 about the bore 14, providing structural stability to the electromagnetic flow meter.

The diameter of the cylinder 34 will depend on the diameter of the bore 14 though being of larger relative diameter. Typical bore 14 diameter range is from 2mm to 2m, though is not limited to this range.

JO The metal cylinder 34 has a plurality of circular perforate holes 35 through its cylindrical wall, being formed by punching, moulding, or other known methods. The cylinder 34 also has a stud (not shown) attached for earthing.

In the example of the cylinder 34 illustrated in Figure 4, the cylindrical wall is approximately 1 mm thick, the diameter of the cylinder 34 is 100mm, the holes are of 4mm diameter and the centres of adjacent holes are 8mm apart. Alternatively, the array of holes may be configured such that edges of adjacent holes are relatively closer, separated by no less than approximately 1 mm.

The cylinder 34 may be formed from a flat sheet of stainless steel, which is then perforated as desired, and formed into a cylinder. In an alternative JO embodiment, the reinforcing metal element includes a partial cylindrical wall such that it does not fully surround the central bore 14. - 6

In manufacturing the conduit 12, a mould is used in which to mould the conduit shape, using known moulding methods. Prior to injecting the polymer into the mould, the metal cylinder 34 is placed in the mould and held apart from mould walls by spacers 36. Molten polymer is then injected into the mould to form the conduit 12. Once the conduit 12 is removed from the mould the conduit incorporates the spacers 36 as well as the metal cylinder 34. It is preferred that the cylinder 34 is holed, since, in the moulding process, the polymer of the conduit 12 can form more integrally with the cylinder 34, wherein the polymer forms in and through the holes 35. Being holed also results in a relatively lighter and cheaper lo meter 10.

An alternative embodiment of the metal holed element is a cylindrical woven wire mesh construction. The dimensions of the mesh wire and relative spaces defined by the mesh are optimised to ensure little or no interference with the field generation and sensing operation of the electrodes. Furthermore, being mesh rather than solid walled results in a flow meter 10 of relatively reduced weight, improving the transportability of the flow meter 10.

The holes in the mesh may be formed in a square, diamond, hexagonal, or other suitable pattern. The wire thickness will usually be 1 mm, and spaced 4mm maximum from an adjacent wire defining the square, diamond, hexagon, etc. shape.

to Wire thickness may alternatively be of different diameters, eg 0.2mm5mm.

As stated above, the method of operation of electromagnetic flow meters such as the flow meter 10 of the present embodiment is well known. Fluid for which the flow rate is to be measured flows along the pipe to which the meter 10 is connected, enters the meter 10 via the fluid inlet end 16 and exits via the fluid outlet end 18. The fluid may be, for example, potable or waste water, processed chemicals, etc. Depending on the flow conditions, the fluid typically exerts substantial positive pressure on the conduit's inner wall 19. Due to the material used to manufacture the conduit 12, normal operating pressures exerted on the inner wall 19 may be in the range to cause elastic or plastic deformation of the :o conduit 12, given the polymer from which it is manufactured. However, the metal cylinder 34 acts to reinforce the conduit 12 to substantially prevent deformation - 7 thereof. Due to the presence of the metal cylinder 34, conduit walls may be relatively thinner than would otherwise be required thus reducing the mass of material and overall size. Furthermore, since the conduit can be made from a simple plastic moulding procedure, manufacturing is simplified.

While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made to the invention without departing from its scope as defined by the appended claims.

Each feature disclosed in this specification (which term includes the claims) lo and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here as part of the

specification.

An electromagnetic flow meter is disclosed for measuring flow rate of a fluid Is passing therethrough. The flow meter comprises a polymeric conduit defining a fluid inlet, a fluid outlet and a central bore therethrough for passage of the fluid. The flow meter also comprises means for generating a magnetic field in the bore and means for detecting electrical potential of the fluid passing through the bore. A reinforcing, non-magnetic, metal, preferably holed, element substantially surrounds the bore. - 8

Claims

Claims 1. An electromagnetic flow meter for measuring flow rate of a

fluid passing therethrough, the electromagnetic flow meter comprising: a polymeric conduit defining a fluid inlet, a fluid outlet and a central s bore therethrough for passage of the fluid;

means for generating a magnetic field in the bore;

means for detecting electrical potential of the fluid passing through the bore; and a reinforcing, non-magnetic, metal element substantially surrounding to the bore.
2. The flow meter of claim 1 wherein the metal element is holed.
3. The flow meter of claim 1 or 2 wherein the reinforcing metal element comprises a perforated sidewall.
4. The flow meter of claim 1 or 2 wherein the reinforcing metal element is a metal mesh.
5. The flow meter of any preceding claim wherein the reinforcing metal element is substantially cylindrical.
6. The flow meter of any preceding claim wherein the reinforcing metal element comprises stainless steel.
7. The flow meter of any of claims 1 to 5 wherein the metal element comprises aluminum.
8. The flow meter of any preceding claim wherein the bore and the metal JO element are cylindrical and co-axial. - 9 -
9. The flow meter of any preceding claim wherein the metal element is at least partially within the polymeric conduit.
10. The flow meter of any preceding claim wherein the metal element is wholly s within the conduit.
11. The flow meter of any preceding claim wherein the conduit is moulded from any one or more of polytetrafluoroethylene, ethylenetetrafluoroethylene, polypropylene, polyvinylchloride, polyethylene terephthalate, acrylonitrile to butadiene styrene, polyethylene, high density polyethylene, polyvinilidene difluoride, polybutylene terephtalate, polyoxymethylene, polyphenylene sulphide or polyetherether ketone.
12. The flow meter of any preceding claim wherein the detecting means includes electrodes moulded in the conduit.
13. An electromagnetic flow meter substantially as herein described with reference to the accompanying drawings.