ELECTROMAGNETIC FLOWMETERS<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> TECHNICAL FIELD formeasurementofconductiveliquidflowinclosedconduits,areElec tromagneticflowmeters, described in the specification of Hritish Standard BS 5792: Part 1 : 1993 (ISO 6817 : 1992). In that specification an electromagnetic flowmeter is defined as a"fiowmercr which creates a magnetic field perpendicular to the flew. so enabling the fiow-rate to be deduced from the induced electromotive force bythemotionofaconductingliquidinthemagneticfield.Theelectrom agneticflowmeter(e.m.f.)produced aprimarydeviceandoneormoresecondarydevices."Asdescribedinthe specification,theconsistsof primary device usually comprises sn electrically-insulated meter tube through which the conductive liquid to be metered. flows. one or more pairs of electrodes, diametrically opposed, across which the signal generated in the liquid is measurd, and an electromagnet for producing a magnetic field in the meter tube. The secondary device comprises circuitry for receiving and amplifying the"flow signal", thar part of the potentat difference between the electrodes (called the"electrode signal") that is generated by the movement of the liquid.

BACKGROUND ART.

A typical primary device, for example as illustrated in the said British Standard, is of massive construction with the electromagnet formed by an iron core comprising opposed pole pieces each surrounded by one or more saddle-shaped coils which seat upon the meter tube. the pole pieces being bolted to two arcuate core parts which hold the pole pieces: n position and complete the magnetic circuit. The meter tube, which must be non-magnetic so as not to interfere with the magnetic Geld and electrically-insulating or insulated at least between the electrodes so as to avoid short-circuiting the electrode signal, may be made wholly of electrically-insulating material which will not be attacked by or react with the liquid to be metered such as glass, ceramic or plastics, or it may be made of non-magnetic metal such as aluminium with electrical insulation surrounding the electrodes. A non-metallic meter tube may be sheathed in metal for strength.

In our P. C. T. Patent Application No. PCT/GB97/01126 we have described an electromagnet for an electromagnetic flowmeter comprising a ferromagnetic core in the shape of a substantially closed figure with confronting inwardlv-directed poles defining between them a field area in which the meter tube is to be located and at least one electricallv-conducting coil surrounding a part of the ferromagnetic core, the coi' having means for connection to an electric current source for generating a magnetic field in the field area and around the core between the poles and the electromagnet being characterized in that the opposite faces of the ferromagnetic core are substantially flat and parallel and only a root part of one of the poles is surrounded by a coil.

We explained in our said Application that by a root part of the pole we mean a part away from the free end of the pole. towards iLS juncsion with the substantially closed figure. It is not essential that the coil extends right up to that junction. it is sufficient that a significant tip pan of the pole extends free of the coi3. The other pole is preferably not surrounded by a coil, but if it is that should also be around a root part of the pole, leaving a significant tip part free. This enables a screening element or flange member to be positioned close to each of the said opposite faces of the core, surrounding the axis of the meter tube and of size such as to overlie the tip parts of the poles and adjacent parts of the substantially closed figure to screen the field area against spurious interfering fields for example electromagnetic fields, directed at acute angles to the axis of the meter tube. These screening or flange members are preferably coaxial with the meter tube and may be pipe unions for connecting the meter tube into a pipeline carrying the liquid whose flow is to be metered or parts of such pipe unions. The ferromagnetic core itself screens the field area and the meter tube against spurious fields directed substantially perpendicular to the axis of the meter tube. The meter tube preferably has end flanges which are precisely spaced to fit against the opposite faces of the core and are overlain by he screening element or flange members. This enables the assembly to be clamped tightly together without causing mechanical damage to or distortion of the meter tube.

The present invention is particularly but not exclusively applicable to electromagnetic Oowmcters as described in the above-mentioned Application. Whilst the efficient screening of the field area and the meter tube against spurious interfering fields which is provided in those flowmeters as described above is important for obtaining accurate How measurements, it is known that the accuracy of a magnetic flowmeter can also be affecte by eddy currents in the core or cores of the electromagnet and by potential differences between parts of a pipeline in which it is connected. The present invention aims to reduce or eliminare those sources of error and also provides an electromagnetic Sowmeter in unitary form, ready for mechanical connection in a pipeline or conduit in which the flow of a liquid is to be measured and electrical connection to indicating or recording means to provide an immediate indication of flow rate through the meter tube.

DISCLOSURE OF THE INVENTION.

According to this invention an electromagnet for an electromagnetic flowmeter is substantially wholly encapsu ated in a casing of moulded plastics material and has terminaLs outside the casing which are electrically connected through the casing to components to or from which electrical signals may be required to be supplied or received.

Further according to the invention a primary device for an electromagnetic flowmeter comprises an electromagnet and a meter tube located between the poles of the electromagnet with electrodes in the meter tube and the primary device is substantially wholly encapsulated in a casing of thermally moulded plastics s material and terminas outside the casing are electrically connected through the casing to components to or electricalsignalsmayberequiredtobesuppliedorreceived.fromwhi ch

PRIOR ART.

It has previously been proposed to enclose the magnetic components of electromagnetic Sowmeters, and sometimes also electrical components and connections, in moulded insulating material. Such propos. ils are described, for example. in the following Patent Specifications: GB 2289514A, GB 2059066A, GB 1072521, GB 877396, US 4774844, US 4567775, US 4098118 and US 4065965, In most of these prior Specifications the insulating materials described are cast around the components of the flowmeters when cold. Most commonly they are epoxy resins which were pourable when cold and cross-linked by catairic action after pouring to form a solid body. For example US 4774844 mentions Palmer chocktite, 3M-5064 and Master r Bond 36 SP A-3. GE 1072521 mentions cement, concrete, synthetic rests or cold pouring rubber. An. n alternative approach described in GB 2289514 uses field coils which are embedded in a flexible liner formed for example of resin-impregnated fabric which is inserted into a pipe, expanded to St the pipe and then hardened by heat or catalyst.

The cold cast bodies of insulating materials described in most of the aforementiored prior Specifications are enclosed in rigid casings, usually of metal, which serve as moulds for the insulting materials during casting. Only in US 4774844 are outer and/or inner moulus not present in the finished primary device and the cold cast body forms the outer surface of the primary device as wel as the meter tube though which the liquid to be metred is caused to slow. However, the Specification describes a problem of cracking due to differential expansion coefficients of the metal frame on which the coils and electrodes are mounted and the encapsulating insulating material. To avoid that problem the metal frame is coated with a thin laver of elastomeric material before casting the insulating material. A prior coating with adhesive may bc necessaw, The cold cast bodies suffer from several other defects. Limitations are imposed by the relatively low duty temperatures of the epoxy resin insulating materials. The ability of such materials to be filied with beneficial materials such as mineral particles and fibres to impart useful characteristics is well-known but due to the nature of the process it is difficult to produce consistent dispersal of the filling materials. Further disadvantages are the high cost of the resins: the long curing time, typically of several hours; the release of solvents during cross-linking and poor mechanical properties such as brittleness and low strength.

MORE DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS.

In contrast, by using thermally moulded plastics materials for encapsulation, either thermoplastic or thermosetting types, these problems are eliminated. The materials are generally lower in cost than cold casting materials and more environmentally-friendly as no solvents are released and thermoplastic types can readily be recycled. Mechanical properties are generally superior, particularly with thermosetting plastics. <BR> <BR> <BR> <BR> duetothehighmoulding[prnperaiures,typicallyaround200degreesC elsius,therma'stabilityinserviceis due to the high moulding temperatures, typically around 200 degrees Celsius, thermal stability in service is far superior to that of cold cast materials.

beverydifficultorimposssibletousethermallymouldedplasticsmat erialswithflowmeterItwould assembles such as those described in the aforementioned prior Specifications because of the very high pressures and temperatures involved in the moulding injecte into moulds, which would cause damage if special precautions were not taken.

The present invention enables a flowmeter to be produced quickly by moulding with magnetic and electrical components located as inserts in the mould. The meter tube may be an integral part of the casing or a separate component. It can be an integral moulded part if the material of the casing is appropriate also to form the meter tube, which will depend inter alia on the kind of liquid which is to flow through the meter tube. Preferably it is a separate component which is located as an insert Ln the mould with other components so that when moulding is complete it rits the remainder of the casing without any significant gap. In a prefened construction the electromagnet and the meter tube are as described in our afore-mentioned Application, with end flanges which fit close against the opposite flat faces of the poles and adjacent parts of the substantially closed figure and are substantially covered by parts of the casing. Those parts of the casing also preferably have substantially flat and parallel opposite outer faces to be overlain by screening elements or flange members as previously mentioned when the meter is assembled in a pipeline or conduit. The casing is preferably moulded around the electromagnet and the meter tube in plastics material.

If the meter tube is formed integrally with the casing, electrodes which are to be exposed in its inner wall are arranged in the mould together with their electrical connections to the relevant terminal so as to be secured in position by the moulding operation.

The electrical connections from the terminals through the casing may include circuitry enclosed within the casing for processing signals supplied to or received from components of the flowmeter. Indeed, the whole secondary device may be enclosed within the casing, with only the terminas exposed ready for connection to current source and recording andlor indicating devices. To protect the connections from the electrodes to the terminals from damage during moulding they may be led through a bore in the ferromagnetic core.

When the casing has flat and parallel opposite faces over the ends of the meter tube, or if end flans of the meter tube are exposed outside the casing, the Gowmeter can be connected into a pipeline or conduit in which liquid flow is to be measured by flanged pipe unions. If the flanges are of suitable material and overlie the tip parts of the poles and adwacent parts of the electromagnet they will provide the desired screening against spurious interfering fields, for example electromagnetic fields, directed at acute angles to the axis of the meter tube. Otherwise separate screening or flange members may be required as previously described. The Sowmeter referabl, has bores to receive boits or other clamping means for securing it between the pipe unions or screening or flange members. If the bores also pass through the core of the arelinedwithportionsofthenon-magneticelectrically-insulating casingwhichareelectromagnetthey

preferably integrally formed with the remainder of the casing by moulding so as to insulate the pipe unions xnd any other metallic components and metallic pipes connected to them from the elctromagnet. Sealing means ma be interposed between the opposite faces of the flowmeter and the pipe unions or screening or ifnecessary.flangemembers In its preferred form the invention thus provides an economically produced electromagnetic flowmeter which is an integral unit which can readily be connected into a pipeline or conduit in which liquid flow is to be measured. having continuous insulated surfaces of hot moulded plastics material from which project only terminals for connection to appropriate electrical supply and instrumentation to read and ! or record signals from the circuitry enclosed within the casing. The continuous insulated surfaces make the Qowmeter most suitable for applications in which hygiene is essential, such as for monitoring the flow of body fluids. in medical equipment or controlling in food production plant or water supply pipeline :-.

Embodiments of the invention are illustrated by wav of example by the accompanying drawings in which : Figure 1 Li an end elevation of s primary device for an electromagnetic flowmeter viewed in the direction of flow of a liquid to be metered. with its encapsulating casing of thermally moulded plastics material sectioned to reveal details of the device, Figure 2 is a side elevation of the device. sectioned on the line 11-11 in Figure 1, also showing Ranges for connecting the flowmeter in a pipeline and a bolt for securing it in position in relation to the fanges. and Figure 3 is a view similar to Figure 1 showing a secondant device connected to a primary device.

Figure 3a is a scrap view showing a part of a primary device with a modified casing.

Figure @ is an end elevation of another primary device-shown prior: o encapsulation.

Figure aplanoftheprimarydeviceshowninFigure4andis Figures 6 and 7 are a side view and plan respectively of the meter tube of the primary device shown in Figure 4.

The @primary device shown in Figure 1 is mainly as described in our afore-mendoned P. C. T. Patent Application, comprising an electromagnet having a ferromagnetic core 1 and a coil 2 with end terminals 3. 4 which can be connected to an electric current source for generating the required magnetic field. The core 1 is of a closed oblong rectangular shape comprising top and bottom limbs 5 and 6 of the rectangle which are joined by two side limbs 7. with confronting poles 8,9 directed inwardly from respective top and botiom limbs 5 and 6. The coil 2 surrounds a root part of the pole !.. which is longer than the pole 9 so as to accommodate the coil and leave s free tip pan. When the coil 2 is energized a magnetic field is generater' along the pole 8. ac:oss the field area defined berween the confronting poles to the pole 9 and bac long thr bottomlimbs5and6andthetwosidelimbs7.Theconfrontingtipsofthep oles8.9arecurvedtotopand

define the cylindrical field area in which a meter tube 10 is located and the opposite faces of the core 1 are flat and parallel at least in the region of the tip part of the pole 8, the pole 9 and adjacent parts of the bottom limb 6 and the side limbs 7 of the closed figure. The meter tube 10 is a true cylinder with outward end flanges 11 which are precisely spaced so that when the tube 10 is located in the field area they lie close against those flat faces of the core, as shown in Figure 2, the free tip part of the longer pole 8 and the whole of the shorter pole 9 fitting between the flanges 11. Two diametrically-opposed electrodes 12 are mounted in the middle of the wall of the true cylinder of the meter tube 10. When an electrically-conducting liquid flows along the meter tube and the coil 2 is energized, an e. m. f. is generated between the electrodes 12 which is proportional to the speed of flow.

The meter tube 10 with flanges 11 is a unitary moulding in plastics material such as polypropylene, with the electrodes 12 positioned as inserts in the mould. Alternative meter tubes could be of metal with the electrodes insulated from the metat and from each other. Such a meter tube could have an insulating lining penetrated by the electrodes. In yet another construction the meter tube could be an integral part of a thermally moulded plastics casing which substantially wholly encloses the primary device.

The primary device shown in Figures 1 and 2 includes a casing 13 which is moulded in a non- magnetic electrically-insulating thermoplastics material and covers almost all the surfaces of the core 1, enclosing the coils 2 and the meter tube 10. As shown, the cylinder of the meter tube 10 is slightly smaller in diameter than the field area defined by the curved tips of the poles 8,9 and is enclosed in a thin layer of the casing material which penetrates between the poles and the tube, but in other embodiments the tube may be a precise fit between the poles so that no casing material penetrates there. The flanges 11 of the meter tube 10 which lie close against the opposite faces of the core 1 are also covered by parts of the casing 13 which have flat and parallel outer faces 14. For mounting the flowmeter in a pipeline which is to carry the liquid to be metered, the core I has bores 15 perpendicular to the its faces and thus also perpendicular to the opposite faces 14. The bores are also lined with the thermoplastic material of the casing 13 and receive bolts 16 which pass through flanges 17 of pipe unions 18 which are formed from electrically-conductive metal. The flanges overlie the poles E, 9 and adjacent parts of the core I and screen the field area against spurious interfering fields. for example electromagnetic fields, directed at acute angles to the axis of the field area and the meter tube. O-ring seals 19 are located between the flat faces 14 of the casing and the Lange. 17.

In other constructions the casing 13 does not extend over the flanges 11 of the meter tube 10 so the 0-ring seals are clamped directly between the fanges t : and 17 or the seals may be omitted if the flanges are fitted to engage each other in sealing relation. If the meter tube has no end flanges the casing may extend over the whole of the opposite faces of the core. Such a meter tube may be inserted after the casing has been mouldedon the electromagnet.

terminals3,4areelectricallyconnectedtothecoll2throughthecasi ngandterminals20,21Theend <BR> zre elect'icallyconnectedthroughthecasingrespectivelytotheelectr odes12andthecoreI.Although thecore1bythecasing13,thepipeunions18areelectricallyconnecte dtogetherbytheboltsinsulatedfrom 16 if those are of conductive material or may be separately connected by a conductor (not shown budging the primary device.

The showninFigure3comprisesmostofthecomponentsdescribedinrelatio ntodevice Figures 1 and 2, which are indicated by corresponding reference numbers, bu ! differs in that a secondary electricalcircuit22,isalsoenclosedinthecasing13.Conductors23 ,24leadfromthecircuit22device,an to the end s of the coil 2 and conductors 25 and 26, respectively from the electrodes 12 and the core 1 lead to the circuit 22. The conductors are all inside the casing 13 and are wholly enclosed by it. Terminals 27 casingareconnectedthroughittothecircuit22andcanbeconnectedto appropriateexternaloutsidethe circuitry for providing the required electric power for the circuit 22 and for transferring electrical signals, for example indicating the liquid flow rate in the tube 10, ta an indicating or recording device. Figure 3 thus shows a complete flowmeter almost wholly enclosed in the casing material which can be installed in a pipeline between flanged pipe unions such as 18 which complete the screening of the field area.

Alternatively, separate screening elements of suirable material could be interposed between the casing 13 or the flanges 11 of the meter tube and pipe unions to overlie the tip parts of the poles 8,9 and adjacent parts of the core 1. Such separate screening elements could be enclosed within the casing and may have electrical connections to the circuit 22. Figure 3a shows a part of a primary device which is identical in all respects to that shown Ln Figure 3 except that instead of a separate meter tube 10 the part of the casing 13 between the poles 8 9 forms an integral meter tube or passage 28 for the liquid to be metered. In the production of this embodiment the electrodes themselves are located as inserts in the mould before moulding.

The primary device shown in Figures 4 and 5 likewise comprises most of the components described in relation to Figures I and 2, which are indicated by corresponding reference numbers, but differs in that a central bore 29 is formed in the pole 8 and thAe conductors 5 from the electrodes 12 are led through tEs bore 29 instead of alongside the side limbs 7 of the ferromagnetic core I. This protects them from damage or displacement during the moulding process due to the high pressure and velocity with which the thermoplastic material is injected into the mould. Figures 6 and 7 show the path of the conductors 25 from the end of the pole 8 to the electrodes 12. As shown in Figure 5, the other ends of these conductors 25 are connected to pins 30 and the ends of the ceil 2 are directly connected to pins 31. the pins 30 and 31 being inthemouldjointduringthemouldingprocess,furtherreducingthepo ssibilityofconvenientlytrapped movement of components during moulding. Those pins and an earth tab 21 are the only projections from the moulded outer surface of the finished Qowmetei.

!nalltheillustratedembodimentstheelectrorBagneticcote1isofsu bstantialconstructionandform:,s<BR> f_' ?..'YhiC VStIFCigidlIf !' SLI ;)rts the 2leterL'f' ? ; p,i ! ; iiS FPCC : OQt' 2SSC11_'i,'2, n, tH ; f CUl , :hViiit3 1S fFiia : j'.'

mounted on the pole 8, which is a centre limb of the frame. The frame is made of a ferrous and highly durable material that can wit. hstand the shock of moulding the casing 13 by injection, compression or transfer mould techniques. Thus in addition to acting as the main mechanical support holding all of the components rigidly in correct positions prior to and during moulding also performs the usual role of magnetic guide for the electromagnetic field produced by the coil 2.