Patent Description:
Electromagnetic flow meters (also referred to as "magnetic flow meters" or even "mag flow meters") are known.

Electromagnetic flow meters can use an electrode assembly comprising a silver chloride-coated silver electrode and a porous graphite plug through which water permeates from the flow channel to reach and come into contact with the silver chloride-coated silver electrode. The plug of graphite is used to protect the electrode. As described in <CIT>, a silver chloride/silver electrode can exhibit low noise energy at frequencies below <NUM>. Using silver electrodes can increase the cost of the flow meter. Furthermore, silver chloride may degrade over a period of time in water having a very low concentration of chloride ions, e.g., desalinised water.

Inert materials, such as gold and platinum, can be used as a low-noise electrode, but are even more expensive. Cheaper metals, however, tend to exhibit more noise and generate unpredictable voltages due to electrochemical reactions. Electrodes formed from electrically-conductive polymers have also been tried and reference is made to <CIT> and <CIT>.

<CIT> describes a magnetic flow meter having electrodes which can each include a silver chloride pellet and a silver pin. The electrodes can be held by graphite plugs. The flow meter may include a seal, such as an O-ring seal positioned between the electrodes and electrode caps.

According to a first aspect of the present invention there is provided an electrode assembly for an electromagnetic flow meter. The electrode assembly comprises a housing having a passage between first and second ends, an electrode comprising a plug (or "piece" or "block") of porous material (for example, which comprises or is formed from graphite, or any porous material predominately formed of carbon, or a porous material made with surfaces of electrochemically inert material such as gold or platinum or carbon) at least partially disposed within the passage proximate the first end and an electrically-conductive polymer connector at least partially disposed within the passage and in direct contact with the electrode (which may also serve as fluid-tight seal).

Using an electrically-conductive polymer connector (i.e., an electrically-conductive part or piece which can be used to provide an electrical connection to the electrode) can help to reduce or even avoid galvanic effects in the electrode-connector interface and, thus, aid reduction in electrical noise energy and/ or unwanted voltages.

The electrode may at least partially be disposed outside the passage, for example, extend or protrude from the passage. The electrically-conductive polymer connector may at least partially be disposed outside the passage, for example, extend or protrude from the passage.

The plug of porous material may include a blind-hole, e.g., a central blind-hole in a connector-facing end, which can help deformation of the electrically-conductive polymer connector and, thus, increase sealing. The plug of porous material may include one or more through-holes, e.g., a central through-hole, between its ends which can help increase wetting throughout the volume of the electrode.

The electrode may have a porosity of greater than or equal to <NUM>%, greater than or equal to <NUM>%, greater than or equal to <NUM>%, greater than or equal to <NUM>%, greater than or equal to <NUM>%, and less than or equal to <NUM>% and less than or equal to <NUM>%. The electrode may have a porosity of between <NUM> and <NUM>%, between <NUM>% and <NUM>% or between <NUM> and <NUM>%. Increasing porosity of the electrode, particularly a graphite electrode, can help to reduce noise.

A substantial number of pores in the electrode may have diameters in the range of <NUM> to <NUM>. Thus, the surface area provided by the electrode may lie in a range <NUM> to <NUM><NUM> per cm<NUM> of electrode. The surface area provided by the electrode may be greater than or equal to <NUM><NUM>g-<NUM>, greater than or equal to <NUM><NUM>g-<NUM> or greater than or equal to <NUM><NUM>g-<NUM> of electrode material. The density of the porous graphite electrode or the carbon-based porous electrode may be greater than or equal to <NUM> gcm-<NUM> and less than or equal to <NUM> gcm-<NUM>.

The electrode may have a volume greater than or equal to <NUM><NUM>, greater than or equal to <NUM><NUM>, greater than or equal to <NUM><NUM>, greater than or equal to <NUM><NUM>, greater than or equal to <NUM><NUM>, and less than or equal to <NUM>,<NUM><NUM>. The electrode may have a volume between <NUM><NUM> and <NUM>,<NUM><NUM>, between <NUM><NUM> and <NUM><NUM>, or between <NUM><NUM> and <NUM><NUM>. Increasing the volume of the electrode can reduce noise and increase measurement repeatability.

The noise density of a pair of electrodes at <NUM> may be less than or equal to 90nV/sqrt(Hz), or less than or equal 6onV/sqrt(Hz), or less than or equal <NUM> nV/sqrt(Hz). The noise density of a pair of electrodes at <NUM> may be greater than or equal to <NUM> nV/sqrt(Hz). The noise density of a pair of electrodes at <NUM> may be between <NUM> nV/sqrt(Hz) to <NUM> nV/sqrt(Hz).

A fluid-facing (or "front") face of the electrode (i.e., the face closest to the first end) may have a diameter greater than or equal to <NUM>, greater than or equal to <NUM>, greater than or equal to <NUM>, or greater than or equal to <NUM>. The electrode may have a diameter between <NUM> and <NUM> or between <NUM> and <NUM>.

The electrode may have a length (i.e., distance between the front face and back face) greater than or equal to <NUM>, greater than or equal to <NUM>, greater than or equal to <NUM>, greater than or equal to <NUM>, greater than or equal to <NUM>. The electrode may have a length between <NUM> and <NUM>, between <NUM> and <NUM>, or more between <NUM> and <NUM>.

The electrode may be insert-moulded or assembled in the housing, which may be a flow tube. The flow tube may have a nominal diameter ranging from DN15 to DN100 inclusive. The flow tube may have a nominal size ranging from <NUM> (⅝-inch nominal size) to <NUM> (<NUM>-inch nominal size) inclusive.

The electromagnetic meter may be a fiscal meter.

The electrode front face may be aligned with the inside face of the flow tube within ±<NUM>, or may be flush or sub flush by less than or equal to <NUM> with the inside face of the flow tube.

The electrically-conductive polymer connector may provide a seal disposed within the passage, interposed between the electrode and a further connector (which may comprise or be predominantly formed of a non-noble metal, such as copper or other transition metal, or an alloy comprising a non-noble metal, e.g., a transition metal), and is arranged to electrically connect the electrode and the further connector and to provide a fluid-tight seal in the passage between the electrode and the further connector.

The further connector may have a coating, for example, of a noble metal, such as gold. The thickness of the coating may be less than <NUM>, less than <NUM> or less than <NUM>. The thickness of the coating may be between <NUM> and <NUM> or between <NUM> and <NUM>.

The electrically-conductive polymer connector may be disposed within the passage in direct electrical contact with the electrode and the electrode assembly may further comprise a seal (such as an 'O'-ring which need not be electrically conductive) to provide a fluid-tight seal between the first end of the passage and a non-wetted section of the flow meter. The seal may be at least partially disposed around a length of the connector.

The electrically-conductive polymer connector may comprise or be predominantly formed from an elastomer. The electrically-conductive polymer connector may abut the electrode. The electrically-conductive polymer connector may abut the further connector. The electrically-conductive polymer connector may be compressed. The electrically-conductive polymer connector may be compressed against the electrode. The electrically-conductive polymer connector may be compressed between the electrode and the connector. The compression force may be at least <NUM> N. This can help to reduce contact resistance. The electrically-conductive polymer connector may comprise or be predominantly formed from a thermoset or thermoplastic or elastomer or a combination of the materials herein described. The electrically-conductive polymer connector may be adhered or moulded to the further connector.

The electrically-conductive polymer connector may be shaped so as to promote spreading in a transverse direction when compress in a direction along the passage. The electrically-conductive polymer connector may be arranged to withstand a pressure of at least <NUM> MPa. The electrically-conductive polymer connector may comprise or is predominantly formed from silicone. The electrically-conductive polymer connector may comprise or may be predominantly formed from ethylene propylene diene monomer rubber. The electrically-conductive polymer connector may comprise particles of electrically-conductive material. The electrically-conductive material may be carbon. The electrically-conductive polymer connector may comprise carbon black. The electrically-conductive polymer connector may comprise carbon nanotubes. The electrically-conductive material may be silver. Resistance of the electrically-conductive polymer connector may be less than or equal to <NUM> kΩ, less than or equal to <NUM>Ω, or less than or equal to <NUM>Ω. Resistance of the electrically-conductive polymer connector may between <NUM> and <NUM> kΩ, between <NUM> and <NUM>Ω or between <NUM> and <NUM>Ω.

The electrically-conductive polymer connector may be seated in the electrode.

According to a second aspect of the present invention there is provided an electrode assembly for an electromagnetic flow meter. The electrode assembly may comprise a housing having a passage between first and second ends, an electrode disposed within the passage proximate the first end, a first connector (or "further connector") disposed within the passage, and an electrically-conductive polymer connector ( or "electrically-conductive polymer seal") disposed within the passage interposed between the electrode and the first connector and arranged to electrically connect the electrode and the first connector and to provide a fluid-tight seal in the passage between the electrode and the first connector.

According to a third aspect of the present invention there is provided an electromagnetic flow meter comprising a flow tube having a flow passage, first and second electrode assemblies of the first aspect disposed on opposite sides of the flow tube and arranged such that respective electrode are in fluid communication with the flow passage; and a magnetic field source for providing a magnetic field across the flow passage between the electrodes.

The first connector or the electrically-conductive polymer connector or may be directly connected to metrology circuitry. For example, the metrology circuitry may comprise a printed circuit board (PCB) and the connector may be mounted on the PCB. Alternatively, the first connector or the electrically-conductive polymer connector may be connected to the PCB by wire(s) or flexible circuit sheet(s) and may include a connector (e.g., plug and socket).

The flow tube may provide respective housings for the first and second electrode assemblies.

The magnetic field source may comprise a length of remanent magnetic material and a coil wound around at least a portion of the length of remanent magnetic material.

The electromagnetic flow meter may further comprise circuitry connected to the connectors arranged to perform a flow measurement.

According to a fourth aspect of the present invention there is provided a magnetic flow meter, which comprises at least one conductive polymer interconnect, at least two electrodes, a flow conduit, and a magnetic field source.

The conductive polymer may form an electrical interconnect with an electrode and a conductive metal. The conductive polymer interconnect may form a least part of the electrical interconnect between the conductive liquid to be measured and an electrical circuit. The compliant conductive material may abut the electrode. The conductive polymer interconnect may be compliant. The compliant conductive material may make a seal. The compliant conductive material may make a seal that stops the conductive liquid reaching one side of conductive polymer interconnect. The compliant conductive material may be compressed. The compliant conductive material may be compressed against an electrode. The compliant conductive polymer may be conductive rubber. The compliant conductive material may be compressed between an electrode and a conductive component. The compliant conductive polymer interconnect may be compressed and sized to enable a seal to be made which resists the flow meter's operational pressure. The compliant conductive material may be compressed and sized to enable a seal to be made which resists the flow meter's burst pressure requirement. The compliant conductive material may be compressed using a screw or using press operation and a "star lock" washer or any form of barbs, or plug retained by welding or heat staking or adhesive. The compliant conductive material may be compressed to a level which enables a seal to made but will maintain the integrity of the electrode. The electrode may be made from porous graphite.

Certain embodiments comprise an electrically conductive polymer that provides electrical continuity in addition it may provide a fluid tight seal between an electrode and the electronics in a magnetic flow meter.

Silver, silver-chloride electrodes which are used as electrodes with a porous graphite shielding plug in a magnetic flow water meter can be replaced with a cheaper graphite electrode and electrically-conductive polymer that can be injection moulded or transfer moulded or extruded or made from sheet or rod.

The application of magnetic flow water meters can be extended to water supplies with low chloride ion content, as this causes the performance of meters with silver, silver chloride pins to degrade.

Referring to <FIG>, a simplified view of an electromagnetic flow meter <NUM> is shown.

The flow meter <NUM> includes a flow tube <NUM> defining a flow passage <NUM> for a fluid <NUM> having a direction of flow <NUM> (in this case, along the x-axis), a magnetic field source in the form of a coil (not shown), first and second poles <NUM> for providing a transverse magnetic field <NUM> (in this case, along the z- axis) to the flow passage <NUM> from the coil (not shown) and a pair of electrodes <NUM> which face each other on opposite sides of the flow tube <NUM> and which are exposed to the flow passage <NUM> so as to be in contact with the fluid <NUM> when it flows through the flow passage. The electrodes <NUM> are arranged along a line <NUM> (in this case, along the y-axis) which is perpendicular to both the direction of flow <NUM> and the magnetic field <NUM>. The flow tube <NUM> comprises or is lined with an electrically-insulating material, such as a suitable plastic.

When an electrically-conductive fluid <NUM>, such as ion-containing water, a mixture of water and glycol, or other suitable fluid, flows through flow passage <NUM> and through the magnetic field <NUM>, an electromotive force (emf) is induced which can be measured by a circuitry <NUM> using the electrodes <NUM>. The emf is proportional to the velocity of the fluid <NUM>. Thus, the flow rate of the fluid <NUM> can be determined.

Referring to <FIG>, an electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The electrode assembly <NUM> comprises a housing <NUM>, which in this case takes the form of the flow tube <NUM> (<FIG>), having a passage <NUM> between first and second ends <NUM><NUM>, <NUM><NUM>. In other words, the passage <NUM> extends through the wall of the flow tube <NUM> (<FIG>) and the first end <NUM><NUM> opens to the inside of the flow tube <NUM> (<FIG>). The wall of the flow tube <NUM> may extend outwardly to provide a neck (or "tower") to accommodate the electrode assembly <NUM>.

The electrode assembly <NUM> comprises an electrode <NUM> (for providing the electrode <NUM> in <FIG>) in the form of a porous graphite plug (which may also be referred to as a "piece" or "block"), disposed within the passage <NUM> proximate the first end <NUM><NUM> of the passage <NUM>. The electrode <NUM> is generally cylindrical and has a front face diameter D1 of about <NUM> and a length L1 of about <NUM> to <NUM>. An inner section of the electrode <NUM> (i.e., the section proximate the first end of the passage) has a slightly smaller diameter than an outer section.

The electrode assembly <NUM> further comprises a first connector <NUM> (or "terminal") in the form of a metal pin, disposed within the passage proximate the second end of the passage <NUM> and an electrically-conductive polymer connector <NUM> (also referred to as an "electrically-conductive polymer seal") disposed within the passage <NUM>, interposed between the electrode <NUM> and the first connector <NUM> (which may also be referred to as a "further connector"). The further connector <NUM> may be made from brass or other relatively inexpensive conductive metal, such as copper, or metal alloy, but may have a surface coating of gold. The further connector <NUM> may be made from a conductive polymer. The electrically-conductive polymer seal <NUM> may be formed from an elastomer, such as silicone or ethylene propylene diene monomer (EPDM) rubber loaded, with particles of electrically-conductive material, such as carbon (for example, in the form of carbon black or carbon nanotubes) or silver (for example, in the form of silver flakes).

The electrically-conductive polymer seal <NUM> is arranged to electrically connect the electrode <NUM> and pin <NUM> and to provide a fluid-tight seal in the passage between the electrode <NUM> and pin <NUM>. The seal <NUM> is generally disc-shaped, having a diameter D2 of about <NUM> and a length L2 of about <NUM>.

The further connector <NUM> includes a disc portion <NUM><NUM> and a rod portion <NUM><NUM> upstanding from the centre of the disc portion <NUM><NUM> extending towards the second end <NUM><NUM> of the passage <NUM>. The electrically-conductive polymer seal <NUM> is compressed between an outwardly-facing face <NUM><NUM> of the electrode <NUM> and an inwardly-facing face <NUM> of the further connector <NUM>. A retainer <NUM> may be used to maintain physical contact between the electrode <NUM> and pin <NUM>. The electrode assembly <NUM> is formed by insert moulding of the electrode <NUM>.

The electrically-conductive polymer seal <NUM> is in direct electrical contact with the graphite electrode <NUM> and is in direct electrical contact with the further connector <NUM>.

In use, an inwardly-facing face <NUM><NUM> (or "front face") of the porous graphite electrode <NUM> is presented to the fluid <NUM>. The fluid <NUM> permeates throughout the porous graphite electrode <NUM> to make a good electrical contact with the large surface area provided by the porous graphite electrode <NUM> and the fluid <NUM> may reach the electrically-conductive polymer seal <NUM>. The fluid <NUM> is in good electrical contact with the large area provided by the porous graphite electrode <NUM> and the conductive polymer seal <NUM> make good electrical contact with the porous graphite electrode <NUM>.

Using a graphite electrode <NUM> can help to reduce the cost of the flow meter while maintaining performance. Furthermore, the electrode assembly can be used in a very low-conductivity fluid (e.g., < <NUM>µSm-<NUM>). Moreover, an 'O'-ring need not be used to prevent fluid from reaching metrology electronics in the register (not shown).

The electrode assembly <NUM> comprises a housing <NUM>, which in this case takes the form of the flow tube <NUM> (<FIG>), having a passage <NUM> between first and second ends <NUM><NUM>, <NUM><NUM>. In other words, the passage <NUM> extends through the wall of the flow tube <NUM> (<FIG>) and the first end <NUM><NUM> opens to the inside of the flow tube <NUM> (<FIG>).

The electrode assembly <NUM> comprises an electrode <NUM> in the form of a porous graphite plug, disposed within the passage <NUM> proximate the first end <NUM><NUM> of the passage <NUM>. The electrode <NUM> is generally cylindrical and has a front face diameter of about <NUM> and a length of about <NUM> to <NUM>. An inner section of the electrode <NUM> (i.e., the section proximate the first end of the passage) has a slightly smaller diameter than an outer section, and thus allows the electrode assembly to assembled after the housing <NUM> (i.e., flow tube) has been moulded.

The electrode assembly <NUM> further comprises a first connector <NUM> in the form of a metal pin, disposed within the passage <NUM> proximate the second end of the passage <NUM> and an electrically-conductive polymer connector <NUM> (also referred to as an "electrically-conductive polymer seal") disposed within the passage <NUM>, interposed between the electrode <NUM> and pin <NUM>. The first connector <NUM> (or "further connector") may be made from brass or other relatively inexpensive conductive metal or metal alloy. The further connector <NUM> may be made from a conductive polymer. The electrically-conductive polymer seal <NUM> may be formed from an elastomer, such as silicone or ethylene propylene diene monomer (EPDM) rubber loaded, with particles of electrically-conductive material, such as carbon (for example, in the form of carbon black or carbon nanotubes) or silver (for example, in the form of silver flakes).

The electrically-conductive polymer seal <NUM> is arranged to electrically connect the electrode <NUM> and pin <NUM> and to provide a fluid-tight seal in the passage between the electrode <NUM> and pin <NUM>. The seal <NUM> is generally disc-shaped, having a diameter of about <NUM> and a length of about <NUM>.

The further connector <NUM> includes a disc portion <NUM><NUM> and a rod portion <NUM><NUM> upstanding from the centre of the disc portion <NUM><NUM> extending towards the second end <NUM><NUM> of the passage <NUM>. The electrically-conductive polymer seal <NUM> is compressed between an outwardly-facing face <NUM><NUM> of the electrode <NUM> and an inwardly-facing face <NUM> of the further connector <NUM>.

A retainer <NUM>, in this case in the form of a starlock washer, may be used to maintain physical contact between the electrode <NUM>, seal <NUM> and further connector <NUM>. The electrode assembly <NUM> is assembled after the housing <NUM> (i.e., flow tube) has been moulded.

The wall of the flow tube <NUM> may extend outwardly to provide a neck <NUM> to accommodate the electrode assembly <NUM>.

In use, an inwardly-facing face <NUM><NUM> (or "front face") of the porous graphite electrode <NUM> is presented to the fluid <NUM>. The fluid <NUM> permeates throughout the porous graphite electrode <NUM> and may reach the electrically-conductive polymer seal <NUM>.

The fluid <NUM> is in good electrical contact with the large area provided by the porous graphite electrode and the conductive polymer seal <NUM> make good electrical contact with the porous graphite electrode <NUM>.

Using a graphite electrode can help to reduce the cost of the flow meter while maintaining performance. Furthermore, the assembly can be used in a very low-conductivity fluid (e.g., < <NUM>µSm-<NUM>). Moreover, an 'O'-ring need not be used to prevent fluid from reaching metrology electronics in the register (not shown).

Referring to <FIG>, a third electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The third electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that the electrode <NUM> has a blind-hole <NUM> in the centre of its outwardly-facing face <NUM><NUM>. The electrode <NUM> may have a through-hole instead of a blind-hole. This can help to increase compression of the seal <NUM>. The addition of the blind hole <NUM> in the electrode <NUM> provides more sealing compression or sealing band pressure between the seal <NUM> and the inside passage <NUM> (or "bore") for a given axial force applied by the further connector <NUM>.

This can help to increase sealing band pressure between the inside of the passage <NUM> (or "bore") and the seal <NUM>, thus enabling operation at potentially higher water pressures.

Other parts of the third electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so will not be described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a fourth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The fourth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that an outwardly-facing face <NUM><NUM> of the electrode <NUM> and the inwardly-facing face <NUM> of the disc portion <NUM><NUM> of the further connector <NUM> are dome-shaped (or "convex"). This can help to increase compression of the seal <NUM>.

The inwardly-facing face <NUM><NUM> of the electrode <NUM> is the same as the inwardly -facing face <NUM><NUM> (<FIG>) of the electrode <NUM> (<FIG>) of the electrode assembly <NUM> (<FIG>). Similarly, the rod portion <NUM><NUM> of the further connector <NUM> is the same as the rod portion <NUM><NUM> (<FIG>) of the further connector <NUM> (<FIG>) of the electrode assembly <NUM> (<FIG>).

Other parts of the fourth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so will not be described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a fifth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The fifth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that it includes a plug-like further connector <NUM> which is arranged to be seated in a cup-shaped seal <NUM> which includes a blind-hole <NUM> for accommodating a distal end portion <NUM><NUM> of the further connector <NUM> and which includes inner and outer circumferential ribs <NUM>, <NUM> and inner and outer central protrusions <NUM>, <NUM>. This can help to provide a radial seal.

Other parts of the fifth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so will not be described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a sixth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The sixth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that the seal <NUM> includes three outer circumferential ribs <NUM> (or "lobes") spaced apart in the direction of the passage. This can help to provide a radial seal.

Other parts of the sixth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so will not be described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a seventh electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The seventh electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that it includes an additional sleeve <NUM> for providing mechanical radial and/or axial stability to the pin <NUM> (i.e., the connector).

The starlock washer <NUM> may be omitted. When the sleeve <NUM> is used without the starlock washer <NUM>, it provides force for compressing the seal. The sleeve <NUM> may be retained by weld(s) (using ultrasonic or thermal welding) or an adhesive.

The sleeve <NUM> includes a through hole <NUM> (or "bore") having slightly larger diameter as the outer diameter of the rod portion <NUM><NUM> of the further connector <NUM>. The sleeve <NUM> includes a stepped outer surface <NUM> which corresponds to the stepped inner surface <NUM> of the passage <NUM>.

The other parts of the electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so will not be described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, an eighth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The eighth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that the connector is provided by a flexible printed circuit sheet <NUM> which is sandwiched between the seal <NUM> and a holding disc <NUM> which may be formed from electrically-insulating material. The flexible printed circuit sheet <NUM> passes through a slot <NUM> in the side wall of the neck <NUM> of the housing <NUM> through which the passage <NUM> passes.

The flexible printed circuit sheet <NUM> comprises a flexible electrically-insulating substrate formed from a suitable plastic, such as polyester, polyimide or PEEK, and one or more tracks (not shown) of metal or electrically-conductive polymer on the seal-facing face of the substrate.

The holding disc <NUM> comprises a main, flat portion <NUM><NUM> and a central boss <NUM><NUM> (or "stub") which can help positioning of the starlock washer <NUM>.

Other parts of the eighth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so are not described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a ninth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The ninth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that a flexible printed circuit sheet <NUM> is additionally provided which is connected to the further connector <NUM>. A conductive washer <NUM> having a flat face <NUM> and a conical face <NUM> can be used to help provide a larger area of attachment (e.g., by soldering) for the flexible printed circuit sheet <NUM> to the top <NUM><NUM> of the further connector <NUM>. The flexible printed circuit sheet <NUM> may be attached to the further connector <NUM> using conductive adhesive.

The further connector <NUM> may be formed of brass and may be gold-coated. However, the further connector <NUM> may formed of electrically-conductive polymer. If the further connector <NUM> is formed of an electrically-conductive polymer, then the seal <NUM> may be omitted and, thus, the connector <NUM> may directly contact the electrode <NUM> provided another seal is used elsewhere. In this arrangement, the further connector <NUM> is referred to as an "electrically-conductive polymer connector".

Other parts of the ninth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so are not described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a tenth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The tenth electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that a further connector <NUM> is used which accommodates an 'O'-ring <NUM> in a circumferential groove <NUM> around the disc portion <NUM><NUM>. A rod portion <NUM><NUM> extends away from the centre of the disc portion <NUM><NUM>.

The further connector <NUM> may be formed of brass and may be gold-coated. However, the further connector <NUM> may formed of an electrically-conductive polymer. If the further connector <NUM> is formed of electrically-conductive polymer, then the seal <NUM> may be omitted and, thus, the connector <NUM> may directly contact the electrode <NUM>. In this arrangement, the connector <NUM> is referred to as an "electrically-conductive polymer connector".

Other parts of the tenth electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so are not described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, an eleventh electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The eleventh electrode assembly <NUM> is the same as the electrode assembly <NUM> (<FIG>) except that an electrically-conductive polymer connector <NUM><NUM> (also referred to as an "electrically-conductive polymer seal") is used which has central blinds holes <NUM>, <NUM> (or "indentations") in inwardly- and outwardly-facing faces <NUM>, <NUM>, respectively. This can help to increase sealing band pressure between the inside of the passage <NUM> (or "bore") and the seal <NUM>, thus enabling operation at potentially higher water pressures.

Other parts of the eleventh electrode assembly <NUM> are the same as those of the electrode assembly <NUM> (<FIG>) and so are not described again. Like parts are denoted by like reference numerals.

Referring to <FIG>, a twelfth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The electrode assembly <NUM> comprises an electrode <NUM> in the form of a porous graphite plug, disposed within the passage <NUM> proximate the first end <NUM><NUM> of the passage <NUM>. The electrode <NUM> is generally cup-shaped and has a front face diameter of about <NUM> and a length of about <NUM> to <NUM>. An inner section of the electrode <NUM> (i.e., the section proximate the first end of the passage) has a slightly smaller diameter than an outer section, although it can be larger. The electrode <NUM> may be insert moulded or inserted after the housing is moulded.

The electrically-conductive polymer connector <NUM> is formed from a rigid, electrically-conductive polymer which is loaded with particles of electrically-conductive material, such as carbon (for example, in the form of carbon black or carbon nanotubes) or silver (for example, in the form of silver flakes).

The plug-like electrically-conductive polymer connector <NUM> is arranged to be seated in the cup-shaped electrode <NUM> which includes a blind-hole <NUM> for accommodating a distal end portion <NUM><NUM> of the electrically-conductive polymer connector <NUM>. The plug-like connector electrically-conductive polymer <NUM> may be press-fitted into the cup-shaped electrode <NUM>. The electrode <NUM> may have through-hole instead of a blind-hole.

The electrode assembly <NUM> further comprises an 'O'-ring <NUM> arranged around the shaft of the electrically-conductive polymer connector <NUM>. The O'-ring <NUM> may comprise an electrically- insulating elastomer material or may comprise an electrically-conductive elastomer material, such as silicone or EPDM rubber, loaded with particles of electrically-conductive material, such as carbon (for example, in the form of carbon black or carbon nanotubes) or silver (for example, in the form of silver flakes).

A retainer <NUM> may be used to maintain physical contact between the electrode <NUM>, and the electrically-conductive polymer connector <NUM>. The electrode assembly <NUM> is formed by insert moulding.

In use, an inwardly-facing face <NUM><NUM> (or "front face") of the porous graphite electrode <NUM> is presented to the fluid <NUM>. The fluid <NUM> permeates throughout electrode <NUM> to make a good electrical contact with the large surface area provided by the porous graphite electrode <NUM> and the fluid <NUM> may reach the electrically-conductive polymer connector <NUM>.

Using a graphite electrode <NUM> can help to reduce the cost of the flow meter. Furthermore, the electrode assembly can be used in a very low-conductivity fluid (e.g., < <NUM>µSm-<NUM>).

Referring to <FIG>, a thirteenth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The electrode assembly <NUM> comprises an electrode <NUM> in the form of a porous graphite plug, disposed within the passage <NUM> proximate the first end <NUM><NUM> of the passage <NUM>. The electrode <NUM> is generally cup-shaped and has a front face diameter of about <NUM> and a length of about <NUM> to <NUM>. An inner section <NUM><NUM> of the electrode <NUM> (i.e., the section proximate the first end of the passage) has a slightly smaller diameter than an outer section <NUM><NUM>, although it can be larger. The electrode <NUM> may be insert moulded or inserted after the housing is moulded. The electrode <NUM> includes a central blind hole <NUM>. The electrode <NUM> may have a through-hole instead of a blind hole.

The electrode assembly <NUM> further comprises a plug-like electrically-conductive polymer connector <NUM> in the form of a headed, electrically-conductive polymer pin having first, second and third sections <NUM><NUM>, <NUM><NUM>, <NUM><NUM>. The first and second sections <NUM><NUM>, <NUM><NUM> are disposed within the passage <NUM>. The third section <NUM><NUM> provides a head which is generally wider than the passage <NUM>.

An inward-facing surface <NUM> (or "underside") of the third section <NUM><NUM> and an outward-facing surface <NUM> (or "upper surface") of the housing <NUM> are correspondingly shaped and are arranged to form an annular face seal, e.g., using ultrasonic welding, adhesive etc. An 'O'-ring need not be used. A radial seal may be formed by ultrasonic welding, for example, between the second section <NUM><NUM> of the electrically-conductive polymer connector <NUM> and the housing <NUM>.

The first section <NUM><NUM> of the electrically-conductive polymer connector <NUM> is arranged to be seated in the blind-hole <NUM> of the cup-shaped electrode <NUM><NUM>. The electrically-conductive polymer connector <NUM> may be press-fitted into the cup-shaped electrode <NUM>.

Referring to <FIG>, a fourteenth electrode assembly <NUM> for use in the electromagnetic flow meter <NUM> (<FIG>) is shown.

The fourteenth electrode assembly <NUM> is the same as the thirteenth electrode assembly <NUM> (<FIG>) except that an 'O' ring <NUM> is used and is disposed in an annular groove <NUM> within the third section <NUM><NUM> of the electrically-conductive polymer connector <NUM>. A radial weld may be formed by ultrasonic welding for example between the second section <NUM><NUM> of the electrically-conductive polymer connector <NUM> and the housing <NUM>.

Other parts of the fourteenth electrode assembly <NUM> are the same as those of the thirteenth electrode assembly <NUM> (<FIG>) and so are not described again. Like parts are denoted by like reference numerals.

In the embodiments herein described, the electrode may be formed from porous graphite.

Referring to <FIG>, a plot of measured noise density exhibited by a pair of electrodes at <NUM> plotted as a function of the porosity of the pair of graphite electrodes is shown.

Spectral voltage noise density is measured using a PC-based data-acquisition system (not shown) in combination with an ultra-low-noise pre-amplifier (not shown). The electrode terminals are connected to the differential inputs of the preamplifier, which applies a gain of <NUM> to the voltage between the terminals, such that it can be readily digitised by the DAQ system with sufficient resolution. Using Welch's method, the spectral noise density is calculated from the acquired time-series. The results for <NUM> are plotted in <FIG>.

The intrinsic noise density of the pre-amplifier and acquisition system is sufficiently low that its contribution to the measured noise density for the electrode pairs can be neglected.

<FIG> shows that noise generally decreases as porosity of the graphite electrode increases.

Referring to <FIG>, a plot of the noise density exhibited by a pair of electrodes at <NUM> plotted as a function of the volume of the individual graphite electrode is shown.

<FIG> shows that noise density decreases as the volume of the graphite electrode increases. In the example shown, the noise density decreases substantially when the electrode volume increases above <NUM><NUM>.

Reducing the magnitude of the noise density of the electrodes is important at it is superimposed on the measured emf that is proportional to the flow velocity. Thus, a lower noise density reduces the time required to average-out any noise when taking a flow measurement. Therefore, a flowmeter with a large turn down ratio (e.g., <NUM> or higher) becomes viable to calibrate and use. In addition, it makes flowmeters with lower turn down ratios (e.g., <NUM> or lower) faster to calibrate in production and so lowers the productions cost.

The noise density of a pair of electrodes at <NUM> can be less than or equal to <NUM> nV/sqrt(Hz), or less than or equal <NUM> nV/sqrt(Hz), or less than or equal <NUM> nV/sqrt(Hz). The noise density of a pair of electrodes at <NUM> can be greater than or equal to <NUM> nV/sqrt(Hz).

It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of electromagnetic flow meters and component parts thereof and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Features of one embodiment may be used in another, different embodiment and vice versa, and modifications made to one embodiment can be made to another, different embodiment.

The electrodes herein described may have multiple holes and/or through holes and/or blind holes, and may be moulded in to a housing and/ or a flowtube or may be assembled into to a housing and/or a flowtube.

The connector may be formed of electrically-conductive polymer. If the connector is formed of an electrically-conductive polymer, then the electrically-conductive seal may be omitted and, thus, the connector may be in direct contact with the electrode.

Claim 1:
An electrode assembly for an electromagnetic flow meter, the electrode assembly comprising:
a housing (<NUM>) having a passage (<NUM>) between first and second ends (<NUM><NUM>, <NUM><NUM>);
an electrode (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) comprising a plug of porous material at least partially disposed within the passage proximate the first end; and
characterised by an electrically-conductive polymer connector (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) at least partially disposed within the passage and in direct contact with the electrode.