FIELD OF INVENTION

The invention relates to magnetic inductive flow meters and measurement tubes therefore, as well as methods for manufacturing such.

BACKGROUND

An example of a known magnetic inductive flow meter is found in the international patent application WO9309403A1.

Challenges with known magnetically inductive flow meters may include that they may be complicated to produce, especially if a high precision is desired. Moreover, when using a very strong magnetic field to obtain a high precision, this entails a high power consumption by the meter itself, which for battery powered meters leads to a shorter operable lifetime.

SUMMARY

The invention relates to a measuring tube for a magnetic inductive flow meter, the measuring tube comprising: a flow tube for carrying a flow of a conductive liquid to be measured, the flow tube having a flow tube wall with an inner wall surface and an outer wall surface, and - at least two metallic electrode elements, each electrode element being arranged in said wall, each electrode element comprising an electrode section having an inner electrode surface with an inner electrode surface area extending along said inner wall surface, and a feed through section having an outer cross section with an outer cross section area at the outer wall surface, the inner electrode surface area being greater than the outer cross section area, wherein the flow tube is a polymeric flow tube.

An advantage of the invention is that precise measurements of the flow rate may be obtained while preserving a very high degree of waterproofness of the flow meter. By using electrode elements having a greater inner wall surface than the cross sectional of the feed-through section a more accurate value of the induced voltage is facilitated while minimizing any leakage due to a combination of the smaller feed- through cross-sectional area and the use of a polymeric flow tube.

A further advantage of the invention is that the measuring tube for the magnetic inductive meter is relatively simple to produce. Thus, a simple-to-manufacture magnetic inductive flow meter having a combination of high measuring precision and effective waterproofness may be obtained. For example, by utilizing a polymeric flow tube, hermetically sealed interfaces between the flow tube walls and the feed-through sections may be obtained e.g. by means of insert molding.

In the present context, the term "electrode element" is understood as an electrode, which may be formed as one monolithic part, or alternatively as an assembly of two or more parts into one electrode element. The electrode section is arranged to collect an induced voltage by the magnetic field. The feed through section extends from the pick-up electrode section to the outside of the measuring tube, i.e. it establishes electrical connection between the electrode section and the outside of the measuring tube, where further electrical connections to the control system can be arranged. The term "metallic" refers to the fact that the electrode elements are formed substantially by metal, i.e. they consist essentially of metal. In this context, the term "metal" is understood as covering both essentially pure metals as well as mixtures thereof, i.e. alloys. While the electrode elements may in some embodiments be formed uniformly from the same material, the electrode elements may in other embodiments comprise zones of different materials, e.g. a bulk zone and a coating applied thereon. In the present context, the term "polymeric flow tube" is understood as a flow tube formed substantially from a polymeric material, i.e. a flow tube consisting substantially of a polymeric material. Suitable materials include, but are not limited to, polyphenylene sulfide (PPS), polyaryletherketone (PAEK), polyether ether ketone (PEEK), polyetherketoneketone (PEKK), polyoxymethylene (POM), or nylon materials. These materials may be in engineering grade or minimum moisture uptake grade.

Thus, when the flow tube is a polymeric flow tube, i.e. is formed by a polymeric material, without any metal casings tube etc., the flow tube is a pressure-carrying, polymeric flow tube. It should be understood that the flow tube is non-conductive.

In the present context, it should be understood that when the inner electrode surface with the inner electrode surface area extends along said inner wall surface, then the inner surface is oriented such that it is parallel with the flow direction, i.e. the longitudinal direction of the flow tube.

As used herein, the term "inner electrode surface" is intended to refer to an inner surface of the electrode section, i.e. the surface of the electrode section facing inwards. This surface may or may not be in direct contact with the liquid during use. Also, it should be understood that the macroscopic area is meant, rather than the microscopic area.

Also, it should be understood that no distinguishing is made when referring to the flow in the measuring tube and the flow in the flow tube, i.e. both terms are used interchangeably.

According to an advantageous embodiment of the invention the flow tube is a monolithic polymeric flow tube.

One advantage of the above embodiment may be that a simpler assembly of a magnetic inductive flow meter comprising the measuring tube is facilitated. Also, this may be done while keeping the measuring tube hermetically sealed, particularly around the electrode elements. This embodiment may be especially advantageous when the electrode elements are embedded in the flow tube walls by insert molding.

According to an advantageous embodiment of the invention the flow tube is a pressure-carrying flow tube, adapted to carry the pressure of the liquid flowing in the flow tube. One advantage of the above embodiment may be that a simpler assembly of a magnetic inductive flow meter comprising the measuring tube is facilitated, since a very simple measuring tube design may be used, e.g. without any metal tube parts or similar incorporated in the measuring tube.

According to an advantageous embodiment of the invention the flow tube is made from polyphenylene sulfide (PPS).

Alternatively, the flow tube is made from polyaryletherketone (PAEK), polyether ether ketone (PEEK), polyetherketoneketone (PEKK), polyoxymethylene (POM), or nylon materials.

According to an embodiment of the invention, the electrode elements are formed by a material selected from the list consisting of stainless steel, titanium, tantalum, silver, corrosive resistant alloys, such as nickel-chromium alloys, or such as

Hastelloy ®, a nickel-molybdenum alloy, such as nickel-molybdenum-chromium- iron alloys.

According to an advantageous embodiment of the invention, for each electrode element, the interface between said flow tube wall and the electrode element forms a hermetical seal.

The hermetical seal is understood to comply at least with class IP65 (IP Code, International Protection Marking, IEC standard 60529: Protected against low- pressure jets from all directions—limited ingress permitted), preferably to comply with class IP66 (protected against direct sprays from all directions—limited ingress permitted), class IP67 (protection against effects of immersion from 15 cm to 1 m) or even class IP68 (protection against complete, continuous submersion in water from 15 m or 50 feet). An advantage of the above embodiment may be that the measuring tube is waterproof. This may be obtained while allowing advantageous manufacturing, e.g. by insert molding. According to an advantageous embodiment of the invention, for each electrode element, the interface between said flow tube wall and the electrode element is formed by direct contact between the flow tube said wall and said feed-through section. One advantage of the above embodiment may be that the measuring tube is very simple to manufacture. At the same time, a hermetic seal between the feed-through section and the flow tube wall may be obtained, e.g. by using advantageous manufacturing methods, such as insert molding. Thus, it should be understood that in the context of the above embodiment, the electrode element is embedded in the flow tube wall, e.g. by a molding process, such as insert molding.

According to an advantageous embodiment of the invention, for each electrode element, the interface between said flow tube wall and the electrode element is formed by a primer coating between said wall and the feed-through section, applied onto said feed-through section.

According to an embodiment of the invention, the electrode elements are embedded in the flow tube. This may for example be realized by insert molding.

One advantage of the above embodiment may be that the primer coating facilitates a hermetic interface seal, thus giving a waterproof measuring tube.

According to an advantageous embodiment of the invention the measuring tube is manufactured by insert molding. An advantage of the above embodiment may be that an effective and hermetic sealed interface between the electrode elements and the flow tube wall is obtained in a relatively simple manner and by a one step process. In fact, this actually allows some further configurations to be manufactured, e.g. where the electrode elements are too large to be inserted into the flow tube after manufacturing of the flow tube. A further advantage of the above embodiment may be that the interface between the electrode elements and the flow tube wall forms a very durable sealing. According to an advantageous embodiment of the invention said electrode elements are too large to be inserted through any of the end openings of the flow tube.

Thus, regardless of the orientation of each of the electrode elements, these electrode elements cannot be inserted through the end openings of the flow tube, through which the liquid to be measured is to flow, during operation. This is because the dimensions of the electrode elements are such, that they do not permit to enter the flow tube through its end openings.

One advantage of the above embodiment is that having large electrode elements may be desirable, and that this embodiment of the invention allows even electrode elements too large to be inserted through the end openings e.g. after molding the flow tube. This is possible as the electrode elements are instead arranged in-situ in said wall, e.g. by means of insert molding. According to an embodiment of the invention, the interface between the electrode elements and the flow tube wall is free of sealants and gaskets.

According to an advantageous embodiment of the invention, for each electrode element, said feed-through section is roughened. An advantage of the above embodiment may be that the bonding of the electrode to the flow tube wall is more effective, i.e. a more effectively sealed interface may be obtained, and a more long-lasting seal may be obtained. According to an advantageous embodiment of the invention, for each electrode element, said feed-through section is chemically etched.

Thus, according to the above embodiment, the feed-through section may be roughened by chemical etching.

An advantage of the above embodiment may be that the bonding of the electrode to the flow tube wall is more effective, i.e. a more effectively sealed interface may be obtained, and a more long-lasting seal may be obtained. According to an advantageous embodiment of the invention, for each electrode element, said feed-through section is plasma treated.

Thus, according to the above embodiment, the feed-through section may be roughened by plasma treatment.

An advantage of the above embodiment may be that the bonding of the electrode to the flow tube wall is more effective, i.e. a more effectively sealed interface may be obtained, and a more long-lasting seal may be obtained. In other alternative embodiments, where the feed-through section is roughened or pretreated, this may e.g. be done by laser ablation or electric discharge machining, or by mechanical treatment, such as abrasion by sand blasting or sand paper treatment.

According to an advantageous embodiment of the invention, for each electrode element, the inner electrode surface is arranged to flush with said inner wall surface. One advantage of the above embodiment may be that advantageous flow

characteristics may be preserved within the advantageous context of the invention. At the same time, the measuring tube of the above embodiment facilitates a precise magnetic inductive flow meter by allowing direct contact between the liquid to be measured and the electrode elements.

According to an advantageous embodiment of the invention, for each electrode element, the ratio between said inner electrode surface area and outer cross section area is at least 5, such as at least 10, such as at least 20, such as at least 50.

An advantage of the above embodiment is that it facilitates a precise magnetic inductive flow meter within the advantageous context of the invention, particularly that the level of precision facilitated by the large inner electrode surface area is high, while keeping potential leakage low.

According to an embodiment if the invention, the ratio between inner electrode surface area and outer cross section area is 5-100, such as at least 10-100, such as at least 20-100, such as at least 50-100. According to an advantageous embodiment of the invention, for each electrode element, the inner electrode surface has a length parallel to a flow direction of the liquid flowing in the flow tube and a height perpendicular to said flow direction, and wherein said length is larger than said height. One advantage of the above embodiment may be that the measuring tube facilitates precise flow measurements while allowing an advantageous design of the measuring tube to be manufactured in relatively simple manner. Particularly, when the electrode elements are embedded in the flow tube walls by e.g. insert molding this embodiment is advantageous. Even further, this embodiment allows a very low impedance of the electrode elements, especially when using very small flow tubes. The above embodiment may for example be realized by using electrode elements having oblong inner electrode surfaces, and orienting these with the longest dimension parallel with the longitudinal direction of the flow tube, i.e. parallel with the flow direction.

According to an advantageous embodiment of the invention each electrode element is arranged to be in direct contact with the liquid.

One advantage of the above embodiment may be that a very precise magnetic flow rate measurements may be obtained, due to the electrode elements being directly coupled to the liquid to be measured.

According to an advantageous embodiment of the invention, each electrode element is a monolithic, metallic electrode element.

In this context, the term "monolithic" means that each of the electrode elements are formed as one part, e.g. by casting each of the electrode elements as one part. Thus, the monolithic electrode elements are not formed by joining two or more parts.

One advantage of the above embodiment may be that it may be very durable and provide electrical connection between the electrode sections to the outer wall surface. Also, the electrode elements may be embedded in the flow tube walls, e.g. by means of insert molding, without compromising the electrical connection.

In an alternative embodiment, each of the electrode elements are formed by joining two or more parts, e.g. an electrode section and a feed-through section, to form the electrode element. The joining may comprise soldering, welding, mechanical engagement fixation, or other suitable fixation, dependent on the application.

According to an advantageous embodiment of the invention, each electrode element has a dimension larger than a flow tube end opening dimension. For example, the inner electrode surface of each electrode element has a length parallel to a flow direction of the liquid flowing in the flow tube and a height perpendicular to said flow direction, such length and height are examples of a dimension of the electrode elements. Also, an inner diameter of the flow tube is an example of a flow tube end opening dimension.

The invention further relates to a magnetic inductive flow meter for measuring a flow rate of a conductive liquid, said flow meter comprising: a magnetic inductive transmitter unit comprising a magnetic field coil and a switching arrangement arranged to control an energy flow through the magnetic field coil to generate a current for transmitting a magnetic field to the liquid, a detector unit comprising a measuring tube according to the invention or any of its embodiments arranged to collect an induced voltage of the liquid, and - a control system for controlling the operation of the magnetic inductive

transmitter unit and the detector unit in establishing a value of said flow rate from the magnetic field and the induced voltage.

It should be understood that in practice, another parameter may often be used instead of the magnetic field in self, as long as such other parameter represents the magnetic field. For example, the current in the magnetic field coil may be used.

The invention further relates to a method for manufacture of a measuring tube for a magnetic inductive flow meter, the method comprising the step of: molding a flow tube having a flow tube wall with an inner wall surface and an outer wall surface, the step of molding including molding at least two metallic electrode elements into said wall by insert molding, each the electrode element comprising an electrode section having an inner electrode surface with an inner electrode surface area extending along said inner wall surface, and a feed through section having an outer cross section with an outer cross section area at the outer wall surface, wherein the flow tube is a polymeric flow tube.

Thus, by molding the flow tube and molding the at least two metallic electrode elements into said flow tube wall by insert molding, the measuring tube is obtained.

According to an embodiment of the invention, the method comprises the step of: - molding a flow tube having a flow tube wall with an inner wall surface and an outer wall surface,

the step of molding including

molding at least two metallic electrode elements into said wall by insert molding, each the electrode element comprising an electrode section extending along said inner wall surface, and a feed through section extending from the electrode section to the outer wall surface,

wherein

the flow tube is a polymeric flow tube. According to an embodiment of the invention, the measuring tube is the measuring tube of the invention or any of its embodiments. According to an advantageous embodiment of the invention, the inner electrode surface area is greater than the outer cross section area.

According to an embodiment of the invention the measuring tube according to the invention or any of its embodiments is made in accordance with the method of the invention or any of its embodiments.

According to an embodiment of the invention the magnetic inductive flow meter according to the invention or any of its embodiments comprises the measuring tube manufactured by the method of the invention or any of its embodiments.

FIGURES

The invention will be described in the following with reference to the figures in which

Figure 1 illustrates a magnetic inductive flow meter according to an embodiment of the invention,

Figures 2A-2B illustrate a measurement tube according to an embodiment of the invention, and

Figures 3 A-3C illustrate an electrode element in a flow tube wall according to an embodiment of the invention.

DETAILED DESCRIPTION

Referring to figure 1, a magnetic inductive flow meter MFM for measuring a flow rate of a conductive liquid is illustrated in accordance with an embodiment of the invention. The flow meter of this embodiment comprises a magnetic inductive transmitter unit MTU, a detector unit DU, and a control system CS for controlling the operation of the magnetic inductive transmitter unit TU and the detector unit DU.

The magnetic transmitter unit MTU comprises a magnetic field coil MFC and a switching arrangement SA. The switching arrangement SA is arranged to control an energy flow through the magnetic field coil MFC to generate a current for transmitting a magnetic field to the liquid. In more detail, the switching arrangement SA ensures that a current flow through the magnetic field coil MFC thereby establishing the magnetic field through the liquid.

The detector unit DU comprises a measuring tube MT arranged to collect an induced voltage of the liquid. The measuring tube MT comprises a flow tube FT for carrying a flow of a conductive liquid to be measured and at least two metallic electrode elements EE1, EE2. The electrode elements EE1, EE2 shown are monolithic, however, in alternative embodiments, electrode elements EE1, EE2 being formed from two or more parts may also be used. Returning to figure 1, the flow tube FT is a polymeric flow tube, meaning that in consists essentially of polymeric material. Various molding processes may be suitable for manufacturing the flow tube FT, for example insert molding.

The flow tube FT has a flow tube wall WLL with an inner wall surface IWS and an outer wall surface OWS. Each of the electrode element EE1, EE2 are arranged in said flow tube wall WLL. In some embodiments, the electrode elements EE1, EE2 are embedded in the flow tube wall WLL, for example by insert molding, whereas in other embodiments the electrode elements EE1, EE2 may be inserted into the flow tube wall WLL after corresponding cavities have been made. One example of a measurement tube MT usable within the embodiment figure 1 is shown on figures 2A and 2B. Further examples of electrode elements EEl usable within the embodiment of figure 1 is shown on figures 3A-3C. With reference to figures 2 A and 2B, each electrode element EEl, EE2 comprises an electrode section ES and a feed through section FTS. Each electrode section has an inner electrode surface IES with an inner electrode surface area. The inner electrode surface area extends along said inner wall surface IWS. Each feed through section FTS has an outer cross section OCS with an outer cross section area at the outer wall surface OWS. As illustrated on figures 2A-2B and on figures 3A-3C, the inner electrode surface area is greater than the outer cross section area.

Returning to figure 1, the control system CS is configured to control the operation of the magnetic inductive transmitter unit TU and the detector unit DU so as to establish a value of said flow rate from the magnetic field and the induced voltage. In this regard, any suitable value may be used to represent the magnetic field, as long as it is suitable for obtaining a value of the flow rate. Similarly, any suitable value may be used to represent the induced voltage, as long as it is suitable for obtaining a value of the flow rate.

Turning now to figure 2A, a top-down cross-sectional view of a measurement tube MT is shown, usable e.g. as in figure 1. As can be seen, each electrode element EEl, EE2 is arranged so as to have its inner electrode surface IES flush with the inner surface IS of the flow tube wall WLL. Figure 2B illustrates the cross-section AA of figure 2A, with an enlarged portion of electrode element EE2 shows the inner electrode surface IES and the outer cross section OSC.

In figures 2A-2B and also in figures 3 A-3B, the feed through section FTS ends at the outer cross section OSC, whereas in other embodiments it may extend further, e.g. to facilitate electrical connection of wiring. This is illustrated on figure 3C. Figures 3 A-3C each illustrate an electrode element EE1 according to an embodiment of the invention.

On figure 3 A, only the feed through section FTS is embedded into the flow tube wall WLL, and therefore the inner electrode surface does not flush with the inner surface IS flow tube wall WLL. The electrode section ES of the electrode element EE1 will be in direct contact with the fluid in the flow tube FT.

On figure 3B, the inner electrode surface IES flushes with the inner surface IS of the flow tube wall WLL. The electrode section ES of the electrode element EE1 will be in direct contact with the fluid in the flow tube FT.

On figure 3C, the electrode section ES of the electrode element EE1 will not be in direct contact with the fluid in the flow tube FT, i.e. this setup is suitable for capacitive type magnetic inductive flow meters.

The inner electrode surface IES faces the inner space of the flow tube FT in all of figures 3A-3C.

FIGURE REFERENCES

MT. Measuring tube

MFM. Magnetic inductive flow meter FT. Flow tube

IWS. Inner wall surface

OWS. Outer wall surface

EEl, EE2. First and second electrode elements

IES. Inner electrode surface

OSC. Outer cross section

ES. Electrode section

FTS. Feed-through section

MTU. Magnetic inductive transmitter unit

MFC. Magnetic field coil

S A. Switching arrangement

DU. Detector unit

CS. Control system