GB2571285A

GB2571285A - Fluid sensor

Info

Publication number: GB2571285A
Application number: GB1802875.3A
Authority: GB
Inventors: Lao Liyun; Sharma Prafull; Falcone Gioia
Original assignee: Cranfield University
Current assignee: Cranfield University
Priority date: 2018-02-22
Filing date: 2018-02-22
Publication date: 2019-08-28
Also published as: GB201802875D0

Abstract

A fluid sensor comprises an enclosure 36 that defines a microwave resonant cavity and an electrode 50 located within the cavity, which is configured to generate a varying electromagnetic field within the cavity. The resonant cavity has a sensing end comprising end wall 42 with an aperture or window 44 through which a fringing electromagnetic field 58a can extend from the cavity into a fluid 56 located adjacent the cavity sensing end. The cavity has a cross-sectional area A at the sensing end and the window has an area Aw that is less than the cross-sectional area A. The fluid sensor may sense the water content of a multiphase fluid located adjacent the sensing end, perhaps in a pipeline. A dielectric window material may cover the aperture 44. Fluid level, film thickness, moisture in a gas, and fluid presence may also be sensed.

Description

The present invention relates to a fluid sensor and in particular, but not exclusively, to a fluid sensor for sensing the water content of a fluid mixture such as an oil/water mixture.

In particular, but not exclusively, the invention relates to a fluid sensor for sensing a flowing fluid mixture. The fluid sensor may also have other applications including for example measuring the water content of a static fluid mixture. The fluid sensor may be used to sense the presence or absence of a liquid, a liquid level, or the level of an interface between two liquids. The fluid sensor may also be used to sense the moisture content of a gas, the thickness of a liquid film, or the salinity of a liquid.

The fluid sensor is concerned primarily with sensing the permittivity, or a change in the dielectric constant, of a fluid using a microwave resonator.

An important application of the invention is the online monitoring of water content -in a multiphase fluid system during petroleum production, processing and transportation. A highly accurate water content measurement is needed for applications such as allocation metering, custody transfer of crude oil, production optimisation etc. In one embodiment the invention provides a novel sensing principle based on a microwave resonator that has been developed for this application.

The fluid sensor of the present invention also has numerous other applications where it is desired to measure the water content of a multi-component fluid mixture comprising at least two liquids or a liquid and a gas.

-2The present invention in one embodiment relates generally to the measurement of fluid flowing in a pipeline. More specifically an embodiment of the present invention relates to measurement of water content, particularly in a multiphase flow in a pipeline transporting hydrocarbon-containing fluids, as commonly occurs in the exploration and production of oil and gas from reservoirs.

The water content of a fluid mixture may be defined in a number of different ways. For example, in petroleum engineering:

• The ratio between the volumetric oil flow rate q_o and the volumetric liquid flow rate (i.e. the volumetric oil flow rate q_o plus the volumetric water flow rate q_w) at actual reservoir conditions is the fractional flow, f_w = ^qw • The fractional flow can be converted to standard conditions by introducing the producing water cut at surface, WC defined as: f_ws = —_B / t where B_w and B_o ¹⁺ΑτΑ are the water and oil formation volume factors, respectively.

• Finally, the water-oil-ratio, WOR is the ratio between the volumetric water flow rate and the volumetric oil flow rate at standard conditions, hence WC = ^W°^R

------- WOR + 1

In this document the term “water content” is used in a generic sense that encompasses these and other methods for defining the water content of a fluid mixture.

Sensing methods based on measuring the permittivity of a fluid (using microwave and capacitive techniques) provide high sensitivity for measuring the water content of a mixture. Other widely used methods of water content measurement are based on the use of a gamma ray densitometer, or a Coriolis densitometer. Within microwave-based methods, there are methods based on transmission, reflection or resonance and combinations of these. In an embodiment, the present method uses a combination of microwave reflection and resonance methods.

The microwave resonance principle is based on measuring the permittivity/dielectric constant of the fluid. Because microwave resonators are inherently stable and the measureable properties of resonance (the resonant frequency and the quality factor or Q

-3factor) can be measured with high accuracy, the microwave resonance method is the most sensitive and accurate method available for measuring the water volume fraction.

A sensing principle based on the use of a dielectric resonator in the form of an open-ended cavity resonator (OECR) for the measurement of wet gas, water fraction or salinity is described in US 8570050 B2.

A prior art OECR sensor 1 of the general type described in US 8570050 B2 is illustrated in figures la, lb and lc. The prior art OECR sensor 1 comprises a cylindrical metallic enclosure 2 that is open at one end 4 and is closed at the other end by a circular end wall 6. The interior of the enclosure 2 comprises an electromagnetic resonator cavity 8, which is filled with a dielectric material 9, for example PolyEtherEtherKetone (PEEK). An electrode 10 extends into the cavity through an insulated sleeve 12 that communicates with a central hole in the end wall 6. The electrode is driven by an alternating electrical signal, typically with a frequency in the range 0.5-10GHz for a dielectric-filled cavity, generating an alternating electromagnetic field within the cavity 8.

In Fig. la the prior art sensor is shown mounted on a fluid flow pipeline 14 (only one side wall of the pipeline being shown), with the open end of the cavity facing the pipe interior

16. The electric field component 18 of the electromagnetic field generated within the cavity 8 during resonance is illustrated by arrows that represent the electric field lines. The electrical field 18 includes a fringe field 18a that extends from the open end 4 of the cavity into the interior 16 of the pipeline 14, where it interacts with a fluid 20 flowing through the pipeline 14 in a region close to the pipe wall. The electric field within the cavity is sensed by a sensor probe, which may be either the driven electrode 10 or a second electrode (not shown) that is mounted within the cavity 8.

The permittivity of the fluid 20 flowing through the pipeline 14, through which the fringe field 18a extends, affects the resonant frequency of the fluid sensor 1. The resonant frequency may be measured by coupling the sensor probe to a suitable measuring instrument such as a vector network analyser. Since the fringe field 18a at the open end of the resonator cavity 8 penetrates the fluid under test, the permittivity of fluid media affects the resonant frequency, as illustrated in Fig. lb. By measuring the resonant frequency and by the use of suitable calibration, the permittivity of the fluid media can be determined. This permittivity

-4value can then be used to detect certain properties of the fluid. For example, it may be used in a mixture model to estimate the water liquid ratio (WLR) of an oil-water mixture.

The properties of an OECR are discussed in an article by Prafull Sharma, Liyun Lao, Gioia Falcone, “A Microwave Cavity Resonator Sensor for Water-In-Oil Measurements, Sensors and Actuators” B: Chemical, Available online 2 February 2018, ISSN 0925-4005, H tps' ·*'0r<y.*’ 0 s 01 ό/ΐ b· ! S 0 (http s ://w w w. sciencedirect .com/science/article/pii/S0925400518302351)

There are several issues that limit the use of the known OECR sensing principle.

The primary issue is the non-monotonic trend of resonance frequency shift with an increase in water content, as shown in figures 2a and 2b, where the water content is shown as watercut, defined as the volumetric fraction of water in the fluid mixture. In particular, the non-monotonicity is evident in the watercut range 20% to 40% (region “A” in figure 2a). The cause of this behaviour is mode conversion, where the electric field distribution of the resonant mode in question is modified to represent a different mode. The resonance curves in figure 2a and 2b show a dual resonance curve for watercut percentages of 30% and 40% indicating a mode conversion issue.

Therefore, although the OECR sensor shows a good correlation between watercut percentage and resonate frequency in watercut ranges from 0% to 20% and from 40% to 100%, which allows the watercut to be determined accurately within these ranges, it cannot be used to sense the watercut percentage reliably when the watercut percentage is in the range of about 20% to 40%.

It is an object of the present invention to provide a fluid sensor that can sense the water liquid ratio (WLR) accurately over a wider WLR range, or at least in an alternative range. Further objectives and advantages of the invention will be set out in the description that follows.

According to one aspect of the invention there is provided a fluid sensor comprising an enclosure that defines a resonant cavity and an electrode located within the resonant cavity, wherein the electrode is configured to generate a varying electromagnetic field within the resonant cavity, wherein the resonant cavity has a sensing end and an end wall at the sensing end of the resonant cavity, and the end wall has a window through which a fringing

-5electromagnetic field can extend from the resonant cavity into a fluid located adjacent the sensing end of the resonant cavity, wherein the resonant cavity has an internal cross-sectional area A_c at the sensing end of the resonant cavity and the window has an area A_w that is less than the internal cross-sectional area A_c at the sensing end of the resonant cavity.

A fluid sensor of the aforesaid type will be referred to herein an as aperture-ended cavity resonator (AECR), to distinguish it from the prior art open-ended cavity resonator (OECR) described above.

We have discovered that by providing an end wall at the sensing end of the resonant cavity, and providing a window in the end wall through which a fringing electromagnetic field can extend into a fluid located adjacent the sensing end of the resonant cavity, the problem of non-monotonicity experienced with prior art open-ended cavity resonators can be avoided. When used for sensing the water volume fraction (WVF) this means that the fluid sensor is able to provide good correlation between the water content percentage and the resonant frequency over a much wider range of values of water content percentage, thereby increasing the usefulness of the fluid sensor.

The resonant cavity has an internal cross-sectional area A_c at the sensing end of the resonant cavity and the window has an area A_w that is less than the internal cross-sectional area A_c at the sensing end of the resonant cavity. The window is therefore smaller than the cavity at the sensing end. We have found that this helps to avoid mode conversion issues, which give rise to the non-monotonicity problems experienced with prior art fluid sensors.

In one embodiment, the window has an area A_w that lies in the range 10% to 90%, preferably 10% to 80%, more preferably 20% to 60%, of the internal cross-sectional area A_c at the sensing end of the resonant cavity.

In one embodiment, the resonant cavity contains a dielectric material, for example PolyEtherEtherKetone (PEEK). This prevents fluid from entering the cavity and ensures that the resonant frequency of the cavity is unaffected by fluid within the cavity. The resonant frequency of the cavity is only affected by the fluid that interacts with the fringing field that extends outwards from the cavity.

-6In another embodiment, the window contains a dielectric window material. The window material prevents fluid from entering the cavity and ensures that the resonant frequency of the cavity is unaffected by fluid within the cavity. In this case, the cavity may be filled with a dielectric material, or it may contain a known fluid (gas or liquid) or a vacuum.

In an embodiment, the enclosure comprises an electrically conductive material, for example a metal.

In an embodiment, the resonant cavity has a resonant frequency in the range 1 MHz to 20GHz. If the resonant cavity contains a dielectric material, the resonant frequency preferably lies in the range 0.5-10GHz.

In an embodiment, the fluid sensor is mounted on a container having an interior for containing a fluid, wherein the sensing end of the fluid sensor is located in the interior of the container so that the fringing electromagnetic field extends into a fluid contained within the container. The container may for example be a pipeline having an interior for containing a flowing fluid, wherein the sensing end of the fluid sensor is located in the interior of the pipeline so that the fringing electromagnetic field extends into a fluid flowing through the pipeline. Alternatively, the container may contain a static fluid.

In an embodiment, the fluid sensor includes a measuring instrument connected to receive an output signal from the fluid sensor, wherein the measuring instrument is configured for sensing a shift in the resonant frequency of the output signal, or the Q-value of the output signal, or a phase shift between the output signal and a driving signal.

In an embodiment, the fluid sensor is configured to sense the water content of a fluid located adjacent the sensing end of the fluid sensor.

In an embodiment, the fluid sensor is configured to sense the permittivity of a fluid located adjacent the sensing end of the fluid sensor.

According to another aspect of the invention there is provided a fluid sensor assembly including a first fluid sensor and a second fluid sensor, wherein the first fluid sensor comprises a fluid sensor according to any one of the preceding statements of invention, and the second fluid sensor comprises an enclosure that defines a resonant cavity, and an

-7electrode located within the resonant cavity, which is configured to generate a varying electromagnetic field within the resonant cavity, wherein the resonant cavity has an open sensing end through which a fringing electromagnetic field can extend from the resonant cavity.

The fluid sensor assembly described above provides the advantage of high sensitivity through use of an OECR as the second fluid sensor, combined with the monotonic response provided by the AECR that comprises the first fluid sensor.

Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure la is a sectional side view of a prior art fluid sensor mounted in a fluid flow pipeline;

Figure lb is a graph illustrating a shift in the resonant frequency of the prior art fluid sensor, caused by a change in the permittivity of a fluid in the pipeline;

Figure lc is an isometric view of the prior art fluid sensor;

Figures 2a and 2b are graphs illustrating a typical sensor output signal for a known sensor of the type shown in Figures la-lc at watercut percentages of 30% and 40%;

Figure 3 a is a side sectional view of a first fluid sensor according an embodiment of the invention, mounted in a fluid flow pipeline;

Figure 3b is an isometric view of the first fluid sensor;

Figures 4a and 4b are graphs illustrating a typical sensor output signal for a fluid sensor according to an embodiment of the invention at watercut percentages of 30% and 40%;

Figure 5a is a side sectional view of a second fluid sensor according an embodiment of the invention; and

Figure 5b is a cross-sectional view of the second fluid sensor, on line V-V of figure 5a.

Figures la to lc and 2a, 2b relate to a prior art fluid sensor, and are described above.

-8Figures 3 a and 3b illustrates a first fluid sensor 30 according an embodiment of the invention, mounted in a fluid flow pipeline 32 (only one side wall 34 of the pipeline 32 being shown). The first fluid sensor comprises a metallic enclosure 36 that includes a cylindrical side wall 38, a first end wall 40 that closes one end of the enclosure, and a second end wall 42 that partially closes the other end of the enclosure. An aperture is formed in the second end wall 42, providing a window 44 that extends through the second end wall. The interior of the enclosure 36 comprises a resonant cavity 46, the shape and size of which is defined by the cylindrical side wall 38, the first end wall 40 and the second end wall 42.

In this embodiment the resonant cavity 46 is filled with a dielectric material 48, for example PEEK. An electrode 50 extends into the cavity through an insulated sleeve 52 that communicates with a central hole in the first end wall 40. The electrode 50 is driven by an alternating electrical signal, typically with a frequency in the range 0.5-10GHz for a dielectric-filled cavity.

In this embodiment the second end wall 42 is annular, providing a circular window 44 that is located centrally with respect to the cylindrical resonant cavity 46 (i.e. co-axially with the cavity). Also, in this embodiment, the circular window 44 has a diameter D_w that is approximately 50% of the internal diameter of the cavity D_c and an area A_w that is approximately 25% of the cross-sectional area A_c of the cavity.

In Fig. 3a the sensor 30 is shown mounted on a fluid flow pipeline 32, with the first end wall 42 facing the pipe interior 56. The electrode 50 is driven by an alternating electrical signal, typically with a frequency in the range 0.5-fOGHz for a dielectric-filled cavity, generating an alternating electromagnetic field within the cavity 46.

The electric field lines of the electric field component 58 of the electromagnetic field generated within the cavity 46 during resonance are illustrated by arrows. The electrical field 58 includes a fringe field 58a that extends from the window 44 into the interior 56 of the pipeline 32, where it interacts with a fluid 60 flowing through the pipeline 32 in a region close to the pipe wall. The electric field 58 within the cavity 46 is sensed by a sensor probe, which may be either the driven electrode 50 or a second electrode (not shown) that is mounted within the cavity 46.

-9The permittivity of the fluid 60 flowing through the pipeline 32, through which the fringe field 58a extends, affects the resonance frequency of the sensor 30. The resonance frequency may be measured by coupling the sensor probe to a suitable measuring instrument such as a vector network analyser. Since the fringe field 58a that extends from the window 44 penetrates the fluid under test, the permittivity of fluid media affects the resonance frequency. By measuring the resonance frequency and by the use of suitable calibration, the permittivity of the fluid media can be determined. This permittivity value can then be used to detect certain properties of the fluid. For example, it may be used in a mixture model to estimate the water liquid ratio (WLR) of an oil-water mixture.

The shift in resonance frequency with an increase in watercut is shown in figures 4a and 4b. The monotonic performance of the sensor is apparent. In particular, it may be noted that the sensor provides a monotonic performance in the watercut range 20% to 40% (compare with region “A” in figure 2a). This improved performance results from the fact that the use of a window with an area less than the cross-sectional area of the cavity helps to maintain mode integrity and avoid mode conversion issues, thus extending the practical usability of the probe and extending its ability to sense a full range of watercut values (from 0% to 100%).

A second fluid sensor 70 according to an embodiment of the invention is illustrated in figures 5a and 5b. The second fluid sensor 70 is similar in most respects to the first fluid sensor 30, and comprises a metallic enclosure 76 that includes a cylindrical side wall 78, a first end wall 80 that closes one end of the enclosure, and a second end wall 82 that partially closes the other end of the enclosure. An aperture is formed in the second end wall 82, providing a window 84 that extends through the second end wall. In the second fluid sensor the window 84 is glazed with a window material 85, for example a suitable dielectric material, which is transparent to the electromagnetic radiation at the resonant frequency. The window material 85 extends across the window 84, thus sealing the resonant cavity 86 within the enclosure 76 comprises.

In this embodiment the resonant cavity 86 may be filled with a dielectric material, for example PEEK, or it may contain a fluid (a gas or liquid), or it may be left empty (i.e. it may contain a vacuum).

-10An electrode 90 extends into the cavity through an insulated sleeve 92 that communicates with a central hole in the first end wall 80. The electrode 90 is driven by an alternating electrical signal, typically with a frequency in the range 0.5-10GHz for a dielectric (PEEK) filled cavity.

In this embodiment the second end wall 82 is annular, providing a circular window 84 that is located centrally with respect to the cylindrical resonant cavity 86 (i.e. co-axially with the cavity). The circular window 84 has a diameter D_w that is approximately 50% of the internal diameter of the cavity D_c and an area A_w that is approximately 25% of the cross-sectional area A_c of the cavity.

As illustrated in figures 4a and 4b, the introduction of window aperture in the AECR helps in maintaining the original mode in the cavity, thereby reducing the possibility of mode conversion within a certain range of watercut, as identified in case of the OECR. The cavity electromagnetic field fringes beyond the cavity at the aperture and interacts with the dielectric fluid surrounding the cavity. This perturbs the resonant electromagnetic field and shifts the resonance corresponding to the permittivity of the dielectric fluid. By measuring the shift in the resonance frequency, using a pre-calibrated model, the watercut can be estimated.

The aperture dimensions also give control over the depth of field penetration and the volume of fluid to be probed, which may be advantageous in many applications such as wet gas or for estimating film thickness.

One consequence of using a small window in the AECR is that the sensitivity of the sensor may be reduced as compared to a conventional OECR. Hence, it may be beneficial in certain circumstances to use an OECR where it shows monotonicity (i.e. in water-dominated mixtures or water-continuous mixtures), and an AECR in watercut ranges where the OECR does not show monotonicity. Here, in a preferred embodiment, the two different sensors may be part of a measurement system where the AECR is used when watercut is low (nominally less than 50%) and is dominated by oil i.e. oil continuous mixture, and the OECR is used when watercut is higher and is dominated by water (nominally more than 50%) i.e. water continuous mixture.

-11The sensor can also be applied to the detection of deposit build-up pipelines, such as wax deposits. The design controllability of aperture size enables control on depth of sensitive field, which in turn finds applications in thickness detection of liquids, measurement of droplets etc. The applications of the sensor also include fraction measurement of mixtures of liquids (e.g. water fraction in diluted methanol). Hence, the potential of the invention goes beyond the oil and gas industry and can be extended to other process industries such as chemicals, food and beverages, dairy etc.

The concept (AECR) is applicable for water content measurement in multiphase flow and is an improvement over existing state of the art (OECR). The applications of this system are in watercut meters and multiphase flow meters, which are usually deployed for oil and gas measurement applications and manufactured by flowmeter manufacturers.

Novelty: creating an aperture at the open end of the resonator to control mode integrity is a novel concept, which results in monotonic response of the sensor leading to practical usability.

Inventive step: the phenomenon of mode conversion affecting the monotonicity of the OECR sensor was not previously recognised and is an outcome of research leading to the present invention. To mitigate this effect, the AECR was created to limit the exposure of electric fields to the fluid. This is not obvious to the person skilled in the art.

Industrial applicability: a number of different commercial flow meters are available in the market for the measurement of the water content of oil. Some meters are based on the use of radioactive radiation, others use capacitive measurement, and others are based on the use of microwaves. Microwave sensors are attractive because they are not limited by the health risks associated with radioactive radiation-based meters and their fairly low accuracy or the undesirable influence of contamination on the capacitive sensors.

It should be understood that the sensor probes 30, 70 described above are only two possible embodiments of the invention. Some possible variants are set out below:

• Shape of enclosure - the enclosure may contain a cavity, which may have an output end that contains a window, wherein the area of the window may be less than the cross-sectional area of the cavity at the output end of the enclosure.

• The enclosure may be made of a conductive material (e.g. a metal).

• Optionally, the cavity may have a substantially uniform cross-sectional shape. However, the cavity need not necessarily be of a constant size: for example, it may be tapered.

• In certain preferred embodiments, the cavity may be circular or polygonal in crosssection.

• The area of the window in the aperture end of the enclosure may be less than 90% of the cross-sectional area of the cavity at the output end of the enclosure, and may preferably be in the range 10-80%, or more preferably in the range 20-60% of the cross-sectional area of the cavity at the output end of the enclosure.

• The cavity may include more than one window, in which case the total area of the windows will be less than the cross-sectional area of the cavity at the output end of the enclosure, and is preferably in the ranges indicated in the preceding paragraph.

• Asa general requirement, the/each window should be large enough to transmit the EM radiation at the intended operating frequency range. In general terms, this requirement can be met by ensuring that the window is larger than the wavelength of the radiating electromagnetic field at the intended operating frequency range.

• The (or each) window may be open, or it may contain a window material that is substantially transparent to the electromagnetic radiation at the intended operating frequency range. The window may for example be made of a suitable nonconductive material, e.g. a non-metallic material such as a dielectric material.

• The cavity may be empty, or it may contain a material that is substantially transparent to the E-M radiation, such as a suitable non-conductive material, e.g. a non-metallic material, for example a dielectric material. If the window contains a window material the cavity may contain a vacuum or it may contain a nonconductive solid or fluid material - for example a gas or a liquid.

• The cavity may contain a single electrode that acts as emitter and receiver, or it may contain separate emitter and receiver electrodes.

• The window may be round or any other suitable shape: e.g. square, rectangular, annular. In most cases a round shape e.g. circular may be preferred.

• The window may be located on- or off-axis, relative to the longitudinal axis of the cavity.

· The operating frequency of the fluid sensor may be in the range 100kHz - 300GHz, or preferably 1MHz - 20 GHz, and may more preferably be in the range 0.5-10GHz if the cavity is filled with a dielectric material (e.g. PEEK).

• The fluid sensor may be mounted flush with wall of pipe, or it may protrude into pipe to sense the flow at a location closer to centre of the pipe.

· The fluid sensor may be used for measuring water content or other properties of fluids. For example, the fluid sensor may be used as a level sensor (for multi-phase fluids), a sensor for detecting fluid interfaces, for sensing moisture content etc.

• The fluid sensor is not restricted to sensing resonant frequency or Q-value: it may for example use phase sensing to sense a phase difference between the emitted and reflected fields.

-14CLAIMS

Claims

1. A fluid sensor comprising an enclosure that defines a resonant cavity and an electrode located within the resonant cavity, which is configured to generate a varying electromagnetic field within the resonant cavity, wherein the resonant cavity has a sensing end and an end wall at the sensing end of the resonant cavity, and the end wall has a window through which a fringing electromagnetic field can extend from the resonant cavity into a fluid located adjacent the sensing end of the resonant cavity, wherein the resonant cavity has an internal cross-sectional area Ac at the sensing end of the resonant cavity and the window has an area Aw that is less than the internal cross-sectional area Ac at the sensing end of the resonant cavity.

2. A fluid sensor according to claim 1, wherein the window has an area Aw that lies in the range 10% to 90%, preferably 10% to 80%, more preferably 20% to 60%, of the internal cross-sectional area Ac at the sensing end of the resonant cavity

3. A fluid sensor according to claim 1 or claim 2, wherein the resonant cavity contains a dielectric material.

4. A fluid sensor according to any one of the preceding claims, wherein the window contains a dielectric window material.

5. A fluid sensor according to any one of the preceding claims, wherein the enclosure comprises an electrically conductive material.

6. A fluid sensor according to any one of the preceding claims, wherein the resonant cavity has a resonant frequency in the range 1 MHz to 20GHz.

7. A fluid sensor according to any one of the preceding claims, wherein the fluid sensor is mounted on a container having an interior for containing a fluid, wherein the sensing end of the fluid sensor is located in the interior of the container so that the fringing electromagnetic field extends into a fluid contained within the container.

8. A fluid sensor according to claim 7, wherein the container is a pipeline having an interior for containing a flowing fluid, and wherein the sensing end of the fluid sensor is located in the interior of the pipeline so that the fringing electromagnetic field extends into a fluid flowing through the pipeline.

9. A fluid sensor according to any one of the preceding claims, including a measuring instrument connected to receive an output signal from the fluid sensor, wherein the measuring instrument is configured for sensing a shift in the resonant frequency of the output signal, or the Q-value of the output signal, or a phase shift between the output signal and a driving signal.

10. A fluid sensor according to any one of the preceding claims, the fluid sensor being configured to sense the water content of a fluid located adjacent the sensing end of the fluid sensor.

11. A fluid sensor according to any one of the preceding claims, the fluid sensor being configured to sense the permittivity of a fluid located adjacent the sensing end of the fluid sensor.

12. A fluid sensor assembly including a first fluid sensor and a second fluid sensor, wherein the first fluid sensor comprises a fluid sensor according to any one of the preceding claims, and the second fluid sensor comprises an enclosure that defines a resonant cavity, and an electrode located within the resonant cavity, which is configured to generate a varying electromagnetic field within the resonant cavity, wherein the resonant cavity has an open sensing end through which a fringing electromagnetic field can extend from the resonant cavity.

Intellectual

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Office

Application No: GB1802875.3

Claims searched: 1-12

Examiner: Simon Colcombe

Date of search: 21 August 2018

Patents Act 1977: Search Report under Section 17