A sensing apparatus

Abstract

A sensing apparatus for monitoring a fluid pipe at two sensing locations separated by a physical sensor spacing comprises: a base module comprising a light emitter configured to generate light pulses and a light detector configured to detect backscattered light pulses; a sensing module comprising a sensing fibre; and an optical coupling assembly configured to optically couple light pulses from the light emitter and detector to the sensing fibre. The sensing fibre comprises two sensing points and a spacer section between the two sensing points. The two sensing points are positioned at the two sensing locations respectively and are configured to generate backscattered light pulses indicative of a property to be measured. The sensing apparatus defines a spatial resolution that allows backscattered light pulses from the two sensing points to be resolved. The spatial resolution is greater than the physical sensor spacing but no more than the spacer section.

Description

[0001] A SENSING APPARATUS

[0002] Technical Field of the Invention

[0003] The present invention relates to a sensing apparatus for monitoring a fluid pipe at two or more sensing locations. In particular, the invention relates to monitoring of the properties of fluid with a fluid pipe using a sensing fibre. The invention further relates to a sensing fibre for monitoring of the two sensing locations as well as a fluid pipe comprising the sensing apparatus. Preferably, the fluid pipe is a water pipe and the sensing apparatus is for monitoring the properties of water within the pipe.

[0004] Background to the Invention

[0005] Optical fibre sensing is a technique that uses the changes in the optical properties of an optical fibre, or sensing fibre, to make measurements of the fibre’s environment, such as pressure, temperature, strain, and vibrations (acoustics). As optical fibres can be made relatively cheaply, they can be run over long distances and then used to make measurements at different points along their length. This makes them very useful for data collection activities where power or access is limited, such as along buried pipes or in remote areas. This can assist in the monitoring of pipe networks such as fresh water, waste water and sewage, and fuels such as oil or gas. It is common to monitor the operation of the network and the condition of pipes. In this manner, blockages, leaks or other issues can be identified and scheduled for repair.

[0006] In order to make measurements, light pulses are coupled into a sensing fibre. The external environment and conditions of the sensing fibre affect backscattered light pulses generated as the light pulses travel through the sensing fibre. These backscattered pulses can then be detected and used to make a measurement of a property of interest at different points along the sensing fibre. There are a number of different techniques that can be employed such as distributed acoustic sensing (DAS) (or distributed vibration sensing (DVS)), distributed strain sensing (DSS) and distributed temperature sensing (DTS). This technique is also further described in WO2019 / 166809A1.

[0007] Many factors affect the resolution of this technique along the length of the sensing fibre, such as: the total length of the sensing fibre; the material and construction of the sensing fibre; the frequency and power of light pulses; pulse width; and pulse spacing. In many instances, a key property is the spatial resolution of the sensing fibre, essentially the minimum resolvable distance between successive backscattering points on the fibre. Whilst certain variations of the above factors can improve the spatial resolution achievable using a fibre, these can have negative impacts on other sensing performance such as signal-to-noise ratio and / or frequency resolution. It can therefore be impractical to obtain spatial resolution better than a particular threshold in many practical implementations.

[0008] With recent advances in data science and machine learning, there is furthermore a need to provide more measurements related to the properties of utility networks during use so that network performance optimised. While optical fibre sensing is theoretically well-placed to assist with providing this data, there remain challenges in making viable sensing systems which can provide the spatial resolution required for advance data collection and analysis.

[0009] It is therefore an object of embodiments of the present invention to at least partially address the above issues.

[0010] Summary of the Invention

[0011] In a broad sense, the invention relates to a sensing fibre for monitoring two sensing locations physically spaced apart by a physical sensor spacing. The sensing fibre may be for monitoring a fluid pipe. The sensing fibre may comprise two sensing points. The sensing fibre may comprise a spacer section between the two sensing points. The two sensing points may be positioned at the two sensing locations respectively. The two sensing points may be configured to generate backscattered light pulses indicative of a property to be measured at each of the two sensing locations. The spacer section may have a length greater than the physical sensor spacing. The physical sensor spacing may be less than the spatial resolution of the sensing fibre or a sensing apparatus comprising the sensing fibre. The spacer section may have a length greater than a spatial resolution of the of the sensing fibre or a sensing apparatus comprising the sensing fibre.

[0012] The invention also relates to a sensing apparatus for monitoring two sensing locations physically spaced apart by a physical sensor spacing. The sensing apparatus may be for monitoring a fluid pipe. The sensing apparatus comprise a light emitter configured to generate light pulses for introduction into the fibre. The sensing apparatus may comprise a light detector configured to detect backscattered light pulses. The sensing apparatus may have a defined spatial resolution. The spatial resolution of the sensing apparatus may be defined as the minimum resolvable distance between successive backscattering points on the fibre.

[0013] According to a first aspect of the present invention there is provided a sensing apparatus for monitoring a fluid pipe at two sensing locations physically spaced apart by a physical sensor spacing, the sensing apparatus comprising: a sensing fibre; a light emitter for introducing light pulses into the fibre; a light detector module configured to detect backscattering of the light pulses from the sensing fibre and output a detector output signal in response thereto; wherein the sensing fibre comprises two sensing points positioned at the two sensing locations respectively, and a spacer section between the two sensing points, wherein the physical sensor spacing is less than the spatial resolution of the sensing apparatus and the spacer section has a length greater than the spatial resolution of the sensing apparatus.

[0014] Advantageously, the spacer section provides the required spatial resolution between the two sensing points along the length of the sensing fibre even when the physical separation of the two sensor locations are less than the spatial resolution. Given sensing fibre is generally relatively cheap, and can be effective over tens or hundreds of kilometres, the addition of spacer sections does not significantly impact the overall cost or complexity of installing the sensing apparatus. In addition, the use of such a spacer section enables reductions in cost / complexity for the system overall as the spatial resolution is advantageously decoupled from the physical spacing of sensing locations enabling lower specification sensing fibres, light emitters and detectors to be used.

[0015] In the context of the present application, the term ‘fluid’ in relation to a fluid pipe or conduit may refer to any material, liquid or gaseous, including fuels such as oil or gas or associated distillates, additionally in industrial uses which may include mining and similar, the invention may more specifically refer to a primarily water-based fluid, such as potable water, pre-treatment water, wastewater or water-based slurries. Similarly, in the context of the present application, the term ‘pipe’ or ‘conduit’ may refer to any fluid conduit used to convey a fluid (gas, liquid or a mixture including a slurry) between two points, spaced apart at or below local ground level. In particular, the ‘pipe’ or ‘conduit’ may traverse at a relatively regular displacement from local ground level, without requiring the ‘pipe’ or ‘conduit’ to be horizontal. Thus, the terms “pipe” and “fluid pipe” may be used interchangeably.

[0016] The backscattered light pulses may be generated by backscattering of the light pulse generated by the light emitter within the sensing fibre. The sensing module may be remote from the base module. In this context, the sensing module may be separated from the base module by at least 1km, at least 5km, at least 10km, at least 20km, at least 50km or at least 100km.

[0017] The sensing fibre may be a single mode optical fibre. In some embodiments, the sensing fibre may be provided with a sheath. The sensing fibre sheath may be opaque.

[0018] The sensing fibre can be any suitable length. In particular embodiments, the desired length of the sensing fibre may be set by desired performance. In this context, in order not to unduly limit performance, the sensing fibre may be less than 20km in length, less than 15km in length, less than 10 km in length, less than 5km in length or less than 1 km in length.

[0019] The sensing apparatus may comprise a sensor provided at one of the two sensing locations. The sensor may be configured to generate a sensor output indicative of the property to be measured. The sensing point provided at the one of the two sensing locations may be arranged to generate backscattered light pulses indicative of the sensor output.

[0020] The property to be measured may be any suitable property of the pipe, and / or fluid in the pipe and / or environmental conditions outside the pipe, and / or any other property of interest or data provided in the vicinity of the pipe. The property to be measured may be a fluid flow inside the pipe, such as a fluid flow speed, and / or fluid flow direction. The property to be measured may be a fluid temperature inside the pipe. The property to be measured may be a fluid pressure inside the pipe. Thus, various properties can be measured and monitored using the sensing fibre.

[0021] The sensor output may comprise anything that alters the properties of backscattered pulses generated by the corresponding sensing point. For example, the sensor output may comprise any one or more of: moving the sensing fibre, changing the curvature of the sensing fibre, vibrations, acoustic output, changing of fibre temperature, changing of pressure, or the like. Thus, a wide range of sensor outputs may be used in conjunction with a suitable sensing fibre and sensing point.

[0022] The sensor may be configured to generate a sensor output indicative of a property of the fluid in the pipe. The sensor may comprise a tube. The tube may be in fluid communication with the pipe. The tube may comprise a sensing element. The sensing element may be configured to generate a sensor output indicative of the property of the fluid within the tube. Thus, the sensing element may be separated from the pipe which can allow for easier and more convenient placement of the sensor to ensure the sensing fibre can detect the sensor output.

[0023] The tube may comprise an isolation valve. The isolation valve may be configured to selectively fluidly isolate the sensor and / or sensing element from the pipe. Each tube may comprise an isolation valve. The isolation valve may comprise any type of suitable valve such as a ball valve, gate valve, plug valve, butterfly valve or the like. Thus, the isolation valve can allow easy connection and disconnection of the sensing element from the pipe as needed, such as for maintenance or if it is no longer required.

[0024] The isolation valve may be provided on a section of the tube configured to, and / or intended to, remain outside the pipe. The isolation valve may be provided outside the pipe. This ensures that the isolation valve remains easily accessible.

[0025] The tube may comprise an opening at one end in fluid communication with the pipe. The tube may extend into the pipe to be monitored. The opening may be provided inside the pipe to be monitored. The isolation valve may be provided between the opening and the sensing element. Thus, the tube is conveniently in communication with the fluid inside the pipe. The opening may be any suitable size and / or shape to sample a suitable cross- sectional area of the fluid within the pipe, preferably the opening may be elliptical or circular, but it may also be lens-shaped, triangular, square, another polygonal shape or irregularly shaped. A major axis of the opening may be aligned vertically. The opening can therefore be suitably sized and positioned to efficiently sample fluid within the pipe.

[0026] The opening may be configured to connect to an access valve provided on the pipe to be monitored. The access valve may be configured to provide fluid communication between the opening and the inside of the pipe. The access valve may be configured to selectively fluidly isolate the pipe. The access valve may comprise any suitable valve, for example as described in relation to the isolation valve. The pipe may comprise an access tube extending from the inside of the pipe to the access valve. In such embodiments, the tube may, or may not, comprise an isolation valve. Thus, the tube need not extend into the pipe where the pipe comprises the necessary structure to facilitate a connection to the tube outside the pipe. An isolation valve may nonetheless be provided on the tube where it is desired to isolate the sensing element from the external environment when not connected to the pipe. Where the tube does not extend into the pipe, the access tube may comprise an access opening provided inside the pipe at an end of the access opening distal from the tube. The access opening may include any one or more features of the opening when it is positioned within the pipe as described above.

[0027] The sensor may be a pressure sensor. The pressure sensor may be configured to generate a sensor output indicative of a fluid pressure inside the pipe. The sensing element may be configured to generate a sensor output indicative of a fluid pressure in the tube. Thus, as the tube is in fluid communication with the pipe, the sensing element may sense the pressure inside the pipe.

[0028] The opening, or access opening, may be arranged to face upstream in the pipe, that is facing into the flow of fluid. Thus, the opening may sample a dynamic fluid pressure. The pressure sensor may therefore be a dynamic pressure sensor. The opening, or access opening, may be arranged to face downstream in the pipe, that is facing the same way as the flow of fluid, or may take the form of a more traditional static pressure tube. Thus, the opening may sample a base fluid pressure. The pressure sensor may therefore be a base pressure sensor. The opening, or access opening, may be arranged perpendicular to flow of fluid in the pipe. Thus, the opening may sample a static fluid pressure. The pressure sensor may therefore be a static pressure sensor. The opening may be provided centrally within the pipe. Thus, the pressure sensors may be configured to measure various different types of fluid pressure.

[0029] The dynamic pressure sensor may sample a relatively larger cross-sectional area of fluid within the pipe than a base pressure sensor and / or static pressure sensor. This arrangement would provide for higher sensitivity to a given dynamic pressure where fluid flow velocity is quite low, for instance in water pipes where it may be in the range 0.2m / s to Im / s. The dynamic pressure sensor may sample an area that is at least twice, at least three times, at least five times or at least seven times the area sampled by a base pressure sensor and / or static pressure sensor.

[0030] The sensing element may comprise a moveable element. The moveable element may move the sensing fibre, preferably at the sensing point, in response to the fluid pressure in the tube. The moveable element may be resiliently biased against fluid pressure within the tube. The moveable element may comprise a wall of the tube. The moveable element may comprise a closed end of the tube. The closed end may be an end distal from the opening. Thus, the moveable element provides a convenient and simple means for monitoring pressure.

[0031] The sensing fibre, and preferably the sensing point, may be provided in contact with, or coupled to, the moveable element. The sensing fibre, and preferably the sensing point, may be provided within a sensing chamber. The sensing chamber may be provided around the moveable element. The sensing chamber may be provided on an outside of the tube. The sensing chamber may be provided at a substantially constant pressure, for example atmospheric pressure. The sensing chamber may be sealed. Thus, the environment on the outside of the moveable element may be better controlled to ensure more repeatable and accurate measurements of fluid pressure in the tube and pipe.

[0032] The moveable element may be configured to change the volume of the sensing chamber in response to the fluid pressure in the tube. The moveable element may be configured to move the sensing fibre and / or change the curvature of the sensing fibre. The sensing fibre may be provided inside the sensing chamber in a curved configuration. This movement will alter the backscattered pulses allowing measurement of the position of the moveable element and by extension the pressure in the tube and pipe.

[0033] The moveable element may comprise a diaphragm. The diaphragm may be configured to deform in response to the fluid pressure in the tube. Thus, the diaphragm provides a simple and reliable method to convert pressure within the tube into movement of the sensing fibre.

[0034] The moveable element may comprise a piston head. The piston head may be configured to translate in response to the fluid pressure in the tube. The moveable element may comprise a piston rod. The piston rod may be connected to the piston head. The piston rod may be received in a piston bore provided by the sensing chamber. The piston rod may slide inside the piston bore to control movement of the piston head. The piston head may be resiliently biased to an equilibrium position depending on the fluid pressure in the tube. The piston rod may comprise a biasing means, such as a spring to set the equilibrium position of the piston head. The piston head may translate along the tube. The sensing chamber may comprise an extension of the tube. The sensing chamber may have the same cross-sectional size / shape as the tube. The sensing chamber may have a larger cross-sectional size / shape than the tube to increase sensitivity from low delta pressure, such as in low fluid flow velocities. The piston head may be shaped to seal the inside of the tube. The piston head may translate along the sensing chamber. Thus, the moveable element may be provided by a piston head, that is preferably combined with a piston rod for more reliable movement.

[0035] A sensor may be provided at each of the two sensing locations. Each sensing point may be arranged in the vicinity of a respective sensor. Each sensing point may be configured to generate backscattered light pulses indicative of the sensor output of a respective sensor. Each sensor may comprise any one or more features of a sensor as described herein. Thus, the sensor output from each sensor can be conveniently detected.

[0036] The two sensing locations may comprise a first sensing location and a second sensing location. A first sensor may be provided at the first sensing location. A second sensor may be provided at the second sensing location. The first and second sensors may both be pressure sensors. A dynamic pressure sensor may be provided at the first sensing location. The dynamic pressure sensor may be arranged to sample a dynamic pressure of fluid inside the pipe. A second pressure sensor may be provided at the second sensing location. The second pressure sensor may be arranged to detect a static pressure, or base pressure, of fluid inside the pipe. Thus, the sensors may be used to detect different types of pressure within the pipe which facilitates computation of more advanced properties of the pipe such as fluid flow.

[0037] The physical sensor spacing may be no more than 100 metres, 10 metres, 1 metre, no more than 50 cm or no more than 5cm. The two sensing locations may be adjacent to one another. The two sensing points may be provided adjacent to one another. The sensors provided at each sensing location may be arranged to sample a property at substantially the same point along the pipe. Thus, the two sensors can efficiently sample the same or different properties at the same place.

[0038] The spacer section may be looped. Thus, the spacer section is arranged in a space-saving manner.

[0039] The spacer section may extend all the way between the two sensing points. Thus, the exact spacing of the two sensing points along the fibre is better defined.

[0040] The spacer section may be at least 10 metres, at least 50 metres, or at least 100 metres in length. The spacer section may be at least two times, three times or four times the spatial resolution. Thus, the spacer section may ensure that the two sensing points are separated by sufficient length of fibre to be easily resolvable.

[0041] The spatial resolution may be affected by any one or more of: the total length of the sensing fibre; the material and construction of the sensing fibre; the frequency and power of light pulses; pulse width; and pulse spacing.

[0042] The sensing apparatus may be configured to monitor more than two sensing locations. The sensing fibre may comprise a sensing point associated with each sensing location. Each sensing point may be provided at a respective sensing location. A physical sensor spacing may be associated with each pair of adjacent sensing points along the sensing fibre. Where the physical sensor spacing is less than the spatial resolution for a given pair of adjacent sensing points, a spacer section may be provided between that pair of adjacent sensing points. Thus, where sensing locations are too close together, a spacer section is provided to ensure that measurements from each are resolvable.

[0043] The pipe to be monitored may be a single unbranched length of pipe. In such embodiments, the sensing fibre may run along the pipe from one end to the other. In other such embodiments the sensing cable may run in a loop from one end of the pipe to be monitored to the other end and back again.

[0044] The pipe to be monitored may comprise a branched network of pipes or part of a branched network of pipes. In such embodiments the sensing cable may run in a loop from an entry point to the far end of each branch in turn.

[0045] The branched network may be any suitable branched network of fluid pipes. In one example, the branched network is a district metered area of a water supply network.

[0046] In some embodiments, the apparatus may be adapted to monitor multiple pipes under test. In such embodiments, each pipe to be monitored may be a single unbranched length of pipe or each pipe to be monitored may be branched network of pipes or part of a branched network of pipes. In further such embodiment, some pipes to be monitored may be single unbranched lengths of pipe and other pipes to be monitored may be branched networks of pipes or parts of branched networks of pipes.

[0047] The light emitter may be a laser. The emitted light may be any suitable wavelength for transmission along and backscattering within the sensing fibre. In some embodiments, the light emitter and light detector may be integrated into a light transceiver unit. Suitable wavelengths are most typically in the infrared wavelengths.

[0048] The optical coupling assembly may comprise any suitable optical device or combination of optical devices. The optical coupling assembly may comprise one or more optical fibres. In one embodiment, the optical coupling assembly may comprise an optical circulator. Beneficially an optical circulator provides efficient coupling of optical signals with minimal power losses. In other embodiments, the optical coupling assembly may comprise an optical switching or optical circulator arrangement. In further embodiments, the optical coupling assembly may comprise one or more power dividers. The power dividers may be 3dB power dividers. Whilst 3dB power dividers do lose roughly half the input power, these are relatively inexpensive devices. As such, embodiments where the optical coupling arrangement comprises one or more power dividers may be more practical in instances where low signal strength is not a concern.

[0049] The sensing apparatus may further comprise a base module comprising the light emitter and the light detector. The base module may comprise a coupling assembly configured to remotely couple light pulses into the sensing fibre and backscattered light pulses out of the sensing fibre.

[0050] The sensing apparatus may comprise a signal analyser configured to process the detector output signal. In some embodiments, the base module may comprise the signal analyser. In other embodiments, the base module may be connected to the signal analyser. In such embodiments, the signal analyser may be provided locally to the base module or remote from the base module.

[0051] The processing by the signal analyser may include any suitable steps. The signal analyser may be configured to extract a component of the detector output signal derived from each said sensing point so as to monitor each sensing point.

[0052] The detector output signal may comprise multiple channels, each channel corresponding to a particular location along the sensing fibre. Each channel may be defined by reference to the round-trip time for backscattered pulses from the particular location. Neighbouring channels may be defined by the minimum resolvable time interval between backscattered pulses from neighbouring sensing fibre locations. Accordingly, each sensing point can correspond to a particular channel within the detector output signal. In such embodiments, the signal analyser may be configured to extract the component of the detector output signal related to each sensing point by reference to particular channels within the detector output signal. The referenced channels may correspond to the location of each sensing point along the length of the sensing fibre. The signal analyser can be configured to output indications of the property to be measured at each of the two sensing locations, and / or the condition of the pipe, and / or events occurring within or in the vicinity of the pipe. Such events may include leaks or the like. This may be achieved by identifying or otherwise analysing the extracted component of the detector output signal corresponding to each sensing point.

[0053] The signal analyser may be in communication with the light emitter. In such embodiments, the signal analyser may be configured to control the light emitter. Light emission may be controlled in order to vary any one or more of: pulse spacing, pulse frequency, pulse width and pulse intensity of the emitted light. In some embodiments, light emission may be controlled in response to analysis of detected backscattered light pulses. Light emission may therefore be controlled to define the spatial resolution.

[0054] The base module may be located at any suitable location. In particular embodiments, the base module may be provided at a building or other structure associated with the fluid pipe or the wider network to which the fluid pipe is connected. In embodiments where the fluid pipe is a water supply pipe or part of a water supply system, the base module may be provided within a substation such as a pumping substation or similar.

[0055] In some embodiments, each connector cable and / or each sensing fibre may additionally comprise one or more data fibres or one or more data fibre bundles. The data fibres or data fibre bundles may be used for carrying network data of a communication network. The communication network may be a network of the type comprising data cables laid for at least part of their length in fluid pipes.

[0056] The sensing module may comprise a pipe fitting. The pipe fitting may be configured to support the sensing fibre. One or more of the two sensing locations may be provided on the pipe fitting. The pipe fitting may be configured to be fitted to the pipe. Thus, the pipe fitting provides convenient attachment of the sensing fibre and sensing location(s) to the pipe to be monitored.

[0057] Two sensing locations may be provided on the pipe fitting. The spacer section may be provided on the pipe fitting between the two sensing locations. Thus, the pipe fitting enables easy mounting of the sensing locations and spacer section at a single point along the pipe.

[0058] The pipe fitting may provide an entry / exit point on the fluid pipe for the sensing fibre. The pipe fitting may provide an entry / exit point on the fluid pipe for the tube of the sensor. The pipe fitting may provide entry / exit points on the fluid pipe for the sensing fibre and the tubes of two sensors, each sensor associated with one of the two sensing locations. Thus, the pipe fitting enables simple and efficient connection to the inside of the pipe.

[0059] The pipe fitting may comprise a semi-rigid tubular arrangement configured to be inserted into the fluid pipe. The tubular arrangement may be configured to resist a fluid flow within the pipe. The sensing fibre may be provided inside the tubular arrangement. The tubular arrangement may be configured to control placement of the sensing fibre within the fluid pipe. Thus, the sensing fibre’s position in the pipe is better controlled.

[0060] In other embodiments, the pipe to be monitored may provide entry / exit points and / or tubular arrangements as described above. The pipe fitting may be configured to mount the sensing fibre and one or more sensing locations (e.g. two sensing locations) to an outside of the pipe to be monitored. Thus the pipe fitting can be simply and easily mountable to the pipe.

[0061] According to a second aspect of the present invention, there is provided a fluid pipe comprising a sensing fibre. The sensing fibre may comprise any one or more features of a sensing fibre as described herein. Preferably, the fluid pipe comprises a sensing apparatus. The sensing apparatus may be the sensing apparatus of the first aspect. The fluid pipe may comprise any one or more features of the pipe, fluid pipe, and / or pipe to be monitored as described above, such as an access tube and access valve.

[0062] The physical sensor spacing may be defined along a length of the pipe from one of the two sensing locations to the other. Where there are more than two sensing locations, the physical sensor spacing between adjacent sensing points may be defined along the length of the pipe from one to the other. Thus, the topography and shape of the pipe is considered allowing more efficient use of spacer sections.

[0063] The two sensing locations may be provided at substantially the same point along the pipe. Thus, properties at a single point along the pipe may be measured efficiently. The two sensing locations may be provided on an outside of the pipe. This may enable more convenient access to the sensing points for maintenance and replacement if required.

[0064] The spacer section may be provided completely outside the pipe. Thus, the spacer section is more conveniently located and does not require passing into / out of the pipe.

[0065] The sensing fibre may be provided at least partially inside the pipe. This enables the sensing fibre to conveniently travel between sensing locations and the base module without needing to separately lay or otherwise install the sensing fibre.

[0066] Where the sensor is a dynamic pressure sensor, either: the opening may extend into the pipe and face upstream; or, the access opening of the access tube may face upstream. Where the sensor is a static pressure sensor, either: the opening may extend into the pipe and face perpendicular to the flow of fluid in the pipe; or, the access opening of the access tube may face perpendicular to the flow of fluid in the pipe. Where the sensor is a base pressure sensor, either: the opening may extend into the pipe and face downstream; or, the access opening of the access tube may face downstream. Thus, the pressure sensors can sample the correct fluid conditions required.

[0067] Where the optical coupling assembly comprises an optical fibre, the optical fibre may be provided at least partially inside the pipe. The optical fibre may extend from the base module to the sensing module. Thus, pulses can be efficiently transmitted over long distances to the sensing module and back.

[0068] The fluid pipe may be a water pipe. The fluid pipe may be part of a water supply network. Thus, the conditions of the water pipe and network may be monitored more efficiently.

[0069] According to a third aspect of the present invention, there is provided a fluid distribution system comprising one or more fluid pipes according to the second aspect of the present invention.

[0070] According to a fourth aspect of the present invention, there is provided a method of installing a sensing fibre for monitoring of two sensing locations physically spaced apart by a physical sensor spacing, the sensing fibre comprising two sensing points and a spacer section between the two sensing points, the method comprising: positioning the two sensing points at the two sensing locations respectively, wherein the two sensing points are configured to generate backscattered light pulses indicative of a property to be measured at each of the two sensing locations, the spacer section is at least a spatial resolution, and the physical sensor spacing is less than the spatial resolution.

[0071] The spatial resolution may define a minimum length of the spacer section where backscattered light pulses from the two sensing points can be resolved.

[0072] The method may comprise installing the sensing fibre at least partially inside a pipe to be monitored. Thus, the sensing fibre may extend within the pipe.

[0073] The method may comprise arranging the spacer section completely outside the pipe. Thus, the spacer section may remain easily accessible outside the pipe.

[0074] The method may comprise connecting a light emitter to the sensing fibre, preferably via an optical coupling assembly. The method may comprise connecting a light detector to the sensing fibre, preferably via the optical coupling assembly.

[0075] According to a fifth aspect of the present invention, there is provided a method for monitoring a fluid pipe at two sensing locations physically spaced apart by a physical sensor spacing, the method comprising: installing the sensing apparatus of the first aspect with the two sensing points provided at the two sensing locations respectively, introducing light pulses into the sensing fibre; detecting backscattered light pulses from the sensing fibre; and processing the backscattered light so as to monitor the two sensing locations.

[0076] The method may comprise installing the sensing fibre according to the method of the third aspect.

[0077] The method may comprise measuring the physical sensor spacing along the fluid pipe. Thus, this can ensure that the shape and topography of the fluid pipe is considered when determining if a spacer section is necessary.

[0078] The method may be a method for monitoring two or more sensing locations.

[0079] The method may comprise measuring a physical sensor spacing between each pair of adjacent sensing locations of the three or more sensing locations. The method may comprise providing a spacer section between a pair of adjacent sensing locations if the physical sensor spacing between the pair of adjacent sensing locations is less than the spatial resolution. Thus, the method ensures all sensing locations are resolvable irrespective of their physical locations.

[0080] The method may comprise closing an isolation valve to isolate a sensing element. The method may comprise disconnecting a sensor from the pipe while the isolation valve is closed. The method may comprise connecting a sensor to the pipe. The method may comprise opening the isolation valve. Thus, the sensors may be conveniently disconnected and connected to the pipe as desired.

[0081] The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the aspects, methods, examples or embodiments described herein may be applied to any other method, aspect, example, embodiment or feature. Further, the description of any aspect, method, example or feature may form part of or the entirety of an embodiment of the invention as defined by the claims. Any of the examples described herein may be an example which embodies the invention defined by the claims and thus an embodiment of the invention.

[0082] Detailed Description of the Invention

[0083] In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0084] Figure 1 is a schematic diagram of a section of a first embodiment of a fluid pipe comprising a sensing apparatus;

[0085] Figure 2 is a schematic diagram of detail A shown in Figure 1 showing a sensing fibre leaving the fluid pipe;

[0086] Figure 3 is a schematic diagram of detail B shown in Figure 2 showing two sensors and the sensing fibre;

[0087] Figure 4 is a schematic diagram of part of a pressure sensor of the sensing apparatus of Figure 1 ; Figure 5 is a schematic diagram of the part of the pressure sensor of Figure 4 where the sensed pressure is higher than that of Figure 4;

[0088] Figure 6 is a schematic diagram of a pressure sensor of a second embodiment of a fluid pipe;

[0089] Figure 7 is a schematic diagram of the pressure sensor of Figure 6 where the sensed pressure is higher than that of Figure 6;

[0090] Figure 8 is a schematic diagram of a section of a third embodiment of a fluid pipe;

[0091] Figure 9 is a schematic diagram of a downstream cross-section of the fluid pipe of Figure 8 showing the opening of the dynamic pressure sensor; and

[0092] Figure 10 is a schematic diagram of an upstream cross-section of the fluid pipe of Figure 8 showing the opening of the base pressure sensor.

[0093] Referring to Figures 1 to 5, a first embodiment of a fluid pipe 1 comprises a sensing apparatus, the sensing apparatus being formed of: a sensing fibre 2; and base module 4. The base module 4 comprises a light emitter 5 to generate light pulses and a light detector 6 to detect backscattered light pulses; and an optical coupling assembly 3.

[0094] The light emitter 5 and detector 6 are optically coupled to the sensing fibre 2 by the optical coupling assembly 3. The optical coupling assembly 3 comprises an optical circulator 7 connected to the light emitter 5 and light detector 6 via an emitter fibre 8 and detector fibre 9 respectively. The optical circulator 7 is also connected to the sensing fibre 2 and is arranged to transmit light pulses from the emitter fibre 8 into the sensing fibre 2 and transmit backscattered light pulses from the sensing fibre 2 into the detector fibre 9.

[0095] The sensing apparatus further comprises a signal analyser 10 provided remote from the base module 4. The signal analyser 10 is connected to the base module 4, for example by a radio connection or the internet, and is configured to control the light emitter 5 and process detected backscattered pulses from the light detector 6 as described in more detail below. The sensing fibre 2 is configured to generate backscattered light pulses indicative of a property to be measured along the sensing fibre 2. The sensing fibre 2 may generate backscattered light pulses in response to various properties such as: moving the sensing fibre, changing the curvature of the sensing fibre, vibrations, acoustic output, changing of fibre temperature, changing of pressure, or the like.

[0096] The signal analyser 10 is configured to process the backscattered light pulses to measure the property at different points along the length of the sensing fibre 2. Where backscattered light pulses originate from two different points along the length of the sensing fibre 2, the signal analyser 10 will be able to resolve the two points if they are separated by a spacing along the sensing fibre 2 that is greater than the spatial resolution of the sensing apparatus. The spatial resolution is the minimum resolvable distance between successive backscattering points on the fibre. The spatial resolution is dependent on various factors such as the length, material and construction of the sensing fibre, as well as light pulse power, frequency, and width. The measurement process and contributing elements of the sensing apparatus and sensing fibre are described further below.

[0097] In this embodiment, the fluid pipe 1 is a water pipe that forms part of a district metering area for a water supply network, with fluid flow in the direction of arrow F in Figure 2. The fluid pipe 1 comprises several fittings 11, 12, 13 that provide an entry / exit point along the fluid pipe 1 for the sensing fibre 2 among other things as described in more detail below. An example of the fittings 11, 12, 13 that may be used for the sensing fibre to enter / exit the fluid pipe 1 are described in PCT / GB2024 / 051555.

[0098] The fittings 11, 12, 13 each comprise a semi-rigid tubular arrangement 14 with a bore extending therethrough to receive the sensing fibre 2. The tubular arrangement in this embodiment is a spiral wound member or spring. The tubular arrangement is straight and sufficiently rigid to resist the fluid flow within the pipe 1, the arrangement 14 extends from the fitting 11, 12, 13, which is generally in an upper part of the pipe 1, across the internal diameter of the pipe 1 to position the sensing fibre 2 along a bottom of the pipe 1. Various options for the semi-rigid tubular arrangement 14 are also described in PCT / GB2024 / 051555. In this embodiment, the sensing fibre 2 extends from the optical circulator 7 into the fluid pipe 1 via an entry fitting 11. The sensing fibre 2 then extends along the inside of the fluid pipe 1 before reaching several pairs of fittings, each comprising a first fitting 12 and second fitting 13. At each pair, the sensing fibre 2 exits the fluid pipe 1 and travels between the first and second fittings 12, 13 on an outside of the pipe 1, before entering the fluid pipe 1 again and extending within the pipe 1 to the next pair of fittings 12, 13. Each pair thereby provides a path for the sensing fibre 2 around an obstacle or object within the pipe 1, such as a valve 14.

[0099] In this embodiment, the sensing fibre 2 is formed as part of a cable of fibres comprising a bundle of data fibres (not shown). As such, the cable may need to break out of the fluid pipe 2 from time to time to provide data connections to different end users. Consequently, a pair of fittings 12, 13 may also be provided where there is no obstacle within the fluid pipe 2.

[0100] In this embodiment, the separation between adjacent pairs of fittings 12, 13 may vary depending on the topography and characteristics of the pipe 1. For example, where many valves or end users are located, the separation may only be a few tens or hundreds of metres, but in more remote locations it may be a number of kilometres.

[0101] In this embodiment, the sensing apparatus is configured to facilitate measurement of the fluid pressure within the fluid pipe 1.

[0102] In this embodiment, the sensing apparatus comprises a dynamic pressure sensor 15 and a base pressure sensor 15’ both provided at each of the first fittings 12. The dynamic pressure sensor (IPS) 15 comprises a tube 16 that extends into the pipe 1 via the first fitting 12. The tube 16 comprises an opening 17 at one end facing upstream against the fluid flow F within the pipe 1, this allows the IPS 15 to sample the dynamic fluid pressure within the pipe 1.

[0103] As shown in Figures 4 and 5, at the other end of the tube 16 there is provided a sensing element in the form of a moveable element, which in this embodiment is a diaphragm 18. The diaphragm 18 forms a closed end of the tube 16 distal from the opening 17 and comprises a flexible material that deforms in response to the fluid pressure within the tube 16. In this embodiment, the IPS 15 further comprises a sensing chamber 19 provided around the diaphragm 18 on an outside of the tube 16. In this embodiment, the sensing chamber 19 is simply an extension of the tube 16 with the diaphragm 18 extending across the cross-sectional profile of the tube 16 to define the sensing chamber 19. A sensing point 20 of the sensing fibre 2 is arranged within the sensing chamber 19 in a curved configuration such that movement / deformation of the diaphragm 18 causes changes in the curvature of the sensing fibre 2 within the sensing chamber 19. Thus, as the sensing fibre 2 (and sensing point 20) are configured to generate backscattered light pulses which depend on the curvature of the sensing fibre 2, the signal analyser 10 can determine the position of the diaphragm 18 and fluid pressure via measurement of the curvature at the sensing point 20 using the backscattered light pulses.

[0104] By way of an example, Figures 4 and 5 show the same IPS 15 where in Figure 4 the fluid pressure is lower than that in Figure 5. As shown, the diaphragm 18 is deformed into the sensing chamber 19 in Figure 5, reducing the available volume in the sensing chamber 19 in Figure 5 and bending the sensing fibre 2 at the sensing point 20 as compared to Figure 4.

[0105] In this embodiment, as shown in Figure 3, the IPS 15 further comprises an isolation valve 21 provided on an outside of the pipe 1 between the opening and diaphragm 18. The isolation valve 21 is configured to fluidly isolate the sensing chamber 19 and diaphragm 18 from the opening 17 when required, and in this embodiment, comprises a gate valve, although any suitable valve may be used. This makes it easier to isolate these components when required for maintenance, removal or other similar activities.

[0106] In other embodiments, the tube may instead be configured to attach to an access tube provided on an outside of the pipe. The access tube providing fluid communication between the tube and the inside of the pipe. In such embodiments, the access tube may comprise an access opening which, for an IPS, would be facing upstream. The access tube may therefore provide the same features as the tube 16 between the opening 17 and isolation valve 21. In this embodiment, the base pressure sensor (BPS) 15’ is very similar to the IPS 15 and therefore like numerals are used to denote the same features. The main difference between the two sensors is that the opening 17’ faces downstream or in a more traditional static tube method, such that it may sample a base fluid pressure within the pipe 1. Otherwise, the IPS and BPS 15, 15’ are substantially identical.

[0107] The sensing fibre 2 extends out of the fitting 12 and into the BPS 15’ where a sensing point 20’ is arranged within the sensing chamber 19’ to detect movement of the diaphragm 18’ of the BPS 15’. The sensing fibre 2 then comprises a spacer section 22, which in this embodiment is a loop of fibre, before extending into the IPS 15 where a sensing point 20 is arranged within the sensing chamber 19 to detect movement of the diaphragm 18. The spacer section 22 is therefore located completely outside the pipe 1.

[0108] The spacer section 22 is sized to ensure that the length of fibre between the two sensing points 20, 20’ is at least as long as the spatial resolution required to resolve backscattered light pulses from the respective sensing points 20, 20’. This is required as the two sensing locations, defined by the two diaphragms 18, 18’, are physically very close together and at substantially the same point along the length of the pipe 1. For example, they may be under 1 metre apart. Thus, a physical sensor spacing, defined as the physical separation of the two sensing locations (or diaphragms 18, 18’), is much less than the spatial resolution. Introduction of the spacer section 22 advantageously decouples the physical separation of the sensing points 20, 20’ from the length of fibre between them, allowing free placement of adjacent sensing points 20, 20’.

[0109] Of course, in other embodiments, different sensors may form part of the sensing apparatus and may be placed at the same or different points along the fluid pipe 1. As the sensors are generally placed in the vicinity of the pipe 1, and the sensing fibre 2 runs along the inside of the pipe 1, then where two adjacent sensors have a physical sensor spacing measured along the pipe 1 that is less than the spatial resolution, a spacer section 22 may be introduced to provide the required separation along the sensing fibre 2 to allow measurements from both sensors to be individually resolved. Consequently, the spacer section in other embodiments may extend within the pipe 1 if necessary. Where the sensing fibre 2 does not run along the pipe 1 between two adjacent sensors, then the physical sensor spacing may simply be the shortest route between the two sensors, for example the shortest route the sensing fibre 2 can take from one to the other.

[0110] To install the sensing apparatus, the sensing fibre 2 is first installed into the pipe 1. This may be done in sections, with the sensing fibre 2 routed between adjacent fittings 11, 12, 13 and then spliced to the adjacent section, or as one single run. Examples of this process are provided in WO2019 / 166809A1. The base module is then provided and connected to the sensing fibre 2 via the optical coupling assembly. The sensing points 20, 20’ of the sensing fibre 2 are then inserted into the sensing chambers 19, 19’ such that they are sensitive to changes in the shape of the diaphragm 18, 18’ and the spacer section 22 is looped and stowed next to the sensing points 20, 20’. The fibre 2 may then extend to the second fitting 13 of the pair and re-enter the pipe 2 to extend to the next fitting.

[0111] The first fitting 12, 12’ is then sealed in place onto the pipe 1 with the openings 17, 17’ inside the pipe 1. If the isolation valves 21, 21’ are closed, they are then opened to allow fluid inside the pipe 1 to fill the tubes 16, 16’ and fluid pressure equalise. The diaphragms 18, 18’ then deform and the sensing apparatus is ready for use.

[0112] During use, the signal analyser 10 controls the light emitter 5 to emit light pulses with a given pulse width, frequency and power. The light pulses are coupled into the sensing fibre 2 by the optical circulator 7. The light pulses travel down the sensing fibre 2 to the sensing points 20, 20’ where backscattered light pulses are generated in dependence upon the curvature of the fibre 2 at each sensing point 20, 20’. The backscattered light pulses travel back down the sensing fibre 2 to the optical circulator 7 where they are passed into the detector fibre 9 and into the light detector 6. The light detector 6 measures the properties of the backscattered light pulse such as its power, frequency, pulse width, evanescent field strength etc, as well as time of arrival, and transmits this information to the signal analyser. The signal analyser 10 then uses the time of arrival information to determine which sensing point 20, 20’ the backscattered pulse has originated from, and given the spacer section 22, the backscattered light pulses from each sensing point 20, 20’ are separately resolvable. The signal analyser 10 then uses the other detected information to determine the curvature of the sensing fibre 2 at the sensing point 20, 20’. This can then be related to the diaphragm 18, 18’ position and fluid pressure within the tube 16, 16’ which allows calculation of the dynamic and base fluid pressure within the pipe 1.

[0113] The optical coupling assembly 3 can facilitate placement of the base module and sensing module at different locations, for example, in this embodiment the base module 4 is close to one end of the sensing fibre 2, but in other embodiments, an optical fibre may be provided such that the sensing fibre 2 and rest of the sensing module is remote from the base module, for example at least 50 km or more from the base module.

[0114] Referring to Figures 6 and 7, a sensing element for the sensors 15, 15’ of a second embodiment of a fluid pipe is shown. This embodiment is the same as the first embodiment except for the differences to the sensing element as described below, consequently like numerals are used for similar / corresponding features. In this embodiment, the sensing element comprises a moveable element in the form of a piston head 18. The sensing chamber 19 is an extension of the tube 16 and like with the diaphragm, the piston head 18 is provided across the entire internal cross-section of the tube / sensing chamber such that changes in the fluid pressure within the tube 16 cause the piston head to translate along the tube / sensing chamber.

[0115] In this embodiment, the moveable element further comprises a piston rod 23 that is received by a piston bore 24 in a wall of the sensing chamber. The piston rod 23 is attached to the piston head 18 to control movement of the piston head 18 and ensure it does not become misaligned or jammed during translational movement.

[0116] The piston rod 23 comprises a spring or other resilient member 25 that is configured to urge the piston head 18 towards the tube opening 17. Thus, as the force applied by the spring depends upon its compression, the equilibrium position of the piston head where the spring force on one side of the piston head 18 matches the fluid pressure on the other side is dependent on fluid pressure.

[0117] As shown in Figures 6 and 7, the pressure in the tube 16 is higher in Figure 7 then Figure 6, as such, in Figure 7 the equilibrium position of the piston head 18 is different as compared to Figure 6 resulting in less available volume in the sensing chamber 19 and increased curvature at the sensing point 20. This increased curvature may then be measured by the signal analyser 10 as described in relation to Figures 1 to 5 and the fluid pressure determined.

[0118] Referring to Figures 8 to 10, a section of a third embodiment of a fluid pipe 1 is shown. This embodiment shares many of the same features of the first embodiment, as such only the differences are discussed below and like numerals are used for the same or corresponding differences.

[0119] In the third embodiment, the IPS 15 comprises an opening 17 with a larger cross-sectional area than the opening 17’ of the BPS 15’. In this embodiment, the opening 17 of the IPS 15 has an elliptical cross-section with a major axis that is approximately 3.5 times larger, and a minor axis that is approximately two times larger, than the diameter of the circular opening 17’ of the BPS 15’. Thus, the cross-sectional area of the IPS 15 opening 17 is approximately seven times larger than the BPS 15’ opening 17’.

[0120] In this embodiment, the major axis of the IPS opening 17 is arranged vertically within the pipe 1. In this fashion a larger surface area orifice may be introduced into the pipe via a limited diameter access port for example 100mm to 200mm diameter.

[0121] This can allow the IPS 15 to be more sensitive to smaller changes in dynamic pressure. Additionally, if the IPS 15 and BPS 15’ are fluidly connected, then it facilitates fluid flow from the IPS 15 to the BPS 15’. This can be useful where additional sensors or components are mounted to the pipe fitting 12, such as flow sensors.

[0122] The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

CLAIMS1. A sensing apparatus for monitoring a fluid pipe at two sensing locations physically spaced apart by a physical sensor spacing, the sensing apparatus comprising: a sensing fibre; a light emitter for introducing light pulses into the fibre; a light detector module configured to detect backscattering of the light pulses from the sensing fibre and output a detector output signal in response thereto; wherein the sensing fibre comprises two sensing points positioned at the two sensing locations respectively, and a spacer section between the two sensing points, wherein the physical sensor spacing is less than the spatial resolution of the sensing apparatus and the spacer section has a length greater than the spatial resolution of the sensing apparatus.

2. The sensing apparatus of claim 1 wherein the sensing apparatus comprises a sensor provided at each of the two sensing locations and configured to generate a sensor output indicative of the property to be measured, wherein the sensing point provided at each of the two sensing locations is arranged to generate backscattered light pulses indicative of the respective sensor output.

3. The sensing apparatus of claim 2 wherein each sensor is arranged to generate a sensor output indicative of a property of the fluid in the fluid pipe, and each sensor comprises a tube in fluid communication with the fluid pipe and a sensing element configured to generate a sensor output indicative of the property of the fluid within the tube, wherein each of the two sensing points is arranged to generate backscattered light pulses indicative of the sensor output from one of the sensors.

4. The sensing apparatus of claim 3 wherein the tube comprises an isolation valve configured to selectively fluidly isolate the sensor from the fluid pipe.

5. The sensing apparatus of claim 3 or 4 wherein the tube extends into the fluid pipe and comprises an opening that facilitates fluid communication of the tube with the fluid pipe.

6. The sensing apparatus of any one of claims 2 to 5 wherein the sensor is a pressure sensor configured to detect a pressure of fluid within the fluid pipe, and the sensing element comprises a moveable element configured to move the sensing fibre at the sensing point in response to the fluid pressure in the tube.

7. The sensing apparatus of claim 6 wherein the moveable element comprises a diaphragm configured to deform in response to the fluid pressure in the tube.

8. The sensing apparatus of claim 6 wherein the moveable element comprises a piston head configured to translate in response to the fluid pressure in the tube.

9. The sensing apparatus of any one of claims 6 to 8 comprising a pressure sensor at each of the two sensing locations: a dynamic pressure sensor arranged to sample a dynamic pressure of fluid inside the pipe; and a second pressure sensor arranged to detect a static pressure, or base pressure, of fluid inside the pipe.

10. The sensing apparatus of claim 9 wherein the opening of the dynamic pressure sensor comprises a larger cross-sectional area than the opening of the second pressure sensor.

11. The sensing apparatus of any one of the preceding claims wherein the spacer section is looped.

12. The sensing apparatus of any one of the preceding claims, wherein the sensing apparatus comprises, or is connected to, a signal analyser configured to process the detector output signal.

13. A fluid pipe comprising the sensing apparatus of any one of the preceding claims.

14. The fluid pipe of claim 13 wherein the physical sensor spacing is defined along a length of the fluid pipe from one of the two sensing locations to the other.

15. The fluid pipe of claim 14 wherein two sensing locations are provided at substantially the same point along the fluid pipe.

16. The fluid pipe of any one of claims 13 to 15 wherein the spacer section is provided completely outside the pipe.

17. The fluid pipe of any one of claims 13 to 16 wherein the two sensing locations are provided outside the pipe.

18. The fluid pipe of any one of claims 13 to 17 wherein the sensing fibre is provided at least partially inside the fluid pipe.

19. The fluid pipe of any one of claims 13 to 18 wherein the optical coupling assembly comprises an optical fibre and the optical fibre is provided at least partially inside the pipe.

20. The fluid pipe of any one of claims 13 to 19 wherein the fluid pipe is a water pipe.

21. A fluid distribution system comprising one or more fluid pipes according to the any one of claims 13 to 20.

22. A method for monitoring a fluid pipe at two sensing locations physically spaced apart by a physical sensor spacing, the method comprising: installing the sensing apparatus of any one of claims 1 to 13 with the two sensing points provided at the two sensing locations respectively, introducing light pulses into the sensing fibre; detecting backscattered light pulses from the sensing fibre; and processing the backscattered light so as to monitor the two sensing locations.

23. The method of claim 22 further comprises measuring the physical sensor spacing along the fluid pipe.

24. The method of claim 23 wherein processing by the signal analyser includes extracting a component of the detector output signal derived from each said sensing point so as to monitor each sensing point.

25. The method of claim 24 wherein the detector output signal comprises multiple channels, each channel corresponding to a particular location along the sensing fibre and extracting the component of the detector output signal related to each sensing point is achieved by reference to particular channels within the detector output signal.

26. The method of any one of claims 22 to 25 for monitoring three or more sensing locations, comprising measuring the physical sensor spacing between each pair of adjacent sensing locations of the three or more sensing locations, and providing a spacer section between a pair of adjacent sensing locations if the physical sensor spacing between the pair of adjacent sensing locations is less than the spatial resolution.

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