Improvements in or relating to relation to monitoring of fluid pipes

Abstract

A pipe monitoring apparatus (200) comprises a base module (210) connected to one end of a sensing fibre (1). The base module (210) comprises a light emitter (211) such as a laser and a light detector (212) to capture backscattered light. The sensing fibre (1) together with an optical coupling assembly (221) defines a sensing module (220). A connector cable (230) comprising an emitter fibre (231) configured to carry light pulses from the light emitter (211) to the optical coupling assembly (221), and a detector fibre (232) configured to carry backscattered light pulses from the optical coupling assembly (221) to the light detector (212) is provided between the base module (210) and the sensing module (220). The separate emitter fibre (231) and detector fibre (232) of the connector cable (230) provide separate routes for emitted light pulses and backscattered pulses between the emitter (211) and detector (212) and the sensing fibre (1). This allows the optical coupling assembly (221) to be provided in the vicinity of the pipe to be monitored whilst the sensing fibre (1) is provided within the pipe to be monitored without adverse impact on sensing performance.

Description

[0001] IMPROVEMENTS IN OR RELATING TO RELATION TO MONITORING OF FLUID PIPES

[0002] Technical Field of the Invention

[0003] The present invention relates to monitoring of fluid pipes. In particular, the present invention is directed to monitoring of fluid pipe integrity, the monitoring of fluid flow within a fluid pipe and / or leak detection. The present invention further relates to an apparatus and a method for monitoring a fluid pipe as well as a network comprising one or more pipes monitored using the apparatus or the method of the present invention.

[0004] Background to the Invention

[0005] Many modem services rely upon a network of pipes to carry or distribute fluids. Examples include 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] Where pipes are provided above ground, monitoring may be achieved by visual inspection of the pipe exterior. In many cases, pipes are not accessible to visual inspection, being buried underground. Accordingly, pressure / acoustic sensors or the like may be utilised to detect vibrations of the pipe and thereby provide information on conditions within a pipe.

[0007] In particular implementations, distributed acoustic sensing (DAS) otherwise referred to as distributed vibration sensing (DVS) has been used for monitoring pipes. DAS involves the detection of backscattering of light pulses introduced into an optical fibre. The time of arrival and intensity of the backscattered light is measured for each pulse, the time at which the backscattered light is detected being related to the distance along the fibre the light has travelled before being scattered. Subsequent changes in the reflected intensity of successive pulses from a common region of the fibre correspond to variations in the strain applied to the fibre at that region, for instance due to vibrations experienced by the region of fibre. In this manner, the DAS fibre can act as a plurality of virtual microphones along the length of the fibre and can locate events causing acoustic signals down to an accuracy of around 1 meter. One example of this technique is our prior application WO2019 / 166809.

[0008] Whilst DAS is effective in many situations for monitoring flow within a pipe and detecting leaks, additional information on the condition of the pipe can be obtained by carrying out distributed strain sensing (DSS) and / or distributed temperature sensing (DTS) using a sensing fibre. DTS may help identify adiabatic cooling in a gaseous fluid in the vicinity of a leak candidate and / or other temperature change indicative of a flow of heat between a pipe and surrounding ground of a different temperature. DSS may help identify changes in strain along the length of a pipe indicative of a potential for future failure of the pipe.

[0009] In a typical pipe monitoring apparatus, a suitable light emitter, such as a laser and a light detector to capture backscattered light are housed in a base module at one end of a fibre under test, along with a local optical coupling assembly configured to couple the emitted light from the emitter into the fibre under test and to couple backscattered light from the fibre under test to the detector. In many cases, the detector may be coupled to a local signal analyser, at the same location. The base module is installed at a convenient location such as a pumping substation, with adequate power and data connections and ready access. The sensing fibre can then run from the base module to the pipe under test (through other pipes or conduits if appropriate) and along the pipe under test. This arrangement is beneficial since high quality emitters and / or analysers can be relatively expensive assets and sensing fibres are routinely supplied in lengths of many kilometres or tens of kilometres. Such an arrangement is also simple to implement and especially well suited to monitoring linear pipes.

[0010] These arrangements are less well suited to monitoring branched networks such as a potable water supply system or a gathering network within an oil or gas field. In a water supply system for example, one or more branched district metered areas (DMA) may each be supplied from a common substation and may be some distance from the substation and / or each other. Given that sensing cables can be relatively long compared to lengths of pipes in a DMA, this difficulty can be partially mitigated by looping a single test fibre around multiple branches of a network. For instance, a fibre of 100km in length could be used to monitor multiple DMAs from a single substation even where the summed length of branches in each DMA is in the 5km to 10km range and / or one or more of the individual DMAs is say 10km or more from the substation housing the emitter and detector.

[0011] In any such arrangement above, there is a fundamental limitation on the rate at which light pulses can be emitted into the fibre under test and reliably detected. More specifically, the rate is limited by the round trip transit time for backscattered pulses between the emitter and detector via the far end of the fibre under test. For a sensing fibre of say 100km in length, the transit time (calculated from twice the fibre length divide by the speed of light in the fibre medium) would typically be -0.001s, thus implying a maximum pulse repetition frequency of 1kHz. Furthermore, due to Nyquist sampling criteria, only acoustic frequencies up to half the pulse repetition frequency may be classified correctly by the apparatus. Accordingly in this example, the maximum detectable acoustic frequency would be ~500Hz. Whilst this maximum frequency would be acceptable in some circumstances, it may not be appropriate in others. For example, when detecting leaks in water pipes the acoustic frequencies of most relevance are typically of the order of 20kHz. Accordingly, achieving a high enough pulse rate to usefully detect acoustic signals of interest may provide a further practical limitation on the maximum practical length of a fibre under test.

[0012] Another issue is that the maximum dynamic range of the fibre under test is linked to the maximum measurable linear strain within a sensing time period. This quantity (sometimes referred to as the stain slew rate) scales with the pulse repetition frequency. For instance, when operating at a pulse repetition frequency of 1kHz, the maximum peak to peak dynamic range detectable on a DAS fibre might be of the order of 28 nanostrain whereas when operation at a pulse repetition frequency of 20kHz, the maximum peak to peak dynamic range detectable on a DAS fibre might be of the order of 560 nanostrain. If high signal amplitudes are experienced and / or if these are at higher frequency, then the dynamic range of the sensing fibre may be exceeded for a given pulse rate. Once such oversaturation occurs, the sensing fibres and the analyser lose their effectiveness to detect across the spectrum, compromising their ability to accurately monitor the pipe as well as conditions proximal to the pipe. This also limits the potential for detecting and interpreting events indicative of the pipe condition. This thereby provides a limitation on the practical length of a fibre under test.

[0013] In view of the above issues, known systems either accept a trade off in performance and / or rely on have multiple separate emitter and detectors and fibres under test for different branches (or sets of branches) within a network. Furthermore, such known systems either accept a trade off in performance and / or rely on having to provide separate emitters / detectors close to each separate dedicated fibre under test rather than providing all emitters / detectors at a common base location.

[0014] It is an object of the present invention to provide methods and apparatus which at least partially overcome or alleviate at least some of the above problems.

[0015] Summary of the Invention

[0016] According to the present invention there is provided a sensing apparatus for monitoring the condition of a fluid pipe. The sensing apparatus may comprise a sensing fibre provided within the pipe. The sensing apparatus may comprise a light emitter for generating light pulses for introduction into the sensing fibre. The sensing apparatus may comprise a light detector configured to detect backscattered light pulses. In the sensing apparatus, one end of the sensing fibre may be coupled to an optical coupling assembly. In the sensing apparatus, the light emitter may be coupled to the optical coupling assembly via an emitter fibre. In the sensing apparatus, the light detector may be coupled to the optical coupling assembly by a detector fibre. In the sensing apparatus, the optical coupling assembly may be provided in the vicinity of the fluid pipe to be monitored. In the sensing apparatus, the optical coupling assembly may be provided remote from the light emitter and the light detector. The sensing apparatus may comprise a base module comprising the light emitter for generating light and the light detector configured to detect backscattered light pulses. The sensing apparatus may comprise a sensing module comprising the sensing fibre provided within the pipe to be monitored and the optical coupling assembly provided in the vicinity of the pipe to be monitored.

[0017] According to a first aspect of the present invention, there is provided a sensing apparatus for monitoring the condition of a fluid pipe, the sensing apparatus comprising: a base module, comprising a light emitter for generating light pulses and a light detector configured to detect backscattered light pulses; a sensing module comprising a sensing fibre provided within the pipe to be monitored and an optical coupling assembly provided in the vicinity of the pipe to be monitored, the optical coupling assembly configured to couple light pulses into the sensing fibre and backscattered light pulses out of the sensing fibre; and a connector cable comprising an emitter fibre configured to carry light pulses from the light emitter to the optical coupling assembly, and a detector fibre configured to carry backscattered light pulses from the optical coupling assembly to the light detector.

[0018] The apparatus of the present invention enables a sensing module comprising the optical coupling assembly and the sensing fibre to be situated remote from a base module comprising the emitter and detector without adverse impact on sensing performance. This is because the separate emitter and detector fibres of the connector cable provide separate roues for emitted light pulses and backscattered pulses between the emitter and detector and the sensing fibre. Accordingly, this reduces the effective round-trip time for resolving separate backscattered pulses to that taken to travel along the length of the sensing fibre and back rather than the total fibre distance between the emitter and detector and the end of the sensing fibre and back again. Accordingly, the present invention enables a high pulse rate to be used for monitoring pipes even if they are separated from the emitter and detector by a significant distance. Consequently, the effective dynamic range of the sensing apparatus can be extended and / or the sensing apparatus can detect signals with a higher acoustic frequency within the pipe to be monitored.

[0019] 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 and 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The branched network may be any suitable branched network of fluid pipes. In one example, the branched network is a DMA zone of a water supply network.

[0027] 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. The emitter fibre may be a single mode optical fibre. In some embodiments, the emitter fibre may be provided with a sheath. The emitter fibre sheath may be opaque. The detector fibre may be a single mode optical fibre. In some embodiments, the detector fibre may be provided with a sheath. The detector fibre sheath may be opaque.

[0028] The emitter fibre may be an extended emitter fibre. The detector fibre may be an extended detector fibre. The emitter fibre may be at least 1km in length, at least 5km in length, at least 10km in length, at least 20km in length, at least 50km in length or at least 100km in length. The detector fibre may be at least 1km in length, at least 5km in length, at least 10km in length, at least 20km in length, at least 50km in length or at least 100km in length.

[0029] The emitter fibre may be a single continuous fibre or may comprise multiple successive sections of fibre. The detector fibre may be a single continuous fibre or may comprise multiple successive sections of fibre.

[0030] The light emitter may be emitter may be a laser. The emitted light may 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.

[0031] The optical coupling assembly may comprise any suitable optical device or combination of optical devices. 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 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. The base module may comprise a signal analyser. The base module may be connected to a signal analyser. In such embodiments, the signal analyser may be provided locally to the base module or remote from the base module.

[0032] The signal analyser may be configured to analyse and / or filter detected light. The signal analyser may be in communication with the light detector. The signal analyser can be configured to output indications of the condition of the pipe and / or events occurring within or in the vicinity of the pipe. Such event may include leaks or the like.

[0033] 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 frequency, pulse length and pulse intensity of the emitted light. In some embodiments, light emission may be controlled in response to analysis of detected backscattered light pulses.

[0034] 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.

[0035] In some embodiments, the base module may comprise multiple emitters and multiple detectors. In such embodiments, the number of emitters may match the number of detectors. In particular, each emitter may have a dedicated detector. In some such embodiment, each emitter may generate light pulses of the same wavelength. In other embodiments, each emitter may generate light pulses of different wavelengths.

[0036] In some embodiments, the sensing apparatus may comprise a single sensing module. In other embodiments, the sensing apparatus may comprise multiple sensing modules. In some embodiments comprising multiple sensing modules, each optical coupling assembly may comprise the same type of optical device or combination of optical devices. In other embodiments comprising multiple sensing modules, each optical coupling assembly may comprise a different type of optical device or combination of optical devices.

[0037] In some embodiments, the sensing apparatus may comprise a single connector cable. In other embodiments, the sensing apparatus may comprise multiple connector cables. In some embodiments, each connector cable may comprise a single emitter fibre and detector fibre pair. In other such embodiments, each connector cable may comprise multiple emitter fibre and detector fibre pairs.

[0038] In embodiments comprising a single sensing module, the sensing apparatus may comprise a single connector cable. In embodiments comprising multiple sensing modules, the sensing apparatus may comprise a dedicated connector cable for each sensing module. In other such embodiments, the sensing apparatus may comprise a single connector cable. In such embodiments, the connector cable may comprise a single emitter fibre and detector fibre pair or multiple emitter fibre and detector fibre pairs. In such embodiments, there may be a dedicated emitter fibre and detector fibre pair for each sensing module.

[0039] In some embodiments, the base module may be provided with a base switching unit. The base switching unit may be an optical switching unit. The base switching unit may be a one to many, many to may or many to one switching unit. The base switching unit may be configured to facilitate connection between multiple connector cables or between multiple emitter fibre and detector fibre pairs within a connector cable. The base switching unit may enable selection of a particular sensing module to be connected to a particular connector cable or to a particular emitter fibre and detector fibre pair.

[0040] The base switching unit may be configured so as to periodically cycle between different cables or different emitter fibre and detector fibre pairs. This thereby enables different pipes to be monitored in turn. Additionally or alternatively, the base switching unit may be configured so as to select a cable or emitter fibre and detector fibre pair for monitoring based on analysis of detected backscattered light pulses. This can enable closer analysis of a particular pipe in response to detected events. The base switching unit may be controlled in response to the signal analyser. In some embodiments, the sensing apparatus may be provided with a zone switching unit for each sensing module. In such embodiment, each zone switch may be an optical switching unit. In some embodiments, each zone switching unit may be provided in series with successive sections of emitter fibre and successive sections of detector fibre. In such cases, each zone switching unit may be configured to enable previous sections of emitter fibre and detector fibre to be selectively connected to either the optical coupling assembly of the particular sensing module or to subsequent sections of emitter fibre and detector fibre. In such embodiments, each zone switching unit may comprise a pair of one to two optical switches. In such embodiments, the previous sections of emitter fibre and detector fibre may be closer to the base module than the subsequent sections of emitter fibre and detector fibre. Such embodiments can allow the zone switch to be used to selectively bypass a particular sensing module or connect the particular sensing module to the base module. Beneficially, such an arrangement can be scaled to add multiple further sensing modules to successive sections of emitter fibre and successive sections of detector fibre.

[0041] Each zone switching unit may be configured so as to periodically cycle between connection to the optical coupling assembly of the particular sensing module or to subsequent sections of emitter fibre and detector fibre. This thereby enables different pipes to be monitored in turn. Additionally or alternatively, each zone switching unit may be configured so as to select connection to the optical coupling assembly of the particular sensing module for monitoring based on analysis of detected backscattered light pulses. This can enable closer analysis of a particular pipe in response to detected events. Each zone switching unit may be controlled in response to the signal analyser.

[0042] In some embodiments, the base module may comprise an optical wavelength multiplexer. The optical wavelength multiplexer may be coupled to multiple light emitters each such emitter configured to generate light pulses of a different wavelength. In such embodiments, the multiplexer may facilitate use of light pulses of different wavelengths on a single emitter fibre.

[0043] In some embodiments, the base module may comprise an optical wavelength demultiplexer. The optical wavelength demultiplexer may be coupled to multiple light detectors. Each such detector configured to detect light pulses of a different wavelength In such embodiments, the demultiplexer may facilitate resolution between backscattered light pulses of different wavelengths on a single detector fibre.

[0044] In such embodiments, the emitter fibre may be provided with a drop multiplexer for each sensing module. Each drop multiplexer may be configured to selectively couple light pulses of a specific wavelength to the optical coupling assembly of the particular sensing module. The drop multiplexer for a particular sensing module may be provided in the vicinity of that sensing module.

[0045] In such embodiments, the detector fibre may be provided with an add multiplexer for each sensing module. Each add multiplexer may be configured to selectively couple light pulses of a specific wavelength from the optical coupling assembly of the particular sensing module. The add multiplexer for a particular sensing module may be provided in the vicinity of that sensing module.

[0046] The apparatus may be provided with an emitter amplifier. The emitter amplifier may be provided between successive sections of emitter fibre. The emitter amplifier may be configured to amplify the light pulses travelling along the emitter fibre. The emitter amplifier may be positioned in the vicinity of the sensing module. In some embodiments, multiple emitter amplifiers may be provided. In some such embodiments, emitter amplifiers may be provided at regular intervals along the emission fibre. In embodiments where multiple sensing modules are connected to a single emission fibre multiple emitter amplifiers may be provided in the vicinity of each sensing module. In embodiments with multiple emission fibres, each emission fibre may be provided with one or more emitter amplifiers. In other such embodiments only selected emission fibres may be provided with one or more emitter amplifiers.

[0047] The apparatus may be provided with a detector amplifier. The detector amplifier may be provided between successive sections of detector fibre The detector amplifier may be configured to amplify the backscattered light pulses travelling along the detector fibre. The detector amplifier may be positioned in the vicinity of the base module. In some embodiments, multiple detector amplifiers may be provided. In some such embodiments, detector amplifiers may be provided at regular intervals along the detector fibre. In other embodiments, where multiple sensing modules are connected to a single detector fibre multiple detector amplifiers may be provided in the vicinity of each sensing module and / or in the vicinity of the base module. In embodiments with multiple detector fibres, each detector fibre may be provided with one or more detector amplifiers. In other such embodiments only selected detector fibres may be provided with one or more detector amplifiers.

[0048] In some embodiments, each connector cable and / or each sensing fibre may additionally comprise one or more data fibres or one or more 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 are laid for at least part of their length in fluid pipes.

[0049] In some such embodiments, the fluid pipe may be provided with one or more other sensors. In such embodiments, the data fibres or data fibre bundles may be configured to carry sensor data from said other sensors alongside said network data. Carrying sensor data alongside network data removes the requirement for a separate sensor data backhaul arrangement.

[0050] According to a second aspect of the present invention, there is provided a method for monitoring a fluid pipe, the method comprising the steps of: installing one or more sensing apparatuses according to the first aspect of the present invention: introducing light pulses into the sensing fibre; detecting backscattered light pulses from the sensing fibre; and processing the backscattered light so as to obtain information about the condition of the pipe and / or events occurring within or in the vicinity of the pipe.

[0051] According to a third aspect of the present invention, there is provided a fluid distribution system comprising one or more fluid pipes where one or more sensing apparatuses according to the first aspect of the present invention are provided to monitor at some of the pipes.

[0052] According to a fourth aspect of the present invention there is provided a data communication network comprising one or more data cables laid for at least part of their length in fluid pipes and additionally comprising one or more sensing apparatuses according to the first aspect of the present invention. In such networks, at least some of sensing apparatuses are provided with connector cables and / or sensing fibres additionally comprising one or more data fibres or one or more one or more data fibre bundles.

[0053] 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.

[0054] Detailed Description of the Invention

[0055] 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:

[0056] Figure 1 shows (a) a schematic block diagram of a sensing apparatus for monitoring the condition of a fluid pipe according to the prior art, (b) a schematic diagram of the sensing apparatus of figure la overlaid on an exemplary water supply system, and (c) a schematic diagram of the sensing apparatus of figure la overlaid on an exemplary water supply system in a different arrangement;

[0057] Figure 2 shows (a) a schematic block diagram of a sensing apparatus for monitoring the condition of a fluid pipe according to the present invention, and (b) a schematic diagram of the sensing apparatus of figure 2a overlaid on an exemplary water supply system;

[0058] Figure 3 shows (a) a schematic block diagram of another embodiment of a sensing apparatus for monitoring the condition of a fluid pipe according to the present invention, and (b) a schematic diagram of the sensing apparatus of figure 3 a overlaid on an exemplary water supply system;

[0059] Figure 4 shows (a) a schematic block diagram of zone switch for use with a sensing apparatus for monitoring the condition of a fluid pipe according to the present invention, and (b) a schematic diagram of a sensing apparatus according to the present invention implemented using the zone switch of figure 4a overlaid on an exemplary water supply system;

[0060] Figure 5 shows a schematic block diagram of another embodiment of a sensing apparatus for monitoring the condition of a fluid pipe according to the present invention; and

[0061] Figure 6 shows a schematic block diagram of another embodiment of a sensing apparatus for monitoring the condition of a fluid pipe according to the present invention incorporating optical amplifiers.

[0062] Figure la is a schematic illustration of a known pipe monitoring apparatus 100 according to the prior art. The pipe monitoring apparatus 100 comprises a base module 110 connected to one end of a sensing fibre 1. The base module 110 comprises a light emitter 111 (such as a laser) and a light detector 112 to capture backscattered light. The base module further comprises a local optical coupling assembly 113 configured to configured to couple light from the emitter 111 to the sensing fibre 1 and to couple backscattered light from the sensing fibre 1 to the detector 112. In this example, the local optical coupling assembly comprises a local optical circulator 113. The skilled person will however appreciate that alternative optical coupling assemblies can be substituted for an optical circulator. For example, the optical coupling assembly may comprise an optical switching arrangement or one or more power dividers, such as 3dB power dividers. Whilst 3dB power dividers do lose roughly half the input power, there are significantly less expensive than optical circulators so may be more practical in instances where low signal strength is not a concern.

[0063] Optionally the detector 112 is connected to a local or remote signal analyser (not shown) for analysing and / or filtering detected light. In this manner, the signal analyser may be configured to output indications of the condition of the pipe and / or events occurring within or in the vicinity of the pipe.

[0064] Turning now to figures lb and 1c, a schematic example of a water supply system 10 is illustrated. In this example, the system comprises a pumping substation 11 within which is housed base module 110. This ensures that the base module 110 can be supplied with adequate power and data connections. It also provides a protected location with ready access in which to house potentially delicate and expensive emitters 111, detectors 112 and / or analysers.

[0065] Extending from the substation 11 is a trunk pipe 12 which supplies water to three illustrated district metred areas (DMAs) 21, 22, 23. Within each district metered area 21-23 are provided one or more local valves 13, one or more local storage tanks 14 and one or more consumption points 15 (only a subset of each item 13-15 is labelled in the drawings for clarity).

[0066] As can be seen in figure lb, the sensing fibre 1 runs from the base module 110 to the pipe under test. In figure lb, the pipe under test is the core of the first DMA 21 between the trunk pipe 12 and the local control valves 13. In order to ensure all of this branched network is adequately monitored, the sensing fibre 1 is looped along each of the individual pipes. In figure 1c, the sensing fibre 1 is looped around all three DMAs 21-23.

[0067] As can be seen in figure lb, a significant fraction 2 of the length of the sensing fibre 1 is lies in the trunk pipe 12 and is not used for monitoring the DMA 21. Similarly, in figure 1c further sections 3 and 4 of the sensing fibre 1 also lie in the trunk pipe 12 and are not needed for monitoring the DMAs 22, 23. In many instances, these ‘transit’ sections 2-4 of the sensing fibre 1 can be 10-50km in length each whereas the active sections of sensing fibre 1 within the DMAs 21-23 may be 5km- 10km each. Accordingly, the transit sections 2-4 significantly limit the effective dynamic range and / or the maximum detectable acoustic frequency within the monitored sections of pipe. This is because the dynamic range and the maximum detectable acoustic frequency are related to the maximum resolvable input light pulse rate. This rate is determined in turn by the round trip time along the sensing fibre 1, which is a function of the length of the sensing fibre 1.

[0068] As illustrated in figure 2a, in the present invention, there is provided a pipe monitoring apparatus 200 comprising a base module 210 connected to one end of a sensing fibre 1. The base module 210 comprises a light emitter 211 such as a laser and a light detector 212 to capture backscattered light. The sensing fibre 1 together with an optical coupling assembly 221 defines a sensing module 220. As with the prior art example, the coupling assembly 221 in this example comprises an optical circulator. This is beneficial as it is relatively efficient coupling arrangement for coupling light between the sensing fibre 1 and light emitter 211 and detector 212. Nevertheless, since optical circulators are relatively expensive, the skilled person will appreciate that alternative optical coupling assemblies may be substituted for the illustrated optical circulator. As in the prior art example, such alternative optical coupling assemblies may comprise an optical switching arrangement or one or more power dividers, such as 3dB power dividers. Whilst 3dB power dividers do lose roughly half the input power, there are significantly less expensive than optical circulators so may be more practical in instances where low signal strength is not a concern.

[0069] A connector cable 230 is provided between the base module 210 and the sensing module 220. The connector cable 230 comprises an emitter fibre 231 configured to carry light pulses from the light emitter 211 to the optical coupling assembly 221, and a detector fibre 232 configured to carry backscattered light pulses from the optical coupling assembly 221 to the light detector 212.

[0070] The provision of the connector cable 230 allows the sensing module 220 to be position remote from the base module 210. This allows the optical coupling assembly 221 to be provided in the vicinity of the pipe to be monitored whilst the sensing fibre 1 is provided within the pipe to be monitored without adverse impact on sensing performance. This is because the separate emitter fibre 231 and detector fibre 232 of the connector cable 230 provide separate routes for emitted light pulses and backscattered pulses between the emitter 211 and detector 212 and the sensing fibre 1. Accordingly, this reduces the effective round-trip time for resolving separate backscattered pulses to that taken to travel along the length of the sensing fibre 1 and back rather than the total fibre distance between the emitter 211, and detector 212 via the end of the sensing fibre. Accordingly, the construction of the present invention enables a high pulse rate to be used for monitoring pipes even if they are separated from the emitter and detector by a significant distance. Consequently, the effective dynamic range of the sensing apparatus can be extended and / or the sensing apparatus can detect signals with a higher acoustic frequency within the pipe to be monitored compared to the prior art example of figure 1.

[0071] This is further illustrated in figure 2b which shows the sensing apparatus 200 overlaid on the water supply system 10 of figures lb and 1c. As in the previous figures, the base module 210 is provided in pumping substation 11. In contrast with figure lb, the transit section 2 of the sensing fibre 1 in figure 1 is replaced by the emitter fibre 231 and detector fibre 232. Since the emitter fibre 231 and detector fibre 232 provide separate routes for the pulses and backscattered pulses the sensing performance of sensing fibre 1 is only limited by the length of the fibre required to adequately loop around DMA 21, which is typically 5- 10km as compared with sensing fibre lengths of 50- 100km in the various arrangements of figure 1.

[0072] Whilst the embodiment of figure 2 provides adequate monitoring for a single DMA 21, it is often desired to monitor multiple DMAs 21-23. This can be achieved using an embodiment as shown in the block diagram of the apparatus in figure 3 a and overlaid on the exemplary water supply network 10 in figure 3b. The embodiment of figure 3 differs from that of figure 2 in that the base module 210 further comprises a base switching unit 214. Additionally, three separate connector cables 230a, 230b and 230c are provided, each connector cable 230a-230c providing a connector to a corresponding optical coupling assembly 221a-221c and sensing fibre la-lc for monitoring DMAs 21-13 respectively. The base switching unit 213 is a one to many optical switching arrangement configured to enable any one of the connector cables 230a-230c to be selectively connected to the emitter 211 and detector 212 as desired for monitoring a corresponding DMA 21-23. The base switching unit 214 can be controlled so as to periodically cycle between monitoring each DMA 21-23. Additionally or alternatively, the base switching unit 214 can be controlled so as to select a DMA 21-23 for monitoring based on analysis of detected backscattered light pulses.

[0073] Turning now to figure 4b, an alternative embodiment suitable for monitoring multiple DMAs 21-23 is shown overlaid on the exemplary water supply network 10. The embodiment of figure 4 differs from that of figure 2 in that the connector cable 230 (and hence emitter fibre 231 and detector fibre 232) is split into successive sections 230’, 230”, 230”’ etc. The respective sections 230’- 230’” are each connected via a zone switching unit 240, each zone switching unit 240a-240c associated with a particular optical coupling assembly 221a-221c and sensing fibre la-lc of a corresponding DMA 21-23. The respective zone switching units 240a-240c are configured to enable sections of emitter fibre 231 ’ -231’ ” and detector fibre 232’ -232’ ’ ’ to be selectively connected to either the optical coupling assembly 221a-221c or to subsequent sections of emitter fibre 231 ’ -231 ” ’ and detector fibre 232’ -232’ ’ ’ .

[0074] Figure 4a illustrates zone switching unit 240c in more detail. As illustrated, the zone switching unit 240c comprises a 1x2 optical switch 241 which is connected to emitter fibre 231’ and a 1x2 optical switch 242 which is connected to detector fibre 232’. If both switches 241 and 242 are set to a first position (‘up’ in the context of figure 4a), the emitter fibre 231’ and detector fibre 232’ are connected to optical coupling assembly 221c and therefore to sensing cable 1c. This allows the condition of DMA 23 to be monitored. If both switches 241 and 242 are set to a second position (‘down’ in the context of figure 4a), the emitter fibre 231’ and detector fibre 232’ are connected to subsequent sections of emitter fibre 231” and detector fibre 232”. Accordingly, the sending fibre 1c is bypassed and it is possible to select sensing fibre la or sensing fibre lb for monitoring using switches zone switching units 240b or 240c respectively. This construction is particularly advantageous as it is scalable. In particular, it is possible to carry on adding additional zone switching units 240 and sensing fibres 1 to monitor any additional DMAs added to the network.

[0075] Each zone switching unit 240a- 240c may be configured so as to periodically cycle between connection to an optical coupling assembly 221a-221c or bypassing that optical coupling assembly 221a-221c. Additionally or alternatively, each zone switching unit 240a- 240c may be configured so as to select connection to the optical coupling assembly 221a-221c of the particular sensing module for monitoring based on analysis of detected backscattered light pulses.

[0076] A further alternative embodiment for monitoring multiple DMAs is illustrated, schematically only, in figure 5. In this embodiment, the base module 210 comprises three pairs of emitters 21 li- 2113 and detectors 2121-2123. The respective emitters 2111- 2113 are adapted to emit light pulses at three different wavelengths ki-fa. The corresponding detectors 2121-2123 to emitters 21 li- 2113 can be adapted to detect backscattered pulses at the corresponding wavelengths X1-X3.

[0077] In this embodiment, the base module 210 also comprises an optical multiplexer 215 to receive light pulses from emitters 21 li- 2113 and output each of these pulses onto emitter fibre 231. In this embodiment, the base module 210 further comprises an optical demultiplexer 216 to receive backscattered light pulses from detector fibre 232. The optical demultiplexer 216 separates the backscattered pulses by wavelength and distributes those of wavelengths ki-fa to the corresponding detector 2121-2123.

[0078] Along the emitter fibre 231 are provided a series of drop multipliers 251-253. Each drop multiplexer 251-253 is configured to separate pulses at particular wavelengths ki-fa from the emitter fibre into a respective optical coupling assembly 221a-221c and corresponding sensing fibre la-lc. Similarly, the detector fibre 232 is provided with a series of add multipliers 261-263. Each add multiplexer 261-263 is configured to add pulses returned from sending fibres la-lc back on to detector fibre 232.

[0079] This embodiment allows multiple sensing fibres la-lc to be simultaneously monitored using different wavelengths of light ki-fa. This can enable continuous monitoring rather than the sequential monitoring envisaged in the embodiment of fires 3 and 4. As with the embodiment of figure 4, this embodiment can be scaled to add further sensing fibres 1 to monitor any additional DMAs 21-23 added to the network, assuming additional emitters of different wavelengths and multiplexer capacity for different wavelengths is available. The skilled person will also understand that such wavelength multiplexing may be applied in combination with the embodiments of figures 2-4, as required or as appropriate.

[0080] Turning now to figure 6, a key benefit of each of the embodiments of the present invention is that the sensing cable 1 can be remote from the base module 210. In these embodiments, the practical limit to the separation between base module 210 and sensing module 220 is the point at which the losses on emitted pulses and / or backscattered pulses in the connector cable 230 render the backscattered pulses undetectable at detector 212. This might typically occur where the connector cable 230 is several lOOkms in length but may also be an issue if backscattered pulses are weak, for example due to small amplitude vibrations within the pipe to monitored. In such embodiments, it is possible to provide one or more optical amplifiers to boost either the emitted light pulses or the backscattered light pulses. This is illustrated schematically in figure 6 wherein the emitter fibre 231 is provided with an emitter amplifier 271 and the detector fibre 232 is provided with a detector amplifier 272. As illustrated, the emitter amplifier 271 can be provided closer to the optical coupling assembly 221 or the sensing module 220 and the detector amplifier 272 can be provided closer to the base module 210. Nevertheless, the skilled person will appreciate that amplifiers 271, 272 can be provided at other locations along the emitter fibre 231 and the detector fibre 232 and / or that multiple amplifiers 271, 272 can be provided along the emitter fibre 231 and the detector fibre 232 where appropriate. The skilled person will also understand that one or more amplifiers 271, 272 could be included in any of the embodiments of figures 2- 5, as required or as appropriate.

[0081] The provision of one or more emitter amplifiers 271 and / or one or more detector amplifiers 272 can also mitigate against signal losses due to using less efficient optical coupling assemblies 221. This can make the use of lower cost optical coupling assemblies such as 3dB power dividers more practical in place of more efficient but more costly optical coupling assemblies such as optical couplers.

[0082] 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 the condition of a fluid pipe, the sensing apparatus comprising: a base module, comprising a light emitter for generating light pulses and a light detector configured to detect backscattered light pulses; a sensing module comprising a sensing fibre provided within the pipe to be monitored and an optical coupling assembly provided in the vicinity of the pipe to be monitored, the optical coupling assembly configured to couple light pulses into the sensing fibre and backscattered light pulses out of the sensing fibre; and a connector cable comprising an emitter fibre configured to carry light pulses from the light emitter to the optical coupling assembly, and a detector fibre configured to carry backscattered light pulses from the optical coupling assembly to the light detector.

2. A sensing apparatus as claims in claim 1, wherein the sensing fibre is less than 20km in length.

3. A sensing apparatus as claims in claim 1 or claim 2, wherein if the pipe to be monitored comprises a branched network of pipes or part of a branched network of pipes, the sensing cable runs in a loop from an entry point to the far end of each branch in turn.

4. A sensing apparatus as claims in any preceding claim, wherein apparatus is adapted to monitor multiple pipes under test.

5. A sensing apparatus as claims in any preceding claim, wherein the emitter fibre is at least 1km in length and the detector fibre is at least 1km in length.

6. A sensing apparatus as claims in any preceding claim, wherein the emitter fibre and / or the detector fibre comprise multiple successive sections of fibre.

7. A sensing apparatus as claims in any preceding claim, wherein the optical coupling assembly comprises an optical circulator.

8. A sensing apparatus as claims in any one of claims 1 to 6, wherein the optical coupling assembly comprises one or more power dividers, optionally 3dB power dividers.

9. A sensing apparatus as claims in any preceding claim, wherein the base module comprises or is connected to a signal analyser.

10. A sensing apparatus as claims in claim 9, wherein the signal analyser is configured to control the light emitter to vary any one or more of: pulse frequency, pulse length and pulse intensity of the emitted light, optionally in response to analysis of detected backscattered light pulses.

11. A sensing apparatus as claims in any preceding claim, wherein the base module comprises multiple emitters and multiple detectors, optionally wherein each emitter generates light pulses of different wavelengths.

12. A sensing apparatus as claims in claim 11, wherein the sensing apparatus comprises multiple sensing modules.

13. A sensing apparatus as claims in any preceding claim, wherein the sensing apparatus comprises a dedicated connector cable for each sensing module.

14. A sensing apparatus as claims in any preceding claim, wherein the connector cable comprises a dedicated emitter fibre and detector fibre pair for each sensing module.

15. A sensing apparatus as claims in claim 13 or claim 14, wherein the base module is provided with a base switching unit configured to facilitate connection between multiple connector cables or between multiple emitter fibre and detector fibre pairs within a connector cable.

16. A sensing apparatus as claims in claim 15, wherein the base switching unit is configured so as to periodically cycle between different cables or different emitter fibre and detector fibre pairs.

17. A sensing apparatus as claims in claim 15 or claim 16, wherein the base switching unit is configured so as to select a cable or emitter fibre and detectorfibre pair for monitoring based on analysis of detected backscattered light pulses.

18. A sensing apparatus as claims in any preceding claim, wherein the sensing apparatus is provided with a zone switching unit for each sensing module.

19. A sensing apparatus as claims in claim 18, wherein each zone switching unit is provided in series with successive sections of emitter fibre and successive sections of detector fibre and wherein each zone switching unit is configured to enable previous sections of emitter fibre and detector fibre to be selectively connected to either the optical coupling assembly of the particular sensing module or to subsequent sections of emitter fibre and detector fibre20. A sensing apparatus as claims in claim 18 or claim 19, wherein each zone switching unit is configured so as to periodically cycle between connection to the optical coupling assembly of the particular sensing module or to subsequent sections of emitter fibre and detector fibre.

21. A sensing apparatus as claims in any one of claims 18 to 20, wherein each zone switching unit is configured so as to select connection to the optical coupling assembly of the particular sensing module for monitoring based on analysis of detected backscattered light pulses.

22. A sensing apparatus as claims in any preceding claim, wherein the base module comprises an optical wavelength multiplexer and an optical wavelength demultiplexer.

23. A sensing apparatus as claims in claim 22, wherein the emitter fibre is provided with a drop multiplexer for each sensing module, each drop multiplexer configured to selectively couple light pulses of a specific wavelength to the optical coupling assembly of the particular sensing module and wherein the detector fibre is provided with an add multiplexer for each sensing module, each add multiplexer configured to selectively couple light pulses of a specific wavelength from the optical coupling assembly of the particular sensing module.

24. A sensing apparatus as claims in any preceding claim, wherein the apparatus is provided with an emitter amplifier configured to amplify the light pulses travelling along the emitter fibre.

25. A sensing apparatus as claims in any preceding claim, wherein the apparatus is provided with a detector amplifier configured to amplify the backscattered light pulses travelling along the detector fibre.

26. A sensing apparatus as claims in any preceding, wherein each connector cable and / or each sensing fibre may additionally comprise one or more data fibres or one or more one or more data fibre bundles for carrying network data of a communication network.

27. A method for monitoring a fluid pipe, the method comprising the steps of: installing one or more sensing apparatuses according any preceding claim: introducing light pulses into the sensing fibre; detecting backscattered light pulses from the sensing fibre; and processing the backscattered light so as to obtain information about the condition of the pipe and / or events occurring within or in the vicinity of the pipe.

28. A fluid distribution system comprising one or more fluid pipes where one or more sensing apparatuses according to any one of claims 1 to 26 are provided to monitor at least some of the pipes.

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