Improvements relating to monitoring of fluid pipes

Abstract

A pipe monitoring apparatus (100) comprises a base module (110) connected to one end of a sensing fibre (1) provided within a pipe (10). The base module (110) comprises a light emitter (111) and a light detector (112) to detect backscattered light and output a detector output signal in response to the detected backscattered light. By analysing the detector output signal, indications can be obtained of the condition of the pipe and / or events occurring within or in the vicinity of the pipe. The apparatus (100) is connected to an edge computer (121) for onward transmission of signals for analysis. A data filtering module (130) is configured to identify saturated detector output signals which exceed the dynamic range of the light detector and exclude said saturated detector output signals from a filtered detector output signal for onward transmission.

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 modern 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 DSS and / or 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 sensing fibre. The detector is typically configured to detect backscattered light pulses from the sensing fibre and output a detector output signal corresponding to the detected backscattered light. In particular, this detector output signal may comprise multiple channels associated with particular locations along the sensing fibre, each channel comprising information relating to the phase of the backscattered light from the particular 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 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] Processing of the detector output signal can enable detected backscattered light to be associated with a particular section of fibre and hence a particular section of pipe based on the time interval between emission of the pulse and receipt of the backscattered light. This can be carried out by a processing unit local to the base module, by a remote processing unit, typically based in the cloud or combination of such processing units. Whilst cloud based processing is advantageous for readily accessing necessary computing power, this may not be practical in many locations as the detector output signal may have a data rate that exceeds 1Gb per second. Accordingly, it is common for a local processing unit such as a local edge computer to carry out some initial processing of the detector output signal. The initial processing can reduce the data volume transmitted on to the remote processing unit in the cloud. Even so, dealing with a data rate that exceeds 1Gb per second imposes considerable processing capacity requirements on the edge computer. As a result, this demands relatively high capability (and thus more expensive) edge computers which typically would stress reliability of operation and increase local power consumption. This also imposes considerable bandwidth requirements on the data connections between the detector and the edge computer and between the edge computer and the master unit. This can result in high cost connections and place stress on reliability of these connections.

[0011] There are some factors that can limit the ability to monitor the condition of the pipe. In particular, certain sections of the pipe may experience significant noise or vibration, often due to activities such as pump or valve operation. Noise may additionally or alternatively be generated due to flow of the fluid within the pipe, including normal flow noise and flow acting upon a sensor cable. Noise can also be associated with ad hoc perturbation of a more normal smooth flow path, for instance location specific increase in surface roughness of the fluid pipe (including deposits, concretions, tubercules and similar), vortices at bends and curves, presence of foreign objects within a pipe, presence of protruding items such as weld beads, significant changes in pipe diameter, presence of pipe devices such as air valves, pressure reduction valves or in-line valves whether in use or otherwise. Additionally, external noise and vibration can be transmitted through the pipe, which might be particularly common in urban areas where there are multiple other sources of mechanical vibration including traffic, industry and the like. In such high-noise or high-vibration section of the pipe, the frequency of phase changes in the backscattered light resulting from high background noise or vibration at a location can exceed the dynamic range of the detector output signal channel for that section of the pipe. When the dynamic range is exceeded, the output response of the detector output signal is no longer linear to the input signal. Such signals are typically described as saturated, but can also be referred to as oversaturated, overloaded, clamped or slew-rate limited. Recently, the issue of saturated channels associated with particular sections of pipe has been addressed by use of algorithms configured to improve the dynamic range of the detector when saturation of a channel is identified. These algorithms typically require very high computational power. Accordingly, even higher power edge computers are required than existing techniques, thereby applying further cost, power and reliability constraints.

[0012] 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.

[0013] Summary of the Invention

[0014] 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 to be monitored. The sensing apparatus may comprise a light emitter configured to generate light pulses which are introduced to the sensing fibre. The sensing apparatus may comprise a light detector configured to detect backscattered light pulses from the sensing fibre and output a detector output signal corresponding to the detected backscattered light. The sensing apparatus may comprise a processing unit configured to process the detector output signal so as to so as to obtain information about the condition of the pipe. The sensing apparatus may comprise a data filtering module configured to identify saturated detector output signals which exceed the dynamic range of the light detector and exclude said saturated detector output signals from a filtered detector output signal for onward transmission.

[0015] Additionally, according to the present invention there is provided a method of monitoring the condition of a fluid pipe. The method may comprise providing a sensing fibre within the pipe to be monitored. The method may comprise introducing light pulses generated by a light emitter into the sensing fibre. The method may comprise detecting backscattered light pulse from the sensing fibre with a light detector configured to output a detector output signal corresponding to the detected backscattered light. The method may comprise processing the detector output signal so as to obtain information about the condition of the pipe. The method may comprise the additional steps of identifying saturated detector output signals which exceed the dynamic range of the detector and excluding said saturated detector output signals from a filtered detector output signal for onward transmission. 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 sensing fibre provided within the pipe to be monitored; a light emitter configured to generate light pulses which are introduced to the sensing fibre; a light detector configured to detect backscattered light pulses from the sensing fibre and output a detector output signal in response to the detected backscattered light, the detector output signal comprising multiple channels, each channel corresponding to a particular location along the sensing fibre; and a data filtering module configured to identify saturated detector output signal channels which exceed the dynamic range of the detector output signal and exclude said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

[0016] According to a second aspect of the present invention, there is provided a method for monitoring the condition of a fluid pipe, the method comprising the steps of: providing a sensing fibre within the pipe to be monitored; introducing light pulses generated by a light emitter into the sensing fibre; detecting backscattered light pulse from the sensing fibre with a light detector configured to output a detector output signal corresponding to the detected backscattered light; identifying saturated detector output signal channels which exceed the dynamic range of the detector output signal; and excluding said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

[0017] The present invention enables the identification and exclusion of saturated detector output signals from onward transmission and / or processing by the processing unit. This reduces the data bandwidth requirements for onward transmission of detector output signals. It also reduces the computational capacity requirements of the processing unit. This can therefore enable less expensive and / or more reliable data connections to be utilised. It can additionally or alternatively enable a less expensive and / or more reliable and / or lower power processing unit to be used.

[0018] 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.

[0019] 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.

[0020] The data filtering module may be provided locally to the detector. The data filtering module may be an edge computer. The data filtering module may be integrated into an edge computer. The data filtering module may be an independent unit provided between the detector and an edge computer.

[0021] The method may comprise the additional step of processing the filtered detector output signal so as to obtain information about the condition of the pipe. The apparatus may further comprise a processing unit configured to process the filtered detector output signal so as to obtain information about the condition of the pipe. In some such embodiments, the edge computer may comprise the processing unit. In other such embodiments, processing unit may be a remote processing unit in communication with the edge computer. In such embodiments, the processing unit may be a cloud based processing unit.

[0022] Each detector output signal channel may comprise phase information related to the phase of the detected backscattered light from the particular fibre location. Each output signal channel may comprise information relating to the phase of the backscattered light from the particular location. 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.

[0023] The detector may comprise a photosensor configured to output signals in response to detected backscattered light. The detector may further comprise a phase module configured to extract phase information from the photosensor output and thereby generate a detector output signal including phase information. Detector output signal channels may be determined to be saturated where the frequency of phase changes in the backscattered light exceeds the dynamic range of the detector output signal channel.

[0024] The data filtering module may comprise a saturation identification engine and a saturation exclusion engine. In such embodiments, the saturation identification engine may be configured to identify saturated detector output signals which exceed the dynamic range of the detector. In such embodiments, the saturation exclusion engine may be configured to exclude saturated detector output signals identified by the saturation identification engine from the filtered detector output signal for onward transmission.

[0025] The filtered detector output signals may be compressed for onward transmission. The compression can be achieved using any suitable compression algorithm. In such embodiments, a compression module may be provided, the compression module configured to compress the filtered detector output signals.

[0026] Identifying saturated detector output signals may involve identifying saturated channels within the detector output signals. This can be achieved by the saturation identification engine, if configured to identify saturated channels within the detector output signal. In such embodiments, excluding said saturated detector output signals from the filtered detector output signal for onward transmission may involve excluding identified saturated channels within the detector output signals. This can be achieved by the saturation exclusion engine, if configured to configured to exclude identified saturated channels within the detector output signals. In such embodiments, any channels within the detector output signals that are not saturated may not be excluded from the filtered detector output signal for onward transmission.

[0027] In some such embodiments, each saturated channel may be identified by a flag or other label. In some such embodiments, each saturated channel may be identified on a bit map of all detector output signal channels. In such embodiments, each saturated channel may be identified on the bit map by a ‘0’ and each unsaturated channel may be identified on the bit map by a ‘ 1’ . In such embodiments, saturated channels may be simply excluded from the filtered detector output signal by reference to the flag, other label or bit map. In other such embodiments, the channel by channel detector output signal may be multiplied by the bit map. This would effectively set all saturated channels to a zero or null value in the filtered detector output signal. In embodiments where the filtered detector output signals are compressed, this can result in transparent removal of all saturated channels.

[0028] In alternative embodiments may identify each saturated channel on the bit map by a ‘1’ and each unsaturated channel by a ‘O’. In such embodiments, subsequent processing steps may be adapted as necessary.

[0029] In some embodiments, saturation of a detector output signal channel may be identified by analysis of the higher frequency components of the detector output signal channel. In some such embodiments, the analysis may comprise isolating frequency components above a reference frequency value and determining whether the isolated frequency components exceed a threshold signal level. In such embodiments, a detector output signal channel may be identified as saturated when the isolated frequency components exceed the threshold signal level. This is effective as one effect of saturation is to cause the lower frequency signal components to ‘fold’ to higher frequencies. In such embodiments, the reference frequency value may be a common preset value for each channel. In some such embodiments, the reference frequency value may be an individual value for each channel. Where individual reference frequency values are used, each individual reference frequency value may be selected by analysis of the past signal for the respective channel. In such embodiments, the threshold signal level may be a common preset value for each channel. In some such embodiments, the threshold signal level may be an individual value for each channel. Where individual threshold signal level values are used, each individual threshold signal level value may be selected by analysis of the past signal for the respective channel.

[0030] In some embodiments, saturation of a detector output signal channel may be identified by analysis of harmonics of particular signal components. This is effective as one effect of saturation is to generate harmonics of original signal components. In some such embodiments, the particular signal components may be pre-exiting signal components for each channel.

[0031] In some embodiments, saturation of a detector output signal channel may be identified by a drop in signal amplitude during integration of the signal. In some embodiments, the detector output signal channel may be identified as saturated if the absolute signal amplitude during integration drops below an absolute reference amplitude value. In other embodiments, the detector output signal channel may be identified as saturated if the relative drop in signal amplitude during integration exceeds a drop reference amplitude value. This is effective as one effect of saturation is to increase the noise level relative to signal level. In such embodiments, the absolute reference amplitude value or drop reference amplitude value may be a common preset value for each channel. In some such embodiments, the absolute reference amplitude value or drop reference amplitude value may be an individual value for each channel. Where individual absolute or drop reference amplitude values are used, each individual absolute or drop reference amplitude value may be selected by analysis of the past signal for the respective channel. In some such embodiments, the individual reference amplitude value or drop reference amplitude values for a channel may be determined by reference to the output of a neighbouring channel. This may only be applied where the neighbouring channel is not saturated. In such cases, lack of saturation within a neighbouring channel may be determined by comparison to the absolute reference amplitude value or drop reference amplitude value.

[0032] 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.

[0033] 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 some embodiments, the sensing fibre may be less than 100km in length, less than 50km in length, or less than 30 km in length. In further embodiments, 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. Shorter sensing fibre length can result in improved sensing fibre performance. In particular, the effective dynamic range of the sensing fibre can be extended and / or the sensing fibre can detect signals with a higher acoustic frequency within the pipe to be monitored.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The light emitter and light detector may be provided within a common base module. 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.

[0039] According to a third aspect of the present invention, there is provided a data filtering module for use with a detector output signal comprising one or more channels, the data filtering module configured to identify saturated detector output signal channels which exceed the dynamic range of the detector output signal and exclude said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

[0040] According to a fourth aspect of the present invention, there is provided a method of operating a data filtering module for use with a detector output signal comprising one or more channels, the method comprising the steps of: identifying saturated detector output signal channels which exceed the dynamic range of the detector output signal; and excluding said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

[0041] According to a fifth 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 or operating according to the second aspect of the invention are provided to monitor at least some of the pipes.

[0042] According to a sixth 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 or operating according to the second aspect of the invention.

[0043] In such networks, at least some of sensing apparatuses are provided with sensing fibres additionally comprising one or more data fibres or one or more one or more data fibre bundles.

[0044] 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.

[0045] Detailed Description of the Invention

[0046] 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:

[0047] Figure 1 is (a) a schematic block diagram of a sensing apparatus for monitoring the condition of a fluid pipe as used in the present invention, and (b) a schematic block diagram of a processing arrangement, according to the prior art, for the sensing apparatus of figure la;

[0048] Figure 2 is (a) a schematic illustration comparing the output of the sensing apparatus of figure la to an input sinusoidal signal of increasing amplitude, and (b) a schematic illustration showing the output of a sensing apparatus according to figure 1 including one or more saturated channels;

[0049] Figure 3 is (a) a schematic block diagram of a processing arrangement, according to the present invention, for the sensing apparatus of the type shown in figure la, and (b) a schematic block diagram of an alternative processing arrangement, according to the present invention, for the sensing apparatus of the type shown in figure la;

[0050] Figure 4 is a schematic illustration showing the output of a sensing apparatus according to figure 1 wherein one or more saturated channels are excluded from onward transmission; and

[0051] Figure 5 show a flow diagram schematically illustrating the method of monitoring a fluid pipe according to the present invention.

[0052] Figure la is a schematic illustration of a pipe monitoring apparatus 100. The pipe monitoring apparatus 100 comprises a base module 110 connected to one end of a sensing fibre 1 provided within a pipe 10. The base module 110 comprises a light emitter 111 (such as a laser) and a light detector 112 to detect backscattered light and output a detector output signal in response to the detected backscattered light. The base module further comprises a local optical coupling assembly 113 configured to couple the emitter 111 and the detector 112 to the sensing fibre 1.

[0053] The detector output signal comprises multiple channels, each channel corresponding to a particular location along the sensing fibre. The detector 112 typically comprises a photosensor configured to output signals in response to detected backscattered light and a phase module configured to extract phase information from the photosensor output and thereby generate a detector output signal including phase information. Accordingly, each detector output signal channel contains phase information related to the phase of the detected backscattered light from the particular fibre location.

[0054] By analysing the detector output signal, indications can be obtained of the condition of the pipe and / or events occurring within or in the vicinity of the pipe. The sensing fibre 1 can be of a pre-set length or may be provided to a length corresponding to that of the pipe 10 to be monitored. If the pipe 10 comprises a branched network, the length of the sensing fibre 1 can be selected to correspond the length of fibre required to loop around all branches of the network to be monitored.

[0055] In typical known arrangements, the apparatus 100 is connected to a local processing unit, in this example edge computer 121, and a cloud processing unit 122. One or more users 123 can receive processed data from cloud processing unit 123, as required or desired. It is not unusual for this type of sensing apparatus to generate detector output signals at a data rate in excess of 1 Gb per second. Accordingly, the edge computer 121 is configured to pre-process some of the detector output signals so as to reduce the bandwidth requirements for onward transmission to the cloud processing unit 122. This nevertheless still imposes a heavy computing burden of the edge computer 121 and thereby requires that the edge computer 121 has a relatively high computational capacity, which tends to increase the expense of the edge computer 121 and the rate of power consumption.

[0056] Turning now to figure 2a, a simplified schematic illustrates a single detector output signal channel 102 in response to an increasing sinusoidal input stimulus 101 for backscattering. As can be seen, when the input stimulus 101 is relatively low, the detector output signal level 102 increases substantially linearly with input stimulus amplitude 101. However, when the input stimulus 101 has an amplitude exceeding the dynamic range of the detector output signal 102, the detector output signal channel 102 is no longer reliably correlated to the input stimulus 101. In such circumstances the detector output signal 102 is referred to as saturated. In other literature, such a signal may alternatively be described as oversaturated, overloaded, clamped or slew-rate limited. Signal saturation can potentially occur due to high noise levels within particular sections of the pipe. In typical operation, the detector output signal 102 can be resolved into multiple channels, each channel corresponding to a particular distance along the sensing fibre 1 and thus to a particular location along the pipe 10. Different channels can be defined by the round trip duration for backscattering of introduced light pulses from the emitter 111. In the example of figure 2b, the evolution of detector output signals for multiple channels over time is illustrated. In this example, different channels correspond to distance along the fibre as set out on the y axis, whilst the evolution of the channel signal over time runs horizontally across the displayed output in correspondence with the detection time set out along the x axis. Within the output, four separate sets of saturated channels can be identified C1-C4. Each of these channels corresponding to locations within the pipe L1-L4 (see figure la) where high background noise is experienced. The high background noise at locations L1-L4 may be due to devices within the pipe 10 such as pumps or valves or due to external factors such as nearby machinery, traffic or the like.

[0057] Turning now to figures 3a and 3b, alternative embodiments of the improved apparatus of the present invention are shown. In each figure, a data filtering module 130 is provided. The data filtering module 130 is configured to identify saturated detector output signal channels which exceed the dynamic range of the light detector and exclude said saturated detector output signal channels from a filtered detector output signal for onward transmission. In figure 3a, the data filtering module 130 is provided separate from the edge computer 121. In the embodiment of figure 3b, the data filtering module is implemented within the edge computer 121.

[0058] The data filtering module 130 comprises a saturation identification engine 131 and a saturation exclusion engine 132. The saturation identification engine 131 is configured to identify saturated detector output signal channels which exceed the dynamic range of the detector output signal 102. As shown in figure 2b, the detector output signal 102 comprises one or more channels, each channel corresponding to a particular location along the sensing fibre 1. In such cases, identifying saturated detector output signals involves identifying saturated channels within the detector output signal 102. The saturation exclusion engine 132 is configured to exclude saturated detector output signal channels identified by the saturation identification engine 131 from the filtered detector output signal for onward transmission. In such embodiments, any channels within the detector output signal 102 that are not saturated are not excluded from the filtered detector output signal for onward transmission

[0059] Optionally, the filtered detector output signals can be compressed for onward transmission using any suitable compression algorithm. This could be implemented directly by edge computer 121 or by a separate dedicated compression (not shown) module configured to compress the filtered detector output signals

[0060] Turing to the saturation identification engine 131, this can be configured to identify saturation of the detector output signal or a channel within the detector output signal in a number of different methods.

[0061] In a first example, the saturation identification engine 131 analyses higher frequency components of the detector output signal channel. In this example, the analysis comprises isolating frequency components above a reference frequency value for each channel and determining whether the isolated frequency components for each channel exceed the threshold signal level. If the isolated frequency components exceed the threshold signal level, that channel can be identified as saturated. This method relies upon saturation causing the lower frequency signal components to ‘fold’ to higher frequencies. The reference frequency value and / or the threshold signal level can each be set to a common value for all channels or may be set to individual values for each channel, as required or appropriate.

[0062] In another example, the saturation identification engine 131 is configured to identify harmonics of particular signal components. Any channel where such harmonics are identified can be identified as saturated. This method relies on the generation of harmonics of original signal components being characteristic of saturated channels.

[0063] In a further example, the saturation identification engine 131 is configured to identify saturation of a detector output signal channel by a drop in signal amplitude during integration of the signal. In such cases, detector output signal channels can be identified as saturated if the absolute signal amplitude drops below an absolute reference amplitude value or if the relative drop in signal amplitude during integration exceeds a drop reference amplitude value. This method relies upon the saturated channels essentially comprising noise rather than distinct consistent signals. The absolute reference amplitude value or drop reference amplitude value may be a common preset value for each channel or an individual value for each channel, as required or appropriate. Where individual absolute or drop reference amplitude values are used, each individual absolute or drop reference amplitude value may be selected by analysis of the past signal for the respective channel. In some implementations, the individual reference amplitude value or drop reference amplitude values for a channel may be determined by reference to the output of a neighbouring channel. This may only be applied where the neighbouring channel is not saturated, for instance if it lackof saturation within a neighbouring channel is determined by comparison to the absolute reference amplitude value or drop reference amplitude value

[0064] The skilled person will appreciate that other suitable identification methods could be substituted for one of the described methods, if desired or if appropriate.

[0065] In each of the above cases, the saturation identification engine 131 is configured to identify each saturated channel by a flag or other label. In one example, each saturated channel is identified on a bit map of all detector output signal channels. For instance, each saturated channel is identified on the bit map by a ‘0’ and each unsaturated channel is identified on the bit map by a ‘1’. The skilled person will appreciate that other flags or labels identification methods could be substituted for one of the described methods, if desired or if appropriate.

[0066] The saturation exclusion engine 132 is configured to exclude saturated channels from the filtered detector output signal by reference to the flag, other label or bit map. In on example, this can be readily achieved by multiplying the channel by channel detector output signal by the bit map. This sets all saturated channels to a zero or null value accordingly reducing the data transmission load. Setting saturated channels to a zero or null value is particularly effective if the filtered detector output signals are compressed before onward transmission, since this effectively results in transparent removal of all saturated channels. An example of this processing is illustrated in figure 4 wherein the output signals of figure 2b have been processed to set eth saturated channels C1-C4 to a null value.

[0067] Turning now to Figures 5a and 5b, there is shown a flow diagram 500 of a first method for monitoring the fluid pipe 1 in accordance with the present invention.

[0068] Turning specifically to flow diagram 500a. At block 502, the sensing fibre 1 and is provided within the pipe 10. For example, the sensing fibre 1 can be provided within a cable comprising an outer sheath and optionally one or more additional data fibres or sensing fibres. Typically, the sensing fibre 1 is and subsequently mounted or otherwise secured to an inside surface of the fluid pipe 1.

[0069] At block 504, the light emitter 111 introduces light pulses with particular characteristics into the sensing fibre 1. The particular characteristics of the light pulses include an initial: pulse width, pulse repetition frequency and gauge length.

[0070] At block 506, the light detector 112 detects backscattering of the light pulses from the sensing fibre 1. At block 508, the light detector 110 is configured to output a detector output signal in response to the detected backscattering of the light pulses from the sensing fibre 1.

[0071] Turning specifically to flow diagram 500b. The subsequent steps outlined in the flow diagram 500b are carried out by the data filtering module 130.

[0072] At block 510, the data filtering module 130, identifies saturated detector output signal channels. This can be achieved by way of any one or more of the above discussed methods. Subsequently at block 512 a bit map is created of all detector output signal channels, each saturated channel is identified on the bit map by a ‘0’ and each unsaturated channel identified on the bit map by a ‘ 1 ’ .

[0073] At block 514, the channel by channel detector output signal is multiplied by the bit map generated at step 514. This generates a filtered detector output signal wherein all saturated channels are set to null value and thereby excluded from onward transmission. Optionally, at block 516, the filtered detector output signal is compressed. In this example, this would this effectively result in transparent removal of all saturated channels.

[0074] At block 518, the filtered detector output signal is transmitted onward for further processing, by the edge computer 121, the cloud based processing unit 122 or end users 123.

[0075] 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 sensing fibre provided within the pipe to be monitored; a light emitter configured to generate light pulses which are introduced to the sensing fibre; a light detector configured to detect backscattered light pulses from the sensing fibre and output a detector output signal in response to the detected backscattered light, the detector output signal comprising multiple channels, each channel corresponding to a particular location along the sensing fibre; and a data filtering module configured to identify saturated detector output signal channels which exceed the dynamic range of the detector output signal and exclude said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

2. A sensing apparatus as claimed in claim 1, wherein the apparatus further comprises a processing unit configured to process the filtered detector output signal so as to obtain information about the condition of the pipe.

3. A sensing apparatus as claimed in any preceding claim, wherein the data filtering module is an edge computer or is integrated into an edge computer or wherein the data filtering module is an independent unit provided between the detector and an edge computer.

4. A sensing apparatus as claimed in any preceding claim, wherein a compression module is provided, the compression module configured to compress the filtered detector output signals.

5. A sensing apparatus as claimed in any preceding claim, wherein the data filtering module comprises a saturation identification engine configured to identify saturated detector output signals which exceed the dynamic range of the detector.

6. A sensing apparatus as claimed in any preceding claim, wherein the data filtering module comprises a saturation exclusion engine configured to exclude saturated detector output signals identified by the saturation identification engine from the filtered detector output signal for onward transmission.

7. A sensing apparatus as claimed in claim 5 or claim 6, wherein the saturation identification engine is configured to identify saturated channels within the detector output signals.

8. A sensing apparatus as claimed in claim 6 or claim 7, wherein the saturation exclusion engine is configured to exclude identified saturated channels within the detector output signals.

9. A sensing apparatus as claimed in claim 7 or claim 8, wherein the saturation identification engine is configured to identify each saturated channel on a bit map of all detector output signal channels and wherein the saturation exclusion engine is configured to multiply the channel by channel detector output signal by the bit map to generate the filtered detector output signal.

10. A sensing apparatus as claimed in any one of claims 7 to 9, wherein saturation of a detector output signal channel is identified by analysis of the higher frequency components of the detector output signal channel, analysis of harmonics of particular signal components and / or a drop in signal amplitude during integration of the signal.

11. A method for monitoring the condition of a fluid pipe, the method comprising the steps of: providing a sensing fibre within the pipe to be monitored; introducing light pulses generated by a light emitter into the sensing fibre; detecting backscattered light pulse from the sensing fibre with a light detector configured to output a detector output signal in response to the detected backscattered light, the detector output signal comprising multiple channels, each channel corresponding to a particular location along the sensing fibre; identifying saturated detector output signal channels which exceed the dynamic range of the detector output signal; and excluding said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing.

12. A method as claimed in claim 11, wherein the method comprises the additional step of processing the filtered detector output signal so as to obtain information about the condition of the pipe.

13. A method as claimed in claim 11 or claim 12, wherein the filtered detector output signals are compressed for onward transmission.

14. A method as claimed in any one of claims 11 to 13, wherein identifying saturated detector output signals involves identifying saturated channels within the detector output signals.

15. A method as claimed in any one of claims 11 to 14, wherein excluding said saturated detector output signals from the filtered detector output signal for onward transmission involves excluding identified saturated channels within the detector output signals.

16. A method as claimed in claim 15, wherein each saturated channel is identified by a flag or other label17. A method as claimed in claim 15 or claim 16, wherein each saturated channel is identified on a bit map of all detector output signal channels.

18. A method as claimed in claim 17, wherein the channel by channel detector output signal is multiplied by the bit map to generate the filtered detector output signal.

19. A method as claimed in any one of claims 11 to 18, wherein saturation of a detector output signal channel is identified by analysis of the higher frequency components of the detector output signal channel.

20. A method as claimed in claim 19, wherein a detector output signal channel is identified as saturated if isolated frequency components above a reference frequency value exceed a threshold signal level.

21. A method as claimed in claim 18, wherein the reference frequency value or the threshold signal level is an individual value for each channel.

22. A method as claimed in any one of claims 11 to 21, wherein saturation of a detector output signal channel may be identified by analysis of harmonics of particular signal components.

23. A method as claimed in any one of claims 11 to 22, wherein saturation of a detector output signal channel is identified by a drop in signal amplitude during integration of the signal.

24. A method as claimed in claim 23, wherein the detector output signal channel is identified as saturated if the absolute signal amplitude during integration drops below an absolute reference amplitude value or if the relative drop in signal amplitude during integration exceeds a drop reference amplitude value.

25. A method as claimed in claim 24, wherein the absolute reference amplitude value or drop reference amplitude value is an individual value for each channel.

26. A data filtering module for use with a detector output signal comprising one or more channels, the data filtering module configured to identify saturated detector output signal channels which exceed the dynamic range of the detector output signal and exclude said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing27. A method of operating a data filtering module for use with a detector output signal comprising one or more channels, the method comprising the steps of: identifying saturated detector output signal channels which exceed the dynamic range of the detector output signal; and excluding said saturated detector output signal channels from a filtered detector output signal for onward transmission and / or processing28. A fluid distribution system comprising one or more fluid pipes where one or more sensing apparatuses according to any one of claims 1 to 10 or operating according to the method of any one of claims 11 to 25 are provided to monitor at least some of the pipes.

29. 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 any one of claims 1 to 10 or operating according to the method of any one of claims 11 to 25.

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