Improvements in or relating to monitoring of fluid pipes

Abstract

A sensing apparatus comprises a light emitter (111) for emitting light into a sensing fibre (1) and a light detector (112) to detect backscattered light from a sensing fibre (1) within a pipe (10). One or more sensors (50) (or devices 60) are provided along pipe (10). Data transmission from sensor (50) (or device 60) is achieved along sensing fibre (1) by the provision of vibrator units (71) said sensors (50) (or devices 60) to apply vibrations to the sensing fibre (1). The vibrations vary backscattering within the sensing fibre (1) and can hence be detected at detector (112). An acoustic sensor (79) is configured to detect background acoustic noise in the vicinity of the sensing fibre (1) and a vibration control unit (72) is configured to dynamically vary the vibration unit (71) output in response to the detected background acoustic noise.

Description

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

[0002] Technical Field of the Invention

[0003] The present invention relates to improvements in or relating to monitoring fluid pipes, in particular networks of fluid pipes, including but not limited to water supply pipes. 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 fluid pipes monitored using the apparatus or the method of the present invention. More particularly, the invention relates to data transmission using a sensing apparatus within a fluid pipe.

[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 or in the vicinity of 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. 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.

[0008] 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.

[0009] Whilst a sensing fibre can provide significant information conditions within or in the vicinity of a pipe, it may be desirable to monitor the pipe or the system within which the pipe is installed using one or more other sensors (flow sensors, pressure sensors, contaminant sensors, access sensors etc) at suitable locations around the system. Such sensors are typically powered by a local low power / low voltage source such as a battery.

[0010] In order to use the sensor output in system management it is necessary to back haul the sensor data back to a system controller. Typically, sensors produce a relatively low amount of data, but the data may be time sensitive. Unless an existing wired data connection is located close to the sensor, which is only common in dense urban areas, a wireless connection is used to back haul sensor data to the system controller. Suitable wireless connections include VHF / UHF, GPRS, 3G, 4G, 5G, loT protocols and the like. As transmitting data wirelessly uses significant power, typically sensor data is stored locally and only transmitted to the system controller periodically. For instance, in many such systems the sensors will be set to transmit data only once in every 24 hour period.

[0011] Periodic transmission allows for a significant extension of battery life for each sensor. This therefore amounts to a considerable saving in the expense of manually replacing batteries for each sensor. The downside of such periodic transmission is that it limits the possibility of using real-time sensor data to monitor and / or control system operation.

[0012] WO2019 / 166809 addresses the data backhaul issue by applying vibrations to the pipe, the fluid or the sensing fibre using a vibrator unit. The applied vibrations vary the backscattering of light from the sensing fibre and can accordingly be detected by the light detector. The applied vibrations are encoded using a dual tone multiple frequency (DTMF) scheme. Accordingly, filtering the detector output signals to frequencies corresponding to the vibrator unit output can allow sensor data encoded by the vibrator unit to be decoded. Whilst this does provide for adequate decoding of signals in some circumstances, in other cases there is a need for an improvement in order to back haul sensor data sufficiently reliably, such as where there is high background noise on a constant or intermittent basis.

[0013] It is therefore an object of embodiments of the present invention to at least partially address the above issues.

[0014] Summary of the Invention

[0015] In a broad sense, the invention relates to a data transmitting apparatus for transmitting data via a sensing apparatus for monitoring the condition of a fluid pipe of the type. The sensing apparatus may be of the type 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 data transmitting apparatus may comprise a vibration unit configured to apply acoustic data signals to the sensing fibre, the acoustic data signals comprising a data payload. The data transmitting apparatus may comprise a data signal processing unit configured to extract a component of the detector output signal derived from said acoustic data signals so as to retrieve the data payload for further processing or onward transmission. The data transmitting apparatus may comprise an acoustic sensor configured to detect a background acoustic noise in the vicinity of the sensing fibre. The data transmitting apparatus may comprise a vibration control unit configured to vary the vibration unit output in response to the detected background acoustic noise.

[0016] The invention also relates to a data transmission method for transmitting data using a sensing apparatus for monitoring a fluid pipe of the type 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 data transmission method may comprise applying acoustic data signals to the sensing fibre using a vibration unit, the acoustic data signals comprising a data payload. The data transmission method may comprise extracting a component of the detector output signal derived from said acoustic data signals for further processing or onward transmission. The data transmission method may comprise detecting background acoustic noise in the vicinity of the sensing fibre. The data transmission method may comprise varying the vibration unit output in response to the detected background acoustic noise.

[0017] According to an aspect of the present invention there is provided a data transmitting apparatus for transmitting data via a sensing apparatus for monitoring the condition of a fluid pipe of the type 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 data transmitting apparatus comprising: a vibration unit configured to apply acoustic data signals to the sensing fibre, the acoustic data signals comprising a data payload; a data signal processing unit configured to extract a component of the detector output signal derived from said acoustic data signals so as to retrieve the data payload for further processing or onward transmission; an acoustic sensor configured to detect a background acoustic noise in the vicinity of the sensing fibre; and a vibration control unit configured to vary the vibration unit output in response to the detected background acoustic noise.

[0018] According to an aspect of the present invention there is provided a method for transmitting data using a sensing apparatus for monitoring a fluid pipe of the type 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 method comprising the steps of: applying acoustic data signals to the sensing fibre using a vibration unit, the acoustic data signals comprising a data payload; extracting a component of the detector output signal derived from said acoustic data signals so as to retrieve the data payload for further processing or onward transmission; wherein the method further comprises detecting background acoustic noise in the vicinity of the sensing fibre; and varying the vibration unit output in response to the detected background acoustic noise.

[0019] The present invention thereby provides for reliable low energy, low bandwidth data backhaul along a sensing fibre, for instance from a sensor or other device. The provision of the acoustic sensor allows background noise level to be sensed / measured and for the vibration unit output to be varied dynamically in response. Beneficially, this allows the vibration unit to increase output signal levels when the local background noise is high thereby ensuring these signals can still be detected on the sensing fibre. Similarly, this allows the vibration unit to decrease output signal levels when the local background noise is low thereby reducing energy consumption and avoiding swamping other local acoustic signals whilst ensuring these signals can still be detected on the sensing fibre.

[0020] 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.

[0021] Similarly, in the context of the present application, the term ‘pipe’ or ‘conduit’ may refer to any fluid conduit used to convey a fluid (gas, liquid or a mixture including a slurry) between two points, spaced apart at or below local ground level. In particular, the ‘pipe’ or ‘conduit’ may traverse at a relatively regular displacement from local ground level, without requiring the ‘pipe’ or ‘conduit’ to be horizontal. Thus, the terms “pipe” and “fluid pipe” may be used interchangeably.

[0022] The acoustic sensor may comprise a microphone. In some embodiments, the acoustic sensor may comprise the sensing fibre.

[0023] The acoustic sensor may be configured to detect background acoustic noise at a pre-set frequency range. This may be achieved intrinsically by the nature of the sensor or by filtering sensor output by frequency. The pre-set frequency range may be related to the frequency of acoustic data signals output by the vibration unit. In some embodiments, the acoustic sensor may be configured to exclude from detection acoustic signals at the same frequency or frequency range as the vibration unit output. This can prevent feedback effects. In other such embodiments, the acoustic sensor and / or the acoustic control unit may be configured to apply a cancellation signal to the detected background noise, the cancellation signal corresponding to and opposing the vibration unit output.

[0024] The acoustic sensor may be configured to detect background acoustic noise constantly. In some embodiments, the acoustic sensor may be configured to switch between an active mode where detection is enabled and an inactive mode where detection is not enabled. In other embodiments, the acoustic sensor may be configured to only detect background noise in between periods of acoustic transmission. This can reduce the energy consumption and / or processing requirements for the acoustic sensor. In some embodiments, the acoustic sensor is configured to switch to active mode in response to an internal trigger or an external trigger. A suitable internal trigger may be a clock signal. A suitable external trigger may be a control signal from the acoustic control unit. In some such embodiments, mode switching may take place at regular intervals. The regular interval between successive active mode periods may be of the order of seconds, tens of seconds, minutes or hours. In some such embodiments, the active mode periods may be of the same duration of the regular intervals. In other such embodiments, the active mode periods may be of different duration to the regular intervals. In particular, active mode periods of shorter duration than regular intervals may help reduce energy and / or processing requirements.

[0025] In some such embodiments, mode switching may take place ad hoc. In particular embodiments, the acoustic sensor may be switched to an active mode when acoustic signals are due to be output by the vibration unit. In such embodiments, the acoustic sensor may be switched to an active mode whilst acoustic signals are output by the vibration unit. This can allow the output level of the acoustic signals to be varied appropriately. In some such embodiments, the active mode period may match the period of output of acoustic signals. In other such embodiments, the active mode period may precede the output of acoustic signals by a pre-set start interval. In further such embodiments, the active mode period may endure until a pre-set end interval after the output of acoustic signals. The start interval and the end interval may be of the same duration or of differing durations. Suitable start and end intervals may be of the order of hundredths of seconds, tenths of seconds, or seconds.

[0026] The acoustic sensor may be configured to output a background noise level value. The acoustic sensor may be configured to output a background noise frequency spectrum. The vibration control unit may be configured to determine a background noise level classification. In other embodiments, the acoustic sensor may be configured to output a background noise level classification. Determining a background noise level classification may be archived by comparing the background noise level value to one or more pre-set classification thresholds. Additionally or alternatively, determining a background noise level classification may be achieved by comparing the background noise frequency spectrum to one or more pre-set classification standards and / or by comparing the output of one or more background frequency spectrum components to one or more pre-set classification standards. In some further embodiments, determining a background noise level classification may be achieved by summing components of the background frequency spectrum.

[0027] The vibration control unit may be configured to vary the vibration unit output level in response to background noise level value or background noise level classification. Where vibration unit output level is varied in response to background noise level, the variation can be determined by a function. The function may be a linear function or may be a non-linear function. In other embodiments where vibration unit output level is varied in response to background noise level value, the variation can be determined by a pre-set look up table. This can simplify processing requirements.

[0028] Where vibration unit output level is varied in response to background noise classification the variation can be determined by a function. The function may be a linear function or may be a non-linear function. In other embodiments where vibration unit output level is varied in response to background noise level classification, the variation can be determined by a pre-set look up table. This can simplify processing requirements.

[0029] The vibration unit may comprise a loudspeaker, buzzer, sounder, vibrator, oscillator or the like. The vibration unit may be configured to generate acoustic signals of a single frequency. The vibration unit may be configured to generate acoustic signals of more than one frequency. Where the vibration unit is configured to generate acoustic signals of more than one frequency, acoustic signals at different frequencies may be generated substantially concurrently or substantially consecutively, as required or desired, at a time.

[0030] The vibration unit may be positioned so as to apply the acoustic signals directly to the sensing fibre or to a cable within which the sensing fibre is provided. In some such embodiments, the vibration unit may be provided inside or outside the pipe. In some such embodiments, the vibration unit may be provided within a junction box. The benefit of direct application is that lower signal power may be required. In other embodiments, the vibration unit may be positioned so as to apply the acoustic signals to the fluid in the pipe or to the pipe or to a pipe fitting. In such embodiments, the vibration unit may be provided inside the pipe. If so, the vibration unit may be mounted to the pipe or to a pipe fitting within the pipe. In other such embodiments the vibration unit may be provided outside the pipe. Such locations may simplify installation of the vibrator unit and ease of access for repair or replacement.

[0031] The acoustic sensor may be positioned within the pipe. This can allow the acoustic sensor to more accurately measure background acoustic noise experienced by the sensing fibre. In such embodiments, the acoustic sensor may be mounted to the pipe or to a pipe fitting within the pipe. This can provide secure and stable mounting for the acoustic sensor.

[0032] In other embodiments the acoustic sensor may be provided outside the pipe. Such locations may simplify installation of the acoustic sensor and ease of access for repair or replacement.

[0033] The acoustic sensor may be positioned adjacent to the vibration unit. This can provide for convenient access to both units for installation or maintenance. Alternatively, the acoustic sensor may be apart from the vibration unit. This may be beneficial where the vibration unit is not mounted within the pipe and thus local background noise may differ from that experienced within the pipe.

[0034] A single acoustic sensor may be provided for the vibration unit. Alternatively, multiple acoustic sensors may be provided for the vibration unit. This can allow an aggregated background noise level to be determined based on the output of the multiple acoustic sensors. This can be useful if some acoustic sensors have limited accuracy at particular frequency / noise levels and / or if some noise levels impacting the sensing fibre are shielded at the location of one of the acoustic sensors.

[0035] In some embodiments, there may be multiple vibration units. In such embodiments, each vibration unit may be provided at separate locations along the sensing fibre. The vibration unit locations may be spaced sufficiently far apart that acoustic signals from each vibration unit can be separately extracted from the sensing fibre. In such embodiments, a single acoustic sensor may be provided for each vibration unit location. Alternatively, multiple acoustic sensors may be provided for some or each vibration unit location.

[0036] The data payload may contain the data to be transmitted. In some embodiments, the acoustic data signals may comprise a start delimiter, an end delimiter and the data payload therebetween. Such embodiments may involve extracting a component of the detector output signal derived from said acoustic data signals and identifying the start delimiter and end delimiter so as to retrieve the data payload for further processing or onward transmission. The data signal processing unit may be configured to extract a component of the detector output signal derived from said acoustic data signals and identify the start delimiter and end delimiter so as to retrieve the data payload for further processing or onward transmission.

[0037] This provides for reliable low energy, low bandwidth data backhaul along a sensing fibre, for instance from a sensor or other device. The provision of acoustic data signals with a data payload provided between a start delimiter and an end delimiter allows data to be reliably identified within an acoustic data signal. As the data payload can be reliably identified the acoustic data signals these can be reliably retrieved even when transmitted asynchronously. This allows for ad hoc data transmission rather than scheduled data transmission which can further reduce energy need for data backhaul. The provision of a start delimiter and end delimiter for each signal also allows data signals to be more readily distinguished from background noise in the vicinity of the sensing fibre.

[0038] The acoustic data signal may additionally comprise a pre-amble. The preamble may precede the start delimiter. The pre-amble may be a pre-set sequence of bits. The pre-amble may help phase lock a receiving clock within the data signal processing unit to the acoustic data signal.

[0039] The acoustic data signal may additionally comprise a data source identifier. The data source identifier may precede the data payload. The data source identifier may be unique to the vibration unit or to a device connected to the vibration unit. This can allow for the source of the vibration data signals to be identified. This is particularly advantageous if multiple sensors or devices are connected to a single vibration unit, or if multiple vibration unit devices are provided at a single location.

[0040] The acoustic data signal may additionally comprise a checksum. The checksum may precede the end delimiter. The checksum may contain the output of a check sum algorithm performed on the data payload or on the data payload and the source identifier. This can enable the integrity of the data payload or data payload and source identifier to be verified on receipt.

[0041] The acoustic data signal may additionally comprise an inter-packet gap. The inter-packet gap may be a pre-set period without transmission. This can ensure adequate spacing between successive acoustic data signals. The inter-packet gap may be provided after the end delimiter. In some embodiments, the inter-packet gap may be incorporated into the end delimiter.

[0042] The acoustic data signals may comprise a square wave. The square wave may have a single clock frequency. Suitable acoustic frequencies may be in the range 250Hz to 2kHz. The acoustic data signals may comprise a phase encoded square wave. The phase encoding may be achieved by applying a Boolean exclusive OR (XOR) function to the data and the square wave. The phase encoding may be of any suitable protocol. Suitable encoding protocols include, but are not limited to Manchester encoding, differential Manchester encoding or the like. In particular, the phase encoding may be of the type wherein information carrying transitions of the encoding wave take place at mid-bit.

[0043] In some embodiments, the acoustic data signals may comprise a combination of different frequency signals. Each different frequency signal may comprise a sine wave, a square wave or other suitable wave form. As above, suitable frequencies may be in the range 250Hz to 2kHz.

[0044] In some such embodiments, the acoustic data signal may be encoded by frequency modulation between two distinct carrier frequencies. In other such embodiments, the acoustic data signal may be encoded by a combination of simultaneous signal frequencies. In some such embodiments, the acoustic data signal may be encoded by a pair of simultaneous signal frequencies. In further such embodiments the acoustic data signal may be encoded by three or more simultaneous signal frequencies. Using multiple simultaneous signal frequencies allows for the acoustic data signals to be provided in a data format comprising more than two characters. For instance, relying on a combination of one frequency selected from a first set of four with another frequency selected from a second set of four can result in 16 different bits or characters being independently encodable.

[0045] In embodiments where simultaneous signal frequencies are used for encoding, the respective frequences may not be harmonically related. This limits the potential for crosstalk between different signal frequencies.

[0046] The or each vibration unit or vibration control unit may comprise or be connected to an encoder unit. The encoder unit may be configured to receive data from one or more connected devices. The encoder unit may be configured to encode received data into an encoding protocol and / or data structure suitable for acoustic data signals applied by the vibrator unit to the sensing fibre.

[0047] The encoder unit may be configured to encode a data source identifier corresponding to the encoder unit. Additionally or alternatively, if the encoder unit is connected to a device, the encoder unit may be configured to encode a data source identifier corresponding to the connected device when encoding data received from said device. If the encoder unit is connected to multiple devices, said data source identifier corresponding to the connected device will correspond to the particular connected device from which received data is being encoded at that time.

[0048] The connected device or devices may comprise one or more sensors. Examples of suitable sensors may include but are not limited to: flow sensors, contaminant sensors, pressure sensors, temperature sensors, strain sensors, water chemistry sensors, chlorine sensors, water quality sensors, turbidity sensors, pH sensors or the like.

[0049] In such embodiments, the data payload of the acoustic data signals may comprise sensor data. The sensor data may in particular comprise data indicative of the sensed quantity but may additionally comprise sensor status information. In such embodiments, the data received by the encoder unit may comprise sensor data. The connected device or devices may additionally or alternatively comprise one or more system devices. Examples of suitable system devices include but are not limited to valves, pumps, energy scavenging devices, power storage devices or the like. Suitable examples of energy scavenging devices may include but are not limited to fluid flow powered generators, photoelectric generators, piezoelectric generators, thermoelectric generators or the like.

[0050] In such embodiments, the data payload of the acoustic data signals may comprise device data. The device data may in particular comprise data indicative of the device operation and / or status. In such embodiments, the data received by the encoder unit may comprise device data.

[0051] The detector output signal may comprise multiple channels, each channel corresponding to a particular location along the sensing fibre. Each channel may be defined by reference to the round-trip time for backscattered pulses from the particular location. Neighbouring channels may be defined by the minimum resolvable time interval between backscattered pulses from neighbouring sensing fibre locations. Accordingly, each vibration unit location can correspond to a particular channel within the detector output signal. In such embodiments, the data signal processing unit may be configured to extract the component of the detector output signal derived from said acoustic data signals by reference to a particular channel within the detector output signal. The referenced channel may correspond to the location of a particular vibration unit along the length of the sensing fibre. Accordingly, if the location of each vibration unit along the length of the sensing fibre is known the component of the detector output signal derived from acoustic data signals generated by a particular vibration unit can be extracted by reference to the corresponding channel within the detector output signal. In embodiments with multiple vibration units, there may be multiple referenced channels. In such cases, each channel may correspond to the location of a vibration unit.

[0052] The data signal processing unit may be configured to identify the acoustic data signal within the extracted component of the detector output signal. In embodiments wherein the acoustic data signals are output at specified frequencies, this may be achieved by filtering the extracted component to one or more acoustic frequency ranges corresponding to the acoustic data signals. The data signal processing unit may be configured to retrieve the data payload for further processing or onward transmission. This may be achieved by recognising the start delimiter and end delimiter. The data signal processing unit may be configured to decode the data pay load of the acoustic data signals. This may be achieved by reference to the encoding protocol and / or the data structure of the acoustic data signals.

[0053] In some embodiments, the vibration unit may be configured to output keep-alive acoustic data signals. Such keep-alive acoustic data signals may be transmitted only after a pre-set keep-alive period has passed since a previous transmission. The keepalive period may be relatively long compared to the expected mean or median interval between successive transmissions. This can ensure that the sensing apparatus does not receive excessive transmissions and / or that such keep-alive acoustic data signals provide reassurance that the data transmitting apparatus is operating correctly.

[0054] In one embodiment, the keep-alive acoustic data signals may be distinguished from other acoustic data signals by the data payload. In particular, the data payload of keep-alive acoustic data signals may contain data relating to the status of the vibration unit and / or any devices connected thereto. This can enable monitoring of the operation of such devices and / or early indications to be identified of potential faults.

[0055] In another embodiment, the keep-alive acoustic data signals may be transmitted at a different acoustic frequency to other acoustic data signals. In some such embodiments, the keep-alive acoustic data signals may be transmitted at a combination of different frequencies to other acoustic data signals. By providing keep-alive acoustic data signals that differ from other acoustic data signals, they can be reliably and confidently identified directly, even from a relatively short transmission duration. In embodiments where keep-alive acoustic data signals comprise a combination of different frequencies, the keep-alive acoustic data signal may comprise simultaneous or successive transmission of the different frequencies. In such embodiments, there may be two different frequencies. Alternatively, there may be three or more different frequencies. In embodiments having multiple vibration units, the keep-alive acoustic data signal may be different for each vibration unit, this may be achieved by using a different frequency or combination of frequencies. In suitable embodiments, this may be achieved by varying the succession of different frequencies in a keep-alive acoustic data signal.

[0056] In further embodiments, the vibration unit may be configured to output fault acoustic data signals, in response to a determination that the vibration unit or any connected device is in a fault condition. The fault acoustic data signals may be distinguished from other acoustic data signals by the data payload and / or by the transmission frequency or combination of frequencies, as above.

[0057] The sensing apparatus may further comprise a base module comprising the light emitter and the light detector. The base module may comprise a coupling assembly configured to remotely couple light pulses into the sensing fibre and backscattered light pulses out of the sensing fibre.

[0058] The sensing apparatus may comprise an analyser to analyse the detector output signal. In some embodiments, the analyser may be provided within the base module. In other embodiments, the analyser may be located remotely from the base module. The analyser may interrogate a specific location of the sensing apparatus. The data signal processing unit may be integrated into the analyser or may be provided separately to the analyser.

[0059] 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.

[0060] 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 more than 20km in length, 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.

[0061] The at least one sensing fibre may be provided as a part of a cable extending with or within the fluid pipe. The cable may be a data cable provided with one or more sensing fibres. In some such embodiments, the data cable may comprise multiple data fibres or multiple bundles of data fibres. In embodiments having multiple data fibre bundles, each data fibre bundle may be provided within an individual sheath. In some embodiments, each data fibre may be a single mode optical fibre. In other embodiments, each data fibres may be a multi-mode optical fibre. In further embodiments, the data cable may comprise a mixture of single mode and multi-mode data fibres.

[0062] The fluid pipe in which the sensing arrangement is provided 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.

[0063] The fluid pipe in which the sensing arrangement is provided 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.

[0064] The branched network may be any suitable branched network of fluid pipes. In one example, the branched network is a district metered area of a water supply network.

[0065] In some embodiments, a sensing arrangement 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.

[0066] The data transmitting apparatus may comprise a tube through which the at least one sensing fibre and / or sensing cable may enter or exit the fluid pipe. Such a tube may be mounted relative to a fluid pipe or pipe fitting, as described below.

[0067] The pipe fitting may be configured to support the sensing fibre and or the tube. The pipe fitting may be configured to be fitted to the pipe. Thus, the pipe fitting provides convenient attachment of the sensing fibre to the fluid pipe.

[0068] The pipe fitting may provide an entry / exit point on the fluid pipe for the sensing fibre. The pipe fitting may provide an entry / exit point on the fluid pipe for the tube of the sensor. The pipe fitting may provide entry / exit points on the fluid pipe for the sensing fibre and the tubes of two sensors, each sensor associated with one of the two sensing locations. Thus, the pipe fitting enables simple and efficient connection to the inside of the pipe. The entry / exit points may be standard access openings on the fluid pipe or may be dedicated openings formed for mounting the sensing fibre and / or the tube of the sensor.

[0069] The tube may comprise an opening at one end in fluid communication with the fluid pipe. The tube may extend into the fluid pipe to be monitored. The opening may be provided inside the fluid pipe to be monitored. Thus, the tube is conveniently in communication with the fluid inside the fluid pipe.

[0070] In an embodiment, the tube may extend into the fluid pipe transversely. The tube may extend to position the opening at the in-pipe end adjacent to but spaced from the pipe invert, which is the fluid pipe wall opposite to the entry end of the tube. This may assist with locating or positioning the at least one sensing fibre and / or sensing cable substantially parallel to the pipe invert. The at least one sensing fibre and / or sensing cable may abut the pipe invert.

[0071] The tube may function as a mount for the vibration unit.

[0072] According to another aspect of the present invention, there is provided a fluid distribution system comprising one or more fluid pipes where one or more data transmitting apparatuses according to the present invention are provided to monitor at some of the pipes.

[0073] According to a further aspect of the present invention there is provided a fluid distribution system comprising one or more system sensors and / or system devices at one or more points within the fluid distribution system; a system controller; and one or more data transmitting apparatuses according to the present invention adapted to carry acoustic data signals from the system sensors or system devices to the system controller.

[0074] According to one more 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, each data cable comprising one or more data fibres for conventional data transmission between transceiver devices at network nodes, wherein at least some of the data cables comprise at least one sensing fibre and wherein at least one data transmitting apparatus according to the present invention is provided to transmit data using said sensing fibre.

[0075] 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.

[0076] Detailed Description of the Invention

[0077] 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:

[0078] 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, and (b) a schematic diagram of the analysis architecture of a sensing apparatus of figure la;

[0079] Figure 2 shows a sensing fibre for a sensing apparatus of figure 1 provided in a single exemplary water pipe

[0080] Figure 3 is a schematic diagram of a sensing fibre configuration for a branched pipe network;

[0081] Figure 4a is a schematic diagram of a data transmitting apparatus according to the present invention;

[0082] Figure 4b is a schematic flow chart illustrating one method of operation of the data transmitting apparatus of figure 4a according to the present invention;

[0083] Figure 5 is a schematic diagram illustrating data encoding used for transmitting data in a data transmitting apparatus according to the present invention;

[0084] Figure 6 illustrates an exemplary dual-tone multi-frequency encoding scheme; and Figure 7 is a schematic diagram illustrating a data structure used for transmitting data in a data transmitting apparatus according to the present invention.

[0085] Figure la is a schematic illustration of a sensing apparatus 100 comprising a base module 110 connected to one end of a sensing fibre 1 provided within a pipe 10. The sensing fibre 1 can be provided as a dedicated cable or may be provided as one or more sensing fibres within a data cable. Such a data cable may additionally comprise one or more data fibres or bundles of data fibres for carrying data between nodes of a data network.

[0086] 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. Typically, the base module 110 is provided outside the pipe 10. This can allow the base module 110 to be readily connected to suitable power and data connections as well as ensuring the relatively complex and expensive components can be both protected and accessed for maintenance. Often, the base module 110 may be provided alongside other key equipment for a fluid distribution network such as a pumping station or the like.

[0087] In typical operation, the detector output signal comprises 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. 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 can contain phase information related to the phase of the detected backscattered light from the particular fibre location.

[0088] 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.

[0089] In typical known arrangements, the apparatus 100 is connected to a local processing unit, in this example edge computer 121, and an analyser 122, which may be cloud based or provided within the base unit 110 as required or desired. One or more users 123 or other devices (such as a fluid distribution system controller) can receive processed data from analyser 122, as required or desired.

[0090] As illustrated in figure 2, the fluid pipe 1 may be a linear pipe. The fluid pipe 10 comprises several fittings 11, 12, 13 that provide an entry / exit point along the fluid pipe 10 for the sensing fibre 1 among other things as described in more detail below. An example of the fittings 11, 12, 13 that may be used for the sensing fibre to enter / exit the fluid pipe 10 are described in PCT / GB2024 / 051555.

[0091] The fittings 11, 12, 13 each comprise a rigid or semi-rigid tubular arrangement 14 with a bore extending therethrough to receive the sensing fibre 1. The tubular arrangement 14 in this embodiment is a spiral wound member or spring. The tubular arrangement 14 is straight and sufficiently rigid to resist the fluid flow within the pipe 1, the arrangement 14 extends from the fitting 11, 12, 13, which is generally in an upper part of the pipe 1, across the internal diameter of the pipe 1 to position the sensing fibre 1 along the invert of the pipe 10. Various options for the semi-rigid tubular arrangement 14 are also described in PCT / GB2024 / 051555.

[0092] In this embodiment, the sensing fibre 1 extends from the base unit 110 into the fluid pipe 10 via an entry fitting 11. The sensing fibre 2 then extends along the inside of the fluid pipe 10 before reaching several pairs of fittings, each comprising a first fitting 12 and second fitting 13. At each pair, the sensing fibre 1 exits the fluid pipe 10 and travels between the first and second fittings 12, 13 on an outside of the pipe 10, before entering the fluid pipe 10 again and extending within the pipe 10 to the next pair of fittings 12, 13. Each pair thereby provides a path for the sensing fibre 1 around an obstacle or object within the pipe 10, such as a valve. In this embodiment, the sensing fibre 1 is formed as part of a cable of fibres comprising a bundle of data fibres (not shown). As such, the cable may need to break out of the fluid pipe 10 from time to time to provide data connections to different end users. Consequently, a pair of fittings 12, 13 may also be provided where there is no obstacle within the fluid pipe 10.

[0093] In this embodiment, the separation between adjacent pairs of fittings 12, 13 may vary depending on the topography and characteristics of the pipe 10. For example, where many valves or end users are located, the separation may only be a few hundred metres, but in more remote locations it may be many kilometres.

[0094] As shown in figure 3, which schematically illustrates an example of a fluid distribution network, the same principle can be extended to branched pipe networks. In particular, figure 3 shows a schematic example of a water supply system 20, comprising a pumping substation 21 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.

[0095] Extending from the substation 21 is a trunk pipe 22 which supplies water to three illustrated district metred areas (DMAs) 31, 32, 33. Within each district metered area 31-33 are provided one or more dwellings or buildings 41 connected to the water supply system by valve 42. As will be appreciated, only an exemplary number of dwellings or buildings 41 are shown in the drawings for clarity.

[0096] As can be seen in figure lb, the sensing fibre 1 runs from the base module 110 through trunk pipe 22 to each DMA 31-33. Within each DMA 31-33, the sensing fibre 1 is looped along each of the individual pipes. The sensing fibre 1 can therefore allow each of the individual branched pipes to be monitored. If the sensing fibre 1 is provided within a data cable, data fibres can be spliced out to connect various dwelling to the network. The skilled person will appreciate that alternative data network layouts could be utilised where required or appropriate.

[0097] In the present invention, one or more fluid distribution system sensors 50 are distributed at key points around the system. In the example of figure 4, a sensor 50 is located at or close to points where the sensing fibre 1 enters / leaves pipe 10. Nevertheless, the skilled person will appreciate that sensors 50 may be additionally or alternatively provided at different points within the pipe 10 or system 20, if desired or appropriate. Typically, the sensors 50 may comprise flow sensors, contaminant sensors, pressure sensors, temperature sensors, strain sensors, water chemistry sensors, chlorine sensors, water quality sensors, turbidity sensors, pH sensors or the like. In particular, sensors 50 may include meters which monitor the volume of flow over time. These are commonly used for billing end users based on volume of water consumption.

[0098] The network may also be provided with one or more system devices 60. In the example of figure 4, a system devices (such as a valve) is located between points where the sensing fibre 1 enters or leaves pipe 10. Nevertheless, the skilled person will appreciate that system devices 60 may be additionally or alternatively provided at different points within the pipe 10 or system 20, if desired or appropriate. Typical system devices 60 include but are not limited to valves, pumps or the like.

[0099] Typically, the sensors 50 and devices 60 are powered by a local low power / low voltage source such as a battery. Additionally or alternatively, a local energy scavenging device such as a fluid flow powered generator, photoelectric generator, piezoelectric generator, thermoelectric generator or the like can also be used to directly power the sensors 50 and devices 60 or to charge the battery.

[0100] A system controller (not shown) can be provided to monitor the operation of sensors 50 and the system devices 60. This monitoring is facilitated in the present invention by using the sensing fibre 1 to facilitate transmission of data from said sensors 50 and / or system devices. In accordance with the present invention, data transmission can be made on an ad hoc basis, which can limit the necessary power requirements potentially extending battery life for each sensor 50 or device 60.

[0101] In the present invention, data transmission is achieved by the provision of vibrator units 71 associated with one or more sensors 50 or devices 60. Each vibrator unit 71 is configured to output acoustic data signals corresponding to data received from sensors 50 and / or devices 60 at one or more specified frequency, typically in the range 250Hz to 2kHz. To manage power consumption, senor or device data can be transmitted periodically or on an ad-hoc basis to the system controller. This can allow a significant extension of battery life for each sensor 50 or device 60.

[0102] By positioning the vibrator unit 71 at a suitable location, the output vibrations impact on the sensing fibre 1 and accordingly vary the backscattered pulses from the region of the sensing fibre 1 where the vibrations are incident. This can vary the detector output signal and hence can be extracted from the detector output signal for onward transmission of processing by local processing unit 121 or analyser 122.

[0103] In the present invention, in order to extract the acoustic data signals, local processing unit 121 is a data signal processing unit 121 configured to extract the component of the detector output signal derived from said acoustic data signals. As each vibration unit 71 location corresponds to a particular channel within the detector output signal, this is achieved by extracting the component of the detector output signal derived from said acoustic data signals by reference to a particular channel within the detector output signal corresponding to the location of the particular vibration unit 71 along the length of the sensing fibre 1.

[0104] The data signal processing unit 21 is configured to identify the acoustic data signal within the extracted component of the detector output signal. This may be achieved by filtering the extracted component to one or more acoustic frequency ranges corresponding to the specified frequency (or frequencies) of the acoustic data signals.

[0105] There will always be at least some background noise within the pipe 10. If the vibration unit 71 output level is too low, it will not be possible to reliably isolate the acoustic data output from the vibration unit 71. Nevertheless, if the vibration unit 71 output level is too high it may saturate some detection channels and / or use excess power. Accordingly, in the present invention, an acoustic sensor 79 is also provided, the acoustic sensor configured to detect background acoustic noise in the vicinity of the sensing fibre 1. The output of the acoustic sensor 79 is provided to a vibration control unit 72 configured to vary the vibration unit 71 output in response to the detected background acoustic noise, as will be described further below in relation to figure 4b. Accordingly, the vibration unit 71 output can be varied dynamically in response to the detected background acoustic noise. Beneficially, this allows the vibration unit 71 to increase output signal levels when the local background noise is high thereby ensuring these signals can still be detected on the sensing fibre 1. Similarly, this allows the vibration unit 71 to decrease output signal levels when the local background noise is low thereby reducing energy consumption and avoiding swamping other local acoustic signals whilst ensuring these signals can still be detected on the sensing fibre 1.

[0106] An exemplary embodiment is shown in figure 4a. In this example, a pair of fittings 12, 13, each comprising a tubular arrangement 14 are used to move sensing fibre 1 into and out of pipe 10 on either side of a device 60, in this instance comprising a valve member 61 and an associated valve control unit 62. The valve control unit 62 may be configured to provide output data indicating the status of the valve member 61. The example of figure 4a also includes a sensor 50, which may be a pressure sensor or the like. The skilled person will also appreciate that multiple sensors 50 may be provided in this area if required or desired.

[0107] In this example, the sensing fibre 1 is provided within two successive sections of cable connected at a junction box 80. Within the junction box 80, multiple fibres within one cable section, including sensing fibre 1, are spliced end to end onto corresponding fibres in the subsequent cable section. The skilled person will appreciate that in some embodiments no junction box 80 is required and that in other embodiments a different form of junction box could be provided.

[0108] The example of figure 4a illustrates multiple vibration units 7 la-7 If at different locations. In practice, whilst any of these locations could be used, one location would be selected depending upon which location is most suitable or feasible in a particular circumstance.

[0109] Vibration unit 71a is provided in the junction box 80 and is configured to apply vibration directly to the cable containing the sensing fibre 1. This arrangement beneficially reduces the power requirement for the vibrator unit 71a and reduces the prospect of attenuation or other distortion of the vibrations between the sensing fibre 1 and the vibrator unit 71a. Such positioning may also afford protection to the vibration unit 71a. Nevertheless, it may be difficult to fit the vibration unit within a standard junction box. Furthermore, the close spacing between the vibrator unit 71a and the cable increases the prospect that the vibrations could exceed the maximum dynamic range measurable using the detector 112 (known as saturation) and thereby inhibit the retrieval of data.

[0110] The skilled person will also appreciate that the vibration unit 71a may be positioned so as to apply vibrations directly to the sensing fibre 1 within the junction box 80 closer to the splice point. This can further limit the power requirement but may increase the danger of saturation of the sensing fibre 1.

[0111] Turning to vibration unit 71b, this is positioned so as to apply vibration directly to the cable outside the junction box 80, this avoids the difficulty of fitting the vibration unit 71b within the junction box 80, and may improve ease of access for fitting and maintenance. Nevertheless, this location potentially leaves the vibration unit 71b more exposed to impact damage.

[0112] Vibration units 71c and 71d illustrate the possibility of applying vibrations to the fitting 12 or the pipe 10. These vibrations will pass through the fitting 12 or the pipe 10 to the sensing fibre directly and may pass indirectly via the fluid. Such locations may provide simple fitting but may require higher power levels. Additionally, there is more prospect of distortion due to vibrations being distorted by passage through different direct and indirect routes. Once again, vibration units 71c, 7 Id are relatively easy to access but relatively exposed to external impacts.

[0113] Vibration units 71e and 7 If illustrate the possibility of providing vibration units mounted within pipe 10 and positioned to apply vibrations into the fluid within pipe 10. These vibrations can travel though the fluid to the sensing fibre 1. Once again, this may require a higher vibration power to achieve the same detectable signal as the earlier location options. It does have the benefit that the vibration units 71e, 7 If are protected from external impact damage.

[0114] The example of figure 4a also illustrates multiple acoustic sensors at different locations. In practice, whilst any of these locations could be used, one location would be selected depending upon which location is most suitable or feasible in a particular circumstance. If multiple acoustic sensors 79a-79f are provided, the output of each acoustic sensor 79a-79f may be used to determine an aggregated background noise level. Acoustic sensor 79a is provided in the junction box 80 and is configured to detect background noise in this location. Such a location is appropriate if the vibration unit 71 is fitted within the junction box and especially appropriate if the level of background noise in the junction box 80 is typically higher than that within the pipe 10.

[0115] Turning to acoustic sensor 79b, this is positioned outside the junction box 80. This avoids any difficulty in fitting acoustic sensor 79b within the junction box 80, and may improve ease of access for fitting and maintenance. Nevertheless, this location potentially leaves the acoustic sensor 79b more exposed to impact damage. Such a location is appropriate if the vibration unit 71 is fitted in the vicinity and is especially appropriate if the level of background noise in this location is typically higher than that within the pipe 10.

[0116] Acoustic sensor 79c is mounted on the pipe fitting 12. Such a location is appropriate if the vibration unit 71 is fitted in the vicinity and is especially appropriate if the level of background noise in this location is typically higher than that within the pipe 10.

[0117] Acoustic sensor 79d and 79e are mounted within pipe 10. These locations provide for direct determination of background noise within pipe 10 and are protected from external impact damage even if they are not protected from impact by any debris within the pipe 10. There may also be a possibility that flow interaction with the acoustic sensor 79 d, 79e may generate additional flow noise. As illustrated, acoustic sensor 79d is provided in the vicinity of the sensing fibre 1 rather than adjacent to any vibration unit 71. Such a location is appropriate if the key components of background noise are flow effects in the vicinity of the sensing fibre 1. In contrast, acoustic sensor 79e is provided in the vicinity of the illustrated vibration units 7 Id, 71e. This can be beneficial if one of these locations is used for vibration sensor 71 and is especially appropriate if the level of background noise in this location is relatively high.

[0118] Acoustic sensor 79f is mounted on tube 14 within the pipe 10. Such a location is appropriate if the vibration unit 71 is fitted in the vicinity and is especially appropriate if the level of background noise in this location is relatively high. Turning now to figure 4b, an exemplary method by which the vibration unit 71 output can be varied dynamically in response to the detected background acoustic noise is described. As illustrated in figure 4b, the method comprises a core series of steps 300 which can form a continuous operational loop if active ongoing transmission of acoustic data signals is required. There are also optional start and end steps 310 which facilitate improving performance where acoustic data signals are transmitted on an intermittent basis. In this instance, the acoustic sensor 79, vibration control unit 72 and vibration unit 71 return to an inactive state B between transmissions of acoustic data signal.

[0119] Turning to core steps 300, starting from an active mode A, at step 301, the background acoustic noise level is detected by acoustic sensor 79 and a detected noise level value is output to vibration control unit 72. At step 302, the vibration control unit 72 is configured to classify the background noise level. This may be achieved by comparing the background noise level value to one or more classification thresholds or by calculating a background noise level classification by a suitable classification function. The classification thresholds may be based on an overall detected noise level or on detected noise levels in specific frequency bands.

[0120] Subsequently, at step 303, the vibration control unit 72 is configured to set a vibration unit 71 output level in response to the classified background noise level. This may be achieved by use of a look up table based on the classification or by applying a suitable function to the classification. The skilled person will also appreciate that the detected noise level could be used directly as an input to the set vibration unit 71 output level step, thereby omitting the classification step. In such cases, the vibration unit 71 output level may be set to a specific value or specific percentage of value above the detected background noise level value.

[0121] At step 304, the vibration unit 71 outputs acoustic data signals at an output level set at step 303.

[0122] The skilled person will appreciate that in order to limit power consumption, the vibration unit 71 may be operated intermittently rather than continuously. Similarly, the acoustic sensor 79 and vibration control unit 72 may be operated intermittently rather than continuously. In one example, this intermittent operation can be achieved using the additional steps 310.

[0123] At step 311, the vibration control unit 72 determines that the vibration unit 71 is to be used to transmit acoustic data signals, for transmission at regular intervals, this can be triggered by reference to a clock signal. If it is desired to operate at ad hoc rather than regular intervals, then this can be triggered by the vibration control unit 72 or another suitable external source, such as sensor 50 or device 60.

[0124] At step 312, the vibration control unit 72 switches the acoustic sensor 79 to an active mode so the acoustic sensor 79 can detect the background noise level as at step 301 in figure 4b. Optionally, the method may involve waiting for a pre-set start interval after switching to active mode before transmitting acoustic data signals. This can improve the accuracy of the background noise measurement.

[0125] As illustrated, at step 313, the vibration control unit 72 switches the acoustic sensor 79 to an inactive mode once transmission of the acoustic data signals is completed. Optionally, the method may involve waiting for a pre-set start interval after transmission is completed to switch to inactive mode. This can enable the acoustic sensor 79 to remain active in case a follow up transmission is required.

[0126] In order that the acoustic data signals applied by vibration unit 71 can be readily processed, they are encoded using a particular data structure and / or a particular encoding protocol. This encoding is carried out by an encoder unit, which may be integrated into vibration control unit 72 as illustrated in figure 4a. The skilled person will however appreciate that a separate encoder unit may be provided if desired or required, connected to the sensor 50 and the device 60. As illustrated in figure 4, there may be a vibration control unit 72 provided for multiple sensors 50 and / or devices 60. The skilled person will appreciate that a single dedicated vibration control unit 72 may be provided for each senor 50 and / or device 60 and / or that vibration control units 72 could be integrated into sensors 50 and / or devices 60.

[0127] Turing now to figure 5, one example of use of a binary encoding protocol is illustrated. In this example, the upper line 91 represents a square wave clock signal at a specified frequency. The second line 92 represents binary data. By applying a Boolean exclusive OR (XOR) function to the square wave 91 and data 92, an output signal 93, 94 can be generated. In this example, the difference between signals 93 and 94 is that each relies on an opposite convention for representing binary data bits 1 and 0. In particular, this type of phase encoding ensures any information carrying transitions occur mid-bit making it particularly robust in a noisy environment.

[0128] In certain circumstances, the skilled person could alternatively apply other encoding protocols such as frequency modulation or utilising simultaneous application of different frequencies to define different data characters. One such example of a dual tone character identification system is illustrated in figure 6 wherein up to 16 characters (0-9, A-D, 8 and #) can be represented by different frequency combinations. In this particular example one frequency selected from a first set of four frequencies Fl and a second frequency is selected from a second set of four frequencies F2 to define the corresponding character within the table illustrated in figure 6. To limit cross talk, none of the frequencies Fl, F2 are harmonics of any of the other frequencies Fl, F2.

[0129] In the present invention, to facilitate ad-hoc transmission of data by vibration units 71, the acoustic data signals each have a defined data structure 200, as illustrated in figure 7. This data structure 200 can be applied to whichever encoding protocol is used. The key elements of the data structure are the start delimiter 202, data payload 204 and end delimiter 206. The start delimiter and end delimiter each comprise standard bit or character sequences indicating start or end of a data transmission. The data payload 204 corresponds to data output by any sensors 50 or devices 60 connected to the vibration control unit 72 used to drive the vibration unit 71.

[0130] The data signal processing unit 121 is be configured to retrieve the data payload for further processing or onward transmission by recognising the start delimiter 202 and end delimiter 202. Subsequently, if required, the data signal processing unit 12 is configured to decode the data payload 204 of the acoustic data signals.

[0131] Optionally, the end delimiter 206 further comprises an inter-packet gap, which may be a pre-set period without transmission. This can ensure adequate spacing between successive acoustic data signals. For improved performance, the data structure may comprise one or more of the additional elements of a pre-amble 201, a data source identifier 203 or a checksum 205.

[0132] In this context, the pre-amble 201 typically precedes the start delimiter 202 and comprises a pre-set sequence of bits. The pre-amble 201 can thus help phase lock a receiving clock within the data signal processing unit 121 to the acoustic data signal.

[0133] The data source identifier 203 typically precedes the data payload 204 and serves to identify the vibration unit 71, vibration control unit 72, sensor 50 and / or device 60 associated with the acoustic data signal. For instance, the data source identifier may be unique to a particular vibrator unit 71 or vibration control unit 72, which can further help the data signal processing unit determine the origin of the acoustic data signal. In other embodiments, especially where multiple sensors 50 or devices 60 are connected to a single vibrator unit 71 or vibration control unit 72 the data source identifier may correspond to the individual sensor 50 or device 60 from which data in the data payload 204 was received, this can enable data from separate sensors 50 or devices 60 to be processed independently, even if it is transmitted using a common vibrator unit 71 and / or vibration control unit 72.

[0134] The checksum 205 typically precedes the end delimiter 206 and contains the output of a checksum algorithm performed on the data payload 204 or on the data payload 204 and the data source identifier 203. This can enable the integrity of the data payload 204 or data pay load 204 and data source identifier 203 to be verified on receipt.

[0135] In some implementations, keep-alive acoustic data signals are transmitted by vibration unit 71 if a pre-set keep-alive period has passed since a previous transmission. This allows continued operation to be verified in the absence of the triggering of other data signals. Similarly, the skilled person will appreciate that fault acoustic data signals can be transmitted by vibration unit 71 if fault condition is determined in the vibration unit 71 or any other connected device. Such keep-alive and fault acoustic data signals can be distinguished from other acoustic data signals by the content of the data pay load. Alternatively, keep-alive and fault acoustic data signals can be distinguished from other acoustic data signals by the transmission frequency or combination of frequencies. In such cases, providing a different transmission frequency or combination of frequencies for each vibration unit 71 can enable reliable identification of keep alive and / or fault signals from multiple different vibration units 71 even from short transmission duration.

[0136] The one or more embodiments are described above by way of example only.

[0137] Many variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

1. CLAIMS1. A data transmitting apparatus for transmitting data via a sensing apparatus for monitoring the condition of a fluid pipe of the type 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 data transmitting apparatus comprising: a vibration unit configured to apply acoustic data signals to the sensing fibre, the acoustic data signals comprising a data payload; a data signal processing unit configured to extract a component of the detector output signal derived from said acoustic data signals so as to retrieve the data payload for further processing or onward transmission; an acoustic sensor configured to detect a background acoustic noise in the vicinity of the sensing fibre; and a vibration control unit configured to vary the vibration unit output in response to the detected background acoustic noise.

2. A data transmitting apparatus as claimed in claim 1 , wherein the acoustic sensor is configured to exclude from detection acoustic signals at the same frequency or frequency range as the vibration unit output or wherein the acoustic sensor and / or the acoustic control unit is configured to apply a cancellation signal to the detected background noise, the cancellation signal corresponding to and opposing the vibration unit output.

3. A data transmitting apparatus as claimed in claim 1 or claim 2, wherein the acoustic sensor is configured to switch between an active mode where detection is enabled and an inactive mode where detection is not enabled.

4. A data transmitting apparatus as claimed in claim 3, wherein an active mode period matches the period of output of acoustic signals; precedes the output of acoustic signals by a pre-set start interval; and / or endures until a pre-set end interval after the output of acoustic signals.

5. A data transmitting apparatus as claimed in any preceding claim, wherein the acoustic sensor is configured to output a background noise level value or wherein the acoustic sensor or the vibration control unit is configured to determine a background noise level classification.

6. A data transmitting apparatus as claimed in claim 5, wherein the vibration control unit is configured to vary the vibration unit output level in response to background noise level value or background noise level classification, the variation determined by a function or by a pre-set look up table.

7. A data transmitting apparatus as claimed in any preceding claim, wherein the vibration unit is positioned so as to apply the acoustic signals directly to the sensing fibre or to a cable within which the sensing fibre is provided.

8. A data transmitting apparatus as claimed in claim 7, wherein the vibration unit is provided within a junction box.

9. A data transmitting apparatus as claimed in any preceding claim, wherein the acoustic sensor is positioned adjacent to the vibration unit.

10. A data transmitting apparatus as claimed in any preceding claim, wherein multiple acoustic sensors are provided for the vibration unit.

11. A data transmitting apparatus as claimed in any preceding claim, wherein there are multiple vibration units, each vibration unit provided at separate locations along the sensing fibre.

12. A data transmitting apparatus as claimed in any preceding claim, wherein the vibration unit or vibration control unit comprises an encoder unit configured to receive data from one or more connected devices and to encode received data into an encoding protocol and / or data structure suitable for acoustic data signals applied by the vibrator unit to the sensing fibre.

13. A data transmitting apparatus as claimed in claim 12, wherein the encoder unit is configured to encode a data source identifier corresponding to the connected device when encoding data received from said device.

14. A data transmitting apparatus as claimed in any preceding claim, wherein the detector output signal comprises multiple channels, each channel corresponding to a particular location along the sensing fibre, and the data signal processing unit is configured to extract the component of the detector output signal derived from acoustic data signals generated by a particular vibration unit by reference to the corresponding channel within the detector output signal.

15. A data transmitting apparatus as claimed in claim 14, wherein the data signal processing unit is configured to identify the acoustic data signal within the extracted component of the detector output signal by filtering the extracted component to one or more acoustic frequency ranges corresponding to the acoustic data signals.

16. A data transmitting apparatus as claimed in any preceding claim, wherein the vibration unit is configured to output keep-alive acoustic data signals after a preset keep-alive period has passed since a previous transmission.

17. A data transmitting apparatus as claimed in claim 18, wherein the keep-alive acoustic data signals are transmitted at a different acoustic frequency to other acoustic data signals or at a combination of different frequencies to other acoustic data signals.

18. A method for transmitting data using a sensing apparatus for monitoring a fluid pipe of the type 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 method comprising the steps of: applying acoustic data signals to the sensing fibre using a vibration unit, the acoustic data signals comprising a data payload; extracting a component of the detector output signal derived from said acoustic data signals so as to retrieve the data payload for further processing or onward transmission;wherein the method further comprises detecting background acoustic noise in the vicinity of the sensing fibre; and varying the vibration unit output in response to the detected background acoustic noise.

19. A method as claimed in claim 18, wherein acoustic signals at the same frequency or frequency range as the vibration unit output are excluded from detection or wherein a cancellation signal is applied to the detected background noise, the cancellation signal corresponding to and opposing the vibration unit output.

20. A method as claimed in claim 18 or claim 19, wherein the method includes switching between an active mode where detection is enabled and an inactive mode where detection is not enabled.

21. A method as claimed in claim 20, wherein an active mode period matches the period of output of acoustic signals; precedes the output of acoustic signals by a pre-set start interval; and / or endures until a pre-set end interval after the output of acoustic signals.

22. A method as claimed in any one of claims 18 to 21 , wherein the method includes outputting a background noise level value and / or determining a background noise level classification.

23. A method as claimed in claim 22, wherein determining a background noise level classification is archived by comparing the background noise level value to one or more pre-set classification thresholds; by comparing a background noise frequency spectrum to one or more pre-set classification standards; by comparing the output of one or more background frequency spectrum components to one or more pre-set classification standards; and / or by summing components of the background frequency spectrum.

24. A method as claimed in claim 22 or claim 23, wherein variation of the vibration unit output level in response to background noise level value or backgroundnoise level classification, is determined by a function or by a pre-set look up table.

25. A method as claimed in any one of claims 18 to 24, wherein the detector output signal comprises multiple channels, each channel corresponding to a particular location along the sensing fibre, and the component of the detector output signal derived from acoustic data signals generated by a particular vibration unit is extracted by reference to the corresponding channel within the detector output signal.

26. A method as claimed in claim 25, wherein the acoustic data signal within the extracted component of the detector output signal is identified by filtering the extracted component to one or more acoustic frequency ranges corresponding to the acoustic data signals.

27. A method as claimed in any one of claims 18 to 26, wherein comprising the step of outputting keep-alive acoustic data signals after a pre-set keep-alive period has passed since a previous transmission.

28. A method as claimed in claim 27, wherein the keep-alive acoustic data signals are transmitted at a different acoustic frequency to other acoustic data signals or at a combination of different frequencies to other acoustic data signals.

29. A fluid distribution system comprising one or more fluid pipes where one or more data transmitting apparatuses according to any one of claims 1 to 17 or operating according to the method of any one of claims 18 to 28 are provided to monitor at some of the pipes.

30. A fluid distribution system comprising one or more system sensors and / or system devices at one or more points within the fluid distribution system; a system controller; and one or more data transmitting apparatuses according to any one of claims 1 to 17 or operating according to the method of any one of claims 18 to 28 are adapted to carry acoustic data signals from the system sensors or system devices to the system controller.

31. A data communication network comprising one or more data cables laid for at least part of their length in fluid pipes, each data cable comprising one or moredata fibres for conventional data transmission between transceiver devices at network nodes, wherein at least some of the data cables comprise at least one sensing fibre and wherein at least one data transmitting apparatus according to according to any one of claims 1 to 17 or operating according to the method of any one of claims 18 to 28 is provided to transmit data using said sensing fibre.

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