Improvements in or related to access control or presence monitoring

Abstract

A sensing fibre (1) forms a read loop (15) extending to a regulated area (20) outside a fluid pipe (10). The read loop (15) defines a read location (16) to which acoustic data signals comprising an identification code can be applied by a user terminal (150). The applied acoustic data signals impact on the sensing fibre (1) and accordingly vary the backscattered pulses from the read location (16). This can vary the detector output signal and hence can be extracted from the detector output signal for onward transmission of processing by a local processing unit (121) or analyser (122) enabling retrieval of the identification code and thereby enabling monitoring of access to the regulated area (20).

Description

[0001] IMPROVEMENTS IN OR RELATED TO ACCESS CONTROL OR PRESENCE MONITORING

[0002] Technical Field of the Invention

[0003] The present invention relates to improvements in or relating to access control or presence monitoring. In particular, the present invention relates to such improvements in relation to monitored networks of fluid pipes, including but not limited to water supply pipes.

[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. Suitablewireless 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] Whilst some key locations within a fluid distribution network may be staffed substantially permanently or semi-permanently, many other locations, especially remote locations, are accessed rarely and often at irregular intervals. It is often desirable to control access to such locations. This prevents unauthorised individuals accessing key system sensors or devices. This can be achieved by use of a suitable mechanical lock, which beneficially will not require a power supply. Nevertheless, access is dependent on an authorised individual being in possession of the correct key. Furthermore, such mechanical locks are vulnerable to weather damage in exposed environments and / or being picked or damaged by unauthorised individuals seeking access. These issues can be partially alleviated by use of electronic locks, but these may require a local power source and / or data backhaul capabilities, especially where the identity credentials of an authorised user are to be updated or checked in real time.Another issue with such locations is that it is desirable to maintain a record of authorised individuals who have accessed the location. This can be useful in the future for auditing any work carried out. If this information is available in real time or quasi-real time, it can be useful in terms of monitoring the activity of an authorised individual. For instance, this may allow potentially dangerous devices at the location to be shut down temporarily. It can also enable an alert to be issued if an individual is overdue to leave a particular location, perhaps due to a maintenance issue being more complex than anticipated or because the individual has become injured or incapacitated or has spent an unexpectedly long time at a remote site. Once again, such functionality requires significant data back haul and local power capacity.

[0014] It is therefore an object of embodiments of the present invention to at least partially address the above issues.

[0015] Summary of the Invention

[0016] In a broad sense, the invention relates to a system for monitoring access to a regulated area. The system may use a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the base module comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and 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 system may comprise a user terminal configured to apply acoustic data signals to the read location of the sensing fibre, the acoustic data signals comprising an identification code. The system 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 identification code. The system may comprise an access management unit configured to receive and process the retrieved identification code from the data signal processing unit.

[0017] The invention also relates to a method for monitoring access to a regulated area. The method may use a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the basemodule comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and 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 may comprise applying acoustic data signals to the read location of the sensing fibre using a user terminal, the acoustic data signals comprising an identification code. The method may comprise extracting a component of the detector output signal derived from said acoustic data signals so as to retrieve the identification code. The method may comprise receiving and processing the retrieved identification code.

[0018] According to a first aspect of the present invention there is provided a system for monitoring access to a regulated area, using a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the base module comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and 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 system comprising:

[0019] a user terminal configured to apply acoustic data signals to the read location of the sensing fibre, the acoustic data signals comprising an identification code; 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 identification code; and

[0020] an access management unit configured to receive and process the retrieved identification code from the data signal processing unit.

[0021] According to a second aspect of the present invention there is provided a method for monitoring access to a regulated area, using a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the base module comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and a light detector configured todetect backscattered light pulses from the sensing fibre and output a detector output signal in response to the detected backscattered light, the method comprising:

[0022] applying acoustic data signals to the read location of the sensing fibre using a user terminal, the acoustic data signals comprising an identification code; extracting a component of the detector output signal derived from said acoustic data signals so as to retrieve the identification code; and

[0023] receiving and processing the retrieved identification code.

[0024] The present invention thereby enables an identification code to be readily received at a base module remote from the regulated area. This can enable the identification code to be received at the base module without installing additional data back haul equipment and without the necessity to provide power for said back haul equipment. This thereby provides for reliable low energy, low bandwidth back haul of identification codes. In turn this simplifies monitoring of users providing such codes on entry / exit from regulated areas and / or monitoring of actual request to access / egress from regulated areas.

[0025] In the context of the present application, the term ‘fluid’ in relation to a fluid pipe or conduit may refer to any material, liquid or gaseous, including fuels such as oil or gas or associated distillates, and additionally in industrial uses which may include mining and similar. The invention may more specifically refer to a primarily waterbased fluid, such as potable water, pre-treatment water, wastewater or water-based slurries.

[0026] 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.

[0027] In the context of the present invention, a sensing fibre is an optical fibre suitable for and / or adapted for use in sensing conditions experienced by or intrinsic to the fibre. In particular, the optical fibre may be suitable for and / or adapted to enable such sensingto take place by analysis of backscattering of light pulses introduced into the optical fibre. In various implementations, the backscattering of light pulses may be used to perform distributed acoustic sensing (DAS) otherwise referred to as distributed vibration sensing (DVS), distributed strain sensing (DSS) and / or distributed temperature sensing (DTS).

[0028] The sensing fibre may be a sensing fibre provided within a pipe. The pipe may be a fluid pipe. The pipe may form part of a fluid distribution system. In one example, the fluid distribution system may be a water supply network or a district metered area of a water supply network.

[0029] The fluid pipe 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 fibre may run in a loop from one end of the pipe to be monitored to the other end and back again.

[0030] The fluid pipe may comprise a branched network of pipes or part of a branched network of pipes. In such embodiments the sensing fibre may run in a loop from an entry point to the far end of each branch in turn.

[0031] 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.

[0032] The sensing fibre may be provided within a data cable comprising multiple optical fibres. In such embodiments, fibres within the data cable other than the sensing fibre may be dedicated to carrying network data. In some such embodiments, the data cable may comprise multiple sensing fibres.

[0033] In embodiments comprising a data cable, the data cable may comprise multiple bundles of optical fibres. In such embodiments, each fibre bundle may be provided within an individual sheath. The data cable may comprise part of a data communication network comprising one or more data cables configured to carry network data.

[0034] The sensing fibre can be any suitable length. In particular embodiments, the desired length of the sensing fibre may be set by desired performance. In this context, in order not to unduly limit performance, the sensing fibre may be less than 20km inlength, less than 15km in length, less than 10 km in length, less than 5km in length or less than 1 km in length.

[0035] The sensing fibre may be provided with one or more sections inside the pipe and with one or more sections outside the pipe. The read location may be within the pipe. The read location may be on a section of the sensing fibre outside the pipe. Such a section of sensing fibre may be referred to as a read loop. In some embodiments where the sensing fibre is provided within a data cable comprising multiple optical fibres, the read loop may comprise a section of sensing fibre separated from and / or outside the data cable.

[0036] The sensing fibre may enter or exit the fluid pipe via a pipe fitting. The pipe fitting may be of any suitable type. In one embodiment, the pipe fitting may comprise a semi-rigid tubular arrangement configured to be inserted into the fluid pipe. The tubular arrangement may be configured to resist a fluid flow within the pipe. The sensing fibre may be provided inside the tubular arrangement. The tubular arrangement may be configured to control placement of the sensing fibre within the fluid pipe. Thus, the sensing fibre position in the pipe is better controlled.

[0037] In some embodiments, the sensing fibre may comprise more than one read location. In some such embodiments, each read location may be inside the pipe. In other such embodiments, each read location may be outside the pipe. In further such embodiments, one or more read locations may be inside the pipe and one or more read locations may be outside the pipe. In further embodiments, it is possible that read locations may be defined on an ad hoc basis. This allows the present invention to be utilised to monitor access at any point along the sensing fibre. This may be useful, for example, where the pipe needs to be repaired for monitoring access to the specific point of the pipe that needs repair. In such examples, the associated read location may be defined with reference to the specific point of the pipe. In particular, the read location may match the location of a fault and / or the location of the nearest pipe entry / exit to the location of a fault.

[0038] Read locations may be provided within a read housing. The read housing may provide mechanical protection for the sensing fibre, enhance or attenuate transmission of acoustic signals and / or indicate the read location to a user, as required or desired.The read housing may define a space within which the read location of the sensor fibre is provided. The sensing fibre may be mounted within the read housing.

[0039] The space within the read housing may be substantially empty. In such cases, there may be air within the space. The space within the read housing may be filled. The filler may comprise any suitable packing material. Suitable packing materials may include but are not limited to selected gases, liquids, gels, powders or solids as required or desired. The packing materials may be selected for their acoustic qualities. In this manner, the packing materials may help enhance or attenuate transmission of acoustic signals as required or desired. In some embodiments, there may be more than one packing material. In such embodiments, a packing material enhancing acoustic transmission may be provided in one part of the space within the read housing and a packing material adapted to attenuate acoustic transmission may be provided in another part of the space within the read housing. This can facilitate detection of acoustic signals from one direction whilst limiting detection of acoustic signals from a different direction. This might helpfully enhance detection when a user positions the terminal at a specified location adjacent to the read housing.

[0040] In some embodiments, the read housing may comprise one or more openings between the exterior of the read housing and the interior space. This may facilitate transmission of acoustic signals. In some embodiments, the read housing may comprise an external indication of the read location to a user. The external indication can comprise printed or painted elements, embossed or recessed elements as required or desired. The elements within the indication can comprise symbols, text, numbers or the like.

[0041] The regulated area may be defined at any suitable location. In particular embodiments, the regulated area may be an inspection chamber, building or other structure associated with the fluid pipe or the wider network to which the fluid pipe is connected.

[0042] 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 supplysystem, the base module may be provided within a substation such as a pumping substation, service reservoir, or similar. In some embodiments, two or more sensing fibres may be provided. In some such embodiments, the two or more sensing fibres may share a common base module. This can enable a single base module to be used to monitor a greater number of regulated areas than might otherwise be possible.

[0043] Receiving and processing the retrieved identification code by the access management unit may comprise storing the identification code in an access log. In such embodiments, the identification code may be stored alongside a timestamp.

[0044] In some such embodiments, the access management unit may be configured to determine whether the identification code was retrieved as part of an access request or an egress request. This may be achieved by detecting an access request or egress request code within the acoustic data signals. Alternatively, this may be achieved if the identification code for access differs from the identification code for egress. In such embodiments, the access request or egress request may be stored alongside a timestamp.

[0045] In some embodiments, the access management unit may be configured to output a welfare signal if an egress request (or a further access request for the same regulated area or a different regulated area) is not received before the end of a welfare time interval. This can help monitor the progress of a user working remotely at a regulated area or at a series of regulated areas. Whilst a missing egress request may typically indicate that a user has forgotten to request egress, it can indicate that a particular task is taking longer than expected and / or that the user has suffered a mishap.

[0046] The welfare time interval may be the same for each regulated area. In further embodiments, the welfare time interval may be varied for different regulated areas. In still further embodiments, the welfare time interval may be varied for a particular regulated area based on the nature of the task required at the regulated area on a particular occasion.

[0047] The welfare signal may trigger an audio and / or visual alarm at the access management unit or at a system control terminal. In this manner, the welfare signal can trigger an operator to take appropriate action. The appropriate action may be determined by the particular circumstances and may include but is not limited tosending a message to a mobile communication device associated with a user, placing a call to a mobile communication device associated with a user, despatching one or more additional users to investigate or the like. The despatch option may be particularly selected if the regulated area is a place where communication is problematic, for instance a rural area with poor cellular network coverage or indeed if a message or call has not promoted a reply. In some embodiments, the access management unit may be configured to automatically trigger action in response to the welfare signal. In such embodiments, the automatic action may comprise sending a message to a mobile communication device associated with a user, placing a call to a mobile communication device associated with a user, despatching one or more additional users to investigate or the like.

[0048] In some embodiments, receiving and processing the retrieved identification code by the access management unit may comprise comparing the retrieved identification code to a list of approved identification codes. In such embodiments, if the retrieved identification code matches an approved identification code, the access management unit may be configured to output an approved signal. In such embodiments, if the retrieved identification code does not match an approved identification code, the access management unit may be configured to output a disapproved signal.

[0049] The disapproved signal may trigger an audio and / or visual alarm at the access management unit or at a system control terminal. In this manner, the disapproved signal can trigger an operator to take appropriate action. The appropriate action may be determined by the particular circumstances and may include but is not limited to sending a message to a mobile communication device associated with a user, placing a call to a mobile communication device associated with a user, despatching one or more additional users to investigate or the like. In some embodiments, the access management unit may be configured to automatically trigger action in response to the disapproved signal. In such embodiments, the automatic action may comprise sending a message to a mobile communication device associated with a user, placing a call to a mobile communication device associated with a user, despatching one or more additional users to investigate or the like.In some embodiments, the access management unit may be configured to automatically trigger action in response to the approved signal. The action may comprise sending a message to a mobile communication device associated with a user or placing a call to a mobile communication device associated with a user. The message or call may comprise information required to unlock or otherwise access the regulated area. For instance, the information may comprise a key code required to operate a lock associated with the regulated area or to deactivate an alarm system associated with the regulated area.

[0050] In some embodiments, the regulated area may be provided with an electronic lock and / or an alarm system and a communication unit configured to receive data signals on behalf of the electronic lock and / or alarm system. In such embodiments, the access management unit may be configured to automatically output an unlock signal in response to the approved signal. In response to receipt of the unlock signal via the communication unit, the electronic lock may be unlocked and / or the alarm system may be deactivated.

[0051] In such embodiments, the access management unit may be additionally configured to automatically output a lock signal. In response to receipt of the lock signal via the communication unit, the electronic lock may be locked and / or the alarm system may be activated. This can allow the regulated area to be locked and / or alarms after a task is completed.

[0052] The lock signal may be output in response to an egress request. The lock signal may be output after a lock time interval. This can allow for automatic locking and alarm activation in the absence of an egress request. The lock time interval may be the same for each regulated area. In further embodiments, the lock time interval may be varied for different regulated areas. In still further embodiments, the lock time interval may be varied for a particular regulated area based on the nature of the task required at the regulated area on a particular occasion.

[0053] The user terminal may comprise a vibration unit configured to generate the acoustic data signals. 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 generateacoustic 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.

[0054] The vibration unit may be configured to operate in response to a vibration control unit. The vibration control unit may be configured to store one or more identification codes. The vibration control unit may be configured to store one or more access or egress codes. The vibration control unit may be configured to store other data as required or as appropriate.

[0055] The vibration control unit may be configured to operate the vibration unit to generate acoustic data signals at periodic intervals. The vibration control unit may be configured to operate the vibration unit to generate acoustic data signals in response to detected input. The detected input may be from a user interface. The user interface may comprise any suitable user actuable inputs and / or any suitable visual / audio output elements as required or desired. In some embodiments, the user terminal may be configured to receive a single user input and the vibration control unit may be configured to operate the vibration unit in response to detection of the single user input. In other embodiments, the user terminal may be configured to receive multiple different user inputs and the vibration control unit may be configured to operate the vibration unit to output different acoustic data signals in response to detection of specific different user inputs. This can allow a user to select different identification codes (for instance for different users) and / or access or egress requests, if required or desired.

[0056] In some embodiments, the vibration control unit may be configured to authenticate the user before operating the vibration unit. In such embodiments, the vibration control unit may be configured to determine whether a security code is correctly input via the user interface. In other embodiments, the user terminal may comprise an authentication sensor configured to determine the user identity and output a corresponding indication to the vibration control unit. The authentication sensor may be of any suitable type. In some embodiments, the authentication sensor is a fingerprint sensor, a fatal recognition sensor, an iris recognition sensor, a voice recognition sensor or the like.In some embodiments, the acoustic data signals may comprise a start delimiter, an end delimiter and the identification code 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 identification code.

[0057] This provides reliably identification of the identification code within an acoustic data signal. As the identification code can be reliably identified this allows for ad hoc data transmission rather than scheduled data transmission.

[0058] 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.

[0059] 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 user terminal. This can allow for the user terminal to be identified in addition to a user.

[0060] 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 identification code to be verified on receipt.

[0061] 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.The acoustic data signals may comprise a square wave. The square wave may have a single clock frequency defining the data rate, which may as an example be between 0.5Hz and 100Hz. Suitable switched acoustic frequencies to transmit actual data 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.

[0062] 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.

[0063] 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.

[0064] In embodiments where simultaneous signal frequencies are used for encoding, the respective frequences may not be harmonically related. This limits the potential for harmonic multiples and thereby crosstalk between different signal frequencies.

[0065] 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 particularlocation. Neighbouring channels may be defined by the minimum resolvable time interval between backscattered pulses from neighbouring sensing fibre locations. Accordingly, each read 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 read location along the length of the sensing fibre is known the component of the detector output signal derived from acoustic data signals applied to a particular read location can be extracted by reference to the corresponding channel within the detector output signal. In embodiments with multiple read locations, there may be multiple referenced channels. In such cases, each channel may correspond to a different read location.

[0066] 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.

[0067] The data signal processing unit may be configured to retrieve the identification code for further processing or onward transmission by recognising the start delimiter and end delimiter. The data signal processing unit may be configured to decode the identification code 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.

[0068] According to a third aspect of the present invention there is provided a user terminal for use in a system according to the first aspect of the present invention or a method according to the second aspect of the present invention, the user terminal comprising a vibration unit configured to generate the acoustic data signals, the vibration control unit configured to operate in response to a vibration control unit.

[0069] According to a fourth aspect of the present invention there is provided a fluid distribution system comprising one or more regulated areas monitored by a systemaccording to the first aspect of the present invention or a method according to the second aspect of the present invention.

[0070] According to a fifth aspect of the present invention there is provided a data network comprising one or more one or more data cables configured to carry network data wherein at least one data cable comprises a sensing fibre, for use in a system according to the first aspect of the present invention or a method according to the second aspect of the present invention.

[0071] 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.

[0072] Detailed Description of the Invention

[0073] 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:

[0074] 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;

[0075] Figure 2 shows a conventional arrangement sensing fibre for a known sensing apparatus of figure 1 provided in a single exemplary water pipe;

[0076] Figure 3 shows an exemplary arrangement of a sensing fibre for a sensing apparatus according to the present invention;

[0077] Figure 4 provides (a) a schematic illustration of a read location of a sensing fibre according to the present invention provided within a gate; and (b) a schematic illustration of two alternative read locations of a sensing fibreaccording to the present invention provided within an inspection chamber;

[0078] Figure 5 is a schematic flow chart illustrating one method of operation of the present invention;

[0079] Figure 6 is a schematic block diagram of a user terminal according to the present invention for applying an acoustic data signal to read location of a sensing fibre;

[0080] Figure 7 is a schematic diagram illustrating an example of a data encoding usable in the present invention;

[0081] Figure 8 illustrates an exemplary dual-tone multi-frequency encoding scheme usable in the present invention; and

[0082] Figure 9 is a schematic diagram illustrating an example of a data structure usable in the present invention.

[0083] 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.

[0084] 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.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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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 upperpart 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.

[0089] As illustrated, 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.

[0090] Typically, 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 circumnavigate in-line devices (such as valves) or negotiate tight bends in a pipe, or 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. In such embodiments, 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.

[0091] Turning now to figure 3, in the present invention, where the sensing fibre 1 exits the fluid pipe 10 between the first and second fittings 12, 13 it forms a read loop 15 extending to a regulated area 20 outside the pipe 1. In this example, there are two regulated areas 20, a pumping station accessed via gate 21 and an inspection chamber (not shown in figure 3) accessed via manhole 22.

[0092] As illustrated in figures 4a and 4b, each read loop 15 defines a read location 16 to which acoustic data signals can be applied by a user terminal 150. As illustrated the read location 16 may be provided within a read housing 17. The read housing 17 can provide mechanical protection to the read location 16. The read housing 17 may define an internal space, optionally filed with a solid or liquid filler material. The filler material may be adapted to enhance or attenuate transmission of acoustic signals fromoutside the read housing 17. Optionally, the exterior of the read housing 17 may be provided with one or more indications aiding a user in identifying the read housing 17 and / or the read location 16.

[0093] Turning to figure 4a, the gate 21 of regulated area 20 is provided with optional additional components comprising an electronic lock 29 and / or an alarm system 28 and a communication unit 27 configured to receive data signals on behalf of the electronic lock 29 and / or alarm system 28. In this manner, the electronic lock 29 can be unlocked or the alarm system 28 can be deactivated in response to the acoustic data signals applied to the read location 16. This optional functionality is described in more detail below. As illustrated in the figure, the read location is provided towards the top of one post of the gates 21, this being a convenient height for a user. This is also the height at which the alarm system 28 is provided, allowing for convenient user input if necessary.

[0094] Turning to figure 4b, this shows optional different read locations 16a, 16b in relation to an inspection chamber 23 provided below a manhole cover 22. The read location 16a is provided within the chamber 23. Accordingly, a user can apply acoustic data signals to this read location 16a to confirm that they have accessed the inspection chamber 23. Similarly, a user can apply acoustic data signals to this read location 16a to confirm that they are about to exit the inspection chamber 23. In contrast the read location 16b is provided outside the chamber 23 and acoustic data signals can be applied form outside the chamber 23. Accordingly, a user can apply acoustic data signals to this read location 16b to confirm that they are about to access the inspection chamber 23. Similarly, a user can apply acoustic data signals to this read location 16b to confirm that they have exited the inspection chamber 23. The skilled person will appreciate that further variations in the position of read locations and workflows can be implemented as desired or as appropriate.

[0095] In use, an acoustic data signal comprising an identification code is applied to a read location 16 by a user terminal 150. The applied acoustic data signals impact on the sensing fibre 1 and accordingly vary the backscattered pulses from the read location 16 where the applied acoustic data signals are applied. 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.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 read location 16 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 particular read location 16 along the length of the sensing fibre 1.

[0096] The data signal processing unit 121 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. In this way, the data signal processing unit 121 can retrieve the identification code within the applied acoustic data signals. The retrieved identification code is received and processed, by an access management unit. The access management unit may be a component of analyser 122 or another device 123 connected to the analyser.

[0097] One example of implementation of the method of the invention is set out in figure 5. At step 301 acoustic data signals are applied to the read location 16 by a user terminal 150. At step 302, the data signal processing unit 121 retrieves the identification code. At step 303 the retrieved identification code is received and processed, by the access management unit 122 (in this example, the access management unit is part of analyser 122). The processing involves storing the identification code in an access log alongside a timestamp. In some embodiments, the identification code applied by the user terminal 150 can vary if the terminal is making a request to access the regulated area 20 or making a request to egress request the regulated area 20. Additionally or alternatively, the identification code could be supplemented by an access code or an egress code.

[0098] These steps 301-303 are sufficient as a method to maintain an access log associated with particular regulated areas 20. Nevertheless, the method can be extended to additional optional steps if desired.Turning back to figure 5, at step 304, with reference to the timestamp stored in the access log, the access management unit 122 may determine whether a welfare interval has passed since a particular access request was received without receiving a corresponding egress request. If it is determined that the welfare interval has been exceeded the access management unit 122 can output a welfare signal at step 305.

[0099] If a user is working remotely at a regulated area 20 (or at a series of regulated areas) a missing egress request could indicate that a particular task is taking longer than expected and / or that the user has suffered a mishap. Accordingly, it may be necessary to contact the user to check whether this is the case or whether they have simply forgotten to request egress. To minimise unnecessary concern, the welfare time interval can be varied for different regulated areas or if different tasks are expected to be completed at a particular regulated area 20.

[0100] The welfare signal may trigger an audio and / or visual alarm at the access management unit 122 or at a system control terminal 123. In this manner, the welfare signal can trigger automated action or indeed an operator to take appropriate action such as sending a message to a mobile communication device associated with a user, placing a call to a mobile communication device associated with a user, despatching one or more additional users to investigate or the like.

[0101] In another optional extension of the method, at step 306, the access management unit 122 compares the retrieved identification code to a list of approved identification codes. If the retrieved identification code does not match an approved code, the access management unit 122 can output a disapproved signal at step 307. The disapproved signal may trigger an audio and / or visual alarm at the access management unit 122 or at a system control terminal 123. This can trigger automated action or an operator to take appropriate action.

[0102] If the retrieved identification code matches an approved code, the access management unit 122 can output an approved signal at step 308. The disapproved signal may trigger an audio and / or visual alarm at the access management unit 122 or at a system control terminal 123. This can trigger automated action or an operator to take appropriate action. The action may comprise sending a message to a mobile communication device associated with a user or placing a call to a mobilecommunication device associated with a user. The message or call may confirm approval and / or comprise information required to unlock or otherwise access the regulated area.

[0103] Optionally, output of the approved signal at step 308 can trigger the access management unit 122 to automatically output an unlock message at step 309

[0104] In embodiments where the regulated area 20 is provided with an electronic lock 29 and / or an alarm system 28 and a communication unit 27 configured to receive data signals, the access management unit 122 optionally is triggered to output an unlock message at step 309. In response to receipt of the unlock signal via the communication unit 27, the electronic lock 29 is unlocked and / or the alarm system 28 is deactivated.

[0105] Optionally, at step 310, the access management unit 122 is also configured to output a lock signal, typically in response to receiving an egress request. In response to receipt of the lock signal via the communication unit 27, the electronic lock 29 is locked and / or the alarm system 28 is activated. In some embodiments, the method can include at step 311, with reference to the timestamp of the unlock signal stored in the access log, the access management unit 122 determining whether a lock time interval has passed since a particular access request was received without receiving a corresponding egress request. If it is determined that the lock time interval has been exceeded the access management unit 122 can output a lock signal automatically at step 310. The skilled person will appreciate that the lock time interval may be varied for different regulated areas or for a particular regulated area based on the nature of the task required at the regulated area on a particular occasion.

[0106] Turning now to figure 6, the user terminal 150 comprises a vibration unit 151 configured to generate the acoustic data signals in response to a vibration control unit 152. The vibration unit may comprise a loudspeaker, buzzer, sounder, vibrator, oscillator or the like and can be configured to generate acoustic signals of a single frequency or of more than one frequency either substantially concurrently or substantially consecutively, as required or desired.

[0107] The vibration control unit 152 is configured to store one or more identification codes and where required store one or more access or egress codes.The vibration control unit 152 is typically configured to operate the vibration unit 151 to generate acoustic data signals in response to detected inputs from a user interface 153. As shown in figures 4a and 4b, the user interface is a touchscreen. Nevertheless, a much simpler interface may be provided in alternative embodiment. For instance, the interface may simply comprise a single button or key which when pressed cause the vibration control unit 152 to operate the vibration unit 151 or for example an embodiment having two buttons, one for an access request and one for an egress request.

[0108] In some embodiments, the user interface 153 is configured to receive multiple different user inputs. This can allow selection of multiple different identification codes or other codes. It can also be used to authenticate a user before outputting acoustic data signal. In such examples, the user may need to input a security code via the user interface 153. The vibration control unit 152 can then determine whether a security code is correctly inputted via the user interface 153 before enabling operation of the vibration unit 151.

[0109] In a further option, also shown in figure 6, the user terminal 150 additionally comprise an authentication sensor 154 configured to determine the user identity and output a corresponding indication to the vibration control unit 152. The authentication sensor 154 is a fingerprint sensor, facial recognition sensor, iris recognition sensor or voice recognition sensor.

[0110] In order that the acoustic data signals applied can be readily processed, they are encoded using a particular data structure and / or a particular encoding protocol. Turning now to figure 7, 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.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 8 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 8. To limit cross talk, none of the frequencies Fl, F2 are harmonics of any of the other frequencies Fl, F2.

[0111] In the present invention, to facilitate ad-hoc transmission of data by user terminals 150, the acoustic data signals each have a defined data structure 200, as illustrated in figure 9. 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, identification code 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 identification code 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.

[0112] The data signal processing unit 121 is be configured to retrieve the identification code 204 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 identification code 204 of the acoustic data signals.

[0113] 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.

[0114] 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.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.

[0115] The data source identifier 203 typically precedes the identification code 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 identification code 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.

[0116] The checksum 205 typically precedes the end delimiter 206 and contains the output of a checksum algorithm performed on the identification code 204 or on the identification code 204 and the data source identifier 203. This can enable the integrity of the identification code 204 or identification code 204 and data source identifier 203 to be verified on receipt. Since transmission is asynchronous and unidirectional, a data packet may be automatically sent a number of times (for instance between two and five times) consecutively to ensure a correct data packet checksum is determined.

[0117] 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 identification code. 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 combinationof 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.

[0118] 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 system for monitoring access to a regulated area, using a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the base module comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and 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 system comprising:a user terminal configured to apply acoustic data signals to the read location of the sensing fibre, the acoustic data signals comprising an identification code;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 identification code; andan access management unit configured to receive and process the retrieved identification code from the data signal processing unit.

2. A system as claimed in claim 1, wherein the sensing fibre is provided within a fluid pipe.

3. A system as claimed in claim 2, wherein the sensing fibre is provided with one or more sections inside the pipe and with one or more sections outside the pipe, the read location on a section of the sensing fibre outside the pipe.

4. A system as claimed in claim 3, wherein the sensing fibre comprises more than one read location, each read location outside the pipe.

5. A system as claimed in any preceding claim, wherein read locations are provided within a read housing.

6. A system as claimed in claim 5, wherein the read housing defines a space within which the read location of the sensor fibre is provided, the space within the housing filled with a packing material.

7. A system as claimed in any preceding claim, wherein the regulated area is an inspection chamber, building or other structure associated with the fluid pipe or a wider network to which the fluid pipe is connected.

8. A system as claimed in any preceding claim, wherein receiving and processing the retrieved identification code by the access management unit comprises storing the identification code in an access log alongside a timestamp.

9. A system as claimed in any preceding claim, wherein the access management unit is configured to determine whether the identification code was retrieved as part of an access request or an egress request.

10. A system as claimed in any preceding claim, wherein the access management unit is configured to output a welfare signal if an egress request (or a further access request for the same regulated area or a different regulated area) is not received before the end of a welfare time interval.

11. A system as claimed in any preceding claim, wherein receiving and processing the retrieved identification code by the access management unit comprises comparing the retrieved identification code to a list of approved identification codes.

12. A system as claimed in 11, wherein if the retrieved identification code matches an approved identification code, the access management unit is configured to output an approved signal and if the retrieved identification code does not match an approved identification code, the access management unit is configured to output a disapproved signal.

13. A system as claimed in any preceding claim, wherein the regulated area is provided with an electronic lock and / or an alarm system and a communication unit configured to receive data signals on behalf of the electronic lock and / or alarm system.

14. A system as claimed in claim 13, wherein the access management unit is configured to automatically output an unlock signal in response to the approved signal.

15. A system as claimed in claim 13 or claim 14, wherein the access management unit is configured to automatically output a lock signal, in response to an egress request or after a lock time interval.

16. A system as claimed in any preceding claim, wherein the user terminal comprises a vibration unit configured to generate the acoustic data signals, the vibration control unit configured to operate in response to a vibration control unit.

17. A system as claimed in claim 16, wherein the vibration control unit is configured to operate the vibration unit to generate acoustic data signals in response to detected input from a user interface.

18. A system as claimed in claim 16 or claim 17, wherein the vibration control unit is configured to authenticate the user before operating the vibration unit.

19. A method for monitoring access to a regulated area, using a sensing apparatus of the type comprising a sensing fibre extending to or to the vicinity of the regulated area, thereby defining a read location on the said sensing fibre; and a base module remote from the access location, the base module comprising a light emitter configured to generate light pulses which are introduced to the sensing fibre; and 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:applying acoustic data signals to the read location of the sensing fibre using a user terminal, the acoustic data signals comprising an identification code;extracting a component of the detector output signal derived from said acoustic data signals so as to retrieve the identification code; and receiving and processing the retrieved identification code.

20. A method as claimed in claim 19, wherein receiving and processing the retrieved identification code comprises storing the identification code in an access log alongside a timestamp.

21. A method as claimed in claim 19 or claim 20, wherein the method includes determining whether the identification code was retrieved as part of an access request or an egress request.

22. A method as claimed in claim any one of claim 19 to 21, wherein the method includes outputting a welfare signal if an egress request (or a further access request for the same regulated area or a different regulated area) is not received before the end of a welfare time interval.

23. A method as claimed in any one of claims 19 to 22, wherein receiving and processing the retrieved identification code comprises comparing the retrieved identification code to a list of approved identification codes.

24. A method as claimed in claim 23, wherein if the retrieved identification code matches an approved identification code, the method includes outputting an approved signal and if the retrieved identification code does not match an approved identification code, the method includes outputting a disapproved signal.

25. A method as claimed in claim 24, wherein if the regulated area is provided with an electronic lock and / or an alarm system and a communication unit configured to receive data signals on behalf of the electronic lock and / or alarm system, the method includes automatically outputting an unlock signal in response to the approved signal.

26. A user terminal for use in a system according to any one of claims 1 to 18 or a method according to any one of claims 19 to 25, the user terminal comprising a vibration unit configured to generate the acoustic data signals, the vibration control unit configured to operate in response to a vibration control unit.

27. A fluid distribution system comprising one or more regulated areas monitored by a system according to any one of claims 1 to 18 or a method according to any one of claims 19 to 25.

28. A data network comprising one or more one or more data cables configured to carry network data wherein at least one data cable comprises a sensing fibre, foruse in a system according to any one of claims 1 to 18 or a method according to any one of claims 19 to 25.

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