Sensor pod

Abstract

A sensor pod for attaching a sensor to a subsea cable comprises: an attachment node configured to provide a connection between a sensor and a subsea cable; and a sensor module configured for connection with at least one sensor; wherein the attachment node is connected to the sensor module via at least one fibre optic cable; and wherein the sensor pod is arranged to be connected in-line with a subsea cable.

Description

[0001] SENSOR POD

[0002] Field of the Invention

[0003] The present invention relates to a sensor pod for subsea communications cables.

[0004] Background to the Invention

[0005] Subsea sensors are used for monitoring the ocean. The sensors obtain extensive real-time data for understanding and managing environmental issues such as climate change and hazards e.g. tsunamis.

[0006] Suitable sensors are already deployed on dedicated cable ocean research observatories and the next step is to integrate these sensors into telecommunication cables to create SMART cable systems.

[0007] SMART (Science Monitoring And Reliable Telecommunications) cables integrate sensors for monitoring the ocean into undersea communications cables, allowing the SMART sensors to piggyback off the power and communication infrastructure already present in millions of kilometers of undersea fibre optic cable.

[0008] In general, a subsea fibre optic communications system comprises the cable (having suitable layers of protection depending on the water depth, seabed conditions, and potential risks), pressure housings containing fibre amplifiers (known as repeaters) which are spaced apart from each other along the length of the cable, power supply equipment that delivers power to the repeaters through an electrical conductor in the cable, and terminal station equipment to transmit and receive signals on the optical fibre strands within the cable. Some subsea communications systems include branching units (BUs) which provide connections to locations along the main cable route.

[0009] Current plans for SMART cables involve integrating suitable sensors with a repeater along the length of the communication cable, called SMART repeaters. The sensors must be isolated from the high voltages present within the repeater and must be fail-safe so that the normal operation of the repeater is not impeded or impacted by faults in the sensors.

[0010] Summary of the Invention

[0011] According to an aspect of the present invention there is provided a sensor pod for attaching a sensor to a subsea cable. The sensor pod comprises an attachment node configured to provide a connection between a sensor and a subsea cable, and a sensor module configured for connection with at least one sensor. The attachment node is connected to the sensor module via at least one fibre optic cable, and the sensor pod is arranged to be connected in-line with a subsea cable.

[0012] Preferably, the attachment node is connected to the sensor module via at least one fibre optic pair and power connection.

[0013] Advantageously, the sensor pod provides a universal concept that allows a sensor to be integrated with subsea cables regardless of the cable structure (for example armoured or light weight). Furthermore, the sensor pod is independent from a repeater and so the sensor pod is not part of the repeater. The sensor pod can be used with both repeated and unrepeated cable systems. Having a sensor pod that is independent from a repeater, and that does not need a direct interface with a repeater, leads to a less complex and less expensive end product. Furthermore, by keeping the sensor separate from a repeater, the sensor does not interfere with or impede normal operation of the repeater. As such, any faults that occur within the sensor do not impact the operation of the repeater. Having a sensor pod that does not need to interface with a repeater may also avoid the need to isolate the sensor from the high voltages present within the repeater.

[0014] The sensor pod may be considered a SMART (Science Monitoring And Reliable Telecommunications) sensor which is able to send a continual stream of information about subsea conditions (for example but not limited to ocean pressure, temperature, acceleration) to specific observatories for analysis. The sensor pod enables scientific monitoring of climate changing forces to be carried across the expanse of the ocean, by integrating the sensor pod with pre-existing subsea cables. This allows early warning signs for disasters (for example but not limited to tsunamis and earthquakes) to be detected. Although the sensor pod is able to monitor in real-time, in some cases the sensor pod may carry out the monitoring on demand for example in accordance with the needs or requirement of a third party. As well as monitoring subsea conditions, the sensor pod may be used for a number of other applications including (but not limited to) cable monitoring, protection, and marine defense applications.

[0015] The sensor pod provides a retro-fit solution that is compatible with current and pre-existing cable systems. A retro-fit solution is a relatively low cost solution to providing SMART cable systems because all pre-existing infrastructure can be used. The retro-fit solution can be provided as part of a planned intervention for a new cable system or a repair on an existing cable system.

[0016] The sensor pod may allow the expansion of existing subsea cable universal jointing technologies through the provision of low cost ancillary connectivity to new markets. The sensor pod may be used by numerous industries for example, but not limited to, defense, sub-sea science, and power cable monitoring, enabling these industries to form new partnerships with existing and new cable system owners.

[0017] Preferably, the sensor module comprises a hermetically sealed chamber. The hermetically sealed chamber may be located inside a housing of the sensor module. The hermetically sealed chamber provides a controlled environment in which to house components.

[0018] The hermetically sealed chamber may comprise electronics configured to provide electrical communication between the sensor and sensor module. In some examples, the hermetically sealed chamber may comprise opto-electronics configured to provide optical-electrical communication between the sensor and sensor module and / or between the sensor module and an onshore computing device. This may ensure that the electronics are not affected by subsea environmental conditions that differ from land-based conditions, such as changes in temperature and pressure.

[0019] In some examples, the at least one sensor may be arranged within the hermetically sealed chamber. This provides an environmentally secure environment in which to house a sensor so that the performance of the sensor is not affected by subsea conditions.

[0020] In some examples, the at least one sensor may be arranged external to the sensor module. This may allow the sensor to accurately capture data about subsea climate conditions, for example temperature and pressure data capture.

[0021] An electronic feed may be arranged between the hermetically sealed chamber and the external sensor in order to provide a communication link between the sensor and the sensor module. An optical feed, in addition to or instead of the electronic feed, may be arranged between the hermetically sealed chamber and the external sensor in order to provide a communication link between the sensor and the sensor module. This allows the main electrical and / or optical components to remain housed within the hermetically sealed chamber rather than be exposed to the subsea environment, which may affect their performance.

[0022] Preferably, the at least one optical fibre cable, preferably at least one fibre optic pair and power connection, is housed within a protection sleeve. The protection sleeve may protect the optical fibre cable, preferably the fibre optic pair and power connection, and prevent them from becoming damaged.

[0023] References to at least one fibre optic cable (or optical fibre cable) preferably comprises references to at least one fibre optic pair and power connection.

[0024] In some examples, the at least one optical fibre cable, and preferably fibre optic pair and power connection, is housed within a helical slot of the protection sleeve. The helical slot may extend along the length of the protection sleeve. The helical slot may be located within an external surface of the protection sleeve. In other words, the helical slot may be considered embedded into the protection sleeve. Similarly, the at least one optical fibre cable, and preferably fibre optic pair and power connection, may be considered as embedded into an external surface of the protection sleeve. This arrangement provides abrasion and crush protection to the optical fibre cable, and preferably fibre optic pair and power connection, by the protection sleeve.

[0025] Preferably, the at least one fibre optic cable, and preferably fibre optic pair and power connection, takes the form of a carrier tube housing at least one fibre optic pair. The carrier tube may be housed within the protection sleeve. The protection sleeve may protect the carrier tube including the optical fibre pair and prevent it from becoming damaged. The carrier tube may be housed within the helical slot of the protection sleeve. The carrier tube may be considered as embedded into an external surface of the protection sleeve. This arrangement provides abrasion and crush protection to the carrier tube by the protection sleeve.

[0026] The carrier tube may be made of an electrically conductive material. The carrier tube may be a metallic carrier tube. The carrier tube may act as an electrical conductor. The carrier tube may provide an electrical power connection between the attachment node and the sensor module. This may reduce the need to break into a main subsea cable and divert an electrical cable towards the sensor module, helping preserve the structural integrity of the main subsea cable.

[0027] In some examples, the protection sleeve may be a modular protection sleeve. The modular protection sleeve may comprise one or more individual sleeve portions that are configured to be attached together to form the protection sleeve. This may allow a variable length protection sleeve to be constructed, which allows for varying distance between the attachment node and the sensor module.

[0028] The one or more sensors may be configured to be mounted on an external surface of the protection sleeve. This may ensure that any heat from the electronics within the sensor module does not affect the sensor, for example the sensor readings or the performance of the sensor.

[0029] Preferably, the sensor module may be configured to be attached to an external surface of a subsea cable. This design allows the main subsea cable to pass through the sensor module in order to avoid the need to make further interruptions to the subsea cable. This helps maintain the structural integrity of the main subsea cable.

[0030] The sensor module may be attached to the subsea cable via at least one clamping component. The clamping component may comprise at least one radially acting fixing, for example a screw. The clamping component may comprise a clamping sleeve. The clamping component may comprise at least one fixing and a clamping sleeve, wherein the clamping sleeve may be arranged to be located between a subsea cable and the sensor module, and further wherein the at least one fixing may be arranged to apply a radially acting clamping force to a subsea cable via the clamping sleeve. A clamping mechanism provides a simple and convenient method for attaching a sensor module to a subsea cable.

[0031] The clamping sleeve may comprise a C-shaped cross section. In this way, the clamping sleeve may comprise a slit that runs the entire length of the clamping sleeve. The slit may enable the clamping sleeve to be inserted round, and attached to, the subsea cable.

[0032] The clamping component may comprise a plurality of fixings that may be arranged along at least part of the length of the sensor module. The plurality of fixings may be arranged to apply a clamping force to the clamping sleeve such that a width of slit in the clamping sleeve is reduced. In this way, the clamping force applied by the fixings acts to close the slit in the clamping sleeve such that the clamping sleeve effectively has an O-shaped cross section. In some arrangements, a portion of heat shrink material may be arranged between the clamping sleeve and the subsea cable. The heat shrink material may be configured to be applied using heat shrink technology.

[0033] A protective material may at least partially encapsulate at least one end portion of the sensor module. The protective material may be potting material. The protective material may encapsulate both ends of the sensor module.

[0034] The at least one clamping component may be inside a housing of the senor module. In this case, the at least one clamping component may be considered as part of the housing. The at least one clamping component may be integral to the housing.

[0035] Alternatively, the at least one clamping component may be external to a housing of the senor module. Thus, the at least one clamping component may be considered as separate from the housing. In this case, the at least one clamping component may be attached to the housing. This allows a much larger housing to be provided, providing more room inside the sensor module for components.

[0036] The sensor pod may be arranged to be connected in-line with a subsea telecommunication cable.

[0037] In some developments, the sensor pod may be arranged to be connected in-line with an unrepeated subsea cable.

[0038] In other developments, the sensor pod may be arranged to be connected in-line with a repeated subsea cable.

[0039] There may be provided a method of attaching a sensor to a subsea cable comprising removing at least one outer layer of the subsea cable from a portion of the subsea cable, attaching a sensor module to an external surface of the subsea cable using at least one clamping component and connecting a sensor to the sensor module. The removing at least one outer layer may comprise removing at least one outer layer to expose a layer of armouring. The removing may comprise removing at least one outer layer comprising polypropylene yams.

[0040] The method may comprise applying a layer of heat shrink material to at least a portion of the exposed armouring.

[0041] The method may comprise inserting the at least one clamping component over the heat shrink material. The sensor module may be inserted over the at least one clamping component. The at least one clamping component may be fixed to the subsea cable, preferably fixed to the heat shrink material using one or more fixings. The at least one clamping component may be fixed to the subsea cable by applying a radial clamping force to the at least one clamping component, wherein the at least one clamping component is preferably a clamping sleeve.

[0042] The method may comprise encapsulating at least one end of the sensor module in a protective material. In some examples, both ends of the sensor module may be encapsulated.

[0043] There may be provided a method for attaching a sensor to a subsea cable using a sensor pod, the method comprising connecting a sensor pod to a subsea cable using an attachment node, connecting a sensor module with at least one sensor, connecting the attachment node to the sensor module via at least one fibre optic cable, wherein the sensor pod is connected in-line with a subsea cable, the method further comprising attaching the sensor module to an external surface of a subsea cable via at least one clamping component.

[0044] Brief Description of the Drawings

[0045] The present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows an example sensor pod;

[0046] Figure 2 is a cross-sectional view of part of a sensor pod;

[0047] Figure 3 shows an example sensor pod;

[0048] Figure 4 shows an example sensor module;

[0049] Figure 5A shows a cross-sectional view of a sensor module;

[0050] Figure 5B shows a cross-sectional view of a part of a sensor module;

[0051] Figure 6 shows an example sensor module;

[0052] Figure 7 shows a sensor pod as part of an unrepeated cable system;

[0053] Figure 8 shows a sensor pod as part of a repeated cable system;

[0054] Figure 9 show another example sensor module;

[0055] Figures 9A, 9B, and 9C shows cross-sectional views of a sensor pod;

[0056] Figure 10 shows part of a subsea cable;

[0057] Figure 11 shows part of a subsea cable;

[0058] Figure 12 shows part of a subsea cable;

[0059] Figure 13 shows part of a subsea cable and a clamping component;;

[0060] Figure 14 shows part of a subsea cable and a clamping component;

[0061] Figure 15 shows a sensor module attached to part of a subsea cable;

[0062] Figure 16 shows a sensor module attached to part of a subsea cable;

[0063] Figure 17 shows a sensor module attached to part of a subsea cable;

[0064] Figure 18 shows a sensor module attached to part of a subsea cable;

[0065] Figure 19 shows a sensor module attached to part of a subsea cable;

[0066] Figure 20 shows a sensor module attached to part of a subsea cable; and Figure 21a, 21b, and 21c show part of a subsea cable.

[0067] Detailed Description

[0068] The invention generally relates to a sensor pod for attaching a sensor to a subsea cable. An example sensor pod 2 is illustrated in Figure 1. The sensor pod comprises an attachment node 4 configured to provide a connection between a sensor and a subsea cable 6, and a sensor module 8 configured for connection with at least one sensor. The attachment node 4 is connected to the sensor module 8 via at least one fibre optic cable 10. The fibre optic cable is preferably a fibre optic pair and power connection 10 (also referred to as an optical-electrical connection). The sensor pod 2 is arranged to be positioned in-line with a subsea cable, as shown in Figure 1 . As the sensor pod 2 is located in-line with a subsea cable, the sensor pod 2 may be considered as being connected in-line with a subsea cable.

[0069] A universal joint is a known technology used for connecting different types of subsea optical telecommunication cable together with a common set of construction equipment and methods.

[0070] The attachment node 4 is a modified version of a universal joint and may be referred to as a node universal joint (node UJ) 4. The node universal joint comprises two ends which may be referred to as a first end 12 and a second end 14. The first end 12 provides a connection between the sensor pod 2 and the subsea cable 6, using standard universal joint technology and so this will not be described further. The second end 14 provides a connection between the attachment node 4 and the sensor module 8 of the sensor pod 2. In addition, the second end 14 also provides a connection between the sensor pod 2 and the subsea cable 6. The first and second ends 12, 14 are bi-directional and both the first and second ends 12, 14 provide a direct connection with the subsea cable 6. The interface between the attachment node 4 and the sensor module 8 occurs at the second end 14 via an insulated optical-electrical connection 10, as will be described in more detail later.

[0071] Generally, power and optical connections between the subsea cable 6 and the sensor module 8 are provided by a breakout of suitable cables from the main cable structure within the subsea cable, the breakout being provided by the output end 14 of the node universal joint 4. Specifically, the breaking out involves breaking out an optical fibre pair and power conductor from the subsea cable 6 which are then connected to the sensor module 8.

[0072] The cable breakout is shown more clearly in Figure 2. An insulated and hermetic penetration is provided within the second end 14 of the node universal joint 4, which provides a passageway for the optical fibre pair and power conductor to be routed away from the main subsea cable 6 towards the sensor module 8. The penetration is achieved using a penetrator 16. The penetrator 16 is sealed within the structure of the second end 14 of the node universal joint 4.

[0073] The optical fibre pair and power conductor form an optical-electrical connection 10 between the node universal joint 4 and the sensor module 8. The optical- electrical connection 10 takes the form of a carrier tube which contains at least one optical fibre pair. The carrier tube is a metallic carrier tube so that the carrier tube, which carries the optical fibre pair, acts as an electrical conductor. The metallic carrier tube is therefore a substitute for the electrical cable in the main cable 6, which avoids the need to break into the main cable structure and divert a power supply to the sensor module 8. The optical-electrical connection 10, in the form of the carrier tube, has a dual functionality in that it provides both a power supply route between the broken out main power conductor and the sensor module 8 as well as providing hydrostatic pressure protection for the broken out optical fibres which connect with the sensor module 8.

[0074] As the carrier tube acts as an electrical power conductor, providing electrical power to the sensor module 8, the carrier tube is electrically insulated by applying an external polyethylene (PE) sheath to the outer surface of the carrier tube. The electrical insulation is amalgamated to the main insulation within the node universal joint 4 through PE over moulding.

[0075] The insulated carrier tube is routed through cable armour anchoring components of the node universal joint 4, allowing the carrier tube to exit into the elastomeric bend limiter 18 of the node universal joint 4 and subsequently routed to the sensor module 8.

[0076] The main subsea cable 6, which does not form part of the breakout, passes through the node universal joint 4, from the first end 12 to the second end 14, in a similar manner to that used with standard universal joints. This can be seen in Figures 1 and 2. As illustrated generally in Figure 1 , and in more detail in Figure 2, the optical- electrical connection 10 is routed external to the main subsea cable 6. In particular, the optical-electrical connection 10 is routed within a helical slot 20 within a protection sleeve 22 surrounding the subsea cable 6, as shown in Figure 3. The helical slot 20 in the protection sleeve 22 provides abrasion and crush resistance for the optical-electrical connection 10.

[0077] The protection sleeve 22, which in some examples may be an elastomeric protection sleeve 22, is bound to the subsea cable 6 for example by over roving. This also helps retain the optical-electrical connection 10 within the helical slot 20 of the protection sleeve 22.

[0078] Since the breakout optical fibre pair is located within the carrier tube, the optical fibre pair can be considered as being housed by the protection sleeve 22 of the main cable 6. In particular, due to the carrier tube being located within a helical slot 20 of the protection sleeve 22 of the main cable 6, the optical fibre pair can be considered as being housed by the helical slot 20 of the protection sleeve 22. The protection sleeve 22 is modular, meaning that it can be made up of one or more individual sleeve portions that can be joined together to form the protection sleeve 22. The module nature of the protection sleeve 22 allows for variation in the separation distance between the node universal joint 4 and the sensor module 8.

[0079] An example sensor module 8 is illustrated in Figure 4. The sensor module 8 comprises a housing 24 having a passageway 26 that passes axially through the housing 24. The passageway 26 allows the sensor module to be externally mounted to the subsea cable 6. This design allows the system cable to pass axially through a housing of the sensor module, without interfering with sensor module. As the subsea cable 6 passes through the housing 24 of the sensor module, via the passageway 26, the sensor module 8 can be considered to surround a portion of the subsea cable 6. Externally mounting the sensor module 8 to an outer surface of the cable 8 avoids the need to make further interruptions to the cable and so avoids the need for further joints within the cable structure. Avoiding unnecessary interruptions to the main cable 6 helps maintain the integrity of the cable strength members, maintaining the overall tensile strength of the subsea cable 6.

[0080] As can be seen in Figure 5B, attachment of the sensor module 8 to the cable 6 is achieved using a clamping component, which takes the form of a plurality of clamping screws 28 and a clamping sleeve 30. The clamping screws 28 act on the clamping sleeve 30, which located between the subsea cable 6 and the sensor module 8 creating a circumferential clamping force on the subsea cable 6. This clamping force is distributed along the entire length of the clamping sleeve 30. In some examples, the clamping sleeve 30 may be integral with the housing 24. In other examples, the clamping sleeve 30 may be positioned at each end of the housing 24. The clamping sleeve can be axially retained in position by a retaining plug 31.

[0081] Any potential axially slippage that may occur between the sensor module 8 and the cable 6, which results from normal deployment and recovery processes, are mitigated by the application of multiple layers of adhesive lined heat shrink 32 located between the cable 6 and the clamping sleeve 30 and supported by a polymeric cold pour moulding.

[0082] The sensor module 8 comprises a hermetically sealed chamber 34, as shown in Figure 5A. The hermetically sealed chamber 34 provides a heat managed, 1 atmosphere environment for relevant sensor electronics 36. The sensor electronics 36 provide communication between the sensor module 8, the SMART sensors, and the subsea cable 6.

[0083] In some examples, the SMART sensors 38 are located within the sensor module 8. In this case, the sensors are located within the hermetically sealed chamber 34. These SMART sensors 38 can be considered as internally mounted sensors.

[0084] In other examples, the SMART sensors 38 are located outside the sensor module 8. In this case, the sensors 38 can be considered as externally mounted sensors. As shown in Figure 6, one or more sensors 36 may be mounted to an external surface of the sensor module 8, for example located within one or more channels which extend axially along the length of the sensor module 8 and are spaced around the circumference of the sensor module 8. Alternatively, or in addition, one or more sensors may be externally mounted to the protection sleeve 22 as shown in Figure 3. In this case the sensors are remote from the sensor module 8. Exemplary remotely and externally mounted sensors 38 may include temperature sensors in order to separate any heat effect from the sensors electronics 36 within the housing 24 from the temperature sensors.

[0085] For any externally mounted sensor 38, a sensor interface 40 is located within the hermetically sealed chamber 34 in order to provide suitable interfacing between the sensor 38 and the sensor electronics 36. A hermetic and electrically insulated feedthrough 42 extends through the housing 24 between the hermetically sealed chamber 34 and an outlet 44 in the housing 24 to allow necessary electronics to be fed from the housing to the external sensor 38 in order to connect the sensor 38 to the sensor module 8.

[0086] For both internally and externally mounted sensors 38, the housing 24 of the sensor module 8 provides appropriate signal conversion suitable for optical cable transmission and application using standard subsea telecommunication equipment and parameters, and so this will not be described further.

[0087] Sensor data from the sensors 38 is transmitted to the sensor module via the dedicated optical fibre pair.

[0088] As has been described, the sensor pod 2 is arranged to be integrated with preexisting subsea cable 6 by attaching the sensor pod 2 in-line with a subsea cable 6. The sensor pod 2 can be attached to the subsea cable system as part of a repair for example as shown in Figure 7. In this case, the sensor pod 2, is one of two joints that form the cable repair and the optical and electrical breakout is achieved within the repair joint formed by the node universal joint 4. The sensor module 8 and sensors 38, and related electronics 36 and power supply, are located in the cable 6 between the two repair joints without the need to break into the cable structure, as shown in Figure 7, resulting in a non-invasive attachment method.

[0089] Alternatively, the sensor pod 2 can be installed at a pre-defined location on any new cable before the cable is laid.

[0090] As the sensor pod 2 is attached in-line with a subsea cable, the sensor pod 2 can be used with both unrepeated cable systems, such as those in Figure 7, and repeated cable systems, such as those in Figure 8.

[0091] For unrepeated cable systems, power to the electronics 36 in the sensor module 8 could be achieved by using a low voltage supply on the power conductor within the cable 6. This is because, for unrepeated systems, the overall span of the cable system is typically relatively short, (typically <500 km).

[0092] For longer repeated cable systems, much higher electrical insulation is required within the sensor pod2, in particular within the node universal joint 4 and the sensor module 8, in order to cope with the higher system voltages required to power the repeated system. For both repeated and unrepeated cable systems, when the sensor pod 2 is used in a repair scenario, the water depth is typically but not restricted to < 2000 m.

[0093] Figure 9 shows another example of a sensor module 108. This sensor module 108 is an expanded form of the previously described sensor module 8, configured to have a larger internal volume within the sensor module 8. This is achieved by removing features and components related to clamping the sensor module onto the cable 6 away from the structure of the housing 124 and instead proving the clamping function externally through suitable clamping components attached to each end of the housing 124. This allows a much larger housing 124 to be provided, containing the sensor electronics, power supply, and sensor interface as before, whilst still allowing the subsea cable 6 to pass axially through the sensor module 108. As shown in Figures 9A-C, the housing 124 can have a number of different forms. Instead of the previously described cylindrical shape, the housing 124 may have a cradle-like form, as shown in Figures 9A, 9B, and 9C, such that the sensor module straddles the subsea cable 6 rather than completely surrounds the subsea cable. In some examples, such as those shown in Figure 9A, the housing 124 comprises a plurality of independent axially mounted housings 121 each having a chamber 121a, 121 b, 121c which may be configured for different functionality, such as sensor electronics 121a, power supply 121 b, and sensor interfacing 121c. In some other examples, such as those shown in Figure 9B, the housing 124 comprises a plurality of axial chambers 123 within the housing 124. These chambers may be configured for different functionality, such as sensor electronics 123a, power supply 123b, and sensor interfacing 123c. In further examples, such as that shown in Figure 9C, the housing 124 comprises a plurality of radially accessed chambers 125 within the housing 124. As before, these chambers may be configured for different functionality, such as sensor electronics 125a, power supply 125b, and sensor interfacing 125c.

[0094] As mentioned in relation to Figure 4, the sensor module 8 is externally mounted to the subsea cable 6 such that the sensor module 8 surrounds the subsea cable 6. The process of attaching the sensor module 8 to the subsea cable 6 will now be described in more detail.

[0095] Figure 10 shows a cross-section of an example subsea cable 6, which in this case is a single armour cable. The cable 6 comprises a central strengthening member 50 (for example comprising a strength member and fibre tube core) surrounded by a conducting layer 52, an inner insulation sheath 54, armouring 56, and an outer sheath comprising a layer of bituminous compound 58 (such as tar) covered by polypropylene yams 60.

[0096] Before the sensor module 8 is mounted the subsea cable 6 is prepared by firstly removing a predefined length of the external layer of yams 60, as shown in Figure 11 , and then removing the layer of tar 58 from the armouring 56 as shown in Figure 12. One or more layers of heat shrink material 32 are applied using heat shrink technology to at least part of the length of the exposed armouring 56, as can be seen in Figure 13. A collar 62 is then centered over the heat shrink material 32. As can be seen in Figure 14, the collar 62 is a split collar, preferably made of plastic, having a c-shaped cross section. The split in the collar allows for easy attachment of the collar 62 over the heat shrink material 32. The collar 62 may perform the same function as the clamping sleeve 30 described previously in relation to Figure 5B, and so the collar 62 and the clamping sleeve 30 can be considered as interchangeable or equivalent components.

[0097] The collar 62 and clamping sleeve 30 act as an anti-rotation feature, preventing the sensor module 8 (when attached) from rotating about the subsea cable 6. The presence of the heat shrink material 32 prevents longitudinal movement of the sensor module 8 along the length of the subsea cable 6.

[0098] The sensor module 8 is then inserted over the collar 62, illustrated in Figure 15, such that a frontal face 61 of the collar 62 is aligned with an inner reference point 9 of the sensor module 8, the alignment indicated by the dashed line in Figure 15. The inner reference point 9 takes the form of an internal shoulder which acts as a point of abutment between the sensor module 8 and the collar 62. The inner reference point 9 ensures that the sensor module 8 is located correctly relative to the collar 62 before the sensor module 8 is fixed in place. In practice, the sensor module 8 may be inserted over the collar 62 and then slid along the collar 62 (for example in the direction of the arrow A in Figure 15), until the inner reference point 9 of the sensor module 8 abuts the frontal face 61 of the collar 62 such that further longitudinal movement of the sensor module 8 in the direction of the arrow A is prevented.

[0099] Figure 16 illustrates a retaining plug 31 which is inserted (in the direction of arrow B) between the sensor module 8 and the collar 62, preferably at an end of the sensor module 8 that is opposite the inner reference point 9 of the sensor module 8, which helps retain the collar 62 and sensor module 8 in place. The retaining plug 31 can also be seen in Figure 5B. Retaining screws 28 tighten the sensor module 8 over the collar 62, clamping the sensor module 8 onto the subsea cable 6. As the screws 28 are tightened, the split within the collar 62 is closed meaning that the collar 62 tightly grips the heat shrink material, and ensuring that the collar 62 is clamped to the subsea cable 6. As can be seen in Figure 17, one or more retaining screws 28 may be inserted through a side wall of the sensor module 8, perpendicular to the subsea cable 6. The screws 28 act on the collar 2 creating a circumferential clamping force on the subsea cable 6. This clamping force is distributed along the length of the collar 62, holding the sensor module 8 in place relative to the subsea cable 6 and preventing rotation of the sensor module 8 about the cable 6.

[0100] Both ends of the sensor module 8 are encapsulated in a protective material 64, preferably a potting material, which is typically a resin or compound. In some examples, the protective material 64 is polyurethane back-fill moulding. The potting material 64 helps fill any gaps created between the sensor module 8 and the subsea cable 6 during the clamping process, ensuring there is a complete seal between the sensor module 8 and the subsea cable 6. As well as providing mechanical protection and electrical insulation, the potting material 64 provides environmental sealing preventing the ingress of moisture, dirt, and other contaminants. The potting material is therefore important for ensuring watertight sealing between the sensor module 8 and the subsea cable 6. In some arrangements, the potting material 64 may help provide strain relief of the optical- electrical connection 10 by providing additional support to the cable and reducing the risk of damage from bending or pulling. The potting material 64 may additionally help prevent longitudinal movement of the sensor module 8 along the subsea cable 6.

[0101] As mentioned previously, power and optical connections between the subsea cable 6 and the sensor module 8 are provided by a breakout of suitable cables from the main cable structure within the subsea cable 6. As shown in Figure 3 and again in Figure 19, the optical-electrical connection 10 is routed to the sensor module 8 via the protection sleeve 22 and helical slot 20. As mentioned previously, the protection sleeve 22 may be modular comprising a plurality of individual sleeve portions, which may be referred to as subsections 22a, 22b, that can be joined together to form the protection sleeve 22. The plurality of subsections 22a, 22b are connected together at an interface 23 as shown in Figure 21a. Each subsection 22a, 22b comprises a male end 25 having one or more connection pins 27 and a female end 29 comprising one or more receiving holes 29a which are sized and shaped to receive the connection pins 27. The male and female ends 25, 29, including the connection pins 27 and receiving holes 29a, can be seen in Figures 21b and 21c. In some examples, such as that shown in Figure 21 b, a ring 70 may be placed around the interface 23 to provide some form of protection against the ingress of dirt at the interface 23.

[0102] Once the optical and power connections have been secured, a cover 66 is installed on the sensor module 8, the cover 66 including a wire clamping portion 68 to retain the optical-electrical connection 10. The cover, shown in Figure 20, helps protect and seal the optical and power connections within the sensor module 8. Bend limiters 18, such as those shown in Figure 2, can be secured at either end of the sensor module 8.

Claims

Claims1 . A sensor pod for attaching a sensor to a subsea cable comprising: an attachment node configured to provide a connection between a sensor and a subsea cable; and a sensor module configured for connection with at least one sensor; wherein the attachment node is connected to the sensor module via at least one fibre optic cable; wherein the sensor pod is arranged to be connected in-line with a subsea cable; wherein the sensor module is configured to be attached to an external surface of a subsea cable via at least one clamping component.

2. The sensor pod of claim 1 wherein the sensor module comprises a hermetically sealed chamber.

3. The sensor pod of claim 2 wherein the hermetically sealed chamber comprises electronics configured to provide electrical communication between the sensor and sensor module.

4. The sensor pod of claim 2 or 3 wherein the at least one sensor is arranged within the hermetically sealed chamber.

5. The sensor pod of claim 2 or 3 wherein the at least one sensor is arranged external to the sensor module.

6. The sensor pod of claim 5 wherein an electronic feed is arranged between the hermetically sealed chamber and the external sensor in order to provide a communication link between the sensor and the sensor module.

7. The sensor pod of any preceding claim wherein the at least one fibre optic cable is preferably at least one fibre optic pair and power connection, and the at leastone fibre optic cable takes the form of a carrier tube housing at least one fibre optic pair.

8. The sensor pod of claim 7 wherein the carrier tube is made of an electrically conductive material.

9. The sensor pod of any preceding claim wherein the at least one optical fibre cable is housed within a protection sleeve.

10. The sensor pod of claim 9 wherein the at least one optical fibre cable is housed within a helical slot of the protection sleeve.

11. The sensor pod of any of claims 9 to 10 wherein the protection sleeve is a modular protection sleeve comprising one or more individual sleeve portions.

12. The sensor pod of any of claims 9 to 11 wherein the one or more sensors are configured to be mounted on an external surface of the protection sleeve.

13. The sensor pod of any preceding claim wherein the clamping component comprises a clamping sleeve, wherein the clamping sleeve is configured to be arranged between a subsea cable and the sensor module,14. The sensor pod of claim 13 wherein the clamping sleeve comprises a C- shaped cross section.

15. The sensor pod of claim 13 or claim 14 wherein the clamping component comprises at least one fixing, wherein the at least one fixing is arranged to apply a radially acting clamping force to a subsea cable via the clamping sleeve.

16. The sensor pod of claim 15 wherein the clamping component comprises a plurality of fixings configured to be arranged along the length of the sensor module.

17. The sensor pod of any of claims 13 to 16 further comprising a portion of heat shrink material is configured to be arranged between the clamping sleeve and a subsea cable.

18. The sensor pod of any preceding claim further comprising a protective material configured to at least partially encapsulate an end portion of the sensor module.

19. The sensor pod of any preceding claim wherein the sensor pod is arranged to be connected in-line with a subsea telecommunication cable.

20. The sensor pod of any preceding claim wherein the sensor pod is arranged to be connected in-line with an unrepeated subsea cable.21 . The sensor pod of any preceding claim wherein the sensor pod is arranged to be connected in-line with a repeated subsea cable.

22. A method of attaching a sensor to a subsea cable comprising: removing at least one outer layer of the subsea cable from a portion of the subsea cable; attaching a sensor module to an external surface of the subsea cable using at least one clamping component; and connecting a sensor to the sensor module.

23. The method of claim 22 wherein the removing at least one outer layer comprises removing at least one outer layers to expose a layer of armouring.

24. The method of claim 23 further comprising applying a layer of heat shrink material to the exposed layer of armouring.

25. The method of claim 24 further comprising inserting the at least clamping component over the heat shrink material.

26. The method of claim 25 comprising encapsulating at least one end of the sensor module in a protective material.

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