Field of the invention

The present invention relates cables, in particular a conduit and arrangement for a seismic cable

Background

Seismic cables are electrical signal-carry cables typically used in harsh, offshore environments. Segments of such cables are often connected to sensor modules, which are connected in series up to several kilometres in length. These lengths of cables can be subjected to enormous pulling forces during deployment, retrieval or towing. Such cables therefore often comprise an elongated tension member in addition to signal carrying wires. The elongated tension absorbing member absorbs the pulling forces, thereby preventing such forces from being exerted on the electrical signal carrying wires and connection points with the sensor electronics. One type of such prior art arrangement comprises an insulated cable having a wire cable at its central core, with a plurality of electrical wires embedded in the insulation surrounding the wire cable core. The wire cable core of a first segment of cable is connected at one end to a sensor housing, and the electrical wires connected to the internal electronic components inside the housing. One end of a second segment of cable section is connected to the other side of the sensor housing in the same manner. Pulling forces are thus absorbed by the wire cable core rather than the electrical wires. Several such sensor housings can be arranged in series.

Such prior art arrangements have various disadvantages known in the art, however. For example, such cables may stretch under the tremendous loads to which they are subjected, and the electrical wires may break. Another disadvantage is that the cables must be prefabricated with a specific number of embedded signal carry wires. New wires cannot be added, and the existing wires cannot be replaced if broken or for other reasons. It is also difficult to arrange a new sensor module along a length of cable, or between existing sensor housings. In such instances it has previously been necessary to recognize whether such new modules may be needed before the cable is even constructed or deployed. In such circumstances, a special cable or length of cable containing a number of prefabricated connection junctions is used. It is often necessary to equip the cable with more junctions than needed, as it is not always known where such junctions will be required.

Summary of the invention

The invention provides for a cable and conduit arrangement for a cable subjected to pulling forces. The invention comprises a central, elongated tension- absorbing member, having termination members at its ends. Surrounding the central member is a plurality of hollow conduits arranged around the circumference of the central member. An outer insulation sheath may surround the conduits, forming an elongated cable arrangement. Signal carrying wires or fiber optic cables or the like may thus be passed though the hollow conduits as desired. In use, one end of the central member is terminated to sensor housing. The signal carrying electrical wires are passed through the hollow conduits, through a "pass-through seal" into the interior of the sensor housing, where they are connected to the internal electrical components. Since the signal carrying wires are not permanently affixed to the cable, the length of the signal-carrying wires can be greater than the length of the central member so that they have a sufficient degree of slack to accommodate stretching of the central member. The cable and conduit arrangement may be water-filled or sealed as needed, and may include for example a boot seal at the transition between the cable and the housing. A similar length of the cable and conduit arrangement is connected to the other side of the sensor housing, and a plurality of such module/cable segments can be connected in series. As can be appreciated, pulling forces are transmitted from the sensor housing to the central member via the termination member, thus preventing the signal carrying wires from breakage. One advantage of the present invention is that the cable and conduit arrangement can be manufactured independent of the signal carrying wires, which can be added later in the number/type desired. Additional wires can be added later through the hollow conduits, and individual damaged wires replaced without the need to replace the entire cable.

Another advantage of this arrangement is that an intermediate module may be easily added. Anywhere along the length of cable, a section of one or more conduits may be cut away, exposing the internal signal carrying wire. Since this wire is sitting loose in the conduit, it may be spliced and attached to an intermediate module that is thereafter clamped around the cable.

Brief description of the drawings

Fig 1 is a perspective sectional view of an embodiment of the cable and conduit arrangement of the invention Fig 2 is a longitudinal section view of the embodiment from fig 1 Fig 3 is a lateral cross sectional view of the embodiment from fig 1

Fig 4 is a side elevational view of the embodiment from fig 1 Fig 5 is a side elevational view of a second embodiment of the invention

Fig 6 is a longitudinal section view of the embodiment from fig 5

Fig 7 is a perspective sectional view of the embodiment from fig 5

Detailed description

As shown in figs 1 and 2, a first embodiment of the invention comprises an elongated, central, tension- absorbing member 10. Tension-absorbing member 10 may be for example a wire cable, a reinforced synthetic rope, or other such material. According to one aspect of the invention a protective sheath 11 as shown in fig 2 may surround member 10. A plurality of hollow, elongated conduits 12 are arranged circumferentially around central member 10. Conduits 12 are preferably flexible and made of a synthetic material such as nylon, PVC or the like. An outer sheath 14 surrounds the conduits forming and elongated cable and conduit arrangement.

As seen in fig 2, one or more signal-carrying wires 16 are passed through conduits 12. These wires can be ordinary copper wires, or can also be fiber optic cables or the like. At the end of central member 10 is a termination member 18. According to one aspect of the invention the termination member can be a conical member attached to the end of central member 10. The termination member 18 engages a corresponding termination receiving member 20 of a sensor housing 22. As shown in fig 2, signal carrying wire 16 passes though a "pass-through seal" 24 into the water-tight interior of sensor housing 22. Signal carrying wires 16 are connected to electronic components 26 housed in housing 22. According to one aspect of the invention, the conduits 12 may be colour coded or otherwise marked to ease identification of the individual signal carrying wires.

As further shown in figs 1 and 2, the length of signal carrying wire 16 is greater than the length of central element 10. The extra length may, for example, be wound about the end of member 10, or otherwise disposed inside housing 22. Fig 4 shows an external boot seal 28 covering the transition between outer sheath 14 and housing 22. As can be appreciated, a similar arrangement can be made at the opposite side of housing 22, and a plurality of suck housings connected in series.

Figs 5-7 illustrate a second embodiment or use of the invention, whereby a sensor module is attached along a length of the cable/conduit arrangement, for example along a single length of cable, or between adjacent sensor housings of a cable comprised of a series of sensor housings as described in the first embodiment.

According to this aspect of the invention, a section of outer heath 14 and a portion of one or more of conduits 12 is removed, creating a gap. If a signal carrying wires has already been threaded through the conduits, this wire may be pulled further out due to the slack, and spliced. A module 30, having an internal chamber 32 containing electronic components 34 may be attached over the exposed section of wire, and the wire ends connected to the components. In this embodiment, the continuous length of central member 10 absorbs all of the pulling forces. Module 30 may therefore simply be affixed to outer sheath 14 by, for example, compression screws 36.