Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Patent
1997-07-28
1999-08-03
Ngo, Hung N.
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
385 58, 385 69, G02B 638
Patent
active
059335564
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a connector for connecting to an end of a conduit tube of the type used to carry fibre-optics cables. More particularly, the invention relates to a gas-tight connector for use at points of entry into buildings.
Fibre-optics cables are becoming increasingly popular as a telecommunications medium and typically are installed alongside existing service installations. A typical fibre-optics communications line consists of a bundle of optical fibres encased in a protective sheath which in turn is carried in a conduit tube or pipe which may for example be formed of a plastics material. The conduit tube is first installed and then the sheathed optical fibres are inserted in the conduit. Insertion of the sheathed optical fibres in the conduit may be effected by a pneumatic method which involves driving the fibre optic cable along the conduit with compressed air, or by pulling or drawing the sheathed fibres along the conduit.
In order to assist the former process, the outer surface of the cable is deliberately provided with a rough surface to increase its air resistance while the inner surface of the conduit is provided with a low friction coating to prevent the cable from being damaged as it is driven along the conduit.
Adjoining lengths of conduit tube are connected by means of connectors which may be of the push-fit variety or can be provided with a threaded collar compression mechanism.
Where installation of the fibre-optic cable is by pneumatic means, the connectors must be sufficiently air-tight to retain the air-pressure needed to drive the cable along the conduit but they do not need to be absolutely air-tight for this purpose. Indeed, as a result of the damage inflicted on the surfaces of conduit tubes by the gripping rings conventionally used in push fit connectors, there is usually a leak path along which gases can escape from the connector, or permeate into the connector.
A major concern of communications installation engineers is to ensure that when a service line enters a building, it does not create a channel along which gases from outside can also enter the building. This is a particular concern when, for example, the service line in question is laid alongside, or in the close vicinity of, a gas main, or is laid in an area where gases are being formed as result of the decomposition of refuse. Although leakage from a gas main may be minimal, permeation of the gas into a service line such as fibre-optic cable channel over a period can lead to significant quantities of gas entering a building unless steps are taken to provide a gas-block at the entry point into the building. This is particularly important when the utility to which the service channel is connected, eg a telephone exchange, is retained within a casing or housing or other confined space. Under such circumstances, a build-up of gases to explosive levels could result, with potentially devastating consequences. It has therefore become standard practice to provide a gas block at the point of entry into buildings.
In order to prevent gases that have permeated into a fibre-optics line from entering a building, it is necessary to provide a seal between the outer surface of the conduit tube and the connector, and a seal between the fibre-optic cable itself and either the conduit tube wall or the wall of the connector. At present connectors provided with a screw collar compression mechanism, in which a resilient sealing member such as an O-ring is clamped down onto the conduit tube, to give the necessary gas-tight seal between conduit tube wall and connector wall. However, in order to provide a seal around the fibre-optic cable, an arrangement as shown in FIG. 8 is employed. Thus, a length of clear plastics tube A is connected to connector B, the clear plastics tube being formed into a loop which must usually be of a minimum radius of 5 mm in order to avoid damage to the fibre-optic cable. At the lowest point L of the loop, a small hole is made and a silicone sealant S introduced by means of a syringe. The silicone sealant
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Extract from Brochure "Hawke Cable Glands," Jul. 1994, illustrating Hawke type 153 cable gland.
"Powerbreaker" Cable Connector, sold by RS Components, Ltd. (1990-1994).
Double Super Seal Bulk Head Connector, Drawing No. NC274, dated Jan. 19, 1990, John Guest Ltd.
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