(54) IMPROVEMENTS IN OR RELATING TO ARRANGEMENTS INCLUDINGFIBRE-OPTIC CABLE AND DEVICES FOR USE THEREIN(71) We, SMITHS INDUSTRIES LIMITED, a British Company of Cricklewood, LondonNW2 6JN, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to arrangements including fibre-optic cable, and devices for use therein.
The invention is concerned especially with arrangements in which a fibre-optic cable is to be used in an environment where it would in the normal events be subject to stress that might fracture or otherwise damage the cable and thereby interfere with light-signal transmission along it. Such circumstances may arise, for example, where the cable is used on an engine and the cable is attached to spaced parts of the engine between which there is differential expansion during engine operation.
It is one object of the present invention to provide an arrangement including a fibreoptic cable, in which provision is made for relief of the stresses imposed upon the cable.
Furthermore, it is another object of the present invention to provide a device that may be used in such an arrangement to achieve the stress relief.
According to one aspect of the present invention there is provided an arrangement that includes a fibre-optic cable, wherein the cable extends through a member that is rotatably mounted on a support, and a sleeve on the cable is a sliding fit within said member so as to facilitate both longitudinal and rotational movement of the cable with respect to said support.
The rotatably-mounted member may be a ball member having a bore therethrough for receiving the sleeve, and in these circumstances the ball member may be retained captive within a ring member of the support.
According to another aspect of the present invention there is provided a device for use in an arrangement including a fibreoptic cable, said device comprising a balljoint mounting having a rotatably-mounted ball member with a bore therethrough, and a sleeve which is to be carried by the cable and which is a sliding fit within said bore.
The said device may be capable of providing a gas-tight seal. In this respect the sleeve may be encircled by an elastomeric, or metal, ring within the bore to enhance the seal provided. Alternatively, the sleeve or the bore may be formed with annular grooves so as to provide a labyrinth seal.
A radiation pyrometer which includes an arrangement and device both in accordance with the present invention, and which is for use in measuring the turbine-blade temperature of a gas-turbine engine, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of the radiation pyrometer as installed in the gas-turbine engine;Figure 2 is a part sectional perspective view of the radiation-pyrometer installation of Figure 1; andFigure 3 illustrates an alternative form of seal device for use in the installation ofFigures 1 and 2.
Referring more especially to figure 1, the radiation pyrometer has a head 1 that is mounted to project through the turbine casing 2 from within the engine by-pass duct 3. The head 1 is directed towards the turbine blades 4 and at its end 5 within the casing 2 has a synthetic-saphire lens 6 for focusing radiation received from the blades 4. The nose 5 of the head 1 within the casing 2 is enclosed by a sighting tube 7 that serves to channel radiation from the blades 4 to the lens 6. The tube 7 also serves in particular to minimise reception of direct or reflected radiation from the combustion chamber of the engine. Air is admitted to the hollow wall of the sighting tube 7 via an opening 3 so as to blow out over the external surface of the lens 6 and thereby reduce the likelihood of fouling of that surface by carbon deposit.
The lens 6 focuses the received radiation onto the end 9 of a fibre-optic cable 10 within the head 1. The cable 10, which consists of a bundle 11 of glass-fibre strands contained within a plastics sheath 12 and protected externally by stainless-steel braiding 13, extends from the head 1 and out through a gas-tight seal device 14 on the engine casing 15, to a detector unit 16. The unit 16 is mounted at a comparatively-cool location on the engine casing 15 and includes a photoresponsive element 17 that serves to convert the optical signal transmitted via the cable 10 into an electrical signal. This electrical signal is supplied via an amplifier 18 to both an indicator 19 and an engine-control unit 20.
During operation of the engine there is differential expansion between the turbine casing 2 and the engine casing 15. This differential expansion (which may be of the order of 0.6 inch) occurs both radially and axially of that portion of the cable 10 extending between the engine casing 15 and the turbine casing 2. In the normal course of events this differential expansion would set up undesirable stresses in the cable 10 where it passed across the duct 3. These stresses, which are capable of fracturing the glassUbre strands or otherwise seriously damaging the cable 10, are relieved in the present case by the seal device 14. In this respect the seal device 14 allows for longitudinal and rotational movements of the cable 10 with respect to the engine casing 15.
Referring now more especially to Figure 2, the seal device 14 is basically a ball joint formed by an axially-bored ball member 21 of stainless-steel that is captive within a stainless-steel ring 22. A stainless-steel sleeve 23 on the cable 10 and brazed or welded to the braid 13, is a sliding fit within the bore 24 of the ball member 21 so as to allow longitudinal movement of the cable 10 through the seal: the sleeve 23 may have a flame-sprayed, hardened outer surface to improve its wear resistance. The ball member 21 is free to rotate within the ring 22 so that rotational as well as longitudinal movement of the sleeve 23 with respect to the casing 15, is enabled to relieve stresses in the cable 10.
The ring 22 may be welded, rather than clamped, into the seal device as illustrated in Figure 3. Furthermore, a ring of an elastomeric material, or a metal (not shown), may be provided in the bore 24 encircling the sleeve 23, to improve the seal efficiency. Alternatively, grooves may be formed about the sleeve 23 or the bore 24 to provide a labyrinth seal. Provision of any such ring or grooves is, however, expected to be unneces sary in normal circumstances where the bore 24 is fol example, of the order of 0.4 inch in length.
The head 1 is clamped to the turbine casing 2 by means of a flange 25. The flange 25 is carried on the head 1 between a spring clip 26 and a collar 27 of the head 1 so as to be free to rotate with respect to the head 1 before clamping to the casing 2. This enables the lay of the cable 10 to be most conveniently established without introduction of undesirable or unnecessary twists, during installation. Once the lay of the cable 10 has been estblished, the flange 25 can be rotated with respect to the head 1 and cable 10 to align the flange 25 with appropriate bolt-holes or studs {not shown) in the casing 2. The flange is then bolted down to bear hard on the collar 27 and clamp it firmly to the casing 2; the frictional abutment of the flange 25 on the collar 27 inhibits any rotation of the head 1 and cable 10 with respect to the flange 25 once the flange 25 is bolted down.
The fact that the lay of the cable 10 can be adjusted as desired during installation, is of advantage in facilitating use of a nonrotatable, keyed coupling between the cable 10 and the detector unit 16. In the latter respect the keyed coupling may involve a key (not shown) on the cable 10 that is required to align with, and engage in, a keyway (not shown) in the unit 16, and such coupling readily enables later disconnection and replacement of the unit 16 without disturbance to the remainder of the installation.
WHAT WE tCLAI3!d IS: 1. An arrangement including a fibreoptic cable, wherein the cable extends through a member that is rotatably mounted on a support, and a sleeve on the cable is a sliding fit within said member so as to facilitate both longitudinal and rotational movement of the cable with respect to said support.
2. An arrangement according to Claim 1 wherein said rotatably-mounted member is a ball member having a bore therethrough for receiving said sleeve.
3. An arrangement according to Claim 2 wherein said ball member is retained captive within a ring member of said support.
4. An arrangement according to any one of the preceding claims wherein said rotatably-mounted member forms a gas-tight seal between said support and said sleeve.
5. An arrangement according to any one of the preceding claims wherein said sleeve is of metal.
6. An arrangement according to Claim 5 wherein said -fibre-ontic cable includes an outer covering of metal braid and wherein said sleeve is secured to said outer covering by brazing or welding.
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