Thermally stabilized fiber optic cable
First Claim
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1. A fiber optic cable for directly transmitting a visible optical signal comprisinga plurality of relatively large diameter optical fibers each having a light-transmitting core and means therearound providing an interface that reflects incident light back into said core,a sheathing layer of elastomeric polymeric material around each optical fiber in intimate contact with the outer surface of said optical fiber, said elastomeric polymeric material being resiliently compressible, having a modulus of elasticity of between about 63 and about 78 kg/cm2 at 23°
- C., having a Shore A of between about 64 and about 68 at 23°
C., 10 sec and having a dynamic temperature range of from about -20°
C. or below to about 105°
C. or above,an axial core including a rigid, substantially non-compressible axial member having a coefficient of thermal expansion closely matched to the coefficient of thermal expansion of said optical fibers, said axial core being located along the center axis of the cable and extending longitudinally along the center axis of the cable, said sheathed optical fibers being cabled around said axial core in a lay length of between about 15 and about 50 cm,said sheathing layers being compressed against said axial core to be deformed thereby over an extended surface contact with the axial core, said sheathing layers being compressed against adjacent sheathing layers to be deformed from a circular cross section, anda jacket surrounding said sheathed fibers formed of polymeric material substantially more rigid than said elastomeric polymeric material having a Shore D of between about 34 and about 39 at 23°
C., 10 sec and a dynamic temperature range of from about -20°
C. or below to about 105°
C. or above, said sheathed fibers being held in compression against said axial core by said jacket, whereby said axial core stabilizes said polymeric material layers against differential thermal expansion and contraction relative to said optical fibers.
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Abstract
A fiber optic cable contains large diameter optical fibers for directly transmitting visible signals, such as those produced by water level indicators, within a steam boiler. The fibers are each sheathed in an extruded layer of polymeric material that remains soft over an operable temperature range of the cable, and the sheathed fibers are cabled in a long lay length about an axial core member that has a coefficient of thermal expansion similar to that of the optical fibers in order to restrain the sheaths, which generally have significantly different thermal coefficients of thermal expansion, from excessively expanding or contracting relative to the fibers. The cabled, sheathed fibers are wrapped in tape, and an inner jacket, which holds the sheathed fibers in compression, is extruded around the tape. Tensile strength is provided by braided yarn surrounding the inner jacket, and crush strength is provided by an outer jacket surrounding the braided yarn.
138 Citations
20 Claims
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1. A fiber optic cable for directly transmitting a visible optical signal comprising
a plurality of relatively large diameter optical fibers each having a light-transmitting core and means therearound providing an interface that reflects incident light back into said core, a sheathing layer of elastomeric polymeric material around each optical fiber in intimate contact with the outer surface of said optical fiber, said elastomeric polymeric material being resiliently compressible, having a modulus of elasticity of between about 63 and about 78 kg/cm2 at 23° - C., having a Shore A of between about 64 and about 68 at 23°
C., 10 sec and having a dynamic temperature range of from about -20°
C. or below to about 105°
C. or above,an axial core including a rigid, substantially non-compressible axial member having a coefficient of thermal expansion closely matched to the coefficient of thermal expansion of said optical fibers, said axial core being located along the center axis of the cable and extending longitudinally along the center axis of the cable, said sheathed optical fibers being cabled around said axial core in a lay length of between about 15 and about 50 cm, said sheathing layers being compressed against said axial core to be deformed thereby over an extended surface contact with the axial core, said sheathing layers being compressed against adjacent sheathing layers to be deformed from a circular cross section, and a jacket surrounding said sheathed fibers formed of polymeric material substantially more rigid than said elastomeric polymeric material having a Shore D of between about 34 and about 39 at 23°
C., 10 sec and a dynamic temperature range of from about -20°
C. or below to about 105°
C. or above, said sheathed fibers being held in compression against said axial core by said jacket, whereby said axial core stabilizes said polymeric material layers against differential thermal expansion and contraction relative to said optical fibers. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
- C., having a Shore A of between about 64 and about 68 at 23°
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20. A fiber optic cable for directly transmitting a visible optical signal comprising
a plurality of optical fibers each having a light-transmitting core and means therearound providing an interface that reflects incident light back into said core, said light-transmitting cores of said fibers having diameters of between about 400 and about 800 micrometers, a sheathing layer of flexible elastomeric polymeric material around each optical fiber in intimate contact with the outer surface of said optical fiber, said elastomeric polymeric material being resiliently compressible, said sheathing layers each being compressed against a pair of adjacent sheathing layers to deform the outer surfaces thereof from a circular surface at the areas of contact therebetween, a centrally located core extending longitudinally along a central axis for the cable and including a rigid, substantially non-compressible axial member having a cross-sectional area between about one-half and about one and one-half times that of the total cross-sectional areas of said light-transmitting cores, said axial member having a coefficient of thermal expansion between about 0.8 and about 3.5 times that of said optical fibers, said sheathed optical fibers being cabled around said axial core in a lay length of between about 15 and about 50 cm, said sheathed optical fibers being compressed against said axial core so that each of said fiber-sheathing layers make contact with said axial core over a surface greater than a tangential line of contact, an inner jacket surrounding said sheathed fibers formed of a polymeric material that is substantially more rigid than said elastomeric polymeric material, said sheathed fibers being held in compression against said axial core by said inner jacket to hold the same against differential thermal expansion and contraction relative to said optical fibers, a tensile strength member comprising a high tensile strength yarn braided around said inner jacket, and an outer jacket around said tensile strength member, said outer jacket being formed of a rigid polymeric material.
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Current AssigneeBelden Wire & Cable Company, LLC (Belden Inc.)
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Original AssigneeCooper Industries, Inc. (Eaton Corporation PLC.)
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InventorsAnderson, Gene S.
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Primary Examiner(s)Sikes, William L.
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Assistant Examiner(s)HEALY, BRIAN
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Application NumberUS06/406,777Time in Patent Office1,001 DaysField of Search350/96.23US Class Current385/103CPC Class CodesG02B 6/4415 Cables for special applicat...G02B 6/4429 Means specially adapted for...G02B 6/4439 Auxiliary devices
