CA1227944A - Optical fiber cable for detecting low temperature - Google Patents
Optical fiber cable for detecting low temperatureInfo
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- CA1227944A CA1227944A CA000461107A CA461107A CA1227944A CA 1227944 A CA1227944 A CA 1227944A CA 000461107 A CA000461107 A CA 000461107A CA 461107 A CA461107 A CA 461107A CA 1227944 A CA1227944 A CA 1227944A
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- optical fiber
- center member
- fiber cable
- fibers
- low temperature
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Abstract
Abstract:
The invention provides an optical fiber cable for detecting a low temperature. The cable comprises a center member made of a material having a low coefficient of linear expansion having one or more longitudinally extending grooves in each of which at least one optical fiber is placed. In one embodiment, at least one optical fiber, which comprises a core and a cladding both made of silica glass, is placed in each of the grooves and optionally the internal space of the groove which is not occupied by the optical fiber or fibers is filled with a resin which has a low glass transition tempera-ture. Alternatively, in another embodiment, at least two optical fibers are placed in the grooves, the optical fibers having different coating structures from each other and/or different fiber structures from each other so as to detect a low temperature in different temperature ranges. Fibers capable of detecting lower temperatures more accurately are thus provided.
The invention provides an optical fiber cable for detecting a low temperature. The cable comprises a center member made of a material having a low coefficient of linear expansion having one or more longitudinally extending grooves in each of which at least one optical fiber is placed. In one embodiment, at least one optical fiber, which comprises a core and a cladding both made of silica glass, is placed in each of the grooves and optionally the internal space of the groove which is not occupied by the optical fiber or fibers is filled with a resin which has a low glass transition tempera-ture. Alternatively, in another embodiment, at least two optical fibers are placed in the grooves, the optical fibers having different coating structures from each other and/or different fiber structures from each other so as to detect a low temperature in different temperature ranges. Fibers capable of detecting lower temperatures more accurately are thus provided.
Description
Optical fiber cable for detecting low temperature The present invention relates to an optical fiber cable having an improved structure useful for continuous detection of low temperatures over a broad temperature range.
An optical fiber for continuously detecting a low temperature is capable of rapidly detecting the tempera-lure of a chilled fluid with accuracy along its length.
In fuel storage facilities, this forms a noteworthy safe low temperature detecting means having little chance of causing an explosion because of its complete isolation from the environment.
A conventional method for detecting a low temperature with an optical fiber comprises detecting the variation of the attenuation through the optical fiber, which is pro-portion Al to the temperature change, by a so-called back scattering method which measures the back scattering of light transmitted through the optical fiber. Such vane-lions of attenuation corresponding to temperature change may be caused by changes of the difference between the refractive indexes of a core and a cladding according to the temperature change or by micro bending of the optical fiber resulted from shrinkage of a coating material on the optical fiber due to temperature change. In order to improve the sensitivity of a low temperature detecting means, it is necessary to amplify the change of Aetna-lion corresponding to the temperature change within an intended temperature range. However, the acceptable variation of attenuation is only about several tens dB/Km at most since the requisite strength of light to be transmitted has its own lower limit, which inevitably limits the detectable temperature range. Accordingly, it is difficult for the conventional optical fibers to detect the variation of attenuation over a wide temperature range, and detecting systems including conventional :~;
optical fibers tend to malfunction.
The prior art is described in further detail below with reference to the accompanying drawings. For convenience, all of the drawings are first briefly described as follows:
Fig. 1 is a graph showing temperature characteristics of refractive indexes of silica glass and a silicone resin.
Figs. 2 and 3 show cross-sectional views of two dip-foreign embodiments of the optical fiber cables of the present invention.
Fig. 4 is a graph showing a relation between Young's modulus of a silicone resin and temperature.
Fig. 5 is a graph showing temperature detecting char-acteristics of conventional optical fiber and the optical fiber of the invention.
Fig. 6 is a graph showing a position detecting char-acteristic of the optical fiber cable shown in Fig. 2.
Fig. 7 is a graph showing temperature detecting char-acteristics of the optical fiber cable shown in Fig . 3 .
A generally known optical fiber through which alien-ration varies with temperature change involves a plastic cladding optical fiber (hereinafter referred to as "PCF").
PCF consists of a core made of silica glass and a cladding made of a silicone resin. Reference is made to Fig. 1 to explain functions of PCF. In Fig. 1, silica glass used as the core shows a stable refractive index against tempera-lure changes (Line A) whereas the refractive index of the silicone resin varies with temperature (Line By There-fore, the difference between the refractive indexes of the core and the cladding decreases or even becomes minus as the temperature of the PCF becomes lower. Thus, the strength of transmitted light is reduced according to the decrease of the difference between the refractive indexes, which results from lowering of the temperature.
However, PCF unavoidably encounters a temperature at which PCF becomes incapable of transmitting light, namely, AL
a temperature at which the refractive index of the core becomes smaller than that of the cladding so that light is not transmitted. In order to lower said temperature, a material having a low refractive index at room tempera-lure, such as a silicone resin, should be used as the cladding material, but such an optical fiber is accom-panted by an increased Raleigh scattering and brings about the undesirable problem that attenuation becomes too great.
Accordingly, an object of the present invention is to overcome the above-described drawbacks of the conventional optical fiber for detecting a low temperature and to pro-vise an optical fiber cable capable of precisely detecting a low temperature over a wide temperature range.
Another object of the present invention is to provide an optical fiber cable capable of detecting a low tempt erasure with high accuracy over a wide temperature range comprising at least two optical fibers which detect a low temperature in a different temperature range.
According to one aspect of the invention there is provided an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least one longitudinally extending groove containing therein at least one optical fiber, wherein the optical fiber comprises a core and a cladding both made of silica glass, the center member is made of a material having a low coefficient of linear expansion, the periphery of the center member is covered with a protecting covering and the interior space of the groove I which is not occupied by the optical fiber or fibers is filled with a resin having a low glass transition temperature.
According to another aspect of the invention there is provided an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least two longitudinally extending grooves in each I
of which one optical fiber is placed, wherein the center member is made of a material having a low coefficient of linear expansion, each of the optical fibers placed in each groove detects a low temperature in a different temperature range and the periphery of the center member is covered with a protecting covering.
Preferred embodiments of the invention are described in the following with reference to the accompanying drawings.
The optical fibers are preferably placed in longitudinally extending grooves of a center member comprising a material having a low coefficient of linear expansion, such as metals (e.g. aluminum, stainless steel, copper, etc.) and non-metallic materials (e.g.
fiber-reinforced plastics (FRY) reinforced, for example, by glass fibers, carbon fibers or Armed fibers).
When the center member is made of a metal, detection with quick response is possible because of their good thermal conductivity. On the other hand, a center member made of a non-metallic material affords a completely non-metallic optical fiber cable which is free from explosion problems.
One embodiment of the present invention provides an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least one longitudinally extending groove containing therein at least one optical fiber, wherein the optical fiber comprises a core and a cladding both made of silica glass, the center member is made of a material having a low coefficient of linear expansion and the internal space of the grooves not occupied by the optical fiber or fibers is filled with a resin which has a low glass transition temperature such as silicone resins and acrylic resins.
The center member has a covering such as a protecting pipe made of aluminum, stainless steel, copper or a flyer-carbon polymer, etch It is preferred to place only one optical fiber in each groove of the center member. When a plurality of optical fibers are placed in one groove, the I
fibers are separated from each other by a filling (e.g. a resin) in order to make the individual fibers fully exert their characteristics intact.
Another embodiment of the present invention provides an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least two longitudinally extending grooves in each of which one optical fiber is placed, wherein the center member is made of a material having a low coefficient of linear expansion such as a metal (e.g. aluminum, stainless steel, copper, etc.), and further each of the optical fibers placed in each groove detects a low temperature in a different temperature range. The periphery of the center member is covered with the protecting covering as in the first embodiment of the invention.
The size of the center member is preferably from 2 to 6 mm, more preferably from 3 to 5 mm, particularly about 4 mm.
The grooves preferably extend helically around the surface of the center member. The pitch of the helical groove is preferably at least 0.1 m, more preferably from 0.1 to 1 m. However, they may extend parallel to the axis of the center member, if desired. There must be at least one groove and preferably at least three. The cross section of the groove may be any form that can contain the optical fiber and is preferably U-shape or V-shape.
The size of the groove may vary with the size of the optical fiber to be contained therein.
The first embodiment of the present invention will be illustrated in greater detail with reference to Fig. 2.
In Fig. 2, at least one, and preferably only one optical fiber 1 having an outer diameter of about 100 to 200 micrometers consisting of a core and a cladding both made of glass is placed in each of the three U-shaped grooves 2 (1 mm depth, 1 mm width), which are helically ~;~279~
provided in the peripheral surface of a spacer 3 (center member). The spacer is made of aluminum, copper or fiber reinforced plastic (FRY) and has a diameter of about 4 mm.
The interior of each groove 2 which is not occupied by the optical fiber is filled with a silicone resin 4.
The periphery of the spacer 3 is covered with a pipe 5 made of aluminum, stainless steel, copper, a fluorocarbon polymer, etc.
While the silicone resin has a low Young's modulus at room temperature and exerts a cushioning effect, it has a low glass transition temperature so that it has a large Young's modulus at low temperature as shown in the graph of Fig. 4, thereby causing micro bending of the optical fiber. When the optical fiber is cooled to a low tempt erasure, attenuation increases due to micro bending, and thereby the low temperature is detected. Accordingly, the optical fiber for detecting a low temperature can be formed by coating the optical fiber with a resin which has a low glass transition temperature such as a silicone resin or an acrylic resin.
conventional optical fiber in which micro bending is caused upon exposure to a low temperature generally comprises a core-cladding structure made of glass, i.e.
a lass optical fiber, having the silicone resin coated thereon and nylon further coated thereon. Such a con-ventional optical fiber cannot be used as a sensor at a temperature lower than -60C as shown by Curve C in the graph of Fig. 5. Whereas, in case of the glass fiber having only a silicone resin coating, attenuation is increased by 10 dim even at -100C as shown by Curve D
of Fig. 5. Thus, according to the present invention, it is possible to detect a temperature as low as -100C by causing micro bending of the optical fiber by making use of the low temperature characteristics of the silicone resin.
Fig. 6 illustrates the temperature characteristics of a position exposed to a low temperature when the middle part of the optical fiber cable of the first embodiment of the present invention was cooled over a length of about 20 meters. According to Fig. 6, no change in attenuation loss was observed when cooled to a temperature of from +20C to -~0C, but a change of the attenuation trays-mission by about 0.3 dub was detected when cooled to -100C.
It was, therefore, found that the optical fiber cable of the invention effectively detects a low temperature of about -80C to -100C or even lower. Further, according to this embodiment, it is not necessary to increase the difference between the refractive indexes of the core and the cladding in case of PCF in order to lower the detectable temperature range, and therefore, a silica glass optical fiber having a standard structure can be employed for detecting a low temperature.
Silicone resin-coated optical fibers generally require protection because of their weakness against lateral pressure. According to the present invention, this problem can be solved by placing the optical fiber in the groove of the center member. Further, a shrinkage of the center member at a low temperature may reduce the low temperature detectability of the optical fiber. However, it can be prevented by using, as the center member, a material having a smaller coefficient of linear expansion than that of the silicone resin, such as a metal (e.g.
aluminum, stainless steel or copper) or FRY. Further-more, when the center member is made of a metal having excellent thermal conductivity as well as a low co-efficient of linear expansion, thermal conductivity and response for low temperature detection are improved.
In the above-described second embodiment of the invention, the term optical fibers having different coating structures" is intended to mean optical fibers having applied thereto a single or multi-layered coating which has different combinations of the kinds of coating material(s), the properties and/or thickness of the Lo Lo coating layer(s), the state of coating, etc. Such optical fibers include, for example, an optical fiber consisting of a core and a cladding both made of silica glass having a primary single or multi-layered coating applied thereto, the same optical fiber having a secondary coating for protection also applied thereon, and a plastic cladding fiber ~PCF) consisting of a core made of silica glass and a cladding made of a plastic. PCF or a glass optical fiber having the primary coating can be formed by applying polyamide resins, silicone resins or acrylic resins onto the silica glass optical fiber and hardening the resin with ultraviolet rays or heat in the step of drawing the silica optical fiber. The secondary coating is applied directly onto the primary coating or with a space there-between. The resins to be used as the secondary coating may include thermoplastic resins (e.g. polyamide, polyp propylene, fluororesins, etc.) and FRY. Even if the primary and the secondary coatings have the same coating structure, the shrinkage rate of the optical fiber at a low temperature can vary when resins having different physical properties are used or when the shrinkage strain of the optical fiber resulting from shrinkage of the coatings after extrusion is changed. Thereby, the de-testable temperature range of the optical fiber can be varied. The detectable temperature range may also vary when the outer diameter and/or refractive index profile of the silica glass fiber is changed.
The second embodiment of the invention will be illustrated in greater detail with reference to Fig. 3.
3C In Fig. 3, a silicone resin-coated optical fiber 11, an optical fiber 12 formed by further coating the above silicone resin-coated optical fiber with tetrafluoro-ethyleneperfluoroalkylvinylether copolymer (PEA), and an acrylic resin-coated optical fiber 13 are respectively placed in each of three U-shaped grooves 2 (1 mm depth, 1 mm width) which are laterally and helically provided in I
the periphery of a spacer 3 made of aluminum, stainless steel, copper or FRY and having a diameter of about 4 mm.
The spacer 3 containing the optical fibers 11, 12 and 13 is covered with a pipe S made of aluminum, stainless steel, copper or a fluorocarbon polymer. the above-described fibers have an outer diameter of about 100 to 200 micrometers. The physical properties of the coating resins and the glass used in the optical fibers 11, 12 and 13 are shown in Table 1 below.
Table 1 Material Glass transit Coefficient of Young's lion temp. linear expansion Modulus (C) tx10-4/C, at 20C) (Kg/mm2,at 20 Silicone I 2 0.1 resin Acrylic -7 2 40 resin Glass - 0.006 7.3 x 103 (fiber) The optical fiber cable of the second embodiment of the present invention comprises optical fibers having different detectable temperature ranges which have been employed collectively so that it is possible to detect a low temperature over a broader temperature range than is capable with the individual fibers.
Fig. 7 shows the low temperature detectability char-acteristics of the optical fiber cable according to the second embodiment of the present invention, wherein Curves E, F and G indicate the temperature characteristics of the optical fibers 11, 12 and 13, respectively. As far as the individual fibers are concerned, since the range from the temperature at which attenuation begins to increase to the temperature at which attenuation drastically increases is restricted, the detectable temperature range is narrowly limited. However, when the different optical fibers are ~L2~9~
contained in one single cable so that their respective detectable temperature ranges overlap, the resulting cable can be applied to a broadened temperature range of from about -30C to -200C.
Further, since only one of the different optical fibers is placed in each of the grooves of the spacer, the respective low temperature detectability can be obtained without any influence among the fibers, and also influences from outside the cable can be shielded by the spacer.
Furthermore, the use of various optical fibers each having a different applicable temperature range makes it possible to conduct cross checking of the sensor fibers and to monitor any malfunctioning of the optical fibers.
I In addition, use of a metal having high thermal conductivity as well as a lower coefficient of linear expansion than that of the coating resins of optical fibers as materials for the spacer and of the protecting covering reduces the time delay of the temperature detection; alleviates the influence exerted by the shrinkage of the spacer; and thus keeps the kirk-teristics of the fiber substantially intact.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof as defined by the following claims.
An optical fiber for continuously detecting a low temperature is capable of rapidly detecting the tempera-lure of a chilled fluid with accuracy along its length.
In fuel storage facilities, this forms a noteworthy safe low temperature detecting means having little chance of causing an explosion because of its complete isolation from the environment.
A conventional method for detecting a low temperature with an optical fiber comprises detecting the variation of the attenuation through the optical fiber, which is pro-portion Al to the temperature change, by a so-called back scattering method which measures the back scattering of light transmitted through the optical fiber. Such vane-lions of attenuation corresponding to temperature change may be caused by changes of the difference between the refractive indexes of a core and a cladding according to the temperature change or by micro bending of the optical fiber resulted from shrinkage of a coating material on the optical fiber due to temperature change. In order to improve the sensitivity of a low temperature detecting means, it is necessary to amplify the change of Aetna-lion corresponding to the temperature change within an intended temperature range. However, the acceptable variation of attenuation is only about several tens dB/Km at most since the requisite strength of light to be transmitted has its own lower limit, which inevitably limits the detectable temperature range. Accordingly, it is difficult for the conventional optical fibers to detect the variation of attenuation over a wide temperature range, and detecting systems including conventional :~;
optical fibers tend to malfunction.
The prior art is described in further detail below with reference to the accompanying drawings. For convenience, all of the drawings are first briefly described as follows:
Fig. 1 is a graph showing temperature characteristics of refractive indexes of silica glass and a silicone resin.
Figs. 2 and 3 show cross-sectional views of two dip-foreign embodiments of the optical fiber cables of the present invention.
Fig. 4 is a graph showing a relation between Young's modulus of a silicone resin and temperature.
Fig. 5 is a graph showing temperature detecting char-acteristics of conventional optical fiber and the optical fiber of the invention.
Fig. 6 is a graph showing a position detecting char-acteristic of the optical fiber cable shown in Fig. 2.
Fig. 7 is a graph showing temperature detecting char-acteristics of the optical fiber cable shown in Fig . 3 .
A generally known optical fiber through which alien-ration varies with temperature change involves a plastic cladding optical fiber (hereinafter referred to as "PCF").
PCF consists of a core made of silica glass and a cladding made of a silicone resin. Reference is made to Fig. 1 to explain functions of PCF. In Fig. 1, silica glass used as the core shows a stable refractive index against tempera-lure changes (Line A) whereas the refractive index of the silicone resin varies with temperature (Line By There-fore, the difference between the refractive indexes of the core and the cladding decreases or even becomes minus as the temperature of the PCF becomes lower. Thus, the strength of transmitted light is reduced according to the decrease of the difference between the refractive indexes, which results from lowering of the temperature.
However, PCF unavoidably encounters a temperature at which PCF becomes incapable of transmitting light, namely, AL
a temperature at which the refractive index of the core becomes smaller than that of the cladding so that light is not transmitted. In order to lower said temperature, a material having a low refractive index at room tempera-lure, such as a silicone resin, should be used as the cladding material, but such an optical fiber is accom-panted by an increased Raleigh scattering and brings about the undesirable problem that attenuation becomes too great.
Accordingly, an object of the present invention is to overcome the above-described drawbacks of the conventional optical fiber for detecting a low temperature and to pro-vise an optical fiber cable capable of precisely detecting a low temperature over a wide temperature range.
Another object of the present invention is to provide an optical fiber cable capable of detecting a low tempt erasure with high accuracy over a wide temperature range comprising at least two optical fibers which detect a low temperature in a different temperature range.
According to one aspect of the invention there is provided an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least one longitudinally extending groove containing therein at least one optical fiber, wherein the optical fiber comprises a core and a cladding both made of silica glass, the center member is made of a material having a low coefficient of linear expansion, the periphery of the center member is covered with a protecting covering and the interior space of the groove I which is not occupied by the optical fiber or fibers is filled with a resin having a low glass transition temperature.
According to another aspect of the invention there is provided an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least two longitudinally extending grooves in each I
of which one optical fiber is placed, wherein the center member is made of a material having a low coefficient of linear expansion, each of the optical fibers placed in each groove detects a low temperature in a different temperature range and the periphery of the center member is covered with a protecting covering.
Preferred embodiments of the invention are described in the following with reference to the accompanying drawings.
The optical fibers are preferably placed in longitudinally extending grooves of a center member comprising a material having a low coefficient of linear expansion, such as metals (e.g. aluminum, stainless steel, copper, etc.) and non-metallic materials (e.g.
fiber-reinforced plastics (FRY) reinforced, for example, by glass fibers, carbon fibers or Armed fibers).
When the center member is made of a metal, detection with quick response is possible because of their good thermal conductivity. On the other hand, a center member made of a non-metallic material affords a completely non-metallic optical fiber cable which is free from explosion problems.
One embodiment of the present invention provides an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least one longitudinally extending groove containing therein at least one optical fiber, wherein the optical fiber comprises a core and a cladding both made of silica glass, the center member is made of a material having a low coefficient of linear expansion and the internal space of the grooves not occupied by the optical fiber or fibers is filled with a resin which has a low glass transition temperature such as silicone resins and acrylic resins.
The center member has a covering such as a protecting pipe made of aluminum, stainless steel, copper or a flyer-carbon polymer, etch It is preferred to place only one optical fiber in each groove of the center member. When a plurality of optical fibers are placed in one groove, the I
fibers are separated from each other by a filling (e.g. a resin) in order to make the individual fibers fully exert their characteristics intact.
Another embodiment of the present invention provides an optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least two longitudinally extending grooves in each of which one optical fiber is placed, wherein the center member is made of a material having a low coefficient of linear expansion such as a metal (e.g. aluminum, stainless steel, copper, etc.), and further each of the optical fibers placed in each groove detects a low temperature in a different temperature range. The periphery of the center member is covered with the protecting covering as in the first embodiment of the invention.
The size of the center member is preferably from 2 to 6 mm, more preferably from 3 to 5 mm, particularly about 4 mm.
The grooves preferably extend helically around the surface of the center member. The pitch of the helical groove is preferably at least 0.1 m, more preferably from 0.1 to 1 m. However, they may extend parallel to the axis of the center member, if desired. There must be at least one groove and preferably at least three. The cross section of the groove may be any form that can contain the optical fiber and is preferably U-shape or V-shape.
The size of the groove may vary with the size of the optical fiber to be contained therein.
The first embodiment of the present invention will be illustrated in greater detail with reference to Fig. 2.
In Fig. 2, at least one, and preferably only one optical fiber 1 having an outer diameter of about 100 to 200 micrometers consisting of a core and a cladding both made of glass is placed in each of the three U-shaped grooves 2 (1 mm depth, 1 mm width), which are helically ~;~279~
provided in the peripheral surface of a spacer 3 (center member). The spacer is made of aluminum, copper or fiber reinforced plastic (FRY) and has a diameter of about 4 mm.
The interior of each groove 2 which is not occupied by the optical fiber is filled with a silicone resin 4.
The periphery of the spacer 3 is covered with a pipe 5 made of aluminum, stainless steel, copper, a fluorocarbon polymer, etc.
While the silicone resin has a low Young's modulus at room temperature and exerts a cushioning effect, it has a low glass transition temperature so that it has a large Young's modulus at low temperature as shown in the graph of Fig. 4, thereby causing micro bending of the optical fiber. When the optical fiber is cooled to a low tempt erasure, attenuation increases due to micro bending, and thereby the low temperature is detected. Accordingly, the optical fiber for detecting a low temperature can be formed by coating the optical fiber with a resin which has a low glass transition temperature such as a silicone resin or an acrylic resin.
conventional optical fiber in which micro bending is caused upon exposure to a low temperature generally comprises a core-cladding structure made of glass, i.e.
a lass optical fiber, having the silicone resin coated thereon and nylon further coated thereon. Such a con-ventional optical fiber cannot be used as a sensor at a temperature lower than -60C as shown by Curve C in the graph of Fig. 5. Whereas, in case of the glass fiber having only a silicone resin coating, attenuation is increased by 10 dim even at -100C as shown by Curve D
of Fig. 5. Thus, according to the present invention, it is possible to detect a temperature as low as -100C by causing micro bending of the optical fiber by making use of the low temperature characteristics of the silicone resin.
Fig. 6 illustrates the temperature characteristics of a position exposed to a low temperature when the middle part of the optical fiber cable of the first embodiment of the present invention was cooled over a length of about 20 meters. According to Fig. 6, no change in attenuation loss was observed when cooled to a temperature of from +20C to -~0C, but a change of the attenuation trays-mission by about 0.3 dub was detected when cooled to -100C.
It was, therefore, found that the optical fiber cable of the invention effectively detects a low temperature of about -80C to -100C or even lower. Further, according to this embodiment, it is not necessary to increase the difference between the refractive indexes of the core and the cladding in case of PCF in order to lower the detectable temperature range, and therefore, a silica glass optical fiber having a standard structure can be employed for detecting a low temperature.
Silicone resin-coated optical fibers generally require protection because of their weakness against lateral pressure. According to the present invention, this problem can be solved by placing the optical fiber in the groove of the center member. Further, a shrinkage of the center member at a low temperature may reduce the low temperature detectability of the optical fiber. However, it can be prevented by using, as the center member, a material having a smaller coefficient of linear expansion than that of the silicone resin, such as a metal (e.g.
aluminum, stainless steel or copper) or FRY. Further-more, when the center member is made of a metal having excellent thermal conductivity as well as a low co-efficient of linear expansion, thermal conductivity and response for low temperature detection are improved.
In the above-described second embodiment of the invention, the term optical fibers having different coating structures" is intended to mean optical fibers having applied thereto a single or multi-layered coating which has different combinations of the kinds of coating material(s), the properties and/or thickness of the Lo Lo coating layer(s), the state of coating, etc. Such optical fibers include, for example, an optical fiber consisting of a core and a cladding both made of silica glass having a primary single or multi-layered coating applied thereto, the same optical fiber having a secondary coating for protection also applied thereon, and a plastic cladding fiber ~PCF) consisting of a core made of silica glass and a cladding made of a plastic. PCF or a glass optical fiber having the primary coating can be formed by applying polyamide resins, silicone resins or acrylic resins onto the silica glass optical fiber and hardening the resin with ultraviolet rays or heat in the step of drawing the silica optical fiber. The secondary coating is applied directly onto the primary coating or with a space there-between. The resins to be used as the secondary coating may include thermoplastic resins (e.g. polyamide, polyp propylene, fluororesins, etc.) and FRY. Even if the primary and the secondary coatings have the same coating structure, the shrinkage rate of the optical fiber at a low temperature can vary when resins having different physical properties are used or when the shrinkage strain of the optical fiber resulting from shrinkage of the coatings after extrusion is changed. Thereby, the de-testable temperature range of the optical fiber can be varied. The detectable temperature range may also vary when the outer diameter and/or refractive index profile of the silica glass fiber is changed.
The second embodiment of the invention will be illustrated in greater detail with reference to Fig. 3.
3C In Fig. 3, a silicone resin-coated optical fiber 11, an optical fiber 12 formed by further coating the above silicone resin-coated optical fiber with tetrafluoro-ethyleneperfluoroalkylvinylether copolymer (PEA), and an acrylic resin-coated optical fiber 13 are respectively placed in each of three U-shaped grooves 2 (1 mm depth, 1 mm width) which are laterally and helically provided in I
the periphery of a spacer 3 made of aluminum, stainless steel, copper or FRY and having a diameter of about 4 mm.
The spacer 3 containing the optical fibers 11, 12 and 13 is covered with a pipe S made of aluminum, stainless steel, copper or a fluorocarbon polymer. the above-described fibers have an outer diameter of about 100 to 200 micrometers. The physical properties of the coating resins and the glass used in the optical fibers 11, 12 and 13 are shown in Table 1 below.
Table 1 Material Glass transit Coefficient of Young's lion temp. linear expansion Modulus (C) tx10-4/C, at 20C) (Kg/mm2,at 20 Silicone I 2 0.1 resin Acrylic -7 2 40 resin Glass - 0.006 7.3 x 103 (fiber) The optical fiber cable of the second embodiment of the present invention comprises optical fibers having different detectable temperature ranges which have been employed collectively so that it is possible to detect a low temperature over a broader temperature range than is capable with the individual fibers.
Fig. 7 shows the low temperature detectability char-acteristics of the optical fiber cable according to the second embodiment of the present invention, wherein Curves E, F and G indicate the temperature characteristics of the optical fibers 11, 12 and 13, respectively. As far as the individual fibers are concerned, since the range from the temperature at which attenuation begins to increase to the temperature at which attenuation drastically increases is restricted, the detectable temperature range is narrowly limited. However, when the different optical fibers are ~L2~9~
contained in one single cable so that their respective detectable temperature ranges overlap, the resulting cable can be applied to a broadened temperature range of from about -30C to -200C.
Further, since only one of the different optical fibers is placed in each of the grooves of the spacer, the respective low temperature detectability can be obtained without any influence among the fibers, and also influences from outside the cable can be shielded by the spacer.
Furthermore, the use of various optical fibers each having a different applicable temperature range makes it possible to conduct cross checking of the sensor fibers and to monitor any malfunctioning of the optical fibers.
I In addition, use of a metal having high thermal conductivity as well as a lower coefficient of linear expansion than that of the coating resins of optical fibers as materials for the spacer and of the protecting covering reduces the time delay of the temperature detection; alleviates the influence exerted by the shrinkage of the spacer; and thus keeps the kirk-teristics of the fiber substantially intact.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof as defined by the following claims.
Claims (12)
1. An optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least one longitudinally extending groove containing therein at least one optical fiber, wherein the optical fiber comprises a core and a cladding both made of silica glass, the center member is made of a material having a low coefficient of linear expansion, the periphery of the center member is covered with a protecting covering and the interior space of the groove which is not occupied by the optical fiber or fibers is filled with a resin having a low glass transition temperature.
2. An optical fiber cable as claimed in Claim 1, wherein the grooves extend helically around the outer surface of the center member.
3. An optical fiber cable as claimed in Claim 1, wherein said center member is made of a metal selected from the group consisting of aluminum, stainless steel and copper.
4. An optical fiber cable as claimed in Claim 1, Claim 2 or Claim 3, wherein said center member is made of a fiber-reinforced plastic.
5. An optical fiber cable as claimed in Claim 1, Claim 2 or Claim 3, wherein said resin filling the unoccupied interior space of the groove is selected from the group consisting of silicone resins and acrylic resins.
6. An optical fiber cable as claimed in Claim 1, Claim 2 or Claim 3, wherein the covering is a pipe made of a material selected from the group consisting of aluminum, stainless steel, copper and a fluorocarbon polymer.
7. An optical fiber cable for detecting a low temperature comprising a center member whose outer surface has at least two longitudinally extending grooves in each of which one optical fiber is placed, wherein the center member is made of a material having a low coefficient of linear expansion, each of the optical fibers placed in each groove detects a low temperature in a different temperature range and the periphery of the center member is covered with a protecting covering.
8. An optical fiber cable as claimed in Claim 7, wherein said optical fibers have different coating structures from each other.
9. An optical fiber cable as claimed in Claim 7, wherein the outer diameter and/or refractive index profile of said optical fibers are different from each other.
10. An optical fiber cable as claimed in Claim 7, wherein the grooves extend helically around the center member.
11. An optical fiber cable as claimed in Claim 7, Claim 8 or Claim 9, wherein said center member is made of a metal selected from the group consisting of alumimium, stainless steel and copper.
12. An optical fiber cable as claimed in Claim 7, Claim 8 or Claim 9, wherein the covering is a pipe made of a material selected from the group consisting of aluminium, copper and a fluorocarbon polymer.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP126254/1983 | 1983-08-15 | ||
| JP14625383 | 1983-08-15 | ||
| JP14625483 | 1983-08-15 | ||
| JP126253/1983 | 1983-08-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1227944A true CA1227944A (en) | 1987-10-13 |
Family
ID=26477132
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000461107A Expired CA1227944A (en) | 1983-08-15 | 1984-08-15 | Optical fiber cable for detecting low temperature |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1227944A (en) |
-
1984
- 1984-08-15 CA CA000461107A patent/CA1227944A/en not_active Expired
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |