WO2021181501A1

WO2021181501A1 - Optical fiber device, temperature measurement system, and optical fiber device manufacturing system

Info

Publication number: WO2021181501A1
Application number: PCT/JP2020/010180
Authority: WO
Inventors: ▲高▼須庸一
Original assignee: 富士通株式会社
Priority date: 2020-03-10
Filing date: 2020-03-10
Publication date: 2021-09-16
Also published as: JP7364960B2; JPWO2021181501A1

Abstract

This optical fiber device comprises: a first metal flexible tube into which an optical fiber has been inserted; a second metal flexible tube into which the first metal flexible tube has been inserted and which is immersed in a liquid in a liquid tank; and an anchor that has a density greater than the density of the liquid and that is connected, in the liquid, to the second metal flexible tube.　

Description

Fiber optic equipment, temperature measurement systems, and methods for manufacturing fiber optic equipment

This case relates to an optical fiber device, a temperature measurement system, and a method for manufacturing an optical fiber device.

As a technique for measuring the temperature of LNG (liquefied natural gas) stored in an LNG tank, a temperature measurement technique using a flexible temperature sensor such as an optical fiber is disclosed. As a structure for protecting an optical fiber, a technique using a metal tube or the like is disclosed (see, for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2-203303 Japanese Unexamined Patent Publication No. 7-218780

In a liquid tank such as an LNG tank, the liquid is flowing by receiving the liquid, discharging the liquid, convection of the liquid, mixing the liquid, and the like. When the liquid flows, the temperature measurement position of the optical fiber may also change. In this case, the temperature measurement accuracy may decrease.

On one aspect, it is an object of the present invention to provide an optical fiber device, a temperature measurement system, and a method for manufacturing the optical fiber device, which can suppress fluctuations in the temperature measurement position of the optical fiber.

In one embodiment, the optical fiber device includes a first metal flexible tube into which the optical fiber is inserted and a second metal flexible tube into which the first metal flexible tube is inserted and immersed in a liquid in a liquid tank. And a weight having a density higher than that of the liquid and connected to the second metal flexible tube in the liquid.

In one embodiment, the optical fiber device and a temperature measuring device for measuring the temperature of the liquid in the liquid tank from the detection result of the backscattered light from the optical fiber are provided.

In one aspect, the method of manufacturing an optical fiber apparatus is to attach a second metal flexible tube to a liquid tank in which a liquid is stored, to which a weight having a density higher than that of the liquid is connected. The first metal flexible tube into which the optical fiber is inserted is inserted into the second metal flexible tube introduced from the entrance.

It is possible to suppress fluctuations in the temperature measurement position of the optical fiber.

(A) to (c) are diagrams for explaining the rollover. It is a figure which illustrates the structure of the tank equipment. It is a figure which illustrates the relationship between the liquid density of LNG and the temperature. (A) is a diagram illustrating the time-dependent changes in the liquid densities of the upper and lower layers in the LNG tank, and (b) is a diagram illustrating the time-dependent changes in the temperatures of the upper and lower layers. It is the schematic of the temperature measurement system which concerns on Example 1. FIG. (A) is a schematic diagram showing the overall configuration of the temperature measuring device, and (b) is a block diagram for explaining the hardware configuration of the control unit. It is a figure which shows the component of the backscattered light. (A) is a diagram illustrating the relationship between the elapsed time after light pulse emission and the light intensity of the Stokes component and the anti-Stokes component, and (b) is the temperature calculated using the detection result of (a). It is a figure which illustrates the optical fiber apparatus which concerns on Example 1. FIG. It is a figure which illustrates the optical fiber apparatus which concerns on Example 2. FIG. It is a figure which illustrates the optical fiber apparatus which concerns on Example 3. FIG. It is a figure which illustrates the temperature measurement system which concerns on Example 4. FIG. It is a flow chart which shows the manufacturing method of an optical fiber apparatus.

Prior to the explanation of the embodiment, the outline of the rollover in the LNG tank, which is an example of the liquid tank, will be described. As illustrated in FIG. 1A, LNG is stored in the LNG tank 200. For efficiency, LNG with different densities from various production areas is required to be stored in the LNG tank 200. For example, the LNG tank 200 may receive LNG from a plurality of ships. In this case, since LNG having different components is accepted, the LNG is multi-layered in the LNG tank 200 due to the density difference based on the component difference of LNG. In the example of FIG. 1A, the LNG in the LNG tank 200 has two layers. As illustrated in FIG. 1 (b), the lower layer is a dense LNG component. The upper layer is a low-density LNG component.

In this state, as illustrated in FIG. 1A, when heat enters the LNG tank 200, convection (double convection) occurs in each layer. When double convection occurs, each component and heat move little by little through the boundary between the upper and lower layers. As a result, the density of the upper layer and the density of the lower layer gradually approach each other. Further, the density of the upper layer and the density of the lower layer gradually approach each other due to the generation of boil-off gas (BOG) from the upper layer. When the difference between the density of the upper layer and the density of the lower layer becomes smaller, the upper layer and the lower layer are mixed, and rapid convection occurs (rollover).

In the two-layered state, the presence of the LNG component in the upper layer suppresses the generation of boil-off gas from the LNG component in the lower layer. However, as illustrated in FIG. 1 (c), at the time of rollover, the LNG component in the lower layer moves to the upper layer, so that a large amount of boil-off gas that has been suppressed until then is generated, and the pressure in the LNG tank 200 becomes abnormal. Ascend to. In addition, in FIG. 1C, the vertical axis shows the amount of boil-off gas.

Next, the tank equipment including the LNG tank 200 will be described. FIG. 2 is a diagram illustrating the structure of the tank equipment. As illustrated in FIG. 2, the tank equipment has a structure in which the chamber 300 is connected to the upper part of the LNG tank 200. The chamber 300 is provided for applications such as preventing leakage and scattering of LNG and boil-off gas into the atmosphere. As described above, LNG is stored in the LNG tank 200. The LNG tank 200 and the chamber 300 are provided with a place where they communicate with each other. Although the communicating portion is sealed with a flange or the like, the LNG boil-off gas may leak from the LNG tank 200 to the chamber 300 through the communicating portion.

Therefore, in order to purge the boil-off gas in the chamber 300, a supply means for supplying an inert gas such as nitrogen gas or a rare gas to the chamber 300 as a purge gas is provided. By supplying the purge gas into the chamber 300, the inside of the chamber 300 is purged.

In order to prevent rollover, it is preferable to grasp the liquid density distribution in the depth direction of the LNG tank 200 and stir the inside of the LNG tank 200. Since the boil-off gas may leak from the place where the sensor is inserted into the LNG tank 200, in the tank equipment illustrated in FIG. 2, it is required to insert the sensor from the chamber 300 and immerse it in the LNG of the LNG tank 200. Be done.

For example, it is conceivable to use a vibrating liquid densitometer as a sensor for measuring the liquid density distribution. Since the height of the tank is about 40 to 50 m, it is desired to be able to measure the length of 40 to 50 m. However, since the vibrating liquid densitometer requires sampling, it is difficult to make continuous measurements spatially and temporally. Further, in the measurement work, the cable or the like for signal acquisition needs to be flexible.

From the above, it is desirable to measure the liquid density of LNG stored in the LNG tank 200 using a sensor other than the vibration type liquid density meter. Therefore, we focus on the relationship between the liquid density of LNG and the temperature. FIG. 3 is a diagram illustrating the relationship between the liquid density of LNG and the temperature. As illustrated in FIG. 3, there is a close relationship between the liquid density of LNG and the temperature. Note that FIG. 3 illustrates the relationship between the liquid density and temperature of LNGs of types A to C.

Next, FIG. 4A is a diagram illustrating the time-dependent changes in the liquid densities of the upper and lower layers in the LNG tank 200. FIG. 4B is a diagram illustrating the time course of the temperature of the upper layer and the lower layer. As illustrated in FIG. 4A, the liquid density of the upper layer and the liquid density of the lower layer become close to each other by the time the rollover occurs, and the liquid density of the upper layer and the liquid density of the lower layer become close to each other when the rollover occurs. It is almost the same. As illustrated in FIG. 4B, the temperature of the upper layer and the temperature of the lower layer are close to each other by the time the rollover occurs, and the temperature of the upper layer and the temperature of the lower layer are substantially the same at the time when the rollover occurs. There is. From the above, it is considered that the occurrence of rollover can be estimated by measuring the change with time of the temperature using the temperature sensor.

Optical fiber can realize continuous temperature measurement in space and time. Further, the optical fiber has flexibility. Therefore, it is desired to use an optical fiber as a temperature sensor. However, the LNG in the LNG tank 200 is constantly flowing due to acceptance / withdrawal, convection, mixing, and the like. In order to measure the temperature with high accuracy, it is desired to suppress the fluctuation of the temperature measurement position by the optical fiber.

Therefore, in the following examples, an optical fiber device, a temperature measurement system, and a method for manufacturing the optical fiber device that can suppress fluctuations in the temperature measurement position of the optical fiber will be described.

FIG. 5 is a schematic view of the temperature measurement system 100 according to the first embodiment. As illustrated in FIG. 5, the temperature measuring system 100 includes a temperature measuring device 10, an optical fiber 20, and the like. The optical fiber 20 is introduced into the chamber 300 from the outside of the chamber 300 through the seal flange 301 of the chamber 300. Further, the optical fiber 20 is introduced into the LNG tank 200 through a seal flange 302 provided at a communication portion between the chamber 300 and the LNG tank 200. The seal flange 301 seals between the chamber 300 and the outside air. The seal flange 302 seals between the chamber 300 and the LNG tank 200.

FIG. 6A is a schematic view showing the overall configuration of the temperature measuring device 10. As illustrated in FIG. 6A, the temperature measuring device 10 includes a measuring device 30, a control unit 40, and the like. The measuring machine 30 includes a laser 31, a beam splitter 32, an optical switch 33, a filter 34, a plurality of

detectors

35a, 35b, and the like. The control unit 40 includes an instruction unit 41, a temperature measurement unit 42, a determination unit 43, and the like.

FIG. 6B is a block diagram for explaining the hardware configuration of the control unit 40. As illustrated in FIG. 6B, the control unit 40 includes a CPU 101, a RAM 102, a storage device 103, an interface 104, and the like. Each of these devices is connected by a bus or the like. The CPU (Central Processing Unit) 101 is a central processing unit. The CPU 101 includes one or more cores. The RAM (Random Access Memory) 102 is a volatile memory that temporarily stores a program executed by the CPU 101, data processed by the CPU 101, and the like. The storage device 103 is a non-volatile storage device. As the storage device 103, for example, a ROM (Read Only Memory), a solid state drive (SSD) such as a flash memory, a hard disk driven by a hard disk drive, or the like can be used. When the CPU 101 executes the temperature measurement program stored in the storage device 103, the control unit 40 is realized with the instruction unit 41, the temperature measurement unit 42, the determination unit 43, and the like. The indicator unit 41, the temperature measurement unit 42, the determination unit 43, and the like may be hardware such as a dedicated circuit.

The laser 31 is a light source such as a semiconductor laser, and emits laser light in a predetermined wavelength range according to the instruction of the indicating unit 41. In the present embodiment, the laser 31 emits light pulses (laser pulses) at predetermined time intervals. The beam splitter 32 incidents the light pulse emitted by the laser 31 on the optical switch 33. The optical switch 33 is a switch that switches the emission destination (channel) of the incident optical pulse. The optical switch 33 alternately injects optical pulses into the first end of the optical fiber 20 at regular intervals according to the instruction of the indicating unit 41.

The optical pulse incident on the optical fiber 20 propagates through the optical fiber 20. The optical pulse gradually attenuates while generating forward scattered light traveling in the propagation direction and backscattered light (return light) traveling in the feedback direction, and propagates in the optical fiber 20. The backscattered light passes through the optical switch 33 and re-enters the beam splitter 32. The backscattered light incident on the beam splitter 32 is emitted to the filter 34. The filter 34 is a WDM coupler or the like, and extracts backscattered light into a long wavelength component (a Stokes component described later) and a short wavelength component (an anti-Stokes component described later). The

detectors

35a and 35b are light receiving elements. The detector 35a converts the received intensity of the short wavelength component of the backscattered light into an electric signal and transmits it to the temperature measuring unit 42. The detector 35b converts the received intensity of the long wavelength component of the backscattered light into an electric signal and transmits it to the temperature measuring unit 42. The temperature measuring unit 42 measures the temperature distribution in the stretching direction of the optical fiber 20 by using the Stokes component and the anti-Stokes component. The determination unit 43 functions as a prediction unit that determines whether or not rollover occurs based on the temperature distribution measured by the temperature measurement unit 42, and predicts when rollover will occur.

FIG. 7 is a diagram showing the components of backscattered light. As illustrated in FIG. 7, backscattered light is roughly classified into three types. These three types of light are Rayleigh scattered light used for OTDR (optical pulse tester), Brilluan scattered light used for distortion measurement, temperature measurement, etc. in descending order of light intensity and incident light wavelength. Raman scattered light used for. Raman scattered light is generated by interference between light and lattice vibration in the optical fiber 20 that changes with temperature. The strengthening interference produces a short wavelength component called an anti-Stokes component, and the weakening interference produces a long wavelength component called a Stokes component.

FIG. 8A shows the elapsed time after the light pulse emission by the laser 31 and the Stokes component (long wavelength component) and the anti-Stokes component (short wavelength component) when light is incident from the first end of the optical fiber 20. It is a figure which illustrates the relationship with light intensity. The elapsed time corresponds to the propagation distance (position in the optical fiber 20) in the optical fiber 20. As illustrated in FIG. 8A, the light intensities of both the Stokes component and the anti-Stokes component decrease over time. This is because the light pulse gradually attenuates while generating forward scattered light and backscattered light and propagates in the optical fiber 20.

As illustrated in FIG. 8A, the light intensity of the anti-Stokes component is stronger than that of the Stokes component at a high temperature position in the optical fiber 20, and is higher than that of the Stokes component at a low temperature position. It becomes weaker. Therefore, by detecting both components with the

detectors

35a and 35b and utilizing the characteristic difference between the two components, the temperature at each position in the optical fiber 20 can be detected. In FIG. 8A, the region showing the maximum is a region heated locally in the optical fiber 20. Further, the region showing the minimum is a region cooled locally in the optical fiber 20.

In this embodiment, the temperature measuring unit 42 measures the temperature from the Stokes component and the anti-Stokes component for each elapsed time. Thereby, the temperature of each sampling position in the optical fiber 20 can be measured. That is, the temperature distribution in the stretching direction of the optical fiber 20 can be measured. Since the characteristic difference between the two components is used, the temperature can be measured with high accuracy even if the light intensity of both components is attenuated according to the distance. FIG. 8B is a temperature calculated using the detection result of FIG. 8A. The horizontal axis of FIG. 8B is a position in the optical fiber 20 calculated based on the elapsed time. As illustrated in FIG. 8B, the temperature at each position in the optical fiber 20 can be measured by detecting the Stokes component and the anti-Stokes component.

FIG. 9 is a diagram illustrating a structure (optical fiber device) that protects the optical fiber 20. As illustrated in FIG. 9, the optical fiber 20 includes a connecting fiber 21, a fusion sleeve 22, and a measuring fiber 23. The first end of the connecting fiber 21 (the first end of the optical fiber 20) is connected to the temperature measuring device 10. The second end of the connecting fiber 21 is connected to the first end of the measuring fiber 23 via the fusion sleeve 22. The measuring fiber 23 extends from outside the chamber 300 through the chamber 300 into the LNG tank 200. Therefore, the second end of the measuring fiber 23 is located in the LNG of the LNG tank 200.

The connection fiber 21, the fusion sleeve 22, and the vicinity of the first end of the measurement fiber 23 are inserted into the connection tube 51. The connecting tube 51 has flexibility and sealability. That is, the connecting tube 51 does not have air permeability and liquid permeability to the outside. The connecting tube 51 extends from the inside of the chamber 300 to the outside through the seal flange 301.

The portion of the measuring fiber 23 that is not inserted into the connecting tube 51 is inserted from the first end of the first metal flexible tube 52 and extends to the vicinity of the second end of the first metal flexible tube 52. .. The first metal flexible tube 52 has flexibility. The first metal flexible pipe 52 does not have ventilation and liquid permeability. The first end of the first metal flexible tube 52 is located in the chamber 300. The second end of the first metal flexible pipe 52 is located in the LNG of the LNG tank 200. The first end of the first metal flexible tube 52 is inserted from the second end of the connecting tube 51. The portion where the first metal flexible tube 52 is inserted into the connecting tube 51 is connected by a sealing member 54. The sealing member 54 seals between the connecting tube 51 and the first metal flexible tube 52.

The second metal flexible tube 53 has flexibility. The second metal flexible tube 53 does not have ventilation and liquid permeability. The first end of the second metal flexible tube 53 is located within the chamber 300. The second end of the second metal flexible pipe 53 is located in the LNG in the LNG tank 200. The second metal flexible pipe 53 extends through the seal flange 302 of the chamber 300 into the LNG tank 200. The first metal flexible pipe 52 passes through the second metal flexible pipe 53 and extends into the LNG in the LNG tank 200. The seal flange 302 seals between the seal flange 302 and the second metal flexible pipe 53. Since the second metal flexible pipe 53 does not have ventilation and liquid permeability, it is possible to prevent LNG in the LNG tank 200 from leaking into the chamber 300. Further, since the sealing member 54 seals between the connecting tube 51 and the first metal flexible tube 52, it is possible to prevent the purge gas in the chamber 300 from leaking out of the chamber 300.

As illustrated in FIG. 5, a weight 55 is connected to the second metal flexible tube 53. As a result, even if LNG flows in the LNG tank 200, fluctuations in the position of the second metal flexible pipe 53 are suppressed. As a result, the fluctuation of the temperature measurement position using the optical fiber 20 can be suppressed, and the decrease in the accuracy of the temperature measurement can be suppressed. The connection position of the weight 55 with respect to the second metal flexible pipe 53 is not particularly limited as long as it is in the LNG in the LNG tank 200, but is, for example, the second end of the second metal flexible pipe 53.

Since the outer wall of the first metal flexible pipe 52 and the inner wall of the second metal flexible pipe 53 are not fixed to each other and are slidable, the weight of the weight 55 is applied to the first metal flexible pipe 52. Is suppressed. As a result, even if the optical fiber 20 is caught on the inner wall of the first metal flexible tube 52, the weight of the weight 55 is suppressed from being applied to the optical fiber 20. As a result, transmission loss of the optical fiber 20 and disconnection of the optical fiber 20 are suppressed.

Since the first metal flexible tube 52 and the second metal flexible tube 53 are flexible and the optical fiber 20 is also flexible, the positions of the seal flange 301 and the seal flange 302 are not limited. The first metal flexible tube 52, the second metal flexible tube 53, and the optical fiber 20 can be inserted into the LNG tank 200 from outside the chamber 300.

Further, since the second metal flexible pipe 53 covering the first metal flexible pipe 52 does not have ventilation and liquid permeability, leakage of LNG or the like is suppressed even if the seal has a simple structure. can do. Further, since the optical fiber 20 can be replaced by pulling out the first metal flexible tube 52 from the inside of the second metal flexible tube 53, the optical fiber 20 can be easily replaced.

Further, the optical fiber 20 has a small diameter. Further, since the optical fiber 20 does not need to be energized, explosion-proof measures are not required, and an explosion-proof protective tube is not required. As a result, the first metal flexible pipe 52 and the second metal flexible pipe 53 do not need to have a large diameter. For example, the diameter of the second metal flexible pipe 53 can be 4 inches or less. In this case, the size of the holes formed in the LNG tank 200 can be reduced. Thereby, leakage and scattering of LNG and boil-off gas, and deterioration of heat insulating performance and the like can be suppressed.

Further, once the optical fiber 20, the first metal flexible tube 52 and the second metal flexible tube 53 are laid, the temperature of a plurality of measurement points in the depth direction of LNG can be measured without moving. For example, unlike a vibrating liquid densitometer, it is not necessary to move it up and down each time sampling is performed. Therefore, the number of times the optical fiber 20, the first metal flexible tube 52, and the second metal flexible tube 53 are moved up and down can be kept to a minimum. As a result, the pressure in the chamber 300 is stabilized even if the purge gas supply to the chamber 300 is stopped. As a result, leakage of gas in the chamber 300 can be suppressed.

Further, since the temperature of a plurality of measurement points can be measured by using the optical fiber 20, it is possible to measure at continuous measurement points in the depth direction and investigate the change with time. Therefore, it becomes easy to predict the stratification and rollover in the LNG tank 200. Further, the generation of boil-off gas can be minimized by efficient dispensing and stirring in the LNG tank 200.

The material of the weight 55 is not particularly limited as long as it does not react with LNG. The weight 55 is, for example, stainless steel. The weight 55 preferably does not have flexibility. The weight of the weight 55 is not particularly limited, but it is preferable that the weight 55 is within a range in which the second metal flexible pipe 53 does not break. The weight 55 has a higher density than LNG. The density of the material itself constituting the weight 55 is preferably higher than the density of the material itself constituting the second metal flexible tube 53. The second metal in the range of being immersed in the LNG, rather than the weight of the LNG equal to the total volume of the volume within the second metal flexible tube 53 and the volume of the weight 55 immersed in the LNG of the LNG tank 200. It is preferable that the total weight of the weight of the flexible tube 53 and the weight of the weight 55 is larger.

The first metal flexible tube 52 may have air permeability. For example, air permeability can be obtained by forming cuts or holes in the metal flexible tube. In this case, the purge gas in the chamber 300 fills the first metal flexible pipe 52, and water vapor is discharged. Therefore, freezing of water vapor is suppressed. In this case, since the purge gas enters the connecting tube 51, the leakage of the purge gas to the outside of the chamber 300 can be suppressed by sealing the first end of the connecting tube 51.

FIG. 10 is a diagram illustrating another example of a structure (optical fiber device) that protects the optical fiber 20. The points different from the structure of FIG. 9 will be described.

In this embodiment, the first metal flexible pipe 52 does not have ventilation and liquid permeability, but the second metal flexible pipe 53 has ventilation and liquid permeability. According to this configuration, LNG also penetrates into the second metal flexible pipe 53. As a result, the outer wall of the first metal flexible tube 52 is exposed to LNG, and the difference between the temperature of LNG and the temperature of the optical fiber 20 in the first metal flexible tube 52 becomes smaller. As a result, the temperature measurement accuracy is improved.

Since the second metal flexible pipe 53 has ventilation and liquid permeability, LNG may leak from the second metal flexible pipe 53 into the chamber 300. Therefore, in this embodiment, a structure for suppressing the leakage of LNG from the second metal flexible pipe 53 into the chamber 300 is provided.

As illustrated in FIG. 10, the second metal flexible pipe 53 is provided with ventilation and liquid permeability prevention measures for the portion of the second metal flexible pipe 53 extending from the LNG tank 200 to the chamber 300. For example, the film member 56 covers the outer periphery of the second metal flexible pipe 53 for the portion. The film member 56 is, for example, a film-like member such as PTFE (polytetrafluoroethylene) having durability against LNG.

Further, a seal member 57 is provided at the first end of the second metal flexible pipe 53. The sealing member 57 seals between the second metal flexible pipe 53 and the first metal flexible pipe 52. Further, a seal member 58 is provided so as to cover the seal member 57. The seal member 58 seals the second metal flexible pipe 53 and the seal member 57. By providing the sealing

members

57 and 58, it is possible to suppress the leakage of LNG from the second metal flexible pipe 53 into the chamber 300.

FIG. 11 is a diagram illustrating another example of a structure (optical fiber device) that protects the optical fiber 20. The points different from the structure of FIG. 10 will be described.

In this embodiment, both the first metal flexible pipe 52 and the second metal flexible pipe 53 have ventilation and liquid permeability. According to this configuration, LNG penetrates into the second metal flexible pipe 53, and further LNG penetrates into the first metal flexible pipe 52. As a result, the optical fiber 20 is exposed to LNG, and the difference between the temperature of the LNG and the temperature of the optical fiber 20 becomes small. As a result, the temperature measurement accuracy is improved.

Since the first metal flexible pipe 52 has ventilation and liquid permeability, LNG may leak from the first metal flexible pipe 52 into the chamber 300. Therefore, in this embodiment, a structure for suppressing the leakage of LNG from the first metal flexible pipe 52 into the chamber 300 is provided.

As illustrated in FIG. 11, the first metal flexible pipe 52 is provided with measures to prevent ventilation and liquid passage from the portion extending from the inside of the seal member 57 of the first metal flexible pipe 52 into the seal member 54. .. For example, a sealing member 59 is provided for the portion so as to cover the outer periphery of the first metal flexible tube 52 and seal between the first metal flexible tube 52 and the measuring fiber 23. With this structure, leakage of LNG from the first metal flexible tube 52 into the chamber 300 can be suppressed.

In Examples 1 to 3, the first end of the optical fiber 20 is connected to the temperature measuring device 10, and the second end of the optical fiber 20 is immersed in the LNG tank 200. However, as illustrated in FIG. 12, the optical fiber 20 passes through the first metal flexible tube 52, is folded back or wound in the LNG tank 200, and further passes through the first metal flexible tube 52 in temperature. It may be connected to the measuring device 10. Specifically, the first end and the second end of the optical fiber 20 are connected to the optical switch 33. The first metal flexible pipe 52 is inserted into the second metal flexible pipe 53 in the LNG tank 200 as in the first to third embodiments, but in FIG. 12, the second metal flexible pipe 53 is inserted. And the weight 55 are not shown. The optical switch 33 switches the emission destination (channel) of the optical pulse incident from the laser 31. In the double-ended system, the optical switch 33 can select the first end and the second end as the incident destinations of the optical pulses on the optical fiber 20 according to the instruction of the indicating unit 41. As a result, even if the optical fiber 20 breaks in the middle, the temperature can be continuously measured.

(Manufacturing method of optical fiber equipment)
FIG. 13 is a flow chart illustrating a method for manufacturing an optical fiber device. As illustrated in FIG. 13, a weight 55 is connected to the second end of the second metal flexible pipe 53 (step S1). Next, the second metal flexible pipe 53 is introduced into the LNG tank 200 by inserting the weight 55 into the seal flange 302 (step S2). Next, the first metal flexible tube 52 into which the measuring fiber 23 is inserted is inserted into the second metal flexible tube 53 (step S3).

According to this method, by connecting the weight 55 to the second metal flexible pipe 53, the position fluctuation of the second metal flexible pipe 53 can be suppressed. In this state, by inserting the first metal flexible tube 52 into which the measuring fiber 23 is inserted into the second metal flexible tube 53, the weight of the weight 55 is suppressed from being applied to the measuring fiber 23. At the same time, the measuring fiber 23 can be introduced into the LNG.

Although the examples of the present invention have been described in detail above, the present invention is not limited to the specific examples, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

10 Temperature measuring device 20 Optical fiber 21 Connecting fiber 22 Fusion sleeve 23 Measuring fiber 30 Measuring machine 40 Control unit 42 Temperature measuring unit 51 Connection tube 52 1st metal flexible tube 53 2nd metal flexible tube 54 Sealing member 55 Weight 56

Film member

57,58 Seal member 59 Seal member 100 Temperature measurement system

Claims

The first metal flexible tube into which the optical fiber is inserted,
The second metal flexible tube into which the first metal flexible tube is inserted and immersed in the liquid in the liquid tank, and the second metal flexible tube,
An optical fiber device having a density higher than that of the liquid and comprising a weight connected to the second metal flexible tube in the liquid.
The light according to claim 1, wherein the second metal flexible tube is provided from a chamber connected to the liquid tank to the inside of the liquid tank and does not have ventilation and liquid permeability. Fiber optics.
The chamber is purged with an inert gas.
The optical fiber device according to claim 2, wherein the first metal flexible tube is provided from the chamber to the inside of the liquid tank and has ventilation and liquid permeability.
The optical fiber device according to claim 1, wherein the second metal flexible tube has ventilation and liquid permeability in a portion of the liquid tank immersed in the liquid.
4. The second metal flexible tube is provided from a chamber connected to the liquid tank to the inside of the liquid tank, and does not have ventilation and liquid permeability in the chamber. The optical fiber apparatus according to.
The optical fiber device according to claim 5, wherein the first metal flexible tube has ventilation and liquid permeability.
The optical fiber apparatus according to any one of claims 1 to 6.
A temperature measuring system including a temperature measuring device for measuring the temperature of the liquid in the liquid tank from the detection result of backscattered light from the optical fiber.
The liquid is LNG and
The temperature measuring system according to claim 7, wherein the temperature measuring device includes a predicting unit that predicts the occurrence time of rollover of the liquid tank by using the measurement result of the temperature measuring device.
A second metal flexible tube to which a weight having a density higher than the density of the liquid is connected is introduced into the liquid tank in which the liquid is stored from the entrance of the liquid tank.
A method for manufacturing an optical fiber device, which comprises inserting a first metal flexible tube into which an optical fiber is inserted into the second metal flexible tube.