An Actively Heated FBG Fiber Shield Tail Seal Detection Composite Sensor

Abstract

The present invention belongs to the technical field related to temperature-measuring optical fibers. It discloses an actively heated FBG optical fiber shield tail seal detection composite sensor, comprising a temperature-measuring optical fiber, a reinforcement assembly, a heating assembly, a high-temperature-resistant silicone gel filler, and an external protective device. The temperature-measuring optical fiber, the reinforcement assembly, and the heating assembly are arranged in a row, adjacent to each other, and together constitute the sensor's central component. The external protective device comprises an inner layer and an outer layer, the inner layer being used to encase the high-temperature-resistant silicone gel filler, and the outer layer being a high-thermal-conductivity sheath. The high-temperature-resistant silicone gel filler is filled between the inner layer and the central component. The present invention utilizes a self-insulating resistance wire for active heating, actively changing the temperature field of the medium surrounding the sensor. Due to the different heat absorption capacities of the leaking material and grease, an FBG optical fiber temperature sensor is used to collect temperature data at each measuring point after heating. The leaking area will show local temperature anomalies, thereby determining the sealing performance of the shield tail seal grease cavity.

Description

Technical Field

[0001] The present invention belongs to the technical field related to temperature measuring optical fibers, and more specifically, relates to an actively heated FBG optical fiber shield tail sealing detection composite sensor. Background Art

[0002] Bragg fiber grating sensors have many advantages, such as small size, easy integration and burial, high resolution and sensitivity, and resistance to interference and corrosion. Because they are made based on optical fibers, they can easily achieve quasi-distributed sensing and measurement, and their measurement range meets most engineering requirements, allowing them to be used in many fields such as aerospace, engineering testing, and medical equipment.

[0003] Because shield construction is carried out in an underground environment, it often faces complex environments such as rivers, lakes, seas, groundwater, and soft geological layers, making the shield tail sealing system prone to leakage. Existing technologies are still insufficient in the field of shield tail sealing system status monitoring. The commonly used grease cavity pressure monitoring system can only achieve real-time monitoring of the oil pressure (medium pressure) in the sealing cavity and timely replenishment of grease, but it cannot accurately determine whether mud and water have seeped into the grease cavity. Currently, there is a lack of endoscopic sensors in this field to monitor changes in the medium of the grease sealing cavity. It is impossible to monitor and warn in advance whether the shield tail seal has been penetrated by groundwater and soil and leaked. As a result, it is impossible to take effective remedial measures when the shield tail grease sealing cavity is completely penetrated and leaks occur.

[0004] Therefore, it is urgent to design an endoscopic fiber Bragg grating sensor to solve the technical problem of real-time detection of the shield tail sealing status. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides an actively heated FBG optical fiber shield tail seal detection composite sensor, the purpose of which is to monitor and warn whether the shield tail seal is penetrated by underground water and soil and leaks through endoscopic sensing, thereby solving the technical problem of real-time detection of the shield tail sealing status.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided an actively heated FBG optical fiber shield tail seal detection composite sensor, comprising a temperature measuring optical fiber 6, a reinforcement component 5, a heating component 4, a high-temperature resistant silicone gel filler 3 and an external protection device; the temperature measuring optical fiber 6, the reinforcement component 5, and the heating component 4 are arranged in a row and closely adjacent to each other, and together constitute the central component of the sensor; the external protection device comprises an inner layer 2 and an outer layer 1, the inner layer 2 is used to wrap the high-temperature resistant silicone gel filler 3, and the outer layer 1 is a high thermal conductivity sheath; the high-temperature resistant silicone gel filler 3 is filled between the inner layer 2 and the central component.

[0007] Preferably, the temperature measuring optical fiber 6 is of the type of FBG optical fiber, and a plurality of grating measuring points are evenly inscribed at equal intervals on the temperature measuring optical fiber 6 .

[0008] Preferably, the grating measurement points are spaced every 5° along the cross-section of the shield tail grease seal cavity. Each grating measurement point measures the ambient temperature and displays the data as wavelength data on the FBG fiber demodulator. FBG fiber has high sensitivity, and through multi-point detection, it can accurately measure changes in the ambient temperature field, facilitating the determination of external muddy water infiltration into the shield tail grease seal cavity and the location of the leak.

[0009] Preferably, the reinforcing component 5 is a high-strength metal reinforcing wire with a diameter of 1 mm. This high-strength metal reinforcing wire strengthens the overall structural rigidity of the composite sensor, prevents breakage of the FBG fiber due to bending and vibration, and facilitates the fixing of the central components. The 1 mm diameter facilitates control of the overall diameter of the composite sensor and facilitates its curved placement within the grease chamber being tested.

[0010] Preferably, the heating component 4 is configured as a self-insulating resistance wire heating belt, the cross section of which is circular and the diameter is 1 mm.

[0011] Preferably, the heating assembly is heated by connecting to an external power source. A self-heating temperature control switch is provided at the external power source to adjust the heating power and temperature. The heating power is set to 25W-40W per meter, and the heating temperature is set to no more than 40°C to prevent the grease from melting. By connecting to an external power source for heating, the temperature field of the composite sensor and the surrounding environment can be actively changed.

[0012] Preferably, the high-temperature-resistant silicone gel filler 3 uniformly wraps the temperature-sensing optical fiber 6, the reinforcing assembly 5, and the heating assembly 4, and serves to separate and secure these components. Its high-temperature resistance ensures that the filler does not melt easily during active heating, maintaining structural stability and achieving waterproof and shock-absorbing properties.

[0013] Preferably, the inner layer 2 is an aluminum-plastic armor layer made of aluminum alloy and having a thickness of 1 mm. The aluminum-plastic armor layer encases the core assembly and provides support, reducing the impact of external environmental stress on the temperature-sensing optical fiber. The aluminum-plastic armor layer has excellent thermal conductivity, allowing for rapid temperature equilibrium between the internal core assembly and the external environment.

[0014] Preferably, the outer layer 1 is a high-thermal-conductivity XLPE sheath with a thickness of 1 mm, made of cross-linked polyethylene, which can be used to protect the core components. Cross-linked polyethylene is a polymer material that transforms polyethylene molecules from a linear structure into a network structure through chemical or physical methods. By doping the material with metal oxide nanoparticles, the thermal conductivity of the sheath can be significantly improved. It has the characteristics of high temperature and high pressure resistance, wear resistance, high insulation resistance, lightweight, and excellent mechanical properties.

[0015] Preferably, the composite sensor 7 is annularly arranged in the shield tail grease sealing cavity 11 , closely attached to the inner surface of the shield shell 8 , and fixed on the shield tail brush pressure plate 10 .

[0016] In general, compared with the prior art, the above technical solution conceived by the present invention provides an active heating FBG optical fiber shield tail seal detection composite sensor with the following main features:

[0017] Beneficial effects:

[0018] 1. This invention, based on fiber grating (FBG) technology, pioneers the use of temperature measurement to design a composite sensor for detecting penetration in the shield tail grease sealing cavity. Quasi-distributed FBG fiber is used to measure the temperature of the grease sealing cavity. Multiple grating measurement points can be flexibly inscribed on the fiber structure based on the required shield diameter. Leveraging its high resolution, sensitivity, and strong anti-interference properties, this sensor rapidly detects changes in the sealing cavity's medium to determine leakage and its location. Testing is performed during pauses in shield tunneling, minimizing the impact of shield vibration and grease pressure changes within the sealing cavity on wavelength data, thereby improving detection accuracy.

[0019] 2. The composite sensor's core assembly incorporates a self-insulating resistance wire heater. This self-heating process actively changes the temperature field surrounding the sensor, enabling the identification of abnormal media within the sealing system. The composite sensor accurately controls the heating power to ensure that the surrounding temperature field is altered without affecting the performance of the grease.

[0020] 3. Aluminum alloy is used as the main material of the aluminum-plastic armor layer. The excellent thermal conductivity and ductility of aluminum alloy can not only quickly achieve the balance of the temperature field inside and outside the sensor, but also facilitate the bending and placement of the composite sensor in the grease-sealed cavity. The aluminum-plastic armor layer has certain strength and toughness, which plays a necessary protective role for the internal structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a structural schematic diagram of an actively heated FBG optical fiber shield tail seal detection composite sensor of the present invention;

[0022] Figure 2 This is a schematic diagram of the composite sensor of the present invention working in the shield tail grease sealing cavity;

[0023] Figure 3 This is a cross-sectional view of the shield tail grease sealing cavity where the composite sensor of the present invention is arranged;

[0024] Figure 4 This is a working data diagram of the composite sensor of the present invention in different media;

[0025] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0026] 1-outer shell; 2-inner shell; 3-high-temperature-resistant silicone gel filler; 4-heating component; 5-reinforcement component; 6-temperature measuring optical fiber; 7-composite sensor; 8-shield; 9-shield tail brush; 10-shield tail brush pressure plate; 11-shield tail grease sealing chamber; 12-pipe segment; 13-shield internal channel. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0028] The present invention discloses an active heating FBG optical fiber shield tail seal detection composite sensor, please refer to Figure 1 , including a temperature measuring optical fiber 6, a reinforcement component 5, a heating component 4, a high-temperature resistant silicone gel filler 3 and an external protection device; the temperature measuring optical fiber 6, the reinforcement component 5, and the heating component 4 are arranged in a row and closely together to constitute the central component of the sensor; the external protection device includes an inner layer 2 and an outer layer 1, the inner layer 2 is used to wrap the high-temperature resistant silicone gel filler 3, and the outer layer 1 is a high thermal conductivity sheath; the high-temperature resistant silicone gel filler 3 is filled between the inner layer and the central component.

[0029] The temperature-measuring fiber 6 is an FBG fiber, with multiple grating measurement points uniformly inscribed on the fiber structure. These grating measurement points are placed every 5° across the cross-section of the shield tail grease-sealed cavity. Each grating measurement point measures the ambient temperature, which is displayed as wavelength data on the FBG interrogator. FBG fiber's high sensitivity allows for precise measurement of changes in the ambient temperature field through multi-point detection, facilitating the determination of external muddy water infiltration into the shield tail grease-sealed cavity and the location of any leaks.

[0030] Reinforcement component 5 is a high-strength metal wire with a diameter of 1 mm. This wire strengthens the overall structural rigidity of the composite sensor, prevents breakage of the FBG fiber due to bending and vibration, and facilitates the securing of the central components. Its thickness of 1 mm facilitates control of the overall diameter of the composite sensor, making it easier to bend and deploy the composite sensor within the grease chamber being tested.

[0031] Heating element 4 is a self-insulating resistance wire heating tape with a circular cross-section and a diameter of 1mm. The heating element is heated by connecting to an external power source. A self-heating temperature control switch is provided at the external power source to adjust the heating power and temperature. The heating power is set between 25W and 40W per meter, and the heating temperature is set to no more than 40°C to prevent grease from melting. By connecting to an external power source for heating, the temperature field between the composite sensor and the surrounding environment can be actively altered.

[0032] A high-temperature-resistant silicone gel filler 3 uniformly wraps the temperature-sensing optical fiber 6, the reinforcement assembly 5, and the heating assembly 4, separating and securing them. Its high-temperature resistance prevents the filler from melting during active heating, maintaining structural stability and providing waterproof and shock-absorbing properties. Furthermore, the filler reduces friction between the central assembly and the external protective device, minimizing the risk of wear on the composite sensor.

[0033] Inner layer 2 is an aluminum-plastic armor layer made of aluminum alloy with a thickness of 1mm. This layer wraps around the core assembly and provides support, reducing the impact of external environmental stress on the temperature-sensing optical fiber. The thermal conductivity of solid aluminum is 237W / (m·K), while that of aluminum alloy is 121-151W / (m·K), far exceeding that of common ferrous metals. Therefore, the aluminum-plastic armor layer offers excellent thermal conductivity, enabling rapid temperature equilibrium between the core assembly and the external environment.

[0034] Outer layer 1 is a high-thermal-conductivity XLPE sheath with a thickness of 1mm. Made of cross-linked polyethylene, it protects the internal core components and prevents external grease and liquids from penetrating the composite sensor, enhancing its safety. Cross-linked polyethylene is a polymer material whose linear molecular structure is transformed into a network structure through chemical or physical methods. The addition of metal oxide nanoparticles significantly improves the sheath's thermal conductivity, resulting in high-temperature and high-pressure resistance, wear resistance, high insulation resistance, lightweight design, and excellent mechanical properties.

[0035] During the use of the composite sensor in this embodiment, please refer to Figure 2After the shield tail brush is welded and before the sealing grease is injected, the composite sensor is arranged in a ring shape in each grease sealing cavity. A composite sensor is arranged in each grease cavity and connected to a portable FBG fiber demodulator and a self-heating temperature control switch through the internal channel of the shield shell. After the composite sensor is arranged in the grease cavity, the FBG fiber demodulator is debugged and heated to ensure the normal operation of each grating measuring point. After the sealing grease is injected, the shield machine starts to advance. After each 30-50 rings of shield advancement, the shield is paused and the self-heating temperature control switch of the sensor is turned on to start heating. After a period of time, the power is turned off and the heating is stopped, and the sensor is allowed to cool down naturally. During the heating and cooling process, the wavelength change data of each grating measuring point is collected, and the leakage in the grease cavity is judged based on the abnormal data.

[0036] For the placement of the composite sensor in this embodiment within the shield, please refer to Figure 3 The shield tail grease sealing cavity 11 is located between the shield shell 8 and the pipe segment 12. The composite sensor 7 is independently arranged in a ring shape in each shield tail grease sealing cavity 11, close to the inner surface of the shield shell 8, and fixed on the shield tail brush pressure plate 10, and connected to the external power supply and FBG optical fiber demodulator through the internal channel 13 of the shield shell.

[0037] The working data of the composite sensor in this embodiment obtained in different media environments can be found in Figure 4 The sensor was heated from room temperature to 40°C in air, pure grease, slurry, and pure water environments, and wavelength data was recorded during the heating and cooling processes. Due to the different environmental media, the grating wavelength change values ​​showed significant differences. This example analyzed the wavelength data of the optical fiber during the test and compared it with the wavelength data of the control group to identify temperature anomalies during the sensor's heating and cooling processes. This allowed the determination of changes in the grease seal chamber medium and the location of leaks.

[0038] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An actively heated FBG optical fiber shield tail seal detection composite sensor, characterized by: The sensor comprises a temperature measuring optical fiber (6), a reinforcing component (5), a heating component (4), a high-temperature resistant silicone gel filler (3) and an external protective device; the temperature measuring optical fiber (6), the reinforcing component (5) and the heating component (4) are arranged in a row and closely adjacent to each other, and together constitute the central component of the sensor; the external protective device comprises an inner layer (2) and an outer layer (1), the inner layer (2) is used to wrap the high-temperature resistant silicone gel filler (3), and the outer layer (1) is a high thermal conductivity sheath; the high-temperature resistant silicone gel filler (3) is filled between the inner layer (2) and the central component; The temperature measuring optical fiber (6) is of the type of FBG optical fiber, and a plurality of grating measuring points are evenly inscribed at equal intervals on the temperature measuring optical fiber (6); The spacing of the grating measuring points is set to: a grating measuring point is arranged every 5° along the cross section of the shield tail grease sealing cavity; each grating measuring point can measure the ambient temperature and present it in the form of wavelength data on the FBG fiber demodulator; The reinforcing component (5) is configured as a high-strength metal reinforcing wire; The heating component (4) is configured as a self-insulating resistance wire heating belt; The inner layer (2) is configured as an aluminum-plastic armor layer; The outer layer (1) is provided as a high thermal conductivity XLPE sheath, which is made of cross-linked polyethylene and can be used to protect the central component.

2. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The heating component is heated by connecting to an external power supply. A heating temperature control switch is provided at the external power supply to adjust the heating power and heating temperature. The heating power is set to 25W-40W per meter, and the heating temperature is set to no more than 40°C to avoid melting of the grease.

3. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The high-temperature resistant silicone gel filler (3) uniformly wraps the temperature measuring optical fiber (6), the reinforcing component (5), and the heating component (4), and is used to separate and fix the temperature measuring optical fiber (6), the reinforcing component (5), and the heating component (4) from each other.

4. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The composite sensor (7) is arranged in a ring shape in the shield tail grease sealing cavity (11), closely attached to the inner surface of the shield shell (8), and fixed on the shield tail brush pressure plate (10).

5. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The diameter of the reinforcement component (5) is 1 mm.

6. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The diameter of the heating component (4) is 1 mm.

7. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The thickness of the inner layer (2) is 1 mm.

8. The active heating FBG optical fiber shield tail seal detection composite sensor according to claim 1, characterized in that: The thickness of the outer layer (1) is 1 mm.

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