Cable interface optical fiber temperature sensor and monitoring method

Abstract

The invention provides a cable interface optical fiber temperature sensor and a monitoring method, the cable interface optical fiber temperature sensor comprises a protective shell, a cable interface and an optical fiber temperature sensor, and the cable interface is detachably arranged in the protective shell; a groove is formed in the protective shell, and the optical fiber temperature sensor is embedded in the groove; the optical fiber temperature sensor comprises a metal tube, a heat conduction layer and a Bragg fiber grating, and the metal tube is embedded in the groove; the heat conduction layer is arranged in the metal tube, the fiber Bragg grating is arranged in the heat conduction layer, one part of a grating area of the fiber Bragg grating is provided with a metal coating section, the other part of the grating area of the fiber Bragg grating is provided with a non-metal coating section, the metal coating section and the non-metal coating section respectively generate independent reflection peaks under the action of temperature, and the wavelength drift is calibrated, so that the wavelength drift of the fiber Bragg grating is calibrated. The optical fiber temperature sensor has the advantages of being good in anti-interference performance and high in precision stability, and the real-time performance and reliability of cable joint temperature monitoring are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system monitoring, in particular to a cable interface optical fiber temperature sensor and a monitoring method. BACKGROUND

[0002] In mountainous wind power and photovoltaic renewable energy projects, due to the distributed, long-distance and underground laying of cables, the operating environment is complex and has strong concealment, and the cable interface is the key part most prone to failure. Poor connection, insulation aging, thermal expansion and contraction and other factors can easily cause local overheating at the interface, and temperature rise is often the earliest manifestation of potential failure. Therefore, real-time monitoring of temperature changes at the cable interface is of great significance for early warning, assessment of cable operating status and prevention of major failures, and is a basic condition for safe and efficient operation of power stations.

[0003] The intelligent temperature monitoring system and method for ultra-high voltage cable joints disclosed in CN119880191A includes a temperature acquisition module, a wireless data processing module, a communication and transmission module, a remote monitoring and alarm module, and an auxiliary protection module. The temperature acquisition module includes a high-precision temperature sensor, a low-power microprocessor, and a wireless communication unit. The wireless data processing module includes a high-performance server, a data acquisition card, a data communication interface, and a data storage device installed in a data center. The communication and transmission module includes a wireless communication base station, optical fiber communication equipment, a router, a signal amplifier, an optical fiber transceiver, a network switch, and a repeater.

[0004] The existing intelligent temperature monitoring system for ultra-high voltage cable joints uses high-precision temperature sensors, but traditional electrical temperature sensors have weak anti-interference ability and poor precision stability in complex cable laying environments such as high electromagnetic interference, high humidity, and high voltage, affecting the real-time performance and reliability of cable joint temperature monitoring. SUMMARY

[0005] Therefore, the present application provides a cable interface optical fiber temperature sensor and a monitoring method, which has good anti-interference ability and high precision stability, and improves the real-time performance and reliability of cable joint temperature monitoring.

[0006] The technical solution of the present application is as follows: In a first aspect, the present application provides a cable interface optical fiber temperature sensor, which includes a protective shell, a cable interface, and an optical fiber temperature sensor.

[0007] The protective shell is hollow inside.

[0008] The cable interface is detachably arranged in the protective shell and extends out of the protective shell at both ends.

[0009] A groove is formed in the protective shell, and the fiber temperature sensor is embedded in the groove to detect the temperature of the cable interface.

[0010] The fiber temperature sensor comprises a metal tube, a heat-conducting layer and a Bragg fiber grating, wherein the metal tube is embedded in the groove and abuts against the surface of the cable interface; the heat-conducting layer is arranged in the metal tube, and the Bragg fiber grating is arranged in the heat-conducting layer; the metal tube transmits the heat of the cable interface to the Bragg fiber grating through the heat-conducting layer for temperature measurement.

[0011] Part of the grating region of the Bragg fiber grating is provided with a metal plating segment, and the other part is provided with a non-metal plating segment; the metal plating segment and the non-metal plating segment respectively generate independent reflection peaks under the action of temperature; the point temperature is demodulated by calibrating the wavelength drift.

[0012] On the basis of the above technical scheme, preferably, the protective shell comprises an upper shell, a lower shell and a plurality of fasteners, wherein,

[0013] The upper shell and the lower shell are oppositely arranged, and a plurality of threaded holes are formed in the relative positions of the upper shell and the lower shell; the plurality of threaded holes are centrally symmetrically arranged;

[0014] The upper shell and the lower shell are oppositely arranged, and a plurality of threaded holes are formed in the relative positions of the upper shell and the lower shell; the plurality of threaded holes are centrally symmetrically arranged;

[0015] The plurality of fasteners are respectively threadedly connected in the threaded holes, and are used for fixing the upper shell, the lower shell and the cable interface.

[0016] On the basis of the above technical scheme, preferably, the upper shell and the lower shell are oppositely arranged, and a plurality of annular limiting grooves are formed in the circumferential direction of the upper shell and the lower shell; the plurality of annular limiting grooves are uniformly arranged in the radial direction of the protective shell; a sealing ring is arranged in each annular limiting groove, and the sealing ring is sleeved on the outside of the cable interface to limit and seal the cable interface.

[0017] On the basis of the above technical scheme, preferably, the upper shell and the lower shell each comprise two fixed parts, an annular part and a reinforcing rib, wherein,

[0018] The two fixed parts are spaced apart, and the annular part and the reinforcing rib are fixed between the two fixed parts; the reinforcing rib is used for dispersing load;

[0019] A plurality of hollow grooves are formed in the outside of the annular part, and the reinforcing rib is located on the side of the annular part away from the cable interface and is spaced apart from the annular part to form a heat dissipation space.

[0020] On the basis of the above technical solutions, preferably, the number of the grooves is multiple, and the multiple grooves are arranged in the through holes of the upper shell and the lower shell and are arranged in parallel with the through holes, the multiple grooves are evenly distributed in a ring shape along the axis of the protective shell, and the optical fiber temperature sensors are embedded and fixed in the grooves.

[0021] On the basis of the above technical solutions, preferably, the grating regions of the multiple optical fiber temperature sensors are arranged in the corresponding metal pipes in sequence at equal intervals along the axial direction of the cable interface, and are used for collecting temperature information at different axial positions of the cable interface.

[0022] On the basis of the above technical solutions, preferably, the metal pipe is a metal copper pipe, the heat-conducting layer is a heat-conducting silica gel, the thermal conductivity is 0.5-5 W / (m·K), the constant-pressure heat capacity is 0.8-1.5 J / (mol·K), and the density is 1.8-2.5 g / cm 3 .

[0023] On the basis of the above technical solutions, preferably, the metal plating layer section is a metal nickel layer, and the plating layer has a thickness of 100-150 μm.

[0024] In a second aspect, the application further provides a monitoring method of a cable interface optical fiber temperature sensor, which is realized by using the cable interface optical fiber temperature sensor and includes the following steps:

[0025] S1, a transmission matrix method is used to model and simulate reflection spectrum behavior under a step strain condition, the grating is equivalently divided into multiple sub-grating sections with equal lengths, each sub-grating section is provided with corresponding axial strain and refractive index modulation depth according to the state of the plating layer;

[0026] S2, a 2*2 transmission matrix is established for each sub-grating section, which is used to represent the relationship between forward and backward propagation light fields in the current sub-grating section, and the transmission matrices of all the sub-grating sections are multiplied in sequence to obtain the total transfer matrix of the whole grating;

[0027] S3, the reflection spectrum under non-uniform strain is solved according to the total transfer matrix, the wavelengths of reflection peaks of the metal plating layer section and the non-metal plating layer section are obtained, and the corresponding plating layer length and thickness are determined and optimized to obtain the optical fiber temperature sensor 3;

[0028] S4, the optical fiber temperature sensor is experimentally calibrated, the actual wavelength drift of the two reflection peaks at different constant temperature points is measured, the measurement data is linearly fitted, and the temperature sensitivity coefficient of the non-metal plating layer section, the temperature sensitivity coefficient of the metal plating layer section and the initial reference wavelength at the reference temperature are calibrated;

[0029] S5. The reflection spectrum of the fiber optic temperature sensor is acquired in real time by a spectral demodulator. The wavelengths of the reflection peaks of the uncoated and metal-coated segments are extracted from the reflection spectrum. The drift of the two reflection peaks is calculated based on the difference between the wavelengths of the two reflection peaks and the corresponding initial reference wavelengths.

[0030] S6. Determine whether the current temperature field is abnormal based on the absolute value of the difference between the drift amounts of the two reflection peaks. Based on the determination result, select the corresponding calculation strategy to calculate the temperature at the measuring point.

[0031] Based on the above technical solution, preferably, step S6 includes: setting an abnormal threshold; comparing the absolute value of the difference between the offsets of the two reflection peaks with the abnormal threshold; if the absolute value of the difference between the offsets of the two reflection peaks is lower than the abnormal threshold, the current temperature field is determined to be uniform and normal; then the temperature at the measuring point is calculated by dividing the drift of any reflection peak by the corresponding temperature sensitivity coefficient; if the absolute value of the difference between the offsets of the two reflection peaks exceeds the abnormal threshold, the current temperature field is determined to be abnormal; then the temperature at the measuring point is calculated by dividing the absolute value of the difference between the offsets of the two reflection peaks by the absolute value of the difference between the two temperature sensitivity coefficients.

[0032] The cable interface fiber optic temperature sensor and monitoring method of the present invention have the following advantages over the prior art:

[0033] (1) By introducing a metal coating in the half region of the fiber grating, a non-uniform strain field is constructed, forming two independent reflection peaks. The distance between the two peaks changes significantly with slight temperature changes, greatly improving the ability to resolve small temperature gradients, and improving the sensor's thermal response speed and detection accuracy. At the same time, the metal coating and the non-metal coating have different thermal response characteristics, so by analyzing the difference in wavelength drift between the two peaks, the temperature change can be judged more accurately, improving the measurement accuracy and the reliability of anomaly detection.

[0034] (2) By using the set metal copper tube and thermally conductive silicone as the heat conduction medium, the metal copper tube can quickly conduct the surface temperature of the cable interface to the internal fiber optic grating, while the thermally conductive silicone ensures that the heat is evenly diffused around the grating, forming a stable thermal field environment, which greatly shortens the heat transfer path and improves the timeliness and accuracy of the temperature monitoring system.

[0035] (3) By uniformly arranging multiple fiber optic temperature sensors in a ring inside the cable interface structure and uniformly distributing them along the axial direction of the cable interface, a multi-point distributed temperature measurement layout is formed, which enables the synchronous acquisition of temperature changes at different measurement points and the monitoring coverage, which helps to improve the real-time assessment and safety early warning capabilities of the power interface operation status. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a perspective view of the cable interface fiber optic temperature sensor of the present invention;

[0038] Figure 2 This is a side view of the cable interface fiber optic temperature sensor of the present invention;

[0039] Figure 3 This is a front view of the cable interface fiber optic temperature sensor of the present invention;

[0040] Figure 4 This is a schematic diagram of the internal structure of the protective housing of the cable interface fiber optic temperature sensor of the present invention.

[0041] Figure 5 This is a cross-sectional view of the fiber optic temperature sensor for the cable interface of the present invention.

[0042] Figure 6 This is a schematic diagram of the Bragg fiber grating region of the fiber optic temperature sensor for the cable interface of the present invention.

[0043] Figure 7 This is a flowchart of the monitoring method for the cable interface fiber optic temperature sensor of the present invention. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] like Figures 1-6As shown, a fiber optic temperature sensor for a cable interface according to the present invention includes a protective housing 1, a cable interface 2, and a fiber optic temperature sensor 3. The protective housing 1 is hollow. The cable interface 2 is detachably disposed within the protective housing 1, with both ends extending outwards from within the protective housing 1. A groove 100 is formed within the protective housing 1, and the fiber optic temperature sensor 3 is embedded within the groove 100 for detecting the temperature of the cable interface 2. The fiber optic temperature sensor 3 includes a metal tube 31, a heat-conducting layer 32, and a Bragg fiber grating 33, wherein the metal tube 31 is embedded within the groove 100. The heat-conducting layer 32 is disposed inside the metal tube 31, and the Bragg fiber grating 33 is disposed inside the heat-conducting layer 32. The metal tube 31 transfers the heat from the cable interface 2 to the Bragg fiber grating 33 through the heat-conducting layer 32 for temperature measurement. A portion of the grating area of ​​the Bragg fiber grating 33 has a metal-coated section 331, and another portion has an uncoated section 332. The metal-coated section 331 and the uncoated section 332 generate independent reflection peaks under the action of temperature. The temperature of the measuring point is obtained by calibrating the wavelength drift and demodulating.

[0046] In this embodiment, the main protective shell 1 is made of epoxy resin composite material, which has excellent insulation, anti-aging and anti-ultraviolet capabilities. It can operate stably for a long time in outdoor environments ranging from -40℃ to 120℃, meets the IP67 waterproof and dustproof rating, and is suitable for harsh conditions such as power plants and mountainous areas.

[0047] In this embodiment, an efficient measurement of the temperature of the cable interface 2 is achieved by embedding an optical fiber temperature sensor 3, comprising a metal tube 31, a heat-conducting layer 32, and a Bragg fiber grating 33, within the protective housing 1. The metal tube 31 abuts against the surface of the cable interface 2, rapidly conducting heat, while the heat-conducting layer 32 further enhances heat conduction efficiency. The Bragg fiber grating 33 has a metal-coated section 331 on one half and an uncoated section 332 on the other, each generating independent reflection peaks under temperature. By calibrating the wavelength drift and demodulating the temperature at the measurement point, the temperature response sensitivity and measurement accuracy are significantly improved. This effectively solves the problems of lag response and difficulty in identifying local thermal anomalies in traditional sensors, while also enhancing the sensor's structural stability and environmental adaptability.

[0048] The protective housing 1 in this embodiment includes an upper housing 11, a lower housing 12, and a plurality of fasteners 13. The upper housing 11 and the lower housing 12 are arranged opposite to each other, and a plurality of threaded holes 110 are provided at the relative positions of the upper housing 11 and the lower housing 12. The plurality of threaded holes 110 are arranged in a centrally symmetrical manner. A through hole 120 is provided on the opposite side of the upper housing 11 and the lower housing 12 along its axial direction. The cable interface 2 abuts and seals between two through holes 120. The plurality of fasteners 13 are threaded into each of the threaded holes 110 to fix the upper housing 11, the lower housing 12, and the cable interface 2.

[0049] It should be noted that the protective shell 1 in this embodiment adopts a split design, consisting of an upper shell 11, a lower shell 12 and multiple fasteners 13. This structure achieves quick assembly and disassembly through modular combination, while meeting the dual requirements of sealing protection and fixing the cable interface 2.

[0050] In this embodiment, the upper housing 11 and the lower housing 12 are provided with a plurality of annular limiting grooves 130 along their circumferential direction, and the plurality of annular limiting grooves 130 are evenly arranged along the radial direction of the protective housing 1; each annular limiting groove 130 is provided with a sealing ring 4, and the sealing ring 4 is sleeved on the outside of the cable interface 2 to limit the cable interface 2 and form a seal.

[0051] It should be noted that the annular limiting groove 130 has a radius of 10.5 mm and a width of 0.5 mm, and the arc-shaped groove 100 has a radius of 0.55 mm, which is slightly larger than the radius of the metal tube 31. The metal tube 31 is a copper tube. The metal tube 31 is made of copper, which has a low coefficient of thermal expansion and excellent thermal conductivity. This improves the heat transfer efficiency while minimizing the mechanical stress interference caused by temperature changes on the fiber optic grating. Copper not only has excellent thermal conductivity and stable thermal response characteristics, but also has good processing performance and cost advantages, making it an ideal choice for large-scale manufacturing and widely used in high-precision thermal sensing structures.

[0052] In this embodiment, multiple evenly arranged annular limiting grooves 130 are provided circumferentially on opposite sides of the upper housing 11 and the lower housing 12, and a sealing ring 4 is installed in the groove and fitted onto the outside of the cable interface 2. This achieves precise positioning and sealing protection of the cable interface. The annular limiting grooves 130 prevent axial displacement of the cable interface 2 through mechanical constraints. At the same time, the sealing ring 4 undergoes elastic deformation under pressure to fill the assembly gap, forming an annular sealing barrier that effectively blocks the intrusion of water vapor and dust, significantly improving the operational reliability of the cable interface in complex environments.

[0053] In this embodiment, both the upper housing 11 and the lower housing 12 include two fixing parts 121, an annular part 122, and a reinforcing rib 123. The two fixing parts 121 are spaced apart, and the annular part 122 and the reinforcing rib 123 are fixed between the two fixing parts 121. The reinforcing rib 123 is used to distribute the load. The outer side of the annular part 122 is provided with several hollow grooves 140, and the reinforcing rib 123 is located on the side of the annular part 122 away from the cable interface 2 and is spaced apart from the annular part 122 to form a heat dissipation space.

[0054] It should be noted that the protective shell 1 adopts a design with a length × width × height of 120mm × 60mm × 40mm, and several hollow grooves 140 are arranged at equal intervals with a depth of 0.5.

[0055] It is understandable that the reinforcing ribs 123 enhance the load-bearing capacity of the device and distribute the load to ensure the stability of the device. At the same time, the several perforated grooves 140 opened on the outside of the annular part 122 help to achieve air convection and heat dissipation, prevent the cable interface from aging due to excessive local temperature, and improve the engineering practicality and service life of the temperature monitoring system.

[0056] In this embodiment, there are multiple grooves 100, and the multiple grooves 100 are respectively opened in the through holes 120 of the upper shell 11 and the lower shell 12, and are arranged parallel to the through holes 120. The multiple grooves 100 are evenly distributed in a ring along the axis of the protective shell 1, and each groove 100 is embedded and fixed with an optical fiber temperature sensor 3.

[0057] Furthermore, in this embodiment, the grating areas of multiple fiber optic temperature sensors 3 are arranged sequentially and at equal intervals in the corresponding metal tubes 31 along the axial direction of the cable interface 2, for collecting temperature information at different axial positions of the cable interface 2.

[0058] It should be noted that in this embodiment, there are four grooves 100, corresponding to four metal tubes 31. The four metal tubes 31 are symmetrically arranged on the upper shell 11 and the lower shell 12 and fixed with epoxy resin. Four optical fibers are arranged along the axial direction of the metal tubes 31 at positions 24mm, 48mm, 72mm and 96mm away from the outlet of the metal tubes 31, respectively, to collect temperature information at different axial positions of the cable interface 2. Through this multi-point distributed arrangement, spatial sensing of the temperature gradient in the cable interface area can be realized, effectively supporting the identification of local temperature rise anomalies and quantitative monitoring of changes in the zoned thermal field.

[0059] In this embodiment, four fiber optic temperature sensors 3 with integrated fiber Bragg gratings are evenly arranged in a ring inside the cable interface 2 structure to form a multi-point distributed temperature measurement layout. This structure can cover multiple key locations around the interface, enabling synchronous acquisition and comparative analysis of temperature changes at different measurement points. Compared with the traditional single-point temperature measurement method, it improves the monitoring coverage, temperature change response speed, and anomaly detection accuracy, which helps to improve the real-time assessment and safety early warning capabilities of the power interface operation status.

[0060] In this embodiment, the thermally conductive layer 32 is made of thermally conductive silicone, with a thermal conductivity of 0.5–5 W / (m·K), a constant-pressure heat capacity of 0.8–1.5 J / (mol·K), and a density of 1.8–2.5 g / cm³. 3 .

[0061] It should be noted that the Bragg fiber grating 33 adopts a tubular packaging, in which the Bragg fiber grating 33 is built into a metal tube 31 and then filled with a thermally conductive material to fix the Bragg fiber grating 33. The metal tube 31 has a radius of 0.5 mm and a length of 120 mm, and the radius of the Bragg fiber grating 33 is 0.0625 mm. The metal tube 31 is manufactured by a precision forming process and has a smooth inner wall, which can achieve a wrap-around protection for the Bragg fiber grating 33, effectively preventing it from being affected by mechanical stress such as compression, bending or vibration during installation or operation, thereby improving the structural stability and long-term reliability of the sensor.

[0062] In this embodiment, the thermally conductive layer 32 is made of thermally conductive silicone, which consists of a silicone matrix, thermally conductive microparticles, and a small amount of functional additives. To improve heat transfer performance, high thermal conductivity fillers such as alumina, silicon oxide, or silicon nitride are uniformly incorporated into the substrate. This not only significantly enhances the thermal conductivity of the material but also fully retains the excellent insulation properties and high-temperature resistance of silicone. The thermally conductive layer 32 has good thermal conductivity and insulation, which can effectively improve the system's heat dissipation efficiency and meet the actual needs for highly reliable thermally conductive materials.

[0063] In this embodiment, the metal plating segment 331 is a nickel layer, and the plating thickness is 100-150μm.

[0064] It should be noted that the fiber metallization process first requires the use of wire strippers to remove the coating layer from the fiber. Then, through processes such as activation, sensitization, chemical plating, and electroplating, a nickel layer is deposited on the surface of the fiber. The coating thickness is 100-150μm. After nickel plating, the fiber grating needs to be tested to ensure that the FBG has normal light intensity and center wavelength and is highly sensitive to temperature.

[0065] The metal coating of the Bragg fiber grating 33 refers to applying a metal coating to one half of the grating region while leaving the other half uncoated, designated as the metal-coated segment 331 and the uncoated segment 332. This embodiment introduces a nickel-plated metal layer into one half of the Bragg fiber grating 33 to construct a non-uniform strain field, achieving a bimodal response mechanism for the fiber grating's reflection spectrum. Compared to the traditional FBG structure, the spacing between the two peaks changes more significantly with slight temperature variations, thereby improving the ability to resolve minute temperature gradients. This effectively solves the problems of thermal response hysteresis and insensitivity to subtle temperature differences in traditional temperature sensors at high cable interface temperatures, providing technical support for early identification of localized overheating at the interface.

[0066] like Figure 7 As shown, in a second aspect, the present invention also provides a monitoring method for a cable interface fiber optic temperature sensor, which is implemented using a cable interface fiber optic temperature sensor and includes the following steps:

[0067] S1. The transmission matrix method is used to model and simulate the reflection spectrum behavior under step strain conditions. The grating is equivalently divided into multiple sub-grating segments of equal length. Each sub-grating segment has a corresponding axial strain and refractive index modulation depth according to the different states of the coating.

[0068] It should be noted that after the Bragg fiber grating 33 is metal coated, due to the difference in the thermal expansion coefficient and stress transmission mechanism of the material, non-uniform residual strain is often introduced in the grating axis. In order to analyze its influence, the grating of length L is equivalently divided into N sub-grating segments of length dL cascaded in sequence. Each sub-segment is subjected to different axial strains due to the different coating structures, thus forming a step-type or gradient-type non-uniform strain distribution as a whole.

[0069] In addition, strain nonuniformity will change the refractive index modulation characteristics of the grating, resulting in structural changes in its reflection spectrum. Specifically, the original single main reflection peak splits into two sub-peaks, forming a "twin peak" phenomenon. This spectral feature not only enhances the system's ability to perceive small strain changes and improves demodulation sensitivity, but also provides an effective means to characterize local strain states and nonuniform stress distribution.

[0070] S2, establish a 2×2 transmission matrix for each sub-grating segment to represent the relationship between the forward and backward propagating light fields in the current sub-grating segment, and multiply the transmission matrices of all sub-grating segments in sequence to obtain the total transmission matrix of the entire grating segment.

[0071] It should be noted that, in simulating the reflection spectral behavior under this step strain condition, the transfer matrix method is used for modeling and analysis. The relationship between the forward and backward propagating light fields in each sub-grating segment is described by constructing a 2×2 transfer matrix. The expression for the transfer matrix of the nth segment is:

[0072]

[0073] In the formula, dL is the length of each sub-grating segment; k n γ is the coupling coefficient of the nth segment; Δβ is the mismatch of the sub-grating of that segment; n Let be the complex propagation constant, where j is the imaginary unit, j 2 =-1; cosh() is the hyperbolic cosine function, defined as sinh() is the hyperbolic sine function, defined as follows:

[0074] Multiplying the transfer matrices of all sub-grating segments sequentially yields the total transfer matrix of the entire grating, expressed as: M = M1·M2……M N .

[0075] S3. Solve the reflection spectrum under non-uniform strain according to the total transfer matrix, obtain the wavelength of the reflection peak of the metal coating section 331 and the non-metal coating section 332, and optimize and determine the corresponding coating length and thickness to obtain the fiber optic temperature sensor 3.

[0076] It should be noted that the boundary conditions are set as follows: the amplitude of the forward light field at the input end is A0 = 1, and the amplitude of the reflected light field at the end is B. N =0, the total transfer matrix can be used to solve the output reflection spectrum, obtain the independent reflection peak wavelengths of the metal-coated segment 331 and the non-metal-coated segment 332, and determine the coating length and thickness through parameter optimization, so that the double peak spacing Δλ can reach more than 0.8nm in the temperature variation range of 0-50℃, which significantly improves the temperature resolution, effectively solves the problem of poor demodulation robustness of traditional single-peak FBG in complex thermal fields, and improves the temperature monitoring accuracy of cable interface.

[0077] S4. Perform experimental calibration on the fiber optic temperature sensor 3, measure the actual wavelength shift of the two reflection peaks at different constant temperature points, perform linear fitting on the measurement data, and calibrate the temperature sensitivity coefficient of the uncoated section 332, the temperature sensitivity coefficient of the metal-coated section 331, and the initial reference wavelength at the reference temperature.

[0078] It should be noted that the fiber optic temperature sensor 3 is arranged at the cable interface 2. When the temperature of the cable interface 2 rises, the heat is conducted to the fiber optic sensing area through the contact interface. The metal plating section 331 near the cable side has a high thermal conductivity and thermal expansion coefficient, which will generate a large axial strain after being heated and will transfer the strain to the fiber grating region, thereby causing the Bragg wavelength to drift.

[0079] The wavelength shift of the unplated segment 332 is expressed as:

[0080]

[0081] In the formula, is the coefficient of thermal expansion of quartz optical fiber. Thermo-optic coefficient;

[0082] The Bragg wavelength shift of the metal coating segment 331, due to the limitations imposed by the thermal expansion and mechanical effects of the metal layer, is expressed as follows:

[0083]

[0084] In the formula, a Ni ε is the coefficient of thermal expansion of nickel, ε is the contribution of axial stress caused by thermal strain, and p is the effective elastic coefficient.

[0085] For the non-metallic coating segment λ B1 :

[0086]

[0087] For the metal coating segment λ B2 :

[0088]

[0089] In the formula, ΔT represents the temperature change;

[0090] in, ε and p can be obtained in advance through experimental calibration or by looking up tables, and the formula can be further simplified to:

[0091] Δλ B1 =K1ΔT

[0092] Δλ B2 =K2ΔT

[0093] In the formula, K1 and K2 are the temperature sensitivity coefficients of the unplated and nickel-plated sections, respectively; K1>K2 reflects that the nickel-plated section is more sensitive to temperature.

[0094] S5. The reflection spectrum of the fiber optic temperature sensor 3 is acquired in real time by a spectral demodulator. The wavelengths of the reflection peaks of the uncoated and metal-coated segments are extracted from the reflection spectrum. The drift of the two reflection peaks is calculated based on the difference between the wavelengths of the two reflection peaks and the corresponding initial reference wavelengths.

[0095] The drift expression for the reflection peak in the non-metallic coating segment is: Δλ1=λ B1 -λ B1,0 The drift expression for the reflection peak in the metal coating segment is Δλ² = λ. B2 -λ B2,0 In the formula, λ B1,0 λ is the wavelength of the unplated segment at the reference initial temperature. B2,0 This represents the wavelength of the metal coating segment at the reference initial temperature.

[0096] S6. Determine whether the current temperature field is abnormal based on the absolute value of the difference between the drift amounts of the two reflection peaks. Based on the determination result, select the corresponding calculation strategy to calculate the temperature at the measuring point.

[0097] The system includes a preset anomaly threshold c. The absolute value of the difference between the offsets of the two reflection peaks is compared with the anomaly threshold. If the absolute value of the difference between the offsets of the two reflection peaks is lower than the anomaly threshold, the current temperature field is determined to be uniform and normal. The temperature at the measuring point is then calculated by dividing the drift of any reflection peak by the corresponding temperature sensitivity coefficient. If the absolute value of the difference between the offsets of the two reflection peaks exceeds the anomaly threshold, the current temperature field is determined to be abnormal. The temperature at the measuring point is then calculated by dividing the absolute value of the difference between the offsets of the two reflection peaks by the absolute value of the difference between the two temperature sensitivity coefficients.

[0098] If |(λ B1 -λ B1,0 )-(λ B2 -λ B2,0 If | ≤ c, then the temperature T at the measuring point is calculated by dividing the drift of any reflection peak by the corresponding temperature sensitivity coefficient. The expression is:

[0099]

[0100] If |(λ B1 -λ B1,0 )-(λ B2 -λ B2,0 If |>c, then the temperature at the measuring point is calculated by dividing the absolute value of the difference between the offsets of the two reflection peaks by the absolute value of the difference between the two temperature sensitivity coefficients. The expression is:

[0101] T = (Δλ2 - Δλ1) / (K2 - K1).

[0102] This embodiment sets regions with different thermal response characteristics on a single fiber Bragg grating, enabling the sensor to have a stronger ability to identify temperature changes at the monitoring point. Among them, the metal-coated section 331 has a faster thermal response speed, while the non-metal-coated section 332 has a relatively stable response. The two sections generate independent reflection peaks under the influence of temperature. By analyzing the difference in their wavelength drift, the actual temperature change at the monitoring point can be determined more accurately, thereby improving the measurement accuracy and the reliability of anomaly detection.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fiber optic temperature sensor with a cable interface, characterized in that, It includes a protective housing (1), a cable interface (2), and a fiber optic temperature sensor (3), wherein, The protective outer shell (1) is hollow inside; The cable interface (2) is detachably installed inside the protective housing (1), and both ends extend outward from inside the protective housing (1); A groove (100) is provided inside the protective housing (1), and an optical fiber temperature sensor (3) is embedded in the groove (100) to detect the temperature of the cable interface (2); The fiber optic temperature sensor (3) includes a metal tube (31), a heat-conducting layer (32), and a Bragg fiber grating (33). The metal tube (31) is embedded in a groove (100) and abuts against the surface of the cable interface (2). The heat-conducting layer (32) is disposed inside the metal tube (31), and the Bragg fiber grating (33) is disposed inside the heat-conducting layer (32). The metal tube (31) transfers the heat from the cable interface (2) to the Bragg fiber grating (33) through the heat-conducting layer (32) for temperature measurement. The Bragg fiber grating (33) has a metal-coated section (331) in one part and a non-metal-coated section (332) in another part. The metal-coated section (331) and the non-metal-coated section (332) generate independent reflection peaks under the action of temperature. The temperature of the measuring point is obtained by demodulation after calibrating the wavelength drift.

2. The fiber optic temperature sensor for cable interfaces as described in claim 1, characterized in that: The protective outer shell (1) includes an upper shell (11), a lower shell (12), and multiple fasteners (13), wherein, The upper shell (11) and the lower shell (12) are arranged opposite to each other, and multiple threaded holes (110) are provided at the relative positions of the upper shell (11) and the lower shell (12), and the multiple threaded holes (110) are arranged in a centrally symmetrical manner; The upper housing (11) and the lower housing (12) are provided with through holes (120) along their axial direction on opposite sides, and the cable interface (2) is abutted and sealed between the two through holes (120); Multiple fasteners (13) are threaded into each threaded hole (110) to fix the upper housing (11), the lower housing (12), and the cable interface (2).

3. The fiber optic temperature sensor for cable interfaces as described in claim 2, characterized in that: On the side opposite to the lower shell (12), the upper shell (11) is provided with a plurality of annular limiting grooves (130) along its circumferential direction, and the plurality of annular limiting grooves (130) are evenly arranged along the radial direction of the protective shell (1); each annular limiting groove (130) is provided with a sealing ring (4), and the sealing ring (4) is sleeved on the outside of the cable interface (2) to limit and seal the cable interface (2).

4. The fiber optic temperature sensor for cable interfaces as described in claim 2, characterized in that: Both the upper shell (11) and the lower shell (12) include two fixing parts (121), an annular part (122), and reinforcing ribs (123), wherein, The two fixing parts (121) are arranged at intervals, and the annular part (122) and the reinforcing rib (123) are both fixed between the two fixing parts (121). The reinforcing rib (123) is used to distribute the load. The outer side of the annular portion (122) is provided with several hollowed-out grooves (140), and the reinforcing ribs (123) are located on the side of the annular portion (122) away from the cable interface (2) and are spaced apart from the annular portion (122) to form a heat dissipation space.

5. The fiber optic temperature sensor for cable interfaces as described in claim 2, characterized in that: The number of grooves (100) is multiple, and the multiple grooves (100) are respectively opened in the through holes (120) of the upper shell (11) and the lower shell (12), and are arranged parallel to the through holes (120). The multiple grooves (100) are evenly distributed in a ring along the axis of the protective shell (1), and each groove (100) is embedded with a fixed fiber optic temperature sensor (3).

6. The fiber optic temperature sensor for cable interfaces as described in claim 5, characterized in that: The grating areas of multiple fiber optic temperature sensors (3) are arranged sequentially and at equal intervals in the corresponding metal tubes (31) along the axial direction of the cable interface (2) to collect temperature information at different axial positions of the cable interface (2).

7. The fiber optic temperature sensor for cable interfaces as described in claim 1, characterized in that: The metal tube (31) is a copper tube, and the heat-conducting layer (32) is thermally conductive silicone with a thermal conductivity of 0.5–5 W / (m·K), a constant-pressure heat capacity of 0.8–1.5 J / (mol·K), and a density of 1.8–2.5 g / cm³. 3 .

8. The fiber optic temperature sensor for cable interfaces as described in claim 1, characterized in that: The metal plating section (331) is a nickel layer with a thickness of 100-150 μm.

9. A monitoring method for a cable interface fiber optic temperature sensor, implemented using the cable interface fiber optic temperature sensor as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. The transmission matrix method is used to model and simulate the reflection spectrum behavior under step strain conditions. The grating is equivalently divided into multiple sub-grating segments of equal length. Each sub-grating segment is provided with corresponding axial strain and refractive index modulation depth according to the different states of the coating. S2, establish a 2×2 transmission matrix for each sub-grating segment to represent the relationship between the forward and backward propagating light fields in the current sub-grating segment, and multiply the transmission matrices of all sub-grating segments in sequence to obtain the total transmission matrix of the entire grating segment. S3, solve the reflection spectrum of the output under non-uniform strain according to the total transfer matrix, obtain the wavelength of the reflection peak of the metal coating section (331) and the non-metal coating section (332), and optimize and determine the corresponding coating length and thickness to obtain the fiber optic temperature sensor (3). S4, perform experimental calibration on the fiber optic temperature sensor (3), measure the actual wavelength shift of the two reflection peaks at different constant temperature points, perform linear fitting on the measurement data, and calibrate the temperature sensitivity coefficient of the uncoated section (332), the temperature sensitivity coefficient of the coated section (331), and the initial reference wavelength at the reference temperature. S5, the reflection spectrum of the fiber optic temperature sensor (3) is acquired in real time by the spectral demodulator, and the wavelengths of the reflection peaks of the non-metallic coating segment and the metallic coating segment are extracted from the reflection spectrum. The drift of the two reflection peaks is calculated based on the difference between the wavelengths of the two reflection peaks and the corresponding initial reference wavelengths. S6. Determine whether the current temperature field is abnormal based on the absolute value of the difference between the drift amounts of the two reflection peaks. Based on the determination result, select the corresponding calculation strategy to calculate the temperature at the measuring point.

10. The monitoring method of the fiber optic temperature sensor for cable interface as described in claim 9, characterized in that, Step S6 includes: setting an abnormal threshold; comparing the absolute value of the difference between the offsets of the two reflection peaks with the abnormal threshold; if the absolute value of the difference between the offsets of the two reflection peaks is lower than the abnormal threshold, the current temperature field is determined to be uniform and normal; then the temperature at the measuring point is calculated by dividing the drift of any reflection peak by the corresponding temperature sensitivity coefficient; if the absolute value of the difference between the offsets of the two reflection peaks exceeds the abnormal threshold, the current temperature field is determined to be abnormal; then the temperature at the measuring point is calculated by dividing the absolute value of the difference between the offsets of the two reflection peaks by the absolute value of the difference between the two temperature sensitivity coefficients.

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