Carbon dioxide micro-leakage monitoring system and method for confined space stratum freezing system

Abstract

The invention discloses a carbon dioxide micro-leakage monitoring system and method for a confined space stratum freezing system, and relates to a light source, a plurality of long-period fiber grating sensors, a spectrum demodulator and a data processing module, and the light source provides a broadband light signal; the plurality of long-period fiber grating sensors are respectively deployed in high-risk areas where leakage occurs, are respectively communicated with the light source, and are connected to the spectrum demodulator through an optical fiber network; the spectrum demodulator demodulates the resonant wavelength drift to generate carbon dioxide gas concentration data; the data processing module extracts leakage signals through dynamic background calibration and concentration gradient analysis according to carbon dioxide gas concentration data generated by the spectrum demodulator. According to the scheme, high-sensitivity gas detection is realized on the basis that the LPFG is matched with the functional coating, and the problems in the prior art can be effectively solved.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide ground freezing technology, and in particular to a carbon dioxide micro-leakage monitoring technology for a closed space ground freezing system. Background Art

[0002] Carbon dioxide ground freezing technology is a new freezing method that uses liquid carbon dioxide as a refrigerant, leveraging its low-temperature properties and latent heat of phase change to achieve rapid ground freezing. However, in actual operation, liquid carbon dioxide may leak through pipelines, valves, and interfaces, leading to the following problems:

[0003] 1. Safety hazards: Carbon dioxide leakage may lead to localized excessive concentrations, causing the risk of suffocation or poisoning in confined spaces;

[0004] 2. Decreased project efficiency: Leakage weakens freezing efficiency, increases construction costs, and may even cause the freezing system to fail;

[0005] 3. Monitoring complexity: The construction environment is characterized by high humidity, high dust content, and interference from mechanical vibration and strong light. Traditional monitoring equipment is unable to operate stably and for a long time in such a complex environment.

[0006] Existing CO2 leak detection technologies include non-dispersive infrared (NDIR) sensors, ultrasonic detection, helium leak detection, and flow monitoring. While these technologies are effective in certain scenarios, they have significant limitations in complex construction environments.

[0007] Existing carbon dioxide leakage monitoring technology has the following major problems in complex construction environments:

[0008] 1. Insufficient sensitivity: The sensitivity of NDIR sensors decreases significantly in high humidity environments, making it difficult to detect trace leaks at the ppm level. Flow monitoring methods can only detect larger leaks and are powerless against trace leaks.

[0009] 2. Poor anti-interference ability: Humidity, dust and mechanical vibration can easily interfere with sensor signals, resulting in false alarms or missed alarms;

[0010] Carbon dioxide exhaled by construction workers, direct sunlight, and fluctuations in ambient temperature and humidity may interfere with monitoring equipment and affect measurement accuracy.

[0011] 3. Insufficient real-time performance: The helium detection method requires a complex operating process and is only suitable for single detection, and cannot achieve real-time monitoring;

[0012] The flow monitoring method has a long response time and is difficult to detect leaks in a timely manner.

[0013] 4. Poor adaptability to the construction environment: The sensor surface coating is easily affected by humidity, dust and corrosive gases, shortening its service life;

[0014] Ambient light may interfere with the fiber optic sensor signal and reduce the reliability of the monitoring system.

[0015] 5. Limited coverage: Point monitoring technologies such as NDIR and ultrasonic cannot cover large areas and cannot accurately locate leaks.

[0016] It can be seen that providing a carbon dioxide micro-leakage monitoring solution for a confined space ground freezing system with high monitoring accuracy and strong environmental adaptability is an issue that needs to be urgently addressed in this field. Summary of the Invention

[0017] In response to the problems existing in the existing carbon dioxide leakage monitoring technology during the carbon dioxide ground freezing construction process, the purpose of the present invention is to provide a carbon dioxide micro-leakage monitoring system and method for a confined space ground freezing system based on a long-period fiber grating sensor. By achieving high-sensitivity gas detection based on LPFG and functionalized coating, the problems existing in the existing technology can be effectively overcome.

[0018] In order to achieve the above-mentioned purpose, the present invention provides a carbon dioxide micro-leakage monitoring system for a confined space ground freezing system, comprising a light source, a plurality of long-period fiber grating sensors, a spectrum demodulator, and a data processing module.

[0019] The light source provides a broadband optical signal; a plurality of long-period fiber grating sensors are respectively deployed in high-risk areas for leakage, are respectively connected to the light source, and are connected to a spectrum demodulator via an optical fiber network; the spectrum demodulator demodulates the resonant wavelength drift to generate carbon dioxide gas concentration data; and the data processing module extracts leakage signals from the carbon dioxide gas concentration data generated by the spectrum demodulator through dynamic background calibration and concentration gradient analysis.

[0020] Furthermore, the long-period fiber grating sensor is coated with a transparent protective coating outside the sensitive coating.

[0021] Furthermore, the spectrum demodulator is composed of a signal acquisition module, a demodulation module and a concentration calculation module;

[0022] The signal acquisition module is used to collect the spectral signal output by the LPFG and capture the drift position of the resonant wavelength;

[0023] The demodulation module uses the fast Fourier transform method to accurately identify the peak position of the spectral signal collected by the signal acquisition module and determine the resonant wavelength drift;

[0024] The concentration calculation module interacts with the demodulation module data, and converts the wavelength drift value obtained by demodulation into carbon dioxide concentration data according to the relationship curve between wavelength drift and carbon dioxide gas concentration (C=f(Δλ)) calibrated in advance.

[0025] Furthermore, when performing dynamic background calibration, the data processing module calibrates the real-time monitored carbon dioxide gas concentration data using the background value of normal fluctuations in the environment to form a corrected carbon dioxide gas concentration value.

[0026] Furthermore, the data processing module locates the specific location of carbon dioxide leakage by calculating the concentration change between adjacent sensors when performing concentration gradient analysis.

[0027] Furthermore, the monitoring system also includes an alarm and linkage module, which interacts with the data processing module to trigger an alarm and initiate protective measures when it detects that the carbon dioxide gas concentration exceeds the standard.

[0028] In order to achieve the above-mentioned object, the present invention provides a method for monitoring carbon dioxide micro-leakage in a confined space ground freezing system based on a long-period fiber grating sensor. The detection method comprises:

[0029] (1) deploying long-period fiber grating sensors in high-risk areas of leakage, connecting the deployed long-period fiber grating sensors to light sources, and connecting them to a spectrum demodulator through an optical fiber network;

[0030] (2) A broadband optical signal is generated by a light source to excite a long-period fiber Bragg grating sensor;

[0031] (3) Demodulating the resonant wavelength drift by a spectrum demodulator to generate carbon dioxide gas concentration data;

[0032] (4) Extracting leakage signals from the carbon dioxide gas concentration data generated by the spectrum demodulator through dynamic background calibration and concentration gradient analysis;

[0033] (5) When the carbon dioxide gas concentration is detected to be above the standard, an alarm is triggered and protective measures are initiated.

[0034] Furthermore, the step (3) of demodulating the resonant wavelength drift to generate carbon dioxide gas concentration data comprises the following steps:

[0035] Signal acquisition: Collect the spectral signal output by the LPFG to capture the drift position of the resonant wavelength;

[0036] Spectral signal demodulation: Using the fast Fourier transform method, the peak position in the spectral signal is accurately identified to determine the resonant wavelength drift;

[0037] Concentration calculation: According to the pre-calibrated relationship curve between wavelength drift and carbon dioxide gas concentration, the wavelength drift value obtained by demodulation is converted into carbon dioxide concentration data.

[0038] Furthermore, when the dynamic background calibration is performed in step (4), the real-time monitored carbon dioxide gas concentration data is calibrated by the background value of normal fluctuations in the environment to form a corrected carbon dioxide gas concentration value.

[0039] Furthermore, when performing the concentration gradient analysis in step (4), the specific location of the carbon dioxide leakage is located by calculating the concentration change between adjacent sensors.

[0040] The carbon dioxide micro-leakage monitoring solution for a confined space ground freezing system based on a long-period fiber grating sensor provided by the present invention has the following advantages over the prior art:

[0041] (1) The present invention is based on LPFG technology and achieves high-sensitivity gas detection through functionalized coatings;

[0042] (2) The solution of the present invention covers a large area through a distributed sensor network, achieving accurate positioning of the leakage point;

[0043] (3) The solution of the present invention can improve the environmental adaptability of the sensor and can work stably for a long time in a high humidity and high dust environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0045] Figure 1 This is a schematic diagram of the overall structure of the carbon dioxide micro-leakage monitoring system for the confined space ground freezing system of the present invention;

[0046] Figure 2 This is an example diagram of the structure of the long-period fiber grating (LPFG) sensor in the present invention. DETAILED DESCRIPTION

[0047] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific illustrations.

[0048] To address the problem of carbon dioxide leakage monitoring in a closed construction environment, the present invention innovatively adopts a long-period fiber grating (LPFG) sensor. Through its high sensitivity to changes in the surrounding refractive index, it further combines functionalized sensitive coatings and dynamic signal processing technology to achieve real-time detection of changes in carbon dioxide concentration.

[0049] See also Figure 1, which is a schematic diagram of the structure of the carbon dioxide micro-leakage monitoring system for the closed space ground freezing system provided by the present invention.

[0050] Based on the diagram, the carbon dioxide micro-leakage monitoring system 100 is mainly composed of a light source 110, a plurality of long-period fiber grating sensors (hereinafter referred to as LPFG) 120, a spectrum demodulator 130, a data processing module 140 and an alarm and linkage module 150.

[0051] The light source 110 can provide a broadband optical signal for exciting the LPFG 120. The specific structure of the light source 110 is not limited here and can be determined according to actual needs.

[0052] The LPFG 120 in this system is used to measure changes in carbon dioxide concentration. In a closed construction environment, several LPFGs 120 are deployed in high-risk areas for leakage, each connected to a light source and connected to the optical spectrum demodulator 130 via an optical fiber network.

[0053] The LPFG 120 used in the present invention is an optical fiber structure whose core refractive index is periodically modulated along the optical fiber axis, capable of coupling the transmission mode into the optical fiber cladding mode, and the resonant wavelength is extremely sensitive to changes in the refractive index of the surrounding environment.

[0054] See also Figure 2 , which shows an example of the structure of the LPFG 120 used in the present invention.

[0055] As shown in the figure, the LPFG 120 mainly comprises an optical fiber substrate 121 and a functionalized sensitive coating 122 coated on the optical fiber substrate 121 .

[0056] The structure of the optical fiber matrix 121 in the LPFG 120 is not limited here and can be determined according to actual needs.

[0057] Here, the functionalized sensitive coating 122 coated on the optical fiber substrate 121 is used to adsorb carbon dioxide molecules. After the functionalized sensitive coating 122 adsorbs CO2, its refractive index changes, which will cause the resonant wavelength of the LPFG to drift.

[0058] Specifically, the functionalized sensitive coating 122 is preferably formed of metal organic framework materials MOFs.

[0059] In order to ensure the long-term stability of the functionalized sensitive coating formed on the metal-organic framework material MOFs in complex environments (such as high humidity and high dust), the metal-organic framework material MOFs first specifically adopts MOFs materials with high selective adsorption of carbon dioxide, such as ZIF-8 and MIL-101, and enhances the adsorption performance by introducing functional groups such as amino and hydroxyl groups; on this basis, the solution spin coating method and self-assembly technology are used for the formed metal-organic framework material MOFs to ensure the uniformity and stability of the coating on the optical fiber surface, and optimize the coating thickness (500nm-1μm) to improve sensitivity.

[0060] The functionalized sensitive coating 122 configured in this manner effectively realizes high-sensitivity gas detection, and specifically can realize accurate detection of trace leaks at the ppm level.

[0061] As a further optimization setting, the solution of the present invention further coats a transparent protective coating on the outer surface of the functional sensitive coating 122 of the LPFG 120. The transparent protective coating has gas permeability and can isolate humidity and dust interference without affecting the diffusion of carbon dioxide molecules.

[0062] The transparent protective coating is specifically formed of polydimethylsiloxane (PDMS). The transparent protective coating thus formed has a high transmittance to carbon dioxide molecules and excellent hydrophobicity (contact angle > 100°), which can effectively isolate humidity interference.

[0063] Furthermore, in order to effectively cooperate with the functionalized sensitive coating 122, the transparent protective coating is coated on the surface of the functionalized sensitive coating 122 by spin coating, and the thickness is controlled at 10-20 μm, thereby ensuring a balance between gas diffusion efficiency and mechanical protection performance.

[0064] At the same time, after being coated on the surface of the functional sensitive coating 122, the transparent protective coating needs to be cured, which is done by heating at 80°C for 2 hours to ensure that the coating surface is smooth and firmly adhered.

[0065] The resulting transparent protective coating's gas permeability ensures rapid diffusion of carbon dioxide molecules onto the MOF surface, resulting in a response time of less than 1ms. Its hydrophobic and dust-resistant properties prevent moisture and dust from affecting sensor sensitivity. The coating's mechanical strength and chemical stability extend the sensor's lifespan, ensuring long-term operation in high-humidity, high-dust environments.

[0066] Based on this transparent protective coating, the moisture resistance, dust resistance and corrosion resistance of the sensitive coating can be effectively enhanced, ensuring long-term stable operation, thereby improving the environmental adaptability of the entire LPFG.

[0067] The optical spectrum demodulator 130 in this system is connected to the LPFG 120 deployed on site through a corresponding optical fiber sensing network. It demodulates the resonant wavelength drift of the optical signal generated by each LPFG 120 and calculates the gas concentration data based on it.

[0068] Specifically, the spectrum demodulator 130 realizes real-time demodulation of the resonance wavelength drift through a high-resolution spectrum analysis method.

[0069] The spectrum demodulator 130 is mainly composed of a signal acquisition module, a demodulation module and a concentration calculation module;

[0070] The signal acquisition module collects the spectral signal output by the LPFG and captures the shift in the resonant wavelength. This spectral signal is generated by a broadband optical signal from a light source stimulating a long-period fiber grating (LPFG) sensor. Carbon dioxide molecules adsorbed on the LPFG's functionalized coating change the refractive index of the surrounding environment, causing a shift in the resonant wavelength (Δλ), which in turn generates the corresponding spectral signal.

[0071] The demodulation module uses the fast Fourier transform (FFT) method to accurately identify the peak position of the spectral signal collected by the signal acquisition module and determine the resonant wavelength drift (Δλ).

[0072] Furthermore, the demodulation module adopts interpolation fitting technology (such as Gaussian fitting) during the demodulation process to further improve the resolution and accuracy of wavelength drift demodulation.

[0073] The concentration calculation module interacts with the demodulation module data, and converts the wavelength drift value obtained by demodulation into carbon dioxide concentration data based on the pre-calibrated relationship curve between wavelength drift and carbon dioxide gas concentration (C=f(Δλ)).

[0074] The calibration curve here is fitted by multiple sets of concentration calibration points in a laboratory environment to ensure the accuracy of concentration calculation.

[0075] This spectrum demodulator uses high-resolution spectrum analysis technology to achieve real-time demodulation of resonant wavelength drift, specifically including the following steps:

[0076] Optical signal input: A broadband optical signal from a light source excites a long-period fiber Bragg grating (LPFG) sensor. Carbon dioxide molecules adsorbed on the LPFG's functionalized coating change the refractive index of the surrounding environment, causing a shift in the resonant wavelength (Δλ).

[0077] Signal acquisition: The spectral signal output by the LPFG is collected through a demodulator to capture the drift position of the resonant wavelength.

[0078] Spectral signal demodulation: The Fast Fourier Transform (FFT) method is used to accurately identify the peak position in the spectral signal and determine the resonant wavelength drift (Δλ). Interpolation fitting techniques (such as Gaussian fitting) are used in the demodulation process to further improve the resolution and accuracy of wavelength drift demodulation.

[0079] Concentration Calculation: The demodulated wavelength shift is converted into CO2 concentration data based on a pre-calibrated curve (C = f(Δλ)) that plots wavelength shift against CO2 concentration. This calibration curve is fitted using multiple concentration calibration points in a laboratory environment to ensure accurate concentration calculations.

[0080] The spectrum demodulator formed based on this acquires and demodulates the resonant wavelength drift value of LPFG in real time, matches the demodulation result (Δλ) with the calibration curve, and outputs high-precision carbon dioxide gas concentration data.

[0081] The spectrum demodulator transmits the generated concentration data to the data processing module 140 , which further extracts and processes the leakage signal in combination with a dynamic background calibration algorithm and concentration gradient analysis.

[0082] The data processing module 140 in this system is data-connected to the optical spectrum demodulator 130 , and is used to perform dynamic background calibration and concentration gradient analysis on the carbon dioxide gas concentration data calculated by the optical spectrum demodulator 130 to extract leakage signals.

[0083] Specifically, the data processing module 140 is mainly composed of a dynamic background calibration submodule and a concentration gradient analysis submodule.

[0084] Among them, the dynamic background calibration submodule is used to adjust the baseline concentration of the monitoring system in real time to eliminate environmental interference signals.

[0085] This dynamic background calibration submodule constructs a background value of normal fluctuations in the environment for the carbon dioxide gas concentration data calculated by the spectral demodulator 130. On this basis, the background value of normal fluctuations in the environment is deducted from the real-time monitored carbon dioxide gas concentration data, thereby calibrating the real-time monitored carbon dioxide gas concentration data and extracting the real changes in the leakage signal.

[0086] As a further explanation, the dynamic background calibration submodule calibrates the real-time monitored carbon dioxide gas concentration data through the following calculation process:

[0087] First, the background concentration is calculated by the sliding window method: the dynamic background calibration submodule extracts the minimum or average value of each LPFG in the window as the dynamic background concentration (C baseline ).

[0088] Next, signal correction is performed: the real-time measurement value (C measured ) minus the background concentration to obtain the corrected concentration (C relative ):

[0089] C relative =C measured -C baseline ;

[0090] C relative : Corrected concentration value for further analysis;

[0091] C measured : The carbon dioxide concentration value measured by the sensor in real time;

[0092] C baseline : The calculated background concentration within the sliding window.

[0093] The concentration gradient analysis submodule in this data processing module 140 interacts with the dynamic background calibration submodule data. Based on the corrected carbon dioxide gas concentration value output by the dynamic background calibration submodule, the specific location of the carbon dioxide leakage is located by calculating the concentration change between adjacent LPFGs (identifying the location where the gas concentration changes most dramatically).

[0094] As a further explanation, the concentration gradient analysis submodule locates the specific location of the carbon dioxide leak through the following calculation process:

[0095] This concentration gradient analysis submodule first calculates the concentration gradient using the following concentration gradient calculation formula:

[0096]

[0097] in, Concentration gradient, which represents the change in concentration per unit distance;

[0098] C i+1 ,C i : Concentration value of adjacent sensors;

[0099] x i+1 ,x i : Spatial positions of adjacent sensors.

[0100] Next, the carbon dioxide leakage point is determined based on the gradient threshold: by setting a gradient threshold (such as 20ppm / m), the calculated concentration gradient is compared with the set gradient threshold. When the concentration gradient exceeds the gradient threshold, it is determined that a leakage point may exist in the current area.

[0101] The alarm and linkage module 150 in the system is configured to interact with the data processing module 140 to trigger an alarm and initiate protective measures when the carbon dioxide gas concentration exceeds the standard.

[0102] Furthermore, the alarm and linkage module 150 determines the carbon dioxide leakage signal by integrating the dynamic background calibration, concentration gradient analysis and time series analysis results in the data processing module 140 .

[0103] Specifically, the alarm and linkage module 150 identifies leakage signals using the following judgment rules based on the characteristics of dynamic background calibration, concentration gradient analysis, and time series results:

[0104] 1) Determination of absolute concentration value:

[0105] Whether the corrected concentration C_relative exceeds the set threshold (e.g., 500 ppm);

[0106] 2) Concentration gradient determination:

[0107] concentration gradient Whether it exceeds the set threshold (such as 20ppm / m3).

[0108] When any of the conditions is met, it is determined that carbon dioxide is leaking and an alarm signal is generated.

[0109] When the alarm signal is generated, the alarm and linkage module 150 triggers the alarm and starts the protection mechanism synchronously. The protection mechanism here can be determined according to actual needs, such as starting the ventilation system.

[0110] The carbon dioxide micro-leakage monitoring system for the confined space ground freezing system formed based on the above scheme has the following performance characteristics compared with the existing technology:

[0111] (1) High sensitivity. Based on the combined design of LPFG sensor and functional coating, the sensitivity to changes in carbon dioxide concentration is significantly improved, and the detection accuracy can reach ppm level for accurate detection of trace leaks, which can effectively overcome the problem of insufficient detection sensitivity of existing technologies.

[0112] (2) Strong environmental adaptability, through coating protection and signal processing technology, it can eliminate interference such as humidity, dust, vibration and ambient light;

[0113] (3) High real-time performance. It uses spectrum matching algorithm and fast Fourier transform (FFT) to achieve a demodulation resolution of 0.01nm and a response time of less than 1ms, meeting the real-time monitoring needs and enabling real-time detection and alarm. It can provide fast response and real-time alarm functions to ensure timely detection of leaks.

[0114] (4) Environmental adaptability: Combined with dynamic background calibration algorithm and transparent protective coating, the system's monitoring stability in high humidity and high dust environments is significantly enhanced;

[0115] (5) Wide coverage, through distributed fiber optic sensing network, large-scale leakage monitoring and accurate positioning can be achieved.

[0116] With respect to the carbon dioxide micro-leakage monitoring system for a confined space ground freezing system provided by the present invention, the application and implementation process thereof are specifically described below.

[0117] See also Figure 1 The specific application of this confined space ground freezing system carbon dioxide micro-leakage monitoring system includes the following steps:

[0118] (1) In a closed construction environment, long-period fiber grating sensors are deployed in high-risk areas where leakage may occur. Specifically, fiber optic sensing points are arranged along pipelines, valves, and high-risk areas where leakage may occur, with one sensing point arranged every 10 meters. At the same time, sensing points are densely arranged in low-lying areas where carbon dioxide is likely to accumulate.

[0119] On this basis, the deployed long-period fiber grating sensors are connected to the light source respectively; at the same time, all fiber optic sensing points are connected to the fiber optic demodulator through the fiber optic network to form a distributed sensing network.

[0120] (2) A broadband optical signal is generated by a light source to excite the long-period fiber grating sensor.

[0121] (3) The spectrum demodulator receives the wavelength drift signal transmitted by the optical fiber sensing point and demodulates the resonant wavelength drift to generate carbon dioxide gas concentration data.

[0122] (4) The data processing module receives the carbon dioxide gas concentration data output by the spectrum demodulator through the interface and performs real-time processing and judgment:

[0123] The leakage signal is extracted from the carbon dioxide gas concentration data generated by the optical spectrum interrogator through dynamic background calibration and concentration gradient analysis.

[0124] (5) When the system detects a leakage signal, it triggers an audible and visual alarm and activates the ventilation equipment on site. This step identifies the leakage signal through the following judgment rules:

[0125] 1) Determination of absolute concentration value:

[0126] Corrected concentration C relative Whether it exceeds the set threshold (such as 500ppm).

[0127] 2) Concentration gradient determination:

[0128] concentration gradient Whether it exceeds the set threshold (such as 20ppm / m3).

[0129] When any of the conditions is met, the alarm is triggered and the linkage equipment (ventilation system) is started.

[0130] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A carbon dioxide micro-leakage monitoring system for a confined space ground freezing system, characterized in that: It includes a light source, several long-period fiber grating sensors, a spectrum demodulator, and a data processing module. The light source provides a broadband optical signal; a plurality of long-period fiber grating sensors are respectively deployed in high-risk areas for leakage, are respectively connected to the light source, and are connected to the optical spectrum demodulator through an optical fiber network; The spectrum demodulator demodulates the resonant wavelength drift to generate carbon dioxide gas concentration data; the data processing module extracts leakage signals through dynamic background calibration and concentration gradient analysis based on the carbon dioxide gas concentration data generated by the spectrum demodulator.

2. The carbon dioxide micro-leakage monitoring system for a confined space ground freezing system according to claim 1 is characterized in that: The long-period fiber grating sensor is coated with a transparent protective coating outside the sensitive coating.

3. The carbon dioxide micro-leakage monitoring system for a confined space ground freezing system according to claim 1 is characterized in that: The spectrum demodulator is composed of a signal acquisition module, a demodulation module and a concentration calculation module; The signal acquisition module is used to collect the spectral signal output by the LPFG and capture the drift position of the resonant wavelength; The demodulation module uses the fast Fourier transform method to accurately identify the peak position of the spectral signal collected by the signal acquisition module and determine the resonant wavelength drift; The concentration calculation module interacts with the demodulation module data, and converts the wavelength drift value obtained by demodulation into carbon dioxide concentration data according to the relationship curve between wavelength drift and carbon dioxide gas concentration (C=f(Δλ)) calibrated in advance.

4. The carbon dioxide micro-leakage monitoring system for a confined space ground freezing system according to claim 1 is characterized in that: When performing dynamic background calibration, the data processing module calibrates the carbon dioxide gas concentration data monitored in real time using the background value of normal fluctuations in the environment to form a corrected carbon dioxide gas concentration value.

5. The carbon dioxide micro-leakage monitoring system for a confined space ground freezing system according to claim 1 is characterized in that: The data processing module locates the specific location of carbon dioxide leakage by calculating the concentration changes between adjacent sensors when performing concentration gradient analysis.

6. The carbon dioxide micro-leakage monitoring system for a confined space ground freezing system according to claim 1 is characterized in that: The monitoring system further comprises an alarm and linkage module, which interacts with the data processing module to trigger an alarm and initiate protective measures when it detects that the carbon dioxide gas concentration exceeds the standard.

7. A method for monitoring carbon dioxide micro-leakage in a confined space ground freezing system, characterized in that: The detection method comprises: (1) deploying long-period fiber grating sensors in high-risk areas of leakage, connecting the deployed long-period fiber grating sensors to light sources, and connecting them to a spectrum demodulator through an optical fiber network; (2) A broadband optical signal is generated by a light source to excite a long-period fiber Bragg grating sensor; (3) Demodulating the resonant wavelength drift by a spectrum demodulator to generate carbon dioxide gas concentration data; (4) Extracting leakage signals from the carbon dioxide gas concentration data generated by the spectrum demodulator through dynamic background calibration and concentration gradient analysis; (5) When the carbon dioxide gas concentration is detected to be above the standard, an alarm is triggered and protective measures are initiated.

8. The method for monitoring carbon dioxide micro-leakage in a confined space ground freezing system according to claim 7, characterized in that: The step (3) of demodulating the resonant wavelength drift to generate carbon dioxide gas concentration data includes the following steps: Signal acquisition: Collect the spectral signal output by the LPFG to capture the drift position of the resonant wavelength; Spectral signal demodulation: Using the fast Fourier transform method, the peak position in the spectral signal is accurately identified to determine the resonant wavelength drift; Concentration calculation: According to the pre-calibrated relationship curve between wavelength drift and carbon dioxide gas concentration, the wavelength drift value obtained by demodulation is converted into carbon dioxide concentration data.

9. The method for monitoring carbon dioxide micro-leakage in a confined space ground freezing system according to claim 7, characterized in that: When the dynamic background calibration is performed in step (4), the real-time monitored carbon dioxide gas concentration data is calibrated by the background value of normal fluctuations in the environment to form a corrected carbon dioxide gas concentration value.

10. The method for monitoring carbon dioxide micro-leakage in a confined space ground freezing system according to claim 7, characterized in that: When performing the concentration gradient analysis in step (4), the specific location of the carbon dioxide leakage is located by calculating the concentration change between adjacent sensors.

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