Gas sensitive optical fiber leakage monitoring and accurate positioning system

Abstract

The invention provides a gas-sensitive optical fiber leakage monitoring and accurate positioning system, which belongs to the field of gas monitoring, and is characterized in that a light source module generates first wavelength laser and second wavelength laser, the first wavelength laser and the second wavelength laser are combined by a wavelength division multiplexer to obtain dual-wavelength composite laser, and the dual-wavelength composite laser is transmitted to each sensing node module through an optical fiber transmission channel; the sensing node module divides the dual-wavelength composite laser into power supply light and signal light, the power supply light is converted into electric energy through photoelectric conversion, a layered heterogeneous gas-sensitive material structure is adopted to detect the environmental gas concentration and output a voltage signal, and phase modulation is performed through a ferroelectric liquid crystal element; the signal processing module calculates according to the modulated signal light to obtain a gas concentration value at each sensing node module and a spatial position of a leakage source; and the control processing module receives and processes the spatial position of the leakage source and the gas concentration value and gives an alarm. According to the invention, simultaneous monitoring and identification of multi-component gas are realized, and high-precision monitoring and accurate positioning of leakage of various gases are realized.

Description

Technical Field

[0001] This invention relates to the field of gas monitoring technology, and in particular to a gas-sensitive fiber optic leak monitoring and precise location system. Background Technology

[0002] In the energy and mining industries, there is a widespread need for hazardous gas leak monitoring, with typical applications including mines, petrochemical refining plants, green hydrogen or green ammonia chemical industrial parks, gas storage facilities, and underground pumping stations. Existing gas leak monitoring technologies primarily rely on electrochemical sensors, catalytic combustion sensors, and fiber optic gas sensing systems. However, these technologies all have significant technical bottlenecks and application limitations. While traditional electrochemical and catalytic combustion sensors are technologically mature and relatively inexpensive, they require complex explosion-proof grilles or enclosures in flammable and explosive environments. Even then, they cannot completely solve the intrinsic safety problem, as electrical components may still generate enough energy to ignite explosive gases in a faulty state. Furthermore, these sensors use a point-based monitoring method, with the effective monitoring radius of a single sensor typically only a few meters. In open areas or environments where gases diffuse rapidly, this can easily create blind spots, leading to missed detections.

[0003] While fiber optic gas sensing systems based on tunable semiconductor laser absorption spectroscopy have achieved remote monitoring in recent years, their application is severely limited by the spectral absorption characteristics of the target gas. Currently, relatively mature applications are limited to a few gases, such as methane, which have obvious absorption lines in the communication band. For gases like hydrogen, which lack absorption peaks in conventional detection bands, specialized mid-infrared laser sources are required, potentially increasing costs by an order of magnitude. When multiple gases need to be monitored simultaneously, theoretically, a laser source and detection system with corresponding wavelengths must be configured for each gas, leading to a geometric increase in system budget. Furthermore, the number of monitoring points supported by a single system is typically limited, making them prohibitively expensive for applications requiring large-scale coverage.

[0004] Chinese patent CN111157493A discloses a method for locatable hydrogen measurement based on single-photon counting. This scheme employs fiber optic lidar technology, using an acousto-optic modulator to modulate continuous laser light into pulsed light. When the pulsed light propagates in a sensing fiber, it generates Rayleigh backscattered light. The surface of the sensing fiber is coated with a hydrogen-sensitive material such as Pd / WO3, Pd / Ag, or Pd / Ni. The interaction between hydrogen and the sensitive material causes a change in the intensity of the scattered light. A single-photon detector receives the scattered light, and combined with lock-in amplification technology, distributed measurement of hydrogen concentration is achieved. The round-trip time of the pulsed light is used to spatially locate the leak point. However, the sensitive membrane is prone to aging and failure during long-term use, and the system still requires an external power supply for the sensor nodes, limiting its deployment in applications where power is unavailable. Summary of the Invention

[0005] In view of this, the present invention proposes a gas-sensitive fiber optic leak monitoring and precise location system, which solves the problems of limited gas types that can be monitored by a single system and the deployment limitations caused by the need for external power supply for the sensing nodes in the existing technology. It adopts fiber optic remote power supply technology to realize the passive design of the sensing nodes and adopts a layered heterogeneous gas-sensitive material structure to realize the simultaneous monitoring and identification of multi-component gases, thereby achieving high-precision monitoring and precise location of leaks of multiple gases.

[0006] The technical solution of this invention is implemented as follows: This invention provides a gas-sensitive optical fiber leakage monitoring and precise positioning system, comprising: The light source module is used to generate a first wavelength laser and a second wavelength laser. The first wavelength laser and the second wavelength laser are combined by a wavelength division multiplexer to obtain a dual-wavelength composite laser. The dual-wavelength composite laser is pulse-modulated and transmitted to each sensing node module through an optical fiber transmission channel. Fiber optic transmission channel for transmitting dual-wavelength composite laser; The sensing node module, distributed along the optical fiber transmission channel, receives dual-wavelength composite laser light and divides it into power supply light and signal light. The power supply light is converted into electrical energy via photoelectric conversion. A layered heterogeneous gas-sensitive material structure is used to detect the ambient gas concentration and output a voltage signal. This voltage signal drives a ferroelectric liquid crystal element to perform phase modulation on the signal light, obtaining modulated signal light carrying gas concentration information. The modulated signal light is reflected and returns along the optical fiber transmission channel. The layered heterogeneous gas-sensitive material structure includes an upper gas-sensitive material and a lower gas-sensitive material with different response speeds. The upper and lower gas-sensitive materials generate resistance changes under the influence of gas, and these resistance changes are converted into a voltage signal. The signal processing module is used to receive the modulated signal light returned by all sensor node modules, calculate the spatial position coordinates of each sensor node module based on the round-trip time of the pulse signal in the modulated signal light, and perform differential operation based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser in the modulated signal light to obtain the gas concentration value at each sensor node module. The spatial position of the leak source is obtained by interpolation operation based on the spatial position coordinates and the gas concentration value. The control and processing module is used to control the output parameters of the light source module, receive and process the spatial location of the leak source and the gas concentration value, and issue a warning according to the preset threshold.

[0007] Based on the above technical solutions, preferably, the wavelength of the first wavelength laser is 1310 nanometers and the wavelength of the second wavelength laser is 1550 nanometers.

[0008] Based on the above technical solutions, preferably, the step of converting the power supply light into electrical energy through photoelectric conversion specifically includes: A portion of the optical power is separated from the dual-wavelength composite laser according to a preset splitting ratio using an optical beam splitter to serve as the power supply light; When the power supply light shines onto the photoelectric conversion device, the photoelectric conversion device converts the power supply light into current. The current is converted into a stable voltage by the voltage regulator circuit, which provides the working power for the layered heterogeneous gas-sensitive material structure and the ferroelectric liquid crystal element.

[0009] Based on the above technical solutions, preferably, the step of generating the modulated signal light specifically includes: The upper and lower gas-sensitive materials are exposed to ambient gas. The ambient gas is adsorbed and reacted on the surfaces of the upper and lower gas-sensitive materials, resulting in changes in the electrical conductivity of the materials. The upper gas-sensitive material has a response time constant The internal resistance changes and outputs the first resistance change signal; the lower gas-sensitive material responds within a time constant. Internally, a resistance change is generated, and a second resistance change signal is output, wherein... Less than ; The first resistance change signal and the second resistance change signal are converted into voltage signals by a voltage divider circuit. The voltage signal input signal conditioning circuit amplifies and applies it to the electrodes of the ferroelectric liquid crystal element after impedance matching. The voltage signal drives the orientation angle of the liquid crystal molecules inside the ferroelectric liquid crystal element to change, resulting in a change in the effective birefringence of the liquid crystal. The signal light transmitted through the ferroelectric liquid crystal element generates a phase delay corresponding to the voltage signal. The phase-delayed signal light is reflected by the optical reflection component, and the reflected light is again phase-modulated by the ferroelectric liquid crystal element to obtain the modulated signal light carrying gas concentration information.

[0010] Based on the above technical solutions, preferably, the signal processing module includes: The photoelectric detection unit is used to receive the modulated signal light returned by all sensing node modules and convert it into a current signal. The current signal is then converted into a voltage signal by a transimpedance amplifier. The analog-to-digital converter unit is used to sample and quantize voltage signals and convert them into digital signals; The digital signal processing unit is used to receive digital signals, calculate the spatial coordinates of each sensor node module based on the round-trip time of the pulse signal using an optical time-domain reflectometry algorithm, calculate the gas concentration value at each sensor node module based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser using a dual-wavelength differential phase demodulation algorithm, and calculate the spatial location of the leak source based on the spatial coordinates and the gas concentration value using a constraint-based cubic spline interpolation algorithm.

[0011] Based on the above technical solutions, preferably, the implementation steps of using the optical time-domain reflectometry algorithm to calculate the spatial position coordinates of each sensing node module based on the round-trip time of the pulse signal include: The pulse width emitted by the control light source module is Pulsed laser, recording the pulse emission time ; The Rayleigh backscattered light returning along the optical fiber transmission channel and the strong reflected light at each sensing node module are received. The intensity of the reflected light is sampled in the time domain to obtain the curve of the reflected light intensity changing with time. The monitoring area is distributed along the optical fiber transmission channel. The first sensing node module identifies the first... Record the peak value of reflected light intensity corresponding to each sensing node module and the time corresponding to that peak value. Calculate round-trip time ,in , This is the sequence number of the sensor node module. ; Based on round-trip time and the speed of light propagation in multimode optical fiber Calculate the first Distance between each sensing node module and the light source module The calculation formula is: ; The distance Converted to spatial position coordinates along the fiber direction This yields the set of spatial coordinates of all sensor node modules. .

[0012] Based on the above technical solutions, preferably, the method of using a dual-wavelength differential phase demodulation algorithm to calculate the gas concentration value at each sensing node module according to the first phase information of the first wavelength laser and the second phase information of the second wavelength laser specifically includes: For the Each sensing node module extracts the first phase information of the first wavelength laser from the modulated signal light. Second phase information of the second wavelength laser ,in This is the serial number of the sensor node module; According to the first phase information Second phase information Constructing differential phase The calculation formula is: ,in This is the compensation coefficient for the wavelength; Based on the preset correspondence between differential phase and gas concentration, from the differential phase Obtain the Gas concentration value at each sensing node module The relationship between the preset differential phase and the gas concentration is obtained by measuring the differential phase in a standard gas environment with known concentration and establishing a calibration curve.

[0013] Based on the above technical solutions, preferably, the sensing node module also identifies multi-component gases through the response characteristics of the layered heterogeneous gas-sensitive material structure, specifically including: Measuring the intensity of the saturation response signal generated by the upper gas-sensitive material under the action of gas. and response time constant The intensity of the saturation response signal generated by the lower gas-sensitive material under the action of gas was measured. and response time constant ; Calculate the resistance value of the upper gas-sensitive material Resistance value of the underlying gas-sensitive material The ratio of the two values ​​is used to construct the response feature vector. ; The response feature vector is compared with the response feature database. Pattern recognition is used to calculate the similarity between the response feature vector and the standard feature vector of each gas in the database. The gas type is determined based on the matching result with the highest similarity. The concentration of each component gas is quantitatively calculated based on the calibration relationship between response signal intensity and concentration.

[0014] Based on the above technical solutions, preferably, the step of determining the spatial location of the leakage source using a constraint-based cubic spline interpolation algorithm specifically includes: right The first sensor node module, input the first... Spatial coordinates of each sensor node module and the corresponding gas concentration values ,in ; In the interval Construct a piecewise cubic polynomial function and combine the cubic polynomials of all piecewise intervals to form a concentration spatial distribution function. ;in ,in This represents the coefficient of the constant term in a cubic polynomial. Denotes the coefficient of the linear term. Denotes the coefficient of the quadratic term. The coefficient of the cubic term; According to the interpolation condition, the function value of the cubic polynomial at the node must equal the measured concentration value. According to the continuity condition, the function values, first derivative values, and second derivative values ​​of adjacent piecewise cubic polynomials at the boundary nodes must be continuous. Therefore, a function value with respect to the coefficients is established. , , , The system of equations; Based on the constraints, a constraint optimization algorithm is used to solve for the optimal coefficients that satisfy all constraints. , , , The constrained optimization algorithm employs either the Lagrange multiplier method or the sequential quadratic programming algorithm. For the spatial distribution function of concentration Find the first derivative over the entire monitoring area ,in This represents the rate of change of concentration with respect to spatial location; Let the first derivative Obtain the set of stationary points, and calculate the second derivative for each stationary point in the set. ,in Representing the rate of change of the concentration gradient, the stationary point where the concentration value is maximum and the second derivative is less than zero is selected as the spatial location of the leakage source. The fact that the second derivative is less than zero indicates that the stationary point is a local maximum.

[0015] More preferably, the constraints specifically include: The concentration non-negativity constraint makes the concentration spatial distribution function Satisfy the requirements of the entire monitoring area ,in Indicates spatial location The gas concentration at that location; The monotonicity constraint requires that the spatial distribution function of the concentration on both sides of the concentration maximum point satisfies the monotonically decreasing property, that is, the concentration decreases with increasing distance on the side of the leakage source and decreases with decreasing distance on the other side of the leakage source. Boundary condition constraints require that the concentration value at the boundary of the monitoring area approach the background concentration. ,in This indicates the ambient background gas concentration when there is no leakage.

[0016] The gas-sensitive fiber optic leakage monitoring and precise location system of the present invention has the following advantages over the prior art: (1) This invention combines fiber optic remote power supply with ferroelectric liquid crystal phase modulation. High-power laser is transmitted through fiber optic to achieve remote power supply. The gas concentration information detected by the gas sensor is converted into optical signal phase change through electro-optic modulation of ferroelectric liquid crystal, which improves the identification capability of multi-component gas and temperature compensation effect. Furthermore, a cubic spline interpolation algorithm based on physical constraints is adopted to improve the spatial positioning accuracy of the leakage source. At the same time, the phase modulation generated by the ferroelectric liquid crystal can achieve very low power consumption, which can save the cost of remote laser power supply. It can maintain good linearity at very low voltage and improve monitoring sensitivity. (2) The present invention adopts a layered heterogeneous gas-sensitive material structure, which expands the dynamic range of concentration measurement and provides time-domain features for the identification of different gases. Through pattern recognition, the gas type is identified and the concentration of each component is quantitatively calculated, so that the system can monitor and identify multiple gases at the same time. (3) The present invention uses a cubic spline interpolation algorithm based on physical constraints to locate the leakage source, making full use of the concentration information of all monitoring nodes. Even if the leakage source is located between adjacent nodes, it can be accurately located through concentration gradient analysis, thus improving the spatial positioning accuracy of the leakage source. (4) The present invention uses an optical time-domain reflectometry algorithm to calculate the spatial coordinates of each sensing node module based on the round-trip time of the pulse signal. By emitting a narrow pulse laser and receiving the strong reflected light generated at each sensing node, the spatial position of the node is determined based on the time delay of the reflected light return, providing an accurate spatial reference for locating the leakage source. Combined with the gas concentration values ​​of each node obtained by the dual-wavelength differential phase demodulation algorithm, the precise coupling demodulation of gas concentration information and spatial position information is realized. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a block diagram of a gas-sensitive optical fiber leakage monitoring and precise positioning system according to the present invention; Figure 2 This is a schematic diagram of a sensing node module of a gas-sensitive fiber optic leakage monitoring and precise positioning system according to the present invention. Figure 3 This is a schematic diagram of the layered heterogeneous gas-sensitive material structure of a gas-sensitive fiber optic leakage monitoring and precise positioning system according to the present invention; Figure 4 This is a schematic diagram illustrating the location of a leak source in a gas-sensitive optical fiber leak monitoring and precise location system according to the present invention. Detailed Implementation

[0019] 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.

[0020] like Figure 1 As shown, the present invention provides a gas-sensitive optical fiber leakage monitoring and precise location system, comprising: The light source module is used to generate a first wavelength laser and a second wavelength laser. The first wavelength laser and the second wavelength laser are combined by a wavelength division multiplexer to obtain a dual-wavelength composite laser. The dual-wavelength composite laser is pulse-modulated and transmitted to each sensing node module through an optical fiber transmission channel. The wavelength of the first wavelength laser is 1310 nanometers and the wavelength of the second wavelength laser is 1550 nanometers. Fiber optic transmission channel for transmitting dual-wavelength composite laser; The sensing node module, distributed along the optical fiber transmission channel, receives dual-wavelength composite laser light and divides it into power supply light and signal light. The power supply light is converted into electrical energy via photoelectric conversion. A layered heterogeneous gas-sensitive material structure is used to detect the ambient gas concentration and output a voltage signal. This voltage signal drives a ferroelectric liquid crystal element to perform phase modulation on the signal light, obtaining modulated signal light carrying gas concentration information. The modulated signal light is reflected and returns along the optical fiber transmission channel. The layered heterogeneous gas-sensitive material structure includes an upper gas-sensitive material and a lower gas-sensitive material with different response speeds. The upper and lower gas-sensitive materials generate resistance changes under the influence of gas, and these resistance changes are converted into a voltage signal. The signal processing module is used to receive the modulated signal light returned by all sensor node modules, calculate the spatial position coordinates of each sensor node module based on the round-trip time of the pulse signal in the modulated signal light, and perform differential operation based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser in the modulated signal light to obtain the gas concentration value at each sensor node module. The spatial position of the leak source is obtained by interpolation operation based on the spatial position coordinates and the gas concentration value. The control and processing module is used to control the output parameters of the light source module, receive and process the spatial location of the leak source and the gas concentration value, and issue a warning according to the preset threshold.

[0021] Preferably, the optical fiber transmission channel can be a multimode optical fiber transmission channel.

[0022] In one embodiment of the present invention, the specific implementation of combining the first wavelength laser and the second wavelength laser using a wavelength division multiplexer to obtain a dual-wavelength composite laser is as follows: The first and second wavelength lasers are combined using a wavelength division multiplexer (WDM) of 1310 nm and 1550 nm. The insertion loss of the WDM should be less than 1 dB and the isolation should be greater than 25 dB to ensure that the two wavelengths can be effectively coupled and that there is little crosstalk between them.

[0023] like Figure 2 As shown, in one embodiment of the present invention, the power supply light is converted into electrical energy through photoelectric conversion, specifically including: A portion of the optical power is separated from the dual-wavelength composite laser according to a preset splitting ratio using an optical beam splitter to serve as the power supply light; When the power supply light shines onto the photoelectric conversion device, the photoelectric conversion device converts the power supply light into current. The current is converted into a stable voltage by the voltage regulator circuit, which provides the working power for the layered heterogeneous gas-sensitive material structure and the ferroelectric liquid crystal element.

[0024] Understandably, the splitting ratio needs to be set by comprehensively considering the power supply required by the node, the energy demand of subsequent nodes, and fiber transmission loss. For example, for nodes closer to the light source, the splitting ratio can be set to 3%-8%, while for nodes farther away, the splitting ratio can be appropriately increased to 10%-20% to compensate for the cumulative effect of fiber transmission loss.

[0025] In one embodiment of the present invention, the electrical power obtained after converting the power supply light into current is: ; ; ; in The photoelectric conversion efficiency of photoelectric conversion devices, For the efficiency of the power management circuit, For the first The optical power extracted from each node Indicates the first The incident light power before the light is split at each node Indicates the first The splitting ratio at each node Indicates the sequence number of the sensor node. Indicates the first The sequence numbers of each node preceding the current node, i.e. j =1, 2, ..., i- 1, This represents the loss coefficient of the optical fiber. Indicates the first The distance between each sensing node and the light source module.

[0026] Understandable. Indicates the distance the light power travels. Attenuation after transmission This represents the cumulative decay after all preceding nodes have extracted energy.

[0027] In one embodiment of the present invention, the step of generating the modulated signal light specifically includes: The upper and lower gas-sensitive materials are exposed to ambient gas. The ambient gas is adsorbed and reacted on the surfaces of the upper and lower gas-sensitive materials, resulting in changes in the electrical conductivity of the materials. The upper gas-sensitive material has a response time constant The internal resistance changes and outputs the first resistance change signal; the lower gas-sensitive material responds within a time constant. Internally, a resistance change is generated, and a second resistance change signal is output, wherein... Less than ; The first resistance change signal and the second resistance change signal are converted into voltage signals by a voltage divider circuit. The voltage signal input signal conditioning circuit amplifies and applies it to the electrodes of the ferroelectric liquid crystal element after impedance matching. The voltage signal drives the orientation angle of the liquid crystal molecules inside the ferroelectric liquid crystal element to change, resulting in a change in the effective birefringence of the liquid crystal. The signal light transmitted through the ferroelectric liquid crystal element generates a phase delay corresponding to the voltage signal. The phase-delayed signal light is reflected by the optical reflection component, and the reflected light is again phase-modulated by the ferroelectric liquid crystal element to obtain the modulated signal light carrying gas concentration information.

[0028] Understandably, ferroelectric liquid crystal elements employ a ferroelectric liquid crystal cell structure, consisting of a ferroelectric liquid crystal layer sandwiched between two transparent conductive glass substrates. The formula for calculating the phase retardation is: ; in This is the phase delay. The thickness of the ferroelectric liquid crystal cell. The incident light wavelength, The effective birefringence of ferroelectric liquid crystals, a parameter that also depends on wavelength. and applied voltage .

[0029] like Figure 3 As shown, in one embodiment of the present invention, the upper gas-sensitive material is a zinc oxide nanowire array, and the lower gas-sensitive material is a tin dioxide porous film or other metal oxide semiconductor material. The response of the lower material is relatively slow, with a response time constant. The time required is approximately tens of seconds to several minutes, but it exhibits better stability and more pronounced selective response characteristics to different gases. A microelectrode is positioned between the two gas-sensitive materials, allowing for the separate measurement of resistance changes in the upper and lower layers.

[0030] This invention employs a layered heterogeneous gas-sensitive material structure, which expands the dynamic range of concentration measurement and provides time-domain features for the identification of different gases. Through pattern recognition, it enables the identification of gas types and the quantitative calculation of the concentration of each component, breaking through the limitations of traditional spectral absorption methods on gas types and enabling the system to simultaneously monitor and identify multiple gases.

[0031] In one embodiment of the present invention, the signal processing module includes: The photoelectric detection unit is used to receive the modulated signal light returned by all sensing node modules and convert it into a current signal. The current signal is then converted into a voltage signal by a transimpedance amplifier. The analog-to-digital converter unit is used to sample and quantize voltage signals and convert them into digital signals; The digital signal processing unit is used to receive digital signals, calculate the spatial coordinates of each sensor node module based on the round-trip time of the pulse signal using an optical time-domain reflectometry algorithm, calculate the gas concentration value at each sensor node module based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser using a dual-wavelength differential phase demodulation algorithm, and calculate the spatial location of the leak source based on the spatial coordinates and the gas concentration value using a constraint-based cubic spline interpolation algorithm.

[0032] Understandably, the digital signal processing unit uses a field-programmable gate array or a digital signal processor to implement optical time-domain reflectometry algorithms, dual-wavelength differential phase demodulation algorithms, and constraint-based cubic spline interpolation algorithms.

[0033] In one embodiment of the present invention, the implementation step of calculating the spatial position coordinates of each sensing node module based on the round-trip time of the pulse signal using the optical time-domain reflectometry algorithm includes: The pulse width emitted by the control light source module is Pulsed laser, recording the pulse emission time ; The Rayleigh backscattered light returning along the optical fiber transmission channel and the strong reflected light at each sensing node module are received. The intensity of the reflected light is sampled in the time domain to obtain the curve of the reflected light intensity changing with time. The monitoring area is distributed along the optical fiber transmission channel. The first sensing node module identifies the first... Record the peak value of reflected light intensity corresponding to each sensing node module and the time corresponding to that peak value. Calculate round-trip time ,in , This is the sequence number of the sensor node module. ; Based on round-trip time and the speed of light propagation in multimode optical fiber Calculate the first Distance between each sensing node module and the light source module The calculation formula is: ; The distance Converted to spatial position coordinates along the fiber direction This yields the set of spatial coordinates of all sensor node modules. .

[0034] Understandably, Rayleigh backscattered light is an intrinsic scattering phenomenon caused by microscopic density fluctuations within the optical fiber. The intensity of the scattered light is relatively weak and decreases exponentially with increasing distance. The optical reflection components installed at each sensing node module generate obvious strong reflection peaks, the amplitude of which is much larger than that of the background Rayleigh scattered light, facilitating identification and localization.

[0035] This invention employs an optical time-domain reflectometry algorithm to calculate the spatial coordinates of each sensing node module based on the round-trip time of the pulse signal. By emitting a narrow-pulse laser and receiving the strong reflected light generated at each sensing node, the spatial position of the node is determined based on the time delay of the reflected light return, providing an accurate spatial reference for locating the leakage source. Combined with the gas concentration values ​​of each node obtained by the dual-wavelength differential phase demodulation algorithm, precise coupling demodulation of gas concentration information and spatial position information is achieved.

[0036] In one embodiment of the present invention, the step of using a dual-wavelength differential phase demodulation algorithm to calculate the gas concentration value at each sensing node module based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser specifically includes: For the Each sensing node module extracts the first phase information of the first wavelength laser from the modulated signal light. Second phase information of the second wavelength laser ,in This is the serial number of the sensor node module; According to the first phase information Second phase information Constructing differential phase The calculation formula is: ,in This is the compensation coefficient for the wavelength; Based on the preset correspondence between differential phase and gas concentration, from the differential phase Obtain the Gas concentration value at each sensing node module The relationship between the preset differential phase and the gas concentration is obtained by measuring the differential phase in a standard gas environment with known concentration and establishing a calibration curve.

[0037] Understandable, compensation coefficient The determination needs to be obtained through calibration experiments. In the calibration experiments, the gas concentration is kept constant, the ambient temperature is changed, and the phase changes at two wavelengths, 1310 nm and 1550 nm, are measured simultaneously. The least squares method is used to fit and obtain the compensation coefficient that makes the temperature correlation term in the differential phase zero or minimum. .

[0038] In one embodiment of the present invention, the sensing node module further identifies multi-component gases through the response characteristics of the layered heterogeneous gas-sensitive material structure, and the specific steps include: Measuring the intensity of the saturation response signal generated by the upper gas-sensitive material under the action of gas. and response time constant The intensity of the saturation response signal generated by the lower gas-sensitive material under the action of gas was measured. and response time constant ; Calculate the resistance value of the upper gas-sensitive material Resistance value of the underlying gas-sensitive material The ratio of the two values ​​is used to construct the response feature vector. ; The response feature vector is compared with the response feature database. Pattern recognition is used to calculate the similarity between the response feature vector and the standard feature vector of each gas in the database. The gas type is determined based on the matching result with the highest similarity. The concentration of each component gas is quantitatively calculated based on the calibration relationship between response signal intensity and concentration.

[0039] Understandably, the response feature database is established through systematic calibration experiments on various target gases such as hydrogen, methane, carbon monoxide, and hydrogen sulfide under different concentration conditions. Each gas stores its standard feature vector in the database. Similarity calculation can use Euclidean distance or Mahalanobis distance; the gas with the highest similarity, i.e., the smallest distance, is determined as the currently detected gas type.

[0040] like Figure 4 As shown, in one embodiment of the present invention, determining the spatial location of the leakage source using a constraint-based cubic spline interpolation algorithm specifically includes: right The first sensor node module, input the first... Spatial coordinates of each sensor node module and the corresponding gas concentration values ,in ; In the interval Construct a piecewise cubic polynomial function and combine the cubic polynomials of all piecewise intervals to form a concentration spatial distribution function. ;in ,in This represents the coefficient of the constant term in a cubic polynomial. Denotes the coefficient of the linear term. Denotes the coefficient of the quadratic term. The coefficient of the cubic term; According to the interpolation condition, the function value of the cubic polynomial at the node must equal the measured concentration value. According to the continuity condition, the function values, first derivative values, and second derivative values ​​of adjacent piecewise cubic polynomials at the boundary nodes must be continuous. Therefore, a function value with respect to the coefficients is established. , , , The system of equations; Based on the constraints, a constraint optimization algorithm is used to solve for the optimal coefficients that satisfy all constraints. , , , The constrained optimization algorithm employs either the Lagrange multiplier method or the sequential quadratic programming algorithm. For the spatial distribution function of concentration Find the first derivative over the entire monitoring area ,in This represents the rate of change of concentration with respect to spatial location; Let the first derivative Obtain the set of stationary points, and calculate the second derivative for each stationary point in the set. ,in Representing the rate of change of the concentration gradient, the stationary point where the concentration value is maximum and the second derivative is less than zero is selected as the spatial location of the leakage source. The fact that the second derivative is less than zero indicates that the stationary point is a local maximum.

[0041] This invention employs a cubic spline interpolation algorithm based on physical constraints to locate the leakage source. It makes full use of the concentration information of all monitoring nodes, and can achieve accurate location through concentration gradient analysis even if the leakage source is located between adjacent nodes, thereby improving the spatial positioning accuracy of the leakage source.

[0042] In one embodiment of the present invention, the constraint conditions specifically include: The concentration non-negativity constraint makes the concentration spatial distribution function Satisfy the requirements of the entire monitoring area ,in Indicates spatial location The gas concentration at that location; The monotonicity constraint requires that the spatial distribution function of the concentration on both sides of the concentration maximum point satisfies the monotonically decreasing property, that is, the concentration decreases with increasing distance on the side of the leakage source and decreases with decreasing distance on the other side of the leakage source. Boundary condition constraints require that the concentration value at the boundary of the monitoring area approach the background concentration. ,in This indicates the ambient background gas concentration when there is no leakage.

[0043] In one embodiment of the present invention, the control processing module receives the spatial location of the leak source and the gas concentration value output by the signal processing module, and issues an alert based on preset thresholds. The preset thresholds include a concentration threshold and a concentration change rate threshold. When the detected gas concentration exceeds the concentration threshold or the concentration change rate exceeds the change rate threshold, the control processing module immediately triggers an audible and visual alarm device and sends alarm information to the monitoring center via a communication interface. The alarm information includes the spatial coordinates of the leak source, the gas concentration value, the gas type, and the detection timestamp.

[0044] This invention combines fiber optic remote power supply with ferroelectric liquid crystal phase modulation. High-power laser is transmitted via fiber optic cable for remote power supply. Gas concentration information detected by the gas sensor is converted into optical signal phase changes through electro-optic modulation of the ferroelectric liquid crystal, improving the identification capability of multi-component gases and temperature compensation effect. Furthermore, a cubic spline interpolation algorithm based on physical constraints is employed to improve the spatial positioning accuracy of the leakage source. Simultaneously, the phase modulation generated by the ferroelectric liquid crystal achieves very low power consumption, saving the cost of remote laser power supply, and maintaining good linearity at very low voltages, thus improving monitoring sensitivity.

[0045] 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 gas-sensitive fiber optic leakage monitoring and precise positioning system, characterized in that: include: The light source module is used to generate a first wavelength laser and a second wavelength laser. The first wavelength laser and the second wavelength laser are combined by a wavelength division multiplexer to obtain a dual-wavelength composite laser. The dual-wavelength composite laser is pulse-modulated and transmitted to each sensing node module through an optical fiber transmission channel. Fiber optic transmission channel for transmitting dual-wavelength composite laser; The sensing node module is distributed along the optical fiber transmission channel. It is used to receive dual-wavelength composite laser and divide it into power supply light and signal light. The power supply light is converted into electrical energy through photoelectric conversion. The layered heterogeneous gas-sensitive material structure is used to detect the concentration of ambient gas and output a voltage signal. The voltage signal drives the ferroelectric liquid crystal element to perform phase modulation on the signal light to obtain modulated signal light carrying gas concentration information. The modulated signal light is reflected and returns along the optical fiber transmission channel. The layered heterogeneous gas-sensitive material structure includes an upper gas-sensitive material and a lower gas-sensitive material with different response speeds. The upper and lower gas-sensitive materials generate resistance changes under the action of gas, and the resistance changes are converted into voltage signals. The signal processing module is used to receive the modulated signal light returned by all sensor node modules, calculate the spatial position coordinates of each sensor node module based on the round-trip time of the pulse signal in the modulated signal light, and perform differential operation based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser in the modulated signal light to obtain the gas concentration value at each sensor node module. The spatial position of the leak source is obtained by interpolation operation based on the spatial position coordinates and the gas concentration value. The control and processing module is used to control the output parameters of the light source module, receive and process the spatial location of the leak source and the gas concentration value, and issue a warning according to the preset threshold.

2. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 1, characterized in that: The first wavelength laser has a wavelength of 1310 nanometers, and the second wavelength laser has a wavelength of 1550 nanometers.

3. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 1, characterized in that: The process of converting optical power into electrical energy through photoelectric conversion specifically includes: A portion of the optical power is separated from the dual-wavelength composite laser according to a preset splitting ratio using an optical beam splitter to serve as the power supply light; When the power supply light shines onto the photoelectric conversion device, the photoelectric conversion device converts the power supply light into current. The current is converted into a stable voltage by the voltage regulator circuit, which provides the working power for the layered heterogeneous gas-sensitive material structure and the ferroelectric liquid crystal element.

4. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 3, characterized in that: The specific steps for generating the modulated signal light include: The upper and lower gas-sensitive materials are exposed to ambient gas. The ambient gas is adsorbed and reacted on the surfaces of the upper and lower gas-sensitive materials, resulting in changes in the electrical conductivity of the materials. The upper gas-sensitive material has a response time constant The internal resistance changes and outputs the first resistance change signal; the lower gas-sensitive material responds within a time constant. Internally, a resistance change is generated, and a second resistance change signal is output, wherein... Less than ; The first resistance change signal and the second resistance change signal are converted into voltage signals by a voltage divider circuit. The voltage signal input signal conditioning circuit amplifies and applies it to the electrodes of the ferroelectric liquid crystal element after impedance matching. The voltage signal drives the orientation angle of the liquid crystal molecules inside the ferroelectric liquid crystal element to change, resulting in a change in the effective birefringence of the liquid crystal. The signal light transmitted through the ferroelectric liquid crystal element generates a phase delay corresponding to the voltage signal. The phase-delayed signal light is reflected by the optical reflection component, and the reflected light is again phase-modulated by the ferroelectric liquid crystal element to obtain the modulated signal light carrying gas concentration information.

5. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 1, characterized in that: The signal processing module includes: The photoelectric detection unit is used to receive the modulated signal light returned by all sensing node modules and convert it into a current signal. The current signal is then converted into a voltage signal by a transimpedance amplifier. The analog-to-digital converter unit is used to sample and quantize voltage signals and convert them into digital signals; The digital signal processing unit is used to receive digital signals, calculate the spatial coordinates of each sensor node module based on the round-trip time of the pulse signal using an optical time-domain reflectometry algorithm, calculate the gas concentration value at each sensor node module based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser using a dual-wavelength differential phase demodulation algorithm, and calculate the spatial location of the leak source based on the spatial coordinates and the gas concentration value using a constraint-based cubic spline interpolation algorithm.

6. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 5, characterized in that: The implementation steps for calculating the spatial position coordinates of each sensing node module based on the round-trip time of the pulse signal using the optical time-domain reflectometry algorithm include: The pulse width emitted by the control light source module is Pulsed laser, recording the pulse emission time ; The Rayleigh backscattered light returning along the optical fiber transmission channel and the strong reflected light at each sensing node module are received. The intensity of the reflected light is sampled in the time domain to obtain the curve of the reflected light intensity changing with time. The monitoring area is distributed along the optical fiber transmission channel. The first sensing node module identifies the first... Record the peak value of reflected light intensity corresponding to each sensing node module and the time corresponding to that peak value. Calculate round-trip time ,in , This is the sequence number of the sensor node module. ; Based on round-trip time and the speed of light propagation in multimode optical fiber Calculate the first Distance between each sensing node module and the light source module The calculation formula is: ; The distance Converted to spatial position coordinates along the fiber direction This yields the set of spatial coordinates of all sensor node modules. .

7. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 6, characterized in that: The method employs a dual-wavelength differential phase demodulation algorithm to calculate the gas concentration value at each sensing node module based on the first phase information of the first wavelength laser and the second phase information of the second wavelength laser. Specifically, this includes: For the Each sensing node module extracts the first phase information of the first wavelength laser from the modulated signal light. Second phase information of the second wavelength laser ,in This is the serial number of the sensor node module; According to the first phase information Second phase information Constructing differential phase The calculation formula is: ,in This is the compensation coefficient for the wavelength; Based on the preset correspondence between differential phase and gas concentration, from the differential phase Obtain the Gas concentration value at each sensing node module The relationship between the preset differential phase and the gas concentration is obtained by measuring the differential phase in a standard gas environment with known concentration and establishing a calibration curve.

8. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 7, characterized in that: The sensing node module also identifies multi-component gases through the response characteristics of the layered heterogeneous gas-sensitive material structure. Specific steps include: Measuring the intensity of the saturation response signal generated by the upper gas-sensitive material under the action of gas. and response time constant The intensity of the saturation response signal generated by the lower gas-sensitive material under the action of gas was measured. and response time constant ; Calculate the resistance value of the upper gas-sensitive material Resistance value of the underlying gas-sensitive material The ratio of the two values ​​is used to construct the response feature vector. ; The response feature vector is compared with the response feature database. Pattern recognition is used to calculate the similarity between the response feature vector and the standard feature vector of each gas in the database. The gas type is determined based on the matching result with the highest similarity. The concentration of each component gas is quantitatively calculated based on the calibration relationship between response signal intensity and concentration.

9. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 8, characterized in that: The calculation of the spatial location of the leak source using a constraint-based cubic spline interpolation algorithm based on spatial coordinates and gas concentration values ​​specifically includes: right The first sensor node module, input the first... Spatial coordinates of each sensor node module and the corresponding gas concentration values ,in ; In the interval Construct a piecewise cubic polynomial function and combine the cubic polynomials of all piecewise intervals to form a concentration spatial distribution function. ;in ,in This represents the coefficient of the constant term in a cubic polynomial. Denotes the coefficient of the linear term. Denotes the coefficient of the quadratic term. The coefficient of the cubic term; According to the interpolation condition, the function value of the cubic polynomial at the node must equal the measured concentration value. According to the continuity condition, the function values, first derivative values, and second derivative values ​​of adjacent piecewise cubic polynomials at the boundary nodes must be continuous. Therefore, a function value with respect to the coefficients is established. , , , The system of equations; Based on the constraints, a constraint optimization algorithm is used to solve for the optimal coefficients that satisfy all constraints. , , , The constrained optimization algorithm employs either the Lagrange multiplier method or the sequential quadratic programming algorithm. For the spatial distribution function of concentration Find the first derivative over the entire monitoring area ,in This represents the rate of change of concentration with respect to spatial location; Let the first derivative Obtain the set of stationary points, and calculate the second derivative for each stationary point in the set. ,in Representing the rate of change of the concentration gradient, the stationary point where the concentration value is maximum and the second derivative is less than zero is selected as the spatial location of the leakage source. The fact that the second derivative is less than zero indicates that the stationary point is a local maximum.

10. The gas-sensitive fiber optic leakage monitoring and precise positioning system as described in claim 9, characterized in that: The constraints specifically include: The concentration non-negativity constraint makes the concentration spatial distribution function Satisfy the requirements of the entire monitoring area ,in Indicates spatial location The gas concentration at that location; The monotonicity constraint requires that the spatial distribution function of the concentration on both sides of the concentration maximum point satisfies the monotonically decreasing property, that is, the concentration decreases with increasing distance on the side of the leakage source and decreases with decreasing distance on the other side of the leakage source. Boundary condition constraints require that the concentration value at the boundary of the monitoring area approach the background concentration. ,in This indicates the ambient background gas concentration when there is no leakage.

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