Fiber bragg grating temperature drift compensation method and device

Abstract

The invention relates to the technical field of gas flow detection, and discloses a fiber bragg grating temperature drift compensation method and device. The method comprises the following steps: acquiring grating wavelength shift and quantum dot fluorescence intensity; inquiring a pre-calibrated temperature-fluorescence intensity-strain mapping table based on the fluorescence intensity, and dynamically matching a strain compensation coefficient corresponding to the current temperature; separating a parasitic strain component caused by temperature by adopting a nonlinear correction algorithm, and outputting a calibrated wavelength offset; and calculating an accurate flow value by combining a strain-flow model. Based on the scheme, the strain measurement precision and the anti-interference capability of the fiber bragg grating in a temperature fluctuation environment are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas flow detection, and particularly to a method and device for compensating temperature drift of fiber Bragg gratings. Background Art

[0002] Due to advantages such as anti-electromagnetic interference, corrosion resistance, and distributed measurement, fiber Bragg grating sensors are widely used in the field of industrial monitoring. However, in practical applications, environmental temperature changes can cause wavelength shifts of fiber Bragg gratings, resulting in strain measurement errors, which is called the temperature drift effect. In the prior art, the double-grating method or temperature compensation database is used for correction, but there are problems such as complex structure, low compensation accuracy, and dependence on historical data. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a method and device for compensating temperature drift of fiber Bragg gratings.

[0004] In a first aspect, the present invention provides a method for compensating temperature drift of fiber Bragg gratings, including:

[0005] Step S1: Obtain the fluorescence intensity signal of the quantum dot temperature-sensitive film coated on the surface of the fiber Bragg grating through a spectrometer, and synchronously detect the wavelength shift amount of the fiber Bragg grating;

[0006] Step S2: According to the fluorescence intensity signal, query the pre-stored temperature-fluorescence intensity-strain mapping table to obtain the strain compensation coefficient corresponding to the current temperature, and the mapping table is generated by experimentally calibrating the relationship between the quantum dot fluorescence intensity and the fiber Bragg grating strain at different temperatures;

[0007] Step S3: Use the strain compensation coefficient to perform non-linear correction on the wavelength shift amount to generate a compensated wavelength shift amount;

[0008] Step S4: Output a calibrated flow value according to the compensated wavelength shift amount and the preset strain-flow relationship model.

[0009] Optionally, the acquisition of the fluorescence intensity signal in step S1 includes:

[0010] Step S1a: Excite the quantum dot temperature-sensitive film to generate fluorescence through a blue light source;

[0011] Step S1b: Use a spectroscope to separate the fluorescence signal and the reflected light signal of the fiber Bragg grating;

[0012] Step S1c: Measure the intensity of the fluorescence signal through a photodetector, and measure the wavelength shift amount of the reflected light signal through the spectrometer.

[0013] Optionally, the establishment of the temperature-fluorescence intensity-strain mapping table in step S2 includes:

[0014] Step S2a: Under a constant temperature environment, calibrate the relationship between the fluorescence intensity of the quantum dot temperature-sensitive film at different temperatures and the strain of the fiber grating.

[0015] Step S2b: Use an interpolation algorithm to generate a continuous temperature-fluorescence intensity-strain mapping table and store it in a database.

[0016] Optionally, the non-linear correction in Step S3 includes:

[0017] Step S3a: Calculate the theoretical strain value at the current temperature according to the fluorescence intensity signal.

[0018] Step S3b: Calculate the difference between the theoretical strain value and the measured strain value of the fiber grating to generate a dynamic compensation coefficient.

[0019] Step S3c: Calculate the compensated wavelength shift according to the dynamic compensation coefficient.

[0020] Optionally, the calculation of the theoretical strain value in Step S3a includes:

[0021] Step S3a1: Extract multiple adjacent data points in the mapping table that match the current fluorescence intensity.

[0022] Step S3a2: Generate a continuous temperature-strain surface based on the radial basis function interpolation algorithm.

[0023] Step S3a3: Interpolate the theoretical strain value on the surface according to the current temperature.

[0024] Optionally, the establishment of the strain-flow relationship model in Step S4 includes:

[0025] Step S4a: Under the calibration working condition, record the compensated strain values converted from the compensated wavelength shifts corresponding to different flow rates.

[0026] Step S4b: Generate a quadratic function relationship between the compensated strain value and the flow rate by least squares fitting.

[0027] Step S4c: Write the quadratic function relationship into the flow calculation module and output the flow rate value in real time.

[0028] Optionally, the method further includes an abnormal data filtering step:

[0029] Step S5: Monitor the fluctuation amplitude of the fluorescence intensity signal.

[0030] Step S6: If the fluctuation amplitude exceeds the preset threshold within multiple consecutive sampling periods, it is determined as the aging signal of the quantum dot temperature-sensitive film.

[0031] Step S7: Trigger an alarm and switch to a backup temperature sensor for compensation.

[0032] Optionally, the excitation light wavelength of the quantum dot temperature-sensitive film is in the blue light band, and the emission light wavelength is in the red light band.

[0033] In a second aspect, the present invention also provides a fiber Bragg grating temperature drift compensation device, including:

[0034] A quantum dot temperature-sensitive film coated on the surface of the fiber Bragg grating for generating a fluorescence signal in response to temperature changes;

[0035] A blue light source arranged to face the quantum dot temperature-sensitive film for exciting fluorescence;

[0036] A splitter connected to the fiber Bragg grating for separating the reflected light signal and the fluorescence signal;

[0037] A spectrometer connected to the splitter for detecting the wavelength shift of the reflected light signal and the intensity of the fluorescence signal;

[0038] A processing module with a built-in temperature-fluorescence intensity-strain mapping table for querying a compensation coefficient according to the fluorescence signal intensity and performing non-linear correction on the wavelength shift;

[0039] A flow calculation unit for outputting a flow value according to the corrected wavelength shift.

[0040] Optionally, the splitter includes:

[0041] A first channel for transmitting the reflected light signal of the fiber Bragg grating to a wavelength demodulator;

[0042] A second channel for transmitting the fluorescence signal of the quantum dot temperature-sensitive film to a photoelectric intensity detector.

[0043] The present invention has the following technical effects:

[0044] The temperature drift compensation method of the present invention fundamentally solves the problem of signal spatio-temporal mismatch caused by sensor separation in traditional temperature compensation through the synchronous detection of the fluorescence intensity of quantum dots and the wavelength shift of fiber Bragg gratings. The co-location coating design of the quantum dot temperature-sensitive film and the fiber Bragg grating ensures that the temperature and strain signals originate from the same physical location, avoiding compensation lag caused by heat conduction delay; the synchronous analysis of the two signals by the spectrometer directly establishes a real-time correspondence between temperature changes and grating wavelength drift, providing accurate input for dynamic correction. Based on the temperature-fluorescence intensity-strain mapping table calibrated over the full temperature range, the interpolation algorithm dynamically adapts to the non-linear variation characteristics of the thermal expansion coefficient and elastic modulus of the fiber material, breaking through the failure bottleneck of traditional fixed compensation coefficients in scenarios of sudden temperature changes. The non-linear correction algorithm strips the parasitic strain component caused by temperature through difference calculation, effectively eliminating the coupling interference between the thermal expansion effect and the temperature sensitivity of the material, so that the strain measurement accuracy is not affected by environmental temperature fluctuations. Finally, the calibrated wavelength shift is combined with the strain-flow model to output the flow value, and the measurement consistency can still be maintained under complex working conditions. Through the three-level compensation mechanism of "signal co-location acquisition - dynamic mapping adaptation - non-linear error stripping", this method forms a closed-loop correction logic, significantly improving the anti-interference ability and measurement reliability of fiber Bragg gratings in a temperature-changing environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 It is a schematic flow chart of a fiber Bragg grating temperature drift compensation method provided by the present invention;

[0047] Figure 2 It is a schematic diagram of the principle of a gas flow meter based on fiber Bragg gratings provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0049] Figure 1 It is a schematic flow chart of a fiber Bragg grating temperature drift compensation method provided by the present invention, including:

[0050] Step S1: Obtain the fluorescence intensity signal of the quantum dot temperature-sensitive film coated on the surface of the fiber grating through a spectrometer, and synchronously detect the wavelength shift of the fiber grating.

[0051] Step S2: According to the fluorescence intensity signal, query the pre-stored temperature-fluorescence intensity-strain mapping table to obtain the strain compensation coefficient corresponding to the current temperature. The mapping table is generated by calibrating the relationship between the quantum dot fluorescence intensity and the fiber grating strain at different temperatures through experiments.

[0052] Step S3: Nonlinearly correct the wavelength shift using the strain compensation coefficient to generate a compensated wavelength shift.

[0053] Step S4: Output the calibrated flow value according to the compensated wavelength shift and the preset strain-flow relationship model.

[0054] Specifically, the quantum dot temperature-sensitive film coated on the surface of the fiber grating can be composed of core-shell structure quantum dots and transparent epoxy resin, and its thickness is controlled at the micron level to maintain the strain sensitivity of the grating.

[0055] When the optical fiber is subjected to external mechanical action, the change in the grating period causes a wavelength shift of the reflection, while the change in temperature changes the fluorescence intensity through the non-radiative recombination of the carriers in the surface state of the quantum dots. The spectrometer synchronously obtains these two independent signals through a spectroscopic device: the wavelength shift of the reflected light reflects the total strain (including the true strain and the thermal expansion strain), and the fluorescence intensity characterizes the real-time temperature.

[0056] The pre-stored temperature-fluorescence intensity-strain mapping table can be constructed through calibration experiments. The specific method is to apply a known mechanical strain to the optical fiber in an incubator and record the corresponding relationship between the quantum dot fluorescence intensity and the grating wavelength shift at different temperatures. In practical applications, the strain compensation coefficient corresponding to the current temperature can be extracted by querying the mapping table according to the real-time fluorescence intensity. This coefficient is essentially a comprehensive characterization of the changes in the thermal expansion coefficient and elastic modulus of the optical fiber material caused by temperature, and is used for nonlinearly correcting the wavelength shift. For example, in the scenario of gas pipeline flow monitoring, when the compensated wavelength shift is input into the strain-flow model, the flow calculation deviation caused by the day-night temperature difference can be significantly eliminated, improving the consistency of the measurement results.

[0057] Based on the above scheme, the quantum dot fluorescence intensity signal and the grating wavelength shift can be synchronously collected, directly correlating the temperature change with the strain error, solving the problem of signal asynchrony caused by the separation of sensors in traditional compensation methods, and improving the real-time performance and accuracy of temperature compensation.

[0058] In some embodiments, the acquisition of the fluorescence intensity signal in Step S1 includes:

[0059] Step S1a: Excite the quantum dot temperature-sensitive film with a blue light source to generate fluorescence.

[0060] Step S1b: Use a beam splitter to separate the fluorescence signal and the reflected light signal of the fiber Bragg grating.

[0061] Step S1c: Measure the intensity of the fluorescence signal with a photodetector and measure the wavelength shift of the reflected light signal with a spectrometer.

[0062] Specifically, the blue light source can be a high-stability LED module, whose emission spectrum is precisely matched with the absorption band of the quantum dot material, ensuring efficient fluorescence excitation while avoiding the photothermal effect. The output end of the light source is coupled to the grating area coated with the quantum dot temperature-sensitive film through a tapered optical fiber. The incident angle of the excitation light is optimized to ensure that the quantum dots are fully excited by the light and avoid the interference of the reflected light on the detection channel.

[0063] The beam splitter can adopt a combined structure of a dichroic mirror and a band-pass filter, that is: the dichroic mirror reflects the blue light to the quantum dot temperature-sensitive film and allows the red fluorescence to pass through at the same time; the band-pass filter further selects the target fluorescence band and suppresses the interference of the fiber background radiation.

[0064] The photodetector can adopt a low-noise avalanche diode, whose spectral response range is aligned with the fluorescence emission peak of the quantum dots to ensure reliable capture of weak fluorescence signals.

[0065] The spectrometer is equipped with a high-resolution grating and an array detector, which can simultaneously analyze the wavelength shift of the grating reflection spectrum and the intensity distribution of the fluorescence spectrum.

[0066] During actual installation, the optical path system can be precisely aligned through a six-dimensional adjustment frame to improve the fluorescence collection efficiency. This design can realize real-time synchronous detection of temperature signals, and the compensation lag time is shortened to the millisecond level.

[0067] Based on the above scheme, the design of the blue light excitation and beam splitting structure avoids signal crosstalk, ensures the purity of the fluorescence intensity detection, and optimizes the optical path layout to enhance the weak light capture ability, significantly improving the temperature detection sensitivity.

[0068] In some embodiments, the establishment of the temperature-fluorescence intensity-strain mapping table in step S2 includes:

[0069] Step S2a: Under a constant temperature environment, calibrate the relationship between the fluorescence intensity of the quantum dot temperature-sensitive film and the strain of the fiber Bragg grating at different temperatures.

[0070] Step S2b: Use an interpolation algorithm to generate a continuous temperature-fluorescence intensity-strain mapping table and store it in a database.

[0071] Specifically, the construction of the temperature-fluorescence intensity-strain mapping table can adopt a multi-stage calibration strategy. The mapping table can include three-dimensional difference data and be stored in the form of a surface.

[0072] First, under the condition of zero mechanical strain, the change curve of the fluorescence intensity of quantum dots with temperature is recorded by a precision temperature control platform with stepwise temperature increase to obtain the corresponding relationship between fluorescence intensity and temperature. Subsequently, at a fixed temperature point, a gradient strain is applied to the optical fiber through a micro-displacement platform, and the linear relationship between the grating wavelength shift and the true strain is recorded. The calibration data cover the operating temperature range of the device, and the strain gradient experimental data at each temperature point form a two-dimensional data slice.

[0073] The interpolation algorithm can adopt a radial basis function network with an adaptive kernel function. By optimizing the kernel function width parameter, it can not only smooth the random noise in the experimental data but also retain the non-linear characteristics of the temperature-strain response.

[0074] The generated mapping table is stored as a hierarchical database: the original calibration data is used for later calibration, and the interpolation parameter table supports real-time fast query.

[0075] Based on the above scheme, due to the adoption of full-temperature-range calibration combined with an interpolation algorithm, covering complex working conditions of temperature sudden change and slow change, and the compensation coefficient dynamically adapting to the change of material thermal characteristics, the limitation of the fixed compensation model is broken through.

[0076] In some embodiments, the non-linear correction in step S3 includes:

[0077] Step S3a: Calculate the theoretical strain value at the current temperature according to the fluorescence intensity signal.

[0078] Step S3b: Calculate the difference between the theoretical strain value and the measured strain value of the fiber grating to generate a dynamic compensation coefficient.

[0079] Step S3c: Calculate the compensated wavelength shift according to the dynamic compensation coefficient.

[0080] Specifically, the core of the non-linear correction algorithm lies in dynamically decoupling the coupling effect between temperature and strain. The theoretical temperature value can be calculated based on the real-time fluorescence intensity, and then combined with the temperature-strain mapping relationship to deduce the theoretical thermal strain caused by the current temperature. Subtracting the theoretical thermal strain from the total measured strain of the grating gives the true mechanical strain component. The dynamic compensation coefficient is essentially the influence factor of temperature on the characteristics of the optical fiber material, and its calculation needs to consider the hysteresis effect of the temperature change rate on the material response. For example, in a scenario of rapid temperature rise, the algorithm will introduce the temperature change acceleration as a correction term to compensate for the model error caused by the heat conduction delay. For example, the dynamic compensation coefficient can be multiplied by the wavelength shift amount, and the result of the multiplication is the wavelength shift amount corresponding to the parasitic strain component caused by temperature, and this product is subtracted from the wavelength shift amount, that is: λ1 = λ0 - K(T) × T. Where λ1 represents the compensated wavelength shift amount, λ0 represents the wavelength shift amount before compensation, K(T) represents the dynamic compensation coefficient, and T represents the temperature. The compensated wavelength shift amount can reconstruct the strain signal through a polynomial fitting algorithm, and its order is adaptively adjusted according to the local curvature of the mapping table.

[0081] In summary, the difference calculation dynamically corrects the thermal expansion and material elasticity changes, achieving adaptive non-linear compensation for temperature drift and avoiding the residual error of traditional linear correction in the scenario of alternating high and low temperatures.

[0082] In some embodiments, the calculation of the theoretical strain value in step S3a includes:

[0083] Step S3a1: Extract multiple adjacent data points in the mapping table that match the current fluorescence intensity.

[0084] Step S3a2: Generate a continuous temperature-strain surface based on the radial basis function interpolation algorithm.

[0085] Step S3a3: Interpolate the theoretical strain value on the surface according to the current temperature.

[0086] Specifically, the calculation of the theoretical strain value can adopt a spatial interpolation strategy. Four calibration data points closest to the current fluorescence intensity can be selected from the mapping table to form a local interpolation unit. The interpolation algorithm based on the radial basis function constructs a three-dimensional response surface to expand the discrete calibration points into a continuous temperature-strain relationship field.

[0087] During the interpolation process, the algorithm automatically identifies the data distribution characteristics: a linear kernel function is used in the region with a high linearity of the temperature-strain relationship, and a Gaussian kernel function is switched in the non-linear mutation region. The theoretical strain value of the current temperature point is obtained through surface projection calculation, and the gradient information of adjacent data points is introduced as the interpolation weight.

[0088] In summary, this embodiment adopts the adjacent data point interpolation strategy combined with the surface projection algorithm, which can accurately capture the non-linear relationship between local temperature and strain, and solves the problem of fitting distortion of a single interpolation function in complex mapping.

[0089] In some embodiments, the establishment of the strain-flow relationship model in step S4 includes:

[0090] Step S4a: Under the calibration condition, record the compensated strain values converted from the wavelength offsets corresponding to different flow velocities.

[0091] Step S4b: Generate a quadratic function relationship between the compensated strain value and the flow velocity by least squares fitting.

[0092] Step S4c: Write the quadratic function relationship into the flow calculation module and output the flow value in real time.

[0093] Specifically, the establishment of the strain-flow relationship model is based on the deep integration of fluid mechanics principles and measured data. In the calibration stage, the fiber Bragg grating is installed in the standard flow calibration device, and the fluid flow velocity is controlled by adjusting the valve, and the compensated wavelength offset and the reference value of the turbine flowmeter are recorded synchronously. The experiment covers various flow states such as laminar flow and turbulent flow to ensure the adaptability of the model to different flow velocity conditions.

[0094] In the data preprocessing stage, moving average filtering is used to eliminate the high-frequency noise introduced by mechanical vibration and retain the low-frequency strain signal related to the flow velocity. When using least squares fitting, the quadratic function form is preferentially selected because it can characterize the non-linear relationship between the flow velocity and the strain on the pipe wall: when the flow velocity is low, the strain increases approximately linearly with the flow velocity; when the flow velocity is high, the pressure pulsation caused by turbulent flow leads to a slowdown in the strain increase rate.

[0095] In the model parameter optimization stage, the genetic algorithm is introduced, and the optimal coefficient combination is selected through multiple generations of iteration.

[0096] In summary, since the quadratic function model in this embodiment matches the physical law of the flow velocity and the strain, combined with data filtering and parameter optimization, it eliminates the interference of turbulent noise on flow inversion and improves the measurement consistency in the high and low flow velocity regions.

[0097] In some embodiments, the method further includes an abnormal data filtering step:

[0098] Step S5: Monitor the fluctuation amplitude of the fluorescence intensity signal.

[0099] Step S6: If the fluctuation amplitude exceeds the preset threshold within multiple consecutive sampling periods, it is determined as the aging signal of the quantum dot temperature-sensitive film.

[0100] Step S7: Trigger an alarm and switch to the standby temperature sensor for compensation.

[0101] Specifically, the abnormal data filtering mechanism can ensure system reliability through joint time-domain and frequency-domain analysis.

[0102] The fluctuation amplitude of the fluorescence intensity signal is monitored by using the sliding window variance calculation method. For example, based on the fluorescence intensity sequence within a set time window, the variance value is calculated as the fluctuation quantization index.

[0103] Threshold setting needs to consider the aging characteristics of the quantum dot temperature-sensitive film. A relatively loose threshold is set initially to avoid false alarms, and the threshold parameter is dynamically tightened as the running time extends.

[0104] When over-limit fluctuations are detected in multiple consecutive sampling periods, the system starts the aging diagnosis process: First, the standby light source is switched to eliminate the influence of excitation light attenuation. Subsequently, the peak position shift between the current fluorescence spectrum and the initial calibrated spectrum is compared. When the film layer aging is confirmed, the system triggers an audible and visual alarm and automatically switches to a redundant temperature sensor (such as a surface-mounted platinum resistance) to maintain the uninterrupted operation of the compensation function.

[0105] The fluctuation threshold determination and redundant switching mechanism trigger a warning in the initial stage of quantum dot aging, which can ensure the continuous reliability of the compensation system when the material performance decays and reduce the frequency of manual maintenance.

[0106] In some embodiments, the excitation light wavelength of the quantum dot temperature-sensitive film is in the blue light band, and the emission light wavelength is in the red light band.

[0107] Specifically, the optical properties of the quantum dot temperature-sensitive film are precisely regulated through material design and structure optimization.

[0108] The core material of the core-shell structure quantum dot can be cadmium selenide, and the shell layer can be zinc sulfide. This combination makes the absorption band edge located in the blue light band (about 450 nm), which highly matches the emission spectrum of the gallium nitride LED, ensuring maximum excitation efficiency.

[0109] The shell layer thickness can be precisely controlled based on the atomic layer deposition process, making the fluorescence emission peak stable in the red light band (620 - 650 nm), forming a significant spectral interval with the working band of the fiber grating (1550 nm) and reducing the risk of signal crosstalk.

[0110] The quantum dot concentration gradient is designed in the film layer thickness direction. For example, the concentration in the area close to the fiber surface is relatively low to ensure the penetration depth of the excitation light; the concentration gradually increases in the outer layer to enhance the fluorescence signal intensity.

[0111] In summary, the spectral regulation design of the core-shell quantum dot can achieve the band isolation of the excitation light and fluorescence, reduce signal cross-interference, and at the same time enhance the anti-attenuation ability of the red light fluorescence in long-distance transmission.

[0112] An embodiment of the present invention further provides a fiber grating temperature drift compensation device, including:

[0113] A quantum dot temperature-sensitive film, coated on the surface of the fiber grating, for generating a fluorescence signal in response to temperature changes.

[0114] A blue light source, arranged to align with the quantum dot temperature-sensitive film, for exciting fluorescence.

[0115] A splitter, connected to the fiber grating, for separating the reflected light signal and the fluorescence signal.

[0116] A spectrometer, connected to the splitter, for detecting the wavelength shift of the reflected light signal and the intensity of the fluorescence signal.

[0117] A processing module, with a built-in temperature-fluorescence intensity-strain mapping table, for querying the compensation coefficient according to the fluorescence signal intensity and performing non-linear correction on the wavelength shift.

[0118] A flow calculation unit, for outputting a flow value according to the corrected wavelength shift.

[0119] Specifically, the compensation device can adopt a modular packaging design, integrating the optical path, circuit and algorithm unit.

[0120] The quantum dot temperature-sensitive film can be coated about 5 cm upstream of the fiber grating. This distance is optimized through hydrodynamic simulation, which can not only avoid stress transfer delay but also reduce the influence of flow field disturbance on the film layer.

[0121] The blue light source module includes a temperature feedback control circuit, which maintains the LED junction temperature constant through a thermoelectric cooler to ensure that the excitation light power fluctuation is less than one percent.

[0122] The splitter adopts a combined structure of a gradient refractive index lens and a dichroic filter to achieve physical separation of the reflected light and the fluorescence signal: the 1550 nm reflected light is collimated by the lens and then enters the fiber optic circulator, and the 620 nm fluorescence signal is focused by the filter to the photodetector.

[0123] The processing module embeds an edge computing unit, runs a temperature compensation algorithm and an anomaly diagnosis program, and supports local real-time processing to reduce transmission delay.

[0124] The device provided by the embodiment of the present invention has the same or similar technical features as the above method, and therefore can also achieve the same or similar technical effects, which will not be elaborated here.

[0125] In some embodiments, the splitter includes:

[0126] A first channel, for transmitting the reflected light signal of the fiber grating to the wavelength demodulator.

[0127] The second channel transmits the fluorescence signal of the quantum dot temperature-sensitive film to the photoelectric intensity detector.

[0128] Specifically, the dual-channel design of the optical splitter is based on the principle of wavelength-selective transmission and reflection.

[0129] The first channel can adopt a high-reflectivity dielectric film coating, and the reflectivity for the 1550 nm grating reflected light exceeds 99.9%, ensuring the detection sensitivity of the strain signal.

[0130] The second channel uses a long-pass filter with a cut-off wavelength set at 580 nm, allowing only the red fluorescence emitted by the quantum dots to pass through.

[0131] An aspherical lens group can be embedded in the optical path structure to perform beam shaping on the two signals respectively: the lens in the reflected light channel collimates the divergent beam into a parallel light to reduce transmission loss; the lens in the fluorescence channel focuses the scattered fluorescence onto the sensitive area of the detector to improve the signal-to-noise ratio.

[0132] In summary, the dual-color beam splitting and the optimization of the lens group improve the separation of the two signals, and the anti-corrosion design of the dielectric coating can maintain the stability of the optical path, ensuring the accuracy of the compensation reference during long-term monitoring.

[0133] In addition, an embodiment of the present invention also provides a gas flowmeter based on a fiber grating, and this gas flowmeter is a vortex street flowmeter. Figure 2 This is a schematic diagram of the principle of a gas flowmeter based on a fiber grating provided by an embodiment of the present invention.

[0134] A triangular prism-shaped vortex generator is set in the fluid, and regular vortices are alternately generated on both sides of the vortex generator. Such vortices are called Karman vortices, and the vortex rows are arranged asymmetrically downstream of the vortex generator. The vortex street flowmeter is a volumetric flowmeter that measures the volumetric flow rate, standard volumetric flow rate, or mass flow rate of gas, steam, or liquid according to the Karman vortex street principle (Kármán Vortex Street). And it can be used as a flow transmitter in an automatic control system.

[0135] The vortex street flowmeter (sensor) measures the flow rate by applying the principle of fluid oscillation. When the fluid passes through the vortex street flow transmitter in the pipeline, two rows of vortices proportional to the flow velocity are alternately generated above and below the triangular prism-shaped vortex generator. The release frequency of the vortices is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, and can be expressed by the following formula:

[0136] f = Stv / d

[0137] Where: f is the release frequency of the vortex, with the unit of Hz; v is the average velocity of the fluid flowing through the vortex generator, with the unit of m / s; d is the characteristic width of the vortex generator, with the unit of m; St is the Strouhal number, dimensionless, and its value range is 0.14 - 0.27.

[0138] St is a function of the Reynolds number, St = f(1 / Re).

[0139] When the Reynolds number Re is in the range of 102 - 105, the value of St is approximately 0.2. In the measurement, it is necessary to try to ensure that the Reynolds number of the fluid is in the range of 102 - 105. At this time, the vortex frequency: f = 0.2v / d; thus, by measuring the vortex frequency, the average velocity v of the fluid flowing through the vortex generator can be calculated, and then from the formula: q = va; the flow rate q can be obtained, where a is the cross-sectional area of the fluid flowing through the vortex generator.

[0140] I. Regarding the structure of the gas flowmeter:

[0141] 1. When the gas flows through the pipeline and a vortex sound generator is set at a specific position in the pipeline, vortices are alternately generated on both sides, and the frequency of the vortex street is related to the gas flow velocity.

[0142] 2. Vortex detection: The grating sensor detects the frequency of the vortex. By measuring the frequency of the vortex street and combining parameters such as the known Strouhal number, the width of the generator, and the nominal diameter of the sensor, the flow velocity of the fluid can be calculated, and then the flow rate of the fluid can be calculated through parameters such as the flow velocity and the cross-sectional area of the pipeline.

[0143] II. Encapsulation and material selection of the fiber Bragg grating:

[0144] 1. Encapsulation protection of the optical fiber: The optical fiber is fixed by a metal elbow and a pipe clamp, which can convert the environmental physical quantity into an optical signal with minimal distortion in the gas flowmeter pipeline and ensure its stability and reliability in a harsh environment. The encapsulation design of the optical fiber protects it from external mechanical stress and temperature changes.

[0145] 2. Material and treatment of the sensor housing: The sensor housing is made of 630 stainless steel material and is heat-treated to reach a mechanical hardness of HRC45 to ensure the durability and stability of the sensor in a high-pressure environment.

[0146] III. Specific structure of the fiber Bragg grating:

[0147] 1. Combination of flow grating, vibration grating and temperature grating: The optical fiber has flow gratings, vibration gratings and temperature gratings arranged at intervals. The flow gratings are fixed on the sensitive diaphragm, and the temperature gratings are fixed on the inner wall of the vortex street chamber. The flow gratings are used to measure the change of the vortex street frequency caused by gas flow. The temperature gratings are used to sense the change of the ambient temperature for temperature compensation to improve the measurement accuracy. The vibration gratings are installed on the outer wall of the pipeline to detect the pipeline vibration data. Through common-mode operation, the influence brought by pipeline vibration is eliminated to ensure the measurement accuracy and improve the stability of the system.

[0148] Temperature compensation mechanism: The temperature gratings compensate the stress measurement error of the flow gratings caused by temperature change to ensure the accuracy of flow measurement. The temperature compensation algorithm uses the calibration data for linear fitting to eliminate the influence of temperature on flow measurement.

[0149] 2. Common-mode cancellation mechanism: The vibration gratings detect the pipeline vibration data. Through common-mode operation, the influence brought by pipeline vibration is eliminated to ensure the measurement accuracy and improve the stability of the system.

[0150] The signal data of the flow gratings, stress gratings and temperature gratings are transmitted back to the system for comprehensive calculation and analysis to achieve high-precision calculation of gas flow and output the most accurate data.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for compensating the temperature drift of fiber Bragg gratings, characterized in that, Including: Step S1: Obtain the fluorescence intensity signal of the quantum dot temperature-sensitive film coated on the surface of the fiber Bragg grating, and synchronously detect the wavelength shift of the fiber Bragg grating; Step S2: According to the fluorescence intensity signal, query the pre-stored temperature-fluorescence intensity-strain mapping table to obtain the strain compensation coefficient corresponding to the current temperature. The mapping table is generated by calibrating the relationship between the fluorescence intensity of the quantum dots and the strain of the fiber Bragg grating at different temperatures through experiments; Step S3: Use the strain compensation coefficient to perform non-linear correction on the wavelength shift to generate a compensated wavelength shift; Step S4: According to the compensated wavelength shift and the preset strain-flow relationship model, output the calibrated flow value.

2. The method according to claim 1, characterized in that, The acquisition of the fluorescence intensity signal in Step S1 includes: Step S1a: Excite the quantum dot temperature-sensitive film to generate fluorescence through a blue light source; Step S1b: Use a spectroscope to separate the fluorescence signal and the reflected light signal of the fiber Bragg grating; Step S1c: Measure the intensity of the fluorescence signal through a photodetector, and measure the wavelength shift of the reflected light signal through the spectrometer.

3. The method according to claim 1, wherein The establishment of the temperature-fluorescence intensity-strain mapping table in Step S2 includes: Step S2a: Under a constant temperature environment, calibrate the relationship between the fluorescence intensity of the quantum dot temperature-sensitive film and the strain of the fiber Bragg grating at different temperatures; Step S2b: Use an interpolation algorithm to generate a continuous temperature-fluorescence intensity-strain mapping table and store it in a database.

4. The method according to claim 1, wherein The non-linear correction in Step S3 includes: Step S3a: Calculate the theoretical strain value at the current temperature according to the fluorescence intensity signal; Step S3b: Perform a difference calculation between the theoretical strain value and the measured strain value of the fiber Bragg grating to generate a dynamic compensation coefficient; Step S3c: Calculate the compensated wavelength shift according to the dynamic compensation coefficient.

5. The method according to claim 4, characterized in that, The calculation of the theoretical strain value in Step S3a includes: Step S3a1: Extract multiple adjacent data points in the mapping table that match the current fluorescence intensity; Step S3a2: Generate a continuous temperature-strain surface based on the radial basis function interpolation algorithm; Step S3a3: Interpolate the theoretical strain value on the surface according to the current temperature.

6. The method according to claim 1, wherein The establishment of the strain-flow relationship model in Step S4 includes: Step S4a: Under the calibrated working conditions, record the compensated strain values converted from the compensated wavelength shifts corresponding to different flow rates; Step S4b: Use the least squares method to fit a quadratic function relationship between the compensated strain value and the flow rate; Step S4c: Write the quadratic function relationship into the flow calculation module to output the flow value in real time.

7. The method according to claim 1, wherein The method further includes an abnormal data filtering step: Step S5: Monitor the fluctuation amplitude of the fluorescence intensity signal; Step S6: If the fluctuation amplitude exceeds the preset threshold within multiple consecutive sampling periods, it is determined as an aging signal of the quantum dot temperature-sensitive film; Step S7: Trigger an alarm and switch to a standby temperature sensor for compensation.

8. The method according to claim 1, characterized in that, The excitation light wavelength of the quantum dot temperature-sensitive film is in the blue light band, and the emission light wavelength is in the red light band.

9. An optical fiber grating temperature drift compensation device, characterized in that Including: A quantum dot temperature-sensitive film, coated on the surface of the fiber Bragg grating, for generating a fluorescence signal in response to temperature changes; A blue light source, arranged to face the quantum dot temperature-sensitive film, for exciting fluorescence; A splitter, connected to the fiber Bragg grating, for separating the reflected light signal and the fluorescence signal; A spectrometer, connected to the splitter, for detecting the wavelength shift of the reflected light signal and the intensity of the fluorescence signal; A processing module, with a built-in temperature-fluorescence intensity-strain mapping table, for querying the compensation coefficient according to the fluorescence signal intensity and performing non-linear correction on the wavelength shift; A flow calculation unit, outputting a flow value according to the corrected wavelength shift.

10. The device according to claim 9, characterized in that, The splitter includes: A first channel, transmitting the reflected light signal of the fiber Bragg grating to a wavelength demodulator; A second channel, transmitting the fluorescence signal of the quantum dot temperature-sensitive film to a photoelectric intensity detector.

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