A fiber grating temperature drift compensation method and device

Abstract

The application relates to the technical field of gas flow detection, and discloses a fiber grating temperature drift compensation method and device. The method comprises the following steps: acquiring grating wavelength offset and quantum dot fluorescence intensity; querying 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; adopting a nonlinear correction algorithm to separate a parasitic strain component caused by the temperature, and outputting a calibrated wavelength offset; and combining a strain-flow model to calculate an accurate flow value. Based on the above scheme, the strain measurement precision and the anti-interference ability of the fiber grating in a temperature fluctuation environment are significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas flow detection, and in particular to a fiber grating temperature drift compensation method and device. BACKGROUND

[0002] The fiber grating sensor is widely used in the industrial monitoring field due to its advantages of anti-electromagnetic interference, corrosion resistance, and distributed measurement. However, in actual application, the change of environmental temperature will cause the wavelength shift of the fiber grating, resulting in strain measurement error, which is called temperature drift effect. In the prior art, the double grating method or temperature compensation database is used for correction, but there are problems of complex structure, low compensation accuracy, and dependence on historical data. SUMMARY

[0003] In order to solve the above technical problems, the present application provides a fiber grating temperature drift compensation method and device.

[0004] In a first aspect, the present application provides a fiber grating temperature drift compensation method, comprising:

[0005] Step S1: obtaining the fluorescence intensity signal of the quantum dot temperature sensitive film coated on the surface of the fiber grating by a spectrometer, and synchronously detecting the wavelength shift amount of the fiber grating;

[0006] Step S2: according to the fluorescence intensity signal, querying a pre-stored temperature-fluorescence intensity-strain mapping table to obtain a 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 grating strain at different temperatures;

[0007] Step S3: using the strain compensation coefficient to nonlinearly correct the wavelength shift amount to generate a compensated wavelength shift amount;

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

[0009] Optionally, the obtaining of the fluorescence intensity signal in step S1 comprises:

[0010] Step S1a: exciting the quantum dot temperature sensitive film to produce fluorescence by a blue light source;

[0011] Step S1b: separating the fluorescence signal and the reflected light signal of the fiber grating by using a beam splitter;

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

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

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

[0015] Step S2b: Generate a continuous temperature-fluorescence intensity-strain mapping table using an interpolation algorithm and store it as a database.

[0016] Optionally, the nonlinear correction in step S3 includes:

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

[0018] Step S3b: performing difference calculation between the theoretical strain value and the measured strain value of the fiber Bragg grating to generate a dynamic compensation coefficient;

[0019] Step S3c: Calculating the compensated wavelength offset according to the dynamic compensation coefficient.

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

[0021] Step S3a1: extracting a plurality of adjacent data points in the mapping table that match the current fluorescence intensity;

[0022] Step S3a2: generating a continuous temperature-strain surface based on a radial basis function interpolation algorithm;

[0023] Step S3a3: interpolating a 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, recording the compensated strain value converted from the compensated wavelength offset corresponding to different flow rates;

[0026] Step S4b: generating a quadratic function relationship between the compensation strain value and the flow velocity by least square fitting;

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

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

[0029] Step S5: monitoring the fluctuation amplitude of the fluorescence intensity signal;

[0030] Step S6: If the fluctuation amplitude exceeds a preset threshold value in multiple consecutive sampling periods, it is determined to be a quantum dot temperature-sensitive film aging signal;

[0031] Step S7: trigger an alarm and switch to the 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 further provides a fiber Bragg grating temperature drift compensation device, comprising:

[0034] Quantum dot temperature-sensitive film, coated on the surface of the fiber Bragg grating, is used to generate fluorescence signals in response to temperature changes;

[0035] A blue light source is aligned with the quantum dot temperature-sensitive film to excite fluorescence;

[0036] An optical splitter connected to the fiber grating and used to separate the reflected light signal from the fluorescent signal;

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

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

[0039] The flow calculation unit outputs a flow value according to the corrected wavelength offset.

[0040] Optionally, the optical splitter includes:

[0041] The first channel transmits the reflected light signal of the fiber grating to the wavelength demodulator;

[0042] The second channel transmits 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 spatiotemporal signal mismatch problem caused by sensor separation in traditional temperature compensation by synchronously detecting quantum dot fluorescence intensity and fiber Bragg grating wavelength offset. 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 thermal conduction delays. The spectrometer's synchronous analysis of the two signals directly establishes a real-time correspondence between temperature changes and grating wavelength drift, providing precise input for dynamic correction. Based on a temperature-fluorescence intensity-strain mapping table calibrated over the entire temperature range, an interpolation algorithm dynamically adapts to the nonlinear variation characteristics of the thermal expansion coefficient and elastic modulus of the optical fiber material, overcoming the failure bottleneck of traditional fixed compensation coefficients in temperature-induced sudden changes. The nonlinear correction algorithm calculates the parasitic strain component caused by the stripping temperature through difference calculation, effectively eliminating the coupling interference between the thermal expansion effect and the material's temperature sensitivity, and ensuring that the strain measurement accuracy is not affected by ambient temperature fluctuations. Finally, the calibrated wavelength offset is combined with the strain-flow model to output the flow value, maintaining measurement consistency even under complex working conditions. This method forms a closed-loop correction logic through a three-level compensation mechanism of "signal co-location acquisition - dynamic mapping adaptation - nonlinear error stripping", significantly improving the anti-interference ability and measurement reliability of fiber Bragg grating in temperature-changing environments. 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 briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

[0047] Figure 2 A schematic diagram of the principle of a gas flow meter based on fiber Bragg grating provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0049] Figure 1 The present invention provides a schematic flow chart of a fiber Bragg grating temperature drift compensation method, comprising:

[0050] Step S1: obtaining 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 detecting the wavelength offset of the fiber Bragg 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 experimentally calibrating the relationship between quantum dot fluorescence intensity and fiber Bragg grating strain at different temperatures.

[0052] Step S3: performing nonlinear correction on the wavelength offset using the strain compensation coefficient to generate a compensated wavelength offset.

[0053] Step S4: outputting a calibrated flow value according to the compensated wavelength offset and a 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 a composite of core-shell structured quantum dots and a transparent epoxy resin, and its thickness is controlled at the micron level to maintain the strain sensitivity of the grating.

[0055] When the fiber is subjected to external mechanical forces, changes in the grating period cause a shift in the reflected wavelength, while temperature changes alter the fluorescence intensity through non-radiative recombination of carriers on the quantum dot surface states. The spectrometer simultaneously captures these two independent signals using a spectrometer: the reflected light wavelength shift reflects the total strain (including true strain and thermal expansion), while the fluorescence intensity represents 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 a constant temperature box and record the correspondence between the quantum dot fluorescence intensity and the grating wavelength offset at different temperatures. In practical applications, the mapping table can be queried based on the real-time fluorescence intensity to extract the strain compensation coefficient corresponding to the current temperature. This coefficient is essentially a comprehensive representation of the changes in the thermal expansion coefficient and elastic modulus of the optical fiber material caused by temperature, and is used to perform nonlinear corrections on the wavelength offset. For example, in the gas pipeline flow monitoring scenario, when the compensated wavelength offset is input into the strain-flow model, the flow calculation deviation caused by the day and night temperature difference can be significantly eliminated, thereby improving the consistency of the measurement results.

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

[0058] In some embodiments, obtaining the fluorescence intensity signal in step S1 includes:

[0059] Step S1a: generate fluorescence by exciting quantum dot temperature sensitive film with blue light source.

[0060] Step S1b: separate fluorescence signal and reflected light signal of fiber grating using a beam splitter.

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

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

[0063] The beam splitter can use a combination of a dichroic mirror and a bandpass filter, i.e., the dichroic mirror reflects blue light to the quantum dot temperature sensitive film while allowing red fluorescence to pass through; the bandpass filter further filters out the target fluorescence wavelength band and suppresses the background radiation interference of the optical fiber.

[0064] The photodetector can use a low-noise avalanche diode with a spectral response range that aligns with the quantum dot fluorescence emission peak, ensuring reliable capture of weak fluorescence signals.

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

[0066] In actual installation, the optical system can be precisely aligned through a six-dimensional adjustment stand to improve fluorescence collection efficiency. This design can achieve real-time synchronous detection of temperature signals, with a lag time shortened to milliseconds.

[0067] Based on the above scheme, the design of blue light excitation and beam splitting structure avoids signal crosstalk, ensuring the purity of fluorescence intensity detection, while optimizing the optical layout to enhance the weak light capture capability, 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: calibrate the relationship between the fluorescence intensity of the quantum dot temperature sensitive film and the strain of the fiber grating at different temperatures in a constant temperature environment.

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

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

[0072] First, under zero mechanical strain, a precision temperature-controlled platform was used to record the quantum dot fluorescence intensity as a function of temperature by increasing the temperature in a stepwise manner, thereby obtaining the corresponding relationship between fluorescence intensity and temperature. Subsequently, a gradient strain was applied to the optical fiber at a fixed temperature using a micro-displacement platform, and the linear relationship between the grating wavelength offset and the actual strain was recorded. The calibration data covers the operating temperature range of the device, and the strain gradient experimental data at each temperature point constitutes 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 nonlinear 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 use of full temperature range calibration combined with interpolation algorithm, complex working conditions of sudden and gradual temperature changes are covered, and the compensation coefficient dynamically adapts to changes in the thermal properties of the material, thus breaking through the limitations of the fixed compensation model.

[0076] In some embodiments, the nonlinear correction in step S3 includes:

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

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

[0079] Step S3c: Calculating the compensated wavelength offset according to the dynamic compensation coefficient.

[0080] Specifically, the core of the nonlinear correction algorithm lies in dynamically decoupling the coupled effects of temperature and strain. The theoretical temperature value can be calculated based on the real-time fluorescence intensity, and then the theoretical thermal strain caused by the current temperature can be inferred by combining the temperature-strain mapping relationship. The actual mechanical strain component is obtained by subtracting the measured total strain from the theoretical thermal strain. The dynamic compensation coefficient is essentially a factor that influences the temperature on the fiber material properties. Its calculation must account for the hysteresis effect of the temperature change rate on the material response. For example, in a rapid temperature rise scenario, the algorithm introduces temperature acceleration as a correction term to compensate for model errors caused by thermal conduction delays. For example, the dynamic compensation coefficient can be multiplied by the wavelength offset. The result of this multiplication is the wavelength offset corresponding to the temperature-induced parasitic strain component. This product is then subtracted from the wavelength offset, i.e., λ1 = λ0 - K(T) × T. Here, λ1 represents the wavelength offset after compensation, λ0 represents the wavelength offset before compensation, K(T) represents the dynamic compensation coefficient, and T represents the temperature. The strain signal after compensation can be reconstructed using a polynomial fitting algorithm, whose order is adaptively adjusted based on the local curvature of the mapping table.

[0081] In summary, the difference calculation dynamically corrects thermal expansion and material elastic changes, realizes adaptive nonlinear compensation for temperature drift, and avoids the residual error of traditional linear correction in high and low temperature alternating scenarios.

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

[0083] Step S3a1: extracting a plurality of adjacent data points in the mapping table that match the current fluorescence intensity.

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

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

[0086] Specifically, the theoretical strain value can be calculated using a spatial interpolation strategy. Four calibration data points closest to the current fluorescence intensity are selected from a mapping table to form a local interpolation unit. A radial basis function-based interpolation algorithm expands the discrete calibration points into a continuous temperature-strain relationship field by constructing a three-dimensional response surface.

[0087] During interpolation, the algorithm automatically identifies data distribution characteristics: a linear kernel function is used in areas of high linearity in the temperature-strain relationship, while a Gaussian kernel function is used in areas of nonlinear abrupt changes. The theoretical strain value at the current temperature point is calculated through surface projection, while the gradient information of adjacent data points is used as interpolation weights.

[0088] In summary, this embodiment adopts the neighboring data point interpolation strategy combined with the surface projection algorithm, which can accurately capture the nonlinear relationship between local temperature and strain and solve 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 working condition, the compensated strain values ​​converted from the compensated wavelength offsets corresponding to different flow rates are recorded.

[0091] Step S4b: Generate a quadratic function relationship between the compensation strain value and the flow velocity by least square 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 strain-flow relationship model is based on a deep fusion of fluid mechanics principles and measured data. During the calibration phase, the fiber Bragg grating (FBG) was installed in a standard flow calibration device. The flow rate was controlled by adjusting a valve, and the compensated wavelength offset and the turbine flowmeter's baseline value were simultaneously recorded. The experiments covered a variety of flow regimes, including laminar and turbulent flow, to ensure the model's adaptability to varying flow conditions.

[0094] During the data preprocessing phase, a sliding average filter was used to eliminate high-frequency noise introduced by mechanical vibration, while retaining the low-frequency strain signal related to flow velocity. A quadratic function was preferred for least-squares fitting because it can characterize the nonlinear relationship between flow velocity and pipe wall strain: at low flow rates, strain increases approximately linearly with flow rate; at high flow rates, pressure pulsations caused by turbulence cause strain growth to slow.

[0095] Genetic algorithm is introduced in the model parameter optimization stage to screen out the optimal coefficient combination through multiple generations of iteration.

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

[0097] In some embodiments, the method further comprises the step of filtering abnormal data:

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

[0099] Step S6: If the fluctuation amplitude exceeds a preset threshold value in a plurality of consecutive sampling periods, it is determined to be an aging signal of the quantum dot temperature-sensitive film.

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

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

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

[0103] The threshold setting needs to take into account the aging characteristics of the quantum dot temperature-sensitive film. A looser threshold should be set initially to avoid false alarms, and the threshold parameters should be dynamically tightened as the operating time increases.

[0104] If excessive fluctuations are detected over multiple consecutive sampling periods, the system initiates an aging diagnostic process: first, switching to a backup light source to eliminate excitation light attenuation, then comparing the peak shifts in the current fluorescence spectrum with those in the initial calibration spectrum. If film aging is confirmed, the system triggers an audible and visual alarm and automatically switches to a redundant temperature sensor (such as a surface-mount platinum resistor) to maintain uninterrupted compensation.

[0105] The fluctuation threshold judgment and redundant switching mechanism triggers an early warning at the early stage of quantum dot aging, which can ensure the continued reliability of the compensation system when 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 quantum dot temperature-sensitive films are precisely controlled through material design and structural optimization.

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

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

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

[0111] In summary, the spectral control design of core-shell quantum dots can achieve band isolation of excitation light and fluorescence, reduce signal cross-interference, and enhance the anti-attenuation ability of red light fluorescence during long-distance transmission.

[0112] The embodiment of the present invention further provides a fiber Bragg grating temperature drift compensation device, comprising:

[0113] Quantum dot temperature-sensitive film, coated on the surface of fiber Bragg grating, is used to generate fluorescence signals in response to temperature changes.

[0114] A blue light source is set at the quantum dot temperature-sensitive film to excite fluorescence.

[0115] The optical splitter is connected to the fiber Bragg grating and is used to separate the reflected light signal and the fluorescence signal.

[0116] The spectrometer is connected to the spectrometer and is used to detect the wavelength shift of the reflected light signal and the intensity of the fluorescence signal.

[0117] The processing module has a built-in temperature-fluorescence intensity-strain mapping table, which is used to query the compensation coefficient according to the fluorescence signal intensity and perform nonlinear correction on the wavelength offset.

[0118] The flow calculation unit outputs a flow value according to the corrected wavelength offset.

[0119] Specifically, the compensation device can adopt a modular packaging design, integrating optical paths, circuits and algorithm units.

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

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

[0122] The beam splitter uses a combination of a gradient refractive index lens and a two-color filter to achieve physical separation of reflected light and fluorescent signals: the 1550nm reflected light is collimated by the lens and enters the fiber circulator, while the 620nm fluorescent signal is focused by the filter to the photodetector.

[0123] The processing module is embedded in the edge computing unit, runs the temperature compensation algorithm and abnormality diagnosis program, supports local real-time processing and reduces transmission delay.

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

[0125] In some embodiments, the optical splitter comprises:

[0126] The first channel transmits the reflected light signal of the fiber Bragg 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 transflection.

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

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

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

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

[0133] In addition, the embodiment of the present invention further provides a gas flow meter based on fiber Bragg grating, which is a vortex flow meter. Figure 2 A schematic diagram of the principle of a gas flow meter based on fiber Bragg grating provided in an embodiment of the present invention.

[0134] When a triangular prism-shaped vortex generator is placed in a fluid, regular vortices are generated alternately on both sides of the generator. These vortices are called Karman vortices, and are arranged asymmetrically downstream of the generator. A vortex flowmeter uses the Karman vortex street principle to measure the volume flow rate, standard volume flow rate, or mass flow rate of gases, steam, or liquids. It can also be used as a flow transmitter in automatic flow control systems.

[0135] The vortex flowmeter (sensor) uses the principle of fluid oscillation to measure flow. When the fluid passes through the vortex flow transmitter in the pipeline, two rows of vortices proportional to the flow velocity are generated alternately up and down behind the vortex generator of the triangular prism. The release frequency of the vortex is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed by the following formula:

[0136] f=Stv / d

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

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

[0139] When the Reynolds number Re is in the range of 102-105, the St value is about 0.2. In the measurement, the Reynolds number of fluid is as far as possible 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 fluid flowing through the vortex generator can be calculated, and then the flow rate q can be calculated by the formula: q=va, wherein a is the cross-sectional area of fluid flowing through the vortex generator.

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

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

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

[0143] II. Packaging and material selection of fiber grating:

[0144] 1. Packaging protection of optical fiber: the optical fiber is fixed by metal elbow and pipe clamp, which can convert environmental physical quantities into optical signals with the least distortion in the gas flowmeter pipeline, and also can ensure its stability and reliability in harsh environment. The packaging design of optical fiber protects it from external mechanical stress and temperature change.

[0145] 2. Material and treatment of sensor shell: the sensor shell is made of 630 stainless steel material and is heat treated to achieve mechanical hardness HRC45, which ensures the durability and stability of the sensor in high pressure environment.

[0146] III. Specific structure of fiber grating:

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

[0148] Temperature Compensation: The temperature grating compensates for flow rate grating stress measurement errors caused by temperature changes, ensuring accurate flow measurement. The temperature compensation algorithm uses calibration data for linear fitting to eliminate the influence of temperature on flow measurement.

[0149] 2. Common mode elimination mechanism: The vibration grating detects pipeline vibration data and eliminates the influence of pipe vibration through common mode operation, ensuring measurement accuracy and improving system stability.

[0150] The signal data of the flow grating, stress grating and temperature grating 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, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A method for compensating temperature drift of a fiber Bragg grating, characterized in that: include: Step S1: obtaining a fluorescence intensity signal of a quantum dot temperature-sensitive film coated on the surface of a fiber Bragg grating (FBG) by a spectrometer, and synchronously detecting a wavelength offset of the fiber Bragg grating; Step S2: According to the fluorescence intensity signal, query a pre-stored temperature-fluorescence intensity-strain mapping table to obtain a strain compensation coefficient corresponding to the current temperature, wherein the mapping table is generated by experimentally calibrating the relationship between quantum dot fluorescence intensity and fiber Bragg grating strain at different temperatures; Step S3: performing nonlinear correction on the wavelength offset using the strain compensation coefficient to generate a compensated wavelength offset; Step S4: outputting a calibrated flow value according to the compensated wavelength offset and a preset strain-flow relationship model.

2. The method according to claim 1, characterized in that The acquisition of the fluorescence intensity signal in step S1 includes: Step S1a: Exciting the quantum dot temperature-sensitive film to generate fluorescence by a blue light source; Step S1b: using a spectrometer to separate the fluorescence signal from the reflected light signal of the fiber grating; Step S1c: measuring the intensity of the fluorescence signal by a photodetector, and measuring the wavelength shift of the reflected light signal by the spectrometer.

3. The method according to claim 1, characterized in that The establishment of the temperature-fluorescence intensity-strain mapping table in step S2 includes: Step S2a: in a constant temperature environment, calibrating 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: Generate a continuous temperature-fluorescence intensity-strain mapping table using an interpolation algorithm and store it as a database.

4. The method according to claim 1, wherein The nonlinear correction in step S3 includes: Step S3a: calculating the theoretical strain value at the current temperature according to the fluorescence intensity signal; Step S3b: performing 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: Calculating the compensated wavelength offset 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: extracting a plurality of adjacent data points in the mapping table that match the current fluorescence intensity; Step S3a2: generating a continuous temperature-strain surface based on a radial basis function interpolation algorithm; Step S3a3: interpolating a theoretical strain value on the surface according to the current temperature.

6. The method according to claim 1, characterized in that The establishment of the strain-flow relationship model in step S4 includes: Step S4a: Under the calibration working condition, recording the compensated strain value converted from the compensated wavelength offset corresponding to different flow rates; Step S4b: generating a quadratic function relationship between the compensation strain value and the flow velocity by least square fitting; Step S4c: writing the quadratic function relationship into the flow calculation module and outputting the flow value in real time.

7. The method according to claim 1, characterized in that The method further comprises the step of filtering abnormal data: Step S5: monitoring the fluctuation amplitude of the fluorescence intensity signal; Step S6: If the fluctuation amplitude exceeds a preset threshold value in multiple consecutive sampling periods, it is determined to be a quantum dot temperature-sensitive film aging signal; Step S7: trigger an alarm and switch to the backup 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. A fiber Bragg grating temperature drift compensation device, characterized in that: include: Quantum dot temperature-sensitive film, coated on the surface of the fiber Bragg grating, is used to generate fluorescence signals in response to temperature changes; A blue light source is aligned with the quantum dot temperature-sensitive film to excite fluorescence; An optical splitter connected to the fiber grating and used to separate the reflected light signal from the fluorescent signal; a spectrometer, connected to the spectrometer, for detecting the wavelength shift of the reflected light signal and the intensity of the fluorescence signal; A processing module having a built-in temperature-fluorescence intensity-strain mapping table for querying a compensation coefficient according to the fluorescence signal intensity and performing nonlinear correction on the wavelength offset; The flow calculation unit outputs a flow value according to the corrected wavelength offset.

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

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