Hot wire type optical fiber wind speed measuring device and demodulation method thereof
By utilizing the bandwidth demodulation effect of cobalt-doped fiber Bragg gratings and combining it with the self-adjustment of optical power in the PD detection unit, high-precision fiber optic anemometer measurement was achieved, solving the problems of cross-sensitivity to ambient temperature and high cost of fiber optic hot-wire anemometers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-03-13
AI Technical Summary
Existing fiber optic hot-wire anemometers suffer from cross-sensitivity to ambient temperature during measurement, and their manufacturing process is complex and costly.
A bandwidth demodulation fiber optic hot-wire anemometer employing the chirp effect of a cobalt-doped fiber Bragg grating (CD-FBG) measures wind speed by monitoring the relationship between reflected bandwidth and wind speed. It utilizes the airflow cooling effect to cause changes in the chirp rate of the cobalt-doped fiber Bragg grating, combined with a PD detection unit for self-adjustment of optical power, to eliminate differences in light intensity and improve detection accuracy.
It effectively solves the problem of cross-sensitivity to ambient temperature, reduces manufacturing difficulty and cost, improves detection accuracy, and avoids errors caused by center wavelength drift.
Smart Images
Figure CN121656590A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of fiber optic sensor technology, and in particular to a hot-wire fiber optic anemometer and its demodulation method. Background Technology
[0002] Wind speed measurement has significant applications in energy production, aerospace engineering, and meteorological monitoring. Traditional electrical anemometers suffer from drawbacks such as dust accumulation, susceptibility to changes in medium composition, probe damage, the need for calibration in conductive fluids, and lack of explosion-proof capabilities. Fiber optic hot-wire anemometers, with their advantages of small size, high sensitivity, resistance to electromagnetic interference, and long-distance measurement capabilities, are gradually becoming a competitive wind speed measurement solution.
[0003] In recent years, fiber optic hot-wire anemometer measurement schemes based on light intensity demodulation have gradually attracted attention. Existing technology proposes an intensity-modulated fiber optic thermal anemometer based on graphene film. This scheme utilizes two graded-index fibers with graphene film coated on their end faces, collimated by a grooved base plate, and heated by a 532nm laser. Intensity-modulated wind speed measurement is achieved by measuring the transmitted power at different wind speeds. Thanks to the excellent heat dissipation performance and open structure of the graphene film, this anemometer exhibits rapid dynamic response characteristics. However, the need for a large grooved base plate for collimation during measurement leads to wind field interference, affecting measurement accuracy.
[0004] Existing technology also proposes an intensity-interrogative fiber optic hot-wire anemometer based on the chirping effect of a fiber Bragg grating (FBG). This scheme coats the FBG surface with a silver film and couples a 1480nm laser beam into the fiber cladding via a long-period grating (LPG). The silver film absorbs the laser energy and converts it into heat. Because the laser power gradually attenuates along the length of the fiber grating, a temperature gradient is formed, which in turn induces the chirping effect of the FBG, leading to a broadening of the reflected spectral bandwidth and an increase in reflected light power. When airflow passes through, the temperature gradient weakens due to cooling, and the chirping rate of the FBG decreases with increasing airflow velocity, thus establishing a relationship between reflected light power and wind speed. However, this type of scheme still requires a mode coupling device and a metal coating, resulting in complex manufacturing processes and high costs. Summary of the Invention
[0005] This application provides a hot-wire fiber optic anemometer and its demodulation method, which can solve the problem of cross-sensitivity to ambient temperature in fiber optic grating hot-wire anemometers.
[0006] To achieve the above objectives, according to a first aspect of this application, a hot-wire fiber optic wind speed measurement device is provided. The device includes a demodulation device and a fiber optic wind speed sensor. The demodulation device includes a main control board, a thermal excitation light source, a broadband light source, a spectral analysis unit, a PD detection unit, a wavelength division multiplexer, and a circulator. The first port of the main control board is connected to the first port of the thermal excitation light source; the second port of the main control board is connected to the first port of the broadband light source; the third port of the main control board is connected to the first port of the spectral analysis unit; and the fourth port of the main control board is connected to the first port of the PD detection unit. The second port of the thermal excitation light source is connected to the first port of the wavelength division multiplexer; the second port of the broadband light source is connected to the first port of the circulator; the second port of the spectral analysis unit is connected to the second port of the PD detection unit; the third port of the PD detection unit is connected to the second port of the circulator; the third port of the circulator is connected to the second port of the wavelength division multiplexer; and the third port of the wavelength division multiplexer is connected to the fiber optic wind speed sensor.
[0007] Furthermore, the power attenuation of the laser emitted by the thermally excited light source in the cobalt-doped fiber Bragg grating follows an exponential distribution law as follows:
[0008] in, for The optical power of the point, For input laser power, This represents the absorption coefficient of the cobalt-doped fiber at the laser wavelength. This is the distance from the entry point to the location of the cobalt-doped fiber Bragg grating.
[0009] Furthermore, the cobalt-doped fiber Bragg grating exhibits a dynamic thermal equilibrium as shown in the following formula;
[0010] in, To absorb the heat transfer coefficient of the cobalt-doped fiber Bragg grating from the laser power, airflow velocity Cobalt-doped fiber Bragg gratings in The temperature of the point, For airflow temperature, , and All are empirical coefficients.
[0011] Furthermore, when the cobalt-doped fiber Bragg grating reaches thermal equilibrium, a temperature gradient is formed along the grating axis, and the maximum temperature difference of the temperature gradient can be described by the following formula:
[0012] in, denoted as the length of the cobalt-doped fiber Bragg grating.
[0013] Furthermore, the bandwidth of the reflection spectrum of the cobalt-doped fiber Bragg grating exhibits the following linear relationship with the temperature gradient: ,in To determine the temperature sensitivity of the cobalt-doped fiber Bragg grating, the following equation is derived based on the linear relationship: The reflection bandwidth of the cobalt-doped fiber Bragg grating is a function of the airflow velocity:
[0014] in, This represents the reflection bandwidth of the cobalt-doped fiber Bragg grating when it is not heated by laser, i.e., the initial state of the cobalt-doped fiber Bragg grating. The change with temperature. This is an empirical coefficient.
[0015] To achieve the above objectives, according to a second aspect of this application, a demodulation method based on a hot-wire fiber optic anemometer is also provided. The demodulation method is applied to the hot-wire fiber optic anemometer as described in the first aspect and includes the following steps: S1. The main control board controls the activation of the broadband light source and the thermal excitation light source. The thermal excitation light source generates a thermal effect in the cobalt-doped fiber Bragg grating in the fiber optic wind speed sensor through the wavelength division multiplexer. S2. The measurement light emitted by the broadband light source enters the optical anemometer through the circulator and wavelength division multiplexer. After the optical anemometer collects the spectrum, it is transmitted to the PD detection unit through the wavelength division multiplexer and circulator. S3, the PD detection unit determines whether the spectrum meets the threshold; if it does not meet the threshold, it performs light source self-adjustment and continues to determine whether the spectrum meets the threshold; if it meets the threshold, it transmits the spectrum to the spectrum analysis unit and continuously acquires the spectrum to obtain the mean spectrum and transmits it to the main control board. S4. The main control board normalizes the mean spectrum, filters it, and calculates the overall bandwidth. ; S5, main control board will integrate bandwidth Substitute the values into the fitting formula to obtain the current gas flow rate; S6. Prepare for the next data collection operation and return to S2.
[0016] Furthermore, step S3 includes the following steps: The PD detection unit is responsible for detecting the intensity of the reflectance spectrum and automatically adjusting the optical power according to a preset threshold; the threshold is the error between the peak intensity of the reflectance spectrum and the calibration value, and the threshold range is [insert range here]. When the spectrum exceeds the preset threshold range, the light source self-adjusts. When the spectrum does not exceed the preset threshold range, the spectral analysis unit collects the reflectance spectral data returned by the sensor, collects several sets each time and takes the average value to obtain the mean spectrum.
[0017] Furthermore, step S4 includes the following steps: The peak values are found in the mean spectrum, and the intensity data of the reflectance spectrum are normalized using the following formula to obtain the normalized intensity spectrum. :
[0018] in, The ordinate value of each point in the spectrum. The Y-axis coordinate corresponding to the maximum spectral value. This represents the Y-axis coordinate corresponding to the minimum value of the spectrum.
[0019] Furthermore, step S4 includes the following steps: In the normalized light intensity spectrum, find the wavelengths corresponding to the 3 dB attenuation position and the 5 dB attenuation position, respectively, and denot them as _____. , , and The corresponding overall bandwidth is calculated using the following formula:
[0020] in, The overall bandwidth is obtained by calculating the spectrum corresponding to the current airflow velocity.
[0021] Furthermore, S5 includes the following steps: The equipment was calibrated, and the overall bandwidth was obtained at several gas flow rates. The gas flow rate is obtained by fitting the corresponding airflow velocity using the following formula. With overall bandwidth Relationship:
[0022] in, It is a constant.
[0023] The demodulation device of this application utilizes a PD detection unit to self-adjust optical power, preventing differences in light intensity caused by dirt or bending on the sensor mating surface, thereby improving detection accuracy. This application employs bandwidth demodulation to avoid the problem of cross-sensitivity caused by drift in the center wavelength of the reflection spectrum due to temperature changes or stress changes such as vibration. Furthermore, the bandwidth demodulation method ensures that although the center wavelength changes, the bandwidth of the reflection spectrum remains essentially unchanged, without significantly altering its internal temperature gradient distribution. This effectively solves the problem of cross-sensitivity to ambient temperature that exists in traditional fiber optic grating hot-wire anemometers when using intensity demodulation. Attached Figure Description
[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0025] Figure 1 This is a structural diagram of the hot-wire fiber optic anemometer provided according to an embodiment of this application; Figure 2 The reflection spectra of cobalt-doped fiber Bragg gratings at different laser powers according to embodiments of this application are shown. Figure 3 This is a graph showing the functional relationship between reflection bandwidth and laser power according to an embodiment of this application; Figure 4 The reflection spectra of cobalt-doped fiber Bragg gratings at different airflow velocities according to embodiments of this application; Figure 5 This is a graph showing the functional relationship between reflectance spectral bandwidth and airflow velocity according to an embodiment of this application. Figure 6 This is a flowchart of a demodulation method based on a hot-wire fiber optic anemometer provided in an embodiment of this application. Figure 7 Provided according to the embodiments of this application Attenuation and Wavelength diagram corresponding to the attenuation position.
[0026] Label Explanation: 1. Main control board first port; 2. Main control board second port; 3. Main control board third port; 4. Main control board fourth port; 5. Thermal excitation light source first port; 6. Thermal excitation light source second port; 7. Broadband light source first port; 8. Broadband light source second port; 9. Spectral analysis unit first port; 10. Spectral analysis unit second port; 11. PD detection unit first port; 12. PD detection unit second port; 13. PD detection unit third port; 14. Circulator first port; 15. Circulator second port; 16. Circulator third port; 17. Wavelength division multiplexer first port; 18. Wavelength division multiplexer second port; 19. Wavelength division multiplexer third port. Detailed Implementation
[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0028] To address the problems existing in the prior art, this application proposes a bandwidth demodulation type fiber hot-wire wind speed measurement device based on the chirp effect of laser-heated cobalt-doped fiber Bragg gratings (CD-FBG). The demodulation method utilizes the characteristic of the chirp rate change of the cobalt-doped fiber Bragg grating caused by the airflow cooling effect, and realizes wind speed measurement by monitoring the relationship between reflection bandwidth and wind speed.
[0029] like Figure 1 The hot-wire fiber optic anemometer of this application comprises two parts: a demodulation device and a sensor. The demodulation device mainly includes: a main control board, a thermal excitation light source, a broadband light source, a spectral analysis unit, a PD detection unit, a wavelength division multiplexer, and a circulator. The sensor includes a fiber optic anemometer. The connections are as follows: the first port 1 of the main control board is connected to the first port 5 of the thermal excitation light source; the second port 2 of the main control board is connected to the first port 7 of the broadband light source; the third port 3 of the main control board is connected to the first port 9 of the spectral analysis unit; and the fourth port 4 of the main control board is connected to the first port 11 of the PD detection unit. The second port 6 of the thermal excitation light source is connected to the first port 17 of the wavelength division multiplexer; the second port 8 of the broadband light source is connected to the first port 14 of the circulator; the second port 10 of the spectral analysis unit is connected to the second port 12 of the PD detection unit; the third port 13 of the PD detection unit is connected to the second port 15 of the circulator; the third port 16 of the circulator is connected to the second port 18 of the wavelength division multiplexer; and the third port 19 of the wavelength division multiplexer is connected to the fiber optic anemometer.
[0030] like Figure 2 As shown, the specific operation flow of the hot-wire fiber optic anemometer of this application is as follows: First, the main control board activates the broadband light source to acquire the reflection spectrum without an excitation source. Then, the main control board activates the thermally excited light source and gradually increases its emission power. When the thermally excited light source is incident on the cobalt-doped fiber Bragg grating within the bandwidth demodulation hot-wire anemometer via a wavelength division multiplexer, a significant thermal effect occurs due to the high absorption coefficient of the cobalt-doped fiber for the thermally excited light source. The cobalt-doped fiber Bragg grating absorbs laser energy and converts it into heat energy, but this thermal effect is not uniform; the laser power exhibits an exponential decay distribution along the axis of the cobalt-doped fiber Bragg grating. The power attenuation of the laser emitted by the thermally excited source within the cobalt-doped fiber Bragg grating follows an exponential distribution law as follows:
[0031] in, for The optical power of the point, For input laser power, This represents the absorption coefficient of the cobalt-doped fiber at the laser wavelength. This is the distance from the splicing point to the position of the cobalt-doped fiber Bragg grating; this attenuation heating causes a temperature gradient to form inside the cobalt-doped fiber Bragg grating, resulting in a chirp effect, specifically manifested as a broadening of the reflectance spectral bandwidth, such as... Figure 2 As shown, with the increase of heating laser power, the bandwidth of its reflection spectrum gradually broadens; as... Figure 3 As shown, the bandwidth broadening is linearly related to the laser heating power.
[0032] At zero airflow velocity, for a specific laser power, the cobalt-doped fiber Bragg grating will reach thermal equilibrium, where the heat generated internally equals the heat dissipated to the surrounding environment, and the temperature reaches a stable maximum value. When airflow passes through the cobalt-doped fiber Bragg grating, the cooling effect of the airflow changes the temperature distribution characteristics of the grating. Specifically, increasing the airflow velocity enhances the cooling effect, leading to a decrease in the axial temperature gradient of the cobalt-doped fiber Bragg grating, which in turn causes a change in the reflectance spectral bandwidth. This dynamic thermal equilibrium process can be described by the following relationship:
[0033] in, To absorb the heat transfer coefficient of the cobalt-doped fiber Bragg grating from the laser power, airflow velocity Cobalt-doped fiber Bragg gratings in The temperature of the point, For airflow temperature, , and All are empirical coefficients.
[0034] When a cobalt-doped fiber Bragg grating reaches thermal equilibrium, a temperature gradient is formed along the grating axis. The maximum temperature difference of this gradient can be described by the following formula:
[0035] in, The length of the cobalt-doped fiber Bragg grating; since the bandwidth of the reflection spectrum of the cobalt-doped fiber Bragg grating is linearly related to the temperature gradient: ,in To determine the temperature sensitivity of the cobalt-doped fiber Bragg grating, the following equation is derived: the reflection bandwidth of the cobalt-doped fiber Bragg grating is a function of the airflow velocity:
[0036] in, This represents the reflection bandwidth of the cobalt-doped fiber Bragg grating when it is not heated by laser, i.e., the initial state of the cobalt-doped fiber Bragg grating. The change with temperature. This is an empirical coefficient.
[0037] The relationship between the aforementioned reflection bandwidth and airflow velocity constitutes the core working principle of the bandwidth demodulation hot-wire anemometer based on the chirp effect of a cobalt-doped fiber Bragg grating. Specific variations are as follows: Figure 4 As shown, with increasing gas flow rate, the bandwidth of its reflectance spectrum gradually decreases, and the trend is as follows. Figure 5 As shown.
[0038] like Figure 6 As shown, this application also provides a demodulation method based on a hot-wire fiber optic anemometer, comprising the following steps: S1. The main control board controls the activation of the broadband light source and the thermal excitation light source. The thermal excitation light source generates a thermal effect in the cobalt-doped fiber Bragg grating in the fiber optic wind speed sensor through the wavelength division multiplexer. S2. The measurement light emitted by the broadband light source enters the optical anemometer through the circulator and wavelength division multiplexer. After the optical anemometer collects the spectrum, it is transmitted to the PD detection unit through the wavelength division multiplexer and circulator. S3, the PD detection unit determines whether the spectrum meets the threshold; if it does not meet the threshold, it performs light source self-adjustment and continues to determine whether the spectrum meets the threshold; if it meets the threshold, it transmits the spectrum to the spectrum analysis unit and continuously acquires the spectrum to obtain the mean spectrum and transmits it to the main control board. S4. The main control board normalizes the mean spectrum, filters it, and calculates the overall bandwidth. ; S5, main control board will integrate bandwidth Substitute the values into the fitting formula to obtain the current gas flow rate; S6. Prepare for the next data collection operation and return to S2.
[0039] Furthermore, in S3, the PD detection unit is responsible for detecting the intensity of the reflected spectrum and adjusting the optical power according to a preset threshold to prevent differences in light intensity caused by dirt, bending, etc., on the sensor mating surface; the threshold is the error between the peak intensity of the reflected spectrum and the calibration value, generally within a certain range. Within a certain range, for example, if the calibration value is 50uw, then the threshold range is 47.5uw-52.5uw. If it is not within the threshold range, then the optical power needs to be self-adjusted. The spectral analysis unit collects the reflectance spectral data returned by the sensor, collects several sets each time, and takes the average value to suppress random noise and improve the signal-to-noise ratio; thus, the mean spectrum is obtained. In a specific embodiment, 10 sets are collected each time and the average value is taken to obtain one set of mean spectrum.
[0040] Furthermore, in S4, peak values are found from the mean spectrum, and the intensity data of the reflected spectrum is normalized using the following formula to obtain a normalized intensity spectrum. Eliminate the influence of light source fluctuations:
[0041] in, The ordinate value of each point in the spectrum. The Y-axis coordinate corresponding to the maximum spectral value. The Y-axis coordinate corresponding to the minimum value of the spectrum; Furthermore, in S4, in the normalized light intensity spectrum, the wavelengths corresponding to the 3 dB attenuation position and the 5 dB attenuation position are found respectively, such as... Figure 7 As shown, they are respectively denoted as , , and The corresponding overall bandwidth is calculated using the following formula:
[0042] in, The overall bandwidth is obtained by calculating the spectrum corresponding to the current airflow velocity; Furthermore, in S5, the above process is repeated to calibrate the equipment and obtain the comprehensive bandwidth at several gas flow rates. The corresponding airflow velocity is fitted using the following formula, such as... Figure 5 As shown, the gas flow rate is obtained according to the fitting formula. With overall bandwidth Relationship:
[0043] in, It is a constant; in a specific embodiment, , , , That is:
[0044] Thus, the gas flow rate of the current embodiment is obtained. With overall bandwidth Relationship:
[0045] The beneficial effects of this application are as follows: 1. Fiber optic wind speed sensors utilize fiber Bragg gratings inscribed on fiber doped with transition metal ions. Thermal excitation light sources are introduced into the fiber doped with transition metal ions, causing the transition metal ions to change from the ground state to the excited state, thus realizing photothermal conversion and transforming themselves into "hot wires". This eliminates the need for metal coatings and mode coupling devices, reducing the manufacturing difficulty and cost of the sensor. 2. The demodulation equipment uses the PD detection unit to self-adjust the optical power, preventing differences in light intensity caused by dirt or bending on the sensor mating surface, thereby improving detection accuracy; 3. By using bandwidth demodulation, the problem of cross-sensitivity caused by the drift of the center wavelength of the reflection spectrum due to changes in temperature or stress such as vibration is avoided. 4. By using the bandwidth demodulation method, although the center wavelength changes, the bandwidth of the reflection spectrum remains basically unchanged and the internal temperature gradient distribution is not significantly altered. This effectively solves the problem of cross-sensitivity to ambient temperature in traditional fiber optic hot-wire anemometers that use intensity demodulation.
[0046] This application also provides a computer program product, including computer instructions. When the computer instructions are executed by a processor, they implement the various steps of the aforementioned hot-wire fiber optic anemometer and demodulation method embodiments, and can achieve the same beneficial effects as the aforementioned hot-wire fiber optic anemometer and demodulation method embodiments. To avoid repetition, they will not be described again here.
[0047] In the several embodiments provided in this application, it should be understood that the disclosed methods and apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.
[0048] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can be physically included separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional units.
[0049] The integrated units implemented as software functional units described above can be stored in a computer-readable storage medium. These software functional units, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute some steps of the transmission and reception methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.
[0050] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles described in this application, and these improvements and modifications should also be considered within the scope of protection of this application.
Claims
1. A hot-wire fiber optic anemometer, characterized in that, The device includes a demodulation unit and an optical fiber wind speed sensor. The demodulation unit includes a main control board, a thermal excitation light source, a broadband light source, a spectral analysis unit, a PD detection unit, a wavelength division multiplexer, and a circulator. The first port (1) of the main control board is connected to the first port (5) of the thermal excitation light source, the second port (2) of the main control board is connected to the first port (7) of the broadband light source, the third port (3) of the main control board is connected to the first port (9) of the spectral analysis unit, and the fourth port (4) of the main control board is connected to the first port (11) of the PD detection unit; the second port (6) of the thermal excitation light source is connected to the first port (17) of the wavelength division multiplexer; the second port (8) of the broadband light source is connected to the first port (14) of the circulator; the second port (10) of the spectral analysis unit is connected to the second port (12) of the PD detection unit; the third port (13) of the PD detection unit is connected to the second port (15) of the circulator; the third port (16) of the circulator is connected to the second port (18) of the wavelength division multiplexer; and the third port (19) of the wavelength division multiplexer is connected to the fiber optic wind speed sensor.
2. The hot-wire fiber optic anemometer according to claim 1, characterized in that, The power attenuation of the laser emitted by the thermally excited light source in the cobalt-doped fiber Bragg grating follows an exponential distribution law as follows: in, for The optical power of the point, For input laser power, This represents the absorption coefficient of the cobalt-doped fiber at the laser wavelength. This is the distance from the entry point to the location of the cobalt-doped fiber Bragg grating.
3. The hot-wire fiber optic anemometer according to claim 2, characterized in that, The cobalt-doped fiber Bragg grating exists in a dynamic thermal equilibrium as shown in the following formula; in, To absorb the heat transfer coefficient of the cobalt-doped fiber Bragg grating from the laser power, airflow velocity Cobalt-doped fiber Bragg gratings in The temperature of the point, For airflow temperature, , and All are empirical coefficients.
4. The hot-wire fiber optic anemometer according to claim 3, characterized in that, When the cobalt-doped fiber Bragg grating reaches thermal equilibrium, a temperature gradient is formed along the grating axis. The maximum temperature difference of the temperature gradient can be described by the following formula: in, denoted as the length of the cobalt-doped fiber Bragg grating.
5. The hot-wire fiber optic anemometer according to claim 4, characterized in that, The bandwidth of the reflection spectrum of the cobalt-doped fiber Bragg grating exhibits the following linear relationship with the temperature gradient: ,in To determine the temperature sensitivity of the cobalt-doped fiber Bragg grating, the following equation is derived based on the linear relationship: The reflection bandwidth of the cobalt-doped fiber Bragg grating is a function of the airflow velocity: in, This represents the reflection bandwidth of the cobalt-doped fiber Bragg grating when it is not heated by laser, i.e., the initial state of the cobalt-doped fiber Bragg grating. The change with temperature. This is an empirical coefficient.
6. A demodulation method based on a hot-wire fiber optic anemometer, characterized in that, The demodulation method, applied to the hot-wire fiber optic anemometer as described in any one of claims 1-5, includes the following steps: S1. The main control board controls the activation of the broadband light source and the thermal excitation light source. The thermal excitation light source generates a thermal effect in the cobalt-doped fiber Bragg grating in the fiber optic wind speed sensor through the wavelength division multiplexer. S2. The measurement light emitted by the broadband light source enters the optical anemometer through the circulator and wavelength division multiplexer. After the optical anemometer collects the spectrum, it is transmitted to the PD detection unit through the wavelength division multiplexer and circulator. S3, the PD detection unit determines whether the spectrum meets the threshold; if it does not meet the threshold, it performs light source self-adjustment and continues to determine whether the spectrum meets the threshold; if it meets the threshold, it transmits the spectrum to the spectrum analysis unit and continuously acquires the spectrum to obtain the mean spectrum and transmits it to the main control board. S4. The main control board normalizes the mean spectrum, filters it, and calculates the overall bandwidth. ; S5, main control board will integrate bandwidth Substitute the values into the fitting formula to obtain the current gas flow rate; S6. Prepare for the next data collection operation and return to S2.
7. The demodulation method based on a hot-wire fiber optic anemometer according to claim 6, characterized in that, S3 includes the following steps: The PD detection unit is responsible for detecting the intensity of the reflectance spectrum and automatically adjusting the optical power according to a preset threshold; the threshold is the error between the peak intensity of the reflectance spectrum and the calibration value, and the threshold range is [insert range here]. When the spectrum exceeds the preset threshold range, the light source self-adjusts. When the spectrum does not exceed the preset threshold range, the spectral analysis unit collects the reflectance spectral data returned by the sensor, collects several sets each time and takes the average value to obtain the mean spectrum.
8. The demodulation method based on a hot-wire fiber optic anemometer according to claim 7, characterized in that, S4 includes the following steps: The peak values are found in the mean spectrum, and the intensity data of the reflectance spectrum are normalized using the following formula to obtain the normalized intensity spectrum. : in, The ordinate value of each point in the spectrum. The Y-axis coordinate corresponding to the maximum spectral value. This represents the Y-axis coordinate corresponding to the minimum value of the spectrum.
9. The demodulation method based on a hot-wire fiber optic anemometer according to claim 8, characterized in that, S4 includes the following steps: In the normalized light intensity spectrum, find the wavelengths corresponding to the 3 dB attenuation position and the 5 dB attenuation position, respectively, and denot them as _____. , , and The corresponding overall bandwidth is calculated using the following formula: in, The overall bandwidth is obtained by calculating the spectrum corresponding to the current airflow velocity.
10. The demodulation method based on a hot-wire fiber optic anemometer according to claim 9, characterized in that, S5 includes the following steps: The equipment was calibrated, and the overall bandwidth was obtained at several gas flow rates. The gas flow rate is obtained by fitting the corresponding airflow velocity using the following formula. With overall bandwidth Relationship: in, It is a constant.