Multi-physical field demodulation system and method based on mixed gas chamber

Abstract

The invention provides a multi-physics field demodulation system and method based on a mixed gas chamber, and the system comprises a scanning light source, a beam splitter, a Bragg fiber grating, the mixed gas chamber, an F-P etalon, an acquisition card and an upper computer which are connected. A light beam emitted by the scanning light source is split by the beam splitter and is divided into three paths to enter the fiber bragg grating, the mixed gas chamber and the F-P etalon, and reflected light of the fiber bragg grating and transmission light of the mixed gas chamber and the F-P etalon respectively enter different channels of the acquisition card and are transmitted to an upper computer. According to the method, the mixed gas chamber is adopted to calibrate the F-P etalon and then calibrate the fiber bragg grating, so that the problem that the accuracy and the stability of a traditional demodulation mode are affected in a port environment is effectively solved.

Description

Technical Field

[0001] The present application belongs to the field of wavelength demodulation technology, and in particular relates to a multi-physical field demodulation system and method based on a mixed gas chamber. Background Art

[0002] Fiber optic sensing technology has been continuously developing since 1977 with the continuous development of optical communications and fiber optic technology. Compared with traditional sensors, fiber grating sensors are widely used in extremely harsh environments such as highly corrosive, flammable and explosive environments, and strong electromagnetic interference environments due to their advantages such as light weight and immunity to electromagnetic interference.

[0003] my country's ports are spread across four major sea areas with very different environments. During their service life, port infrastructure is not only impacted by strong waves such as typhoons and storm surges, but also by ship impact loads. Therefore, under the multiple effects of the environment and loads, higher challenges are posed to the sensing system. At present, fiber Bragg grating sensors are capable of performing most wavelength demodulation tasks, but in some cases, the linear relationship between the central wavelength and voltage of the fiber Bragg grating will be destroyed, affecting the demodulation accuracy. The application of FP standards can effectively solve the zero-point drift problem of fiber Bragg gratings and achieve wavelength calibration, but its temperature stability is not high enough and is not suitable for the complex and changeable marine climate. The air chamber is insensitive to changes in ambient temperature and has high temperature stability.

[0004] Therefore, it is of great significance to carry out research on demodulation using gas chambers to achieve improved stability while ensuring demodulation accuracy. Summary of the Invention

[0005] In view of this, the present application aims to propose a multi-physics field demodulation system and method based on a mixed gas chamber to solve the problem that the accuracy and stability of traditional demodulation methods will be affected in port environments.

[0006] To achieve the above objectives, the technical solution of this application is implemented as follows:

[0007] In a first aspect, the present application provides a multi-physics field demodulation system based on a mixed gas chamber, comprising a connected scanning light source, a beam splitter, a Bragg fiber grating, a mixed gas chamber, an FP etalon, an acquisition card, and a host computer;

[0008] The light beam emitted by the scanning light source is split by the beam splitter and divided into three paths to enter the Bragg fiber grating, the mixed gas chamber and the FP standard. The reflected light of the Bragg fiber grating and the transmitted light of the mixed gas chamber and the FP standard respectively enter different channels of the acquisition card and are transmitted to the host computer.

[0009] In a second aspect, based on the same inventive concept, the present application further provides a demodulation method of a multi-physical field demodulation system based on a mixed gas chamber as described in the first aspect, comprising:

[0010] Collecting spectral signals of the mixed gas chamber, the FP etalon, and the fiber Bragg grating, and performing peak search processing on the collected spectral signals to respectively find the peak positions corresponding to the mixed gas chamber, the FP etalon, and the fiber Bragg grating;

[0011] Performing peak processing according to the peak position of the mixed gas chamber, and calibrating the peak position of the FP etalon based on the peak processing result to obtain a calibrated FP etalon peak wavelength;

[0012] Based on the FP etalon peak position sampling points and the calibrated FP etalon peak wavelength, the data is fitted by a linear interpolation method to obtain a fitted linear function;

[0013] Substituting the peak position of the fiber Bragg grating into the linear function to obtain the calibrated center wavelength of the fiber Bragg grating;

[0014] According to the difference in central wavelength between the calibrated FBG and the installed FBG, and based on the environmental sensitivity of the FBG, the environmental parameters of the FBG are obtained.

[0015] Compared with the prior art, the multi-physics field demodulation system and method based on a mixed gas chamber described in this application has the following beneficial effects:

[0016] This application adopts the method of calibrating the FP standard tool in a mixed gas chamber and then calibrating the fiber Bragg grating, which effectively solves the problem that the accuracy and stability of the traditional demodulation method will be affected in the port environment, and can achieve the purpose of improving stability while ensuring the demodulation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0018] Figure 1 This is a schematic diagram of a multi-physics field demodulation system based on a mixed gas chamber according to an embodiment of the present application;

[0019] Figure 2 This is a flow chart of a multi-physics field demodulation method based on a mixed gas chamber according to an embodiment of the present application;

[0020] Figure 3Schematic diagram of the spectrum of the mixed gas chamber and the FP etalon described in the embodiment of the present application;

[0021] Figure 4 This is the temperature demodulation result when the mixed gas cell and the FP etalon described in the embodiment of the present application are used together;

[0022] Figure 5 This is the temperature demodulation result when the FP etalon described in the embodiment of the present application is used alone;

[0023] Figure 7 This is the strain demodulation result when the FP etalon described in the embodiment of the present application is used alone;

[0024] Figure 6 This is the strain demodulation result when the mixed gas cell and the FP etalon described in the embodiment of the present application are used together;

[0025] Figure 8 This is the water pressure demodulation result when the mixed gas chamber and the FP etalon described in the embodiment of the present application are used together;

[0026] Figure 9 This is the water pressure demodulation result when the FP etalon described in the embodiment of the present application is used alone;

[0027] Figure 10 The results of calibrating the central wavelength of the fiber Bragg grating using the FP etalon at different temperatures described in the embodiments of the present application;

[0028] Figure 11 These are the results of calibrating the central wavelength of the fiber Bragg grating using the mixed gas chamber and the FP etalon at different temperatures as described in the embodiments of the present application. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0030] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should have the usual meanings understood by people with ordinary skills in the field to which this application belongs. The "first", "second" and similar words used in the embodiments of the present application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0031] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0032] See also Figure 1 As shown, this embodiment provides a multi-physics field demodulation system based on a mixed gas chamber, including a connected scanning light source, a beam splitter, a Bragg fiber grating, a mixed gas chamber, an FP etalon, an acquisition card, and a host computer;

[0033] The light beam emitted by the scanning light source is split by a beam splitter and divided into three paths to enter the fiber Bragg grating, the mixed gas chamber and the FP etalon. The reflected light of the fiber Bragg grating and the transmitted light of the mixed gas chamber and the FP etalon respectively enter different channels of the acquisition card and are transmitted to the host computer.

[0034] Specifically, in this embodiment, the wavelength range of the scanning light source is 1527-1568 nm, the step size is 10 pm, and 4101 points can be scanned in 1 second. The gas in the mixed gas chamber is a mixture of acetylene and carbon monoxide, with a ratio of 2 torr of acetylene and 300 torr of carbon monoxide. The optical path is 80 cm, and there are a large number of obvious absorption peaks near 1535 nm and 1560 nm. The free spectral range of the FP etalon is 5.1×10 10 nm,

[0035] The light emitted by the scanning light source enters the fiber Bragg grating, mixed gas chamber and FP etalon respectively through a 1×3 beam splitter. The reflected light of the fiber Bragg grating and the transmitted light of the mixed gas chamber and FP etalon respectively enter different channels of the acquisition card and are transmitted to the host computer.

[0036] Based on the same inventive concept, corresponding to any of the above-mentioned embodiment systems, the embodiment of the present application also provides a demodulation method for a multi-physical field demodulation system based on a mixed gas chamber. The scanning light source starts from 1527nm and scans the fiber Bragg grating sensor with a step length of 10pm to 1568nm. The reflected light is collected by the acquisition card and uploaded to the host computer. At the same time, the reflection peaks of the mixed gas chamber and the FP standard are collected. The peak position of the FP standard is calibrated using the peak of the mixed gas chamber. The peak of the calibrated FP standard is used to calibrate the peak of the fiber Bragg grating sensor. The changes in environmental parameters such as temperature, pressure and strain of the current environment are obtained using the peak of the calibrated fiber Bragg grating sensor. Figure 2 As shown, the specific steps include:

[0037] Step S101 : collecting spectral signals of the mixed gas chamber, FP etalon and FBG, and performing peak search on the collected spectral signals to respectively find the peak positions corresponding to the mixed gas chamber, FP etalon and FBG.

[0038] Specifically, in this embodiment, the scanning light source is turned on, and the mixed gas chamber absorbs the light. The acquisition card collects its spectral signal, and the inverse operation is performed to obtain the opposite spectral signal, and the peak position of the mixed gas chamber is found.

[0039] At the same time, the collected spectral signals of the FP etalon and the Bragg fiber grating are subjected to peak search processing to find the peak positions of the FP etalon and the Bragg fiber grating respectively. The spectrum diagram of the mixed gas chamber and the FP etalon is shown in the figure below. Figure 3 shown.

[0040] Step S102 : performing peak processing according to the peak position of the mixed gas chamber, and calibrating the peak position of the FP etalon based on the peak processing result to obtain the calibrated peak wavelength of the FP etalon.

[0041] Specifically, in this embodiment, the peak position of the mixed gas chamber is compared with the preset reference peak value, and the peak values ​​with a difference of less than 50 pm are retained, and the retained peak wavelength is replaced with the reference peak value;

[0042] Since the peak position of the mixed gas chamber is mainly located at the front end of the scanning light source, a certain number of peaks (i.e., reference peaks) are taken, and each selected peak is combined with the first peak on its left to form a peak pair. The quotients of the wavelength difference and the peak sampling point difference of these peak pairs are calculated respectively, and finally the average of these quotients is obtained.

[0043] The peak processing formula is:

[0044]

[0045] Where Q represents the quotient; λ 第一峰值 Indicates the first number of the peak pair, that is, the peak with a relatively large wavelength, λ 第二峰值 Indicates the second number of the peak pair, representing the peak with relatively smaller wavelength; ε1 represents the sampling point of the right peak, and ε2 represents the sampling point of the left peak.

[0046] Take a certain number of peaks at the front end and find the gas cell peak position closest to these peaks. If the gas cell peak position is to the left of the selected FP standard peak, the peak calibration formula is:

[0047] λ 校准后 =λ 气室 +(λ 标准具 -λ 气室 )×ΔQ

[0048] If the gas cell peak position is to the right of the selected FP etalon peak position, the peak calibration formula is:

[0049] λ 校准后 =λ 气室 -(λ 气室 -λ 标准具 )×ΔQ

[0050] Where λ 校准后 represents the peak wavelength of the calibrated FP etalon, λ 气室 Indicates the wavelength of the gas cell peak closest to the selected etalon peak, λ 标准具 represents the selected etalon peak wavelength, and ΔQ represents the average quotient value obtained by peak processing.

[0051] The obtained FP etalon peaks are processed separately to obtain the calibrated FP etalon peak wavelengths.

[0052] Step S103 : Based on the FP etalon peak position sampling points and the calibrated FP etalon peak wavelength, data fitting is performed by a linear interpolation method to obtain a fitted linear function.

[0053] Specifically, in this embodiment, a linear interpolation method is used, with the peak position sampling point of the FP etalon as the horizontal coordinate and the peak wavelength of the calibrated FP etalon as the vertical coordinate, and these discrete points are fitted into a linear function (representing the relationship between the peak position and wavelength of the FP etalon) through linear fitting.

[0054] It should be noted that the linear difference method and the fitting method described in this embodiment are conventional technical means in this field, and this application does not make any technical improvements thereto. Therefore, they will not be described in detail.

[0055] Step S104: Substitute the peak position of the fiber Bragg grating into the linear function to obtain the calibrated center wavelength of the fiber Bragg grating.

[0056] Specifically, in this embodiment, the peak position of the fiber Bragg grating obtained by peak search is substituted into the linear function in step S103, and the calibrated center wavelength of the fiber Bragg grating is output.

[0057] Step S105 : Obtaining the environmental parameters of the fiber Bragg grating according to the difference in central wavelength between the calibrated fiber Bragg grating and the installed fiber Bragg grating and the environmental sensitivity of the fiber Bragg grating.

[0058] Specifically, in this embodiment, taking the temperature grating as an example, the ambient temperature is the product of the difference between the central wavelength of the detection grating and the central wavelength during installation and the temperature sensitivity. By modifying the temperature sensitivity to strain sensitivity and pressure sensitivity accordingly, the environmental variables such as temperature, strain and pressure of different fiber gratings can be obtained.

[0059] Among them, the temperature parameter formula of the Bragg fiber grating is:

[0060] T = μ(λ-λ0);

[0061] Where T represents temperature, μ represents the temperature sensitivity of the grating, λ represents the central wavelength of the calibrated FBG, and λ0 represents the central wavelength of the installed FBG.

[0062] The strain parameter formula of the fiber Bragg grating is:

[0063] σ=μ1(λ2-λ3);

[0064] σ represents strain, μ1 represents the strain sensitivity of the grating, λ2 represents the central wavelength of the calibrated fiber Bragg grating, and λ3 represents the central wavelength of the installed grating;

[0065] The strain parameter formula of the fiber Bragg grating is:

[0066] τ=μ2(λ4-λ5);

[0067] τ represents strain, μ2 represents the strain sensitivity of the grating, λ4 represents the central wavelength of the calibrated fiber Bragg grating, and λ5 represents the central wavelength of the installed grating.

[0068] This method retains the accuracy of traditional FP standard tool detection, has higher stability and smaller standard deviation of measurement results, and has good application prospects.

[0069] Embodiment 1: Only the ambient temperature of the sensor is changed to monitor the temperature demodulation.

[0070] The sensor is placed in an incubator, and the FP standard and the mixed gas chamber are placed in an open environment with an ambient temperature of 10°C. The ambient temperature of the incubator is then changed starting from 10°C in increments of 10°C. After each temperature change, the incubator is kept running for 1 hour to obtain a stable temperature. At the same time, the actual temperature in the incubator is obtained using relevant instruments. The fiber Bragg grating spectra at 10°C, 20°C, 30°C, 40°C, and 50°C are read respectively. The spectra are then calibrated using the mixed gas chamber and the FP standard. The temperature change after calibration is calculated. The demodulation results of the mixed gas chamber and the FP standard are shown as follows: Figure 4 As shown in the table, the first line is the actual temperature difference in the temperature box, and the second line is the demodulated temperature difference. The demodulation results using only the FP standard are as follows: Figure 5 As shown in Figure 2, it can be found that both methods can be used for fiber Bragg grating demodulation with a certain degree of accuracy. Considering various errors, the results of both methods can be considered to be accurate.

[0071] Embodiment 2: Stretch the sensor and monitor the strain demodulation.

[0072] The sensor is placed in a cantilever beam, and the FP standard and the mixed gas chamber are left untreated and placed in a room temperature environment. The sensor is then stretched, starting from 0με and increasing the applied strain in units of 300με. The central wavelength of the fiber Bragg grating is read at 300με, 600με, 900με, 1200με and 1500με respectively. As in Example 1, the spectrum is calibrated using the mixed gas chamber and the FP standard, and the strain change after calibration is calculated. The demodulation results using the mixed gas chamber and the FP standard are shown in Figure 1. Figure 6 As shown in the table, the first line is the actual strain difference of the sensor, and the second line is the strain difference obtained by demodulation. Figure 7 shown.

[0073] Embodiment 3: Changing the water pressure applied to the sensor to monitor pressure demodulation.

[0074] The sensor is placed in a water pressure tester. The FP standard and the mixed gas chamber are left untreated and placed in a room temperature environment. Then the water pressure applied by the tester is changed, starting from 0 MPa and increasing the applied water pressure by 0.4 MPa. The central wavelength of the fiber Bragg grating is read at 0.4 MPa, 0.8 MPa, 1.2 MPa, 1.6 MPa, and 2 MPa respectively. As in Example 1, the spectrum is calibrated using the mixed gas chamber and the FP standard. The water pressure change after calibration is calculated. At the same time, the demodulation results of the mixed gas chamber and the FP standard are used as shown in FIG. Figure 8As shown in the table, the first line is the set water pressure in the water pressure tester, and the second line is the pressure difference obtained by demodulation. Figure 9 shown.

[0075] Example 4: Changing the ambient temperature of the experimental system and monitoring the change of the calibrated FBG center wavelength

[0076] Place the FP standard and the mixed gas chamber in an incubator, place the sensor in a room temperature environment, and continuously change the temperature of the incubator. As in Example 1, change the ambient temperature of the incubator starting from 10° with a change value of 10°. Keep the incubator running for 1 hour after each temperature change to obtain a stable temperature. At the same time, use relevant instruments to obtain the actual temperature in the incubator. Read the FP standard and mixed gas chamber spectra at 10°C, 20°C, 30°C, 40°C, and 50°C, as well as the sensor spectrum at room temperature. Then, use the FP standard and mixed gas chamber spectra at the five temperatures taken to calibrate the sensor spectrum at room temperature. The results are as follows: Figure 10 and Figure 11 The results show that without the gas cell, the maximum difference was 6.3pm and the standard deviation was 3.2pm. After using the gas cell calibration etalon, the maximum difference dropped to 3.7pm, a 41.3% reduction, and the standard deviation dropped to 1.7pm, a 46.875% reduction. Therefore, it can be concluded that the use of a mixed gas cell has a certain effect on eliminating the sensor's zero drift.

[0077] It should be noted that the above description is limited to some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in an order different from that described in the above embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0078] The embodiments of the present application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of this application.

Claims

1. A multi-physics field demodulation system based on a mixed gas chamber, characterized in that: It includes connected scanning light source, beam splitter, Bragg fiber grating, mixed gas chamber, FP standard tool, acquisition card and host computer; The light beam emitted by the scanning light source is split by the beam splitter and divided into three paths to enter the Bragg fiber grating, the mixed gas chamber and the FP standard. The reflected light of the Bragg fiber grating and the transmitted light of the mixed gas chamber and the FP standard respectively enter different channels of the acquisition card and are transmitted to the host computer.

2. The system according to claim 1, wherein: The wavelength range of the scanning light source is 1527-1568 nm, and the step length is 10 pm.

3. The system according to claim 1, wherein: The mixed gas chamber includes acetylene with a ratio of 2 torr and carbon monoxide with a ratio of 300 torr.

4. The system according to claim 1, wherein: The free spectral range of the FP etalon is 5.1×10 10 nm.

5. A demodulation method of a multi-physical field demodulation system based on a mixed gas chamber according to any one of claims 1 to 4, characterized in that: include: Collecting spectral signals of the mixed gas chamber, the FP etalon, and the fiber Bragg grating, and performing peak search processing on the collected spectral signals to respectively find the peak positions corresponding to the mixed gas chamber, the FP etalon, and the fiber Bragg grating; Performing peak processing according to the peak position of the mixed gas chamber, and calibrating the peak position of the FP etalon based on the peak processing result to obtain a calibrated FP etalon peak wavelength; Based on the FP etalon peak position sampling points and the calibrated FP etalon peak wavelength, the data is fitted by a linear interpolation method to obtain a fitted linear function; Substituting the peak position of the fiber Bragg grating into the linear function to obtain the calibrated center wavelength of the fiber Bragg grating; According to the difference in central wavelength between the calibrated FBG and the installed FBG, and based on the environmental sensitivity of the FBG, the environmental parameters of the FBG are obtained.

6. The method according to claim 5, characterized in that: Performing an inversion operation and a peak search process on the collected spectrum signal of the mixed gas chamber to find the peak position of the mixed gas chamber; The collected spectral signals of the FP etalon and the fiber Bragg grating are subjected to peak-finding processing to respectively find the peak positions of the FP etalon and the fiber Bragg grating.

7. The method according to claim 5, characterized in that The performing peak processing according to the peak position of the mixed gas chamber includes: Compare the found peak position of the mixed gas chamber with the preset reference peak value, retain the peak value that meets the preset conditions, and replace the retained peak value with the reference peak value; Each selected reference peak and the first peak on its left form a peak pair, and peak processing is performed based on the peak pair and the peak sampling point. The peak processing formula is as follows: Where Q represents the quotient; λ 第一峰值 Indicates the first number of the peak pair, that is, the peak with a relatively large wavelength, λ 第二峰值 Indicates the second number of the peak pair, representing the peak with relatively smaller wavelength; ε1 represents the sampling point of the right peak, and ε2 represents the sampling point of the left peak.

8. The method according to claim 7, characterized in that The step of calibrating the peak position of the FP etalon based on the peak processing result to obtain a calibrated peak wavelength of the FP etalon includes: In response to the gas cell peak position being to the left of the selected FP etalon peak position, the peak calibration formula is as follows: l 校准后 =λ 气室 +(λ 标准具 -l 气室 )×ΔQ; In response to the gas cell peak position being to the right of the selected FP etalon peak position, the peak calibration formula is as follows: l 校准后 =λ 气室 -(l 气室 -l 标准具 )×ΔQ; Where λ 校准后 represents the peak wavelength of the calibrated FP etalon, λ 气室 Indicates the wavelength of the gas cell peak closest to the selected etalon peak, λ 标准具 represents the selected etalon peak wavelength, and ΔQ represents the average quotient value obtained by peak processing.

9. The method according to claim 7, characterized in that The method of fitting the data based on the FP etalon peak position sampling point and the calibrated FP etalon peak wavelength by a linear interpolation method to obtain a fitted linear function includes: The linear interpolation method is used to fit the data with the peak position sampling point of the FP etalon as the abscissa and the peak wavelength of the calibrated FP etalon as the ordinate to obtain a fitted linear function.

10. The method according to claim 7, wherein: The temperature parameter formula of the Bragg fiber grating is: T = μ(λ-λ0); Where T represents temperature, μ represents the temperature sensitivity of the grating, λ represents the central wavelength of the calibrated FBG, and λ0 represents the central wavelength of the installed FBG. The strain parameter formula of the Bragg fiber grating is: σ=μ1(λ2-λ3); σ represents strain, μ1 represents the strain sensitivity of the grating, λ2 represents the central wavelength of the calibrated fiber Bragg grating, and λ3 represents the central wavelength of the installed grating; The strain parameter formula of the Bragg fiber grating is: τ=μ2(λ4-λ5); τ represents strain, μ2 represents the strain sensitivity of the grating, λ4 represents the central wavelength of the calibrated fiber Bragg grating, and λ5 represents the central wavelength of the installed grating.

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