Optical fiber flow sensing device and method

Abstract

This invention belongs to the field of flow measurement technology and discloses an optical fiber flow sensing device and method. The adsorption of carbon dioxide by a sensitive substance is related not only to the concentration of carbon dioxide but also to the flow rate of the fluid being measured. The degree to which the adsorption of carbon dioxide by the sensitive substance changes with flow rate is only related to the concentration of carbon dioxide in the fluid being measured. When the flow rate of the fluid being measured changes, even if the concentration of carbon dioxide in the fluid remains constant, the intensity of the adsorption of carbon dioxide by the sensitive substance will change, leading to a change in the refractive index of the sensitive substance. The optical fiber flow sensing device and method proposed in this invention ensure that the flow measurement accuracy is only related to the concentration of carbon dioxide in the fluid being measured; the concentrations of other media components in the fluid do not affect the accuracy of the flow measurement.

Description

Technical Field

[0001] This invention relates to the field of flow measurement technology, and specifically to an optical fiber flow sensing device and method. Background Technology

[0002] Gas flow sensing technology plays a vital role in petrochemical, nuclear power, aerospace, environmental protection, and medical fields. Currently, the main flow meters used in industrial settings include: Coriolis flow meters, differential pressure flow meters, thermal flow meters, and ultrasonic flow meters. These flow meters are completely dependent on the fluid medium, requiring knowledge of all components in the measured fluid to correct the material parameters used in flow calculations. Summary of the Invention

[0003] The purpose of this invention is to provide an optical fiber flow sensing device and method. Based on the discovered characteristic that the absorption efficiency of carbon dioxide by carbon dioxide-sensitive substances is affected by flow rate, the device achieves flow sensing of carbon dioxide-containing gases. The flow measurement performance is only related to the carbon dioxide concentration in the fluid being measured, and other media components in the fluid being measured do not affect the accuracy of the flow measurement.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: an optical fiber flow sensing device, comprising a light source, a sensing system, and a signal analysis system;

[0005] The light source provides light signals for the operation of the sensing system;

[0006] The sensing system includes a circulator, an optical fiber, a sensitive material, and a test pipe. The test pipe is connected to a flow measurement pipe, allowing the fluid to be measured to flow through the sensitive material. The sensitive material absorbs carbon dioxide in the fluid, and the concentration of carbon dioxide in the fluid is known. The absorption intensity is related to the carbon dioxide flow rate. The sensitive material is coated on the end face of the optical fiber to form a Fabry-Perot interferometer. The circulator receives the light signal emitted by the light source and guides the light signal into the Fabry-Perot interferometer formed by the optical fiber and the sensitive material. It also receives the reflected light signal from the Fabry-Perot interferometer and transmits it to the signal analysis system.

[0007] The signal analysis system obtains the flow rate value of the fluid being measured by analyzing the light signal emitted by the sensing system.

[0008] The sensitive material is polyhexamethylene biguanide hydrochloride.

[0009] The light source is a broadband light source.

[0010] An optical fiber flow sensing device, the working principle of which is as follows:

[0011] The sensing material used in the sensing system undergoes a reversible chemical reaction with carbon dioxide, adsorbing carbon dioxide from the measured fluid. The refractive index of the sensing material changes after adsorbing carbon dioxide. Experimental research has shown that the adsorption of carbon dioxide by the sensing material is related not only to the concentration of carbon dioxide but also to the flow rate of the measured fluid. Furthermore, the degree to which the adsorption of carbon dioxide by the sensing material changes with the flow rate is only related to the concentration of carbon dioxide in the measured fluid. Therefore, when the flow rate of the measured fluid changes, even if the concentration of carbon dioxide in the measured fluid remains unchanged, the intensity of the adsorption of carbon dioxide by the sensing material will change, leading to a change in the refractive index of the sensing material.

[0012] The output spectrum of the Fabry-Perot interferometer formed by the sensitive material and the fiber end face can be expressed as:

[0013] (1)

[0014] Where I0 represents the input light intensity; λ represents the light wavelength; I represents the light intensity at wavelength λ; n represents the refractive index of the sensitive material; L represents the thickness of the sensitive material; and φ represents the initial phase. When the flow rate causes a change in the refractive index of the sensitive material, the spectrum shifts accordingly. The shift of the spectral peaks or troughs... The relationship between the flow rate Q and the flow rate Q can be expressed as:

[0015] (2)

[0016] in, , , , It is the coefficient in formula (2). By performing spectral analysis on the spectrum, the phase change of the spectrum can be obtained. , The relationship between the flow rate Q and the flow rate Q can be expressed as:

[0017] (3)

[0018] in, , , , It is the coefficient in formula (3). , , , , , , , It is related to the purity of the sensitive substance, the concentration of carbon dioxide, and the geometry of the sensitive substance and the test pipeline. , , , , , , , It needs to be calibrated after testing at standard carbon dioxide concentration and standard flow rate. The flow rate value can be obtained by measuring the shift of a peak or trough in the spectrum or measuring the phase change of the spectrum through a signal analysis system, and by analyzing the correspondence between the wavelength or phase obtained from the calibration and the flow rate. According to formulas (2) and (3), as the flow rate increases, the sensitivity of the wavelength and phase change with the flow rate decreases. When the wavelength or phase shift is too small and exceeds the detection capability of the signal analysis system, the upper limit of the flow measurement of the sensing device is reached. The relationship between the upper limit of the flow measurement R and the carbon dioxide concentration η can be expressed as:

[0019] (4)

[0020] Among them, a R b R c R The coefficient in formula (4) needs to be obtained through testing in fluid media with different carbon dioxide concentrations. Since the sensitive substance does not react chemically with other gaseous components in the fluid being measured, the concentration of other gaseous components in the fluid being measured will not affect the flow measurement performance.

[0021] A fiber optic flow sensing method, its , , , , , , , a R b R c R The coefficient testing method is as follows:

[0022] Step 1: Prepare a testing device that can generate different concentrations of carbon dioxide and different gas flow rates;

[0023] Step 2: Connect the test pipeline to the test device;

[0024] Step 3: Set the output carbon dioxide concentration of the testing device to the minimum required carbon dioxide concentration;

[0025] Step 4: Set the output flow rate of the test device to the required minimum flow rate value;

[0026] Step 5: Observe the spectral signal collected by the signal analysis system until the spectrum stabilizes;

[0027] Step 6, record the traffic Q iAnd spectral signals, and analyze the changes in peaks or troughs. Analyze the spectral phase change ;

[0028] Step 7: Increase the output flow rate of the testing device to the next flow rate test value;

[0029] Step 8: Repeat steps 5 through 7 until the spectrum no longer changes with increasing flow rate. Record the upper limit R of the flow rate measurement at this point. i and carbon dioxide concentration η i Increase the carbon dioxide concentration output by the testing device to the next concentration test value;

[0030] Step 9: Repeat steps 4 through 8 until all carbon dioxide concentration values ​​have been tested.

[0031] Step 10, record the concentrations η during the test. i and traffic Q i The result obtained , R i Substitute these values ​​into formulas (2), (3), and (4) to obtain the corresponding coefficient values, and store them in the signal analysis system.

[0032] A fiber optic flow sensing method includes the following steps when measuring flow:

[0033] Step 1: Install the sensing system into the flow measurement pipeline, so that the fluid containing carbon dioxide in the pipeline flows through the sensing system;

[0034] Step 2: Start the light source and signal analysis system, and input the carbon dioxide concentration in the fluid into the signal analysis system;

[0035] Step 3: The signal analysis system displays the flow measurement value.

[0036] The concentration of carbon dioxide in the fluid is known and constant.

[0037] The beneficial effects of the present invention are as follows: the fiber optic flow sensing method and device proposed in this invention have flow measurement accuracy that is only related to the carbon dioxide concentration in the fluid being measured, and the concentration of other media components in the fluid being measured does not affect the flow measurement accuracy. Attached Figure Description

[0038] Figure 1 A schematic diagram of the fiber optic flow sensing device provided by the present invention.

[0039] Figure 2 A schematic diagram illustrating the relationship between wavelength change and flow rate in the fiber optic flow sensing device provided by the present invention.

[0040] Figure 3 A schematic diagram illustrating the relationship between phase change and flow rate of the fiber optic flow sensing device provided by the present invention;

[0041] Figure 4 This is a schematic diagram illustrating the media influence characteristics of the fiber optic flow sensing device provided by the present invention.

[0042] In the diagram: 1-Light source; 2-Sensing system; 3-Signal analysis system; 21-Circulator; 22-Fiber optic cable; 23-Sensitive substance; 24-Test pipeline. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0044] like Figure 1 As shown, an optical fiber flow sensing device includes a light source 1, a sensing system 2, and a signal analysis system 3.

[0045] The light source 1 provides light signals for the operation of the sensing system 2;

[0046] The sensing system 2 includes a circulator 21, an optical fiber 22, a sensitive substance 23, and a test pipe 24. The test pipe 24 is connected to a flow measurement pipe, allowing the fluid to be measured to flow through the sensitive substance 23. The sensitive substance 23 absorbs carbon dioxide in the fluid being measured, and the concentration of carbon dioxide in the fluid is known. The absorption intensity is related to the carbon dioxide flow rate. The sensitive substance 23 is coated on the end face of the optical fiber 22 to form a Fabry-Perot interferometer. The circulator 21 receives the light signal emitted by the light source 1 and guides the light signal into the Fabry-Perot interferometer formed by the optical fiber 22 and the sensitive substance 23. It also receives the reflected light signal from the Fabry-Perot interferometer and transmits it to the signal analysis system 3.

[0047] The signal analysis system 3 obtains the flow rate value of the fluid being measured by analyzing the optical signal emitted by the sensing system 2.

[0048] The sensitive substance 23 is polyhexamethylene biguanide hydrochloride.

[0049] The light source 1 is a broadband light source.

[0050] An optical fiber flow sensing device, the working principle of which is as follows:

[0051] The sensitive substance 23 used in the sensing system undergoes a reversible chemical reaction with carbon dioxide, thus adsorbing carbon dioxide in the measured fluid. The refractive index of the sensitive substance 23 changes after adsorbing carbon dioxide. Experimental research has shown that the adsorption of carbon dioxide by the sensitive substance 23 is related not only to the concentration of carbon dioxide but also to the flow rate of the measured fluid. Furthermore, the degree to which the adsorption of carbon dioxide by the sensitive substance 23 changes with the flow rate is only related to the concentration of carbon dioxide in the measured fluid. Therefore, when the flow rate of the measured fluid changes, even if the concentration of carbon dioxide in the measured fluid remains unchanged, the adsorption strength of the sensitive substance 23 on carbon dioxide will change, leading to a change in the refractive index of the sensitive substance 23.

[0052] The output spectrum of the Fabry-Perot interferometer formed by the sensitive material 23 and the end face of the optical fiber 22 can be expressed as:

[0053] (1)

[0054] Where I0 represents the input light intensity; λ represents the light wavelength; I represents the light intensity at wavelength λ; n represents the refractive index of the sensitive material 23; L represents the thickness of the sensitive material 23; and φ represents the initial phase. When the flow rate causes a change in the refractive index of the sensitive material 23, the spectrum shifts accordingly. The shift of the peaks or troughs in the spectrum... The relationship between the flow rate Q and the flow rate Q can be expressed as:

[0055] (2)

[0056] in, , , , It is the coefficient in formula (2). By performing spectral analysis on the spectrum, the phase change of the spectrum can be obtained. , The relationship between the flow rate Q and the flow rate Q can be expressed as:

[0057] (3)

[0058] in, , , , It is the coefficient in formula (3). , , , , , , , The purity of the sensitive substance 23, the carbon dioxide concentration, and the geometry of the sensitive substance 23 and the test pipe 24 are all relevant factors. , , , , , , , It needs to be calibrated after testing at standard carbon dioxide concentration and standard flow rate. The flow rate value can be obtained by measuring the shift of a peak or trough in the spectrum or measuring the phase change of the spectrum through the signal analysis system 3, and by analyzing the correspondence between the wavelength or phase obtained from the calibration and the flow rate. According to formulas (2) and (3), as the flow rate increases, the sensitivity of the wavelength and phase change with the flow rate decreases. When the wavelength or phase shift is too small and exceeds the detection capability of the signal analysis system 3, the upper limit of the flow rate measurement of the sensing device is reached. The relationship between the upper limit of the flow rate measurement R and the carbon dioxide concentration η can be expressed as:

[0059] (4)

[0060] Among them, a R b R c R The coefficient in formula (4) needs to be obtained through testing under different carbon dioxide concentration fluid media environments. Since the sensitive substance 23 does not react chemically with other gas components in the fluid being measured, the concentration of other gas components in the fluid being measured will not affect the flow measurement performance.

[0061] A fiber optic flow sensing method, its , , , , , , , a R b R c R The coefficient testing method is as follows:

[0062] Step 1: Prepare a testing device that can generate different concentrations of carbon dioxide and different gas flow rates;

[0063] Step 2: Connect the test pipe 24 to the test device;

[0064] Step 3: Set the output carbon dioxide concentration of the testing device to the minimum required carbon dioxide concentration;

[0065] Step 4: Set the output flow rate of the test device to the required minimum flow rate value;

[0066] Step 5: Observe the spectral signal collected by signal analysis system 3 until the spectrum stabilizes;

[0067] Step 6, record the traffic Q i And spectral signals, and analyze the changes in peaks or troughs. Analyze the spectral phase change ;

[0068] Step 7: Increase the output flow rate of the testing device to the next flow rate test value;

[0069] Step 8: Repeat steps 5 through 7 until the spectrum no longer changes with increasing flow rate. Record the upper limit R of the flow rate measurement at this point. i and carbon dioxide concentration η i Increase the carbon dioxide concentration output by the testing device to the next concentration test value;

[0070] Step 9: Repeat steps 4 through 8 until all carbon dioxide concentration values ​​have been tested.

[0071] Step 10, record the concentrations η during the test. i and traffic Q i The result obtained , R i Substitute these values ​​into formulas (2), (3), and (4) to obtain the corresponding coefficient values, and store them in the signal analysis system 3.

[0072] A fiber optic flow sensing method, which includes the following steps when measuring flow:

[0073] Step 1: Install the sensing system 2 into the flow measurement pipe so that the fluid containing carbon dioxide in the pipe flows through the sensing system 2;

[0074] Step 2: Start the light source 1 and signal analysis system 3, and input the carbon dioxide concentration in the fluid into the signal analysis system 3;

[0075] Step 3: The signal analysis system 3 displays the flow measurement value.

[0076] The concentration of carbon dioxide in the fluid is known and constant.

[0077] To verify the rationality of the scheme, an experimental fiber optic carbon dioxide flow sensor was fabricated. The sensing material 23 was polyhexamethylene biguanide hydrochloride, with a thickness L of approximately 16.19 μm. The relationship between flow rate and wavelength shift at various carbon dioxide concentrations is as follows: Figure 2 As shown, the relationship between flow rate and phase change is as follows: Figure 3 As shown, this demonstrates that the prepared sensing device is capable of measuring the flow rate of carbon dioxide-containing gas. After testing and calibration, the coefficients in formulas (2) and (3), which express the relationship between flow rate, wavelength, and phase, are as follows:

[0078] =4.64; =0.6; ; = =0.35; ; .

[0079] In the verification scheme, a spectrometer with a wavelength resolution of 0.02 nm was used. Under the above experimental conditions, the coefficients in formula (4) which expresses the upper limit of flow measurement at various carbon dioxide concentrations are: a R =-12.07、b R =0.4068、c R =36.74. The flow rate measurement range reached 29 L / min when the carbon dioxide concentration reached 100%.

[0080] Simultaneously, flow performance tests were conducted on three test gases, all with a carbon dioxide concentration of 8%, but with other components of 92% nitrogen, 42% nitrogen + 50% helium, and 42% nitrogen + 50% argon, respectively. The results are as follows: Figure 4 As shown, the sensor exhibits the same response characteristics to each flow rate under the three gases, proving that the flow measurement characteristics of the prepared sensing device are not affected by other media components.

Claims

1. A fiber optic flow sensing device, characterized in that, It includes a light source (1), a sensing system (2), and a signal analysis system (3); The light source (1) provides light signals for the operation of the sensing system (2); The sensing system (2) includes a circulator (21), an optical fiber (22), a sensitive substance (23), and a test pipe (24). The test pipe (24) is connected to the flow measurement pipe, so that the fluid being measured flows through the sensitive substance (23). The sensitive substance (23) has an absorption effect on carbon dioxide in the fluid being measured. The concentration of carbon dioxide in the fluid being measured is known, and the absorption intensity is related to the carbon dioxide flow rate. The sensitive substance (23) is coated on the end face of the optical fiber (22) to form a Fabry-Perot interferometer. The circulator (21) receives the light signal emitted by the light source (1) and guides the light signal into the Fabry-Perot interferometer formed by the optical fiber (22) and the sensitive substance (23). It receives the reflected light signal from the Fabry-Perot interferometer and transmits it to the signal analysis system (3). The signal analysis system (3) obtains the flow rate value of the fluid being measured by analyzing the light signal emitted by the sensing system (2).

2. The fiber optic flow sensing device according to claim 1, characterized in that, The sensitive substance (23) is polyhexamethylene biguanide hydrochloride.

3. The fiber optic flow sensing device according to claim 1, characterized in that, The light source (1) is a broadband light source.

4. The fiber optic flow sensing device according to any one of claims 1-3, characterized in that, The output spectrum of the Fabry-Perot interferometer formed by the sensitive material (23) and the end face of the optical fiber (22) is expressed as follows: Where I0 represents the input light intensity; λ represents the light wavelength; I represents the light intensity value at wavelength λ; n represents the refractive index value of the sensitive material (23); L represents the thickness of the sensitive material (23); φ represents the initial phase; when the flow rate causes a change in the refractive index of the sensitive material (23), the spectrum shifts accordingly. The shift of the peaks or troughs of the spectrum The relationship between the flow rate Q and the flow rate Q is expressed as follows: in, , , , The coefficient is used; the phase change of the spectrum is obtained by performing spectral analysis. , The relationship between the flow rate Q and the flow rate Q is expressed as follows: in, , , , For coefficients; , , , , , , , Related to the purity of the sensitive substance (23), the concentration of carbon dioxide, and the geometry of the sensitive substance (23) and the test pipeline (24), , , , , , , , The standard carbon dioxide concentration and standard flow rate are tested and calibrated; the shift of a certain peak or trough in the spectrum is measured by the signal analysis system (3), or the phase change of the spectrum is measured, and the flow rate value is obtained according to the correspondence between the wavelength or phase obtained by calibration and the flow rate.

5. A fiber optic flow sensing method, characterized in that, The process, implemented using any one of the fiber optic flow sensing devices described in claims 1-4, includes the following steps: Step 1: The sensing system (2) is installed in the flow measurement pipe so that the fluid containing carbon dioxide in the pipe flows through the sensing system (2). Step 2: Start the light source (1) and signal analysis system (3), and input the carbon dioxide concentration in the fluid into the signal analysis system (3); Step 3: The signal analysis system (3) displays the flow measurement value.

6. The fiber optic flow sensing method according to claim 5, characterized in that, The output spectrum of the Fabry-Perot interferometer formed by the sensitive material (23) and the end face of the optical fiber (22) is expressed as follows: Wherein, I0 represents the input light intensity; λ represents the light wavelength; I represents the light intensity value at wavelength λ; n represents the refractive index value of the sensitive material (23); L represents the thickness of the sensitive material (23); φ represents the initial phase; when the flow rate causes the refractive index of the sensitive material (23) to change, the output spectrum will shift accordingly. The shift of a certain peak or trough in the spectrum is measured by the signal analysis system (3), or the phase change of the spectrum is measured, and the flow rate value is obtained according to the correspondence between the wavelength or phase obtained by calibration and the flow rate.

7. The fiber optic flow sensing method according to claim 5, characterized in that, The concentration of carbon dioxide in the fluid is known and constant.

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