Fluid temperature-pressure-flow optical fiber synchronous composite sensing device and method

Abstract

The invention provides a fluid temperature-pressure-flow optical fiber synchronous composite sensing device and method.The fluid temperature-pressure-flow optical fiber synchronous composite sensing device comprises a cantilever beam, a temperature, pressure and flow sensor, a demodulator and an upper computer; the temperature, pressure and flow sensor is used for converting the collected temperature, pressure and flow of the fluid into optical signals and outputting the optical signals to the demodulator; the demodulator is used for recording the optical signals and converting the optical signals into spectral data to be called by the upper computer; and the upper computer is used for performing fitting operation according to the called spectral data of the demodulator to obtain the central wavelength of the FBG and the cavity lengths of the two F-P cavities, and obtaining the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length and the fluid flow corresponding to the cavity length according to a preset rule. The temperature, pressure and flow sensor is small in size and high in precision, can measure three parameters of flow, pressure and temperature at the same time, reduces parts, is convenient to install in a narrow space, is simple in installation process, and facilitates distributed networking multi-point monitoring.

Description

Technical Field

[0001] The invention relates to the technical field of multi-parameter measurement, and in particular to an optical fiber synchronous composite sensing device for fluid temperature-pressure-flow. Background Art

[0002] The traditional method of measuring the flow rate, temperature and pressure of the fluid in a closed pipeline is to use flow metering instruments, temperature metering instruments and pressure metering instruments to measure the flow rate, temperature and pressure respectively, which has been relatively mature in the industrial field. Flow meters, thermometers and pressure gauges are widely used in the fields of nuclear power industry, petrochemical industry, energy measurement, etc. Among them, flow meters are a kind of metering equipment that can be used to measure the flow rate of fluid in a pipeline within a certain period of time.

[0003] Flow meters mainly include mechanical, electromagnetic, and ultrasonic flow meters. Mechanical flow meters have a complex structure and are bulky, and are not suitable for measuring high-speed flowing fluid media. When measuring high-viscosity media, flow resistance and fluid leakage are prone to occur, leading to measurement errors. In addition, since mechanical flow meters involve mechanical movement, there is a risk of wear and damage, and parts need to be replaced regularly. Electromagnetic flow meters can only be used to measure fluid flow in conductive media and are easily affected by external magnetic fields and vibrations. Ultrasonic flow meters are a type of non-contact flow meter that cannot be used for high-temperature fluid flow measurement. They have high requirements for the installation environment and poor resistance to external environmental interference. In addition, their circuits are large and complex and they are expensive.

[0004] In the prior art, the flow rate, temperature and pressure of the fluid are measured separately by flow meters, thermometers and pressure gauges. There is no measuring instrument that can measure the flow rate, temperature and pressure of the fluid at the same time, which results in a large number of measuring instruments. It is inconvenient to install when the installation space is small, and the installation process is cumbersome and time-consuming. In addition, most flow meters have the disadvantages of being large in size, susceptible to electromagnetic interference, and not convenient for distributed networking and multi-point monitoring. Summary of the invention

[0005] In view of this, the present invention proposes a fluid temperature-pressure-flow optical fiber synchronous composite sensing device and method to solve the technical problems proposed in the above background technology that the flow rate, temperature and pressure of the fluid are measured separately by flow meters, thermometers and pressure gauges, and the number of measuring instruments is large, which makes it inconvenient to install when the installation space is narrow, and the installation process is cumbersome and time-consuming. Most flow meters have the disadvantages of being large in size, susceptible to electromagnetic interference, and not convenient for distributed networking and multi-point monitoring.

[0006] The technical solution of the present invention is achieved in this way: In a first aspect, the present invention provides a fluid temperature-pressure-flow optical fiber synchronous composite sensing device, which is installed on a pipeline and includes a cantilever beam, a temperature pressure flow sensor, a demodulator and a host computer, wherein: The pipeline is provided with a mounting portion, and a fluid flows in the pipeline; One end of the cantilever beam is mounted on the mounting portion, and the other end extends into the pipe; The temperature, pressure and flow rate sensor is mounted on the mounting surface of the cantilever beam, and the mounting surface is located on the opposite side of the side washed by the fluid. The temperature, pressure and flow rate sensor is a fiber grating sensor based on an FBG and two FP cavities, and the temperature, pressure and flow rate sensor is used to convert the collected temperature, pressure and flow rate of the fluid into optical signals and output them to the demodulator; The demodulator is respectively connected to the temperature, pressure and flow sensor and the host computer electrical signal, and is used to record the optical signal and convert it into spectral data for the host computer to retrieve; The host computer is used to retrieve the spectrum data of the demodulator, perform fitting calculations based on the spectrum data to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtain the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow corresponding to the cavity length according to preset rules.

[0007] On the basis of the above technical solution, preferably, obtaining the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow rate corresponding to the cavity length according to a preset rule includes: According to the pre-stored experimental calibration data of pressure-cavity length and the experimental calibration data of temperature-center wavelength, the pressure value corresponding to the current cavity length and the temperature value corresponding to the center wavelength are obtained; The strain value corresponding to the current cavity length is obtained according to the pre-stored strain-cavity length experimental calibration data, and the flow value corresponding to the strain value corresponding to the current cavity length is obtained according to the pre-stored strain-flow experimental calibration data.

[0008] On the basis of the above technical solution, preferably, the cantilever beam includes a connecting block, a connecting rod and a force-bearing plate, the connecting block is sealed and connected to the mounting portion, the two ends of the connecting rod are respectively connected to the connecting block and the force-bearing plate, and the temperature, pressure and flow sensor is installed on the connecting rod.

[0009] On the basis of the above technical solution, preferably, the load-bearing plate is cylindrical and coaxial with the pipe.

[0010] On the basis of the above technical solution, preferably, the cross-sectional area of ​​the connecting rod is smaller than the cross-sectional area of ​​the load-bearing plate.

[0011] On the basis of the above technical solution, preferably, the connection block is provided with a lead hole for the jumper wire connected to the temperature, pressure and flow sensors to pass through.

[0012] Based on the above technical solution, preferably, the temperature, pressure and flow sensor includes a FBG probe, a first FP probe and a second FP probe; the FBG probe is located at the end of the connecting rod away from the force-bearing plate, and is used to measure the temperature of the fluid; the first FP probe is located at the end of the connecting rod close to the force-bearing plate, and is used to measure the flow rate of the fluid; the second FP probe is located between the FBG probe and the first FP probe, and is used to measure the pressure of the fluid.

[0013] In a second aspect, the present invention provides a method for synchronous optical fiber composite sensing of fluid temperature, pressure and flow rate, using the synchronous optical fiber composite sensing device for fluid temperature, pressure and flow rate described in the first aspect, comprising: Make temperature, pressure and flow sensors; Installing the temperature, pressure and flow sensors on the cantilever beam, and connecting and fixing the cantilever beam to the installation part of the pipeline; The temperature, pressure and flow rate of the fluid collected are converted into optical signals through the temperature, pressure and flow rate sensors and output to the demodulator; The optical signal is recorded by a demodulator and converted into spectral data for access by a host computer; The host computer performs fitting calculations based on the spectral data of the demodulator to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtains the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow rate corresponding to the cavity length according to preset rules.

[0014] On the basis of the above technical solution, preferably, the host computer performs fitting operation according to the spectrum data of the demodulator retrieved to obtain the cavity length of the FP cavity, including: calculating the cavity length of the FP cavity according to the following formula: ; In the formula, L is the cavity length of the FP cavity, λ1 and λ2 are wavelengths, and the phase difference is 2π.

[0015] On the basis of the above technical solution, preferably, the host computer performs fitting operation according to the spectrum data of the demodulator retrieved to obtain the central wavelength of the FBG, including: calculating the central wavelength of the FBG according to the following formula: ; In the formula, Δλ FBG is the central wavelength shift of FBG, ΔL1 and ΔL2 are the displacements of the two FP cavities, and k P1 and k T1 are the sensitivities of the FP cavity displacement to pressure P and temperature T, respectively. P2 and k T2 are the sensitivities of the central wavelength shift of FBG with respect to pressure P and temperature T, respectively. P3and k T3 are the sensitivities of the FP cavity displacement for measuring flow rate with respect to pressure P and temperature T, k ε k is the sensitivity of the FP cavity displacement to the strain ε, q is the sensitivity of the cantilever beam strain to the flow rate Q, ΔP, ΔT and ΔQ are the pressure, temperature and flow rate changes of the environment where the temperature pressure flow sensor is located, respectively.

[0016] The optical fiber synchronous composite sensing device and method for fluid temperature, pressure and flow rate of the present invention have the following beneficial effects compared with the prior art: (1) The temperature, pressure and flow sensor is a fiber grating sensor based on one FBG and two FP cavities. The temperature is measured by the spectral change of the FBG, and the pressure and flow are measured respectively by the cavity length displacement of the two FP cavities. The flow, pressure and temperature measurements can be decoupled from each other. At high temperatures, there will be no zero drift and sensitivity change caused by the temperature, so there will be no cross-influence of temperature, pressure and flow, which can reduce errors. The sensor is insensitive to electromagnetic interference and can withstand extreme conditions, and has good stability. The temperature, pressure and flow sensor based on the FP cavity and FBG is small in size and high in precision. One sensor can measure the three parameters of flow, pressure and temperature at the same time, reducing parts and facilitating installation in a small space. The installation process is simple, facilitating distributed networking and multi-point monitoring. (2) The pressure value corresponding to the current cavity length and the temperature value corresponding to the central wavelength are obtained based on the pre-stored experimental calibration data of pressure-cavity length and the experimental calibration data of temperature-center wavelength; the strain value corresponding to the current cavity length is obtained based on the pre-stored experimental calibration data of strain-cavity length, and the flow value corresponding to the strain value corresponding to the current cavity length is obtained based on the pre-stored experimental calibration data of strain-flow rate. The flow, pressure and temperature of the fluid in the pipeline can be measured in real time. This method is relatively convenient and fast, and has good accuracy. (3) The force-bearing plate is cylindrical and coaxial with the pipe, which can increase the force-bearing area, increase the cantilever beam strain, and make the force more uniform, thereby improving the measurement accuracy; (4) By making the cross-sectional area of ​​the connecting rod smaller than the cross-sectional area of ​​the load-bearing plate, the strain amplitude of the connecting rod after the load-bearing plate is stressed is made larger, thereby increasing the strain sensitivity of the cantilever beam and improving the measurement accuracy; (5) The host computer performs fitting calculations based on the spectrum data of the demodulator to obtain the cavity length of the FP cavity, including: based on the phase demodulation method, the wavelength is scanned in the range of λ1~λ2, and the cavity length of the FP cavity can be obtained according to the phase change of the interference fringes, that is, the cavity length of the FP cavity can be calculated according to the formula recorded in the text; (6) The host computer performs fitting operation based on the spectral data of the retrieved demodulator to obtain the central wavelength of the FBG, including: since the central wavelength offset of the FBG and the cavity length displacement of the two FP cavities are linearly related to the temperature, pressure and flow changes, a third-order mapping matrix is ​​established between the input and output of the temperature, pressure and flow sensors to obtain the formula in the article. According to the formula, it can be seen that the pressure measurement and flow measurement can be decoupled from the temperature, and the temperature can also be detected, so that the central wavelength of the FBG can be calculated according to the formula. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 Schematic diagram of the structure of a fluid temperature-pressure-flow optical fiber synchronous composite sensor device in an embodiment of the present invention; Figure 2 is a schematic diagram of the structure of a pipeline in an embodiment of the present invention; Figure 3 is a schematic structural diagram of a cantilever beam in an embodiment of the present invention; Figure 4 It is a schematic diagram of the structure of the temperature, pressure and flow rate sensor installed on the cantilever beam in an embodiment of the present invention; Figure 5 It is a schematic diagram of the principle of the measurement of the temperature-pressure-flow rate of the fluid in the embodiment of the present invention. Figure 6 It is a structural schematic diagram of a demodulator and a host computer in an embodiment of the present invention; Figure 7 Schematic diagram of the flow of the optical fiber synchronous composite sensing method of fluid temperature-pressure-flow in an embodiment of the present invention.

[0019] Description of reference numerals: 1-cantilever beam, 2-temperature, pressure and flow sensor, 3-demodulator, 4-host computer; 100-pipe, 101-mounting portion, 102-mounting hole; 11-connecting block, 111-threaded hole, 112-lead hole, 12-connecting rod, 13-force plate; 21-FBG probe, 22-first FP probe, 23-second FP probe, 24-high temperature glue. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Reference Figure 1-7 As shown, the first embodiment of the present invention proposes a fluid temperature-pressure-flow optical fiber synchronous composite sensing device, which is installed on a pipeline 100 and includes a cantilever beam 1, a temperature pressure flow sensor 2, a demodulator 3 and a host computer 4, wherein: The pipeline 100 is provided with a mounting portion 101. A fluid flows in the pipeline 100. The mounting portion 101 may be a round tube. The axial direction of the mounting portion 101 is perpendicular to the axial direction of the pipeline 100. One end of the cantilever beam 1 is mounted on the mounting portion 101, and the other end extends into the pipe 100; the cantilever beam 1 includes a connecting block 11, a connecting rod 12 and a force plate 13, the connecting block 11 is sealed and connected to the mounting portion 101, and the two ends of the connecting rod 12 are respectively connected to the connecting block 11 and the force plate 13, the temperature, pressure and flow sensor 2 is mounted on the connecting rod 12, a threaded hole 111 is provided on the connecting block 11, and the threaded hole 111 is fixed to the mounting hole 102 on the round tube by bolts, the end of the connecting rod 12 close to the connecting block 11 (i.e., the root) is wide and thick, and the end of the connecting rod 12 close to the force plate 13 (i.e., the middle of the cantilever beam 1) is narrow and thin, and the force plate 13 (head) is fan-shaped, which can increase the strain in the middle of the cantilever beam 1 and reduce the strain at the root, while increasing the wind receiving area and increasing the sensitivity; The temperature, pressure and flow rate sensor 2 is mounted on the mounting surface of the cantilever beam 1, and the mounting surface is located on the opposite side of the side washed by the fluid. The temperature, pressure and flow rate sensor 2 is a fiber grating sensor based on an FBG and two FP cavities. The temperature, pressure and flow rate sensor 2 is used to convert the collected temperature, pressure and flow rate of the fluid into optical signals and output them to the demodulator 3; the FBG is used to measure the temperature of the fluid, and the two FP cavities are used to measure the pressure and flow rate of the fluid respectively; The demodulator 3 is electrically connected to the temperature, pressure and flow sensor 2 and the host computer 4 respectively, and is used to record the optical signal and convert it into spectral data for the host computer 4 to retrieve; The host computer 4 is used to retrieve the spectral data of the demodulator 3, perform fitting calculations based on the spectral data to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtain the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow corresponding to the cavity length according to preset rules.

[0022] The present embodiment proposes a fluid temperature-pressure-flow optical fiber synchronous composite sensing device, wherein the temperature, pressure and flow sensor 2 is a fiber grating sensor based on one FBG and two FP cavities, and the temperature is measured by the spectral change of the FBG, and the pressure and flow are respectively measured by the cavity length displacement of the two FP cavities. The flow, pressure and temperature measurements can be decoupled from each other, and the problem of zero drift and sensitivity change caused by temperature will not occur at high temperatures, so that the cross-influence of temperature, pressure and flow will not be formed, thereby reducing errors, and the device is insensitive to electromagnetic interference and can withstand extreme conditions, and has good stability. The temperature, pressure and flow sensor 2 based on the FP cavity and FBG is small in size and high in precision. One sensor can measure the three parameters of flow, pressure and temperature at the same time, reducing parts, facilitating installation in a small space, and the installation process is simple, facilitating distributed networking and multi-point monitoring.

[0023] In some embodiments, obtaining the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow rate corresponding to the cavity length according to a preset rule includes: According to the pre-stored experimental calibration data of pressure-cavity length and the experimental calibration data of temperature-center wavelength, the pressure value corresponding to the current cavity length and the temperature value corresponding to the center wavelength are obtained; The strain value corresponding to the current cavity length is obtained according to the pre-stored strain-cavity length experimental calibration data, and the flow value corresponding to the strain value corresponding to the current cavity length is obtained according to the pre-stored strain-flow experimental calibration data.

[0024] In this embodiment, the pressure value corresponding to the current cavity length can be obtained by substituting the cavity length into the experimental calibration data of pressure-cavity length, and the temperature value corresponding to the central wavelength can be obtained by substituting the central wavelength into the experimental calibration data of temperature-central wavelength; the strain value corresponding to the current cavity length is obtained by substituting the cavity length into the experimental calibration data of strain-cavity length, and the flow value corresponding to the strain value corresponding to the current cavity length is obtained by substituting the strain value into the experimental calibration data of strain-flow, thereby realizing the measurement of temperature, pressure and flow of the fluid in the pipeline 100. This method is relatively convenient and fast, and has good accuracy.

[0025] In some embodiments, the stress plate 13 is cylindrical and coaxial with the pipe 100. By making the stress plate 13 cylindrical and coaxial with the pipe 100, the stress area can be increased, the strain of the cantilever beam 1 can be increased, and the stress can be made more uniform, thereby improving the accuracy of the measurement.

[0026] In some embodiments, the cross-sectional area of ​​the connecting rod 12 is smaller than the cross-sectional area of ​​the force-bearing plate 13. The connecting rod 12 is a slender rod, and the cross-sectional area of ​​the connecting rod 12 is smaller than the cross-sectional area of ​​the force-bearing plate 13, so that the strain amplitude of the connecting rod 12 after the force-bearing plate 13 is larger, thereby increasing the strain sensitivity of the cantilever beam 1 and improving the accuracy of measurement.

[0027] In some embodiments, the connection block 11 is provided with a lead hole 112 for the jumper wire connected to the temperature, pressure and flow sensor 2 to pass through. In order to facilitate the jumper wire to be led out of the pipeline 100, the lead hole 112 is provided on the connection block 11, and after marking the ends of the jumper wires in turn, they are all tied with fine wires of high temperature resistant materials and led out of the pipeline 100 through the lead hole 112, so as to facilitate the jumper wire to be led out of the pipeline 100 more conveniently.

[0028] In some embodiments, the temperature, pressure and flow sensor 2 includes a FBG probe 21, a first FP probe 22 and a second FP probe 23; the FBG probe 21 is located at the end of the connecting rod 12 away from the force plate 13, and is used to measure the temperature of the fluid; the first FP probe 22 is located at the end of the connecting rod 12 close to the force plate 13, and is used to measure the flow of the fluid; the second FP probe 23 is located between the FBG probe 21 and the first FP probe 22, and is used to measure the pressure of the fluid. The temperature, pressure and flow sensor 2 is fixed to the cantilever beam 1 with a high temperature glue 24.

[0029] Based on the same concept, the second embodiment of the present invention proposes a method for synchronous optical fiber composite sensing of fluid temperature, pressure and flow rate, using the synchronous optical fiber composite sensing device for fluid temperature, pressure and flow rate described in the first embodiment, including: Step S1: making a temperature, pressure and flow sensor 2; Step S2: installing the temperature, pressure and flow rate sensor 2 on the cantilever beam 1, and connecting and fixing the cantilever beam 1 to the mounting portion 101 of the pipeline 100; Step S3: converting the collected temperature, pressure and flow of the fluid into optical signals through the temperature, pressure and flow sensor 2 and outputting them to the demodulator 3; Step S4: recording the optical signal through the demodulator 3 and converting it into spectrum data for the host computer 4 to retrieve; Step S5: The host computer 4 performs fitting calculations based on the spectrum data retrieved from the demodulator 3 to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtains the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow corresponding to the cavity length according to preset rules.

[0030] In some embodiments, according to the principle of white light interference, when broadband light is incident into the optical fiber, the output spectrum of the sensor can be determined as: (1); Formula (1), a(λ) is the spectral profile of the background light source; b(λ) is the interference fringe contrast, λ and L are the scanning wavelength and length of the microbubble FP cavity respectively. In addition, is the phase of the interference spectrum, and its relationship with L can be expressed as: (2); In formula (2), is the phase of the interference spectrum, and are the phases of the interference spectra of λ1 and λ2 respectively; Therefore, the phase demodulation method is adopted, and the wavelength is scanned within the range, and the cavity length of the FP cavity can be determined according to the phase change of the interference fringes; that is, the upper computer 4 performs fitting calculation according to the spectrum data of the demodulator 3 to obtain the cavity length of the FP cavity, including: calculating the cavity length of the FP cavity according to the following formula: (3); In formula (3), L is the cavity length of the FP cavity, λ1 and λ2 are wavelengths, and the phase difference is 2π.

[0031] In some embodiments, when the pressure and temperature are coupled to act on the designed FP cavity for measuring pressure, the cavity length of the FP cavity for measuring pressure will change. Therefore, the displacement of the FP cavity for measuring pressure can be expressed as: (4); In formula (4), ΔL1 is the displacement of the FP cavity for measuring pressure, k P1 and k T1 are the sensitivities of the displacement of the FP cavity with respect to pressure P and temperature T, respectively, and ΔP and ΔT are the pressure and temperature changes of the environment in which the temperature pressure flow sensor 2 is located, respectively.

[0032] In some embodiments, when the flow rate, pressure and temperature are coupled to the designed FP cavity for measuring flow rate, the cavity length of the FP cavity for measuring flow rate will change, so the displacement of the FP cavity for measuring flow rate can be expressed as: (5); In formula (5), ΔL2 is the displacement of the FP cavity for measuring flow, k P3 and k T3 and k ε are the sensitivities of the displacement of the FP cavity with respect to pressure P, temperature T and strain ε, respectively. ΔP, ΔT and Δε are the pressure, temperature and strain changes of the environment in which the temperature-pressure flow sensor 2 is located, respectively.

[0033] The Δε in the above formula can be expressed as: (6); In formula (6), k q is the sensitivity of the strain of the cantilever beam 1 to the flow rate Q, and ΔQ is the flow rate change of the environment where the temperature and pressure flow sensor 2 are located.

[0034] Since the center wavelength shift of FBG is linearly related to the pressure and temperature changes, the relationship between the center wavelength shift and the temperature and pressure changes can be expressed as: (7); In formula (7), Δλ FBG is the center wavelength shift, k P2 and k T2 are the sensitivities of the central wavelength shift of FBG with respect to pressure P and temperature T, respectively. ΔP and ΔT are the pressure and temperature changes of the environment in which the temperature pressure flow sensor 2 is located, respectively.

[0035] The host computer 4 performs fitting operation according to the spectrum data of the demodulator 3 to obtain the central wavelength of the FBG, including: calculating the central wavelength of the FBG according to the following formula, that is, the third-order mapping matrix between the input and output of the temperature, pressure and flow sensor 2 can be obtained according to formulas (4), (5) and (7): (8); In formula (8), Δλ FBG is the central wavelength shift of FBG, ΔL1 and ΔL2 are the displacements of the two FP cavities, and k P1 and k T1 are the sensitivities of the FP cavity displacement to pressure P and temperature T, respectively. P2 and k T2 are the sensitivities of the central wavelength shift of FBG with respect to pressure P and temperature T, respectively. P3 and k T3 are the sensitivities of the FP cavity displacement for measuring flow rate with respect to pressure P and temperature T, k ε k is the sensitivity of the FP cavity displacement to the strain ε, q is the sensitivity of the strain of the cantilever beam 1 with respect to the flow rate Q, ΔP, ΔT and ΔQ are the pressure, temperature and flow rate changes of the environment in which the temperature, pressure and flow rate sensor 2 is located, respectively.

[0036] It can be seen from formula (8) that pressure measurement and flow measurement can be decoupled from temperature, and temperature can also be detected. On the premise that the cavity lengths of the two FP cavities are obtained according to formula (3), the central wavelength of the FBG can be calculated according to the above formulas (4) to (8).

[0037] In some embodiments, in step S1, the manufacturing of the temperature, pressure and flow sensor 2 specifically includes the following steps: Step S11: Take a single-mode optical fiber with an appropriate length and FBG grating, and strip off the coating layer; Step S12: Dip a piece of dust-free paper in alcohol and wipe the bare optical fiber stripped of its coating layer clean; Step S13: cutting the optical fiber with a cutting knife (obtaining a bare optical fiber end with a flat end face and appropriate length); Step S14: Take a hollow optical fiber with an inner diameter of 75 microns of a suitable length and strip off the coating layer; Step S15: Dip a dust-free paper in alcohol and wipe the bare hollow-core optical fiber with the coating removed clean; Step S16: cutting the hollow-core optical fiber with a cutting knife (obtaining a bare hollow-core optical fiber end with a flat end face and appropriate length); Step S17: Use a fusion splicer to fusion-splice two bare optical fibers with smooth end faces. Step S18: using a cutting knife to cut the hollow-core fiber end of the FBG+ hollow-core fiber obtained in step S17 flat, until the remaining length is 100 to 200 microns; Step S19: Take a single-mode optical fiber of suitable length and repeat steps S11 to S13; Step S20: using a fusion splicer to fusion-splice the hollow-core fiber end of the FBG+ hollow-core fiber obtained in step S18 with the flattened end of the single-mode fiber obtained in step 9; Step S21: Cut the single-mode fiber end of the FBG+hollow-core fiber+single-mode fiber obtained in step S20 flat with a cutting knife until about 5 cm is left; Step S22: Take a hollow core optical fiber with an inner diameter of 125 microns of appropriate length and repeat steps S11 to S13; Step S23: Take a single-mode optical fiber of appropriate length and repeat steps S11 to S13; Step S24: placing the optical fiber obtained in step S22 and step S23 in a fusion splicer, inserting the single-mode optical fiber into the hollow-core optical fiber to a length of about 1 cm, and then fusion splicing the end face of the hollow-core optical fiber with the single-mode optical fiber; Step S25: Cut the hollow-core fiber portion of the hollow-core fiber + single-mode fiber obtained in step 14 into about 5 cm using a cutting knife; Step S26: putting the FBG+hollow-core fiber+single-mode fiber obtained in step S21 and the hollow-core fiber+single-mode fiber obtained in step S25 into a fusion splicer, and inserting the single-mode fiber end of the former into the hollow-core fiber end of the latter; Step S27: Keeping the optical fiber in the state of step S26, fix it to the cantilever beam 1 with high temperature glue 24. Note that the single-mode end of the FBG should pass through the lead hole 112 on the cantilever beam 1.

[0038] The optical fiber synchronous composite sensing device for fluid temperature, pressure and flow rate of the present invention has the following advantages: 1. The traditional measuring meter measures a single physical quantity and cannot measure flow, pressure and temperature at the same time. The present invention provides a temperature, pressure and flow sensor 2 based on FP and FBG, which can measure the temperature, pressure and flow of the fluid at the same time, reducing the complexity of the measurement system; 2. Most traditional flow meters are bulky and inconvenient to be distributed and networked for multi-point detection. The optical fiber synchronous composite sensing device for fluid temperature, pressure and flow provided by the present invention is small in size, easy to install, and can be distributed and networked for multi-point measurement; 3. It is not sensitive to electromagnetic interference and can withstand extreme conditions, including high temperature, high pressure, strong shock and vibration, and is easy to install and small in size.

[0039] In summary, the present invention is economical and effective, and meets the urgent needs of flow, pressure and temperature measurement. This method applies fiber grating sensors based on FP and FBG to flow detection, which has great originality and application value in the academic field and is bound to have certain prospects in the future market.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A fiber optic synchronous composite sensor device for fluid temperature, pressure and flow, installed on a pipeline, characterized in that: It includes a cantilever beam, a temperature, pressure and flow sensor, a demodulator and a host computer, wherein: The pipeline is provided with a mounting portion, and a fluid flows in the pipeline; One end of the cantilever beam is mounted on the mounting portion, and the other end extends into the pipe; The temperature, pressure and flow rate sensor is mounted on the mounting surface of the cantilever beam, and the mounting surface is located on the opposite side of the side washed by the fluid. The temperature, pressure and flow rate sensor is a fiber grating sensor based on an FBG and two FP cavities, and the temperature, pressure and flow rate sensor is used to convert the collected temperature, pressure and flow rate of the fluid into optical signals and output them to the demodulator; The demodulator is respectively connected to the temperature, pressure and flow sensor and the host computer electrical signal, and is used to record the optical signal and convert it into spectral data for the host computer to retrieve; The host computer is used to retrieve the spectrum data of the demodulator, perform fitting calculations based on the spectrum data to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtain the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow corresponding to the cavity length according to preset rules.

2. The optical fiber synchronous composite sensor device for fluid temperature, pressure and flow rate as claimed in claim 1, characterized in that: The method of obtaining the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow rate corresponding to the cavity length according to a preset rule includes: According to the pre-stored experimental calibration data of pressure-cavity length and the experimental calibration data of temperature-center wavelength, the pressure value corresponding to the current cavity length and the temperature value corresponding to the center wavelength are obtained; The strain value corresponding to the current cavity length is obtained according to the pre-stored strain-cavity length experimental calibration data, and the flow value corresponding to the strain value corresponding to the current cavity length is obtained according to the pre-stored strain-flow experimental calibration data.

3. The optical fiber synchronous composite sensor device for fluid temperature, pressure and flow rate as claimed in claim 1, characterized in that: The cantilever beam comprises a connecting block, a connecting rod and a force-bearing plate. The connecting block is sealed and connected to the mounting portion. Two ends of the connecting rod are respectively connected to the connecting block and the force-bearing plate. The temperature, pressure and flow sensors are mounted on the connecting rod.

4. The optical fiber synchronous composite sensor device for fluid temperature, pressure and flow rate as claimed in claim 3, characterized in that: The stress-bearing plate is cylindrical and coaxial with the pipeline.

5. The optical fiber synchronous composite sensor device for fluid temperature, pressure and flow rate as claimed in claim 4, characterized in that: The cross-sectional area of ​​the connecting rod is smaller than the cross-sectional area of ​​the force-bearing plate.

6. The optical fiber synchronous composite sensor device for fluid temperature, pressure and flow rate as claimed in claim 3, characterized in that: The connection block is provided with a lead hole for the jumper wire connected to the temperature, pressure and flow sensors to pass through.

7. The fluid temperature-pressure-flow optical fiber synchronous composite sensor device according to claim 3, characterized in that: The temperature, pressure and flow sensor includes a FBG probe, a first FP probe and a second FP probe; the FBG probe is located at the end of the connecting rod away from the force-bearing plate, and is used to measure the temperature of the fluid; the first FP probe is located at the end of the connecting rod close to the force-bearing plate, and is used to measure the flow rate of the fluid; the second FP probe is located between the FBG probe and the first FP probe, and is used to measure the pressure of the fluid.

8. A method for synchronous optical fiber composite sensing of fluid temperature, pressure and flow rate, using a synchronous optical fiber composite sensing device for fluid temperature, pressure and flow rate as claimed in any one of claims 1 to 7, characterized in that: include: Make temperature, pressure and flow sensors; Installing the temperature, pressure and flow sensors on the cantilever beam, and connecting and fixing the cantilever beam to the installation part of the pipeline; The temperature, pressure and flow rate of the fluid collected are converted into optical signals through the temperature, pressure and flow rate sensors and output to the demodulator; The optical signal is recorded by a demodulator and converted into spectral data for access by a host computer; The host computer performs fitting calculations based on the spectral data of the demodulator to obtain the central wavelength of the FBG and the cavity lengths of the two FP cavities, and obtains the fluid temperature corresponding to the central wavelength, the fluid pressure corresponding to the cavity length, and the fluid flow rate corresponding to the cavity length according to preset rules.

9. The method for synchronous optical fiber composite sensing of fluid temperature, pressure and flow rate as claimed in claim 8, characterized in that: The host computer performs fitting calculation according to the spectrum data of the demodulator retrieved to obtain the cavity length of the FP cavity, including: calculating the cavity length of the FP cavity according to the following formula: ； In the formula, L is the cavity length of the FP cavity, λ1 and λ2 are wavelengths, and the phase difference is 2π.

10. The method for synchronous optical fiber composite sensing of fluid temperature, pressure and flow rate as claimed in claim 8, characterized in that: The host computer performs fitting calculation according to the spectrum data of the demodulator to obtain the central wavelength of the FBG, including: calculating the central wavelength of the FBG according to the following formula: ； In the formula, Δλ FBG is the central wavelength shift of FBG, ΔL1 and ΔL2 are the displacements of the two FP cavities, and k P1 and k T1 are the sensitivities of the FP cavity displacement to pressure P and temperature T, respectively. P2 and k T2 are the sensitivities of the central wavelength shift of FBG with respect to pressure P and temperature T, respectively. P3 and k T3 are the sensitivities of the FP cavity displacement for measuring flow rate with respect to pressure P and temperature T, k ε k is the sensitivity of the FP cavity displacement to the strain ε, q is the sensitivity of the cantilever beam strain to the flow rate Q, ΔP, ΔT and ΔQ are the pressure, temperature and flow rate changes of the environment where the temperature pressure flow sensor is located, respectively.

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