Differential pressure type flowmeter flow measurement system and method based on strain and temperature self-compensation

Abstract

The invention relates to the technical field of flow measuring systems, in particular to a differential pressure type flowmeter flow measuring system based on strain and temperature self-compensation, which comprises a differential pressure type flowmeter meter body, a mounting component, a differential pressure part, a strain sensor, an optical fiber, a fiber bragg grating demodulator, a microprocessor and a power supply device, mounting assemblies assembled with a measuring pipeline are mounted at the two ends of the outer side of the differential pressure type flow meter body, a differential pressure piece arranged at the center of a section of pipeline is mounted at the center of the interior of the differential pressure type flow meter body, and two sets of strain sensors symmetrically arranged on the two sides of the differential pressure piece are pasted to the differential pressure type flow meter body; the strain difference value change of the differential pressure type flowmeter is measured by pasting the strain sensor, no hole needs to be formed, the internal flow field of the differential pressure type flowmeter is not affected, the flow measurement accuracy is improved, when the strain difference value is calculated, the variable quantity brought by the temperature is offset, and the problem that the temperature and stress are sensitive in a cross mode when the strain sensor is used for measuring is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of flow measurement systems, and in particular to a flow measurement system and method of a differential pressure flow meter based on strain and temperature self-compensation. Background Art

[0002] In the development process of key military models such as rocket engines and aircraft engines, the flow values ​​of propellants and oxidizers are key parameters that have a significant impact on the test models during the test process. Effectively mastering the flow values ​​during the test can provide reliable data support for engine performance verification, fault analysis and improved design.

[0003] At present, more than 40% of flow measurements in the industry still use differential pressure flowmeters. When measuring flow, it is necessary to open pressure holes on both sides of the differential pressure part of the differential pressure flowmeter, and connect the differential pressure transmitter to the pressure holes to measure the differential pressure value on both sides. However, during the actual test of rocket engines, the above-mentioned differential pressure flowmeter will produce stress concentration at the opening due to the high pressure in the flowmeter measurement pipeline, resulting in material fatigue damage and propellant or oxidizer leakage. In addition, the test site will inevitably produce high temperature, strong vibration, water spray and other harsh working conditions. Conventional differential pressure transmitters cannot adapt to the use requirements of the on-site environment, which makes flow measurement very difficult.

[0004] In order to meet the development or test requirements of engines, a flow measurement method is needed that does not damage the flow measurement medium pipeline and has high reliability and high measurement accuracy. Summary of the invention

[0005] The present invention provides a flow measurement system and method for a differential pressure flowmeter based on strain and temperature self-compensation, which can avoid opening a pressure hole on the differential pressure flowmeter, solve the technical problems of low measurement accuracy, poor vibration resistance, and inability to achieve non-contact measurement in the prior art, and meet the requirements of using the differential pressure flowmeter in the harsh working conditions of a test site.

[0006] The technical solution of the present invention is: a flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation, the system comprising a differential pressure flowmeter body, a mounting assembly, a differential pressure part, a strain sensor, an optical fiber, a fiber Bragg grating demodulator, a microprocessor and a power supply device; both ends of the outer side of the differential pressure flowmeter body are equipped with mounting assemblies for assembly with a measuring pipeline, a differential pressure part arranged at the center of a section of pipeline is installed at the center of the differential pressure flowmeter body, two groups of strain sensors symmetrically arranged on both sides of the differential pressure part are attached to the differential pressure flowmeter, optical fibers for transmitting optical signals are installed on the outer sides of the two groups of strain sensors, the other end of the optical fiber is connected to the fiber Bragg grating demodulator, a microprocessor connected through an electrical interface is installed on the outer side of the fiber Bragg grating demodulator, and a power supply device is installed on the outer side of the microprocessor; The fiber Bragg grating demodulator includes a light source module for generating a stable optical signal, a demodulation module, a signal processing module and a communication interface; The microprocessor includes a central processing unit that controls the operation of the entire system, a memory, an input and output interface, and a communication interface; The power supply device includes a power conversion module that converts input AC or DC power into DC power or AC power of a specific voltage required by the system, a protection module, and a monitoring module that monitors the output voltage and current of the power supply.

[0007] Preferably, the installation assembly includes flanges fixedly connected to both sides of the differential pressure flowmeter body, and fastening screw holes are provided inside the flanges, and fastening bolts are detachably connected inside the fastening screw holes.

[0008] Preferably, the differential pressure member is any one of a standard orifice plate, a conical cut-off member, a wedge-shaped cut-off member, an eccentric orifice plate, a multi-hole orifice plate, a bent pipe and an average velocity pipe.

[0009] Preferably, the two groups of strain sensors further use FBG sensor a arranged upstream of the flow and FBG sensor b arranged downstream of the flow, and the reflection wavelength range of FBG sensor a and FBG sensor b is between 1500nm-1580nm. When light passes through FBG sensor a and FBG sensor b, the reflection wavelength of light is:

[0010] in is the effective refractive index, is the Bragg period of the fiber Bragg grating.

[0011] Preferably, both sides of the differential pressure piece are provided with sticking measuring points, and the FBG sensor a and the FBG sensor b are connected to the fiber grating demodulator through optical fiber, and the strain values ​​of the FBG sensor a and the FBG sensor b are collected and calculated by the fiber grating demodulator.

[0012] Preferably, the demodulation module receives the optical signal and demodulates it into an electrical signal corresponding to the physical quantity, and the signal processing module further processes the demodulated electrical signal, including filtering, amplification and digitization.

[0013] Preferably, the memory stores programs and data, including operating systems, applications and measurement data, and the communication interface performs data communications with other systems, including remote monitoring and data uploading.

[0014] As a preference, the flow measurement system of the strain and temperature self-compensated differential pressure flowmeter is calibrated before use, assuming that the standard flow rate is The fluid flows through the differential pressure flow meter body, and the strain value collected by the fiber grating demodulator at FBG sensor a is The strain value collected by the fiber Bragg grating demodulator at sensor b is , then the strain difference for:

[0015] Measure multiple groups of standard flow values ​​through standard flow calibration device and grating fiber demodulator And the corresponding multiple sets of strain differences ; The flow rate is calculated as: a+b

[0016] in is the strain difference, in units of ; It is the standard flow rate, and the unit is L / min.

[0017] A flow measurement method of a differential pressure flow meter based on strain and temperature self-compensation, comprising a flow measurement system of a differential pressure flow meter based on strain and temperature self-compensation as described above, and the steps are as follows: S1: Calibration Process S11: Install the differential pressure flow meter body to the measuring pipeline of the standard flow calibration device through the flange, ensuring that the connection is tight and leak-free; S12: Connect the optical fiber to the FBG sensor a and the FBG sensor b, and then connect to the fiber grating demodulator to transmit and receive optical signals, start the motor through the controller, and then drive the ball screw and the piston rod to make the piston reciprocate in the active volume tube to simulate different flow rates; S13: Initialize the data collector and computer, set data acquisition parameters, including sampling frequency and data storage path, and the optical fiber demodulator receives the strain signals of FBG sensor a and FBG sensor b and converts them into digital signals for computer processing; S14: Open the first control valve, the second control valve and the third control valve to allow the fluid to flow from the oil tank into the active volume tube. Different flow rates are generated through the movement of the piston. Under different flow rates, the computer receives the strain signals of the FBG sensor a and the FBG sensor b transmitted by the fiber grating demodulator through the data acquisition device, and records the corresponding flow values ​​at the same time. Repeat the above steps to measure multiple groups of flow values and the corresponding strain difference ; S15: Multiple groups of flow values ​​measured and the corresponding strain difference Import it into the computer for processing, use the least square method or other suitable fitting method to calculate the flow value and strain difference Perform fitting to obtain the corresponding relationship between them, establish the mathematical model of the flow meter according to the fitting results, and perform subsequent flow measurement and calibration; S16: Reinstall the calibrated flow meter to the actual measurement pipeline, perform actual flow measurement, compare the measurement result with the standard flow value measured by other high-precision flow meters, and verify the accuracy of the calibration result; S2: Paste FBG sensor a and FBG sensor b After the calibration is completed, the differential pressure flow meter body is installed on the pipeline to be tested through the flange. First, use sandpaper to clean the stains, oxide layer, and rust covering layer on the surface of the pasting measuring point; then use clean absorbent cotton dipped in anhydrous ethanol to scrub the pasting measuring point until there is no stain on the absorbent cotton ball; finally, place FBG sensor a and FBG sensor b on the polished pasting measuring point, evenly apply the colloid, and wait for it to solidify before measuring; S3: When FBG sensor a and FBG sensor b are subjected to stress, they are stretched or contracted, causing the effective refractive index and grating period of the fiber Bragg grating to change, resulting in a corresponding change in the wavelength of the reflected spectrum. When the temperature of FBG sensor a and FBG sensor b changes, FBG sensor a and FBG sensor b will expand and contract, which will change the period length of the fiber grating sensor, thereby causing the center wavelength of the reflection spectrum to move. A specific wavelength corresponds to a specific temperature. Therefore, the temperature of the fiber grating area is measured by measuring the center wavelength of the reflection spectrum.

[0018] Preferably, during flow measurement, the strain sensors attached to both sides of the differential pressure piece are affected by temperature and stress at the same time. Since the pipeline medium is in a long-term flow state during measurement, the temperature change dynamics of the strain sensors on both sides of the differential pressure piece are the same, and the impact of temperature on the strain sensors is also equal. Therefore, when calculating the strain difference, the impact of temperature is eliminated to achieve the purpose of temperature self-compensation. Taking FBG sensor a and FBG sensor b as examples, the changes in the central wavelength of the reflection spectrum caused by temperature are basically equal, and taking the strain gauge as an example, the resistance change value caused by temperature is also basically equal.

[0019] Beneficial effects of the present invention: The differential pressure flowmeter currently used requires holes to be opened on both sides of the differential pressure part to measure the pressure difference, while the present invention measures the change in the strain difference of the differential pressure flowmeter by pasting a strain sensor. It does not require holes to be opened and does not affect the internal flow field of the differential pressure flowmeter, thereby improving its flow measurement accuracy. When calculating the strain difference, the change caused by temperature is offset, solving the problem of cross-sensitivity of the strain sensor to temperature and stress during measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 What is shown is a schematic diagram of the three-dimensional structure of a differential pressure flow meter body of a flow measurement system of a differential pressure flow meter based on strain and temperature self-compensation of the present invention; Figure 2 Shown is a three-dimensional structural schematic diagram of an FBG sensor a and an FBG sensor b of a flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation of the present invention; Figure 3 What is shown is a schematic diagram of the calibration of a flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to the present invention.

[0021] Explanation of the reference numerals in the accompanying drawings: 1. Differential pressure flow meter body; 3. Differential pressure part; 4. Strain sensor; 5. Optical fiber; 6. Fiber Bragg grating demodulator; 7. Microprocessor; 8. Power supply device; 9. Motor; 10. Ball screw; 11. Piston rod; 12. Piston; 13. Active volume tube; 14. First control valve; 15. Second control valve; 16. Third control valve; 17. Oil tank; 101. Measuring point; 201. Flange; 202. Fastening screw hole; 203. Fastening bolt; 401. FBG sensor a; 402. FBG sensor b. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] See also Figure 1-3 The present invention provides an embodiment: the system comprises a differential pressure flow meter body 1, a mounting assembly, a differential pressure part 3, a strain sensor 4, an optical fiber 5, an optical fiber Bragg grating demodulator 6, a microprocessor 7 and a power supply device 8; both ends of the outer side of the differential pressure flow meter body 1 are installed with mounting assemblies for assembly with the measuring pipeline, a differential pressure part 3 arranged at the center of a section of pipeline is installed at the center of the inner side of the differential pressure flow meter body 1, two groups of strain sensors 4 symmetrically arranged on both sides of the differential pressure part 3 are attached to the differential pressure flow meter body 1, optical fibers 5 for transmitting optical signals are installed on the outer sides of the two groups of strain sensors 4, the other end of the optical fiber 5 is connected to the optical fiber Bragg grating demodulator 6, a microprocessor 7 connected through an electrical interface is installed on the outer side of the optical fiber Bragg grating demodulator 6, and a power supply device 8 is installed on the outer side of the microprocessor 7; The fiber Bragg grating demodulator 6 includes a light source module for generating a stable optical signal, a demodulation module, a signal processing module and a communication interface; The microprocessor 7 includes a central processing unit, a memory, an input / output interface and a communication interface for controlling the operation of the entire system; The power supply device 8 includes a power conversion module for converting input AC power or DC power into DC power or AC power of a specific voltage required by the system, a protection module, and a monitoring module for monitoring the output voltage and current of the power supply.

[0024] Example 1 The present invention provides an embodiment: the system comprises a differential pressure flow meter body 1, an installation assembly, a differential pressure part 3, a strain sensor 4, an optical fiber 5, a fiber grating demodulator 6, a microprocessor 7 and a power supply device 8; both ends of the outer side of the differential pressure flow meter body 1 are installed with installation assemblies for assembly with a measuring pipeline, a differential pressure part 3 arranged at the center of a section of pipeline is installed at the center of the differential pressure flow meter body 1, two groups of strain sensors 4 symmetrically arranged on both sides of the differential pressure part 3 are attached to the differential pressure flow meter body 1, optical fibers 5 for transmitting optical signals are installed on the outer sides of the two groups of strain sensors 4, the other end of the optical fiber 5 is connected to the fiber grating demodulator 6, the microprocessor 7 connected through an electrical interface is installed on the outer side of the fiber grating demodulator 6, and the microprocessor 7 is installed on the outer side of the microprocessor 7 The power supply device 8, the installation assembly includes a flange 201 fixedly connected to both sides of the differential pressure flow meter body 1, a fastening screw hole 202 is provided inside the flange 201, and a fastening bolt 203 is detachably connected inside the fastening screw hole 202. The differential pressure member 3 specifically adopts any one of a standard orifice plate, a conical intercepting member, a wedge-shaped intercepting member, an eccentric orifice plate, a multi-hole orifice plate, a bend pipe and a velocity-averaging pipe. The two sets of strain sensors 4 also adopt an FBG sensor a401 arranged upstream of the flow and an FBG sensor b402 arranged downstream of the flow. The reflection wavelength range of the FBG sensor a401 and the FBG sensor b402 is between 1500nm and 1580nm. When light passes through the FBG sensor a401 and the FBG sensor b402, the reflection wavelength of the light is:

[0025] in is the effective refractive index, is the Bragg period of the fiber Bragg grating.

[0026] Preferably, both sides of the differential pressure member 3 are provided with sticking measuring points 101, and the FBG sensor a401 and the FBG sensor b402 are connected to the fiber grating demodulator 6 through the optical fiber 2, and the strain values ​​of the FBG sensor a401 and the FBG sensor b402 are collected and calculated by the fiber grating demodulator 6; The fiber Bragg grating demodulator 6 includes a light source module for generating a stable optical signal, a demodulation module, a signal processing module and a communication interface. The demodulation module receives the optical signal and demodulates it into an electrical signal corresponding to the physical quantity. The signal processing module further processes the demodulated electrical signal, including filtering, amplification and digitization; The microprocessor 7 includes a central processing unit that controls the operation of the entire system, a memory, an input and output interface, and a communication interface. The memory stores programs and data, including an operating system, application programs, and measurement data. The communication interface communicates data with other systems, including remote monitoring and data uploading. The power supply device 8 includes a power conversion module for converting input AC power or DC power into DC power or AC power of a specific voltage required by the system, a protection module, and a monitoring module for monitoring the output voltage and current of the power supply.

[0027] Before use, calibrate the flow measurement system of the strain and temperature self-compensated differential pressure flowmeter, assuming the standard flow is The fluid flows through the differential pressure flow meter body 1, and the strain value collected by the fiber grating demodulator 6 at the FBG sensor a401 is The strain value collected by the fiber Bragg grating demodulator 6 at the sensor b402 is , then the strain difference for:

[0028] Measure multiple groups of standard flow values ​​through standard flow calibration device and grating fiber demodulator And the corresponding multiple sets of strain differences , as shown in the following table:

[0029] Table 1 Correspondence table of standard flow value and strain difference The flow rate is calculated as: a+b

[0030] in is the strain difference, in units of ; It is the standard flow rate, and the unit is L / min.

[0031] Then the least square method is used to calculate the data in Table 1, and we can get: intercept a: -0.512352, unit L / min, slope b: 0.986362, unit L / (min* ); Substituting the above formula into the flow value =-0.512352+0.986362 .

[0032] A flow measurement method of a differential pressure flow meter based on strain and temperature self-compensation, comprising a flow measurement system of a differential pressure flow meter based on strain and temperature self-compensation as described above, and the steps are as follows: S1: Calibration Process S11: Install the differential pressure flow meter body 1 to the measuring pipeline of the standard flow calibration device through the flange 201, and ensure that the connection is tight and leak-free; S12: Connect the optical fiber 5 to the FBG sensor a401 and the FBG sensor b402, and then to the fiber grating demodulator 6 to transmit and receive optical signals, start the motor 9 through the controller, and then drive the ball screw 10 and the piston rod 11, so that the piston 12 reciprocates in the active volume tube 13 to simulate different flow rates; S13: Initialize the data acquisition device and the computer, set the data acquisition parameters, including the sampling frequency and the data storage path, and the optical fiber demodulator 6 receives the strain signals of the FBG sensor a401 and the FBG sensor b402 and converts them into digital signals for computer processing; S14: Open the first control valve 14, the second control valve 15 and the third control valve 16, so that the fluid flows from the oil tank 17 into the active volume tube 13, and different flow rates are generated by the movement of the piston 12. Under different flow rates, the computer receives the strain signals of the FBG sensor a401 and the FBG sensor b402 transmitted by the fiber grating demodulator 6 through the data acquisition device, and records the corresponding flow values ​​at the same time. Repeat the above steps to measure multiple groups of flow values and the corresponding strain difference ; S15: Multiple groups of flow values ​​measured and the corresponding strain difference Import it into the computer for processing, use the least square method or other suitable fitting method to calculate the flow value and strain difference Perform fitting to obtain the corresponding relationship between them, establish the mathematical model of the flow meter according to the fitting results, and perform subsequent flow measurement and calibration; S16: Reinstall the calibrated flow meter to the actual measurement pipeline, perform actual flow measurement, compare the measurement result with the standard flow value measured by other high-precision flow meters, and verify the accuracy of the calibration result; S2: Paste FBG sensor a401 and FBG sensor b402 After the calibration is completed, the differential pressure flow meter body 1 is installed on the pipeline to be tested through the flange 201. First, use sandpaper to clean the stains, oxide layer, and rust covering layer on the surface of the pasting measuring point 101; then use clean absorbent cotton dipped in anhydrous ethanol to scrub the pasting measuring point 101 until there is no stain on the absorbent cotton ball; finally, place the FBG sensor a401 and the FBG sensor b402 on the polished pasting measuring point 101, evenly apply the colloid, and wait for solidification before measuring; S3: When the FBG sensor a401 and the FBG sensor b402 are subjected to stress, they are stretched or contracted, causing the effective refractive index and grating period of the fiber grating to change, resulting in a corresponding change in the wavelength of the reflected spectrum. changes, and indirectly measures the strain value changes on both sides of the measured differential pressure piece; when the temperature of FBG sensor a401 and FBG sensor b402 changes, FBG sensor a401 and FBG sensor b402 undergo thermal expansion and contraction deformation, which changes the period length of the fiber grating sensor, thereby causing the central wavelength of the reflection spectrum to move. A specific wavelength corresponds to a specific temperature. Therefore, by measuring the central wavelength of the reflection spectrum, the temperature of the fiber grating area is measured; when measuring the flow rate, the strain sensor 4 pasted on both sides of the differential pressure piece 3 is affected by temperature and stress at the same time. Since the pipeline medium is in a long-term flow state during measurement, the temperature change dynamics of the strain sensors 4 on both sides of the differential pressure piece 3 are the same, and the influence of temperature on the strain sensor 4 is also equal. Therefore, when calculating the strain difference, the influence of temperature is eliminated to achieve the purpose of temperature self-compensation. Taking FBG sensor a401 and FBG sensor b402 as examples, the changes in the central wavelength of the reflection spectrum caused by temperature are basically equal, and taking the strain gauge as an example, the resistance change value caused by temperature is also basically equal.

Claims

1. A flow measurement system of a differential pressure flow meter based on strain and temperature self-compensation, the system comprising a differential pressure flow meter body (1); characterized in that: The invention also comprises a mounting assembly, a differential pressure piece (3), a strain sensor (4), an optical fiber (5), a fiber Bragg grating demodulator (6), a microprocessor (7) and a power supply device (8); both ends of the outer side of the differential pressure flow meter body (1) are mounted with mounting assemblies for assembly with the measuring pipeline; a differential pressure piece (3) arranged at the center of a section of pipeline is mounted at the center of the differential pressure flow meter body (1); two groups of strain sensors (4) symmetrically arranged on both sides of the differential pressure piece (3) are attached to the differential pressure flow meter body (1); optical fibers (5) for transmitting optical signals are mounted on the outer sides of the two groups of strain sensors (4); the other end of the optical fiber (5) is connected to the fiber Bragg grating demodulator (6); a microprocessor (7) connected via an electrical interface is mounted on the outer side of the fiber Bragg grating demodulator (6); and a power supply device (8) is mounted on the outer side of the microprocessor (7); The fiber Bragg grating demodulator (6) comprises a light source module for generating a stable optical signal, a demodulation module, a signal processing module and a communication interface; The microprocessor (7) includes a central processing unit for controlling the operation of the entire system, a memory, an input and output interface, and a communication interface; The power supply device (8) comprises a power conversion module for converting input alternating current or direct current into direct current or alternating current of a specific voltage required by the system, a protection module, and a monitoring module for monitoring the output voltage and current of the power supply.

2. A flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: The installation assembly comprises flanges (201) fixedly connected to both sides of the differential pressure flow meter body (1), a fastening screw hole (202) is provided inside the flange (201), and fastening bolts (203) are detachably connected inside the fastening screw hole (202).

3. The flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: The differential pressure member (3) is specifically any one of a standard orifice plate, a conical cut-off member, a wedge-shaped cut-off member, an eccentric orifice plate, a multi-hole orifice plate, a bent pipe and an average velocity pipe.

4. The flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: The two sets of strain sensors (4) also use a FBG sensor a (401) arranged upstream of the flow and a FBG sensor b (402) arranged downstream of the flow. The reflection wavelength range of the FBG sensor a (401) and the FBG sensor b (402) is between 1500nm and 1580nm. When light passes through the FBG sensor a (401) and the FBG sensor b (402), the reflection wavelength of the light is: in is the effective refractive index, is the Bragg period of the fiber Bragg grating.

5. The flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: Adhesive measuring points (101) are provided on both sides of the differential pressure piece (3); the FBG sensor a (401) and the FBG sensor b (402) are connected to a fiber optic Bragg grating demodulator (6) via an optical fiber (2); and the strain values ​​of the FBG sensor a (401) and the FBG sensor b (402) are collected and calculated by the fiber optic Bragg grating demodulator (6).

6. A flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: The demodulation module receives the optical signal and demodulates it into an electrical signal corresponding to the physical quantity. The signal processing module further processes the demodulated electrical signal, including filtering, amplification and digitization.

7. The flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: The memory stores programs and data, including operating systems, applications, and measurement data, and the communication interface communicates data with other systems, including remote monitoring and data uploading.

8. The flow measurement system of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 1, characterized in that: Before use, calibrate the flow measurement system of the strain and temperature self-compensated differential pressure flowmeter, assuming the standard flow is The fluid flows through the differential pressure flow meter body (1), and the strain value collected by the fiber grating demodulator (6) at the FBG sensor a (401) is The strain value collected by the fiber Bragg grating demodulator 6 at the sensor b (402) is , then the strain difference for: Measure multiple groups of standard flow values ​​through standard flow calibration device and grating fiber demodulator And the corresponding multiple sets of strain differences ; The flow rate is calculated as: a+b in is the strain difference, in units of ; It is the standard flow rate, and the unit is L / min.

9. A flow measurement method of a differential pressure flowmeter based on strain and temperature self-compensation, characterized in that A flow measurement system of a differential pressure flow meter based on strain and temperature self-compensation according to claims 1-8, wherein the steps are as follows: S1: Calibration Process S11: Install the differential pressure flow meter body 1 onto the measuring pipeline of the standard flow calibration device through the flange (201), ensuring that the connection is tight and leak-free; S12: Connect the optical fiber (5) to the FBG sensor a (401) and the FBG sensor b (402), and then connect to the fiber grating demodulator (6) to transmit and receive optical signals, start the motor (9) through the controller, and then drive the ball screw (10) and the piston rod (11), so that the piston (12) reciprocates in the active volume tube (13) to simulate different flow rates; S13: Initializing the data acquisition device and the computer, setting data acquisition parameters, including sampling frequency and data storage path, and the optical fiber demodulator (6) receives the strain signals of the FBG sensor a (401) and the FBG sensor b (402), and converts them into digital signals for computer processing; S14: Open the first control valve (14), the second control valve (15) and the third control valve (16), so that the fluid flows from the oil tank (17) into the active volume tube (13), and different flow rates are generated through the movement of the piston (12). Under different flow rates, the computer receives the strain signals of the FBG sensor a (401) and the FBG sensor b (402) transmitted by the fiber optic Bragg grating demodulator (6) through the data acquisition device, and records the corresponding flow values ​​at the same time. Repeat the above steps to measure multiple groups of flow values and the corresponding strain difference ; S15: Multiple groups of flow values ​​measured and the corresponding strain difference Import it into the computer for processing, use the least square method or other suitable fitting method to calculate the flow value and strain difference Perform fitting to obtain the corresponding relationship between them, establish the mathematical model of the flow meter according to the fitting results, and perform subsequent flow measurement and calibration; S16: Reinstall the calibrated flow meter to the actual measurement pipeline, perform actual flow measurement, compare the measurement result with the standard flow value measured by other high-precision flow meters, and verify the accuracy of the calibration result; S2: Paste FBG sensor a (401) and FBG sensor b (402) After the calibration is completed, the differential pressure flow meter body (1) is installed on the pipeline to be tested through the flange (201). First, the stains, oxide layer, and rust covering layer on the surface of the pasting measuring point (101) are polished clean using sandpaper; then, the pasting measuring point (101) is scrubbed with clean absorbent cotton dipped in anhydrous ethanol until there is no stain on the absorbent cotton ball; finally, the FBG sensor a (401) and the FBG sensor b (402) are placed on the polished pasting measuring point (101), and the colloid is evenly applied, and the measurement is performed after the colloid is cured; S3: When the FBG sensor a (401) and the FBG sensor b (402) are subjected to stress, they are stretched or contracted, causing the effective refractive index and grating period of the fiber grating to change, resulting in a corresponding change in the wavelength of the reflection spectrum. By measuring the wavelength of the spectrum When the temperature of the FBG sensor a (401) and the FBG sensor b (402) changes, the FBG sensor a (401) and the FBG sensor b (402) expand and contract due to heat, which changes the period length of the fiber grating sensor, thereby causing the center wavelength of the reflection spectrum to move. A specific wavelength corresponds to a specific temperature. Therefore, by measuring the center wavelength of the reflection spectrum, the temperature of the fiber grating area is measured.

10. The flow measurement method of a differential pressure flowmeter based on strain and temperature self-compensation according to claim 9, characterized in that: During flow measurement, the strain sensors (4) attached to both sides of the differential pressure piece (3) are affected by temperature and stress at the same time. Since the pipeline medium is in a long-term flow state during measurement, the temperature change dynamics of the strain sensors (4) on both sides of the differential pressure piece (3) are the same, and the influence of temperature on the strain sensors (4) is also equal. Therefore, when calculating the strain difference, the influence of temperature is eliminated to achieve the purpose of temperature self-compensation. Taking FBG sensor a (401) and FBG sensor b (402) as examples, the changes in the central wavelength of the reflection spectrum caused by temperature are basically equal. Taking the strain gauge as an example, the resistance change value caused by temperature is also basically equal.

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