A flow rate and temperature simultaneous sensing system and method

Abstract

The present application belongs to the technical field of optical fiber sensing and flow velocity detection, and discloses a flow velocity and temperature synchronous sensing system and method. The sensing probe is placed in the measured fluid during work for measuring flow velocity and temperature. The sensing probe comprises a first sensor, a second sensor and a quartz glass sleeve. The first sensor and the second sensor are arranged side by side in the quartz glass sleeve, and the sensing end faces are arranged in a flush manner. The first sensor is a short-cavity Fabry-Perot interference sensor formed by fusion splicing of a first single-mode optical fiber and a first hollow optical fiber section without a gold-plated film. The second sensor is a long-cavity Fabry-Perot interference sensor formed by fusion splicing of a second single-mode optical fiber and a second hollow optical fiber section with a gold-plated film on the sensing end face. The optical signal unit is used for injecting wide-spectrum optical signals with different powers into the two sensors of the sensing probe. The optical spectrum acquisition and processing unit is used for acquiring the optical signals output by the sensing probe, analyzing the optical spectrum of the optical signals, and performing demodulation operation on the optical spectrum to obtain the flow velocity and temperature values.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing and flow velocity detection technology, specifically to a flow velocity and temperature synchronous sensing system and method. Background Technology

[0002] Flow velocity measurement has significant applications in downhole oil and gas extraction, oil and gas pipeline transportation, petrochemicals, and process industry monitoring. Compared with traditional electrothermal flow velocity sensing methods, fiber optic flow velocity sensing offers advantages such as resistance to electromagnetic interference, corrosion resistance, intrinsic safety, small probe size, and high information transmission efficiency, thus attracting widespread attention.

[0003] Fiber optic thermal flow velocity sensing typically utilizes the thermal equilibrium between the heating of the sensing material and the convective cooling of the fluid to characterize changes in flow velocity. When an optical signal is coupled into the sensing channel, the sensing material absorbs the light energy and heats up; when external fluid flows through, the fluid carries away the heat and re-establishes a thermal equilibrium state, which in turn causes a change in the optical path difference of the interference cavity, ultimately manifesting as a change in the reflected interference spectrum or phase information. By demodulating this change, flow velocity measurement can be achieved.

[0004] However, existing fiber optic thermal velocity sensing technology generally suffers from measurement errors caused by the cross-sensitivity between flow velocity and temperature in complex fluid environments. In-situ temperature changes directly affect the thermal equilibrium state of the sensing probe, causing the output phase to drift under the same flow velocity conditions. This results in the demodulated flow velocity value deviating from the true value, severely affecting measurement accuracy.

[0005] To address these issues, existing technologies typically employ solutions such as external electronic temperature probes, fiber optic temperature sensors, distributed temperature measurement devices, or periodically switching heating light sources. However, these methods still suffer from problems such as inconsistent spatial locations, complex structures, insufficient real-time performance, or the inability to achieve truly in-situ temperature measurement, making it difficult to simultaneously meet the requirements for resistance to temperature interference and in-situ synchronous measurement in complex flow velocity environments.

[0006] Therefore, there is a need for a flow velocity and temperature synchronous sensing system and method that is compact, requires no additional independent temperature sensor, and can simultaneously measure flow velocity and in-situ temperature. Summary of the Invention

[0007] The purpose of this invention is to provide a flow velocity and temperature synchronous sensing system and method, which can simultaneously measure the flow velocity of the fluid being measured and perform in-situ temperature measurement, and reduce the influence of temperature on the flow velocity measurement results by jointly demodulating the two sensing signals.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A flow rate and temperature synchronous sensing system includes a sensing probe, an optical signal unit, and a spectrum acquisition and processing unit; The sensing probe is placed in the fluid being measured during operation to measure flow rate and temperature. The sensing probe includes a first sensor, a second sensor, and a quartz glass sleeve. The first sensor and the second sensor are arranged side by side inside the quartz glass sleeve, and the sensing end faces of the first sensor and the second sensor are flush. The first sensor is a short-cavity Fabry-Perot interferometer sensor formed by fusing a first single-mode fiber and a first hollow fiber segment to form an uncoated gold film, with a cavity length of 195μm-205μm. The first hollow fiber segment is filled with a PDMS thermistor material whose refractive index varies with temperature to form a first PDMS cavity. The first PDMS cavity and the corresponding reflective interface form a first Fabry-Perot interferometer cavity. The second sensor is a long-cavity Fabry-Perot interferometer sensor formed by fusing a second single-mode fiber and a second hollow fiber segment to form a gold film coated on the sensing end face, with a cavity length of 275μm-285μm. The second hollow fiber segment is filled with a PDMS thermistor material whose refractive index varies with temperature to form a second PDMS cavity. The second PDMS cavity, the corresponding reflective interface, and the gold film together form a second Fabry-Perot interferometer cavity. The sensing end is the end of the second hollow fiber segment that is furthest from the second single-mode fiber. The optical signal unit is used to inject broadband optical signals of different powers into the two sensors of the sensing probe; The spectral acquisition and processing unit is used to acquire the optical signal output by the sensor probe, analyze the spectrum of the optical signal, and perform demodulation operations on the spectrum to obtain the flow rate and temperature values.

[0009] The ratio of the cavity length of the first sensor to that of the second sensor is 1.3-1.5.

[0010] The quartz glass sleeve encapsulates and protects the first sensor and the second sensor, which are fixed inside the same quartz glass sleeve by UV adhesive.

[0011] The optical signal unit includes an ASE broadband light source, a 2×2 fiber coupler, an erbium-doped fiber amplifier, a first circulator, and a second circulator. The broadband optical signal output from the ASE broadband light source is split into two sensing optical paths after entering the 2×2 fiber coupler. The first sensing optical path enters the first sensor through the first circulator, and the second sensing optical path is amplified by the erbium-doped fiber amplifier and then enters the second sensor through the second circulator. The incident optical power of the first sensing optical path is 18mW-22mW, and the incident optical power of the second sensing optical path is 195mW-205mW.

[0012] The spectral acquisition and processing unit includes an optical switch, a spectral acquisition device, and a signal processing and demodulation unit. The optical switch is connected to a first circulator and a second circulator, respectively, and is used to switch the two reflection interference spectra returned by the first and second sensors. The spectral acquisition device is connected to the optical switch and is used to acquire the reflection interference spectra after being selected by the optical switch. The signal processing and demodulation unit is used to perform fast Fourier transform phase extraction, weighted differential velocity demodulation, numerical superposition vernier spectrum construction, vernier envelope phase extraction, and in-situ temperature inversion on the two reflection interference spectra.

[0013] The specific processing procedure of the signal processing and demodulation unit is as follows: The phase of the reflection interference spectra output by the two sensors is extracted, and a flow rate demodulation quantity resistant to temperature interference is constructed by weighted difference; the two reflection interference spectra are numerically superimposed to form a vernier spectrum, and in-situ temperature inversion is achieved by extracting the vernier envelope phase; The interference intensity of the first Fabry-Perot interferometer and the second Fabry-Perot interferometer is expressed as follows: (1) in, and The intensity of the two reflected interference spectra of the two beams involved in the interference. The phase difference between the two reflected interference spectra; The light signals injected into the first and second sensors continuously heat the PDMS thermosensitive material; when the fluid flows past the outside of the sensing probe, it undergoes convective heat transfer with the outer surface of the quartz glass sleeve, and the heat is transferred through the quartz glass sleeve to the first and second sensors, causing the two sensors to establish corresponding thermal equilibrium states; under the combined influence of photothermal effect and heat transfer between the quartz glass sleeve and the measured fluid, the first... Steady-state cavity temperature of each sensor Represented as: (2) in, The in-situ temperature of the fluid being measured. For the first The incident light power of each sensor, For the first The photothermal conversion efficiency of each sensor To match the flow rate Relevant heat transfer functions; Because the incident light powers of the first and second sensors are different, and the outer end face of the second sensor is coated with a gold film, the two sensors establish different thermal equilibrium states under the same in-situ temperature and flow rate conditions; under the fast Fourier transform phase demodulation condition, the first... Phase changes of individual sensors Represented as: (3) in, For the first Thermal sensitivity coefficient of each sensor; As an ambient temperature interference factor, since the two sensors are packaged in the same sensing probe and experience approximately the same local thermal field, In the two-way phase expression, it is represented as a common-mode term; Based on the difference in thermal sensitivity between the two sensors, the weighting coefficient is as follows: (4) After weighted differential sampling of the phase changes from the first sensor and the second sensor, the differential phase is obtained. : (5) As can be seen from equation (5), by weighting the two phase signals, the common-mode interference caused by the in-situ temperature can be weakened, and the resulting differential phase is mainly related to the flow velocity, thereby achieving flow velocity demodulation.

[0014] During in-situ temperature measurement, the reflection interference spectra of the first sensor and the reflection interference spectra of the second sensor are numerically superimposed. A vernier spectrum is formed based on the period difference between the two reflection interference spectra, and the vernier envelope phase is extracted. The vernier envelope phase is expressed as: (6) in, This represents the equivalent sensitivity coefficient of the vernier envelope phase to temperature. The equivalent transfer function related to flow velocity, The velocity correlation coefficient is used; the velocity result obtained according to equation (5) is substituted into equation (6) to obtain the in-situ temperature.

[0015] A method for synchronously sensing flow velocity and temperature, implemented using a synchronous flow velocity and temperature sensing system, works as follows: Step 1: Place the sensor probe in the fluid being measured, so that the first sensor and the second sensor are simultaneously in the same heat transfer environment corresponding to the local thermal field and flow field. Step 2: A broadband optical signal is emitted from the ASE broadband light source and split into two sensing optical paths through a 2×2 fiber coupler. The first sensing optical path enters the first sensor through the first circulator, and the second sensing optical path is amplified by the erbium-doped fiber amplifier and then enters the second sensor through the second circulator. Step 3: The two reflected interference spectra returned by the first and second sensors are switched by an optical switch, and the reflected interference spectrum after the channel is selected is acquired by the spectral acquisition device; Step 4: The signal processing and demodulation unit analyzes and calculates the two reflection interference spectra to obtain the flow velocity and temperature results; Step 5: Output the flow rate and in-situ temperature of the fluid being measured.

[0016] Step 5 specifically involves: Step 5.1: Perform fast Fourier transform on the reflection interference spectra of the first sensor and the second sensor respectively to extract the two phase signals; Step 5.2: Perform weighted differential on the two phase signals according to equations (4) and (5) to obtain the differential phase corresponding to the flow velocity, and demodulate the flow velocity according to the relationship between the differential phase and the flow velocity. Step 5.3: Numerically superimpose the reflection interference spectra of the first sensor and the second sensor to form a vernier spectrum, and extract the vernier envelope phase; Step 5.4: Substitute the flow rate demodulation result into equation (6) to obtain the in-situ temperature of the fluid being measured.

[0017] In the aforementioned synchronous flow velocity and temperature sensing system, the optical signals emitted by the light source enter each unit in the following order: the broadband light emitted by the ASE broadband light source first enters the 2×2 fiber coupler, and after beam splitting, forms the first sensing optical path and the second sensing optical path; the first sensing optical path enters the first sensor through the first circulator, and the second sensing optical path enters the second sensor through the second circulator after being amplified by the erbium-doped fiber amplifier; the two optical signals are photothermally excited in the first and second sensors respectively, and form corresponding reflection interference spectra through the heat exchange between the quartz glass sleeve and the measured fluid; the two reflection interference spectra return through the corresponding circulators and are output to the optical switch; the optical switch selects the two reflection interference spectra according to the set channel and outputs the selected two reflection interference spectra to the spectral acquisition device; after obtaining the two reflection interference spectra selected by the optical switch, the spectral acquisition device sends them to the signal processing and demodulation unit, which completes the flow velocity demodulation and temperature inversion, and outputs the final measurement result.

[0018] The working principle of the flow rate and temperature synchronous sensing system is as follows: This invention utilizes two Fabry-Perot interferometers with different thermal coupling characteristics to synchronously respond to the same local flow and thermal fields. The reflected interference spectra output by the two sensors are first used for phase extraction, and a flow velocity demodulation quantity resistant to temperature interference is constructed through weighted differential. Simultaneously, the two reflected interference spectra are numerically superimposed to form a vernier spectrum, and in-situ temperature inversion is achieved by extracting the vernier envelope phase. The flow velocity demodulation and temperature inversion process includes four parts: interference modulation of the first and second Fabry-Perot interferometer cavities, photothermal-fluid heat transfer balance, dual-channel weighted differential flow velocity demodulation, and in-situ temperature inversion of the vernier envelope.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The present invention sets two Fabry-Perot sensors with different thermal coupling characteristics in the same sensing probe, realizing the synchronous measurement of flow velocity and in-situ temperature.

[0020] (2) By implementing weighted differential demodulation on the two phase signals, the present invention effectively reduces the common-mode interference caused by in-situ temperature, thereby improving the accuracy of flow velocity measurement.

[0021] (3) This invention achieves in-situ temperature inversion by numerically superimposing two reflection interference spectra and extracting the vernier envelope phase without introducing an independent temperature sensor. The overall system structure is compact and suitable for online monitoring in complex fluid environments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the flow rate and temperature synchronous sensing system described in this invention. Figure 2 This is a schematic diagram of the sensing probe structure described in this invention; Figure 3 This is a schematic diagram of the test connection between the sensing probe and the standard flow rate calibration device described in this invention; Figure 4 The graphs show the reflectance spectral shifts of the first and second sensors under different flow rates; (a) shows the spectra of FPI1 at 2 m / s, 4 m / s, 6 m / s and 8 m / s at 26 °C and the corresponding spectral shifts. (b) shows the spectra of FPI2 at 2 m / s, 4 m / s, 6 m / s and 8 m / s at 26 °C and the corresponding spectral shifts.

[0023] Figure 5 The following are the flow rate response curves without temperature compensation: (a) is the phase-flow rate response curve of FPI1 at 22℃, 26℃, 30℃ and 34℃. (b) is the phase-flow rate response curve of FPI2 at 22℃, 26℃, 30℃ and 34℃.

[0024] Figure 6 The flow velocity response curve after temperature compensation; Figure 7 This is a graph showing the results of in-situ temperature measurements.

[0025] In the diagram: 1. Sensing probe; 1-1. First single-mode fiber; 1-2. Second single-mode fiber; 1-3. First hollow fiber segment; 1-4. Second hollow fiber segment; 1-5. First PDMS cavity; 1-6. Second PDMS cavity; 1-7. Gold film; 1-8. Quartz glass sleeve; 2. Optical signal unit; 2-1. ASE broadband light source; 2-2. 2×2 fiber coupler; 2-3. Erbium-doped fiber amplifier; 2-4. First circulator; 2-5. Second circulator; 2-6. First sensing optical path; 2-7. Second sensing optical path; 3. Spectrum acquisition and processing unit; 3-1. Optical switch; 3-2. Spectrum acquisition device; 3-3. Signal processing and demodulation unit; 4. Standard flow rate calibration device. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, a flow rate and temperature synchronous sensing system includes a sensing probe 1, an optical signal unit 2, and a spectrum acquisition and processing unit 3. The sensing probe 1 is used to sense the flow rate and in-situ temperature information of the fluid being measured; the optical signal unit 2 is used to inject broadband optical signals of different powers into two sensing channels in the sensing probe 1; the spectrum acquisition and processing unit 3 is used to acquire the reflection interference spectrum output by the sensing probe 1 and demodulate the reflection interference spectrum to obtain the flow rate and in-situ temperature values ​​of the fluid being measured.

[0028] The optical signal unit 2 includes an ASE broadband light source 2-1, a 2×2 fiber coupler 2-2, an erbium-doped fiber amplifier 2-3, a first circulator 2-4, a second circulator 2-5, a first sensing optical path 2-6, and a second sensing optical path 2-7. The ASE broadband light source 2-1 outputs a broadband optical signal, which is split into two paths after entering the 2×2 fiber coupler 2-2: the first sensing optical path 2-6 enters the first sensor in the sensing probe 1 via the first circulator 2-4; the second sensing optical path 2-7 is amplified by the erbium-doped fiber amplifier 2-3 and then enters the second sensor in the sensing probe 1 via the second circulator 2-5. This allows the first and second sensors to obtain different incident light powers, resulting in different thermal equilibrium states and different thermal response characteristics.

[0029] The spectral acquisition and processing unit 3 includes an optical switch 3-1, a spectral acquisition device 3-2, and a signal processing and demodulation unit 3-3. The optical switch 3-1 is connected to the first circulator 2-4 and the second circulator 2-5, respectively, and is used to switch the channels of the two reflected interference spectra returned by the first and second sensors. The spectral acquisition device 3-2 is connected to the optical switch 3-1 and is used to acquire the two reflected interference spectra after the optical switch 3-1 has selected the channel. The signal processing and demodulation unit 3-3 is used to perform fast Fourier transform phase extraction, weighted differential velocity demodulation, numerical superposition vernier spectrum construction, vernier envelope phase extraction, and in-situ temperature inversion on the acquired reflected interference spectra, thereby obtaining the flow velocity and in-situ temperature values ​​of the measured fluid.

[0030] like Figure 2 As shown, the sensing probe 1 includes a first single-mode fiber 1-1, a second single-mode fiber 1-2, a first hollow fiber segment 1-3, a second hollow fiber segment 1-4, a first PDMS cavity 1-5, a second PDMS cavity 1-6, a gold film 1-7, and a quartz glass sleeve 1-8. The first single-mode fiber 1-1 and the first hollow fiber segment 1-3 are connected to form a first sensor, and the second single-mode fiber 1-2 and the second hollow fiber segment 1-4 are connected to form a second sensor. The first sensor and the second sensor are arranged side by side inside the quartz glass sleeve 1-8, and the sensing end faces of the first sensor and the second sensor are flush.

[0031] The first sensor comprises a first single-mode fiber 1-1 and a first hollow fiber segment 1-3. PDMS thermistor material is filled within the first hollow fiber segment 1-3 to form a first PDMS cavity 1-5, which, together with the corresponding reflective interface, forms a first Fabry-Perot interference cavity. The second sensor comprises a second single-mode fiber 1-2, a second hollow fiber segment 1-4, PDMS thermistor material, and a gold film 1-7. The PDMS thermistor material is filled within the second hollow fiber segment 1-4 to form a second PDMS cavity 1-6. The gold film 1-7 is disposed at the end face of the second hollow fiber segment 1-4 away from the second single-mode fiber 1-2. The PDMS thermistor material, the corresponding reflective interface, and the gold film 1-7 together form a second Fabry-Perot interference cavity. A quartz glass sleeve 1-8 is fitted over the first and second sensors for encapsulation and protection. The first and second sensors can be fixed within the quartz glass sleeve 1-8 using UV adhesive.

[0032] In this embodiment, the first hollow optical fiber segment 1-3 is filled with PDMS thermistor material, thereby forming a first Fabry-Perot interferometer cavity without gold plating, with a cavity length of 195μm to 205μm. The second Fabry-Perot interferometer cavity, formed by the second PDMS cavity 1-6 and the gold film 1-7, is a long cavity structure with gold plating on the outer end face, with a cavity length of 275μm to 285μm. The ratio of the cavity length of the second Fabry-Perot interferometer cavity to that of the first Fabry-Perot interferometer cavity is 1.3 to 1.5. Both the first PDMS cavity 1-5 and the second PDMS cavity 1-6 are filled with PDMS thermistor material. After encapsulation, the front end diameter of the sensing probe 1 is approximately 1.8mm. In use, the sensing probe 1 can be placed in the fluid being measured, with the outer surface of the quartz glass sleeve 1-8 in contact with the fluid. The first sensor and the second sensor establish a heat exchange relationship with the fluid being measured through the quartz glass sleeve 1-8.

[0033] In this embodiment, the incident light power corresponding to the first sensing optical path 2-6 is 18mW to 22mW; the incident light power corresponding to the second sensing optical path 2-7 is 195mW to 205mW. Because the incident light powers of the first and second sensors are different, and the second sensor is equipped with a gold film 1-7, the two sensors can form different thermal equilibrium states and different thermal response characteristics under the same flow rate and in-situ temperature conditions.

[0034] During the measurement process, the broadband optical signal output from the ASE broadband light source 2-1 is split into two paths via a 2×2 fiber coupler 2-2. The first sensing optical path enters the first sensor via a first circulator 2-4, and the second sensing optical path is amplified by an erbium-doped fiber amplifier 2-3 and then enters the second sensor via a second circulator 2-5. The two optical signals are photothermally excited in the first and second sensors respectively, and form corresponding reflection interference spectra through heat exchange between the quartz glass sleeve 1-8 and the measured fluid. The two reflection interference spectra are returned via the corresponding circulators and output to the optical switch 3-1. The optical switch 3-1 selects the channel of the two reflection interference spectra according to the set channel and outputs the two reflection interference spectra after channel selection to the spectral acquisition device 3-2. After obtaining the two reflection interference spectra selected by the optical switch 3-1, the spectral acquisition device 3-2 sends them to the signal processing and demodulation unit 3-3. The signal processing and demodulation unit 3-3 completes the flow rate demodulation and temperature inversion, and outputs the final measurement result.

[0035] Specifically, the signal processing and demodulation unit 3-3 first performs a fast Fourier transform on the two reflection interference spectra selected by the optical switch 3-1 and acquired by the spectral acquisition device 3-2 to extract the two phase signals; then, according to the weighted differential principle, it performs weighted differential on the two phase signals to obtain the differential phase corresponding to the flow velocity, and demodulates the flow velocity according to the relationship between the differential phase and the flow velocity; subsequently, it numerically superimposes the reflection interference spectra of the first sensor and the second sensor to form a vernier spectrum and extracts the vernier envelope phase; finally, it substitutes the flow velocity demodulation result into the temperature inversion model to obtain the in-situ temperature of the measured fluid.

[0036] The specific processing procedure of the signal processing and demodulation unit 3-3 is as follows: The phase of the reflection interference spectra output by the two sensors is extracted, and a flow rate demodulation quantity resistant to temperature interference is constructed by weighted difference; the two reflection interference spectra are numerically superimposed to form a vernier spectrum, and in-situ temperature inversion is achieved by extracting the vernier envelope phase; The interference intensity of the first Fabry-Perot interferometer and the second Fabry-Perot interferometer is expressed as follows: in, and The intensity of the two reflected interference spectra of the two beams involved in the interference. The phase difference between the two reflected interference spectra; The light signals injected into the first and second sensors continuously heat the PDMS thermosensitive material; when the fluid flows past the outside of the sensing probe, it undergoes convective heat transfer with the outer surface of the quartz glass sleeve, and the heat is transferred through the quartz glass sleeve to the first and second sensors, causing the two sensors to establish corresponding thermal equilibrium states; under the combined influence of photothermal effect and heat transfer between the quartz glass sleeve and the measured fluid, the first... Steady-state cavity temperature of each sensor Represented as: in, The in-situ temperature of the fluid being measured. For the first The incident light power of each sensor, For the first The photothermal conversion efficiency of each sensor To match the flow rate Relevant heat transfer functions; Because the incident light powers of the first and second sensors are different, and the outer end face of the second sensor is coated with a gold film, the two sensors establish different thermal equilibrium states under the same in-situ temperature and flow rate conditions; under the fast Fourier transform phase demodulation condition, the first... Phase changes of individual sensors Represented as: in, For the first Thermal sensitivity coefficient of each sensor; As an ambient temperature interference factor, since the two sensors are packaged in the same sensing probe and experience approximately the same local thermal field, In the two-way phase expression, it is represented as a common-mode term; Based on the difference in thermal sensitivity between the two sensors, the weighting coefficient is as follows: After weighted differential sampling of the phase changes from the first sensor and the second sensor, the differential phase is obtained. : By weighted differential of the two phase signals, the common-mode interference caused by in-situ temperature can be reduced, and the resulting differential phase is mainly related to the flow velocity, thereby achieving flow velocity demodulation.

[0037] During in-situ temperature measurement, the reflection interference spectra of the first sensor and the reflection interference spectra of the second sensor are numerically superimposed. A vernier spectrum is formed based on the period difference between the two reflection interference spectra, and the vernier envelope phase is extracted. The vernier envelope phase is expressed as: in, This represents the equivalent sensitivity coefficient of the vernier envelope phase to temperature. The equivalent transfer function related to flow velocity, The velocity correlation coefficient is used to obtain the velocity result based on the differential phase. Substituting this result into the vernier envelope phase expression formula, the in-situ temperature is obtained by inversion.

[0038] In test or calibration embodiments, such as Figure 3 As shown, the standard flow rate calibration device 4 is used to provide a test fluid environment with a set flow rate. The sensing probe 1 is placed in the standard flow rate calibration device 4 for testing. During the test, the in-situ temperature can be set to 22℃, 26℃, 30℃, and 34℃, and the flow rate range can be set to 0m / s to 10m / s; wherein, the sampling interval in the range of 0m / s to 7m / s is 0.5m / s, and the sampling interval in the range of 7m / s to 10m / s is 1m / s.

[0039] like Figure 4As shown, under the condition of an in-situ temperature of 26℃, when the flow velocities are 2m / s, 4m / s, 6m / s and 8m / s respectively, the reflection spectra of both the first and second sensors shift towards the short-wavelength direction, and the arrows indicate a blue shift. Moreover, the shift amplitude of the reflection spectrum of the second sensor is greater than that of the first sensor, indicating that the two sensors have different response characteristics to changes in flow velocity, which provides a basis for subsequent weighted differential flow velocity demodulation and in-situ temperature inversion.

[0040] like Figure 5 The figure shows the flow velocity response curve without temperature compensation. The flow velocity response curve shows a significant shift under different in-situ temperature conditions, indicating that changes in in-situ temperature affect the flow velocity measurement results.

[0041] like Figure 6 As shown, the flow velocity response curves after temperature compensation are displayed. After weighted differential processing, the flow velocity response curves under different in-situ temperature conditions tend to be consistent, indicating that the cross-sensitivity effect of temperature is effectively suppressed, thereby improving the accuracy of flow velocity measurement.

[0042] like Figure 7 The figure shown is a graph of the in-situ temperature measurement results. The in-situ temperature results obtained by inversion have good consistency with the set temperature, indicating that the system described in this invention can achieve in-situ temperature measurement.

[0043] This invention is not limited to the embodiments described above. For those skilled in the art, any equivalent substitutions or transformations made to the sensor probe structure, optical path connection form, signal processing method, and calibration method without departing from the spirit and essence of this invention should be considered to fall within the protection scope of this invention.

Claims

1. A flow rate and temperature synchronous sensing system, characterized in that, The flow rate and temperature synchronous sensing system includes a sensing probe (1), an optical signal unit (2), a spectrum acquisition and processing unit (3). The sensing probe (1) is placed in the fluid being measured during operation to measure flow rate and temperature; the sensing probe (1) includes a first sensor, a second sensor and a quartz glass sleeve (1-8); the first sensor and the second sensor are arranged side by side in the quartz glass sleeve (1-8), and the sensing end faces of the first sensor and the second sensor are flush. The first sensor is a short-cavity Fabry-Perot interferometer sensor formed by fusing a first single-mode fiber (1-1) and a first hollow fiber segment (1-3) to form an unplated gold film. The cavity length is 195μm-205μm. The first hollow fiber segment (1-3) is filled with a PDMS thermistor material whose refractive index varies with temperature to form a first PDMS cavity (1-5). The first PDMS cavity (1-5) and the corresponding reflective interface form a first Fabry-Perot interferometer cavity. The second sensor is a second single-mode fiber. The first-mode fiber (1-2) is fused with the second hollow fiber segment (1-4) to form a long-cavity Fabry-Perot interferometer sensor with a gold film (1-7) coated on the sensing end face. The cavity length is 275μm-285μm. The second hollow fiber segment (1-4) is filled with PDMS thermistor material whose refractive index changes with temperature to form a second PDMS cavity (1-6). The second PDMS cavity (1-6), together with the corresponding reflective interface and the gold film (1-7), forms a second Fabry-Perot interferometer cavity. The optical signal unit (2) is used to inject broadband optical signals of different powers into the two sensors of the sensing probe (1); The spectral acquisition and processing unit (3) is used to acquire the optical signal output by the sensing probe (1), analyze the spectrum of the optical signal, and perform demodulation operation on the spectrum to obtain the flow rate and temperature values.

2. The flow rate and temperature synchronous sensing system according to claim 1, characterized in that, The ratio of the cavity length of the first sensor to that of the second sensor is 1.3-1.

5.

3. The flow rate and temperature synchronous sensing system according to claim 1, characterized in that, The quartz glass sleeve (1-8) encapsulates and protects the first sensor and the second sensor, which are fixed in the same quartz glass sleeve (1-8) by UV adhesive.

4. The flow rate and temperature synchronous sensing system according to claim 1, characterized in that, The optical signal unit (2) includes an ASE broadband light source (2-1), a 2×2 fiber coupler (2-2), an erbium-doped fiber amplifier (2-3), a first circulator (2-4), and a second circulator (2-5). The broadband optical signal output from the ASE broadband light source (2-1) is divided into two sensing optical paths after entering the 2×2 fiber coupler (2-2). The first sensing optical path (2-6) enters the first sensor through the first circulator (2-4), and the second sensing optical path (2-7) is amplified by the erbium-doped fiber amplifier (2-3) and then enters the second sensor through the second circulator (2-5). The incident light power of the first sensing optical path (2-6) is 18mW-22mW, and the incident light power of the second sensing optical path (2-7) is 195mW-205mW.

5. The flow rate and temperature synchronous sensing system according to claim 4, characterized in that, The spectral acquisition and processing unit (3) includes an optical switch (3-1), a spectral acquisition device (3-2), and a signal processing and demodulation unit (3-3). The optical switch (3-1) is connected to the first circulator (2-4) and the second circulator (2-5) respectively, and is used to switch the two reflection interference spectra returned by the first sensor and the second sensor. The spectral acquisition device (3-2) is connected to the optical switch (3-1) and is used to acquire the reflection interference spectrum after it has been selected by the optical switch (3-1).

6. The flow rate and temperature synchronous sensing system according to claim 5, characterized in that, The specific processing procedure of the signal processing and demodulation unit (3-3) is as follows: The phase of the reflection interference spectra output by the two sensors is extracted, and a flow rate demodulation quantity resistant to temperature interference is constructed by weighted difference; the two reflection interference spectra are numerically superimposed to form a vernier spectrum, and in-situ temperature inversion is achieved by extracting the vernier envelope phase; The interference intensity of the first Fabry-Perot interferometer and the second Fabry-Perot interferometer is expressed as follows: （1） in, and The intensity of the two reflected interference spectra of the light involved in the interference. The phase difference between the two reflected interference spectra; The light signals injected into the first and second sensors continuously heat the PDMS thermosensitive material; when the fluid being measured flows past the outside of the sensing probe (1), it undergoes convective heat transfer with the outer surface of the quartz glass sleeve, and the heat is transferred through the quartz glass sleeve to the first and second sensors, so that the two sensors establish corresponding thermal equilibrium states respectively; under the combined influence of photothermal effect and heat transfer between the quartz glass sleeve and the fluid being measured, the first... Steady-state cavity temperature of each sensor Represented as: （2） in, The in-situ temperature of the fluid being measured. For the first The incident light power of each sensor, For the first The photothermal conversion efficiency of each sensor To match the flow rate Relevant heat transfer functions; Two sensors establish different thermal equilibrium states under the same in-situ temperature and flow rate conditions; under fast Fourier transform phase demodulation conditions, the first... Phase changes of individual sensors Represented as: （3） in, For the first Thermal sensitivity coefficient of each sensor; Based on the difference in thermal sensitivity between the two sensors, the weighting coefficient is as follows: （4） After weighted differential sampling of the phase changes from the first sensor and the second sensor, the differential phase is obtained. : （5） During in-situ temperature measurement, the reflection interference spectra of the first sensor and the reflection interference spectra of the second sensor are numerically superimposed. A vernier spectrum is formed based on the period difference between the two reflection interference spectra, and the vernier envelope phase is extracted. The vernier envelope phase is expressed as: （6） in, This represents the equivalent sensitivity coefficient of the vernier envelope phase to temperature. The equivalent transfer function related to flow velocity, The velocity correlation coefficient is used; the velocity result obtained according to equation (5) is substituted into equation (6) to obtain the in-situ temperature.

7. A method for synchronously sensing flow rate and temperature, characterized in that, The flow rate and temperature synchronous sensing system described in any one of claims 1-6 is used, and the working process is as follows: Step 1: Place the sensor probe (1) in the fluid to be measured, so that the first sensor and the second sensor are simultaneously in the same heat transfer environment corresponding to the local thermal field and flow field. Step 2: A broadband optical signal is emitted from the ASE broadband light source (2-1) and split into two sensing optical paths through a 2×2 fiber coupler (2-2). The first sensing optical path (2-6) enters the first sensor through the first circulator (2-4), and the second sensing optical path (2-7) is amplified by the erbium-doped fiber amplifier (2-3) and then enters the second sensor through the second circulator (2-5). Step 3: The two reflected interference spectra returned by the first and second sensors are switched by optical switch (3-1), and the reflected interference spectra after the channel is selected are acquired by the spectral acquisition device (3-2). Step 4: The signal processing and demodulation unit (3-3) analyzes and calculates the two reflection interference spectra to obtain the flow velocity and temperature results; Step 5: Output the flow rate and in-situ temperature of the fluid being measured.

8. The method for synchronously sensing flow rate and temperature according to claim 7, characterized in that, Step 5 specifically involves: Step 5.1: Perform fast Fourier transform on the reflection interference spectra of the first sensor and the second sensor respectively to extract the two phase signals; Step 5.2: Perform weighted differential on the two phase signals according to equations (4) and (5) to obtain the differential phase corresponding to the flow velocity, and demodulate the flow velocity according to the relationship between the differential phase and the flow velocity. Step 5.3: Numerically superimpose the reflection interference spectra of the first sensor and the second sensor to form a vernier spectrum, and extract the vernier envelope phase; Step 5.4: Substitute the flow rate demodulation result into equation (6) to obtain the in-situ temperature of the fluid being measured.

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