Coaxial pressure detection device and detection method

Abstract

The invention provides a coaxial pressure detection device and a detection method. The device comprises a light source module, a data acquisition module, a pressure input end and a pressure sensor, the pressure sensor comprises a pressure sensing diaphragm, an optical fiber fixing substrate of a T-shaped structure, an FPI sensing optical fiber and a double-FBG sensing optical fiber, wherein the FPI sensing optical fiber and the double-FBG sensing optical fiber are coaxially integrated. External pressure sensed by the pressure sensing diaphragm is converted into optical fiber axial strain, and spectral shift of the FPI sensing optical fiber and the double-FBG sensing optical fiber is triggered. According to the invention, through cooperation of a mechanical conduction structure and multi-sensor cooperative sensing, pressure detection with high sensitivity and wide range is realized, meanwhile, the differential layout of the double FBG sensing optical fibers is utilized to effectively inhibit the influence of ambient temperature on a pressure measurement result, and the sensor has the advantages of stable structure, high measurement precision and temperature and pressure self-compensation.

Description

Technical Field

[0001] This invention relates to the field of pressure detection and temperature compensation, and in particular to a pressure detection device and method, especially a temperature and pressure co-detection device based on fiber optic sensing technology and its application. Background Technology

[0002] In modern industry, particularly in oil and gas extraction, aerospace, and chemical sectors, real-time monitoring of temperature and pressure is crucial. However, traditional pressure and temperature sensors often face numerous challenges in extreme environments, such as insufficient sensitivity, cross-interference, range limitations, and poor environmental adaptability. Most existing pressure sensors rely on resistance strain gauges or mechanical sensors, which have limited reliability and stability under high temperature and pressure conditions and typically cannot achieve simultaneous and accurate detection of temperature and pressure.

[0003] Most existing methods focus on the design and application of pressure sensors for a single pressure measurement task. For example, the paper "Simultaneous Measurement of Temperature and Pressure Based on Fabry-Perot Interferometry for Marine Monitoring" proposes a temperature and pressure sensing method based on a Fabry-Perot interferometer combined with an FBG (fiber optic gauging unit) in a polyimide (PI) tube. This method compensates for temperature effects by integrating the FBG into the FPI cavity. While it can simultaneously obtain pressure and temperature information, its structure depends on specific tube materials and adhesive fixing methods. Furthermore, its sensitivity and stability are significantly affected by material properties and environmental coupling, making it difficult to meet long-term stable detection requirements under extreme high temperature and high pressure conditions. Another example is the paper "High-sensitive fiber-optic pressure sensor based on Fabry-Perot interferometer filled with ultraviolet glue film and Vernier..." The high-sensitivity FPI pressure sensor based on UV film and Vernier effect proposed in the paper "effect" improves pressure sensitivity through the dual-cavity Vernier effect, but this approach is mainly optimized for a single pressure range and cannot simultaneously achieve wide range and temperature compensation functions. Another example is the all-quartz fiber Fabry-Perot high-temperature pressure sensor proposed in the paper "All-quartz fiber Fabry-Perot high-temperature pressure sensor," which uses high-temperature bonding technology to operate at 800℃. However, this method has extremely high requirements for manufacturing processes and mainly focuses on high-temperature stability. Pressure detection under high pressure environments remains a significant challenge, and temperature interference compensation still relies on additional measurement methods. Existing multifunctional pressure sensing technologies have not yet fully achieved the integration and high stability detection of both temperature and pressure indicators. They typically require a combination of sensing systems based on multiple principles or rely on complex temperature compensation algorithms or multi-source switching mechanisms. This not only increases system complexity but may also lead to response delays and insufficient long-term stability, making it difficult to meet the pressure detection requirements of high sensitivity, wide detection range, and high stability simultaneously. Summary of the Invention

[0004] This application proposes a coaxial pressure detection device and method, aiming to solve the technical challenges of existing fiber optic pressure sensors in extreme conditions such as downhole oil and gas wells, where sensitivity and measurement range are difficult to balance, and where temperature and pressure cross-sensitivity limits measurement accuracy, through structural innovation and multi-sensor collaborative sensing. This invention has significant advantages such as robust structure, high sensitivity, wide measurement range, and autonomous temperature compensation.

[0005] The technical solution adopted in this invention is: a coaxial pressure detection device, comprising: a display module, a transmitting and receiving module, a pressure sensor, an optical fiber sensing component, a pressure input terminal, and a constant temperature chamber;

[0006] The display module is connected to the transmitting and receiving module and is used to display the spectral characteristic waveforms of the pressure sensing process in real time.

[0007] The transmitting and receiving module is connected to the pressure sensor. The transmitting and receiving module integrates a light source module and a data acquisition module. The light source module is used to output laser signals. The data acquisition module is integrated with the light source module to acquire and demodulate the reflection spectrum from the pressure sensor in real time, and to retrieve pressure and temperature data by using the offset of the spectral characteristic peaks.

[0008] The pressure sensor integrates an optical fiber sensing component, which includes a pressure-sensing diaphragm, an optical fiber fixing substrate, an FPI sensing substrate, and a dual FBG sensing substrate. The FPI sensing substrate and the dual FBG sensing substrate each have optical fiber fixing slots, and the dual FBG sensing optical fiber and the FPI sensing optical fiber are respectively installed in the optical fiber fixing slots. The pressure input end provides an adjustable calibration or test pressure for the pressure sensor.

[0009] The optical fiber fixing base is a T-shaped structure, which includes a crossbeam and a vertical beam connected perpendicularly to the crossbeam. The upper surface of the center of the pressure-sensing diaphragm is rigidly connected to the bottom surface of the vertical beam of the T-shaped structure of the optical fiber fixing base. The upper ends of the dual FBG sensing optical fiber and the FPI sensing optical fiber are respectively fixed to the crossbeam, and their lower ends are respectively fixed to the fixing base of the pressure sensor.

[0010] The coaxially arranged FPI sensing substrate and dual FBG sensing substrate described above are used to convert the pressure sensed by the pressure-sensing diaphragm into the axial extension and retraction displacement of the fiber optic sensing component.

[0011] The aforementioned FPI sensing fiber is composed of a microcavity structure formed by fusion splicing single-mode fiber and hollow fiber, with a cavity length ranging from 50μm to 500μm.

[0012] The wavelength of the aforementioned light source module is in the 1510nm-1590nm band. The laser light source of the light source module emits a laser beam and acquires spectral information from the pressure sensor through the data acquisition module.

[0013] The aforementioned dual FBG sensing fiber includes a pressure grating FBG1 with a center wavelength of 1535nm and a temperature grating FBG2 with a center wavelength of 1565nm. The pressure grating FBG1 is responsible for large-range pressure monitoring due to its wide measurement range. The temperature grating FBG2 is arranged in the stress isolation zone, and the detection signal of the temperature grating FBG2 is used to perform temperature compensation on the detection signals of the FPI sensing fiber and the pressure grating FBG1.

[0014] The data acquisition module described above uses a binary linear decoupling matrix to correct the pressure measurement results of the FPI sensing fiber and the pressure grating FBG1 in real time based on the wavelength drift of the temperature grating FBG2.

[0015] The aforementioned data acquisition module is equipped with temperature and pressure regional compensation logic: it uses the temperature grating FBG2 located in the stress isolation zone to extract the real-time change in ambient temperature, and based on the preset temperature drift characteristic curve, it performs wavelength compensation correction on the FPI sensing fiber and pressure grating FBG1 located in the strain zone of the beam, so as to eliminate the cross-interference of ambient temperature on high-sensitivity pressure detection and wide-range pressure detection.

[0016] The pressure sensor also includes a pressure input interface, which is connected to the pressure-receiving side of the pressure-sensing diaphragm and is used to introduce an external pressure signal to be measured.

[0017] The device suppresses temperature-pressure cross-sensitivity using a dual-FBG sensing fiber temperature compensation algorithm. The data acquisition module calculates the contribution of ambient temperature to the signals from the FPI sensing fiber and the pressure grating FBG1 based on the spectral shift caused by temperature acquired by the temperature grating FBG2. By establishing a pressure-temperature cross-sensitivity matrix in the algorithm, independent extraction and correction of the pressure signal are achieved.

[0018] A method for pressure detection using a coaxial pressure detection device includes the following steps:

[0019] (1) Signal excitation and coupling: The light source module is activated to input a laser beam into the fiber optic sensing component; the light source module emits a broadband laser into the fiber optic sensing component, and the laser beam interferes and reflects in the coaxially integrated FPI sensing fiber and the dual FBG sensing fiber.

[0020] (2) Deformation transmission: External pressure is input at the pressure input end to drive the pressure-sensitive diaphragm to deform. The cavity length of the FPI sensing fiber microcavity changes slightly through the T-shaped structure of the fiber-fixed substrate, and at the same time, the pressure grating FBG1 generates axial tensile strain.

[0021] (3) Spectral acquisition and demodulation: The data acquisition module acquires the superimposed spectrum containing the interference fringes of the FPI sensing fiber and the reflection peak of the dual FBG sensing fiber in real time, and locks the wavelength position of each characteristic peak.

[0022] (4) Temperature and pressure decoupling calculation: The ambient temperature change is calculated by using the wavelength drift of temperature grating FBG2, and the high-sensitivity pressure data of FPI sensing fiber and the wide-range pressure data of pressure grating FBG1 are decoupled and compensated accordingly.

[0023] (5) Synchronous output: The real-time pressure monitoring value after temperature correction is finally calculated.

[0024] The decoupling operation constructs a system of two linear equations using pre-calibrated pressure sensitivity coefficients and temperature sensitivity coefficients, and solves for the true pressure value after eliminating temperature drift.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This application overcomes the performance limitations of single-sensor principles. By encapsulating the fiber optic fixed substrate in a T-shaped structure and spatially coaxially integrating FPI sensing fiber interferometry and dual FBG sensing fiber optic technology, it not only achieves simultaneous detection of micro-level pressure (high sensitivity) and megapascal-level pressure (wide range), but also solves the problem of temperature and pressure cross-sensitivity in high-temperature environments such as oil and gas wells by constructing a temperature-sensing grating scheme. The device has a simple structure, good linearity, and strong mechanical stability, and possesses extremely high engineering application value.

[0027] 2. This application achieves mechanical gain in displacement through the unbalanced mechanical design of a T-shaped structure with an optical fiber fixed substrate. Compared to the traditional method of directly attaching gratings to diaphragms, this invention converts the central deflection of the diaphragm into the axial rigid displacement of the crossbeam through the vertical beam in the T-shaped structure with the optical fiber fixed substrate, thereby improving the equivalent sensitivity of pressure sensing by 3-5 times. Simultaneously, the coaxial arrangement ensures that the FPI sensing fiber and the dual FBG sensing fiber are in the same thermal field, reducing the real-time deviation of temperature-pressure decoupling to the millisecond level, effectively solving the transient error problem caused by temperature gradients in extreme environments. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the specification, serve to illustrate the technical solutions of this disclosure.

[0029] Figure 1 This is a schematic diagram of the overall system architecture of the pressure detection device according to an embodiment of the present disclosure;

[0030] Figure 2 This is a schematic diagram of the mechanical coupling structure between the T-shaped transmission beam and the coaxial sensing component in a pressure sensor according to an embodiment of the present disclosure;

[0031] Figure 3 The microcavity structure of the FPI sensing fiber and its fabrication process flow diagram are shown in the disclosed embodiments.

[0032] Figure 4 This is a simulation diagram of the flexural deformation of the pressure-sensitive diaphragm under external pressure load in an embodiment of this disclosure;

[0033] Figure 5 This is a schematic diagram of the FPI-FBG composite reflectance spectra under different FPI cavity length parameters in the embodiments of this disclosure;

[0034] Figure 6 This is a linear fitting diagram of wavelength shift of FPI optical fibers with different initial cavity lengths under pressure response according to embodiments of this disclosure;

[0035] Figure 7 This is a schematic diagram illustrating the spectral drift characteristics and compensation fitting of FPI and dual FBG optical fibers under temperature gradients in an embodiment of this disclosure.

[0036] Figure 8 This is a flowchart illustrating the precision CNC machining process of the T-beam structure according to an embodiment of this disclosure;

[0037] Figure 9 This is a schematic diagram of the T-shaped beam base structure prepared according to an embodiment of the present disclosure. Detailed Implementation

[0038] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0039] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0040] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this application can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0041] The pressure detection method provided in this disclosure can be executed by a terminal device, a server, or an application-specific integrated circuit (ASIC). In some possible implementations, the pressure detection method can be implemented by a processor calling computer-readable instructions stored in memory to control the light source module and the data acquisition module.

[0042] like Figure 1The diagram shown is a structural schematic of a pressure detection device according to an embodiment of this application. The device includes: a display module 100, a transmitter / receiver module 200 integrating a light source module and a data acquisition module, a pressure sensor 300, an optical fiber sensing component 400, a pressure input terminal 500, and a constant temperature chamber 600. The constant temperature chamber 600 integrates a high-precision heating element and a temperature-equalizing air duct, designed to provide a stable and controlled thermal field for the pressure sensor 300, enabling temperature detection of the pressure sensor 300 for subsequent temperature compensation.

[0043] The display module 100 is connected to the transmitter / receiver module 200 and is used to display the spectral characteristic waveforms during the pressure sensing process in real time. The pressure-wavelength fitting curve, temperature compensation data, and real-time spectrum generated by the pressure input terminal 500 can be transmitted to the display module 100 for visualization, thereby further analyzing the linearity and sensitivity of the sensor.

[0044] The transmit / receive module 200 integrates a light source module and a data acquisition module into a single design. The light source module is used to output laser signals. The light source module includes a laser source (such as a broadband light source) capable of emitting coherent light at a preset wavelength. The laser emitted by the light source module has a power range of 0.06-0.25mW and a preset center wavelength of 1510nm to 1590nm (C-band) to ensure low signal loss during fiber optic transmission and compatibility with the demodulation system.

[0045] The data acquisition module acquires and demodulates the reflection spectrum from the pressure sensor 300 in real time, using the shift of spectral characteristic peaks to invert pressure and temperature data. This module receives and detects wavelength change signals caused by pressure and temperature variations, and demodulates the wavelength shifts caused by these changes. It can simultaneously control the emission and demodulation of the light source, ensuring the synchronization and stability of the entire sensing process. The data acquisition module analyzes and records the spectral characteristic information sensed by the pressure sensor 300. This module includes a high-resolution spectrometer. The spectrometer is installed at the signal receiving end of the pressure sensing system and captures the interference spectrum of the FPI sensing fiber 402 and the reflection peaks of the dual FBG sensing fiber 401 by adjusting the wavelength scanning range and sampling frequency.

[0046] The data acquisition module is equipped with temperature and pressure regional compensation logic: the temperature grating FBG2 located in the stress isolation zone is used to extract the real-time change of ambient temperature, and based on the preset temperature drift characteristic curve, wavelength compensation correction is performed on the FPI sensing fiber 402 and pressure grating FBG1 located in the strain zone of the beam, so as to eliminate the cross-interference of ambient temperature on high-sensitivity pressure detection and wide-range pressure detection.

[0047] The pressure sensor 300 and the transmitter / receiver module 200 are connected via an optical fiber link to sense external pressure and provide spectral signals. The pressure sensor 300 integrates a coupled optical fiber sensing component 400, which includes a pressure-sensing diaphragm 204, an optical fiber fixing substrate 201, an FPI sensing substrate 205, and a dual FBG sensing substrate 203. The pressure-sensing diaphragm 204 is rigidly connected to the optical fiber fixing substrate 201. The optical fiber fixing substrate 201 is a T-shaped structure with vertical and horizontal beams, and the FPI sensing substrate 205 and the dual FBG sensing substrate 203 are coaxially arranged. The FPI sensing substrate 205 and the dual FBG sensing substrate 203 are provided with optical fiber fixing slots 202, in which dual FBG sensing optical fibers 401 and FPI sensing optical fibers 402 are respectively installed. The crossbeam of the fiber optic fixing substrate 201 has fixed ends at both ends, and the middle part of the crossbeam is connected to the pressure-sensitive diaphragm 204 via a vertical beam. The dual FBG sensing fiber 401 and FPI sensing fiber 402 are fabricated from optical fibers with microcavities and gratings. One end of the dual FBG sensing fiber 401 and FPI sensing fiber 402 is connected to the data acquisition module to receive and transmit the laser light source. The other end of the dual FBG sensing fiber 401 and FPI sensing fiber 402 is finely stripped and coated, and then nested or bonded to the fiber optic fixing substrate 201. The fiber optic fixing substrate 201 receives the normal displacement transmitted by the pressure-sensitive diaphragm 204 and converts it into axial strain on the surface of the crossbeam of the fiber optic fixing substrate 201, forming a strain sensing region. The diameter or thickness of the crossbeam of the fiber optic fixing substrate 201 remains consistent, and the stress center of the crossbeam is symmetrically distributed relative to the two fixed ends. The pressure sensor 300 has a mechanical coupling structure that enables efficient strain transmission, and the connection between the pressure-sensing diaphragm 204 and the optical fiber fixing substrate 201 is formed by laser spot welding to create a stable stress transmission interface.

[0048] In the following text, FPI sensing fiber is abbreviated as FPI, dual FBG sensing fiber is abbreviated as FBG, pressure grating FBG1 is abbreviated as FBG1, and temperature grating FBG2 is abbreviated as FBG2. The fabrication method of the fiber optic sensing component includes:

[0049] The FPI sensing fiber 402 is a microcavity structure formed by fusing single-mode fiber (SMF) - hollow-core fiber (HOF) - single-mode fiber (SMF) using arc discharge fusion splicing technology. Figure 3The diagram illustrates the fabrication process of fiber micromachining and the microcavity FP sensor structure. Single-mode fiber (SMF) and hollow-core fiber (HOF) are fixed by a clamp and fused together via electrode discharge. Subsequently, based on the required length of the HOF, a precision displacement stage is used to control the length of the HOF, and an excess portion is removed using a fiber optic cleaver. The single-mode fiber segment is then fused to the HOF to construct an SMF-HOF-SMF connection structure. The sandwich cavity formed by the single-mode fiber and the HOF is a microcavity with a length ranging from 50 μm to 500 μm (preferably 60 μm). The microcavity of the FPPI sensing fiber 402 is suspended between the crossbeam and the fiber fixing groove 202, utilizing the Fabry-Perot interference principle to capture minute pressure and strain. Dual FBG sensing fiber 401 writing and cascading: Using an excimer laser and a phase mask method, a pressure grating (FBG1) with a center wavelength of 1535nm and a temperature grating (FBG2) with a center wavelength of 1565nm are sequentially written on the same fiber, with the spacing between the two gratings set to 2mm.

[0050] The fiber optic fixing base 201 includes a vertical beam extending from the center of the pressure-sensitive diaphragm 204 and a horizontal beam connected to the vertical beam. The upper ends of the dual FBG sensing fiber 401 and the FPI sensing fiber 402 are respectively fixed to the two fixed ends of the horizontal beam of the fiber optic fixing base 201, and their lower ends are respectively fixed to the fixing base of the pressure sensor, so that the displacement of the horizontal beam directly drives the fiber optic sensing assembly 400 to produce axial expansion and contraction. The T-shaped fiber optic fixing base 201 converts the normal deformation of the pressure-sensitive diaphragm 204 into the axial strain of the fiber. When external pressure is applied to the pressure-sensitive diaphragm 204, the center of the pressure-sensitive diaphragm 204 produces maximum flexural deformation, which drives the vertical beam of the fiber optic fixing base 201 to produce axial displacement, thereby driving the dual FBG sensing fiber 401 and the FPI sensing fiber 402 to produce axial expansion and contraction. Through this mechanical transmission mechanism, the stress state of the dual FBG sensing fiber 401 and the FPI sensing fiber 402 exhibits a good linear relationship with the pressure change.

[0051] Figure 2 This diagram illustrates the mechanical coupling structure between the T-beam structure of the fiber optic fixed substrate 201 and the coaxial sensing dual FBG sensing substrate 203 and FPI sensing substrate 205. The pressure sensor 300, based on the external mechanical pressure applied to the pressure-sensing diaphragm 204, utilizes the displacement transmission mechanism of the fiber optic fixed substrate 201. The coaxially arranged FPI sensing substrate 205, dual FBG sensing substrate 203, and T-beam work together to convert the pressure sensed by the pressure-sensing diaphragm 204 into axial displacement of the fiber optic sensing assembly 400. This causes synchronous changes in the center wavelength of the internal dual FBG sensing fiber 401 and the microcavity length of the FPI sensing fiber 402, thereby achieving multi-parameter coordinated monitoring of pressure and temperature.

[0052] The types of the dual FBG sensing fiber 401 and FPI sensing fiber 402 include, but are not limited to, single-mode fiber. The material of the fiber fixing substrate 201 includes, but is not limited to, Invar alloy with an extremely low coefficient of thermal expansion. The use of Invar alloy material, due to its extremely low coefficient of thermal expansion, effectively reduces thermal strain interference on the sensor structure caused by environmental temperature fluctuations.

[0053] The pressure sensor 300 is connected to the pressure input terminal 500 via a sealed interface. The pressure input terminal 500 provides an adjustable calibration or test pressure for the pressure sensor 300. The pressure sensor 300 also includes a pressure input interface, which communicates with the pressure-receiving side of the pressure-sensing diaphragm 204 to introduce an external pressure signal to be measured. The pressure-sensing diaphragm 204 is located within the pressure field provided by the pressure input terminal 500. A pressure transmission medium (such as aviation hydraulic oil or silicone oil) fills the hydraulic lines to transmit the precise pressure generated by the pressure input terminal 500 to the pressure-sensing diaphragm 204 of the fiber optic sensing component 400. Furthermore, a high-pressure protective sleeve is provided at the connection between the pressure sensor 300 and the pressure input terminal 500 pipeline to prevent media leakage during overpressure testing.

[0054] The dual-FBG sensing fiber 401 on the dual-FBG sensing substrate 203 includes a pressure grating FBG1 and a temperature grating FBG2. The temperature grating FBG2 is arranged in the stress isolation region, and the detection signal of the temperature grating FBG2 performs temperature compensation on the detection signals of the FPI sensing fiber 402 and the pressure grating FBG1. The pressure grating FBG1, with its wide measurement range, is responsible for large-scale pressure monitoring. The data acquisition module uses a binary linear decoupling matrix to correct the pressure measurement results of the FPI sensing fiber 402 and the pressure grating FBG1 in real time based on the wavelength drift of the temperature grating FBG2.

[0055] The microcavity length of the FPI sensing fiber 402 is in the range of 50-500μm (preferably 60μm), the grating wavelength range of the dual FBG sensing fiber 401 is 1510nm-1590nm, the grating region length of the pressure grating FBG1 and the temperature grating FBG2 is in the range of 2-5mm (preferably 3mm), the spacing between the pressure grating FBG1 and the temperature grating FBG2 is in the range of 1-5mm (preferably 2mm), and the span of the fiber fixing substrate 201 is in the range of 10-30mm.

[0056] Furthermore, the pressure sensor 300 is configured to convert the external pressure applied to the measured medium into a spectral signal displacement based on the mechanical strain transmission force formed by the T-shaped structure and the interference / diffraction phase shift formed by the laser source. Specifically, the coupling interface formed by the fiber optic fixing substrate 201 and the fiber optic sensing component 400 amplifies the micron-level displacement generated by the pressure-sensitive diaphragm 204 and applies it to the dual FBG sensing fiber 401 and the FPI sensing fiber 402, generating axial strain forces inside the dual FBG sensing fiber 401 and the FPI sensing fiber 402, with a highly linear relationship between their magnitude and the external pressure. This strain force can act on the center wavelength of the dual FBG sensing fiber 401 and the microcavity of the FPI sensing fiber 402, especially the microcavity of the FPI sensing fiber located at the position of maximum strain at the center of the beam, causing a significant wavelength shift or fringe movement, thereby converting the physical pressure signal into demodulated optical data.

[0057] Based on this, decoupling analysis of the interference fringes of the FPI sensing fiber and the reflection peak of the dual FBG sensing fiber 401 is achieved through real-time acquisition of the reflection spectrum. Specifically, since the FPI sensing fiber 402 microcavity and the dual FBG sensing fiber 401 are fixed to the coaxial pressure sensor and integrated on the same fiber via coupler 410, the coupler 410 is used to multiplex the FPI sensing fiber microcavity and the dual FBG sensing fiber, which are coaxially fixed to the end of the pressure sensor, integrating them into a single fiber. This enables synchronous transmission of multi-sensor signals and integrated demodulation of the data acquisition module. The data acquisition module acquires a composite spectrum containing the interference spectrum of the FPI sensing fiber and the discrete wavelength reflection peaks of the dual FBG sensing fiber. Figure 5 This is a schematic diagram of the FPI-FBG composite reflection spectrum under different FPI sensing fiber cavity length parameters.

[0058] Furthermore, in order to address the issue of temperature and pressure cross-sensitivity in complex environments, a temperature self-compensation mechanism was established through a differentiated layout of dual FBG sensing fibers.

[0059] In this embodiment, the temperature grating FBG2 only exhibits wavelength drift response to changes in ambient temperature; while the pressure grating FBG1, located in the strain region at the center of the beam, and the FPI sensing fiber microcavity are simultaneously affected by both the mechanical strain of the beam and the ambient temperature. Based on this physical constraint, this embodiment establishes a temperature-pressure sensitivity matrix and uses the real-time temperature reference value provided by the temperature grating FBG2 to perform nonlinear compensation on the measurement results of the FPI sensing fiber and the pressure grating FBG1, thereby extracting the pure pressure-induced spectral shift.

[0060] The following section will elaborate on the detailed process of pressure detection and temperature-pressure decoupling in the embodiment, using specific mechanical models and optical sensing equations.

[0061] The first-stage pressure-sensing element of this device is a pressure-sensing diaphragm 204. When a static pressure P is applied to the pressure input terminal 500 in the pressurized environment, the original force balance state on the surface of the pressure-sensing diaphragm 204 is broken, and an inward normal bending deformation is generated under the action of pressure difference. Figure 4 This is a simulation diagram of the flexural deformation of the pressure-sensitive diaphragm 204 under external pressure load. Based on the theory of large deflection of a circular thin plate in elasticity, the normal displacement at the center point of the pressure-sensitive diaphragm 204 is... It is the key physical quantity that determines the initial sensitivity of the entire pressure sensor. Since one end of the vertical beam is rigidly connected to the center point of the pressure-sensing diaphragm 204, and the other end is supported at the force center of the horizontal beam, the normal displacement of the pressure-sensing diaphragm 204 drives the horizontal beam to undergo synchronous displacement changes through the vertical beam.

[0062] According to the circular thin-plate theory in elasticity, the normal displacement at the center point of the pressure-sensitive diaphragm 204 is... The pressure P satisfies the following relationship:

[0063]

[0064] In the formula: μ is the Poisson's ratio of the material; The radius of the diaphragm; The elastic modulus of the diaphragm material; This refers to the thickness of the diaphragm. Since the fiber optic sensing assembly 400 (including the FPI sensing fiber microcavity and the dual FBG sensing fiber) is fixed at both ends between the moving crossbeam and the fixed base, the overall displacement of the crossbeam... It is directly converted into the elongation or shortening of the fiber optic axis. At this point, the effective axial strain generated inside the optical fiber... Defined as:

[0065]

[0066] Where L is the initial effective length of the optical fiber between fixed points. This process achieves rigid transmission from external pressure → diaphragm displacement → structural displacement → axial expansion and contraction of the optical fiber. The pressure-strain transfer coefficient is defined as... Then the axial strain of the optical fiber It has the following linear relationship with the external pressure P:

[0067]

[0068] Center reflection wavelength of fiber optic grating Depends on effective refractive index and grating period :

[0069]

[0070] When the ambient temperature and axial strain When (caused by pressure) the wavelength shift occurs, It can be represented as:

[0071]

[0072] Among them, P e For the effective elastic coefficient, The coefficient of thermal expansion of optical fiber. The thermo-optic coefficient is denoted as .

[0073] For pressure grating FBG1: its wavelength shift Driven by both pressure, strain, and temperature.

[0074] For the temperature grating FBG2: due to its stress isolation zone fixed to the base, its offset Affected only by temperature:

[0075]

[0076] Among them, K T2 The temperature coefficient is related not only to temperature changes, but also to the manufacturing process and material composition of the optical fiber.

[0077] This device employs a microcavity interference structure formed by single-mode fiber, hollow-core fiber, and single-mode fiber. The characteristic wavelength at the trough of the interference spectrum... satisfy:

[0078]

[0079] Where n is the refractive index of the medium inside the cavity, and L is the cavity length. When pressure causes a change in the cavity length... At this time, the characteristic wavelength will shift significantly. k represents the interference order, k = 0, 1, 2, 3, 4... The free spectral range (FSR) of the interference fringes is defined as:

[0080]

[0081] Here, λ represents the wavelength of the incident light. As the cavity length L increases, the FSR gradually decreases. In this embodiment, a cavity length of 60 μm is preferred to obtain the highest pressure sensitivity.

[0082] To eliminate the cross-interference of temperature on pressure measurements, this paper establishes the following sensitivity matrix:

[0083]

[0084] Among them, K P and KT These are the pre-calibrated pressure and temperature sensitivity coefficients, respectively. The coefficients are derived beforehand using FBG2. Substituting into the above formula, we can achieve pressure... Precise decoupling. This represents the offset of the FPI sensor wavelength. This represents the offset of the FBG1 wavelength.

[0085] Real-time temperature measured by introducing FBG2 This allows for precise compensation of pressure signals.

[0086]

[0087] The pressure-sensitive diaphragm 204 was set with a radius r = 10 mm and a thickness h = 0.6 mm, and the span of the T-beam was 20 mm. After calibration testing, based on the aforementioned principle of displacement transmission and strain amplification of the T-beam, the average pressure sensitivity of the FPI sensing fiber reached 955.81 pm / MPa, approximately 5 times higher than that of the FBG sensor, and its linearity R within the 0-30 MPa range was also excellent. 2 Better than 0.999. Figure 6 The image shows a linear fitting plot of the wavelength shift of FPI units with different initial microcavity lengths under pressure response. Further experimental results show that as the ambient temperature increases from 30℃ to 90℃, the spectral characteristics of each sensing unit exhibit a linear redshift with increasing temperature. Figure 7 As shown, the temperature sensitivity coefficients of each unit were obtained through linear fitting: the temperature sensitivity of the FPI sensing fiber located in the strain region is approximately 3.69 pm / °C (R0). 2 =0.957), the temperature sensitivity of the pressure grating FBG1 is approximately 13.13 pm / °C (R 2 =0.966); while the temperature grating FBG2 located in the stress isolation zone exhibits the highest linearity and temperature sensing capability, with a sensitivity of 19.68 pm / °C (R 2 =0.992).

[0088] The light source module and data acquisition module in this embodiment are also equipped with a range adaptive switching mechanism, which is used to automatically switch and fuse data between high-resolution monitoring mode and wide-range monitoring mode according to the current pressure detection requirements. Specifically, the data acquisition module presets a pressure threshold P. th When the real-time monitored pressure value is lower than the pressure threshold P th When the system automatically enters high-sensitivity mode, it uses the phase change feedback from the FPI sensing fiber as the main output signal, utilizing its high sensitivity to capture minute pressure fluctuations; when the real-time pressure value reaches or exceeds the pressure threshold P... thWhen switching modes, the system automatically and seamlessly switches to a wide-range mode, using the center wavelength drift of the FPI sensing fiber as the primary output signal. Its excellent linear strain range ensures that the signal does not distort or aliasing under high pressure. Furthermore, in the critical region of mode switching, the data acquisition module uses a weighted averaging algorithm to fuse the signals from the FPI sensing fiber and the pressure grating FBG1, eliminating transient jumps during switching and ensuring the continuity and smoothness of the pressure monitoring sequence.

[0089] Specifically, by extracting spectral features from the fiber optic sensing component, at least two detection modes that can coexist in the demodulation algorithm can be formed. This involves adjusting the demodulation frequency, wavelength scan step size, and cutoff frequency of the spectral filtering algorithm, and setting corresponding sampling values ​​to determine the signal mode input to the processor.

[0090] High-sensitivity mode (based on FPI): mainly used for monitoring small pressure fluctuations (such as 0-2MPa), utilizing the high sensitivity of FPI to changes in microcavity length, and obtaining high-precision pressure data through a phase tracking algorithm.

[0091] Wide range mode (based on FBG1): mainly used in high pressure and dynamic pressure environments (such as 2-30MPa), utilizing the linear shift characteristics of the FBG reflection peak under strain to ensure that the signal is not distorted under high pressure.

[0092] In this embodiment, the mechanical strain experienced by the fiber optic sensing component causes an overall shift in the spectral envelope. Based on the decoupling principle described in the above embodiment, when at least two characteristic peak signals are generated, the algorithm can be applied to the FPI phase and the FBG center wavelength respectively, thereby forming a plurality of data feedback points. By arranging the physical parameters corresponding to each characteristic signal, a corresponding pressure monitoring sequence can be formed.

[0093] In addition, the embodiments also provide methods for fabricating fiber optic sensing components and fiber optic fixing substrates. Figure 8 This is a schematic diagram of the precision CNC machining and aging process for preparing an optical fiber fixing substrate with a T-shaped crossbeam structure in this embodiment.

[0094] Considering the potential for instantaneous pulse pressure downhole in oil and gas wells, this embodiment includes a mechanical displacement limiting block below the crossbeam of the fiber optic fixing substrate. When the external pressure exceeds a preset safety range limit (e.g., 35 MPa), the crossbeam displacement contacts the limiting block, thereby preventing further stretching of the fiber optic cable. This avoids the risk of breakage of the fiber optic sensing component due to excessive deformation and significantly improves the sensor's lifespan under extreme fluctuation conditions.

[0095] in addition, Figure 9This diagram illustrates the fabrication of an optical fiber fixing substrate with a T-shaped crossbeam structure, as shown in this embodiment. The fabrication method includes:

[0096] High-precision CNC machine tools are used to cut and process the Invar alloy preform to form a crossbeam with uniform thickness and a vertical beam perpendicular to the center of the crossbeam. The surface is then polished to ensure the flatness of the fiber optic attachment.

[0097] Precision packaging: A high-precision three-dimensional robotic arm is used to coaxially align the fiber optic sensing component with the T-shaped crossbeam of the fiber optic fixing substrate, and fiber optic positioning adhesive is used to fix the fiber optic cable to the strain-sensitive area of ​​the crossbeam.

[0098] To better understand the principle and process of the pressure detection device for multi-functional monitoring of temperature and pressure provided in the embodiments of this application, the following exemplary description is provided:

[0099] This embodiment can control the light source module to emit a laser beam with a wavelength covering 1510nm-1590nm. In the downhole environment of oil and gas wells, the external medium pressure acts on the pressure-sensitive diaphragm, driving the vertical beam of the fiber optic fixing substrate to generate a normal displacement, which in turn stretches the fiber optic sensing component on the horizontal beam of the fiber optic fixing substrate. The FPI sensing fiber microcavity and pressure grating FBG1, which move to the strain zone of the horizontal beam, are subjected to mechanical stress, resulting in spectral shift. At the same time, the temperature grating FBG2 senses the ambient temperature. The data acquisition module extracts temperature field information by monitoring the wavelength drift of the temperature grating FBG2 in real time, and performs real-time compensation on the pressure data of the FPI sensing fiber microcavity and pressure grating FBG1 according to a preset sensitivity matrix, achieving high-precision pressure detection.

[0100] When the downhole temperature fluctuates drastically (e.g., from 30℃ to 90℃), the system activates a thermal compensation algorithm. Due to the absorption characteristics of water or crude oil at specific wavelengths and ambient thermal convection, a small temperature gradient forms inside the sensor. At this time, by adjusting the sampling weights of the demodulation module, the thermal drift component of the pressure is canceled out by the feedback signal from the temperature grating FBG2.

[0101] In addition, by adjusting the output power and signal gain, monitoring thresholds can be set for high-sensitivity and wide-range measurement areas. When the collected pressure resultant value is in the low-pressure range, the system automatically locks the FPI sensor fiber optic signal output; when the value exceeds the threshold and enters the high-pressure range, the system seamlessly switches to the pressure grating FBG1 signal to achieve accurate monitoring and sorting within specific pressure ranges.

[0102] In summary, the pressure detection device and method provided in this application, through a self-developed T-shaped crossbeam fiber optic fixed substrate, successfully transforms the diaphragm deflection induced by external fluid pressure into the axial rigid displacement of the fiber optic sensing component, ensuring the linearity and stability of pressure transmission from a physical mechanism perspective. This application, through the coaxial integration of FPI interferometry and cascaded dual FBG technology, not only utilizes the high sensitivity of FPI to accurately capture minute pressure fluctuations but also leverages the wide range characteristics of FBG to ensure detection capabilities under high pressure conditions. More importantly, by introducing a temperature reference grating in a stress isolation zone and combining it with a binary decoupling matrix algorithm, the interference of temperature and pressure cross-sensitivity on measurement accuracy in complex environments such as oil and gas wells is eliminated. The Invar alloy material selection, precision welding process, and three-dimensional displacement platform packaging scheme adopted in this application jointly construct a sensing system with high robustness, autonomous temperature compensation, and high dynamic response. This system not only improves the engineering applicability of fiber optic pressure sensors in extreme environments such as oil extraction and deep-sea exploration but also lays a solid technical foundation for the subsequent realization of large-scale, high-density downhole real-time monitoring networks.

[0103] In some embodiments, the functions or modules of the apparatus provided in this disclosure can be used to perform the methods described in the above method embodiments. The specific implementation can be referred to the description of the above method embodiments, and for the sake of brevity, it will not be repeated here.

Claims

1. A coaxial pressure detection device, comprising: The system includes a display module (100), a transmitter / receiver module (200), a pressure sensor (300), an optical fiber sensing assembly (400), a pressure input terminal (500), and a constant temperature chamber (600). The display module (100) is connected to the transmitting and receiving module (200) and is used to display the spectral characteristic waveforms in the pressure sensing process in real time; The transmitting and receiving module (200) is connected to the pressure sensor (300). The transmitting and receiving module (200) integrates a light source module and a data acquisition module. The light source module is used to output laser signals. The data acquisition module and the light source module are integrated into one unit design to acquire and demodulate the reflection spectrum from the pressure sensor (300) in real time, and to retrieve pressure and temperature data by using the offset of the spectral characteristic peaks; The pressure sensor (300) integrates an optical fiber sensing component (400), which includes a pressure-sensitive diaphragm (204), an optical fiber fixing substrate (201), an FPI sensing substrate (205), and a dual FBG sensing substrate (203). The FPI sensing substrate (205) and the dual FBG sensing substrate (203) are respectively provided with optical fiber fixing slots (202), and the dual FBG sensing optical fiber (401) and the FPI sensing optical fiber (402) are respectively installed in the optical fiber fixing slots (202). The pressure input terminal (500) provides an adjustable calibration or test pressure for the pressure sensor (300). The optical fiber fixing base (201) has a T-shaped structure, which includes a crossbeam and a vertical beam connected perpendicularly to the crossbeam. The upper center surface of the pressure-sensitive diaphragm (204) is rigidly connected to the bottom surface of the vertical beam of the T-shaped structure of the optical fiber fixing base (201). The upper ends of the dual FBG sensing optical fiber (401) and the FPI sensing optical fiber (402) are respectively fixed to the crossbeam, and their lower ends are respectively fixed to the fixing base of the pressure sensor.

2. The pressure detection device according to claim 1, characterized in that, The coaxially arranged FPI sensing substrate (205) and dual FBG sensing substrate (203) are used to convert the pressure sensed by the pressure-sensing diaphragm (204) into the axial extension and retraction displacement of the fiber optic sensing assembly (400).

3. The pressure detection device according to claim 1, characterized in that, The FPI sensing fiber (402) is composed of a microcavity structure formed by fusion splicing single-mode fiber and hollow fiber, with a cavity length ranging from 50μm to 500μm.

4. The pressure detection device according to claim 1, characterized in that, The wavelength of the light source module is in the 1510nm-1590nm band. The laser light source of the light source module emits a laser beam and acquires spectral information from the pressure sensor (300) through the data acquisition module.

5. The pressure detection device according to claim 1, characterized in that, The dual FBG sensing fiber (401) includes a pressure grating FBG1 with a center wavelength of 1535nm and a temperature grating FBG2 with a center wavelength of 1565nm; the pressure grating FBG1 is responsible for large-range pressure monitoring using its wide range characteristics; the temperature grating FBG2 is arranged in the stress isolation area, and the detection signal of the temperature grating FBG2 is used to perform temperature compensation on the detection signal of the FPI sensing fiber (402) and the pressure grating FBG1.

6. The pressure detection device according to claim 5, characterized in that, The data acquisition module uses a binary linear decoupling matrix to correct the pressure measurement results of the FPI sensing fiber (402) and the pressure grating FBG1 in real time based on the wavelength drift of the temperature grating FBG2.

7. The pressure detection device according to claim 5, characterized in that, The data acquisition module is configured with temperature and pressure regional compensation logic: the temperature grating FBG2 located in the stress isolation zone is used to extract the real-time change of ambient temperature, and based on the preset temperature drift characteristic curve, wavelength compensation correction is performed on the FPI sensing fiber (402) and pressure grating FBG1 located in the strain zone of the beam, so as to eliminate the cross-interference of ambient temperature on high-sensitivity pressure detection and wide-range pressure detection.

8. The pressure detection device according to claim 1, characterized in that, The pressure sensor (300) also includes a pressure input interface, which is connected to the pressure-receiving side of the pressure-sensing diaphragm (204) and is used to introduce an external pressure signal to be measured.

9. A pressure detection method using the device according to any one of claims 1 to 8, comprising the following steps: (1) Signal excitation and coupling: Start the light source module to input the laser beam into the fiber optic sensing component (400); The light source module emits broadband laser light into the fiber optic sensing component (400). The laser beam is reflected and interfered with the coaxially integrated dual FBG sensing fiber (401) and FPI sensing fiber (402). (2) Deformation transmission: The pressure input end (500) inputs external pressure to drive the pressure-sensitive diaphragm (204) to deform. Through the T-shaped structure of the fiber fixed substrate (201), the cavity length of the microcavity of the FPI sensing fiber (402) changes slightly, and at the same time, the pressure grating FBG1 generates axial tensile strain. (3) Spectral acquisition and demodulation: The data acquisition module acquires the superimposed spectrum containing the interference fringes of the FPI sensing fiber (402) and the reflection peak of the dual FBG sensing fiber (401) in real time, and locks the wavelength position of each characteristic peak. (4) Temperature and pressure decoupling calculation: The ambient temperature change is calculated by using the wavelength drift of temperature grating FBG2, and the high-sensitivity pressure data of FPI sensing fiber (402) and the wide-range pressure data of pressure grating FBG1 are decoupled and compensated accordingly. (5) Synchronous output: The real-time pressure monitoring value after temperature correction is finally calculated.

10. The method according to claim 9, characterized in that, The decoupling operation constructs a system of two linear equations using pre-calibrated pressure sensitivity coefficients and temperature sensitivity coefficients, and solves for the true pressure value after eliminating temperature drift.

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