Differential fiber-optic pressure sensor based on spring mass and method for sensing pressure

Abstract

The application relates to a spring mass differential type optical fiber pressure sensor and a pressure sensing method, and belongs to the technical field of optical fiber sensing. The spring mass differential type optical fiber pressure sensor comprises an external packaging steel pipe, a waterproof hydraulic film, a No.1 sealing head, an internal sensor steel pipe, a No.1 optical fiber grating, a sensitized spring mass film, a No.2 optical fiber grating, an optical fiber fixing frame and a No.2 sealing head. The method is as follows: a light beam emitted by a broadband light source enters a No.1 port of an optical fiber circulator through an optical isolator, the light beam is output from a No.2 port of the optical fiber circulator and enters the spring mass differential type optical fiber pressure sensor, pressure sensing is carried out, pressure information is output to a spectrum analyzer, and the spectrum analyzer analyzes the pressure information to realize pressure detection.

Description

Technical Field

[0001] This invention relates to a pressure sensor structure and a sensing method based on the pressure sensor, belonging to the field of fiber optic sensing technology. Background Technology

[0002] In fields such as water conservancy engineering, aerospace and military industries, oil and gas transportation, biomedicine, and marine hydrological information monitoring, the detection of pressure indicators is particularly important. Conventional pressure sensors represent changes in pressure signals as changes in material frequency, which are then output as electrical signals for detection. Traditional pressure sensors are limited by harsh environments and cannot operate for extended periods in extreme conditions. In contrast, fiber optic pressure sensors offer advantages over traditional pressure sensors, including high-temperature resistance, small size, resistance to electromagnetic interference, and fast response speed, meeting the specific needs of various application scenarios. Fiber optic pressure sensors obtain information about changes in the external environment by detecting changes in the intensity, phase, or frequency of light transmitted within the fiber optic cable as a result of changes in the surrounding environment.

[0003] However, current fiber optic pressure sensors rely on their own material being under pressure or on a pressure membrane structure, resulting in low sensitivity, and they can generally only detect air pressure. Summary of the Invention

[0004] To address the problems of low sensitivity, complex manufacturing process, and limited application scenarios of existing fiber optic pressure sensors, this invention provides a differential fiber optic pressure sensor based on a spring-mass block and a pressure sensing method.

[0005] The differential fiber optic pressure sensor based on a spring mass block according to the present invention comprises an external encapsulation steel tube 4-1, a waterproof hydraulic membrane 4-2, a No. 1 sealing head 4-3, an internal sensor steel tube 4-4, a No. 1 fiber optic grating 4-6, a sensitivity-enhancing spring mass block membrane 4-7, a No. 2 fiber optic grating 4-8, a fiber optic fixing frame 4-9, and a No. 2 sealing head 4-10.

[0006] The outer encapsulation steel tube 4-1 and the inner sensor steel tube 4-4 are nested inside each other. The outer encapsulation steel tube 4-1 is open at both ends, and the inner sensor steel tube 4-4 is open at the rear end. The rear end of the outer encapsulation steel tube 4-1 is sealed by sealing head 1 4-3, and the rear end of the inner sensor steel tube 4-4 is sealed by sealing head 2 4-10. The side walls and rear ends of the outer encapsulation steel tube 4-1 and the inner sensor steel tube 4-4 are concentrically fixed together by adhesive material 4-11.

[0007] The front end of the external encapsulation steel pipe 4-1 is sealed by a waterproof hydraulic membrane 4-2. There is a working gap between the front end of the external encapsulation steel pipe 4-1 and the front end of the internal sensor steel pipe 4-4. A side air hole 4-5 is provided on the side wall of the internal sensor steel pipe 4-4 near the front end.

[0008] The inner cavity of the internal sensor steel tube 4-4 is divided into three sections along the axial direction from the front end to the rear end by the sensitizing spring mass block diaphragm 4-7 and the optical fiber fixing frame 4-9. These sections are the positive tension sensing cavity, the negative tension sensing cavity, and the data transmission cavity. The positive tension sensing cavity is connected to the inner cavity of the external encapsulation steel tube 4-1 through the side air hole 4-5, while the negative tension sensing cavity is a sealed cavity.

[0009] A fiber optic grating is installed inside the internal sensor steel tube 4-4 to receive and output pressure information. The fiber optic grating is divided into three sections according to its location in the cavity: fiber optic grating 1 (4-6), fiber optic grating 2 (4-8), and single-mode fiber (4-12). The first end of the fiber optic grating is connected to the inner wall of the first end of the internal sensor steel tube 4-4. The fiber optic grating passes through the sensitizing spring mass block membrane 4-7 and is fixed after being prestressed. The fiber optic grating continues to pass through the fiber optic fixing frame 4-9 and is fixed after being prestressed. Finally, the sensed pressure information is transmitted out through the single-mode fiber optic 4-12.

[0010] Preferably, the sensitive spring mass block membrane 4-7 includes a mass block 4-7-1, a pull-out elastic spring unit, and a diaphragm 4-7-3. The pull-out elastic spring unit is formed by at least three layers of sheet-like rings 4-7-2 concentrically nested together. Adjacent layers of sheet-like rings 4-7-2 are radially connected by a pair of radially symmetrical connecting pieces 4-7-4. The innermost sheet-like ring 4-7-2 is connected to the mass block 4-7-1 by a pair of radially symmetrical connecting pieces 4-7-4. Adjacent pairs of connecting pieces are staggered by 90 degrees.

[0011] The outermost sheet-like circular ring 4-7-2 is fixedly connected to and sealed to the inner wall of the internal sensor steel tube 4-4;

[0012] The center hole 4-7-5 of the mass block 4-7-1 is used for the fiber optic grating to pass through and be sealed and fixed.

[0013] Preferably, the fiber optic mounting bracket 4-9 is fixedly connected to and sealed to the inner wall of the internal sensor steel tube 4-4.

[0014] Preferably, fiber Bragg grating 4-6 (No. 1), fiber Bragg grating 4-8 (No. 2), and single-mode fiber 4-12 are on the same horizontal line.

[0015] Preferably, sealing head 1 (4-3) and sealing head 2 (4-10) are potted with sound-permeable polyurethane rubber and left to stand at room temperature and pressure for 48 hours to allow the polyurethane to fully vulcanize.

[0016] The present invention also provides another technical solution, a pressure sensing method, which is based on the differential fiber optic pressure sensor based on a spring mass block. The light beam emitted by the broadband light source 1 enters port 1 of the fiber optic circulator 3 through the optical isolator 2. The light beam is output from port 2 of the fiber optic circulator 3 and enters the differential fiber optic pressure sensor 4 based on a spring mass block. The differential fiber optic pressure sensor 4 based on a spring mass block performs pressure sensing and carries the sensed pressure information back to port 2 of the fiber optic circulator 3 via the return light beam. Then, it is output from port 3 of the fiber optic circulator 3 to the spectrometer 5. The spectrometer 5 analyzes the pressure information to realize pressure detection.

[0017] Preferably, the pressure sensing process of the differential fiber optic pressure sensor 4 based on a spring-mass block is as follows:

[0018] External liquid hydraulic pressure is applied to the waterproof hydraulic membrane 4-2, and the gas inside the outer encapsulated steel pipe 4-1 is squeezed into the positive tension sensing cavity through the side air hole 4-5;

[0019] When the sensitizing spring mass block membrane 4-7 deforms, the No. 1 fiber grating 4-6 and the No. 2 fiber grating 4-8, which are fixed to the sensitizing spring mass block membrane 4-7, are subjected to tension. The No. 1 fiber grating 4-6 is subjected to positive tension and generates a wavelength offset Δλ1, while the No. 2 fiber grating 4-8 is subjected to negative tension and generates a wavelength offset Δλ2.

[0020] The two wavelength offsets are sent to the spectral analyzer 5 as the sensed pressure information.

[0021] Preferably, the process by which the spectrometer 5 analyzes the pressure information to achieve pressure detection is as follows:

[0022] The strain change Δε after the fiber grating is stretched is obtained by the following formula:

[0023]

[0024] In the formula, λ1 is the center wavelength of fiber grating 4-6 of type 1.

[0025] λ2 is the center wavelength of fiber grating 4-8, No. 2.

[0026] Δε represents the strain change of the fiber Bragg grating after it is stretched.

[0027] K ε For the strain-tensile sensitivity of fiber Bragg gratings,

[0028] The strain change Δε of the fiber grating after it is stretched is used to characterize the pressure detection result.

[0029] The beneficial effects of this invention are as follows: This invention overcomes the problem that traditional pressure sensors cannot be used in harsh environments. By using a spring-mass model, the pressure displacement of the pressure-sensing diaphragm is increased. Utilizing the differential fiber optic grating measurement principle, the relationship between different pressure conditions of the diaphragm is fitted based on the wavelength changes of the two gratings, thereby improving the sensitivity of the fiber optic pressure sensor and eliminating the temperature crosstalk problem. The differential fiber optic pressure sensing method based on the spring-mass model is not only lightweight, easy to fabricate, and inexpensive, but also stable in performance and highly sensitive. It utilizes a dual enhancement approach to improve pressure measurement sensitivity, meeting the pressure measurement needs in different environments and enabling high-precision pressure index measurement. It has significant implications and broad application prospects in biomedicine, marine information monitoring, and environmental data acquisition.

[0030] The pressure sensor of this invention is low in cost, compact in structure, easy to manufacture, and resistant to electromagnetic interference. It has important significance and broad application prospects in biomedicine, marine information monitoring, and environmental data acquisition. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a system for pressure measurement using a differential fiber optic pressure sensor based on a spring-mass block as described in this invention.

[0032] Figure 2 This is a three-dimensional structural diagram of a differential fiber optic pressure sensor based on a spring-mass block.

[0033] Figure 3 This is a schematic diagram of the structure of the sensitizing spring mass block membrane;

[0034] Figure 4 This is a schematic diagram of the structure of a pull-out elastic spring unit;

[0035] Figure 5 This is a schematic diagram of the planar structure of the sensitizing spring mass block membrane;

[0036] Figure 6 yes Figure 5 AA section view;

[0037] Figure 7 This is a schematic diagram of the planar structure of the sensitizing spring mass block membrane, compared to Figure 5 Rotate 45 degrees;

[0038] Figure 8 yes Figure 7 BB cross-sectional view. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0042] Specific Implementation Method 1: The following is combined with... Figures 1 to 8 This implementation method is described below. Figure 1 The pressure measurement system shown is implemented using the spring-mass-based differential fiber optic pressure sensor 4 described in this invention. The pressure measurement system includes a broadband light source 1, an optical isolator 2, a fiber optic circulator 3, the spring-mass-based differential fiber optic pressure sensor 4, and a spectrometer 5.

[0043] The light beam emitted by the broadband light source 1 enters port ① of the fiber optic circulator 3 through the optical isolator 2. The light beam is output from port ② of the fiber optic circulator 3 and enters the differential fiber optic pressure sensor 4 based on a spring-mass block. The differential fiber optic pressure sensor 4 based on a spring-mass block senses the pressure and carries the sensed pressure information back to port ② of the fiber optic circulator 3 via the return light beam. Then, it is output from port ③ of the fiber optic circulator 3 to the spectrometer 5. The spectrometer 5 analyzes the pressure information to achieve pressure detection.

[0044] See Figure 2 The differential fiber optic pressure sensor 4 based on a spring-mass block includes an external encapsulation steel tube 4-1, a waterproof hydraulic membrane 4-2, a sealing head 4-3, an internal sensor steel tube 4-4, a fiber optic grating 4-6, a sensitivity-enhancing spring-mass block membrane 4-7, a fiber optic grating 4-8, a fiber optic fixing frame 4-9, and a sealing head 4-10.

[0045] The outer encapsulation steel tube 4-1 and the inner sensor steel tube 4-4 are nested inside each other. The outer encapsulation steel tube 4-1 is open at both ends, and the inner sensor steel tube 4-4 is open at the rear end. The rear end of the outer encapsulation steel tube 4-1 is sealed by sealing head 1 4-3, and the rear end of the inner sensor steel tube 4-4 is sealed by sealing head 2 4-10. The side walls and rear ends of the outer encapsulation steel tube 4-1 and the inner sensor steel tube 4-4 are concentrically fixed together by adhesive material 4-11.

[0046] The front end of the external encapsulation steel pipe 4-1 is sealed by a waterproof hydraulic membrane 4-2. There is a working gap between the front end of the external encapsulation steel pipe 4-1 and the front end of the internal sensor steel pipe 4-4. A side air hole 4-5 is provided on the side wall of the internal sensor steel pipe 4-4 near the front end.

[0047] The inner cavity of the internal sensor steel tube 4-4 is divided into three sections along the axial direction from the front end to the rear end by the sensitizing spring mass block diaphragm 4-7 and the optical fiber fixing frame 4-9. These sections are the positive tension sensing cavity, the negative tension sensing cavity, and the data transmission cavity. The positive tension sensing cavity is connected to the inner cavity of the external encapsulation steel tube 4-1 through the side air hole 4-5, while the negative tension sensing cavity is a sealed cavity.

[0048] A fiber optic grating is installed inside the internal sensor steel tube 4-4 to receive and output pressure information. The fiber optic grating is divided into three sections according to its location in the cavity: fiber optic grating 1 (4-6), fiber optic grating 2 (4-8), and single-mode fiber (4-12). The first end of the fiber optic grating is connected to the inner wall of the first end of the internal sensor steel tube 4-4. The fiber optic grating passes through the sensitizing spring mass block membrane 4-7 and is fixed after being prestressed. The fiber optic grating continues to pass through the fiber optic fixing frame 4-9 and is fixed after being prestressed. Finally, the sensed pressure information is transmitted out through the single-mode fiber optic 4-12.

[0049] See Figures 3 to 8 The sensitive spring mass block membrane 4-7 includes a mass block 4-7-1, a pull-out elastic spring unit, and a diaphragm 4-7-3. The pull-out elastic spring unit is composed of at least three layers of sheet-like rings 4-7-2 concentrically nested together. Adjacent layers of sheet-like rings 4-7-2 are radially connected by a pair of radially symmetrical connecting pieces 4-7-4. The innermost sheet-like ring 4-7-2 is connected to the mass block 4-7-1 by a pair of radially symmetrical connecting pieces 4-7-4. Adjacent pairs of connecting pieces are staggered by 90 degrees.

[0050] The outermost sheet-like circular ring 4-7-2 is fixedly connected to and sealed to the inner wall of the internal sensor steel tube 4-4;

[0051] The center hole 4-7-5 of the mass block 4-7-1 is used for the fiber optic grating to pass through and be sealed and fixed.

[0052] The sensitizing spring mass block diaphragm 4-7 has three stepped diaphragm thicknesses. The thickest part is the mass block 4-7-1 in the middle, the second thickest part is the pull-out elastic spring unit, and the thinnest part is the diaphragm 4-7-3. The pull-out elastic spring unit utilizes the pull-out structure to give it a spring-like function. When the sensitizing spring mass block diaphragm 4-7 is compressed by air, the middle mass block 4-7-1 moves to the right, pulling the multi-layered interlocking ring structure of the pull-out elastic spring unit, causing the diaphragm 4-7-3 in the gaps to deform accordingly. This structure can increase the deformation of the diaphragm 4-7-3 and reduce the fatigue of the sensor. When the air pressure at the location of fiber grating 4-6 increases, it drives the mass block membrane 4-7 of the sensitizing spring to move towards the positive tension sensing cavity where fiber grating 4-6 is located. The thickest mass block 4-7-1 in the middle has the largest inertial deformation, and the second thickest pull-out elastic spring unit has similar spring characteristics, which can realize the maximum elastic displacement of mass block 4-7-1.

[0053] The sensitizing spring mass membrane 4-7 isolates the gas spaces of fixed fiber optic grating 4-6 (No. 1) and fiber optic grating 4-8 (No. 2), creating a pressure difference in their respective regions. Fixed fiber optic grating 4-6 and fiber optic grating 4-8 are subjected to positive and negative tension forces, and the wavelength shift of the two gratings is measured. Using the differential fiber optic grating measurement principle, the relationship between the membrane under different pressure conditions is fitted based on the ratio of the sum of the wavelength changes of the two gratings to their respective wavelength changes.

[0054] When the pressure sensor is placed in the hydraulic environment to be tested, the waterproof hydraulic membrane 4-2 can sense the pressure change, compressing the gas inside the sensor. This creates a pressure difference between fiber grating 1 (4-6) and fiber grating 2 (4-8) through the side vent 4-5. A sensitive-enhancing spring mass block membrane 4-7 is placed between the two gratings. This membrane can seal the air pressure in the negative tension sensing cavity where fiber grating 2 (4-8) is located. Due to the deformation caused by the pressure difference between the two gratings, wavelength shifts of Δλ1 and Δλ2 are generated in fiber grating 1 (4-6) and fiber grating 2 (4-8), respectively.

[0055] The fiber optic bracket 4-9 is fixedly connected to and sealed to the inner wall of the internal sensor steel tube 4-4. The fiber optic bracket 4-9 is a non-deformable component, and its function is to fix the fiber optic grating, through which the optical fiber passes and is sealed.

[0056] The sensitive enhancement spring mass block membrane 4-7 and the fiber optic fixing bracket 4-9 are fixed to the inner wall of the internal sensor steel tube 4-4 with pressure-resistant sealant. During the process of fixing fiber optic grating 4-6 (No. 1) and fiber optic grating 4-8 (No. 2), prestress needs to be applied to the two fiber optic gratings.

[0057] Fiber Bragg grating 1 (4-6), fiber Bragg grating 2 (4-8), and single-mode fiber 4-12 are on the same horizontal line.

[0058] During the manufacturing process, the externally encapsulated steel pipe 4-1 must achieve a waterproof seal. The entire cavity is sealed using polyurethane potting to form a closed cavity.

[0059] To convert the hydraulic pressure to be measured into pneumatic pressure, the outer encapsulation steel tube (4-1) and the inner sensor steel tube (4-4) are tightly bonded together. Sealing head 1 (4-3) and sealing head 2 (4-10) are potted with sound-permeable polyurethane rubber and left to stand at room temperature and pressure for 48 hours to allow the polyurethane to fully vulcanize.

[0060] Broadband light source 1 can use fiber broadband light source based on stimulated emission amplification, with a spectral range of 1530-1630nm, because broadband light sources have advantages such as stable output spectrum, less susceptibility to environmental influences, and easy transmission and coupling in optical devices.

[0061] A single-mode optical fiber is equipped with two fiber gratings with grating lengths of 2 mm and center wavelengths of 1550 nm and 1545 nm, respectively, and a reflection wavelength bandwidth of 0.2 nm. The sensitizing spring mass block 4-7 has a central hole 4-7-5 with a diameter of 125 μm. The fiber grating passes through the central hole 4-7-5, is prestressed, and then fixed with sealant.

[0062] Specific Implementation Method Two: The following is combined with... Figures 1 to 8 This embodiment further explains Embodiment 1, providing a pressure sensing method based on the differential fiber optic pressure sensor based on a spring-mass block as described in claim 2. The method is characterized in that a beam emitted from a broadband light source 1 enters port ① of a fiber optic circulator 3 via an optical isolator 2. The beam is then output from port ② of the fiber optic circulator 3 and enters the differential fiber optic pressure sensor 4 based on a spring-mass block. The differential fiber optic pressure sensor 4 senses the pressure and carries the sensed pressure information back to port ② of the fiber optic circulator 3 via a return beam. The information is then output from port ③ of the fiber optic circulator 3 to a spectrometer 5, where the spectrometer 5 analyzes the pressure information to achieve pressure detection.

[0063] The pressure sensing process of the differential fiber optic pressure sensor 4 based on a spring-mass block is as follows:

[0064] External liquid hydraulic pressure is applied to the waterproof hydraulic membrane 4-2, and the gas inside the outer encapsulated steel pipe 4-1 is squeezed into the positive tension sensing cavity through the side air hole 4-5;

[0065] When the sensitizing spring mass block membrane 4-7 deforms, the No. 1 fiber grating 4-6 and the No. 2 fiber grating 4-8, which are fixed to the sensitizing spring mass block membrane 4-7, are subjected to tension. The No. 1 fiber grating 4-6 is subjected to positive tension and generates a wavelength offset Δλ1, while the No. 2 fiber grating 4-8 is subjected to negative tension and generates a wavelength offset Δλ2.

[0066] The two wavelength offsets are sent to the spectral analyzer 5 as the sensed pressure information.

[0067] The process by which the spectral analyzer 5 analyzes pressure information to achieve pressure detection is as follows:

[0068] The strain change Δε after the fiber grating is stretched is obtained by the following formula:

[0069]

[0070] In the formula, λ1 is the center wavelength of fiber grating 4-6 of type 1.

[0071] λ2 is the center wavelength of fiber grating 4-8, No. 2.

[0072] Δε represents the strain change of a fiber Bragg grating after it is stretched. The strain changes of fiber Bragg grating 4-6 (No. 1) and fiber Bragg grating 4-8 (No. 2) after being stretched are equal and are both represented by Δε.

[0073] K ε For the strain-tensile sensitivity of fiber Bragg gratings, fiber Bragg grating 1 (4-6) and fiber Bragg grating 2 (4-8) have the same performance and identical strain-tensile sensitivity, both denoted by K. ε express.

[0074] The strain change Δε of the fiber grating after it is stretched is used to characterize the pressure detection result.

[0075] This embodiment of the pressure sensing method utilizes only simple and common materials and equipment, such as broadband laser sources, fiber optic gratings, fiber optic circulators, single-mode optical fibers, and a spectrometer, to achieve system assembly. It not only enhances the sensitivity of the pressure sensor through spring-mass thin film and differential fiber optic grating wavelength demodulation, but also compensates for the temperature effect on the pressure sensor using a differential pressure demodulation method, achieving temperature self-compensation. Compared with traditional pressure sensing devices based on electrical principles, it has advantages such as resistance to electromagnetic interference, strong environmental adaptability, compact structure, simple process, low cost, and high effectiveness and stability, making it of great significance in biomedicine, marine information monitoring, and environmental data acquisition.

[0076] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A differential fiber optic pressure sensor based on a spring-mass block, characterized in that, The differential fiber optic pressure sensor (4) based on a spring mass block includes an external encapsulation steel tube (4-1), a waterproof hydraulic membrane (4-2), a No. 1 sealing head (4-3), an internal sensor steel tube (4-4), a No. 1 fiber grating (4-6), a sensitivity-enhancing spring mass block membrane (4-7), a No. 2 fiber grating (4-8), a fiber optic fixing frame (4-9), and a No. 2 sealing head (4-10). The outer encapsulation steel tube (4-1) and the inner sensor steel tube (4-4) are nested together. The outer encapsulation steel tube (4-1) is open at both ends, and the inner sensor steel tube (4-4) is open at the rear end. The rear end of the outer encapsulation steel tube (4-1) is sealed by sealing head 1 (4-3), and the rear end of the inner sensor steel tube (4-4) is sealed by sealing head 2 (4-10). The side walls and rear ends of the outer encapsulation steel tube (4-1) and the inner sensor steel tube (4-4) are concentrically fixed together using adhesive material 4-11. The front end of the external encapsulation steel pipe (4-1) is sealed by a waterproof hydraulic membrane (4-2). There is a working gap between the front end of the external encapsulation steel pipe (4-1) and the front end of the internal sensor steel pipe (4-4). A side air hole (4-5) is provided on the side wall of the internal sensor steel pipe (4-4) near the front end. The inner cavity of the internal sensor steel tube (4-4) is divided into three sections along the axial direction from the front end to the rear end by the sensitive spring mass block membrane (4-7) and the fiber optic fixing frame (4-9). These sections are the positive tension sensing cavity, the negative tension sensing cavity, and the data transmission cavity. The positive tension sensing cavity is connected to the inner cavity of the external encapsulation steel tube (4-1) through the side air hole (4-5), while the negative tension sensing cavity is a sealed cavity. A fiber optic grating is installed inside the internal sensor steel tube (4-4) to receive and output pressure information. The fiber optic grating is divided into three sections according to its location in the cavity: fiber optic grating No. 1 (4-6), fiber optic grating No. 2 (4-8), and single-mode fiber (4-12). The first end of the fiber optic grating is connected to the inner wall of the first end of the internal sensor steel tube (4-4). The fiber optic grating passes through the sensitizing spring mass block membrane (4-7) and is fixed after being prestressed. The fiber optic grating continues to pass through the fiber optic fixing frame (4-9) and is fixed after being prestressed. Finally, the sensed pressure information is transmitted out through the single-mode fiber (4-12). The sensitive spring mass block membrane (4-7) includes a mass block (4-7-1), a pull-out elastic spring unit, and a diaphragm (4-7-3). The pull-out elastic spring unit is composed of at least three layers of sheet-like rings (4-7-2) concentrically nested together. Adjacent layers of sheet-like rings (4-7-2) are radially connected by a pair of radially symmetrical connecting pieces (4-7-4). The innermost sheet-like ring (4-7-2) is connected to the mass block (4-7-1) by a pair of radially symmetrical connecting pieces (4-7-4). Adjacent pairs of connecting pieces are staggered by 90 degrees. The outermost sheet-like ring (4-7-2) is fixedly connected to and sealed to the inner wall of the internal sensor steel tube (4-4); The center hole (4-7-5) of the mass block (4-7-1) is used for the fiber optic grating to pass through and be sealed and fixed. The sensitizing spring mass block membrane (4-7) has three stepped membrane thicknesses. The thickest part is the middle mass block (4-7-1), the second thickest part is the pull-out elastic spring unit, and the thinnest part is the membrane (4-7-3). The pull-out elastic spring unit uses the pull-out structure to give it a spring-like function. When the sensitizing spring mass block membrane (4-7) is compressed by air, the middle mass block (4-7-1) moves to the right, pulling the multi-layered interlocking ring structure of the pull-out elastic spring unit, causing the membrane (4-7-3) in the gaps to deform accordingly.

2. The differential fiber optic pressure sensor based on a spring-mass block according to claim 1, characterized in that, The fiber optic bracket (4-9) is fixedly connected to and sealed to the inner wall of the internal sensor steel tube (4-4).

3. The differential fiber optic pressure sensor based on a spring-mass block according to claim 1, characterized in that, Fiber Bragg grating No. 1 (4-6), fiber Bragg grating No. 2 (4-8), and single-mode fiber (4-12) are on the same horizontal line.

4. The differential fiber optic pressure sensor based on a spring-mass block according to claim 1, characterized in that, Sealing head No. 1 (4-3) and sealing head No. 2 (4-10) are potted with sound-permeable polyurethane rubber and left to stand at room temperature and pressure for 48 hours to allow the polyurethane to fully vulcanize.

5. A pressure sensing method, the method being implemented based on the differential fiber optic pressure sensor based on a spring-mass block as described in claim 1, characterized in that, The light beam emitted by the broadband light source (1) enters port ① of the fiber optic circulator (3) through the optical isolator (2). The light beam is output from port ② of the fiber optic circulator (3) and enters the differential fiber optic pressure sensor (4) based on the spring mass block. The differential fiber optic pressure sensor (4) based on the spring mass block performs pressure sensing and carries the sensed pressure information through the return light beam into port ② of the fiber optic circulator (3). Then, it is output from port ③ of the fiber optic circulator (3) to the spectrometer (5). The spectrometer (5) analyzes the pressure information to realize pressure detection.

6. The pressure sensing method according to claim 5, characterized in that, The pressure sensing process of the differential fiber optic pressure sensor (4) based on a spring-mass block is as follows: External liquid hydraulic pressure is applied to the waterproof hydraulic membrane (4-2), and the gas inside the outer encapsulated steel pipe (4-1) is squeezed into the positive tension sensing cavity through the side air hole (4-5); When the sensitizing spring mass block membrane (4-7) deforms, the No. 1 fiber grating (4-6) and the No. 2 fiber grating (4-8) fixed to the sensitizing spring mass block membrane (4-7) are subjected to tensile force. Among them, the No. 1 fiber grating (4-6) is subjected to positive tensile force and produces a wavelength shift. Fiber Bragg grating No. 2 (4-8) is subjected to negative tension and produces wavelength offset. ; The two wavelength offsets are sent to the spectrometer as the sensed pressure information (5).

7. The pressure sensing method according to claim 6, characterized in that, The process by which the spectral analyzer (5) analyzes pressure information to achieve pressure detection is as follows: The strain change of a fiber Bragg grating after it has been stretched is obtained by the following formula. : In the formula, The center wavelength of fiber grating 1 (4-6) The center wavelength of fiber grating No. 2 (4-8) This represents the change in strain after the fiber Bragg grating is stretched. For the strain-tensile sensitivity of fiber Bragg gratings, The strain change of the fiber grating after it is stretched Used to characterize pressure detection results.

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