Combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress

Abstract

The present invention discloses a prestressed and precisely adjustable combined long-gauge fiber Bragg grating strain sensor, which relates to the field of sensor technology and solves the technical problem that the elastic modulus of the packaging structure material of the existing strain sensor does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot be deformed in coordination, thus causing inaccurate monitoring accuracy. The prestressed and precisely adjustable combined long-gauge fiber Bragg grating strain sensor of the present invention comprises: a fiber Bragg grating assembly, a first fixed chassis, a second fixed chassis, an adjustment assembly and a fiber Bragg grating demodulator; one end of the fiber Bragg grating assembly is arranged on the first fixed chassis, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis; the adjustment assembly is sleeved on the fiber Bragg grating assembly and fixed on the second fixed chassis, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating; the fiber Bragg grating demodulator is connected to the fiber Bragg grating assembly and is close to the second fixed chassis.

Description

Technical Field

[0001] The invention relates to the technical field of sensors, and in particular to a combined long-gauge-length optical fiber Bragg grating strain sensor with accurately adjustable prestress. Background Art

[0002] As a passive fiber device, the detection of physical quantities by FBG is mainly caused by the change of grating period and effective refractive index. The package with prestress is of great significance for the effective measurement of physical quantities. Under the process specification of applying prestress, the FBG strain sensor not only has high compression linearity, but also improves the measurement range of compression strain, greatly improves the sensing performance of FBG, improves the accuracy of negative strain measurement and increases sensitivity, which helps to have more advantages in high-frequency measurement.

[0003] In highway structures, traditional strain gauges can no longer meet current measurement requirements. Since the measuring device needs to be buried in the foundation, it is easy to be damaged during the foundation rolling process. In addition, in long-term high temperature weather, ordinary strain gauges will age, which makes measurement very difficult. The elastic modulus of the packaging structure material of most strain sensors does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot deform in coordination, resulting in inaccurate monitoring accuracy. The use of materials such as polytetrafluoroethylene can withstand high temperatures and have a certain degree of flexibility, thereby achieving the purpose of adjusting the prestress of the fiber grating.

[0004] Therefore, how to provide a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress has become a technical problem that technical personnel in this field need to solve urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress, which can solve the technical problem that the elastic modulus of the packaging structure material of the existing strain sensor does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot be deformed in coordination, thereby causing inaccurate monitoring accuracy.

[0006] The present invention provides a combined long-gauge fiber Bragg grating strain sensor with accurately adjustable prestress, comprising: a fiber Bragg grating assembly, a first fixed chassis, a second fixed chassis, an adjustment assembly and a fiber Bragg grating demodulator;

[0007] One end of the fiber Bragg grating assembly is arranged on the first fixed chassis, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis; the adjustment assembly is sleeved on the fiber Bragg grating assembly and fixed on the second fixed chassis, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating; the fiber Bragg grating demodulator is connected to the fiber Bragg grating assembly and is close to the second fixed chassis.

[0008] Furthermore, the adjustment assembly comprises: a fixed collar, a threaded tube, a force-adjusting screw cap and a tensioning wire;

[0009] The threaded tube is sleeved on the fixed clamp ring; the force-adjusting screw cover is sleeved on the threaded tube, and the threaded tube and the force-adjusting screw cover are threadedly matched; one end of the tension wire is arranged on the fiber optic grating component, and this connection is located on the outside of the second fixed chassis, and the other end of the tension wire passes through the gap between the fiber optic grating component and the fixed clamp ring, and is fixed on the force-adjusting screw cover.

[0010] Furthermore, the length of the fixed collar is greater than the length of the force-adjusting screw cap, and the length of the force-adjusting screw cap is greater than the length of the threaded tube.

[0011] Furthermore, the adjustment component further includes: a pointer 24; the pointer 24 is arranged on the outside of the fixed collar and close to the top of the force adjustment rotary cover;

[0012] The top of the force adjustment screw cap is provided with a scale, and the pointer 24 is used to indicate the adjustment scale of the adjustment component.

[0013] Further, the second fixed chassis is provided with an inner annular groove and an outer annular groove on a side away from the first fixed chassis, and the inner annular groove is located on the inner side of the outer annular groove;

[0014] The fixing collar and the threaded tube are arranged on the second fixing chassis through the inner annular groove.

[0015] Furthermore, it also includes: a protective cover; the protective cover is arranged on the second fixed chassis through the outer annular groove, and the protective cover is used for sealing and protecting the adjustment component.

[0016] Furthermore, the fiber Bragg grating assembly comprises: a fiber Bragg grating and a protective layer; the protective layer is sleeved on the fiber Bragg grating, and the fiber Bragg grating is connected to the fiber Bragg grating demodulator.

[0017] Furthermore, it also includes: a protective shell; the protective shell is sleeved on the fiber grating assembly, and one end of the protective shell is arranged on the first fixed chassis, and the other end of the protective shell is arranged on the second fixed chassis.

[0018] Furthermore, the protective layer is a sleeve made of polytetrafluoroethylene.

[0019] Compared with the prior art, the combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestressing force described in the present invention has the following advantages:

[0020] The present invention provides a combined long-gauge fiber Bragg grating strain sensor with accurately adjustable prestress, comprising: a fiber Bragg grating assembly, a first fixed chassis, a second fixed chassis, an adjustment assembly and a fiber Bragg grating demodulator;

[0021] One end of the fiber Bragg grating assembly is arranged on the first fixed chassis, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis; the adjustment assembly is sleeved on the fiber Bragg grating assembly and fixed on the second fixed chassis, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating; the fiber Bragg grating demodulator is connected to the fiber Bragg grating assembly and is close to the second fixed chassis. The prestressed and precisely adjustable combined long-gauge fiber Bragg grating strain sensor provided by the present invention solves the technical problem that the elastic modulus of the packaging structure material of the existing strain sensor does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot be deformed in coordination, thereby causing inaccurate monitoring accuracy.

[0022] When the first fixed chassis and the second fixed chassis are fixed, the middle adjustment component of the present invention can drive the tensioning wire to pull the fiber optic Bragg grating and the protective layer together in the direction of the second fixed chassis by rotating the force adjustment rotary cover, thereby changing the tensioning degree of the fiber optic Bragg grating and achieving the purpose of adjusting the size of the prestress; the pointer 24 set on the fixed clamping ring and the scale set on the force adjustment rotary cover ensure the precision and accuracy of the adjustment of the adjustment component.

[0023] The present invention also provides a sensor, which also solves to a certain extent the technical problem that the elastic modulus of the packaging structure material of the existing strain sensor does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot deform in coordination, thereby causing inaccurate monitoring accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic diagram of the structure of a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress in the length direction provided by an embodiment of the present invention;

[0026] Figure 2 A schematic diagram of the structure of an adjustment component provided in an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of the local axial structure of a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress provided in an embodiment of the present invention.

[0028] Figure numerals: 10 - fiber Bragg grating; 11 - protective layer; 20 - fixed clamp; 21 - threaded tube; 22 - force adjustment screw cap; 23 - tension wire; 24 - pointer; 30 - first fixed chassis; 40 - second fixed chassis; 50 - protective shell; 60 - protective cover; 70 - fiber Bragg grating demodulator. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0031] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] See also Figure 1-Figure 3 , Figure 1 A schematic diagram of the structure of a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress in the length direction provided by an embodiment of the present invention; Figure 2 A schematic diagram of the structure of an adjustment component provided in an embodiment of the present invention; Figure 3A schematic diagram of the local axial structure of a combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress provided in an embodiment of the present invention.

[0033] The present invention provides a combined long-gauge fiber Bragg grating strain sensor with accurately adjustable prestress, comprising: a fiber Bragg grating assembly, a first fixed chassis 30, a second fixed chassis 40, an adjustment assembly and a fiber Bragg grating demodulator 70;

[0034] One end of the fiber Bragg grating assembly is arranged on the first fixed chassis 30, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis 40; the adjustment assembly is sleeved on the fiber Bragg grating assembly and fixed on the second fixed chassis 40, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating 10; the fiber Bragg grating demodulator 70 is connected to the fiber Bragg grating assembly and is close to the second fixed chassis 40.

[0035] Further explanation, compared with the prior art, the combined long gauge length fiber Bragg grating strain sensor with precisely adjustable prestress in the embodiment of the present invention has the following advantages:

[0036] The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress provided in the embodiment of the present invention comprises: a fiber Bragg grating assembly, a first fixed chassis 30, a second fixed chassis 40, an adjustment assembly and a fiber Bragg grating demodulator 70;

[0037] One end of the fiber Bragg grating assembly is arranged on the first fixed chassis 30, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis 40; the adjustment assembly is sleeved with the fiber Bragg grating assembly and fixed on the second fixed chassis 40, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating 10; the fiber Bragg grating demodulator 70 is connected to the fiber Bragg grating assembly and is close to the second fixed chassis 40. The combined long-gauge fiber Bragg grating strain sensor and sensor with precisely adjustable prestress provided by the present invention solves the technical problem that the elastic modulus of the packaging structure material of the existing strain sensor does not match the elastic modulus of the soil to be measured, and the packaging structure and the soil to be measured cannot be deformed in coordination, thereby causing inaccurate monitoring accuracy.

[0038] Specifically, when the first fixed chassis 30 and the second fixed chassis 40 are fixed, the middle adjustment component of the present invention can drive the tensioning wire 23 to pull the fiber grating 10 and the protective layer 11 in the direction of the second fixed chassis 40 by rotating the force adjustment screw cover 22, thereby changing the tensioning degree of the fiber grating 10 and achieving the purpose of adjusting the prestress; the pointer 24 set on the fixed clamping ring 20 and the scale set on the force adjustment screw cover 22 ensure the precision and accuracy of the adjustment of the adjustment component.

[0039] More specifically, one end of the fiber grating assembly is provided with a groove thread that fits and is fixed to the first fixed chassis 30, and the collar end of the fiber grating assembly is provided with a small hole on the same plane as the second fixed chassis 40 disk to fix the fiber grating assembly, so that the fiber grating assembly measures the average strain between the first fixed chassis 30 and the second fixed chassis 40.

[0040] Further, preferably, the fiber grating assembly is provided with an annular groove 25 mm away from the small hole away from the second fixed chassis 40 for the tension wire 23 to be positioned; the distance between the first fixed chassis 30 and the second fixed chassis 40 is 150-500 mm, and this distance can be adjusted according to the measurement needs of the object being measured.

[0041] Furthermore, the inner diameter of the first fixed chassis 30 is 13mm, and the inner wall close to the second fixed chassis 40 is provided with a groove thread, which fits the fiber optic Bragg grating component. The outer diameter is 60mm and the disc thickness is 8mm. The size of the outer diameter can also be adjusted according to the difficulty of deformation of the object under test.

[0042] In one embodiment of the present invention, in order to achieve the purpose of accurately adjusting the prestressing force, see Figure 1-Figure 3 As shown; the adjustment assembly of the present invention comprises: a fixed collar 20, a threaded tube 21, a force adjustment screw cap 22 and a tension wire 23;

[0043] The threaded tube 21 is sleeved on the fixed clamp ring 20; the force adjusting screw cover 22 is sleeved on the threaded tube 21, and the threaded tube 21 and the force adjusting screw cover 22 are threadedly matched; one end of the tension wire 23 is set on the fiber optic Bragg grating component, and this connection is located on the outside of the second fixed chassis 40, and the other end of the tension wire 23 passes through the gap between the fiber optic Bragg grating component and the fixed clamp ring 20 and is fixed on the force adjusting screw cover 22.

[0044] Specifically, the threaded tube 21 is threadably matched with the force-adjusting screw cap 22, that is, when the force-adjusting screw cap 22 is rotated, the force-adjusting screw cap 22 moves along the length direction of the threaded tube 21, and one end of the tensioning wire 23 is connected to the fiber optic grating assembly, and the other end is connected to the force-adjusting screw cap 22, so that the prestress can be adjusted.

[0045] In one embodiment of the present invention, in order to ensure the stability of the adjustment component during adjustment, see Figure 1-Figure 3 As shown; the length of the fixed collar 20 of the present invention is greater than the length of the force adjusting screw cap 22, and the length of the force adjusting screw cap 22 is greater than the length of the threaded tube 21.

[0046] Specifically, when the length of the fixed clamp ring 20 is greater than the length of the force-adjusting screw cap 22, and the length of the force-adjusting screw cap 22 is greater than the length of the threaded tube 21, after the tension wire 23 passes through the gap between the fiber optic grating assembly and the fixed clamp ring 20, it fits tightly with the top of the fixed clamp ring 20, and then is fixed to the force-adjusting screw cap 22, so that the tension wire 23 is V-shaped.

[0047] More specifically, when the force-adjusting rotary cover 22 moves toward the direction approaching the second fixed chassis 40, the tension wire 23 pulls the fiber grating assembly to stretch, thereby increasing the prestress. Conversely, when the force-adjusting rotary cover 22 moves toward the direction away from the second fixed chassis 40, the tension wire 23 no longer pulls the fiber grating assembly to stretch, thereby reducing the prestress.

[0048] Furthermore, the pitch of the thread is set to 1.5 mm, that is, when the force-adjusting rotary cover 22 is in the initial position, the fiber Bragg grating assembly extends 1.5 mm for each rotation of the force-adjusting rotary cover 22.

[0049] Furthermore, the number of tension wires 23 in the present invention is preferably three, one is arranged every 120° around the circumference of the fiber grating assembly, three slots are evenly arranged on the top of the fixed clamp ring 20 for the three tension wires 23 to pass through, and three small holes are evenly arranged on the upper end of the force adjusting rotary cover 22 for the three tension wires 23 to pass through and be fixed; the three tension wires 23 are evenly distributed so that the fiber grating assembly is evenly stressed.

[0050] In one embodiment of the present invention, in order to accurately know the magnitude of the prestress, reference is made to Figure 2-Figure 3 As shown; the adjustment assembly of the present invention further includes: a pointer 24; the pointer 24 is arranged on the outside of the fixed collar 20 and close to the top of the force adjustment cover 22;

[0051] The top of the force adjustment screw cap 22 is provided with a scale, and the pointer 24 is used to indicate the adjustment scale of the adjustment component.

[0052] Specifically, the pointer 24 is used to indicate the size of the prestress. When the force-adjusting rotary cap 22 is in the initial position, the pointer 24 is in a position where the prestress is zero. There are 72 scales evenly arranged on the top of the force-adjusting rotary cap 22. By rotating the force-adjusting rotary cap 22, the tensioning wire 23 is driven to stretch the fiber optic Bragg grating assembly, thereby changing the tensioning degree of the fiber optic Bragg grating assembly to achieve the purpose of adjusting the size of the prestress.

[0053] More specifically, the scale of the force-adjusting rotary cover 22 can be appropriately reduced or increased according to the prestressing accuracy requirements.

[0054] In one embodiment of the present invention, in order to make the combined long gauge length fiber Bragg grating strain sensor with precisely adjustable prestress more stable, Figure 1 and Figure 3The second fixed chassis 40 of the present invention is provided with an inner annular groove and an outer annular groove on a side away from the first fixed chassis 30, and the inner annular groove is located on the inner side of the outer annular groove;

[0055] The fixing collar 20 and the threaded tube 21 are arranged on the second fixing base plate 40 through an inner annular groove.

[0056] Specifically, the cross section of the second fixed chassis 40 in the axial direction is E-shaped, and the two grooves of the E-shape are the inner annular groove and the outer annular groove.

[0057] In one embodiment of the present invention, it further comprises: a protective cover 60; the protective cover 60 is disposed on the second fixed chassis 40 through an outer annular groove, and the protective cover 60 is used for sealing and protecting the adjustment component.

[0058] Specifically, the outer annular groove is provided with threads, which cooperate with the protective cover 60 to provide sealing protection for the adjustment assembly.

[0059] In one embodiment of the present invention, in order to obtain accurate results, see Figure 1-Figure 3 As shown; the fiber Bragg grating assembly of the present invention comprises: a fiber Bragg grating 10 and a protective layer 11; the protective layer 11 is sleeved on the fiber Bragg grating 10, and the fiber Bragg grating 10 is connected to the fiber Bragg grating demodulator 70.

[0060] Specifically, the protective layer 11 enhances the coordinated deformation capability and high temperature and aging resistance of the prestressed and precisely adjustable combined long-gauge fiber Bragg grating strain sensor and the measured structure, and further protects the fiber Bragg grating 10 .

[0061] More specifically, the fiber Bragg grating 10 is a diffraction grating formed by periodically modulating the refractive index of the fiber core in an axial direction by a certain method, and is a passive filter device. Since the grating fiber has the advantages of small size, small fusion loss, full compatibility with optical fiber, and can be embedded in smart materials, and its resonant wavelength is sensitive to changes in the external environment such as temperature, strain, refractive index, and concentration, it has been widely used in the field of optical fiber communication and sensing.

[0062] The fiber Bragg grating 10 utilizes the photosensitivity of the optical fiber material to write the incident light coherent field pattern into the fiber core by ultraviolet light exposure, and produces a periodic change in the refractive index along the axial direction of the fiber core, thereby forming a permanent spatial phase grating, which essentially forms a narrow-band (transmission or reflection) filter or reflector in the fiber core. When a beam of wide spectrum light passes through the fiber Bragg grating 10, the wavelengths that meet the Bragg condition of the fiber Bragg grating 10 will be reflected, and the remaining wavelengths will continue to be transmitted through the fiber Bragg grating 10.

[0063] Furthermore, the fiber Bragg grating demodulator 70 has the small size, high precision, large dynamic range fiber Bragg grating sensor measurement capability and accurate spectrum analysis capability. It is mainly used for real-time monitoring of structural strain and temperature in the fields of bridges, dams, high-rise buildings, tunnels, highways, electric power, petrochemicals, fire protection, HVAC, etc.

[0064] In one embodiment of the present invention, in order to protect the fiber Bragg grating assembly, see Figure 1-Figure 3 As shown; it also includes: a protective shell 50; the protective shell 50 is sleeved on the fiber grating assembly, and one end of the protective shell 50 is set on the first fixed chassis 30, and the other end of the protective shell 50 is set on the second fixed chassis 40.

[0065] Specifically, the protective shell 50 is disposed between the first fixed chassis 30 and the second fixed chassis 40, which can fully protect the fiber Bragg grating assembly and prevent the normal operation of the prestressed and precisely adjustable combined long-gauge fiber Bragg grating strain sensor from being crushed in actual engineering applications.

[0066] More specifically, the protective shell 50 of the present invention is preferably a protective shell 50 made of stainless steel.

[0067] In one embodiment of the present invention, in order to better protect the fiber Bragg grating 10, see Figure 1-Figure 3 As shown; the protective layer 11 of the present invention is a sleeve made of polytetrafluoroethylene.

[0068] Specifically, the material selected for the protective layer 11 is polytetrafluoroethylene as a deformable component, which improves the high temperature aging resistance and enhances the coordinated deformation ability with the structure.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress, characterized in that: include: A fiber Bragg grating assembly, a first fixed chassis, a second fixed chassis, an adjustment assembly and a fiber Bragg grating demodulator; one end of the fiber Bragg grating assembly is arranged on the first fixed chassis, and the other end of the fiber Bragg grating assembly is passed through and fixed on the second fixed chassis; the adjustment assembly is sleeved on the fiber Bragg grating assembly and fixed on the second fixed chassis, and the adjustment assembly is used to adjust the tension of the fiber Bragg grating; The fiber Bragg grating demodulator is connected to the fiber Bragg grating assembly and is close to the second fixed chassis; The adjusting assembly comprises: a fixing collar, a threaded tube, a force adjusting screw cap and a tensioning wire; The threaded tube is sleeved on the fixed collar; the force-adjusting screw cap is sleeved on the threaded tube, and the threaded tube and the force-adjusting screw cap are threadedly matched; one end of the tension wire is arranged on the fiber optic grating component, and the connection is located on the outside of the second fixed chassis, and the other end of the tension wire passes through the gap between the fiber optic grating component and the fixed collar, and is fixed on the force-adjusting screw cap; The length of the fixed collar is greater than the length of the force-adjusting screw cap, and the length of the force-adjusting screw cap is greater than the length of the threaded tube.

2. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 1 is characterized in that: The adjustment component also includes: a pointer; the pointer is arranged on the outside of the fixed collar and close to the top of the force adjustment screw cap; the top of the force adjustment screw cap is provided with a scale, and the pointer is used to indicate the adjustment scale of the adjustment component.

3. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 1 is characterized in that: The second fixed chassis is provided with an inner annular groove and an outer annular groove on a side away from the first fixed chassis, wherein the inner annular groove is located inside the outer annular groove; the fixed collar and the threaded tube are arranged on the second fixed chassis via the inner annular groove.

4. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 3 is characterized in that: Also includes: Protective cover; The protective cover is arranged on the second fixed chassis through the outer annular groove, and the protective cover is used for sealing and protecting the adjustment component.

5. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 1 is characterized in that: The fiber grating assembly comprises: a fiber grating and a protective layer; the protective layer is sleeved on the fiber grating, and the fiber grating is connected to the fiber grating demodulator.

6. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 1 is characterized in that: Also includes: A protective shell; the protective shell is sleeved on the fiber grating assembly, and one end of the protective shell is arranged on the first fixed chassis, and the other end of the protective shell is arranged on the second fixed chassis.

7. The combined long-gauge fiber Bragg grating strain sensor with precisely adjustable prestress according to claim 5 is characterized in that: The protective layer is a sleeve made of polytetrafluoroethylene.

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