A fiber grating unidirectional strain sensor

Abstract

The present invention discloses a fiber Bragg grating unidirectional strain sensor. The fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention comprises a temperature compensation sensing module with temperature compensation and a strain sensor module with a function of desensitizing the fiber Bragg grating. The three-ring desensitizing substrate fixing fiber Bragg grating region in the strain sensor module adopts a three-ring parallel structure. Thus, when the fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention is used for stress monitoring, the desensitization design and temperature compensation design of the fiber Bragg grating are realized, the structure is simple, the monitoring sensitivity is improved, and the measuring range is improved.

Description

Technical Field

[0001] The invention relates to a stress monitoring technology of an object, and in particular to a fiber grating unidirectional strain sensor for stress monitoring. Background Art

[0002] Fiber Bragg (FBG) sensor is a kind of fiber optic sensor. The sensing process based on fiber Bragg obtains sensing information by modulating the Bragg wavelength of the fiber by external physical parameters. It is a wavelength modulated fiber optic sensor. Fiber Bragg sensor can be attached to the structure to be measured to realize direct measurement of the temperature and strain of the structure to be measured. Fiber Bragg sensor can be divided into fiber Bragg temperature sensor and fiber Bragg strain sensor according to type. As one of the most rapidly developed and widely used fiber passive devices in recent years, fiber Bragg sensor has the advantages of simple structure, good reliability, corrosion resistance, strong anti-electromagnetic interference ability and strong multiplexing ability compared with traditional electrical signal sensors. It can form a sensing network with multiple connection methods, realizing large-area measurement and multi-point measurement of the structure to be measured. Because fiber Bragg sensor itself has many irreplaceable advantages, it is favored by more and more scientific researchers and engineering technicians.

[0003] The stress monitoring technology of the structure to be measured is generally used in the field where the structure is relatively complex, the strain range is large, and the stability of the structure to be measured is relatively high. Therefore, increasing the range, increasing the stability of the structure to be measured, and simplifying the packaging process are the first problems that need to be solved in the research of fiber Bragg grating strain sensors. However, the strain range of the fiber Bragg grating used in the fiber Bragg grating strain sensor is ±2000με, which is far lower than the strain range required by the structure to be measured. This requires the fiber Bragg grating strain sensor to be desensitized to meet the requirements. At present, there are two design schemes for fiber Bragg grating strain sensors: one is a fiber Bragg grating strain sensor with a substrate structure, whose sensitivity coefficient is 1.05pm / με and linearity is about 0.99. Its sensitivity and linearity still cannot meet the requirements of the structure to be measured; the other is a fiber Bragg grating strain sensor with a spiral tilted composite structure, which cleverly desensitizes the strain of the optical fiber in the structure, but the structure is complex and not easy to achieve.

[0004] When the above two fiber Bragg grating strain sensors are applied to the large-scale measurement of the structure to be measured, one has the problem that the linearity and sensitivity accuracy need to be improved, and the other has the problem that the structure is complex, difficult to implement and has a high cost. Therefore, there is currently no fiber Bragg grating strain sensor that has both a simple structure and can improve the range and monitoring sensitivity. Summary of the invention

[0005] An embodiment of the present invention provides a fiber Bragg grating unidirectional strain sensor for stress monitoring, which has a simple structure and can improve monitoring sensitivity and increase the measuring range.

[0006] The embodiment of the present invention is implemented as follows:

[0007] A fiber Bragg grating unidirectional strain sensor for stress monitoring includes: a strain sensor module, a temperature compensation sensor module, a sensor base plate, a sensor protective housing and an optical fiber cable. The strain sensor module is welded in the middle of the sensor base plate, and a temperature compensation sensor module is placed on the upper part. The sensor protective housing completely covers the temperature compensation sensor module, the strain sensor module and the sensor base plate.

[0008] The optical fiber cable comprises a grating in the middle, optical fiber loose tubes at both ends of the grating, and armored tubes at two side ends;

[0009] The strain sensor module includes a three-ring desensitizing substrate and sensor welding blocks respectively connected to two ends of the three-ring desensitizing substrate, the grating is encapsulated on the first groove of the three-ring desensitizing substrate, and three annular structures are evenly distributed in parallel in the direction of the first groove of the three-ring desensitizing substrate, the armored tube is fixed on the sensor welding block and the sensor welding block is welded to the surface of the structure to be measured;

[0010] The temperature compensation sensing module includes a temperature compensation substrate and a temperature compensation substrate connected to one end of the temperature compensation substrate, the temperature compensation substrate is fixed on the sensor welding block, a second groove is arranged in the temperature compensation substrate to place the grating, third grooves are arranged at both ends of the second groove of the temperature compensation substrate in the extending direction to place the optical fiber loose tube, and a fourth groove on the temperature compensation substrate along the extending direction of the third groove is arranged to place the armored tube.

[0011] As can be seen from the above, the fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention includes a temperature compensation sensing module with temperature compensation and a strain sensor module with the function of desensitizing the fiber Bragg grating, wherein the three-ring desensitizing substrate fixed fiber Bragg grating region in the strain sensor module adopts a three-ring parallel structure. Thus, when the fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention is used for stress monitoring, the desensitization design and temperature compensation design of the fiber Bragg grating are realized, the structure is simple, and the monitoring sensitivity and the measuring range are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of the overall structure of a fiber Bragg grating unidirectional strain sensor for stress monitoring provided by an embodiment of the present invention;

[0013] Figure 2 A schematic diagram of the structure of a strain sensor module provided by an embodiment of the present invention;

[0014] Figure 3 A schematic diagram of the structure of a three-ring desensitizing substrate in a strain sensor module provided by an embodiment of the present invention;

[0015] Figure 4 A schematic diagram of the structure of a welding block in a strain sensor module provided by an embodiment of the present invention;

[0016] Figure 5 A schematic diagram of the structure of an optical cable fixing block in a strain sensor module provided in an embodiment of the present invention;

[0017] Figure 6 A schematic diagram of the structure of a temperature compensation sensor module provided by an embodiment of the present invention;

[0018] Figure 7 A schematic diagram of the structure of a sensor base plate provided by an embodiment of the present invention;

[0019] Figure 8 A schematic diagram of the structure of a sensor protection housing provided in an embodiment of the present invention.

[0020] Reference numerals

[0021] 1-Strain sensor module

[0022] 101-Tricyclic Desensitizing Base Sheet

[0023] 1011-First end piece

[0024] 1012-Second end piece

[0025] 1013-First Ring

[0026] 1014-Second Ring

[0027] 1015-Third Ring

[0028] 1016-First connecting piece

[0029] 1017-Second connecting piece

[0030] 102-Sensor welding block

[0031] 103-Fiber optic cable 5 fixing block

[0032] 2-Temperature compensation sensor module

[0033] 201-Temperature compensation substrate

[0034] 202-Temperature compensation substrate

[0035] 3-Sensor base plate

[0036] 33-Sensor base plate welding frame

[0037] 31-Fiber optic cable fixing block

[0038] 4-Sensor protection housing

[0039] 5-Fiber Optic Cable DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0041] In order to realize the desensitization design and temperature compensation design of the fiber Bragg grating when the fiber Bragg grating unidirectional strain sensor provided by the present invention performs stress monitoring, the embodiment of the present invention includes a temperature compensation sensing module with temperature compensation and a strain sensor module with the function of desensitizing the fiber Bragg grating, wherein the three-ring desensitization substrate fixed fiber Bragg grating area in the strain sensor module adopts a three-ring parallel structure. In this way, the fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention has a simple structure, improved monitoring sensitivity and increased range.

[0042] Furthermore, when the fiber Bragg grating unidirectional strain sensor provided in the embodiment of the present invention uses the physical parameter measurement result of the fiber Bragg grating to monitor the stress of the structure to be measured, it measures the stress of the structure to be measured in one direction, so it is called a fiber Bragg grating unidirectional strain sensor.

[0043] Figure 1 The overall structural diagram of the fiber Bragg grating unidirectional strain sensor for stress monitoring provided by the embodiment of the present invention includes: a strain sensor module 1, a temperature compensation sensor module 2, a sensor base plate 3, a sensor protective housing 4 and an optical fiber cable 5. The strain sensor module 1 is welded in the middle of the sensor base plate 3, and the temperature compensation sensor module 2 is placed on the upper part thereof. The sensor protective housing 4 completely covers the temperature compensation sensor module 2, the strain sensor module 1 and the sensor base plate 3, wherein:

[0044] The optical fiber cable 5 includes a bare optical fiber in the middle, optical fiber loose tubes at both ends of the bare optical fiber, and armored tubes at two side ends;

[0045] The strain sensor module 1 includes a three-ring desensitizing substrate 101 and a sensor welding block 102 respectively connected to two ends of the three-ring desensitizing substrate 101, the exposed optical fiber is encapsulated on the first groove of the three-ring desensitizing substrate 101, and three annular structures are evenly distributed in parallel in the direction of the first groove of the three-ring desensitizing substrate 101, the armored tube is fixed on the sensor welding block 102 and the sensor welding block 102 is welded to the surface of the structure to be measured;

[0046] The temperature compensation sensing module 2 includes a temperature compensation substrate 201 and a temperature compensation substrate 202 connected to one end of the temperature compensation substrate 201, the temperature compensation substrate 202 is fixed on the sensor welding block 102, a second groove is provided in the temperature compensation substrate 201 to place the exposed optical fiber, third grooves are provided at both ends of the second groove of the temperature compensation substrate 201 in the extending direction to place the optical fiber loose tube, and a fourth groove on the temperature compensation substrate 202 along the extending direction of the third groove is provided to place the armored tube.

[0047] In this structure, the optical fiber cable 5 is composed of bare optical fiber, optical fiber loose tube and armored tube from inside to outside, the strain sensor module 1 and the temperature compensation sensor module 2 fix the optical fiber cable 5, and a fiber grating area is arranged in the middle of the bare optical fiber. When monitoring the structure to be measured, the fiber grating is arranged on the fiber grating unidirectional strain sensor, and the fiber grating unidirectional strain sensor is welded on the surface of the structure to be measured. The deformation of the structure to be measured drives the fiber grating on the fiber grating unidirectional strain sensor to deform, and the change of the central wavelength of the fiber grating is measured, and the strain of the structure to be measured is determined according to the change of the central wavelength.

[0048] Figure 2 The structural diagram of the strain sensor module provided by the embodiment of the present invention is as follows: the strain sensor module 1 comprises a three-ring desensitizing substrate 101, a sensor welding block 102 connected to both ends of the three-ring desensitizing substrate 101, and an optical fiber cable 5 fixing block 103. Figure 3 The schematic diagram of the structure of the three-ring desensitizing substrate 101 is shown, Figure 4 The schematic diagram of the structure of the sensor welding block 102 is shown, and Figure 5 The structural diagram of the optical fiber cable 5 fixing block 103 shown in FIG. 1 is used to explain the strain sensor module in detail.

[0049] like Figure 3As shown, the three-ring desensitizing substrate 101 is integrally composed of a first end piece 1011, a second end piece 1012, a first annular body 1013, a second annular body 1014, a third annular body 1015, a first connecting piece 1016 and a second connecting piece 1017, wherein the first annular body 1013 is close to the first end piece 1011, the second annular body 1014 is close to the second end piece 1012, and the third annular body 1015 is arranged between the first annular body 1013 and the second annular body 1014, and is respectively connected to the first annular body 1013 through the first connecting piece 1016 and connected to the second annular body 1014 through the second connecting piece 1017, and the axial directions of the first annular body 1013, the second annular body 1014 and the third annular body 1015 are perpendicular to the planes of the first connecting piece 1016 and the second connecting piece 1017. A first groove is provided on the first connecting piece 1016 and the second connecting piece 1017 to place the exposed optical fiber Bragg grating. Two circular holes are provided in the first groove symmetrically to the third annular body 1015 to fix the grating area in the exposed optical fiber Bragg grating between the two circular holes. Threaded holes are provided in the first end piece 1011 and the second end piece 1012 symmetrically to the first groove to coincide with the threaded holes provided in the sensor welding block 102, and the three-ring desensitizing substrate 101 is fixed to the sensor welding block 102 with screws.

[0050] In this structure, the two circular holes can prevent glue from penetrating into the grid area, and the first annular body 1013, the second annular body 1014, and the third annular body 1015 can play a desensitizing role. When the structure to be measured is deformed, the three annular bodies can withstand most of the deformation, and the grid area between the two circular holes is only subject to a smaller deformation, thereby increasing the range. The strain range of the fiber Bragg grating for long-term operation is ±2000με. Through finite element analysis and theoretical calculation, the sensor provided by the embodiment of the present invention is used, and the desensitization ratio provided by the three annular bodies is 2.9. While ensuring desensitization, it also greatly ensures the accuracy of the sensor provided by the embodiment of the present invention, and the strain range that its material can withstand within the elastic range is ±5000με.

[0051] like Figure 4 As shown, the sensor welding block 102 is provided with a first threaded hole that coincides with the threaded hole of the three-ring desensitizing substrate 101, and the three-ring desensitizing substrate 101 is fixed to the sensor welding block 102 by screws; a second threaded hole for fixing the temperature compensation sensor module 2 and a third threaded hole for fixing the optical fiber cable 5 fixing block are also provided; the first groove of the three-ring desensitizing substrate 101 extends in the sensor welding block 102 and extends to the first sub-groove and the second sub-groove in sequence, wherein the extension of the first groove is placed with a bare optical fiber, the first sub-groove is placed with an optical fiber loose tube, and the second sub-groove is placed with an armored tube. In this way, the radius size of the second sub-groove is the same as the radius size of the armored tube. The problem that the three-ring desensitizing substrate 101 is difficult to weld to the sensor welding block 102 due to its special material is solved.

[0052] like Figure 5 As shown, the optical fiber cable 5 fixing block 103 has a convex groove for placing the armored tube and threaded holes symmetrically arranged on both sides of the convex groove, wherein the threaded hole coincides with the third threaded hole on the sensor welding block 102, so that the sensor welding block 102 and the optical fiber cable 5 fixing block 103 are fixed with screws to press the armored tube, and the radius size of the convex groove for placing the armored tube is the same as the radius size of the armored tube.

[0053] like Figure 6 As shown, the second groove in the temperature compensation substrate 201 is symmetrically arranged on both sides of the first threaded hole of the temperature compensation substrate 201 and the second threaded hole of the temperature compensation substrate 202, the two threaded holes overlap, and the temperature compensation substrate 201 and the temperature compensation substrate 202 are fixed by screws. A third threaded hole is arranged outside the second threaded hole of the temperature compensation substrate 202 to overlap with the second threaded hole of the sensor welding block 102, and the temperature compensation substrate 202 and the sensor welding block 102 are fixed by screws. Here, the principle of the temperature compensation sensing module 2 is to eliminate the wavelength drift of the fiber grating caused by the temperature influence in the strain sensor. Therefore, the material of the temperature compensation substrate 201 is set to be the same as that of the three-ring desensitizing substrate 101 to ensure that the thermal expansion coefficients of the two are the same. In this way, the error influence of the thermal temperature expansion mismatch on the result is offset each other during calculation, which can ensure the accuracy of the measurement result. Furthermore, the temperature compensation substrate 201 adopts a cantilever beam structure and is fixed to the sensor welding block 102 through the temperature compensation substrate 202, so that it is not affected by external stress. When the object to be measured is a curved surface or a vertical surface, the advantage of this buffer design structure is that it can improve the center of gravity position and reduce the influence of the material's own gravity, and can be applied to the situation of external environmental load. At the same time, it can also reduce the area of ​​the entire fiber Bragg grating unidirectional strain sensor and increase the applicable space.

[0054] like Figure 7 As shown, Figure 7A schematic diagram of the sensor base structure provided by an embodiment of the present invention. The sensor base 3 is composed of a sensor base welding frame 33 and an optical cable fixing block 31. The sensor base welding frame 33 is welded to the periphery of the strain sensor module 1. A groove is provided at the entrance and exit position of the armored tube of the fiber grating and a convex groove is provided on the optical cable fixing block 31. The groove and the convex groove cooperate with each other to fix the armored tube of the grating optical cable. Threaded holes are symmetrically provided on both sides of the convex groove of the optical cable fixing block 31, which overlap with the threaded holes symmetrically provided on the groove of the sensor base welding frame 33. The sensor base welding frame 33 and the optical cable fixing block 31 are fixed by screws through the overlapping threaded holes. The apertures of the groove and the convex groove are consistent with the aperture of the armored tube of the fiber grating. In this way, the armored tube of the grating optical cable can be firmly fixed to the sensor base 3 to prevent sliding. A number of threaded holes for fixing with the sensor protective housing 4 by screws are also provided on the sensor base welding frame 33 to prevent the fiber grating unidirectional strain sensor from being damaged by the outside world.

[0055] Figure 8 A schematic diagram of the sensor protection housing structure provided by an embodiment of the present invention, wherein the sensor protection housing 4 structure is provided with a plurality of threaded holes for fixing with the sensor base plate 3 by screws, and a convex groove is provided at the entry and exit position of the armored tube of the fiber grating, and the aperture is consistent with the aperture of the armored tube of the fiber grating, so that the armored tube of the fiber grating can enter and exit. The threaded holes can be provided at the frame edge of the sensor protection housing 4 structure and evenly distributed.

[0056] It can be seen from the above description that the fiber Bragg grating unidirectional strain sensor provided by the embodiment of the present invention has the following advantages:

[0057] 1) Small size: The size of the packaged sensor is 79*38*29mm. The small size means that the sensor itself has little impact on the monitored object and is less likely to be accidentally damaged;

[0058] 2) Large measuring range: The long-term working strain range of the fiber Bragg grating used in the fiber Bragg grating strain sensor is ±2000με, while the sensor provided by the present invention has a three-ring desensitizing substrate 1, whose material has a small elastic modulus and a large yield stress, so that the measuring range of the sensor can reach ±5000με; the measuring range and application scope of the sensor are greatly improved;

[0059] 3) High precision: The sensor provided by the present invention has a three-ring desensitization substrate 11, and the desensitization coefficient is appropriate, so that the precision of the sensor is improved;

[0060] 4) Temperature compensation: The sensor provided by the present invention is provided with a temperature compensation sensing module 2 to achieve temperature compensation, thereby improving the accuracy of engineering applications;

[0061] 5) Long-term stability and high lifespan: Since the connection method of the three-ring desensitizing substrate 11 and the sensor welding block in the sensor provided by the present invention is screw connection, there is no long-term creep and aging problem that occurs in the existing organic bonding method. It is relatively stable and reliable during long-term operation, and its service life is greatly improved;

[0062] 6) The installation process is simple and has high reliability: Since the installation process adopts argon arc welding, the installation process is simple, does not require complicated treatment of the welding surface, and also avoids installation problems caused by inadequate surface treatment.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fiber Bragg grating unidirectional strain sensor for stress monitoring, characterized in that: include: The invention is composed of a strain sensor module (1), a temperature compensation sensor module (2), a sensor base plate (3), a sensor protective housing (4) and an optical fiber cable (5). The strain sensor module (1) is welded in the middle of the sensor base plate (3), the temperature compensation sensor module (2) is placed on the upper part thereof, and the sensor protective housing (4) completely covers the temperature compensation sensor module (2), the strain sensor module (1) and the sensor base plate (3), wherein: The optical fiber cable (5) comprises a grating in the middle, optical fiber loose tubes at both ends of the grating, and armored tubes at two side ends; The strain sensor module (1) comprises a three-ring desensitizing substrate (101) and sensor welding blocks (102) respectively connected to two ends of the three-ring desensitizing substrate (101); the grating is packaged on a first groove of the three-ring desensitizing substrate (101); three annular structures are evenly distributed in parallel in the direction of the first groove of the three-ring desensitizing substrate (101); the armored tube is fixed on the sensor welding block (102) and the sensor welding block (102) is welded to the surface of the structure to be measured; The temperature compensation sensing module (2) comprises a temperature compensation substrate (201) and a temperature compensation substrate (202) connected to one end of the temperature compensation substrate (201); the temperature compensation substrate (202) is fixed on the sensor welding block (102); a second groove is arranged in the temperature compensation substrate (201) to place the grating; third grooves are arranged at both ends of the second groove of the temperature compensation substrate (201) in an extending direction to place the optical fiber loose tube; and a fourth groove on the temperature compensation substrate (202) along an extending direction of the third groove is arranged to place the armored tube; The three-ring desensitizing substrate (101) is integrally formed by a first end piece (1011), a second end piece (1012), a first annular body (1013), a second annular body (1014), a third annular body (1015), a first connecting piece (1016) and a second connecting piece (1017), wherein: The first annular body (1013) is close to the first end piece (1011), and the second annular body (1014) is close to the second end piece (1012). A third annular body (1015) is disposed between the first annular body (1013) and the second annular body (1014). The third annular body (1015) is connected to the first annular body (1013) through a first connecting piece (1016) and to the second annular body (1014) through a second connecting piece (1017). The first annular body (1013), the second annular body (1014) and the third annular body (1015) are axially aligned with the first connecting piece (1016). and the plane of the second connecting piece (1017), the first connecting piece (1016) and the second connecting piece (1017) are provided with a first groove for placing the exposed optical fiber Bragg grating, two circular holes are provided in the first groove symmetrically to the third annular body (1015), and the grating area in the exposed optical fiber Bragg grating is fixed between the two circular holes; threaded holes are provided in the first end piece (1011) and the second end piece (1012) symmetrically to the first groove to overlap with the threaded holes provided in the sensor welding block (102), and the three-ring desensitizing substrate (101) is fixed to the sensor welding block (102) by screws; The material of the temperature compensation substrate (201) is the same as that of the three-ring desensitizing substrate (101).

2. The sensor according to claim 1, characterized in that The sensor welding block (102) is provided with a first threaded hole that overlaps with the threaded hole of the three-ring desensitizing substrate (101), and the three-ring desensitizing substrate (101) is fixed to the sensor welding block (102) by screws; The sensor welding block (102) is also provided with a second threaded hole for fixing the temperature compensation sensor module (2), and a third threaded hole for fixing the optical fiber cable (5) fixing block; the first groove of the three-ring desensitizing substrate (101) extends in the sensor welding block (102) and extends to the first sub-groove and the second sub-groove in sequence, wherein the extended part of the first groove is placed with a bare optical fiber, the first sub-groove is placed with an optical fiber loose tube, and the second sub-groove is placed with an armored tube.

3. The sensor according to claim 2, characterized in that The strain sensor module (1) further comprises an optical fiber cable (5) fixing block (103) having a convex groove for accommodating the armored tube and threaded holes symmetrically arranged on both sides of the convex groove, wherein the threaded holes coincide with the third threaded holes on the sensor welding block (102), so that the sensor welding block (102) and the optical fiber cable (5) fixing block (103) are fixed by screws.

4. The sensor according to claim 2 or 3, characterized in that The second groove in the temperature compensation substrate (201) is symmetrically arranged on both sides of a first threaded hole in the temperature compensation substrate (201) and a second threaded hole in the temperature compensation substrate (202), the two threaded holes overlap, and the temperature compensation substrate (201) and the temperature compensation substrate (202) are fixed by screws; A third threaded hole is arranged outside the second threaded hole of the temperature compensation substrate (202) to overlap with the second threaded hole of the sensor welding block (102), and the temperature compensation substrate (202) and the sensor welding block (102) are fixed by screws.

5. The sensor according to claim 1, characterized in that The sensor base plate (3) is composed of a sensor base plate welding frame (33) and an optical cable fixing block (31); the sensor base plate welding frame (33) is welded to the periphery of the strain sensor module (1); a groove is provided at the entry and exit position of the armored tube of the optical fiber cable (5) and a convex groove is provided at the optical cable fixing block (31); the groove and the convex groove are integrally fixed to the armored tube; Threaded holes are symmetrically arranged on both sides of the convex groove of the optical cable fixing block (31) and overlap with the threaded holes symmetrically arranged on the concave groove of the sensor bottom plate welding frame (33), and the sensor bottom plate welding frame (33) and the optical cable fixing block (31) are fixed by screws through the overlapping threaded holes; and a plurality of threaded holes for fixing the sensor bottom plate welding frame (33) with the sensor protective housing (4) by screws are also arranged on the sensor bottom plate welding frame (33).

6. The sensor according to claim 1, characterized in that The sensor protection housing (4) is provided with a plurality of threaded holes for fixing the sensor to the sensor base plate (3) by means of screws, and a convex groove is provided at the entry and exit position of the armored tube of the optical fiber cable (5).

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