A fiber optic strain sensor based on low-temperature glass welding process

Abstract

This utility model discloses a fiber optic grating strain sensor based on a low-temperature glass welding process, comprising a pressure terminal, a spring holder, a spring, a strain grating, and an outer tube. Spring holders are respectively provided at opposite ends of the spring. The strain grating passes through the interior of the spring and is fixed to the spring holder. An outer tube is provided between the spring holder and the outside of the spring. The pressure terminal is detachably connected to the spring holder. This utility model has a simple overall structure, is convenient to transport, and is quick to install. It reflects the strain change of the measured object through the stretching and compression of the strain grating, enabling high-precision monitoring of the strain of the measured object, with a measurement range of ±1000~±15000uε. The strain grating and temperature-compensated grating are encapsulated using a low-temperature glass welding process, which improves the sensor's resistance to high and low temperatures and water resistance compared to glue bonding. The low-temperature glass and the fiber optic grating are made of the same material and have the same coefficient of thermal expansion, which helps to reduce the influence of temperature on the sensor.

Description

Technical Field

[0001] This utility model belongs to the field of fiber optic grating sensor technology, specifically relating to a fiber optic grating strain sensor based on a low-temperature glass welding process. Background Technology

[0002] Since their invention, fiber Bragg gratings have been widely used in the field of fiber optic sensing. Fiber Bragg grating sensors offer advantages such as resistance to electromagnetic interference, corrosion resistance, electrical insulation, high sensitivity, low cost, and good compatibility with ordinary optical fibers, thus attracting increasing attention.

[0003] Fiber Bragg grating strain sensors, as a novel high-precision measuring device, have broad application prospects in fields such as structural health monitoring, aerospace, and petrochemicals. Because the resonant wavelength of fiber Bragg gratings is sensitive to changes in stress, strain, and temperature, they are primarily used for measuring temperature, stress, and strain. In recent years, with the rapid development of intelligent manufacturing and IoT technologies, the market demand for strain monitoring has shown a continuous growth trend. Simultaneously, with the advancement of the new infrastructure strategy and the acceleration of smart city construction, the demand for structural health monitoring is increasing. Especially in important infrastructure such as large bridges, high-rise buildings, and tunnels, the application prospects of fiber Bragg grating strain sensors are very broad. However, with the continuous improvement of application requirements, this technology still faces many challenges, the primary one being improving the sensor's sensitivity and measurement range. Although traditional fiber Bragg grating strain sensors can achieve a resolution accuracy of 1‰, it is still difficult to meet requirements in certain extreme environments.

[0004] Chinese utility model patent, publication number CN 113340223 A, discloses a range-adjustable fiber Bragg grating strain sensor and its fabrication and usage method. While possessing range-adjustable functionality, the patent uses adhesive bonding for the fiber Bragg grating encapsulation. This adhesive is prone to becoming brittle at low temperatures and softening at high temperatures, and it also tends to peel off when immersed in water, making it unsuitable for extreme environments such as low temperatures, high temperatures, and water immersion. Furthermore, the patent employs a fully adhesive-bonded temperature compensation grating for temperature compensation, while the strain grating uses a point-by-point bonding method. This difference in encapsulation methods between the temperature compensation and strain gratings increases temperature compensation deviation, thus affecting the final temperature compensation accuracy of the sensor.

[0005] Chinese utility model patent CN 112902864 A discloses a surface-mounted fiber Bragg grating strain sensor, and Chinese patent CN 216645249 U discloses a highly stable fiber Bragg grating strain sensor. Both of these patents use glue encapsulation for the fiber Bragg grating, making them unsuitable for extreme environments such as low temperatures, high temperatures, and water immersion. Furthermore, the sensor's accuracy and measurement range are not adjustable, only fixed, and no temperature compensation is added. In practical use, strain is significantly affected by temperature, and strain gauges without temperature compensation have low testing accuracy and inaccurate data. Chinese patent CN 222689111 U discloses a temperature-compensated fiber Bragg grating strain sensor. However, this patent uses glue encapsulation for the fiber Bragg grating, making it unsuitable for extreme environments such as low temperatures, high temperatures, and water immersion. The sensor uses a single-ended lead-out, preventing series connection with other fiber Bragg grating sensors and hindering multi-sensor series measurement. Additionally, the single-ended lead-out poses a risk of sensor failure if a single line is damaged.

[0006] To address the problems of low accuracy, small measurement range, non-adjustable accuracy and measurement range, and inability to adapt to extreme environments such as high and low temperatures and immersion in water, this invention develops a fiber optic strain sensor based on a low-temperature glass welding process. Utility Model Content

[0007] To address the problems in the prior art, the purpose of this utility model is to provide a fiber optic strain sensor based on a low-temperature glass welding process.

[0008] To achieve the above objectives and technical effects, the technical solution adopted by this utility model is as follows:

[0009] A fiber optic strain sensor based on low-temperature glass welding technology includes a pressure terminal, a spring holder, a spring, a strain grating, and an outer tube. The spring is provided with spring holders at opposite ends. The strain grating passes through the inside of the spring and is fixed on the spring holder. An outer tube is provided on the spring holder and the outside of the spring. The spring holder is detachably connected to the pressure terminal for pressing and fixing the optical fiber cable.

[0010] Furthermore, the outer side of the crimp terminal is provided with an optical cable outer sheath to protect the lead optical cable.

[0011] Furthermore, there are two spring fixing seats, symmetrically arranged at opposite ends of the spring, and the interior of each spring fixing seat is hollow.

[0012] Furthermore, the spring fixing seat is provided with several sealing ring mounting grooves, and a sealing ring is installed and fixed in the sealing ring mounting groove, so as to tightly connect the spring fixing seat and the outer tube through the sealing ring.

[0013] Furthermore, the two opposite ends of the strain gauge pass through the interior of the spring and are respectively fixed to the temperature compensation terminal and the welding terminal, which are respectively fixed to the spring fixing seat on the same side.

[0014] Furthermore, the two opposite ends of the strain grating are respectively welded to the temperature compensation terminal and the welding terminal using a low-temperature glass welding process.

[0015] Furthermore, the temperature compensation terminal is fixed to the spring fixing seat on the same side by an adjusting nut, and the welding terminal is fixed to the spring fixing seat on the same side by an adjusting nut.

[0016] Furthermore, a temperature-compensated grating is welded onto the temperature-compensated terminal using a low-temperature glass welding process.

[0017] Furthermore, the spring holder is provided with threads for installing and fixing the pressure terminal.

[0018] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0019] This utility model discloses a fiber optic strain sensor based on low-temperature glass welding technology. The overall structure is simple, easy to transport, and quick to install. It reflects the strain changes of the measured object through the stretching and compression of the strain grating, and eliminates the influence of temperature on the strain of the measured object through the temperature-compensated grating. It can perform high-precision monitoring of the strain of the measured object, with a large and adjustable measurement range (±1000uε~±15000uε). Both the strain grating and the temperature-compensated grating are encapsulated using low-temperature glass welding technology, which improves the sensor's resistance to high and low temperatures and water resistance compared to glue bonding. It can adapt to extreme environments such as high and low temperatures and immersion in water. Because the low-temperature glass and the fiber optic grating are made of the same material and have the same coefficient of thermal expansion, it helps to reduce the influence of temperature on the sensor and improve measurement accuracy. Major components such as the wire terminals, spring fixing seats, outer tube, welding terminals, adjusting nuts, and temperature-compensated terminals are made of stainless steel, which is corrosion- and rust-proof. The spring is made of spring steel, overcoming the problems of condensation inside the sensor and electromagnetic interference in humid air, greatly extending the sensor's service life, improving its reliability, and significantly expanding its application scenarios. It has significant market promotion and application value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0021] Figure 2 This is a schematic diagram showing the connection of the strain gauge, temperature compensation gauge, and temperature compensation terminal of this utility model. Detailed Implementation

[0022] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more definite definition of the scope of protection of the present invention.

[0023] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0024] like Figure 1-2 As shown, this utility model discloses a fiber optic grating strain sensor based on a low-temperature glass welding process, including an optical cable outer sheath 1, a wire clamping terminal 2, a spring fixing seat 3, a sealing ring 4, a temperature-compensated grating 5, a temperature-compensated terminal 6, a spring 7, a strain grating 8, an outer tube 9, a welding terminal 10, and an adjusting nut 11. The spring fixing seat 3 has a hollow internal structure, and there are two spring fixing seats 3, symmetrically arranged at opposite ends of the spring 7 by welding. A strain grating 8 passes through the interior of the two spring fixing seats 3 and the spring 7 welded to them. The opposite ends of the strain grating 8 are welded to the welding terminal 10 and the temperature-compensated terminal 6 respectively by a low-temperature glass welding process. The temperature-compensated terminal 6 is fixed to the spring fixing seat 3 on the same side by the adjusting nut 11. The welding terminal 10... The spring 7 is fixed to the spring mounting base 3 on the same side by adjusting nut 11. A temperature compensation grating 5 is welded to the temperature compensation terminal 6 using a low-temperature glass welding process. The spring mounting base 3 has several sealing ring mounting grooves for installing and fixing sealing rings 4. An outer tube 9 is provided outside the spring mounting base 3 and the spring 7 to cooperate with the spring mounting base 3 to press the sealing rings 4. The sealing rings 4 ensure a tight connection between the spring mounting base 3 and the outer tube 9, thereby ensuring a sealing effect, preventing moisture from entering, protecting the internal core structure of the sensor, and increasing the sensor's service life. A thread is provided on the spring mounting base 3 (at the end away from the strain grating 8) for installing and fixing the pressure terminal 2. The pressure terminal 2 presses and fixes the lead optical cable. An outer sheath 1 is provided outside the pressure terminal 2 to protect the lead optical cable. The above sensor has a simple overall structure, high testing accuracy, and is easy to install.

[0025] In some implementations, the outer sheath 1, the crimp terminal 2, the sealing ring 4, and the spring fixing seat 3 are symmetrically arranged, and the number of each is symmetrical. This ensures that the sensor has two-way output, which facilitates series connection with other fiber optic grating sensors to achieve single-channel demodulation of multiple sensor data. At the same time, the sensor's two-way output ensures that if one end is damaged, the other end can still continue to work, ensuring redundancy.

[0026] In some embodiments, the low-temperature glass welding process involves melting the low-temperature glass 12 at 250°C and then using the melted low-temperature glass 12 to weld the two ends of the strain grating 8 to the temperature compensation terminal 6 and the welding terminal 10, respectively. This ensures that the grating regions of the strain grating 8 and the temperature compensation grating 5 are in a fixed-point tensile state. Since the low-temperature glass material and the fiber optic grating are of the same origin and have the same substrate, their coefficients of thermal expansion are the same and they are affected by temperature in the same way. The temperature compensation grating 5 is only affected by temperature. Temperature compensation can be achieved by subtracting the temperature wavelength change from the wavelength change of the strain grating. The accuracy is higher after temperature compensation. At the same time, the use of low-temperature glass welding can enable the sensor to adapt to higher temperature environments (-60°C to 200°C).

[0027] In some embodiments, the temperature compensation terminal 6 is provided with a groove that matches the temperature compensation grating 5, and the two ends of the temperature compensation grating 5 are welded to the temperature compensation terminal 6 using a low-temperature glass welding process to eliminate the influence of external temperature on strain.

[0028] In some embodiments, the lead optical cable is an armored optical cable, the outer sheath 1 of the optical cable is made of PVC rubber tubing, the crimp terminal 2, spring fixing seat 3, outer tube 9, welding terminal 10, adjusting nut 11 and temperature compensation terminal 6 are all made of stainless steel, which can prevent corrosion and rust and increase service life. The spring 7 is made of spring steel to ensure elasticity and overcome the problems of condensation inside the sensor and electromagnetic interference in humid air, which greatly extends the service life of the sensor and improves the reliability of the sensor. The temperature compensation grating 5 and the strain grating 8 are both high-intensity femtosecond gratings with high strength and high precision.

[0029] In some implementations, the strain grating 8 and the temperature-compensated grating 5 are two grating regions on a single optical fiber, eliminating splice loss and increasing the sensor's pass rate.

[0030] In some embodiments, the strain grating 8 is a high-intensity femtosecond grating with a wavelength variation of up to 30nm. With the adjustment nut 11, the resolution of the sensor can be adjusted from 1‰ to 0.03‰ (0.3 ten-thousandths), and the measurement range can also be adjusted from ±1000uε to ±15000uε, which can meet different measurement requirements.

[0031] In some embodiments, there are two adjusting nuts 11, located at both ends of the strain grating 8. By rotating the adjusting nuts 11, the two adjusting nuts 11 can be moved towards each other or away from each other, thereby adjusting the pretension of the strain grating 8, and thus adjusting the resolution and measurement range of the sensor.

[0032] The method of using a fiber optic strain sensor based on a low-temperature glass welding process, as described above, includes the following steps:

[0033] In use, the spring holder 3 is first rigidly connected to the object being measured to complete the sensor installation. When the strain of the object changes, the object will stretch / compress the spring holder 3, which in turn stretches / compresses the spring 7, ultimately causing the strain grating 8 fixed on the spring holder 3 to stretch / compress, affecting the wavelength change of the internal light and reflecting the strain change of the object. The temperature-compensated grating 5 eliminates the influence of temperature on the strain of the object, providing a large amount of reliable data for subsequent strain monitoring. The wavelength change of the fiber optic grating is linearly related to the external strain change, and the strain S is calculated using the following formula:

[0034] S=K λ *[(λ-λ0)-K T *(λ T -λ T0 )]

[0035] Among them, K λ K is the proportionality coefficient between strain and wavelength change. T λ is the temperature compensation coefficient for the wavelength change, λ is the measured value of the strain wavelength, λ0 is the initial measured value of the strain wavelength, and λ T For the temperature-compensated wavelength measurement, λ T0 This is the initial measurement value for the temperature-compensated wavelength.

[0036] The parts or structures not specifically described in this utility model can be made using existing technology or existing products, and will not be elaborated here.

[0037] The above description is merely an embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made based on the content of this utility model specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.

Claims

1. A fiber Bragg grating strain sensor based on low temperature glass welding process, characterized by, It includes a wire clamping terminal, a spring retainer, a spring, a strain gauge, and an outer tube. The spring is provided with spring retainers at opposite ends. The strain gauge passes through the inside of the spring and is fixed on the spring retainer. The spring retainer and the outside of the spring are provided with an outer tube. The spring retainer is detachably connected to the wire clamping terminal for clamping and fixing the optical fiber cable.

2. A fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 1, characterized in that, The pressure terminal is provided with an outer sheath for optical cable to protect the lead optical cable.

3. The fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 1, wherein, There are two spring fixing seats, symmetrically arranged at opposite ends of the spring, and the inside of the spring fixing seats is hollow.

4. The fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 1, wherein, The spring mounting base is provided with several sealing ring mounting slots, and a sealing ring is installed in the sealing ring mounting slot to tightly connect the spring mounting base and the outer tube.

5. A fiber optic strain sensor based on a low-temperature glass welding process according to claim 1, characterized in that, The two opposite ends of the strain gauge pass through the inside of the spring and are fixed to the temperature compensation terminal and the welding terminal, respectively. The temperature compensation terminal and the welding terminal are fixed to the spring fixing seat on the same side.

6. A fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 5, characterized in that, The temperature compensation terminal is fixed to the spring fixing seat on the same side by adjusting nuts, and the welding terminal is fixed to the spring fixing seat on the same side by adjusting nuts.

7. The fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 5, wherein, A temperature-compensated grating is welded onto the temperature-compensated terminal.

8. The fiber Bragg grating strain sensor based on low temperature glass welding process according to claim 1, wherein, The spring holder is provided with threads for installing and fixing the pressure terminal.

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