Marine fiber grating strain sensor system with integrated measurement and calibration

Abstract

The present invention relates to a measurement and calibration integrated marine fiber grating strain sensor system, which consists of a fiber grating strain sensor and a sensor calibration device. The two ends of the fiber grating are respectively fixedly connected to the fixed end of the sensor and the movable end of the sensor. The fixed end of the sensor is fixedly connected to a positioning plate through a fixed end welding base, and the movable end of the sensor is connected to the positioning plate through a movable end welding base. The movable end welding base can move forward and backward along the positioning plate, so that the distance between the two fixed points of the fiber grating is an effective strain length L; a high-precision differential screw is fixedly connected to the positioning plate through a screw mounting seat, and the screw mounting seat is connected to the movable end welding base through a return spring. The high-precision differential screw cooperates with the return spring to control the sliding of the movable end of the sensor in the forward and backward directions, and can accurately control the displacement ΔL of the sliding of the movable end of the sensor, thereby applying a standard strain amount ε=ΔL / L to the fiber grating strain sensor, thereby realizing the installation or calibration of the fiber grating strain sensor.

Description

Technical Field

[0001] The invention relates to a fiber grating strain sensor system, which is mainly suitable for measuring or long-term monitoring the overall deformation of a ship body. Background Art

[0002] Fiber Bragg grating strain sensors have the advantages of anti-electromagnetic interference, corrosion resistance, light weight, and small size, and they play a huge role in the ship structure health monitoring system. On the one hand, during the navigation of the ship, the stress and fatigue damage of key parts of the hull can be monitored in real time, and early warnings can be issued in case of dangerous situations to ensure the safe navigation of the ship; on the other hand, the collected monitoring data can be used to continuously optimize the design of large ships, improve the structure, and enhance the shipbuilding capacity, making the ship safer and more reliable. It is not difficult to see that the accuracy of the measurement value of the fiber Bragg grating strain sensor is crucial.

[0003] However, the traceability system of this type of sensor is not perfect at present. Most sensors do not have the function of multiple installation and calibration. For a few calibrated sensors, their calibration devices can only be used in laboratories, which brings great inconvenience to strain sensors that serve on ships for a long time. Therefore, it is of great significance to develop a fiber Bragg grating strain sensor system that can be used for on-site calibration to ensure the accuracy and uniformity of the measurement values ​​of the ship structure health monitoring system. Summary of the invention

[0004] In order to improve the reliability and accuracy of data of a ship structure health monitoring system, the present invention aims to provide a ship-used fiber Bragg grating strain sensor system with integrated measurement and calibration.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present invention is: a ship-used fiber Bragg grating strain sensor system with integrated measurement and calibration, which is composed of a fiber Bragg grating strain sensor and a sensor calibration device. The fiber Bragg grating strain sensor has a fiber Bragg grating, and the two ends of the fiber Bragg grating are respectively fixedly connected to the fixed end of the sensor and the movable end of the sensor. The fixed end of the sensor is fixedly connected to the positioning plate through a fixed end welding base, and the movable end of the sensor is connected to the positioning plate through a movable end welding base, and the movable end welding base can be adjusted and moved forward and backward along the positioning plate, so that the distance between the two fixed points of the fiber Bragg grating is the effective strain length L The sensor calibration device comprises a high-precision differential screw and a return spring. The high-precision differential screw is fixedly connected to the positioning plate through a screw mounting seat. The screw mounting seat is connected to the movable end welding base through a return spring, so that the top of the high-precision differential screw is always in contact with the movable end welding base. The high-precision differential screw cooperates with the return spring to control the sliding of the movable end of the sensor in the forward and backward directions, and can accurately control the sliding displacement ΔL of the movable end of the sensor, thereby applying a standard strain ε=ΔL / L to the fiber grating strain sensor, thereby realizing the installation or calibration of the fiber grating strain sensor.

[0006] Furthermore, the fiber grating is protected by a protective steel pipe in the middle, and the protective steel pipe is fixedly connected to the fixed end of the sensor by means of threads, and is connected to the movable end of the sensor by means of an oil seal, so that the movable end of the sensor can slide freely along the axial direction of the protective steel pipe, thereby transmitting the deformation between the fixed end of the sensor and the movable end of the sensor to the fiber grating.

[0007] Furthermore, the fixed end of the sensor and the movable end of the sensor are respectively installed together with the fixed end welding base and the movable end welding base through fastening screws, and the fixed end welding base and the movable end welding base are installed on the measured surface by welding.

[0008] Furthermore, the fixed end of the sensor is placed in the fixed end slot of the positioning plate, the two sides of the fixed end slot limit the left and right movement of the fixed end of the sensor, and a limit screw is used to prevent the fixed end of the sensor from sliding forward and backward, and the movable end of the sensor is placed in the movable end slot of the positioning plate, and the two sides of the movable end slot limit the left and right movement of the movable end of the sensor.

[0009] A method for installing and calibrating a marine fiber Bragg grating strain sensor system with integrated measurement and calibration, including an initial installation calibration method and a method for calibrating and replacing the fiber Bragg grating strain sensor during use.

[0010] (1) Initial installation calibration method

[0011] First, the fixed end of the sensor is initially welded and fixed on the measured surface, and the fiber Bragg grating strain sensor is calibrated: the high-precision differential screw is used to support the active end of the sensor, so that the fiber Bragg grating is in a relaxed state, and the return spring is installed, and the high-precision differential screw is loosened to stretch the fiber Bragg grating. When the central wavelength begins to increase and change, the initial position of the high-precision differential screw is recorded, and the fiber Bragg grating is continued to be stretched. The standard strain ε is applied to the fiber Bragg grating strain sensor. At this time, the change in the central wavelength of the fiber Bragg grating is Δλ, and the sensitivity coefficient of the fiber Bragg grating strain sensor can be obtained as k ε =Δλ / ε, and then preliminarily weld and fix the active end of the sensor to the measured surface. Then, remove the sensor calibration device and positioning plate, and then further weld and fix the fixed end and active end of the sensor.

[0012] (2) Methods for calibrating and replacing fiber Bragg grating strain sensors during use

[0013] First, install the sensor calibration device, the fixed end welding base, the movable end welding base and the positioning plate, remove the fastening screws between the movable end of the sensor and the welding base, so that the movable end of the sensor can slide freely in the movable end slot, and then calibrate the fiber Bragg grating strain sensor using the calibration fiber Bragg grating strain sensor in the initial installation calibration method; after calibration, if the sensitivity coefficient of the fiber Bragg grating strain sensor changes within the rated range, fasten the movable end of the sensor to the welding base again, restore the original state, and reset the sensitivity coefficient in the software; if the sensitivity coefficient of the fiber Bragg grating strain sensor changes beyond the rated range or even changes linearly, remove the fastening screws at the fixed end of the sensor and replace it with another calibrated fiber Bragg grating strain sensor.

[0014] The present invention has the following beneficial effects:

[0015] 1. The fiber Bragg grating strain sensor system of the present invention has been calibrated and is accurate and reliable;

[0016] 2. The fiber Bragg grating strain sensor installation tool and calibration device of the present invention are the same set of components, which can be calibrated on site, are easy to use, and can ensure the consistency of the state of the sensor during installation.

[0017] 3. The fiber Bragg grating strain sensor system of the present invention can be calibrated before installation and during use, which can ensure the stability of the sensor in long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of the fiber Bragg grating strain sensor and its calibration device of the present invention.

[0019] Figure 2 It is a schematic structural diagram of the fiber Bragg grating strain sensor of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] like Figure 1 As shown in Figure 2, a measurement and calibration integrated marine fiber Bragg grating strain sensor system consists of a fiber Bragg grating strain sensor and a sensor installation tool (calibration device). The fiber Bragg grating strain sensor includes a sensor fixed end 1, a sensor movable end 2, a protective steel pipe 3, a fiber Bragg grating 4, a fixed end welding base 8, a movable end welding base 9, and the installation tool (calibration device) includes a positioning plate 5, a high-precision differential screw 6, and a return spring 7.

[0022] One end of the pigtail of the fiber grating 4 is fixed on the fixed end 1 of the sensor, and the other end is fixed on the movable end 2 of the sensor. The distance between the two points of the fixed fiber grating 4 is the effective strain length L. The middle of the fiber grating 4 is protected by a protective steel pipe 3. The protective steel pipe 3 is fixedly connected to the fixed end 1 by a thread, and is connected to the movable end 2 by an oil seal. In this way, the movable end 2 can slide freely along the axial direction of the protective steel pipe 3, thereby transmitting the deformation between the fixed end 1 and the movable end 2 of the sensor to the fiber grating 4. The fixed end 1 and the movable end 2 are installed together with their respective welding bases by fastening screws, and the two welding bases are installed on the measured surface by welding;

[0023] The fixed end 1 of the sensor is placed in the fixed end slot of the positioning plate 5. The two sides of the fixed end slot limit the left and right movement of the fixed end 1. The limit screws are used to prevent the fixed end 1 of the sensor from sliding forward and backward. The movable end 2 of the sensor is placed in the movable end slot of the positioning plate 5. The movable end 2 of the sensor cannot move left and right in the movable end slot. The high-precision differential screw 6 is used in conjunction with the return spring 7 to control the sliding of the movable end 2 of the sensor in the forward and backward directions, and the sliding displacement ΔL can be accurately controlled, thereby applying a standard strain ε=ΔL / L to the strain sensor to achieve the installation or calibration of the fiber Bragg grating strain sensor.

[0024] The general technical concept of the present invention is that the sensitive unit of the strain sensor is a fiber Bragg grating, and its strain measurement is directly realized by stretching or compressing the fiber Bragg grating, and the structural part of the sensor is mainly used for the protection, sealing, and installation and fixing of the sensor. The two ends of the fiber Bragg grating that senses the overall deformation of the hull are respectively fixed at the fixed end of the sensor and the movable end of the sensor, and the periphery is protected by a stainless steel pipe, one end of the steel pipe is sealed and fixedly connected to the fixed end of the sensor, and the other end is sealed and slidably connected to the movable end of the sensor, and the distance between the two points where the fiber Bragg grating is fixed is a certain value, which is called the effective strain length.

[0025] According to the physical definition of strain, the corresponding relationship between strain and length change and effective strain length is established. A high-precision screw micrometer mechanism is used to generate standard displacement change, and strain calibration is achieved using the corresponding relationship between strain and length, so that the strain can be traced back to the length standard.

[0026] The calibration and installation method of the integrated measurement and calibration marine fiber Bragg grating strain sensor system of the present invention is as follows:

[0027] (1) Method for calibrating fiber Bragg grating strain sensors

[0028] The fixed end 1 of the sensor is placed in the fixed end slot of the positioning plate 5. A limit screw is used to prevent the fixed end 1 from sliding forward and backward. The movable end 2 of the sensor is placed in the movable end slot of the positioning plate 5. A high-precision differential screw 6 is used to support the movable end 2 of the sensor to make the fiber Bragg grating 4 in a relaxed state. A return spring is installed, and the differential screw 6 is loosened to stretch the fiber Bragg grating 4. When the central wavelength begins to change (increase), the initial position of the differential screw is recorded, and the fiber Bragg grating is continued to be stretched. The standard strain ε is applied to the sensor. At this time, the change in the central wavelength of the fiber Bragg grating is Δλ, and the sensitivity coefficient of the fiber Bragg grating strain sensor can be obtained as k. ε =Δλ / ε. If more calibration points are measured, the performance indicators such as the linearity of the sensor can be obtained.

[0029] (2) Installation method of fiber Bragg grating strain sensor

[0030] Place the installation tool at the sensor installation position. The surface of the installation position needs to be pre-processed. The fixed end 1 of the sensor (installed together with the welding base) is placed in the fixed end slot of the positioning plate 5. Use the limit screw to prevent the fixed end 1 from sliding forward and backward. The movable end 2 (installed together with the welding base) is placed in the movable end slot of the positioning plate 5. The fixed end 1 of the sensor is initially welded and fixed to the surface of the installation position. Use a high-precision differential screw 6 to support the movable end 2 so that the fiber grating 4 is in a relaxed state. Install the return spring, loosen the differential screw 6 to stretch the fiber grating 4. When the central wavelength begins to change (increase), record the initial position of the differential screw, continue to stretch the fiber grating, and apply a standard strain ε to the sensor. The size of ε is determined by the measurement range of the sensor (for example, if you need to measure -2000με~+2000με, then ε=+2000με). At this time, the movable end 2 is initially welded and fixed to the installation surface. After removing the installation tool, the fixed end 1 and the movable end 2 are further welded and fixed.

[0031] (3) Methods for calibrating and replacing fiber Bragg grating strain sensors during use

[0032] Install the calibration device on the sensor according to the method described above, remove the fastening screws between the sensor movable end 2 and the welding base, and the sensor movable end 2 can slide freely in the slot. At this time, the sensor can be calibrated using the method described above.

[0033] After calibration, if the sensitivity coefficient of the sensor does not change much, fasten the active end 2 of the sensor to the welding base again, restore the original state, and reset the sensitivity coefficient in the software. If the sensitivity coefficient of the sensor changes greatly or even changes linearly, remove the fastening screws at the fixed end and replace it with another calibrated strain sensor.

[0034] The present invention utilizes a high-precision differential screw to measure the deformation of a fiber Bragg grating strain sensor, designs a suitable structure to apply a standard strain signal to the sensor, and traces the strain to a length reference, thereby realizing the calibration of the fiber Bragg grating strain sensor. The ingenious structure designed by the present invention realizes integrated measurement and calibration, and uses the same system, so that the sensor can be conveniently calibrated in the laboratory or on-site, before installation or during use.

[0035] The technology of the present invention ensures the reliability of the measurement value of the marine fiber grating strain sensor, improves the ship structure health monitoring system to a certain extent, and ensures the reliability and accuracy of the monitoring data.

Claims

1. A method for installing and calibrating a ship-based fiber Bragg grating strain sensor system with integrated measurement and calibration, the ship-based fiber Bragg grating strain sensor system with integrated measurement and calibration, comprising a fiber Bragg grating strain sensor and a sensor calibration device, the fiber Bragg grating strain sensor having a fiber Bragg grating, the two ends of which are respectively fixedly connected to a fixed end of the sensor and a movable end of the sensor, the fixed end of the sensor being fixedly connected to a positioning plate via a fixed end welding base, the movable end of the sensor being connected to the positioning plate via a movable end welding base, and the movable end welding base being adjustable and movable along the positioning plate, so that the distance between the two fixed points of the fiber Bragg grating is an effective strain length L; the sensor calibration device having a high-precision differential screw and a return spring, the high-precision differential screw being fixedly connected to the positioning plate via a screw mounting seat, The screw mounting seat is connected to the movable end welding base through a return spring, so that the top of the high-precision differential screw is always in contact with the movable end welding base. The high-precision differential screw cooperates with the return spring to control the sliding of the movable end of the sensor in the front-back direction, and can accurately control the displacement ΔL of the sliding movable end of the sensor, thereby applying a standard strain ε=ΔL / L to the fiber optic Bragg grating strain sensor, thereby realizing the installation or calibration of the fiber optic Bragg grating strain sensor; the fiber optic Bragg grating is protected by a protective steel pipe in the middle, and the protective steel pipe is fixedly connected to the fixed end of the sensor by a threaded manner, and is connected to the movable end of the sensor by an oil seal, so that the movable end of the sensor can slide freely along the axial direction of the protective steel pipe, thereby transmitting the deformation between the fixed end of the sensor and the movable end of the sensor to the fiber optic Bragg grating, characterized in that The method includes the initial installation calibration method and the method of calibrating and replacing the fiber Bragg grating strain sensor during use: (1) Initial installation calibration method First, the fixed end of the sensor is initially welded and fixed on the measured surface, and the fiber Bragg grating strain sensor is calibrated: the high-precision differential screw is used to support the active end of the sensor, so that the fiber Bragg grating is in a relaxed state, and the return spring is installed, and the high-precision differential screw is loosened to stretch the fiber Bragg grating. When the central wavelength begins to increase and change, the initial position of the high-precision differential screw is recorded, and the fiber Bragg grating is continued to be stretched. The standard strain ε is applied to the fiber Bragg grating strain sensor. At this time, the change in the central wavelength of the fiber Bragg grating is Δλ, and the sensitivity coefficient of the fiber Bragg grating strain sensor can be obtained as k ε =Δλ / ε, and then preliminarily weld and fix the active end of the sensor to the measured surface. Then, after removing the sensor calibration device and positioning plate, further weld and fix the fixed end and active end of the sensor. (2) Methods for calibrating and replacing fiber Bragg grating strain sensors during use First, install the sensor calibration device, the fixed end welding base, the movable end welding base and the positioning plate, remove the fastening screws between the movable end of the sensor and the welding base, so that the movable end of the sensor can slide freely in the movable end slot, and then calibrate the fiber Bragg grating strain sensor using the calibration fiber Bragg grating strain sensor in the initial installation calibration method; After calibration, if the sensitivity coefficient of the fiber Bragg grating strain sensor changes within the rated range, tighten the active end of the sensor to the welding base again, restore the original state, and reset the sensitivity coefficient in the software. If the sensitivity coefficient of the fiber Bragg grating strain sensor changes beyond the rated range or even changes linearly, remove the fastening screws at the fixed end of the sensor and replace it with another calibrated fiber Bragg grating strain sensor.

2. The installation and calibration method of the integrated measurement and calibration marine fiber Bragg grating strain sensor system according to claim 1 is characterized by: The fixed end of the sensor and the movable end of the sensor are respectively installed with the fixed end welding base and the movable end welding base through fastening screws, and the fixed end welding base and the movable end welding base are installed on the measured surface by welding.

3. The installation and calibration method of the integrated measurement and calibration marine fiber Bragg grating strain sensor system according to claim 1, characterized in that: The fixed end of the sensor is placed in the fixed end slot of the positioning plate, and the two sides of the fixed end slot limit the left and right movement of the fixed end of the sensor, and a limit screw is used to prevent the fixed end of the sensor from sliding forward and backward. The movable end of the sensor is placed in the movable end slot of the positioning plate, and the two sides of the movable end slot limit the left and right movement of the movable end of the sensor.

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