High-temperature strain calibration device and method for all-metal packaged fiber grating sensor

Abstract

The application discloses a high-temperature strain calibration device and method for a full-metal packaged fiber grating sensor, and the device mainly comprises a small temperature control furnace, a temperature measurement and control assembly, a sensor clamping and loading assembly, a double-channel non-contact optical displacement assembly, an FBG demodulation assembly and a synchronous acquisition and data processing assembly. The device provides a stable temperature environment for the sensor in the range from room temperature to 600 DEG C, axial quasi-static loads are applied through an out-of-furnace actuator and a through-furnace thrust rod, two non-contact optical displacement measurement channels are used to obtain the relative displacement between two optical measuring points of the sensor, and the obtained mechanical strain and FBG central wavelength change are synchronously fitted. The device mainly solves the problems of sub-micron displacement measurement of a high-temperature small-gauge sample, rigid body displacement elimination, thermal drift suppression and wavelength-strain data alignment.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a high-temperature strain calibration device and method for an all-metal packaged fiber Bragg grating sensor. Background Technology

[0002] Existing all-metal packaged fiber Bragg grating (FBG) sensors are typically strain calibrated at room temperature, with temperature sensitivity coefficients and decoupling algorithms used to correct the measurement results for high-temperature applications. However, FBGs are highly sensitive to temperature changes, and the thermal expansion coefficients of the metal substrate, encapsulation layer, and silica fiber differ. At 500–600 °C, the encapsulation structure may also experience residual stress release, high-temperature creep, and changes in strain transfer efficiency, making it difficult to completely separate the temperature response from the strain response using algorithms. Therefore, room-temperature calibration results cannot accurately reflect the actual high-temperature strain characteristics of the sensor; calibration must be performed at the target temperature and under the actual encapsulation conditions.

[0003] Existing all-metal packaged fiber Bragg grating (FBG) sensors are typically strain calibrated at room temperature, and there is a lack of dedicated calibration devices for their high-temperature service conditions. However, the material properties, packaging structure, and strain transfer relationship of the sensor may change under high-temperature environments, making it difficult for room-temperature calibration results to accurately reflect its actual strain sensitivity, linearity, hysteresis, and repeatability under conditions of 500–600 °C.

[0004] Current general-purpose high-temperature strain testing typically employs a high-temperature tensile testing machine, coupled with a high-temperature extensometer, a high-temperature strain gauge, or a digital image correlation (DIP) measurement system. However, high-temperature extensometers are limited by contact force, installation space, and probe lifespan; high-temperature strain gauges are difficult to install on small-sized metal substrates, and their temperature compensation process may introduce additional errors; digital image correlation methods are easily affected by high-temperature speckle stability, window imaging quality, and furnace heat flow disturbances. For an all-metal packaged FBG sensor with an overall length of approximately 23.5 mm and a load elongation of only a few micrometers, existing general-purpose equipment struggles to simultaneously meet the requirements of small-scale high-temperature environment construction, precise axial loading, sub-micrometer-level non-contact displacement measurement, and synchronous acquisition of the FBG center wavelength.

[0005] The existing technology has the following drawbacks: 1. Measure the absolute displacement at one end of the sample. The overall movement and thermal expansion of the furnace body, fixture, push rod and mounting frame will be added to the elongation of the sample.

[0006] 2. If the beam of light shines vertically onto the sample surface through the side window of the furnace body, and the sample is subjected to force in the horizontal direction, the optical measurement direction is inconsistent with the axial displacement direction, and the axial elongation cannot be directly obtained.

[0007] 3. Multi-interface reflection of the quartz window, thermal deformation, and fluctuations in the refractive index of hot air inside the furnace can cause optical path drift and pseudo-displacement.

[0008] 4. The center wavelength of the FBG is affected by both temperature and mechanical strain; if a zero-load baseline is not established at each temperature point, the temperature drift will be mistaken for a strain response.

[0009] 5. The total length of the sensor is not necessarily equal to the effective gauge length. If the two optical measuring points do not fall at the endpoints of the total length, directly converting to 23.5 mm will result in systematic errors.

[0010] Therefore, it is necessary to develop a high-temperature strain calibration device suitable for all-metal packaged FBG sensors. Summary of the Invention

[0011] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a high-temperature strain calibration device and method for an all-metal packaged fiber Bragg grating sensor. This device mainly consists of a small temperature-controlled furnace, a temperature measurement and control component, a sensor clamping and loading component, a dual-channel non-contact optical displacement component, an FBG demodulation component, and a synchronous acquisition and data processing component. The device provides a stable temperature environment for the sensor within the range of room temperature to 600 °C. An axial quasi-static load is applied through an external actuator and a through-furnace thrust rod. Two non-contact optical displacement measurement channels are used to obtain the relative displacement between two optical measurement points of the sensor, and the obtained mechanical strain is synchronously fitted with the change in the center wavelength of the FBG. The device focuses on solving the problems of submicron displacement measurement, rigid body displacement rejection, thermal drift suppression, and wavelength-strain data alignment for high-temperature, small-gauge-length samples.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is: a high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, comprising: Temperature-controlled furnace, used to create a high-temperature calibration environment for all-metal packaged fiber Bragg grating sensors; A fixing fixture is installed at the first end inside the temperature-controlled furnace to hold the first end of the all-metal packaged fiber Bragg grating sensor. A movable clamp, installed at the second end inside the temperature-controlled furnace, is used to hold the second end of the all-metal packaged fiber Bragg grating sensor. An external actuator is located outside the temperature-controlled furnace and connected to the moving clamp via a thrust rod, used to drive the moving clamp to move axially. A load measurement component, which is disposed between the external actuator and the thrust rod, is used to measure the axial load transmitted to the sensor in real time; A dual-channel non-contact optical displacement component is disposed outside the temperature-controlled furnace and is used to measure the displacement changes at both ends of the all-metal packaged fiber optic grating sensor. Fiber Bragg grating demodulation component: It is connected to the all-metal packaged fiber Bragg grating sensor and led out from the temperature-controlled furnace, and is used to collect the spectral signals of the all-metal packaged fiber Bragg grating sensor under different temperatures and strain conditions.

[0013] Preferably, the temperature control furnace operates in the range of room temperature to 600 ℃. The furnace chamber of the temperature control furnace is provided with a sensor installation space and a fixture installation space, forming an effective temperature uniform zone with a length of not less than 50 mm along the sensor axis. The side of the temperature control furnace is provided with an optical measurement window, a thrust rod through hole, and a fiber optic cable lead-out hole.

[0014] Preferably, it also includes a temperature measurement and control component, which is installed on the temperature-controlled furnace for closed-loop control and independent monitoring of the furnace temperature; the temperature measurement and control component includes at least a temperature controller, a heating element, a control thermocouple and an independent monitoring thermocouple, the control thermocouple is used to feed back temperature signals to the temperature controller to adjust the heating power; the independent monitoring thermocouple is set near the sensor and is used to measure the actual temperature of the test area where the sensor is located.

[0015] Preferably, the fixing clamp is installed on the furnace support structure, the clamping center line of the fixing clamp coincides with the loading axis of the thrust rod, the fixing clamp is made of high temperature resistant metal material, and a clamping groove or positioning surface adapted to the shape of the sensor packaging substrate is provided.

[0016] Preferably, it also includes a sealing guide assembly, which is disposed at the furnace body through hole, so that the thrust rod moves only axially and reduces the radial swing of the thrust rod; a labyrinth seal, ceramic fiber heat insulation filler or flexible high temperature resistant sealing structure is provided between the thrust rod and the furnace wall; The thrust rod extends into the furnace chamber through a through hole on the side of the furnace body. Its inner end is connected to the moving clamp, and its outer end is connected to the actuator. It is used to transmit the axial displacement and load generated by the actuator to the sensor. The moving clamp moves along the sensor axis under the action of the thrust rod, applying tensile or compressive load to the sensor.

[0017] Preferably, the external actuator drives the thrust rod to move axially, thereby performing graded loading, load holding, and unloading of the all-metal packaged fiber optic grating sensor; the external actuator employs a precision micro-displacement stage, a lead screw loading mechanism, or an electric push-pull actuator, and is equipped with a displacement fine-tuning and position locking structure.

[0018] Preferably, it also includes an optical window assembly, which is disposed on the side wall of the furnace body to provide an optical path for dual-channel non-contact optical displacement measurement. The optical window assembly adopts two independent fused silica windows corresponding to the measurement positions at both ends of the sensor. A heat insulation screen, a light shield, and an air-cooled or water-cooled structure are disposed on the outside of the window of the optical window assembly.

[0019] Preferably, the dual-channel non-contact optical displacement assembly includes two independent optical measurement channels, corresponding to the first and second optical measurement points at both ends of the all-metal packaged fiber optic grating sensor, respectively. The two optical measurement heads are mounted on a common low thermal expansion reference frame and located outside the temperature-controlled furnace, and non-contact measurement of the measurement position inside the furnace is performed through the fused silica window.

[0020] Preferably, the sensor's fiber optic cable is led out through the fiber optic cable lead-out hole in the furnace body and connected to a fiber optic grating demodulator outside the furnace. A protective structure is provided at the position where the fiber optic cable passes through the furnace wall. The fiber optic grating demodulator outputs the sensor's center wavelength, peak intensity, and spectral signal-to-noise ratio parameters in real time. Among these parameters, the change in center wavelength serves as the main optical response quantity for high-temperature strain calibration and is displayed in real time on the industrial control computer.

[0021] A calibration method for a high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, characterized by comprising the following steps: Step 1: Install the sensor to be calibrated between the fixed fixture and the moving fixture, so that the sensor axis, the push rod axis and the actuator axis coincide; measure and record the actual gauge length L0 between the two optical measuring points; Step 2: Adjust the positions of the two optical measuring heads, windows, and reflective targets to ensure the light spot is stably positioned on the two measuring interfaces; determine the proportional coefficient, zero point, and geometric transformation coefficient C of each channel using a standard displacement stage at room temperature. g ; Step 3: Connect the pigtail to the fiber optic demodulator, and connect the thermocouple, load sensor, and two-channel optical displacement signal to the synchronous acquisition system; apply preload to eliminate mechanical backlash; Step 4: Set the target temperature T and raise the temperature. Using independent thermocouple monitoring as a reference, wait until the sample area remains stable at ±0.5 ℃ within the specified time, and the temperature difference between the two ends meets the preset limit. Then, record the zero-load baseline d. 1,0 d 2,0 and λ0,d 1,0 λ is the position of the first optical measuring point, λ is the position of the second optical measuring point, and λ0 is the center wavelength; Step 5: Load the load stepwise according to the predetermined load or displacement steps; hold each step until the temperature, displacement and center wavelength signals stabilize and then collect the average value, and then unload according to the same steps. Repeat the cycle at least multiple times for each temperature point. Step 6: Calculate the mechanical elongation ΔL and axial strain ε using the two-point difference formula, and calculate the center wavelength change Δλ based on the zero carrier length at the same temperature. B and for Δλ B The calibration is completed by fitting the -ε relationship.

[0022] The beneficial effects of this invention are: 1. Achieve high-temperature in-situ calibration: Apply mechanical load directly at the actual working temperature of 500-600 ℃ and perform strain calibration, overcoming the problem that it is difficult to accurately reflect the high-temperature strain characteristics when combined with room temperature calibration and algorithm decoupling.

[0023] 2. Dual-channel differential non-contact measurement is adopted: the displacement at both ends of the sensor is measured separately, and the actual elongation is obtained through differential calculation, which can effectively reduce common mode errors such as furnace body thermal deformation, overall movement of fixtures and environmental vibration.

[0024] 3. Improved measurement capability for minute strains: For all-metal packaged FBG sensors with a length of approximately 23.5 mm and an elongation of only submicron to several micrometers, non-contact optical measurement is adopted to avoid additional forces generated by contact probes.

[0025] 4. Integration of high-temperature environment and axial loading: The design integrates a small temperature-controlled furnace, high-temperature resistant fixture, thrust rod, sealing guide assembly and optical window to achieve accurate and continuous axial loading while ensuring temperature stability.

[0026] 5. Achieve multi-parameter synchronous calibration: Synchronously acquire temperature, load, dual-channel displacement and FBG center wavelength, and use the same temperature zero-load baseline and gauge length correction method to obtain parameters such as strain sensitivity, linearity, hysteresis and repeatability at different temperatures. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a high-temperature calibration device; Figure 2 This is a schematic diagram of the overall structure of the high-temperature strain calibration device. Detailed Implementation

[0028] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0030] This invention provides a high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, which can be applied to at least the following fields and scenarios: 1. Nuclear and thermal power valves: High-temperature calibration of all-metal encapsulated FBG strain sensors used on valve stems, valve bodies, and actuators.

[0031] 2. Aerospace and Gas Turbines: Calibration of small metal-encapsulated FBG sensors for hot-end components, pipelines and support structures.

[0032] 3. Petrochemical and high-temperature pipelines: Calibration of strain monitoring sensors for high-temperature and high-pressure pipelines, reactors, flanges, and load-bearing components.

[0033] 4. Scientific Research and Metrology: Used to study the sensitivity, hysteresis, creep, repeatability and temperature-strain coupling characteristics of metal-encapsulated FBGs at different temperatures.

[0034] Specifically, the present invention provides a high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, comprising: Small Temperature-Controlled Furnace 1: This furnace is used to create a high-temperature calibration environment for the all-metal packaged FBG sensor. Its operating temperature range is room temperature to 600℃, with a key operating temperature range of 500 to 600℃. The furnace chamber contains sensor mounting space and fixture mounting space, forming an effective temperature homogenization zone with a length of no less than 50 mm along the sensor axis, ensuring that the sensor body and its measurement areas at both ends are in a relatively uniform temperature field. During testing, the actual temperature stability of the sensor area is controlled within ±0.5℃. The side of the furnace body features an optical measurement window, a thrust rod through-hole, and a fiber optic 31 lead-out hole to meet the needs of non-contact displacement measurement, mechanical loading, and FBG signal transmission.

[0035] Temperature Measurement and Control Component 4: Used for closed-loop control and independent monitoring of furnace temperature, including at least a temperature controller, heating element, control thermocouple, and independent monitoring thermocouple. The control thermocouple feeds back temperature signals to the temperature controller to adjust the heating power; the independent monitoring thermocouple is positioned close to the sensor to measure the actual temperature of the test area where the sensor is located. Depending on the need for temperature uniformity verification, additional temperature measuring points can be added at both ends of the sensor's axial direction to monitor the temperature difference between the two ends. During calibration, the actual temperature measured by the independent monitoring thermocouple is used as the basis for temperature determination.

[0036] Fixture 21: Clamps the first end of the all-metal packaged FBG sensor body 3 (strain gauge) via a connecting block, restricting its axial and radial movement. Fixture 21 is mounted on the furnace support structure, with its clamping centerline coinciding with the loading axis of the thrust rod to reduce bending deformation caused by eccentric loading. Fixture 21 is made of high-temperature resistant metal and features clamping grooves or positioning surfaces adapted to the shape of the sensor packaging substrate. The clamping position is separated from the optical measurement position to prevent clamping deformation from directly affecting the displacement measurement results.

[0037] The movable clamp 22 clamps the second end of the all-metal encapsulated FBG sensor body 3 (strain gauge) via a connecting block and is connected to the thrust rod. The movable clamp 22 can move axially along the sensor under the action of the thrust rod, thereby applying tensile or compressive loads to the sensor. The movable clamp 22 is constrained in the radial direction to ensure the sensor axis remains stable during loading, reducing tilting, torsion, and additional bending. Sufficient clamping force should exist between the movable clamp 22 and the sensor to prevent relative slippage during high-temperature loading.

[0038] Thrust rod 51 and sealing guide assembly: The thrust rod 51 extends into the furnace chamber through the through hole 12 on the side of the furnace body. Its inner end is connected to the moving clamp 22, and its outer end is connected to the actuator, used to transmit the axial displacement and load generated by the external actuator 52 to the sensor. A high-temperature resistant guide assembly is provided at the through hole of the furnace body to ensure that the thrust rod 51 moves only axially and to reduce the radial swing of the thrust rod 51. The guide assembly can be a ceramic guide sleeve, a high-temperature resistant bushing, or other low-friction, high-temperature resistant structure. A labyrinth seal, ceramic fiber insulation filler, or a flexible high-temperature resistant sealing structure is provided between the thrust rod 51 and the furnace wall to reduce heat leakage at the through hole location and to avoid excessive additional friction force on the thrust rod 51 from the sealing structure.

[0039] External actuator 52: Used to drive the thrust rod 51 to move axially, realizing the graded loading, holding, and unloading of the all-metal packaged FBG sensor. External actuator 52 can be a precision micro-displacement stage, a lead screw loading mechanism, or an electric push-pull actuator, and is equipped with displacement fine-tuning and position locking structures. The actuator is located outside the furnace body to reduce the impact of the high-temperature environment on its motion accuracy and service life. During loading, the load is applied step-by-step according to the set displacement or load step, and held for a certain period of time under each load level. After the temperature, displacement, and center wavelength signals stabilize, calibration data is collected.

[0040] Load measurement component 53: Located between the external actuator 52 and the thrust rod 51, it is used to measure the axial load transmitted to the sensor in real time. The load measurement component 53 can employ a tension / compression sensor and is installed in series with the thrust rod 51. Its measurement results are mainly used to monitor the loading process, limit the maximum load, and identify situations such as friction of the thrust rod 51, fixture slippage, or abnormal force on the sensor. Since the sensor packaging material and fixture structure may undergo thermal deformation under high-temperature conditions, the strain calibration results of this device are based on dual-channel optical displacement measurement values, and the load measurement results serve as a basis for monitoring the loading status and for auxiliary verification.

[0041] Optical window assembly: Located on the side wall of the furnace body, it provides the optical path for dual-channel non-contact optical displacement measurement. The optical window can be two independent fused silica windows, corresponding to the measurement positions at both ends of the sensor. A heat shield, a light shield, and an air-cooling or water-cooling structure are installed on the outside of the window to reduce the influence of furnace heat radiation and hot airflow on the optical measurement. If necessary, a gas purging structure can also be installed to reduce contamination and fogging on the window surface. The window glass can be installed at an angle, have a wedge-shaped structure, or be treated with anti-reflection to reduce interference from multiple reflections and stray light on the measurement results.

[0042] Dual-channel non-contact optical displacement components 61 and 62: include two independent optical measurement channels, corresponding to the first and second optical measurement points at both ends of the all-metal packaged FBG sensor, respectively. Figure 2 (Two black dots on the sensor). Two optical measuring heads are mounted on a common low thermal expansion reference frame and located outside the temperature-controlled furnace. They perform non-contact measurements of the measurement positions inside the furnace through a fused silica window. Two channels output the displacement changes at the two ends of the sensor. By calculating the difference in displacement changes between the two channels, the axial elongation of the effective gauge length of the sensor is obtained, thereby reducing the influence of common-mode errors such as furnace thermal drift, overall fixture movement, and reference frame vibration.

[0043] When using a measurement device based on the principle of spectral interferometry, a relatively fixed transparent reference interface is set in each measurement channel, and a reflective target surface that moves synchronously with the sensor is set at both ends of the sensor. The measurement device obtains the axial displacement of the corresponding measurement point by changing the optical distance between the measurement reference interface and the reflective target surface.

[0044] FBG demodulation component: Used to acquire the spectral signals of the all-metal packaged FBG sensor under different temperature and strain conditions. The sensor's fiber optic cable 31 is led out through the fiber optic cable lead-out hole 11 in the furnace body and connected to the FBG demodulator 7 outside the furnace. A high-temperature resistant ceramic protective tube, flexible heat insulation filler, or other protective structure is installed where the fiber optic cable passes through the furnace wall to prevent the fiber optic cable from being squeezed, excessively bent, or damaged by localized high temperatures. The FBG demodulator 7 outputs parameters such as the sensor's center wavelength, peak intensity, and spectral signal-to-noise ratio in real time. The change in center wavelength serves as the main optical response quantity for high-temperature strain calibration and is displayed in real time on the industrial control computer 8.

[0045] A calibration method for a high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, characterized by comprising the following steps: Step 1: Install the sensor to be calibrated between the fixed fixture 21 and the movable fixture 22, so that the sensor axis, the push rod 51 axis and the actuator axis coincide; measure and record the actual gauge length L0 between the two optical measuring points; Step 2: Adjust the positions of the two optical measuring heads, windows, and reflective targets to ensure the light spot is stably positioned on the two measuring interfaces; determine the proportional coefficient, zero point, and geometric transformation coefficient C of each channel using a standard displacement stage at room temperature. g ; Step 3: Connect the pigtail to the fiber optic demodulator, and connect the thermocouple, load sensor, and two-channel optical displacement signal to the synchronous acquisition system; apply preload to eliminate mechanical backlash; Step 4: Set the target temperature T and raise the temperature. Using an independently monitored thermocouple as a reference, wait until the sample area remains stable at ±0.5 ℃ within the specified time, and the temperature difference between the two ends meets the preset limit. Then, record the zero-load baseline d. 1,0 d 2,0 and λ0,d 1,0 λ is the position of the first optical measuring point, λ is the position of the second optical measuring point, and λ0 is the center wavelength; Step 5: Load the load stepwise according to the predetermined load or displacement steps; hold each step until the temperature, displacement and center wavelength signals stabilize and then collect the average value, and then unload according to the same steps. Repeat the cycle at least multiple times for each temperature point. Step 6: Calculate the mechanical elongation ΔL and axial strain ε using the two-point difference formula, and calculate the center wavelength change Δλ based on the zero carrier length at the same temperature. B and for Δλ B The -ε relationship was fitted to form Δλ. B The correspondence between ε and Δλ is established to complete the calibration. B It can be directly measured, therefore, when referencing it, it is based on Δλ. B The axial strain ε can then be obtained.

[0046] Change the temperature setpoint and repeat the above steps to obtain K. ε (T) The variation law with temperature; complete the no-load thermal cycle and standard displacement verification to evaluate the thermal drift of the window and reference frame.

[0047] The two-point differential displacement measurement process is as follows: Two optical measurement channels measured the displacement readings d1 and d2 of the first and second measuring points relative to a common reference frame, respectively. At the temperature setpoint T... j After stabilization, the differential displacement baseline is first acquired under zero mechanical load: D0(T j ) = d2(T j, 0) - d1(T j ,0) When the load increases to level k F k At that time, the corresponding differential displacement is collected: D k (T j ,F k ) = d2(T j ,F k ) - d1(T j ,F k ) The sensor at temperature T j Load F k The mechanical elongation under the given conditions is calculated using the following formula: ΔL(T j ,F k ) = C g × [D k (T j ,F k ) - D0(T j )] The corresponding axial strain is calculated using the following formula: ε(T j ,F k ) = ΔL(T j ,F k ) ÷ L0(T j ) × 10 6 The unit is με.

[0048] In the formula, C g C is the optical geometric transformation coefficient used to convert displacement in the optical measurement direction into actual displacement in the sensor loading axis direction. When the optical measurement direction is parallel to the loading axis and the positive displacement directions of the two measurement channels are defined in the same way, C... g Take 1; when there is an angle between the measurement direction and the loading axis, or when a structure such as a 45° reflecting surface or a deflecting optical path is used, C gThe numerical value and sign should be determined by calibration using a room temperature standard displacement stage.

[0049] L0(T j (T) represents temperature T j The effective gauge length between two optical measurement points under certain conditions. When it is necessary to compare calibration results under different temperature conditions, the effective gauge length can be corrected according to the coefficient of thermal expansion of the sensor packaging substrate material, or the zero-load effective gauge length independently measured at that temperature can be used.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor, characterized in that, include: Temperature-controlled furnace, used to create a high-temperature calibration environment for all-metal packaged fiber Bragg grating sensors; A fixing fixture is installed at the first end inside the temperature-controlled furnace to hold the first end of the all-metal packaged fiber Bragg grating sensor. A movable clamp, installed at the second end inside the temperature-controlled furnace, is used to hold the second end of the all-metal packaged fiber Bragg grating sensor. An external actuator is located outside the temperature-controlled furnace and connected to the moving clamp via a thrust rod, used to drive the moving clamp to move axially. A load measurement component, which is disposed between the external actuator and the thrust rod, is used to measure the axial load transmitted to the sensor in real time; A dual-channel non-contact optical displacement component is disposed outside the temperature-controlled furnace and is used to measure the displacement changes at both ends of the all-metal packaged fiber optic grating sensor. Fiber Bragg grating demodulation component: It is connected to the all-metal packaged fiber Bragg grating sensor and led out from the temperature-controlled furnace, and is used to collect the spectral signals of the all-metal packaged fiber Bragg grating sensor under different temperatures and strain conditions.

2. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 1, characterized in that, The temperature control furnace operates in the range of room temperature to 600 ℃. The furnace chamber is provided with a sensor installation space and a fixture installation space, forming an effective temperature uniform zone with a length of not less than 50 mm along the sensor axis. The side of the temperature control furnace is provided with an optical measurement window, a thrust rod through hole, and a fiber optic lead-out hole.

3. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 1, characterized in that, It also includes a temperature measurement and control component, which is installed on the temperature-controlled furnace for closed-loop control and independent monitoring of the furnace temperature; the temperature measurement and control component includes at least a temperature controller, a heating element, a control thermocouple and an independent monitoring thermocouple. The control thermocouple is used to feed back a temperature signal to the temperature controller to adjust the heating power; the independent monitoring thermocouple is set near the sensor and is used to measure the actual temperature of the test area where the sensor is located.

4. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 1, characterized in that, The fixing clamp is installed on the furnace support structure. The clamping center line of the fixing clamp coincides with the loading axis of the thrust rod. The fixing clamp is made of high temperature resistant metal material and has a clamping groove or positioning surface that matches the shape of the sensor packaging substrate.

5. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 2, characterized in that, It also includes a sealing guide assembly, which is installed at the furnace body through hole to allow the thrust rod to move only axially and reduce the radial swing of the thrust rod; a labyrinth seal, ceramic fiber heat insulation filler or flexible high temperature resistant sealing structure is provided between the thrust rod and the furnace wall; The thrust rod extends into the furnace chamber through a through hole on the side of the furnace body. Its inner end is connected to the moving clamp, and its outer end is connected to the actuator. It is used to transmit the axial displacement and load generated by the actuator to the sensor. The moving clamp moves along the sensor axis under the action of the thrust rod, applying tensile or compressive load to the sensor.

6. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 5, characterized in that, The external actuator drives the thrust rod to move axially, thereby performing graded loading, load holding, and unloading of the all-metal packaged fiber optic grating sensor. The external actuator employs a precision micro-displacement stage, a lead screw loading mechanism, or an electric push-pull actuator, and is equipped with a displacement fine-tuning and position locking structure.

7. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 1, characterized in that, It also includes an optical window assembly, which is set on the side wall of the furnace body to provide an optical path for dual-channel non-contact optical displacement measurement. The optical window assembly adopts two independent fused silica windows corresponding to the measurement positions at both ends of the sensor. The outer side of the optical window assembly is provided with a heat insulation screen, a light shield, and an air-cooled or water-cooled structure.

8. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 7, characterized in that, The dual-channel non-contact optical displacement assembly includes two independent optical measurement channels, corresponding to the first and second optical measurement points at both ends of the all-metal packaged fiber optic grating sensor, respectively. The two optical measurement heads are mounted on a common low thermal expansion reference frame and located outside the temperature-controlled furnace, and non-contact measurement of the measurement position inside the furnace is performed through the fused silica window.

9. The high-temperature strain calibration device for an all-metal packaged fiber Bragg grating sensor according to claim 2, characterized in that, The sensor's fiber optic cable is led out through the fiber optic cable lead-out hole in the furnace body and connected to the fiber optic grating demodulator outside the furnace. A protective structure is provided at the point where the fiber optic cable passes through the furnace wall. The fiber optic grating demodulator outputs the sensor's center wavelength, peak intensity, and spectral signal-to-noise ratio parameters in real time. Among these parameters, the change in center wavelength serves as the main optical response quantity for high-temperature strain calibration and is displayed in real time on the industrial control computer.

10. The calibration method of the high-temperature strain calibration device for the all-metal packaged fiber Bragg grating sensor according to claim 1, characterized in that, Includes the following steps: Step 1: Install the sensor to be calibrated between the fixed fixture and the moving fixture, so that the sensor axis, the push rod axis and the actuator axis coincide; measure and record the actual gauge length L0 between the two optical measuring points; Step 2: Adjust the positions of the two optical measuring heads, windows, and reflective targets to ensure the light spot is stably positioned on the two measuring interfaces; determine the proportional coefficient, zero point, and geometric transformation coefficient C of each channel using a standard displacement stage at room temperature. g ; Step 3: Connect the pigtail to the fiber optic demodulator, and connect the thermocouple, load sensor, and two-channel optical displacement signal to the synchronous acquisition system; Apply preload to eliminate mechanical backlash; Step 4: Set the target temperature T and raise the temperature. Using independent thermocouple monitoring as a reference, wait until the sample area remains stable at ±0.5 ℃ within the specified time, and the temperature difference between the two ends meets the preset limit. Then, record the zero-load baseline d. 1,0 d 2,0 and λ0,d 1,0 λ is the position of the first optical measuring point, λ is the position of the second optical measuring point, and λ0 is the center wavelength; Step 5: Load the load stepwise according to the predetermined load or displacement steps; hold each step until the temperature, displacement and center wavelength signals stabilize and then collect the average value, and then unload according to the same steps. Repeat the cycle at least multiple times for each temperature point. Step 6: Calculate the mechanical elongation ΔL and axial strain ε using the two-point difference formula, and calculate the center wavelength change Δλ based on the zero carrier length at the same temperature. B and for Δλ B The calibration is completed by fitting the -ε relationship.

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