A multi-point grating optical cable temperature calibration device and calibration method

Abstract

The present invention discloses a multi-point grating optical cable temperature calibration device and calibration method, comprising a first optical cable reel for winding and placing a multi-point grating optical cable to be calibrated; a second optical cable reel for receiving the multi-point grating optical cable released from the first optical cable reel and passing through a constant temperature box, and the released multi-point grating optical cable being wound and arranged on the second optical cable reel; a constant temperature box having through holes on at least two opposite sides, allowing the multi-point grating optical cable to pass through one through hole into the box and pass through the other through hole out of the box; a grating demodulator connected to the multi-point grating optical cable for real-time acquisition of the reflection spectrum or central wavelength variation data of all gratings in the multi-point grating optical cable over time; and a computer for calculating and obtaining the temperature sensitivity and thermal time constant of all gratings in the multi-point grating optical cable. Therefore, the present invention can complete the calibration of the temperature sensitivity and thermal time constant of each grating in the optical cable at one time, providing more comprehensive grating temperature response characteristic parameters.

Description

Technical Field

[0001] The invention relates to a multi-point grating optical cable temperature calibration device and a calibration method, and relates to the technical field of optical fiber sensing. Background Art

[0002] Optical cables containing multiple Fiber Bragg Gratings (FBGs) are widely used in temperature monitoring. To ensure accurate temperature measurements, each FBG in the cable must be calibrated for temperature sensitivity. This involves determining how the FBG's center wavelength changes with temperature (temperature sensitivity). Furthermore, when measuring rapidly changing temperatures, the cable's structure and material affect the speed at which temperature is transferred to the FBGs in the fiber, thereby affecting the FBG's response time. The thermal time constant is often used to characterize this dynamic thermal response. Accurately understanding and compensating for this thermal time constant is crucial for improving measurement accuracy in certain applications, such as real-time monitoring of temperature transients.

[0003] Existing FBG temperature sensitivity calibration is typically performed in the laboratory using a constant temperature device (such as a thermostat or water bath). The optical cable to be calibrated is placed in a constant temperature environment, the ambient temperature is varied, and the stable value of the FBG center wavelength after reaching thermal equilibrium is recorded. A linear fit is then performed to obtain the temperature sensitivity. However, for long optical cables containing numerous FBGs, placing the entire cable in a constant temperature device for calibration is difficult. Segmented calibration requires coiling the cable and placing it in a small constant temperature chamber, which is not only inefficient, but the stress generated by the coiling can also affect the accuracy of the calibration results.

[0004] Measuring the thermal time constant typically requires rapidly subjecting the FBG to a temperature step, recording the time-varying curve of its central wavelength, and then fitting it using an exponential response model. Independently performing this temperature step response measurement on each FBG in a long-distance optical cable to obtain the thermal time constant also suffers from inefficiency and operational complexity. Furthermore, when coiling the optical cable for thermal time constant measurement, the cable structure in the coiled section may differ from the heat transfer characteristics of the straightened cable, affecting the accuracy of the measurement results.

[0005] Therefore, the prior art lacks a device and method that can efficiently and accurately calibrate the temperature sensitivity and thermal time constant of each FBG simultaneously for a long-distance optical cable containing multiple FBGs. Summary of the Invention

[0006] The present invention aims to address at least one of the technical problems existing in the prior art. To address this issue, the present invention provides a device and method for temperature calibration of a multi-point grating optical cable. These methods address the prior art issues of low efficiency, complex operation, and potentially inaccurate results in temperature sensitivity and thermal time constant calibration of long-distance optical cables containing multiple FBGs. These methods enable accurate calibration of the temperature sensitivity and thermal dynamic response characteristics of each FBG in a multi-point grating optical cable.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a multi-point grating optical cable temperature calibration device, the device comprising a first optical cable drum, a second optical cable drum, a constant temperature box, a grating demodulator, a multi-point grating optical cable and a computer, wherein:

[0009] The first optical cable reel is used for winding and placing the multi-point grating optical cable to be calibrated;

[0010] The second optical cable drum is used to receive the multi-point grating optical cable released from the first optical cable drum and passing through the constant temperature box, and the released multi-point grating optical cable is wound and arranged on the second optical cable drum;

[0011] The constant temperature box is provided with through holes on at least two opposite sides, so that the multi-point grating optical cable can pass through the box through one through hole and pass through the box through the other through hole;

[0012] The grating demodulator is connected to the multi-point grating optical cable and is used to collect the reflection spectrum or central wavelength change data of all gratings in the multi-point grating optical cable over time in real time;

[0013] The computer is used to obtain the data collected by the grating demodulator and perform fitting processing on the collected data to obtain the temperature sensitivity and thermal time constant of the gratings of all the multi-point grating optical cables.

[0014] In some possible embodiments, the constant temperature box has precise temperature control capabilities and can stabilize the temperature inside the box at multiple preset target temperature points. There are multiple constant temperature boxes, and the multiple constant temperature boxes are arranged in series to set different temperatures respectively to achieve more complex temperature profiles or faster temperature changes.

[0015] In some possible implementations, the grating interrogator is fixed to the side wall of the first optical cable drum and rotates synchronously with the first optical cable drum. The head end of the multi-point grating optical cable extends through the hole on the drum inside the first optical cable drum to the side wall and is connected to the grating interrogator. The grating interrogator sends the collected data to the computer via wired or wireless means.

[0016] In some possible implementations, a flexible sealing material is used to seal the gap at the through hole to reduce heat loss.

[0017] In some possible implementations, the first optical cable reel and the second optical cable reel both use electric optical cable reels or manual optical cable reels in conjunction with a length measuring device to achieve precise movement of the multi-point grating optical cable and grating positioning.

[0018] In a second aspect, the present invention can also provide a calibration method for a multi-point grating cable temperature calibration device, comprising:

[0019] Install and fix all components of the multi-point grating cable temperature calibration device as required;

[0020] The temperature of the constant temperature box is set to the first target temperature T1, and the temperature inside the constant temperature box is waited for to stabilize. The grating demodulator collects the reflection spectrum or central wavelength change data of the grating located in the constant temperature box over time in real time; the second optical cable drum is rotated to reel in the cable, so that the multi-point grating optical cable is released from the first optical cable drum and passes through the constant temperature box; the temperature of the constant temperature box is set to the next target temperature T2. After stabilization, the optical cable drum is rotated in the opposite direction so that the multi-point grating optical cable is released from the second optical cable drum and passes through the constant temperature box. And so on, multiple target temperature points T are set. N , and repeat the measurement for each target temperature to obtain the reflection spectrum or central wavelength change data of all gratings at several target temperatures over time;

[0021] Based on the collected reflection spectrum or central wavelength variation data of each grating at several target temperatures, a single-point single-temperature wavelength-time curve fitting is performed to obtain the fitting coefficients [b(T1), b(T2), ..., b(T N )] and [c(T1),c(T2),……,c(T N )];

[0022] For each raster, [T1, T2, ..., T N ] is the independent variable, and the fitting coefficients [c(T1), c(T2), ..., c(T N )] is the dependent variable and the temperature sensitivity of the grating is obtained by linear fitting;

[0023] For each grating, based on the fitting coefficients [b(T1), b(T2), ..., b(T N )] and the measured temperature points [T1, T2, ..., T N ], and the thermal time constant τ of the grating is calculated.

[0024] In some possible implementations, all components of the multi-point grating cable temperature calibration device are installed and fixed, including:

[0025] The multi-point grating optical cable winding reel to be calibrated is placed on the first optical cable reel. The head end of the multi-point grating optical cable extends to the side wall through the hole on the inner drum of the first optical cable reel. The grating demodulator is fixed on the side wall of the first optical cable reel. The head end of the multi-point grating optical cable is connected to the grating demodulator. The tail end of the multi-point grating optical cable is released from the first optical cable reel and connected to the second optical cable reel through the constant temperature box.

[0026] In some possible implementations, a single-point single-temperature wavelength-time curve fitting is performed based on the collected data of the reflection spectrum or central wavelength variation over time at several target temperatures of each grating to obtain a fitting coefficient, specifically:

[0027]

[0028] Where λ B (T, t) represents the central wavelength of the grating at constant temperature T and time t, a(T), b(T), and c(T) are the fitting coefficients at constant temperature T. The fitting coefficients of each grating at the target temperature can be obtained by fitting: [a(T1), a(T2), ..., a(T N )]、[b(T1),b(T2),……,b(T N )] and [c(T1),c(T2),……,c(T N )].

[0029] In some possible implementations, for each grating, [T1, T2, ..., T N ] is the independent variable, and the fitting coefficients [c(T1), c(T2), ..., c(T N )] is the dependent variable and the temperature sensitivity of the grating is obtained by linear fitting. The specific formula is:

[0030] ;

[0031] Where S is the temperature sensitivity of the grating and K is a constant.

[0032] In some possible implementations, for each grating, based on the fitting coefficients [b(T1), b(T2), ..., b(T N )] and the measured temperature points [T1, T2, ..., T N ], the thermal time constant τ of the grating is calculated, and the specific formula is:

[0033] ;

[0034] Where N is the number of temperature points measured, T i is the temperature point of measurement.

[0035] The present invention adopts the above technical solution, which has the following characteristics:

[0036] 1. Simultaneous calibration of temperature sensitivity and thermal time constant: The present invention can complete the calibration of temperature sensitivity and thermal time constant of each FBG in the optical cable at one time, providing more comprehensive FBG temperature response characteristic parameters.

[0037] 2. High efficiency: The present invention can efficiently perform batch calibration on long-distance optical cables containing multiple FBGs through a dual-cable reel guiding method, which greatly saves time and manpower.

[0038] 3. High precision: The present invention performs calibration in a controlled constant temperature box environment, avoiding interference from complex factors in the on-site environment; the straightened optical cable state is closer to the actual deployment condition (compared to coiling), and the obtained sensitivity and time constant are more accurate.

[0039] 4. Characterization of dynamic response: The present invention can accurately measure the thermal time constant affected by the optical cable structure, which helps to perform data compensation in dynamic temperature measurement applications and improve measurement accuracy.

[0040] 5. Automatic control: The entire calibration process of the present invention can be automatically controlled, including the rotation of the optical cable reel, the temperature setting of the constant temperature box, data collection and data processing.

[0041] In summary, the present invention has a wide range of applications and can be widely used in temperature characteristic calibration of various long-distance optical cables containing FBGs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0043] Figure 1 Schematic diagram of the structure of a multi-point grating optical cable temperature calibration device according to an embodiment of the present invention.

[0044] Figure 2 This is a flow chart of a multi-point grating optical cable temperature calibration method according to an embodiment of the present invention.

[0045] Figure 3 This is the FBG center wavelength-temperature acquisition and fitting result of an embodiment of the present invention.

[0046] Figure 4This is the grating temperature sensitivity fitting result of an embodiment of the present invention. DETAILED DESCRIPTION

[0047] It should be understood that the terms used herein are for the purpose of describing specific example embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "comprise", "include", "contain" and "have" are inclusive and therefore specify the presence of stated features, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the specific order described or illustrated, unless the order of execution is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0048] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates otherwise, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0049] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside," "outside," "inner side," "outer side," "lower," "upper," etc. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0050] The existing technology lacks a method that can efficiently and accurately calibrate the temperature sensitivity and thermal time constant of each FBG simultaneously for a long-distance optical cable containing multiple FBGs. The present invention provides a multi-point grating optical cable temperature calibration device and calibration method. The device comprises a first optical cable reel, a second optical cable reel, a constant temperature box, a grating demodulator, a multi-point grating optical cable, and a computer. The first optical cable reel is used for winding and placing the multi-point grating optical cable to be calibrated; the second optical cable reel is used for receiving the multi-point grating optical cable released from the first optical cable reel and passing through the constant temperature box, and the released multi-point grating optical cable is wound and arranged on the second optical cable reel; the constant temperature box has through holes on at least two opposite sides, so that the multi-point grating optical cable can pass through one through hole into the box and pass through the other through hole out of the box; the grating demodulator is connected to the multi-point grating optical cable and is used for real-time acquisition of data on the reflection spectra or central wavelength changes over time of all gratings in the multi-point grating optical cable; and the computer is used for acquiring data acquired by the grating demodulator and performing fitting processing on the acquired data to obtain the temperature sensitivity and thermal time constant of the gratings of all the multi-point grating optical cables. Therefore, the present invention can complete the calibration of the temperature sensitivity and thermal time constant of each FBG in the optical cable at one time, and provides more comprehensive FBG temperature response characteristic parameters.

[0051] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0052] Example 1: Figure 1 As shown, the multi-point grating optical cable temperature calibration device provided in this embodiment includes: a first optical cable drum 1, a second optical cable drum 2, a constant temperature box 3, a grating demodulator 4, a multi-point grating optical cable 5 and a computer 6, wherein:

[0053] The first optical cable drum 1 is used for winding and placing the multi-point grating optical cable 5 to be calibrated;

[0054] The second cable drum 2 is used to receive the multi-point grating optical cable 5 released from the first cable drum 1 and passing through the constant temperature box 3 . The released multi-point grating optical cable 5 is wound on the second cable drum 2 .

[0055] The constant temperature box 3 has through holes on at least two opposite sides, so that the multi-point grating optical cable 5 can pass through the box from one through hole and pass through the box from another through hole. The constant temperature box 3 can stabilize the internal temperature of the box at multiple preset target temperature points.

[0056] The grating demodulator 4 is connected to the multi-point grating optical cable 5 and is used for real-time and high-speed acquisition of the reflection spectra or central wavelength variation data of all FBGs in the multi-point grating optical cable 5 over time.

[0057] The computer 6 is used to obtain the data collected by the grating demodulator 4 and fit the collected FBG reflection spectrum or central wavelength change data over time to obtain the temperature sensitivity and thermal time constant of each FBG.

[0058] In a preferred embodiment of the present invention, the first cable drum 1 and the second cable drum 2 can both use electric cable drums or manual cable drums in conjunction with a length measuring device to achieve precise movement of the multi-point grating cable 5 and FBG positioning.

[0059] In a preferred embodiment of the present invention, the thermostat 3 may use a high and low temperature box, a water bath, or a temperature control device capable of achieving rapid temperature steps, that is, the thermostat 3 needs to have precise temperature control capabilities.

[0060] Furthermore, the number of the thermostats 3 can be set to multiple. When multiple thermostats 3 are set, the multiple thermostats 3 can be connected in series and set to different temperatures respectively to achieve more complex temperature profiles or faster temperature changes.

[0061] Furthermore, there is no requirement for the size of the constant temperature box 3 , but it is necessary to ensure that at least one grating is in the constant temperature box 3 in each time period.

[0062] Furthermore, measures should be taken at the through holes of the thermostat box 3 to reduce heat loss, such as using flexible sealing materials to seal the pores.

[0063] In a preferred embodiment of the present invention, the grating interrogator 4 can collect the central wavelengths of all FBGs in the multi-point grating optical cable 5. The selection of the data acquisition frequency of the central wavelength depends on the thermal time constant of the optical cable. Since the thermal time constant is related to the temperature gradient, for example, the thermal time constants of heating from 20 degrees to 30 degrees and from 20 degrees to 40 degrees are different, a relatively suitable data acquisition frequency is set to capture the details of the thermal response.

[0064] In a preferred embodiment of the present invention, the grating interrogator 4 is fixed to the side wall of the first cable drum 1 and rotates synchronously with the first cable drum 1. The head end of the multi-point grating optical cable 5 extends through the hole on the drum inside the first cable drum 1 to the side wall and is connected to the grating interrogator 4.

[0065] Furthermore, the grating demodulator 4 sends the collected data to the computer 6 in real time via wireless means such as Bluetooth or WiFi. The grating demodulator 4 can also be connected to the computer 6 in a wired manner through an electric slip ring and send the collected data to the computer 6 in real time.

[0066] Example 2: Figure 2 As shown, this embodiment also provides a multi-point grating cable temperature calibration method, including:

[0067] S1. Device connection and preparation.

[0068] In this embodiment, the winding drum of the multi-point grating optical cable 5 to be calibrated is placed on the first optical cable drum 1, and the head end of the multi-point grating optical cable 5 extends to the side wall through the hole on the drum inside the first optical cable drum 1. The grating demodulator 4 is fixed to the side wall of the first optical cable drum 1, and the head end of the multi-point grating optical cable 5 is connected to the grating demodulator 4. The tail end of the multi-point grating optical cable 5 is released from the first optical cable drum 1 and connected to the second optical cable drum 2 through the constant temperature box 3.

[0069] S2. Set the first target temperature and stabilize it.

[0070] In this embodiment, the temperature of the constant temperature box 3 is set to a first target temperature T1 (for example, 30° C.), and the temperature inside the box is waited for to stabilize to ensure that the temperature fluctuation is within the allowable range, and the current target temperature T1 is recorded.

[0071] S3. Optical cable rotation and data collection.

[0072] In this embodiment, the optical cable rotation and data collection include:

[0073] The second cable drum 2 is rotated to reel in the cable, so that the multi-point grating optical cable 5 is released from the first cable drum 1 and enters the constant temperature box 3. The first FBG is placed in the constant temperature box 3, and then the grating interrogator 4 is turned on to record the center wavelength of the FBG (for example, one center wavelength is recorded every 1 second, this is used as an example, but is not limited to this). The recording time is long enough (for example, 2 times or more of the estimated maximum thermal time constant) to ensure that the FBG reaches thermal equilibrium. Thermal equilibrium means that the temperature of the optical cable has reached the temperature inside the constant temperature box. For example, if the ambient temperature is 20 degrees Celsius, the temperature of the optical cable is 20 degrees Celsius when it is first placed in the constant temperature box. The constant temperature box is set to 30 degrees Celsius, and the optical cable begins to heat up. When the temperature of the optical cable itself reaches 30 degrees Celsius, thermal equilibrium is reached.

[0074] The second optical cable drum 2 is rotated to reel in the cable, so that the second FBG enters the constant temperature box 3, and then the above data collection process is repeated, so that data from all FBGs on the optical cable are collected.

[0075] S4. Repeat the temperature step and data acquisition.

[0076] In this embodiment, repeated temperature steps and data acquisition include:

[0077] First, the temperature of the thermostat 3 is set to the next target temperature T2 (eg, 40° C.), and the temperature is waited for stabilization.

[0078] Then, by rotating the cable drum in the opposite direction (for example, rotating the first cable drum 1 to reel in the cable), the multi-point grating cable 5 is released from the second cable drum 2 and passes through the constant temperature box 3. The data collection process of step S3 is repeated, and multiple target temperature points T1, T2, ..., T N (e.g. covering the operating temperature range of the optical cable), and repeating steps S2 and S3 for each target temperature.

[0079] In this embodiment, in addition to placing the FBG in the constant temperature box 3 for temperature increase measurement, the FBG can also be removed from the constant temperature box 3 to measure its dynamic response during the temperature reduction process, which will not be described in detail here.

[0080] S5. Single-point single-temperature wavelength-time curve fitting.

[0081] In this embodiment, for each FBG collected during the process from room temperature to a stable temperature (for example, from room temperature to T1 or from room temperature to T2, etc.), a curve fitting is performed on the change of its central wavelength over time. For example, from room temperature to T1, the grating demodulator records a set of central wavelength data every 1 second. At time t1, the central wavelength is λ B (T1, t1), the central wavelength at time t2 is λ B (T2, t2), and so on, curve fitting is performed on these data, with time t as the independent variable, λ B (T, t) is the dependent variable for fitting, and the fitting adopts the following formula:

[0082] ;

[0083] Where λ B (T, t) represents the central wavelength of the FBG at constant temperature T and time t, and a(T), b(T), and c(T) are the fitting coefficients at constant temperature T. By fitting, the fitting coefficients of each FBG at a specific temperature can be obtained:

[0084] [a(T1),a(T2),……,a(T N )]、[b(T1),b(T2),……,b(T N )] and [c(T1),c(T2),……,c(T N )].

[0085] S6. Grating temperature sensitivity calibration.

[0086] In this embodiment, for each FBG, the stable central wavelength value c(T) after it reaches thermal equilibrium at different target temperatures is extracted, and the value is expressed as [T1, T2, ..., T N ] is the independent variable, [c(T1),c(T2),……,c(T N)] is the dependent variable and the following linear fitting is performed:

[0087] ;

[0088] Where S is the temperature sensitivity of the FBG and K is a constant. By fitting each FBG, the temperature sensitivity of each FBG can be obtained.

[0089] S7. Thermal time constant calibration.

[0090] In this embodiment, for a specific FBG, its thermal time constant τ is calculated by the following formula:

[0091] ;

[0092] Where N is the number of temperature points measured, b(T i ) is the fitting coefficient of formula (1), T i is the temperature point of measurement.

[0093] like Figure 3 The central wavelength data points and linear fitting curves for a specific FBG after reaching thermal equilibrium at different target temperatures are shown. Data were collected every 30 seconds, with the oven maintained at 29.5°C, 39.0°C, and 48.6°C, respectively. The parameter fitting results are shown in Table 1.

[0094]

[0095] The coefficient c is fitted using formula (2), as follows: Figure 4 As shown, the fitting formula is, so the temperature sensitivity of the grating is 10.1 pm / °C. According to the coefficient b and formula (3), the thermal time constant of the grating can be calculated to be 6.79 s / °C.

[0096] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the reference terms "a preferred embodiment", "further", "specifically", "in the present embodiment", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A multi-point grating cable temperature calibration device, characterized in that: The device comprises a first optical cable drum, a second optical cable drum, a constant temperature box, a grating demodulator, a multi-point grating optical cable and a computer, wherein: The first optical cable reel is used for winding and placing the multi-point grating optical cable to be calibrated; The second optical cable drum is used to receive the multi-point grating optical cable released from the first optical cable drum and passing through the constant temperature box, and the released multi-point grating optical cable is wound and arranged on the second optical cable drum; The constant temperature box is provided with through holes on at least two opposite sides, so that the multi-point grating optical cable can pass through the box through one through hole and pass through the box through the other through hole; The grating demodulator is connected to the multi-point grating optical cable and is used to collect the reflection spectrum or central wavelength change data of all gratings in the multi-point grating optical cable over time in real time; The computer is used to obtain the data collected by the grating demodulator and perform fitting processing on the collected data to obtain the temperature sensitivity and thermal time constant of the gratings of all the multi-point grating cables, specifically: Based on the collected reflection spectrum or central wavelength variation data of each grating at several target temperatures, a single-point single-temperature wavelength-time curve fitting is performed to obtain the fitting coefficients [b(T1), b(T2), ..., b(T N )] and [c(T1),c(T2),……,c(T N )]; For each grating, several target temperatures [T1, T2, ..., T N ] is the independent variable, and the fitting coefficients [c(T1), c(T2), ..., c(T N )] is the dependent variable and the temperature sensitivity of the grating is obtained by linear fitting. The specific formula is: Where S is the temperature sensitivity of the grating, and K is a constant; For each grating, based on the fitting coefficients [b(T1), b(T2), ..., b(T N )] and the measured temperature points [T1, T2, ..., T N ], the thermal time constant τ of the grating is calculated, and the specific formula is: ； Where N is the number of temperature points measured, T i is the temperature point of measurement.

2. The multi-point grating optical cable temperature calibration device according to claim 1, characterized in that: The constant temperature box has precise temperature control capabilities and can stabilize the temperature inside the box at multiple preset target temperature points. There are multiple constant temperature boxes, and the multiple constant temperature boxes are arranged in series to set different temperatures respectively to achieve more complex temperature profiles or faster temperature changes.

3. The multi-point grating optical cable temperature calibration device according to claim 1, characterized in that: The grating demodulator is fixed on the side wall of the first optical cable drum and rotates synchronously with the first optical cable drum. The head end of the multi-point grating optical cable extends to the side wall through the hole on the drum inside the first optical cable drum and is connected to the grating demodulator. The grating demodulator sends the collected data to the computer via wired or wireless means.

4. The multi-point grating optical cable temperature calibration device according to claim 1, characterized in that: A flexible sealing material is also used to seal the gap at the through hole to reduce heat loss.

5. The multi-point grating optical cable temperature calibration device according to claim 1, characterized in that: The first optical cable drum and the second optical cable drum both use an electric optical cable drum or a manual optical cable drum in conjunction with a length measuring device to achieve precise movement of the multi-point grating optical cable and grating positioning.

6. A calibration method based on the multi-point grating cable temperature calibration device according to any one of claims 1 to 5, characterized in that: include: Install and fix all components of the multi-point grating cable temperature calibration device as required; The temperature of the constant temperature box is set to the first target temperature T1, and the temperature inside the constant temperature box is waited for to stabilize. The grating demodulator collects the reflection spectrum or central wavelength change data of the grating located in the constant temperature box over time in real time; the second optical cable drum is rotated to reel in the cable, so that the multi-point grating optical cable is released from the first optical cable drum and passes through the constant temperature box; the temperature of the constant temperature box is set to the next target temperature T2. After stabilization, the optical cable drum is rotated in the opposite direction so that the multi-point grating optical cable is released from the second optical cable drum and passes through the constant temperature box. And so on, multiple target temperature points T are set. N , and repeat the measurement for each target temperature to obtain the reflection spectrum or central wavelength change data of all gratings at several target temperatures over time; Based on the collected reflection spectrum or central wavelength variation data of each grating at several target temperatures, a single-point single-temperature wavelength-time curve fitting is performed to obtain the fitting coefficients [b(T1), b(T2), ..., b(T N )] and [c(T1),c(T2),……,c(T N )]; For each raster, [T1, T2, ..., T N ] is the independent variable, and the fitting coefficients [c(T1), c(T2), ..., c(T N )] is the dependent variable and the temperature sensitivity of the grating is obtained by linear fitting; For each grating, based on the fitting coefficients [b(T1), b(T2), ..., b(T N )] and the measured temperature points [T1, T2, ..., T N ], and the thermal time constant τ of the grating is calculated.

7. The calibration method according to claim 6, characterized in that: Install and fix all components of the multi-point grating cable temperature calibration device, including: The multi-point grating optical cable winding reel to be calibrated is placed on the first optical cable reel. The head end of the multi-point grating optical cable extends to the side wall through the hole on the inner drum of the first optical cable reel. The grating demodulator is fixed on the side wall of the first optical cable reel. The head end of the multi-point grating optical cable is connected to the grating demodulator. The tail end of the multi-point grating optical cable is released from the first optical cable reel and connected to the second optical cable reel through the constant temperature box.

8. The calibration method according to claim 6, characterized in that: Based on the collected data on the change of reflection spectrum or central wavelength over time at several target temperatures of each grating, a single-point single-temperature wavelength-time curve is fitted to obtain the fitting coefficient, specifically: Where λ B (T, t) represents the central wavelength of the grating at constant temperature T and time t, a(T), b(T), and c(T) are the fitting coefficients at constant temperature T. The fitting coefficients of each grating at the target temperature can be obtained by fitting: [a(T1), a(T2), ..., a(T N )]、[b(T1),b(T2),……,b(T N )] and [c(T1),c(T2),……,c(T N )].

9. The calibration method according to claim 8, characterized in that: For each raster, [T1, T2, ..., T N ] is the independent variable, and the fitting coefficients [c(T1), c(T2), ..., c(T N )] is the dependent variable and the temperature sensitivity of the grating is obtained by linear fitting. The specific formula is: Where S is the temperature sensitivity of the grating and K is a constant.

10. The calibration method according to claim 9, characterized in that: For each grating, based on the fitting coefficients [b(T1), b(T2), ..., b(T N )] and the measured temperature points [T1, T2, ..., T N ], the thermal time constant τ of the grating is calculated, and the specific formula is: ； Where N is the number of temperature points measured, T i is the temperature point of measurement.

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