Optical fiber temperature measuring method and optical fiber temperature measuring device

Abstract

The invention discloses an optical fiber temperature measuring method and an optical fiber temperature measuring device, and relates to the technical field of temperature detection.According to the optical fiber temperature measuring method, a wide temperature measuring range is divided into fine temperature measuring sub-intervals, each reference temperature corresponds to a set of reference spectrum signals, and when temperature measurement is conducted, the temperature measuring sub-intervals are divided into a plurality of fine temperature measuring sub-intervals; the measurement spectral signal is compared with each reference spectral signal, so that the corresponding reference temperature and the reference spectral signal can be used as reference regardless of the temperature change, the problem of errors caused by overlarge spectral displacement or small spectral similarity and the like is avoided, the temperature measurement error is greatly reduced, and the accuracy of temperature measurement is improved. And the problem of temperature measurement errors is avoided.

Description

Technical Field

[0001] This invention relates to the field of temperature detection technology, and in particular to an optical fiber temperature measurement method and an optical fiber temperature measurement device. Background Technology

[0002] Localized overheating in the windings of oil-immersed power transformers is a significant factor affecting their normal operation. This abnormal temperature rise accelerates the aging of materials such as insulating paperboard and insulating oil, thus shortening the transformer's lifespan. Measuring the transformer oil temperature and winding hot spot temperature can not only proactively enhance heat dissipation but also be used for early fault detection and diagnosis, preventing potential failures.

[0003] Currently, point-type temperature measurement is the most commonly used technology and product for transformer temperature measurement. This includes mechanical temperature controllers that use mechanical temperature bulbs and capillary structures, as well as fiber optic temperature measurement systems that use fluorescence, semiconductors, or fiber optic gratings. These are all point-type temperature measurements, which only measure the temperature at the location of the sensor. In order to improve the temperature measurement range of the sensor, distributed fiber optic temperature measurement technology has now been introduced, in which the entire fiber optic cable is a temperature sensor and can measure a wide range of temperatures.

[0004] In distributed fiber optic temperature measurement technology, the optical frequency domain reflectance (OFDR)-based distributed fiber optic temperature measurement technology measures temperature by detecting the frequency shift of Rayleigh scattered light in the optical fiber. This technology offers high spatial resolution, down to the millimeter level, and a measurement distance of up to hundreds of meters, making it ideal for distributed measurement of temperatures within transformers (including the temperatures of transformer oil, windings, and core).

[0005] However, existing distributed fiber optic temperature measurement techniques based on optical frequency domain reflectance (OFDR) have the following problems: When calculating temperature using the discrete cross-correlation method, the measurement range is wide. When the temperature of the measured signal does not change significantly compared to the reference signal, the spectral shift is also small, the proportion of the new spectrum in the measured spectrum is small, and the similarity between the two sets of spectra is high. However, when the temperature changes significantly, the shift of the measured spectrum relative to the reference spectrum is also large, and the proportion of the new spectrum is also large, leading to a decrease in the similarity between the two spectra. Therefore, this method has a wide measurement range, which easily leads to large calculation errors in the spectral shift, or even incorrect error calculation, resulting in large errors in the measured temperature, or even measurement errors. Summary of the Invention

[0006] The main objective of this invention is to provide a fiber optic temperature measurement method and device, which aims to solve the problem that in the prior art, a wide temperature measurement range can easily lead to large errors in temperature measurement, or even temperature measurement errors.

[0007] To achieve the above objectives, the present invention proposes an optical fiber temperature measurement method, which includes the following steps: Within the temperature measurement range, N reference temperatures are set, and a temperature measurement sub-interval is formed between any two adjacent reference temperatures, so that the temperature measurement range is divided into N-1 temperature measurement sub-intervals, where N≥3, and the reference temperatures are set at both ends of the temperature measurement range. Temperature calibration data is obtained through pre-testing, wherein the temperature calibration data includes N reference spectral signals corresponding to the reference temperatures and N-1 temperature coefficients corresponding to the temperature measurement sub-intervals; Acquire the measurement spectral signal from the temperature-sensing optical fiber; Based on the measured spectral signal and the reference spectral signal, the reference temperature and the temperature measurement sub-interval corresponding to the measured spectral signal are selected; The measurement temperature is determined based on the reference temperature obtained through screening, the temperature measurement sub-interval, the measurement spectral signal, and the temperature calibration data.

[0008] In one embodiment, the step of obtaining temperature calibration data through pre-testing includes: A temperature-sensing optical fiber is sequentially adjusted to each of the aforementioned reference temperatures, and reference spectral signals of the temperature-sensing optical fiber at each of the aforementioned reference temperatures are collected to obtain N sets of the aforementioned reference spectral signals. Each set of reference spectral signals is divided into M (M≥2) segments through a sliding window of length Δx, and each segment of the reference spectral signal is processed to obtain M local reference spectral signals; The spectral frequency shift of the corresponding segment of the two sets of local reference spectral signals for each of the temperature measurement sub-intervals is obtained by cross-correlation. Based on the spectral frequency shift and the two reference temperatures, the temperature coefficient of the temperature measurement sub-interval is obtained. The local reference spectral signal and temperature coefficient are used as the temperature calibration data.

[0009] In one embodiment, the step of filtering the reference temperature and the temperature measurement sub-interval based on the measured spectral signal and the reference spectral signal includes: The measured spectral signal is divided into M segments by a sliding window of the same length Δx, and the M segments of the measured spectral signal are processed to obtain M local measured spectral signals, wherein each segment of the local measured spectral signal corresponds to a position of the temperature measuring optical fiber. Calculate the correlation coefficient between the local measured spectral signal of each segment and the N sets of local reference spectral signals, and select the reference temperature and the local reference spectral signal corresponding to the maximum correlation coefficient; Calculate the spectral frequency shift of the local measured spectral signal and the corresponding local reference spectral signal for each segment, and select the corresponding temperature measurement sub-interval based on the reference temperature and the spectral frequency shift.

[0010] In one embodiment, the step of calculating the spectral frequency shift of each segment of the local measured spectral signal and the corresponding local reference spectral signal, and selecting the corresponding temperature measurement sub-interval based on the reference temperature and the spectral frequency shift, includes: Based on each of the reference temperatures, two temperature measurement sub-intervals adjacent to the left and right of the reference temperatures are selected; Calculate the spectral frequency shift of the local measured spectral signal and the corresponding local reference spectral signal; Based on the sign of the spectral frequency shift, the temperature measurement sub-interval to the right or to the left of the reference temperature is selected as the temperature measurement sub-interval corresponding to the local measured spectral signal.

[0011] In one embodiment, the step of determining the measurement temperature based on the selected reference temperature, the temperature measurement sub-interval, the measurement spectral signal, and the temperature calibration data includes: The temperature change is obtained by multiplying the spectral frequency shift by the temperature coefficient corresponding to the temperature measurement sub-interval. The measured temperature of the local measurement spectral signal is obtained by superimposing the temperature change amount with the reference temperature corresponding to the local measurement spectral signal.

[0012] In one embodiment, the step of acquiring the measurement spectral signal of the temperature-measuring optical fiber includes: Acquire the P signal and S signal carrying the temperature information of the temperature measuring optical fiber; The P signal and the S signal are subjected to Fast Fourier Transform respectively to obtain the P spectral signal and the S spectral signal, and the P spectral signal and the S spectral signal are combined to obtain the measurement spectral signal; The steps of dividing the measured spectral signal into M segments through a sliding window of the same length Δx, and processing the M segments of the measured spectral signal to obtain the M segment local measured spectral signals include: The measured spectral signal is divided into M segments by passing it through a sliding window of the same length Δx; Perform a fast inverse Fourier transform on each segment of the measured spectral signal to obtain M segments of the local measured spectral signal.

[0013] The present invention also provides an optical fiber temperature measuring device, comprising: A tunable laser for outputting linearly frequency-modulated laser light; A first beam splitter is disposed at the output end of the tunable laser and is used to split the linearly frequency-modulated laser into a first beam and a second beam. A temperature-sensing optical fiber, wherein the temperature-sensing optical fiber is disposed on the device under test; The main interferometer includes a first fiber circulator, a polarization beam splitter, and a coupling module. The first fiber circulator is connected to both the temperature-sensing fiber and the polarization beam splitter. After the first light beam enters the main interferometer, it passes through the first fiber circulator and enters the temperature-sensing fiber. After passing through the temperature-sensing fiber, the first light beam forms backscattered Rayleigh light carrying fiber temperature information. The backscattered Rayleigh light returns to the first fiber circulator and enters the polarization beam splitter, which splits it into P-beams and S-beams. The P-beams and S-beams enter the coupling module and are coupled separately. The backscattered Rayleigh light, coupled by the coupling module, is input into the optical detection module, and P and S signals are output from the optical detection module. The clock module includes an auxiliary interferometer, a photodetector, and a frequency multiplier module that are sequentially turned on. After the second beam enters the auxiliary interferometer, it is converted into a sinusoidal beat frequency signal by the photodetector. The frequency multiplier module is used to multiply and amplify the sinusoidal beat frequency signal and convert it into a clock signal. The signal acquisition and analysis module acquires the clock signal, the P signal, and the S signal. The information acquisition and analysis module converts the P signal and the S signal into a measurement spectral signal and executes the above-described fiber optic temperature measurement method to obtain the temperature of the device under test.

[0014] In one embodiment, the main interferometer further includes a second beam splitter and a third beam splitter, the coupling module includes a first coupler and a second coupler, the second beam splitter is connected to the first beam splitter, the two outputs of the second beam splitter are connected to the first fiber circulator and the third beam splitter respectively, the polarization beam splitter is connected to the first coupler and the second coupler respectively, and the third beam splitter is connected to the first coupler and the second coupler respectively; The first beam is split into a first sub-beam and a second sub-beam by the second beam splitter. The first sub-beam is injected into the temperature-sensing fiber through the first fiber circulator. After passing through the temperature-sensing fiber, the first sub-beam forms back Rayleigh scattered light carrying fiber temperature information. The back Rayleigh scattered light returns to the first fiber circulator and is injected into the polarization beam splitter. The polarization beam splitter splits the back Rayleigh scattered light into P-beam and S-beam, and injects the P-beam and the S-beam into the first coupler and the second coupler, respectively. The second sub-beam is split by the third beam splitter and then incident on the first coupler and the second coupler respectively. The first coupler is used to couple the P-beam with a portion of the second sub-beam and input it into the optical detection module. The second coupler is used to couple the S-beam with another portion of the second sub-beam and input it into the optical detection module. The optical detection module includes a first balanced detector and a second balanced detector. The first balanced detector is connected to the first coupler, and the second balanced detector is connected to the second coupler. The first balanced detector is used to convert the mixed light output from the first coupler into a P-signal and output it to the signal acquisition and analysis module. The second balanced detector is used to convert the mixed light output from the second coupler into an S-signal and output it to the signal acquisition and analysis module.

[0015] In one embodiment, the auxiliary interferometer includes a second fiber optic circulator, a fourth beam splitter, a first Faraday rotator, and a second Faraday rotator. The second fiber optic circulator is connected to the first beam splitter, the fourth beam splitter, and the frequency multiplication module. The two outputs of the fourth beam splitter are connected to the first Faraday rotator and the second Faraday rotator, respectively. A time-delay fiber is disposed between the second Faraday rotator and the fourth beam splitter. The second beam enters the fourth beam splitter through the second fiber optic circulator. The second beam is split into a third sub-beam and a fourth sub-beam by the fourth beam splitter. The third sub-beam is reflected back to the fourth beam splitter after being reflected by the first Faraday rotator. The fourth sub-beam enters the second Faraday rotator after passing through the time-delay fiber, and after being reflected by the second Faraday rotator, it returns to the fourth beam splitter after passing through the time-delay fiber again. The third sub-beam reflected by the first Faraday rotator and the fourth sub-beam reflected by the second Faraday rotator are combined and then enter the photodetector through the second fiber optic circulator. The frequency multiplication module includes a harmonic generator, a frequency selection circuit, an amplifier, and a waveform converter that are sequentially turned on. The sinusoidal beat frequency signal generates harmonics through the harmonic generator. The frequency selection circuit is used to suppress the fundamental frequency and other unwanted harmonics, so as to output the harmonics of the harmonics to the amplifier. The amplifier is used to amplify the harmonics and output them to the waveform converter. The waveform converter is used to convert the amplified harmonics into the clock signal in the form of a square wave.

[0016] In one embodiment, the temperature-measuring optical fiber includes an optical fiber body, a first sleeve, and a second sleeve sequentially sleeved from the inside out. The outer edge of the optical fiber body slides in contact with the inner wall of the first sleeve, and the outer wall of the first sleeve slides in contact with the inside of the second sleeve.

[0017] In the technical solution of this invention, based on the temperature measurement accuracy requirements, reference spectral signals corresponding to N reference temperatures and temperature coefficients corresponding to N-1 temperature measurement sub-intervals are obtained through pre-testing. Correlation coefficients are calculated between the measured spectral signals and the reference spectral signals corresponding to the N reference temperatures. Based on the correlation coefficients, the reference temperature closest to the measured spectral signal and the reference spectral signal corresponding to that reference temperature are obtained. Then, the difference between the spectral signal and the reference spectral signal is measured to obtain the rise or fall of the measured temperature relative to the reference temperature, thereby obtaining the temperature measurement sub-interval where the measured temperature is located. Finally, the temperature change of the measured temperature relative to the reference temperature is calculated using the temperature measurement sub-interval, the reference temperature, and the temperature coefficients in the temperature calibration data, thereby accurately obtaining the measured temperature.

[0018] This invention divides a wide temperature measurement range into finely segmented temperature measurement sub-intervals. Each reference temperature corresponds to a set of reference spectral signals. During temperature measurement, the measured spectral signal is compared with each reference spectral signal. This ensures that regardless of the magnitude of the temperature change, there is always a corresponding reference temperature and reference spectral signal as a reference. This avoids problems such as excessive spectral shift or low spectral similarity that could lead to errors, thus significantly reducing temperature measurement errors and eliminating the problem of temperature measurement mistakes. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 A flowchart of an embodiment of the fiber optic temperature measurement method provided by the present invention; Figure 2 This is a schematic diagram of a fiber optic temperature measurement device provided in an embodiment of the present invention.

[0021] Explanation of icon numbers: 100. Fiber optic temperature measurement device; 10. Tunable laser; 20. First beam splitter; 30. Temperature-measuring fiber; 40. Main interferometer; 401. Second beam splitter; 402. Third beam splitter; 403. Polarization beam splitter; 41. First fiber optic circulator; 42. Coupler module; 421. First coupler; 422. Second coupler; 50. Optical detection module; 51. First balanced detector; 52. Second balanced detector; 60. Clock module; 61. Auxiliary interferometer; 611. Second fiber optic circulator; 612. Fourth beam splitter; 613. First Faraday rotator; 614. Second Faraday rotator; 615. Delay fiber; 62. Optical detector; 63. Frequency multiplier module; 631. Harmonic generator; 632. Frequency selection circuit; 633. Amplifier; 634. Waveform converter; 70. Signal acquisition and analysis module; 80. Switching optical switch.

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0025] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0026] Existing distributed fiber optic temperature measurement technology based on optical frequency domain reflectance (OFDR) suffers from the following problems: When calculating temperature using the discrete cross-correlation method, its temperature measurement range is wide. When the temperature of the measured signal does not change significantly compared to the reference signal, the spectral shift is also small, the proportion of the new spectrum in the measured spectrum is small, and the similarity between the two sets of spectra is high. However, when the temperature change is large, the shift of the measured spectrum relative to the reference spectrum is also large, and the proportion of the new spectrum is also large, leading to a decrease in the similarity between the two spectra. Therefore, this method has a wide temperature measurement range, which easily leads to large calculation errors in the spectral shift, or even incorrect error calculation, resulting in large errors in the measured temperature, or even measurement errors.

[0027] To address the above problems, this invention proposes a fiber optic temperature measurement method.

[0028] Please see Figure 1 The fiber optic temperature measurement method in this embodiment includes the following steps: S100: N reference temperatures are set within the temperature measurement range, and a temperature measurement sub-interval is formed between any two adjacent reference temperatures, so as to divide the temperature measurement range into N-1 temperature measurement sub-intervals, where N≥3, and the reference temperatures are set at both ends of the temperature measurement range. The number of reference temperatures is set according to the temperature measurement accuracy requirements of the device under test. If the temperature measurement accuracy requirement of the device under test is high, the value of N is increased; if the temperature measurement accuracy requirement of the device under test is low, the value of N is decreased. According to the designed temperature measurement range, N discrete reference temperature points are selected within the temperature measurement range, so that two adjacent reference temperatures form a temperature measurement sub-interval, thereby dividing the entire temperature measurement range into N-1 continuous temperature measurement sub-intervals. Specifically, when applied to transformer temperature measurement, the temperature measurement range can be selected from -40 to 200℃. Within the range, -40℃, 0℃, 40℃, 80℃, 120℃, 160℃, and 200℃ are set, for a total of 7 reference temperatures and 6 temperature measurement sub-intervals. For the 7 reference temperatures, 7 sets of reference signals are collected and local reference spectral signals are calculated. For the 6 temperature measurement sub-intervals, 6 sets of temperature coefficients are obtained through calibration calculation. For transformers, this temperature measurement range and temperature measurement sub-interval can meet the temperature monitoring needs of transformers under various operating conditions such as low temperature start-up, high load operation and abnormal overheating. It is conducive to realizing accurate and reliable distributed measurement of the temperature of key parts of transformers, and provides a reliable data foundation for transformer operation status assessment and fault early warning. S200: Temperature calibration data is obtained through pre-testing, wherein the temperature calibration data includes N reference spectral signals corresponding to the reference temperatures and N-1 temperature coefficients corresponding to the temperature measurement sub-intervals; Pre-testing to obtain temperature calibration data provides a reference for subsequent actual temperature measurements; S300: Acquires the measurement spectral signal from the temperature-measuring fiber; S400: Based on the measured spectral signal and the reference spectral signal, filter the reference temperature and the temperature measurement sub-interval corresponding to the measured spectral signal; S500: Determine the measurement temperature based on the reference temperature obtained through screening, the temperature measurement sub-interval, the measurement spectral signal, and the temperature calibration data.

[0029] In the technical solution of this invention, based on the temperature measurement accuracy requirements, reference spectral signals corresponding to N reference temperatures and temperature coefficients corresponding to N-1 temperature measurement sub-intervals are obtained through pre-testing. Correlation coefficients are calculated between the measured spectral signals and the reference spectral signals corresponding to the N reference temperatures. Based on the correlation coefficients, the reference temperature closest to the measured spectral signal and the reference spectral signal corresponding to that reference temperature are obtained. Then, the difference between the spectral signal and the reference spectral signal is measured to obtain the rise or fall of the measured temperature relative to the reference temperature, thereby obtaining the temperature measurement sub-interval where the measured temperature is located. Finally, the temperature change of the measured temperature relative to the reference temperature is calculated using the temperature measurement sub-interval, the reference temperature, and the temperature coefficients in the temperature calibration data, thereby accurately obtaining the measured temperature.

[0030] This invention divides a wide temperature measurement range into finely segmented temperature measurement sub-intervals. Each reference temperature corresponds to a set of reference spectral signals. During temperature measurement, the measured spectral signal is compared with each reference spectral signal. This ensures that regardless of the magnitude of the temperature change, there is always a corresponding reference temperature and reference spectral signal as a reference. This avoids problems such as excessive spectral shift or low spectral similarity that could lead to errors, thus significantly reducing temperature measurement errors and eliminating the problem of temperature measurement mistakes.

[0031] In one embodiment, step S200 includes: S210: The temperature-sensing optical fiber is sequentially adjusted to each of the aforementioned reference temperatures, and the reference spectral signals of the temperature-sensing optical fiber at each of the aforementioned reference temperatures are collected respectively to obtain N sets of the aforementioned reference spectral signals; S220: Divide each set of reference spectral signals into M (M≥2) segments through a sliding window of length Δx, and process each segment of the reference spectral signal to obtain M local reference spectral signals; Each set of reference spectral signals is divided into M segments by a sliding window of length Δx, and each segment of the reference spectral signal is processed to obtain M segments of local reference spectral signals. A total of N sets of local reference spectral signals corresponding to N reference temperatures are obtained. Each set of local reference spectral signals includes M segments of local reference spectral signals, where Δx is 1mm~20mm. It should be noted that the number of segments M into which the reference spectral signal is divided is equal to the length of the temperature-sensing fiber optic cable and the sliding window step size. Generally, the step size can be taken as equal to the sliding window length Δx. The length Δx of the sliding window is the temperature measurement spatial resolution, which can be set manually. In this application, it is 1mm to 20mm, and its value cannot be less than the system's highest spatial resolution. ( The smaller the value, the higher the spatial resolution.

[0032] in, Here, λ is the center wavelength of the tunable laser discussed later, and n is the refractive index of the fiber core. This section describes the frequency tuning range of the tunable laser. It should be emphasized that this section is an explanation of how this temperature testing method is implemented in the testing device and does not affect the procedure of this method.

[0033] S230: Obtain the spectral frequency shift of the corresponding segment of the two sets of local reference spectral signals for each of the temperature measurement sub-intervals by using cross-correlation; and obtain the temperature coefficient of the temperature measurement sub-interval based on the spectral frequency shift and the two reference temperatures. Each of the temperature measurement sub-intervals has two reference temperatures at its two ends. Cross-correlation is performed on the corresponding segments of the two sets of local reference spectral signals corresponding to each temperature measurement sub-interval to obtain the spectral frequency shift. The spectral frequency shift is then divided by the temperature difference between the two reference temperatures in the corresponding temperature measurement sub-interval to obtain the temperature coefficient corresponding to the temperature measurement sub-interval. A total of N-1 temperature coefficients are obtained. S240: Use the local reference spectral signal and temperature coefficient as the temperature calibration data; The temperature calibration data consists of N sets of local reference spectral signals corresponding to N reference temperatures and N-1 temperature coefficients corresponding to N-1 temperature measurement sub-intervals.

[0034] In this embodiment, reference spectral signals at various reference temperatures are acquired during the pre-testing phase. N sets of local reference spectral signals are obtained by segmenting the data using a sliding window of 1mm to 20mm. Furthermore, the temperature coefficients corresponding to the temperature measurement sub-intervals are calculated based on the local reference spectral signals corresponding to adjacent reference temperatures, ultimately constructing complete temperature calibration data. By discretizing the originally continuous and relatively wide temperature measurement range into multiple reference temperatures and multiple temperature measurement sub-intervals, a reference basis highly matched to the local measured spectral signals is always present during the temperature calculation process. This avoids calculation errors caused by excessive overall spectral shift due to large temperature variations, thereby significantly improving the stability and accuracy of temperature measurement.

[0035] In one embodiment, step S400 includes: S410: Divide the measured spectral signal into M segments through a sliding window of the same length Δx, and process the M segments of the measured spectral signal to obtain M segments of local measured spectral signals, wherein each segment of the local measured spectral signal corresponds to a position of the temperature measuring optical fiber. S420: Calculate the correlation coefficient between the local measured spectral signal of each segment and the N sets of local reference spectral signals, and select the reference temperature and the local reference spectral signal corresponding to the maximum correlation coefficient; S430: Calculate the spectral frequency shift of the local measured spectral signal and the corresponding local reference spectral signal for each segment, and select the corresponding temperature measurement sub-interval based on the reference temperature and the spectral frequency shift.

[0036] The measured spectral signal is divided into M segments by a sliding window of length Δx. Each segment is then processed to obtain a local measured spectral signal, ensuring that the length of the local measured spectral signal corresponds to the length of the local reference spectral signal, thus improving the comparison accuracy. The correlation coefficient of each local measured spectral signal is calculated with N sets of local reference spectral signals. Based on the correlation coefficient, the closest reference temperature and the corresponding local reference spectral signal are obtained. The spectral frequency shift of the local measured spectral signal and its corresponding local reference spectral signal are then calculated to obtain the change in temperature between the measured temperature and the reference temperature. This identifies the temperature measurement sub-interval where the measured temperature is located. The temperature change between the measured temperature and the reference temperature is calculated using the spectral frequency shift and the temperature coefficient corresponding to the temperature measurement sub-interval, thereby accurately obtaining the measured temperature.

[0037] In one embodiment, step S430 includes: S431: Select two temperature measurement sub-intervals that are adjacent to the left and right of the reference temperatures based on the reference temperatures; S432: Calculate the spectral frequency shift of the local measured spectral signal and the corresponding local reference spectral signal; S433: Based on the sign of the spectral frequency shift, select the temperature measurement sub-interval to the right or to the left of the reference temperature as the temperature measurement sub-interval corresponding to the local measurement spectral signal.

[0038] By first selecting adjacent temperature measurement sub-intervals based on the reference temperature, and then accurately selecting the temperature measurement sub-interval corresponding to the current local measurement spectral signal based on the positive or negative relationship between the spectral frequency shift between the local measured spectral signal and the corresponding local reference spectral signal, the temperature calculation is limited to the closest temperature measurement sub-interval. This avoids the problems of excessive displacement and reduced similarity caused by directly calculating the spectral frequency shift within a wide temperature measurement range, ensuring that the spectral frequency shift remains within a small range. This effectively reduces the risk of misjudging the temperature measurement sub-interval and making temperature calculation errors, thereby improving the reliability of the temperature measurement results.

[0039] In one embodiment, step S500 includes: S510: The temperature change is obtained by multiplying the spectral frequency shift by the temperature coefficient corresponding to the temperature measurement sub-interval; S520: The temperature change is superimposed with the reference temperature corresponding to the local measurement spectral signal to obtain the measured temperature of the local measurement spectral signal.

[0040] In one embodiment, step S300 includes: S310: Acquire the P signal and S signal carrying the temperature information of the temperature-measuring optical fiber; Specifically, a distributed optical fiber temperature measurement system based on optical frequency domain reflection is used to scan the temperature measuring fiber and collect the P signal and S signal formed by Rayleigh scattering in the temperature measuring fiber. The P signal and the S signal respectively carry the spatial distribution information and frequency domain information of the temperature measuring fiber under the current temperature state. S320: Perform fast Fourier transform on the P signal and the S signal respectively to obtain the P spectral signal and the S spectral signal, and synthesize the P spectral signal and the S spectral signal to obtain the measurement spectral signal; Specifically, the P signal and the S signal are processed by Fast Fourier Transform to convert the time-domain or spatial-domain signals to the frequency domain, resulting in the corresponding P-spectral signal and S-spectral signal. Subsequently, the P-spectral signal and the S-spectral signal are synthesized to form a measurement spectral signal that can completely characterize the temperature information of the temperature-measuring fiber, providing basic data for subsequent segmentation processing and temperature calculation.

[0041] In this embodiment, P-signal and S-signal carrying temperature information from the temperature-measuring fiber are acquired separately, and fast Fourier transforms are performed on the P-signal and S-signal respectively to obtain P-spectral signal and S-spectral signal. Then, the P-spectral signal and S-spectral signal are synthesized to obtain the measurement spectral signal, which simultaneously incorporates the temperature-related information contained in the P-signal and S-signal. This improves the completeness and stability of the measurement spectral signal in representing the temperature change of the temperature-measuring fiber, providing higher signal-to-noise ratio and more comprehensive basic data for subsequent segmented processing, correlation coefficient calculation, and spectral frequency shift calculation, thus improving the accuracy and reliability of temperature calculation.

[0042] Step S410 includes: S411: Divide the measured spectral signal into M segments through a sliding window of the same length Δx; S412: Perform a fast inverse Fourier transform on each segment of the measured spectral signal to obtain the M segments of the local measured spectral signal.

[0043] The measured spectral signal is divided into M segments by a sliding window of length Δx. Each segment undergoes an inverse fast Fourier transform to obtain M local measured spectral signals, ensuring a one-to-one correspondence between each local measured spectral signal and a specific spatial location on the temperature-sensing fiber. This achieves spatial resolution processing of the measured spectral signal, transforming temperature measurement from a holistic measurement to a distributed measurement along the temperature-sensing fiber. This lays the foundation for subsequent segment-by-segment matching of reference temperatures and temperature-sensing sub-intervals, thereby improving the spatial resolution and local temperature measurement accuracy of the temperature measurement system.

[0044] It should be noted that when obtaining temperature calibration data during the pre-test, i.e., in steps S210 and S220, the acquisition of the reference spectral signal and the local reference signal adopts the same method as the acquisition of the measured spectral signal and the local measured spectral signal.

[0045] More specifically, step S210 includes: S211: The temperature-sensing optical fiber is sequentially adjusted to N reference temperatures, and N sets of P signals and S signals of the temperature-sensing optical fiber are acquired, wherein each set of P signals and S signals corresponds to a reference temperature. S212: Perform fast Fourier transform on the N sets of P signals and the S signals respectively to obtain N sets of P spectral signals and S spectral signals, and synthesize the N sets of P spectral signals and the S spectral signals respectively to obtain N sets of reference spectral signals, so as to obtain N sets of reference spectral signals corresponding to N reference temperatures. Step S220 includes: S221: Divide the N sets of reference spectral signals into M segments by passing them through sliding windows of the same length Δx, to obtain M segments of reference spectral signals; S222: Perform a fast inverse Fourier transform on each of the reference spectral signals in the N groups to obtain M local reference spectral signals, and obtain a total of N groups of local reference spectral signals corresponding to the N reference temperatures. Each group of local reference spectral signals includes M local reference spectral signals.

[0046] The reference spectral signal and the measured spectral signal are processed in the same way, which ensures the comparability and consistency between the reference spectral signals at different reference temperatures, reduces the systematic error introduced by the inconsistency of signal processing methods, and thus improves the accuracy of subsequent local reference spectral signal matching and temperature coefficient calibration.

[0047] Existing distributed fiber optic temperature measurement technologies based on optical frequency domain reflection (OFDR) still have the following problems: When compensating for the nonlinearity of the tunable laser sweep frequency using an auxiliary interferometer, the Nyquist sampling theorem restricts the use of the auxiliary interferometer's beat frequency signal as the sampling clock, resulting in the temperature-sensing fiber not exceeding one-quarter of the optical path difference length of the auxiliary interferometer fiber, thus limiting the sensing distance; the auxiliary interferometer's beat frequency signal is not used as a clock signal, but is acquired by the acquisition card along with the main interferometer's beat frequency signal, and when compensated by the algorithm, it increases the signal processing computation and data processing time, bringing a huge computational burden.

[0048] Please see Figure 1The fiber optic temperature measurement device 100 of this embodiment includes a tunable laser 10, a first beam splitter 20, a temperature-sensing fiber 30, a main interferometer 40, a light detection module 50, a clock module 60, and a signal acquisition and analysis module 70. The tunable laser 10 is used to output linearly frequency-modulated laser light. The first beam splitter 20 is disposed at the output end of the tunable laser 10 and is used to split the linearly frequency-modulated laser light into a first beam and a second beam. The temperature-sensing fiber 30 is disposed on the device under test. The main interferometer 40 includes a first fiber circulator 41, a polarization beam splitter 403, and a coupling module 42. The first fiber circulator 41 is connected to the temperature-sensing fiber 30 and the polarization beam splitter 403, respectively. After the first beam enters the main interferometer 40, it enters the temperature-sensing fiber 30 through the first fiber circulator 41. After passing through the temperature-sensing fiber 30, the first beam forms backscattered Rayleigh light carrying fiber temperature information. The backscattered Rayleigh light returns to the first fiber circulator 41 and enters the device under test. A polarization beam splitter 403 splits the beam into P-beams and S-beams, which are then coupled into a coupling module 42. The backscattered Rayleigh beam after coupling by the coupling module 42 is input into a photodetector module 50, which outputs P-signals and S-signals. A clock module 60 includes an auxiliary interferometer 61, a photodetector 62, and a frequency multiplier module 63, which are sequentially activated. After the second beam enters the auxiliary interferometer 61, it is converted into a sinusoidal beat frequency signal by the photodetector 62. The frequency multiplier module 63 amplifies the sinusoidal beat frequency signal and converts it into a clock signal. The clock signal, P-signal, and S-signal are all input into a signal acquisition and analysis module 70. The signal acquisition and analysis module 70 acquires the clock signal, P-signal, and S-signal, converts the P-signal and S-signal into the spectrum signal to be measured, and performs the fiber optic temperature measurement method described above to obtain the temperature of the device under test.

[0049] When the fiber optic temperature measuring device 100 of the present invention is used, the tunable laser 10 is first activated to output linear frequency modulated laser. The output linear frequency modulated laser is split into a first beam and a second beam by a first beam splitter. The first beam is used to enter the main interferometer 40 and enter the temperature measuring fiber 30 to measure the temperature of the temperature measuring fiber 30. The second beam is used to enter the clock module 60 and output a clock signal to provide a clock reference. After the first beam enters the main interferometer 40, it first enters the first fiber optic circulator 41, which guides the first beam into the temperature-sensing fiber 30. The first beam propagates along the temperature-sensing fiber 30, generating Rayleigh scattering at various scattering points. The backscattered Rayleigh light carrying temperature information at various locations on the fiber returns along the temperature-sensing fiber 30 and re-enters the first fiber optic circulator 41. The first fiber optic circulator 41 guides the backscattered Rayleigh light to the polarization beam splitter 403, which splits the backscattered Rayleigh light into P-beams and S-beams and injects them into the coupling module 42. The coupling module 42 couples the P-beams and S-beams and transmits them to the optical detection module 50. The optical detection module 50 converts the backscattered Rayleigh light into P-signals and S-signals carrying temperature information of the temperature-sensing fiber 30 and outputs them to the signal acquisition and analysis module 70. After the second beam enters the auxiliary interferometer 61, a fixed optical path difference is formed between the two optical paths of the auxiliary interferometer 61. Since the tunable laser 10 outputs a linearly frequency-modulated laser, the optical path difference between the two optical paths will form a time-varying beat frequency signal on the photodetector 62. The sinusoidal beat frequency signal from the photodetector 62 enters the frequency multiplier module 63, which multiplies the sinusoidal beat frequency signal, increasing its frequency several times, and outputs it as a clock signal to the signal acquisition and analysis module 70. Since the frequency is effectively increased, the optical path difference of the auxiliary interferometer 61 is effectively "amplified", thus enabling the system to support a longer temperature-sensing fiber optic cable 30. The signal acquisition and analysis module 70 receives the clock signal output by the frequency multiplier module 63; using this clock signal as the sampling clock, it performs high-speed analog-to-digital conversion on the P signal and S signal output by the photodetector module 50, and uses the above-mentioned fiber optic temperature measurement method to solve the P signal and S signal into the specific temperature information of the temperature-sensing fiber optic cable 30, thereby obtaining the actual temperature information of the transformer.

[0050] In the technical solution of this invention, after the second beam enters the auxiliary interferometer 61, it is converted into a sinusoidal beat frequency signal by the photodetector 62. Then, the sinusoidal beat frequency signal is multiplied and amplified by the frequency multiplier module 63 to obtain a high-frequency clock signal. The information acquisition module uses this clock signal to perform analog-to-digital conversion on the P signal and S signal carrying the fiber temperature signal, and then performs temperature calculation. Thus, the temperature at each position of the temperature-measuring fiber 30 is calculated through the P signal and S signal, and the temperature of the device under test is reflected by the temperature of the temperature-measuring fiber 30. Since the beat frequency signal generated by the auxiliary interferometer 61 is not acquired together with the main interferometer 40 and compensated by the algorithm, there is no problem of increasing the signal processing computation and data processing time, thus reducing the computational burden. Furthermore, because the sinusoidal beat frequency signal is amplified by the frequency multiplier module 63, normally the fiber length needs to be extended to obtain a high frequency. However, the auxiliary interferometer 61 can achieve a high frequency without extending the fiber through the frequency multiplier module 63. Increasing the frequency is equivalent to the auxiliary interferometer 61 obtaining a larger optical path difference, thereby increasing the length of the temperature-sensing fiber 30 and increasing the sensing distance. This invention increases the signal frequency in the auxiliary interferometer 61 by using the frequency multiplier module 63 and processes the beat frequency signal of the auxiliary interferometer 61 as a clock signal, which reduces the increase in signal processing computation and data processing time, lowering the computational burden, and also extends the length of the temperature-sensing fiber 30.

[0051] In one embodiment, the first beam splitter 20 has a splitting ratio of 95:5, wherein 95% of the light enters the main interferometer 40 as the first beam and 5% of the light enters the clock module 60 as the second beam.

[0052] Since the main interferometer 40 needs to process the backscattered Rayleigh light generated in the temperature-sensing fiber 30 and relies on high optical power to improve the contrast of the interference fringes, allocating 95% of the light to the main interferometer 40 can effectively improve the signal-to-noise ratio of P-beams to S-beams, making the interference signal obtained by the main interferometer 40 more stable and with less fluctuation. The clock module 60 is mainly used to generate a clock signal in the form of a square wave after frequency doubling. Its optical power requirement is much lower than that of the main interferometer 40. Therefore, inputting 5% of the light into the clock module 60 is sufficient to meet the normal operation of the harmonic generator 631, the frequency selection circuit 632, the amplifier 633, and the waveform converter 634, while taking into account the overall energy distribution efficiency of the system.

[0053] In one embodiment, the tunable laser 10 has a linewidth of 100 kHz, an actual sweep width of 20 nm, and a maximum luminous power of 13 dBm.

[0054] In one embodiment, the main interferometer 40 further includes a second beam splitter 401 and a third beam splitter 402. The coupling module 42 includes a first coupler 421 and a second coupler 422. The second beam splitter 401 is connected to the first beam splitter 20. The two outputs of the second beam splitter 401 are connected to the first fiber optic circulator 41 and the third beam splitter 402, respectively. The polarization beam splitter 403 is connected to the first coupler 421 and the second coupler 422, respectively. The third beam splitter 402 is connected to the first coupler 421 and the second coupler 422, respectively. The first beam is split into a first sub-beam and a second sub-beam by the second beam splitter 401. The first sub-beam is injected into the temperature-sensing fiber optic 3 through the first fiber optic circulator 41. Within 0, the first sub-beam, after passing through the temperature-measuring fiber 30, forms backscattered Rayleigh light carrying fiber temperature information. The backscattered Rayleigh light returns to the first fiber circulator 41 and is then injected into the polarization beam splitter 403. The polarization beam splitter 403 splits the backscattered Rayleigh light into P-beams and S-beams, and then injects the P-beams and S-beams into the first coupler 421 and the second coupler 422, respectively. The second sub-beam, after being split by the third beam splitter 402, is injected into the first coupler 421 and the second coupler 422, respectively. The first coupler 421 is used to couple the P-beam with a portion of the second sub-beam and input it into the optical detection module 50. The second coupler 422 is used to couple the S-beam with another portion of the second sub-beam and input it into the optical detection module 50.

[0055] Compared to traditional polarization diversity optical paths that use two costly polarization beamsplitters 403, this scheme uses only one polarization beamsplitter 403, resulting in lower costs. The first beam is split into a first sub-beam and a second sub-beam, which serve as the "measurement light" and "reference light," respectively. The first sub-beam enters the temperature-measuring fiber 30 independently, ensuring that the temperature information is carried independently and is not subject to crosstalk from the reference light. The second sub-beam is further rationally distributed in the third beam splitter 402, so that the first coupler 421 and the second coupler 422 obtain reference light with consistent intensity, improving the contrast of the interference fringes. The polarization beamsplitter 403 splits the backscattered Rayleigh light into P-beams and S-beams, which are then mixed with the second sub-beam through the first coupler 421 and the second coupler 422, respectively, to achieve dual-polarization signal acquisition. This effectively reduces measurement errors caused by random fluctuations in polarization state and improves the stability and repeatability of the temperature curve.

[0056] In the main interferometer 40, the splitting ratio of the second beam splitter 401 is 99:1, of which 99% of the light enters the fiber optic circulator 1 and 1% of the light enters the third beam splitter 402; the splitting ratio of the third beam splitter 402 is 50:50; the splitting ratio of the first coupler 421 and the second coupler 422 is 50:50.

[0057] Sending 99% of the light into the first fiber optic circulator 41 allows for higher intensity backscattered Rayleigh light within the temperature-sensing fiber 30, improving the signal-to-noise ratio of the temperature measurement signal. Sending only 1% of the light into the third beam splitter 402 prevents excessively high reference arm power, thus preventing saturation when the P-beam, S-beam, and second sub-beam mix with the first coupler 421 and the second coupler 422, maintaining the linear operation of the balanced detector. The third beam splitter 402 has a 50:50 splitting ratio, ensuring symmetrical reference light between the first coupler 421 and the second coupler 422. This facilitates the formation of a reference light path with consistent intensity and phase characteristics, thereby reducing interference bias errors caused by power imbalance.

[0058] In one embodiment, the light detection module 50 includes a first balanced detector 51 and a second balanced detector 52. The first balanced detector 51 is connected to a first coupler 421, and the second balanced detector 52 is connected to a second coupler 422. The first balanced detector 51 is used to convert the mixed light output from the first coupler 421 into a P signal and output it to the signal acquisition and analysis module 70. The second balanced detector 52 is used to convert the mixed light output from the second coupler 422 into an S signal and output it to the signal acquisition and analysis module 70.

[0059] The first balanced detector 51 and the second balanced detector 52, in conjunction with the polarization beam splitter 403 in the main interferometer 40, can eliminate the signal-to-noise ratio reduction caused by polarization fading. The balanced detectors eliminate common-mode noise through differential methods, effectively suppressing laser intensity noise and improving the dynamic range of the photoelectric conversion signal. This enhances the detection capability of weak Rayleigh scattering interference light, which is particularly evident in the long-distance temperature-measuring fiber optic cable 30. They also provide high-quality P and S signals to the signal acquisition and analysis module 70, improving the accuracy of subsequent temperature calculations. In one embodiment, the auxiliary interferometer 61 includes a second fiber optic circulator 611, a fourth beam splitter 612, a first Faraday rotator 613, and a second Faraday rotator 614. The second fiber optic circulator 611 is connected to the first beam splitter 20, the fourth beam splitter 612, and the frequency multiplication module 63, respectively. The two outputs of the fourth beam splitter 612 are connected to the first Faraday rotator 613 and the second Faraday rotator 614, respectively. A delay fiber 615 is disposed between the second Faraday rotator 614 and the fourth beam splitter 612. The second beam passes through the second fiber optic circulator 611 and enters the fourth beam splitter 612. The second beam is split into a third sub-beam and a fourth sub-beam by the fourth beam splitter 612. The third sub-beam is reflected back to the fourth beam splitter 612 after being reflected by the first Faraday rotator mirror 613. The fourth sub-beam is sent into the second Faraday rotator mirror 614 after being delayed by the fiber optic cable 615, and after being reflected by the second Faraday rotator mirror 614, it is sent back to the fourth beam splitter 612 after being delayed by the fiber optic cable 615 again. The third sub-beam reflected by the first Faraday rotator mirror 613 and the fourth sub-beam reflected by the second Faraday rotator mirror 614 are combined and sent into the photodetector 62 through the second fiber optic circulator 611.

[0060] The delay fiber 615 is used to extend the round-trip time of the fourth sub-beam, so that it can generate a stable interference signal with the third sub-beam. The frequency of the beat frequency signal is determined by the laser sweep speed and the optical path difference. The delay fiber 615 can provide a higher frequency, making the input signal of the harmonic generator 631 clearer.

[0061] The splitting ratio of the fourth beam splitter is 50:50, and the length of the delay fiber 615 is 80m. The output of the photodetector 62 is an AC-coupled output, that is, a sinusoidal beat frequency signal without DC component.

[0062] In one embodiment, the frequency multiplication module 63 includes a harmonic generator 631, a frequency selection circuit 632, an amplifier 633, and a waveform converter 634, which are sequentially turned on. The sinusoidal beat frequency signal generates harmonics through the harmonic generator 631. The frequency selection circuit 632 is used to suppress the fundamental frequency and other unwanted harmonics, so that the harmonics of the multiple harmonics are output to the amplifier 633. The amplifier 633 is used to amplify the harmonics and output them to the waveform converter 634. The waveform converter 634 is used to convert the amplified harmonics into a clock signal in the form of a square wave.

[0063] In one embodiment, the frequency selection circuit 632, the amplifier 633, and the waveform converter 634 form a set of amplification components. There are multiple sets of amplification components, which are arranged sequentially. The waveform converter 634 of each set of amplification components is connected to the frequency selection circuit 632 of the next set of amplification components.

[0064] The harmonic generator 631 uses a zero-crossing comparator or Schmitt trigger circuit to convert the sinusoidal beat frequency signal output by the photodetector 62 into a square wave, thereby generating harmonics. Then, a frequency selection circuit 632 suppresses the fundamental frequency and other unwanted harmonics, allowing only specific harmonic frequencies to be output. The signal is then amplified by an amplifier 633 to output a harmonic sine wave of frequency a. A waveform converter 634 converts the sine wave into a clock signal of frequency a. The harmonic generator 631 can also use the nonlinear characteristics of diodes or transistors to generate harmonics, followed by subsequent frequency selection, amplification, and waveform conversion to output a high-frequency sampling clock signal. The amplification components are group b; by cascading the amplification components, a high-frequency output of frequency a can be achieved. b A clock signal with a frequency multiple of 100.

[0065] In one embodiment, the number of temperature-sensing optical fibers 30 is one or more. When the number of temperature-sensing optical fibers 30 is multiple, the optical fiber temperature measuring device 100 further includes a switching optical switch 80 that can be connected to multiple temperature-sensing optical fibers 30 respectively. The switching optical switch 80 is electrically connected to the signal acquisition and analysis module 70, and the signal acquisition and analysis module 70 is used to control the switching optical switch 80 to connect to each temperature-sensing optical fiber 30 in sequence.

[0066] By switching the optical switch 80, temperature measurement of multiple optical fibers can be achieved using only one tunable laser 10, one main interferometer 40, and one auxiliary interferometer 61, reducing equipment costs. The signal acquisition and analysis module 70 controls the switching optical switch 80 to switch between different temperature-measuring optical fibers 30, achieving signal acquisition and temperature measurement of multiple temperature-measuring optical fibers 30 through polling.

[0067] In one embodiment, the temperature-measuring optical fiber 30 includes an optical fiber body, a first sleeve, and a second sleeve sequentially arranged from the inside out. The outer edge of the optical fiber body slides in contact with the inner wall of the first sleeve, and the outer wall of the first sleeve slides in contact with the inside of the second sleeve.

[0068] The temperature-sensing optical fiber 30 adopts a two-layer loose tube structure of single-mode quartz optical fiber: Quartz single-mode optical fiber is used as the temperature-sensing optical fiber 30, and the outer surface of the optical fiber is coated with a high-temperature resistant polyimide coating. A first sleeve and a second sleeve are sequentially arranged outside the optical fiber. The inner diameter of the first sleeve is larger than the outer diameter of the optical fiber, and the inner diameter of the second sleeve is larger than the outer diameter of the first sleeve. The inner walls of the first and second sleeves are smooth, allowing the optical fiber and the first sleeve to slide automatically within the first and second sleeves respectively. The two-layer loose tube structure with smooth inner walls avoids the influence of external stress and strain on the temperature measurement of the temperature-sensing optical fiber 30. Small holes are set at regular intervals on the tube walls of the first and second sleeves. The second sleeve can also use a spiral wound structure to facilitate the circulation of insulating oil and temperature conduction. The two-layer loose tube structure of the temperature-sensing optical fiber 30 avoids the influence of external stress and strain on the temperature measurement accuracy.

[0069] The above are merely optional embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the concept of the present invention using the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method of optical fiber temperature measurement, characterized by, The optical fiber temperature measurement method comprises the following steps: N reference temperatures are set in a temperature measurement range, and each two adjacent reference temperatures form a temperature measurement sub-interval, so that the temperature measurement range is divided into N-1 temperature measurement sub-intervals, wherein N≥3, and both ends of the temperature measurement range are provided with the reference temperatures; Temperature calibration data is obtained through pre-test, wherein the temperature calibration data comprises reference spectrum signals corresponding to the N reference temperatures and temperature coefficients corresponding to the N-1 temperature measurement sub-intervals; A measurement spectrum signal of a temperature measurement fiber is obtained; Based on the measurement spectrum signal and the reference spectrum signal, the reference temperature and the temperature measurement sub-interval corresponding to the measurement spectrum signal are screened out; Based on the screened reference temperature and the temperature measurement sub-interval, the measurement spectrum signal and the temperature calibration data, a measurement temperature is determined.

2. The optical fiber temperature measurement method of claim 1, wherein, The step of obtaining temperature calibration data through pre-test comprises: A temperature measurement fiber is sequentially adjusted to each reference temperature, and reference spectrum signals of the temperature measurement fiber at each reference temperature are respectively collected to obtain N groups of reference spectrum signals; Each group of reference spectrum signals is divided into M (M≥2) segments by a sliding window with a length of Δx, and M local reference spectrum signals are obtained by processing each segment of the reference spectrum signals; Spectral frequency shifts of two groups of corresponding segments of the local reference spectrum signals corresponding to each temperature measurement sub-interval are obtained by using cross-correlation, and based on the spectral frequency shifts and two reference temperatures, the temperature coefficient of the temperature measurement sub-interval is obtained; The local reference spectrum signals and the temperature coefficient are taken as the temperature calibration data.

3. The optical fiber temperature measurement method of claim 2, wherein, The step of screening the reference temperature and the temperature measurement sub-interval based on the measurement spectrum signal and the reference spectrum signal comprises: M segments of the measurement spectrum signal are divided by a sliding window with a length of Δx, and M local measurement spectrum signals are obtained by processing M segments of the measurement spectrum signal, wherein each segment of the local measurement spectrum signal corresponds to a position of the temperature measurement fiber; Correlation coefficients of each segment of the local measurement spectrum signal and N groups of the local reference spectrum signals are calculated, and the reference temperature and the local reference spectrum signal corresponding to the maximum correlation coefficient are screened out; Spectral frequency shifts of each segment of the local measurement spectrum signal and the local reference spectrum signal corresponding thereto are calculated, and the corresponding temperature measurement sub-interval is screened out according to the reference temperature and the spectral frequency shift.

4. The optical fiber temperature measurement method of claim 3, wherein, The step of calculating the spectral frequency shifts of each segment of the local measurement spectrum signal and the local reference spectrum signal corresponding thereto and screening out the corresponding temperature measurement sub-interval according to the reference temperature and the spectral frequency shift comprises: Two temperature measurement sub-intervals adjacent to the left and right of each reference temperature are screened out according to the reference temperature; The spectral frequency shifts of the local measurement spectrum signal and the local reference spectrum signal corresponding thereto are calculated; According to the positive and negative of the spectral frequency shift, the temperature measurement sub-interval on the right side of the reference temperature or the temperature measurement sub-interval on the left side of the reference temperature is selected as the temperature measurement sub-interval corresponding to the local measurement spectrum signal.

5. The optical fiber temperature measurement method of claim 3, wherein, The step of determining the measurement temperature based on the reference temperature, the temperature measurement sub-interval, the measured spectrum signal and the temperature calibration data comprises: multiplying the temperature coefficient corresponding to the spectrum frequency shift amount and the temperature measurement sub-interval to obtain a temperature change amount; superimposing the temperature change amount and the reference temperature corresponding to the local measurement spectrum signal to obtain the measurement temperature of the local measurement spectrum signal.

6. The optical fiber temperature measurement method of claim 3, wherein, The step of obtaining the measurement spectrum signal of the temperature measurement fiber comprises: obtaining P signals and S signals carrying temperature information of the temperature measurement fiber; performing fast Fourier transform on the P signals and the S signals respectively to obtain P spectrum signals and S spectrum signals, and synthesizing the P spectrum signals and the S spectrum signals to obtain a measurement spectrum signal; dividing the measurement spectrum signal into M segments by a sliding window with a length of Δx, and processing the M segments of the measurement spectrum signal to obtain M segments of local measurement spectrum signals, the step comprising: dividing the measurement spectrum signal into M segments by a sliding window with a length of Δx; performing inverse fast Fourier transform on each segment of the measurement spectrum signal to obtain M segments of the local measurement spectrum signal.

7. A fiber optic temperature measurement device, characterized by, comprise: a tunable laser for outputting a linear frequency modulation laser; a first beam splitter arranged at an output end of the tunable laser and configured to split the linear frequency modulation laser into a first light beam and a second light beam; a temperature measurement fiber arranged on a device to be measured; a main interferometer comprising a first fiber loop, a polarization beam splitter and a coupling module, the first fiber loop being in communication with the temperature measurement fiber and the polarization beam splitter, the first light beam being injected into the temperature measurement fiber through the first fiber loop after being injected into the main interferometer, the first light beam forming back Rayleigh scattering light carrying temperature information of the fiber after passing through the temperature measurement fiber, the back Rayleigh scattering light returning to the first fiber loop and being injected into the polarization beam splitter, the P light and the S light being split by the polarization beam splitter and being coupled into the coupling module respectively; a light detection module, the back Rayleigh scattering light coupled by the coupling module being input into the light detection module, and P signals and S signals being output by the light detection module; a clock module comprising an auxiliary interferometer, a light detector and a frequency multiplication module connected in sequence, the second light beam being injected into the auxiliary interferometer, and being converted into a sinusoidal beat frequency signal by the light detector, the frequency multiplication module being configured to amplify and convert the sinusoidal beat frequency signal into a clock signal; a signal acquisition and analysis module configured to obtain the clock signal, the P signal and the S signal, and configured to convert the P signal and the S signal into a measurement spectrum signal, and to perform the fiber temperature measurement method according to any one of claims 1 to 6 to obtain the temperature of the device to be measured.

8. The fiber optic temperature measurement device of claim 7, wherein, The main interferometer further comprises a second beam splitter and a third beam splitter, the coupling module comprises a first coupler and a second coupler, the second beam splitter is in communication with the first beam splitter, two output ends of the second beam splitter are in communication with the first fiber optic circulator and the third beam splitter respectively, the polarization beam splitter is in communication with the first coupler and the second coupler respectively, and the third beam splitter is in communication with the first coupler and the second coupler respectively; The first light beam is split into a first sub-beam and a second sub-beam by the second beam splitter, the first sub-beam enters the temperature measurement fiber through the first fiber optic circulator, the first sub-beam forms the back Rayleigh scattering light carrying the temperature information of the fiber after passing through the temperature measurement fiber, the back Rayleigh scattering light returns to the first fiber optic circulator and enters the polarization beam splitter, the polarization beam splitter splits the back Rayleigh scattering light into P light and S light, and the P light and the S light enter the first coupler and the second coupler respectively; The second sub-beam enters the first coupler and the second coupler respectively after being split by the third beam splitter, the first coupler is used for coupling the P light with a part of the second sub-beam and inputting the mixed light into the light detection module, and the second coupler is used for coupling the S light with another part of the second sub-beam and inputting the mixed light into the light detection module; the light detection module comprises a first balanced detector and a second balanced detector, the first balanced detector is in communication with the first coupler, the second balanced detector is in communication with the second coupler, the first balanced detector is used for converting the mixed light output by the first coupler into a P signal and outputting the P signal to the signal acquisition and analysis module, and the second balanced detector is used for converting the mixed light output by the second coupler into an S signal and outputting the S signal to the signal acquisition and analysis module.

9. The fiber optic temperature measurement device of claim 7, wherein, The auxiliary interferometer comprises a second fiber optic circulator, a fourth beam splitter, a first Faraday rotating mirror and a second Faraday rotating mirror, the second fiber optic circulator is in communication with the first beam splitter, the fourth beam splitter and the frequency multiplication module respectively, two output ends of the fourth beam splitter are in communication with the first Faraday rotating mirror and the second Faraday rotating mirror respectively, and a delay fiber is arranged between the second Faraday rotating mirror and the fourth beam splitter; The second light beam enters the fourth beam splitter through the second fiber optic circulator, the second light beam is split into a third sub-beam and a fourth sub-beam by the fourth beam splitter, the third sub-beam returns to the fourth beam splitter after being reflected by the first Faraday rotating mirror, the fourth sub-beam enters the second Faraday rotating mirror after passing through the delay fiber, is reflected by the second Faraday rotating mirror, passes through the delay fiber again and returns to the fourth beam splitter, and the third sub-beam reflected by the first Faraday rotating mirror and the fourth sub-beam reflected by the second Faraday rotating mirror are combined and enter the light detector through the second fiber optic circulator; The frequency multiplication module comprises a harmonic generator, a frequency selection circuit, an amplifier and a waveform converter in turn, the sinusoidal wave beat frequency signal generates harmonics through the harmonic generator, the frequency selection circuit is used for suppressing the fundamental frequency and other useless harmonics, so as to output the frequency multiplication harmonic in the harmonics to the amplifier, the amplifier is used for amplifying the frequency multiplication harmonic and then outputting to the waveform converter, and the waveform converter is used for converting the amplified frequency multiplication harmonic into the clock signal in the form of square wave.

10. The fiber optic temperature measurement device of claim 7, wherein, The temperature measurement optical fiber comprises an optical fiber body, a first sleeve and a second sleeve which are sequentially sleeved from inside to outside, the outer edge of the optical fiber body is in sliding contact with the inner wall of the first sleeve, and the outer wall of the first sleeve is in sliding contact with the inner part of the second sleeve.

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