Signal enhancement and abnormal diagnosis method of raman distributed fiber temperature sensing system

Abstract

The application discloses a signal enhancement and abnormal diagnosis method of a Raman distributed optical fiber temperature sensing system, and relates to the technical field of distributed optical fiber sensing. The signal enhancement method is: through decoupling the collection process of Stokes and anti-Stokes signals in the time domain, independently configuring laser pulse parameters, without sacrificing the spatial resolution of the system, the detectable intensity of the anti-Stokes signal is significantly enhanced, the accuracy of long-distance temperature measurement is improved, and the technical problem of low signal-to-noise ratio of the system caused by the weak intrinsic intensity of the anti-Stokes signal in the Raman distributed optical fiber temperature sensing system is solved. On the basis of time-sharing independent collection, the loss difference of the two curves of the anti-Stokes signal and the Stokes signal is compared in real time, and the optical fiber abnormality is diagnosed.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing technology, and in particular to a method for signal enhancement and anomaly diagnosis of a Raman distributed optical fiber temperature sensing system. Background Technology

[0002] Real-time, continuous, and accurate monitoring of temperature fields is crucial in fields such as industrial production, energy transmission, rail transportation, power facilities, and geological monitoring. Compared to traditional point-based temperature sensing technologies, distributed temperature sensing (DTS) systems offer advantages such as long measurement distances, strong resistance to electromagnetic interference, intrinsic safety, and the ability to achieve continuous measurement across the entire fiber optic cable. Therefore, they are widely used in long-distance, large-scale temperature monitoring scenarios. Among various distributed fiber optic temperature sensing principles, distributed fiber optic temperature sensing systems based on the Raman scattering effect have become one of the mainstream solutions in current engineering applications due to their mature structure, relatively controllable cost, and high temperature measurement accuracy.

[0003] In Raman distributed fiber optic temperature sensing systems, temperature demodulation primarily relies on the intensity change of the anti-Stokes signal. However, limited by the Raman scattering mechanism, the intrinsic intensity of the anti-Stokes Raman scattered light is low. Under the combined effects of long-distance fiber transmission and system noise, the anti-Stokes signal is prone to insufficient signal-to-noise ratio, thus affecting the accuracy and stability of temperature measurement and becoming a key factor restricting system performance improvement. Furthermore, fiber bending, compression, and splice loss are highly sensitive to wavelength; the longer the wavelength, the greater the bending loss. Therefore, when the fiber is locally bent, compressed, or the splice deteriorates, the 1660nm Stokes signal will produce a much larger attenuation step than the 1450nm anti-Stokes signal. Since temperature demodulation depends on the ratio of the two, this asymmetric sudden attenuation will present a "pseudo-peak temperature" on the demodulation curve.

[0004] Existing distributed fiber optic temperature sensing (DTS) systems generally employ a "same laser pulse, dual-channel synchronous acquisition" operating mode. This mode presents an inherent physical contradiction: spatial resolution and temperature measurement accuracy (signal-to-noise ratio) are difficult to balance. To achieve high spatial resolution, extremely narrow laser pulses must be used. However, the cross-section of anti-Stokes Raman scattered light is extremely small (its intrinsic intensity is much weaker than that of Stokes Raman scattered light), and the extremely narrow pulse results in very low effective photon energy injected into the fiber. In long-distance measurements, the anti-Stokes signal at the far end is easily overwhelmed by the thermal noise of the photodetector and subsequent amplification circuit, leading to a sharp deterioration in the system's signal-to-noise ratio (SNR) and a significant increase in temperature measurement error. Simply increasing the light energy by widening the pulse would result in a simultaneous decrease in positioning accuracy and spatial resolution. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology where spatial resolution and signal-to-noise ratio are mutually constrained, this invention provides a signal enhancement method for a Raman distributed fiber optic temperature sensing system. By decoupling the acquisition processes of Stokes and anti-Stokes signals in the time domain and independently configuring laser pulse parameters, the detectable intensity of the anti-Stokes signal is significantly enhanced without sacrificing the system's spatial resolution. This improves the accuracy of long-distance temperature measurement and solves the technical problem of weak intrinsic strength of the anti-Stokes signal in the Raman distributed fiber optic temperature sensing system, which leads to a low system signal-to-noise ratio.

[0006] To achieve the above objectives, the present invention adopts the following technical solution, including: The signal enhancement method of the Raman distributed fiber optic temperature sensing system adopts a time-division independent acquisition strategy, which separates the acquisition process of Stokes signal and anti-Stokes signal in time, and uses different laser pulse parameter configurations in the acquisition process of Stokes signal and anti-Stokes signal; wherein, the pulse width in the acquisition process of anti-Stokes signal is greater than the pulse width in the acquisition process of Stokes signal.

[0007] Preferably, the Raman distributed fiber optic temperature sensing system includes: a laser, a sensing fiber, an optical system, a spectrum acquisition module, an FPGA main control module, and a host computer; When the system is working, the laser injects pulsed laser light into the sensing fiber under the drive of the FPGA main control module; the pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect, generating Stokes Raman scattered light and anti-Stokes Raman scattered light; after the backscattered light is spectrally separated by the optical system, it enters the spectrum acquisition module for photoelectric conversion, signal conditioning and digital acquisition; the spectrum acquisition module transmits the acquired raw spectrum signal to the FPGA main control module and the host computer to complete temperature demodulation processing and visualization display.

[0008] Preferably, the Raman distributed fiber optic temperature sensing system operates as follows: S1, System Initialization: After the system completes fault self-check and reset, the host computer sends a start command and sets the initial pulse parameters and initial acquisition mode. S2, Stokes signal acquisition: The FPGA main control module drives the laser to emit pulsed laser light with a first pulse width. The pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect. The optical system separates the Stokes Raman scattered light. The spectrum acquisition module acquires the Stokes signal, performs cumulative averaging on the acquired data, and determines whether the current accumulation count has reached the preset accumulation count. If it has, it means that the cumulative averaging is complete and the Stokes signal acquisition is complete; otherwise, continue to execute step S2 to continue acquiring the Stokes signal and performing cumulative averaging until the preset accumulation count is reached. S3, Switch Acquisition Mode: Without changing the system optical path structure, switch to anti-Stokes signal acquisition mode; S4, Anti-Stokes signal acquisition: The FPGA main control module drives the laser to emit pulsed laser light with a second pulse width greater than the first pulse width. The pulsed laser light propagates in the sensing fiber and excites Raman scattering. The optical system separates the anti-Stokes Raman scattered light. The spectrum acquisition module acquires the anti-Stokes signal, performs cumulative averaging on the acquired data, and determines whether the current accumulation count has reached the preset accumulation count. If it has, the cumulative averaging is completed, and the acquisition of the anti-Stokes signal is complete; otherwise, continue to execute step S3 to continue acquiring the anti-Stokes signal and performing cumulative averaging until the preset accumulation count is reached. S5, Temperature Demodulation: Based on the intensity ratio of the Stokes signal and the anti-Stokes signal, and combined with the system calibration parameters, the temperature data is demodulated. S6, Output Results: The acquired raw spectral signal and demodulated temperature data are transmitted to the host computer for visualization.

[0009] Preferably, temperature demodulation is performed based on the acquired Stokes and anti-Stokes signals, as follows: Based on the speed of light and refractive index, spatial coordinate interpolation is performed to align Stokes signals and anti-Stokes signals. Using the aligned Stokes signal and anti-Stokes signal, calculate the intensity ratio of the anti-Stokes signal and the Stokes signal at any cross section of the optical fiber, i.e., at any spatial coordinate. For the fiber reference cross-section, the known temperature of the fiber reference cross-section is measured as follows: i The intensity ratio of the anti-Stokes signal to the Stokes signal on the fiber reference section is . R ( i ); Temperature on arbitrary cross-section of inverted fiber T : ; in, R ( i )and R ( T These are the intensity ratios of the anti-Stokes signal and the Stokes signal calculated on the fiber reference section and the arbitrary fiber section, respectively. k Boltzmann's constant, h It is Planck's constant; v’ = Δv / c , v’ For the frequency shift of Raman scattering, c At the speed of light, ΔvThis is the Raman frequency shift of the fiber molecule, which is the wavenumber difference between the injected pulsed laser and the Raman scattered light.

[0010] The preferred method for spatial coordinate interpolation alignment is as follows: Spatial coordinates ; in, c The speed of light; n g The refractive index of the fiber core group; t The pulsed laser emitted by the laser originates from the starting end of the optical fiber and travels to a point where the fiber length is... z The time it takes for the backscattered light generated to be received by the photodetector; z These are the spatial distance coordinates along the fiber optic line, and their values ​​are taken as the fiber length. For anti-Stokes signals, spline interpolation or linear interpolation algorithms are used to resample the anti-Stokes signals and map them onto the spatial coordinates of the Stokes signals.

[0011] Preferably, during the anti-Stokes signal acquisition stage, based on the flight time of the backscattered signal, i.e. the optical fiber spatial distance, the system sequentially transmits a sequence of interrogation pulses with different pulse widths; for the near-end fiber, a data segment excited by a short pulse is extracted; for the far-end fiber, a data segment excited by a long pulse is extracted; and finally, the extracted data segments are spliced ​​and fused in the spatial coordinate system.

[0012] This invention also provides an anomaly diagnosis method for a Raman distributed fiber optic temperature sensing system. The method utilizes the Stokes signal and anti-Stokes signal acquired by the signal enhancement method of the Raman distributed fiber optic temperature sensing system to perform fiber optic anomaly diagnosis. The specific method is as follows: For any cross-section of the optical fiber, a sliding window of a certain length is selected in the spatial coordinate domain, and the step attenuation amplitude of the Stokes signal intensity before and after the sliding window is calculated respectively. Step attenuation amplitude of anti-Stokes signal strength If detected If the attenuation difference between the two signals exceeds the set Stokes signal step attenuation threshold, and the attenuation difference characteristic is also greater than the set dual-channel attenuation difference threshold, then it is determined that a physical anomaly has occurred in the optical fiber at that cross-section location, and the temperature abrupt change at that cross-section location is not a true abrupt change in ambient temperature; wherein, the attenuation difference characteristic is... and The difference or ratio is expressed as a value.

[0013] Preferably, after identifying the fiber optic anomaly, the temperature demodulation result corresponding to the anomaly is marked as an invalid temperature value. A preset length of adjacent effective temperature intervals is selected on both sides of the anomaly, and the average temperature of the adjacent effective temperature intervals on both sides is used as the replacement temperature value at the anomaly.

[0014] Preferably, when a physical anomaly in the optical fiber is detected or the system is in anti-interference mode, the laser is controlled to output a laser pulse with a wider pulse width.

[0015] The present invention also provides a computer program product, which includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the anomaly diagnosis method of the Raman distributed fiber optic temperature sensing system.

[0016] The advantages of this invention are: (1) This invention proposes a signal-to-noise ratio (SNR) enhancement method for Raman distributed fiber optic temperature sensing systems. Based on the relatively gradual temperature variation along the fiber, this method optimizes the Raman scattering signal acquisition method to enable differentiated operating parameters at different scattering signal acquisition stages. During signal acquisition, Stokes Raman scattering and anti-Stokes Raman scattering are acquired in a time-division manner. In the anti-Stokes signal detection stage, the time characteristics of the incident pulse light are adjusted to increase the effective scattered light energy, thereby enhancing the detectability of the anti-Stokes signal. Through this method, the SNR characteristics of the anti-Stokes signal are effectively improved without significantly increasing the system hardware complexity, thus improving the overall SNR of the Raman distributed fiber optic temperature sensing system and providing technical support for achieving high-precision, long-distance distributed temperature measurement.

[0017] (2) This invention breaks the physical constraint between spatial resolution and signal-to-noise ratio. In the prior art, improving spatial resolution requires compressing the pulse width, which leads to a deterioration in the anti-Stokes signal's signal-to-noise ratio; improving the signal-to-noise ratio requires widening the pulse, which leads to a decrease in spatial resolution. This invention, through time-division independent excitation, enables the Stokes channel to retain a narrow pulse to anchor high spatial resolution, while simultaneously enabling the anti-Stokes channel to obtain a wide pulse to acquire high photon energy. Without sacrificing the overall spatial positioning accuracy of the system, a significant improvement in the anti-Stokes signal's signal-to-noise ratio is achieved.

[0018] (3) This invention combines an adaptive pulse width broadening mechanism based on spatial distance. During the anti-Stokes signal acquisition stage, the system sequentially transmits interrogation pulse sequences (such as short pulses, medium pulses, and long pulses) with different pulse widths according to the flight time of the backscattered signal (i.e., the spatial distance of the optical fiber). For the near-end optical fiber, a high spatial resolution data segment excited by a short pulse is extracted; for the far-end optical fiber with severe attenuation, a high signal-to-noise ratio data segment excited by a long pulse is extracted. Finally, the effective data segments are spliced ​​and fused in the spatial coordinate system. This invention can inject energy to address the severe attenuation at the far end of the optical fiber, effectively avoiding the problems of near-end detector saturation and far-end signal being submerged by noise, flattening the signal-to-noise ratio distribution across the entire range, significantly extending the effective sensing distance of the system, and improving the accuracy of far-end temperature measurement.

[0019] (4) Compared with the existing DTS technology of "single pulse, dual channel synchronous acquisition", this invention achieves a dual breakthrough in physical mechanism and hardware architecture.

[0020] (5) The present invention has a highly economical hardware reuse rate. In terms of hardware implementation, the present invention does not require the addition of expensive dual-channel high sampling rate ADC and dual front-end transimpedance amplifier circuits. It directly uses time-division multiplexing mechanism to enable the core processing unit (FPGA main control module) to efficiently schedule underlying computing and storage resources in different time slots, which greatly reduces the system's BOM (Bill of Materials) cost and improves the reliability and integration of industrial-grade hardware.

[0021] (6) The present invention also provides a method for accurately distinguishing between real temperature abrupt changes and optical fiber physical anomalies (such as macrobending, poor splicing, connector contamination, etc.) by utilizing the different physical characteristics of Stokes Raman scattered light (long wavelength, such as 1660nm) and anti-Stokes Raman scattered light (short wavelength, such as 1450nm) to optical fiber bending / compression stress by monitoring the difference in attenuation slope or loss step of the two backscattered signals at the same spatiotemporal node.

[0022] (7) When the present invention detects a physical anomaly in the optical fiber or the system is in anti-interference mode, the system controls the laser to output a laser pulse with a wider pulse width (second pulse width). By utilizing the larger spatial resolution generated in the optical fiber by the wide pulse, the photodetector receives the integrated energy of the backscattered light from the optical fiber within the same sampling period. This physical process is equivalent to introducing a moving average low-pass filter in the spatial domain, which smooths out the transient loss abrupt changes caused by local stress, thereby avoiding the output of erroneous peak temperatures by the demodulation algorithm. Attached Figure Description

[0023] Figure 1 This is a block diagram of the Raman distributed fiber optic temperature sensing system (DTS) of the present invention.

[0024] Figure 2This is a diagram of the experimental setup for the Raman distributed fiber optic temperature sensing system of the present invention.

[0025] Figure 3 This is a flowchart illustrating the operation of the Raman distributed fiber optic temperature sensing system of the present invention. Detailed Implementation

[0026] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention addresses the problems of weak intrinsic strength of the anti-Stokes signal and low signal-to-noise ratio (SNR) in Raman distributed fiber optic temperature sensing (DTS) systems by proposing a SNR enhancement technique based on time-division independent acquisition and adaptive pulse parameter adjustment. This technique, through coordinated control of the Raman scattering signal acquisition timing and laser pulse parameters, enhances the effective energy of the anti-Stokes signal without significantly increasing system hardware complexity, thereby improving the overall temperature measurement performance of the system.

[0028] Figure 1 A block diagram of the Raman distributed fiber optic temperature sensing system (DTS) of the present invention is shown. The DTS system mainly includes: a laser, a sensing fiber, an optical system, a spectrum acquisition module (containing a photoelectric conversion circuit, a signal conditioning circuit, and an analog-to-digital conversion circuit), an FPGA main control module, a host computer, and a power supply module; the modules are connected to each other through optical signals or electrical signals to form a complete distributed temperature sensing and demodulation link.

[0029] During system operation, the laser, driven by the FPGA main control module, injects pulsed laser light into the sensing fiber. The pulsed laser propagates in the sensing fiber and excites Raman scattering, generating Stokes Raman scattered light and anti-Stokes Raman scattered light. The backscattered light is spectrally separated by the optical system and then enters the spectral acquisition module. It sequentially passes through the photoelectric conversion circuit, signal conditioning circuit, and analog-to-digital conversion circuit in the spectral acquisition module to complete photoelectric conversion, signal conditioning, and digital acquisition. Finally, the acquired raw spectral signal is transmitted to the FPGA main control module and the host computer for subsequent temperature demodulation processing and visualization.

[0030] In traditional DTS systems, Stokes signals and anti-Stokes signals are usually acquired synchronously under the same laser pulse parameters, making it difficult to take into account the differences in signal strength and noise characteristics between the two.

[0031] This invention takes into full consideration the following physical characteristics: Anti-Stokes signals are highly temperature sensitive but have weak intrinsic strength; Stokes signals have higher strength but lower temperature sensitivity; in practical engineering applications, temperature changes relatively slowly along the spatial distribution of optical fibers.

[0032] Based on the above characteristics, the present invention separates the acquisition process of Stokes signal and anti-Stokes signal in time and adopts a time-division independent acquisition strategy. The system uses different laser pulse parameter configurations in the acquisition process of Stokes signal and anti-Stokes signal.

[0033] In a preferred embodiment of the present invention, the laser pulse parameters include at least the pulse width, the pulse repetition frequency, and the pulse amplitude. The pulse width, as an important parameter affecting the energy of the Raman scattered light, is used for focused adjustment.

[0034] Therefore, during the Stokes signal acquisition phase, the system employs a relatively narrow pulse width to ensure high spatial resolution and avoid unnecessary energy redundancy. During the anti-Stokes signal acquisition phase, the system appropriately increases the pulse width to increase the effective optical energy injected into the fiber per unit pulse, thereby increasing the probability of anti-Stokes Raman scattering. Since the intrinsic strength of the anti-Stokes signal is weak, its signal-to-noise ratio is mainly limited by the number of effectively scattered photons. This method allows for a significant enhancement of the anti-Stokes signal strength without increasing the peak power.

[0035] Figure 3 The workflow of the Raman distributed fiber optic temperature sensing system of the present invention is demonstrated, specifically including the following steps: S1, System Initialization After completing the system fault self-check and reset, the host computer sends a start command and sets the initial acquisition mode and corresponding initial pulse parameters.

[0036] S2, Stokes signal acquisition The FPGA main control module drives the laser to emit pulsed laser light with a first pulse width. The pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect. The optical system separates the Stokes Raman scattered light. The spectrum acquisition module acquires the Stokes signal. The FPGA main control module performs cumulative averaging on the acquired data and determines whether the current accumulation count has reached the preset accumulation count. If it has, it means that the cumulative averaging is completed and the Stokes signal acquisition is completed; otherwise, step S2 is continued to be executed to continue acquiring the Stokes signal and performing cumulative averaging until the preset accumulation count is reached.

[0037] S3, switch acquisition mode Without changing the optical path structure, the system switches to anti-Stokes signal acquisition mode.

[0038] S4, Enhanced Acquisition of Anti-Stokes Signal The FPGA main control module drives the laser to emit pulsed laser light with a second pulse width greater than the first pulse width. The pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect. The optical system separates the anti-Stokes Raman scattered light, and the spectrum acquisition module acquires the anti-Stokes signal. The FPGA main control module performs cumulative averaging on the acquired data and determines whether the current accumulation count has reached the preset accumulation count. If it has, it means that the cumulative averaging is completed and the acquisition of the anti-Stokes signal is completed; otherwise, step S3 is continued to be executed to continue acquiring the anti-Stokes signal and performing cumulative averaging until the preset accumulation count is reached.

[0039] S5, Temperature Demodulation Based on the intensity ratio of the Stokes reference signal and the anti-Stokes reference signal, and combined with the system calibration parameters, the temperature data is demodulated.

[0040] S6, Output Results The acquired raw spectral signal and demodulated temperature data are transmitted to a host computer or display terminal to visualize the temperature distribution.

[0041] Example 1: Time-division acquisition and temperature demodulation Figure 2 The experimental setup diagram of the Raman distributed fiber optic temperature sensing system (DTS) of this embodiment is shown.

[0042] like Figure 1 and Figure 2 As shown, after the system is powered on, the FPGA main control module (using a Xilinx Zynq series FPGA) initializes the timing generator. The decision rule for separation in the time domain is mainly based on a preset hardware accumulation average number or a real-time signal-to-noise ratio threshold: when the acquisition accumulation number of a certain channel (Stokes channel or anti-Stokes channel) reaches the set threshold, the FPGA determines that the signal acquisition of that channel has ended and triggers a timing switching command to enter the signal acquisition of the next channel.

[0043] The underlying logic of the cumulative averaging process is as follows: The FPGA main control module controls the laser to continuously emit N pulses at a fixed repetition frequency (e.g., 1kHz). The backscattered light corresponding to each pulse is converted into a digital sequence by a high-speed ADC, and then the corresponding spatial coordinates are arithmetically accumulated multiple times in the FPGA's on-chip memory (e.g., BRAM / URAM). When the number of accumulations reaches a preset N, the accumulation result is divided by N, thereby reducing the variance of random white noise through multiple averaging, and achieving a signal-to-noise ratio that varies with the input signal. The magnitude of the increase.

[0044] Furthermore, the real-time signal-to-noise ratio (SNR) determination refers to the FPGA extracting the background noise variance of the signal-free section at the end of the optical fiber and the signal amplitude at the effective end of the optical fiber in real time during the accumulation process, and calculating the real-time SNR. When the real-time SNR exceeds a set safety threshold, an interrupt is directly triggered, prematurely ending the accumulation process of the current channel, thereby dynamically improving the system's measurement refresh rate.

[0045] The processing procedure in this embodiment is as follows: (1) Stokes signal acquisition: The FPGA control and driving circuit enables the laser to emit narrow pulsed laser light. After the backscattered light is separated by the wavelength division multiplexer (WDM, i.e., optical system), only the Stokes Raman scattered light is guided into the photodetector (i.e., spectrum acquisition module). The high-speed ADC (i.e., analog-to-digital converter) digitizes the photoelectric converted signal. The FPGA internal logic stores the massive amount of data points (e.g., 80,000 depth points) in the on-chip URAM / BRAM and performs n hardware accumulation and averaging to obtain a high spatial resolution Stokes signal curve. Among them, the wavelength division multiplexer (WDM) separation is the core optical communication technology that accurately splits multiple optical signals of different wavelengths transmitted in a single optical fiber to their respective independent output ports according to wavelength.

[0046] (2) Anti-Stokes signal acquisition: After completing the above steps, the FPGA switches the timing to control the laser to emit a wider pulse laser. At this time, the wavelength division multiplexer (WDM) channel switches or the photodetector selects the anti-Stokes Raman scattered light. The wide pulse injection brings higher scattered photon energy, which significantly improves the amplitude of the weak signal at the far end. Similarly, the ADC performs high-speed sampling and the FPGA performs accumulation and averaging to obtain a high signal-to-noise ratio anti-Stokes signal curve.

[0047] (3) Signal alignment and temperature demodulation: Because the two pulse widths are different, their spatial convolution effects differ. The FPGA logic first performs spatial coordinate interpolation and alignment on the two sets of signals based on the speed of light and refractive index.

[0048] Known fiber space coordinates ; in, c The speed of light; n g The refractive index of the fiber core group; t The pulsed laser emitted by the laser originates from the starting end of the optical fiber and travels to a point where the fiber length is... z The time it takes for the backscattered light generated to be received by the photodetector; z The coordinates represent the spatial distance along the fiber optic cable, and the value is the fiber length.

[0049] To address the low spatial resolution inverse Stokes signal caused by wide pulses, the system employs spline interpolation or linear interpolation algorithms to resample and map it onto the spatial coordinates of the high spatial resolution Stokes signal corresponding to narrow pulses, ensuring that the two sets of signals are in the same spatial coordinates. z Bottom alignment.

[0050] Using the aligned Stokes signal and anti-Stokes signal, the intensity ratio of the anti-Stokes signal and the Stokes signal at any cross section of the optical fiber, i.e., at any spatial coordinate, is calculated.

[0051] temperature T Calculated from the intensity ratio of the anti-Stokes signal and the Stokes signal, according to the expression: ; in, v’ = Δv / c , v’ For the frequency shift of Raman scattering, c At the speed of light, Δv This is the Raman frequency shift of the fiber molecule, i.e., the wavenumber difference between the injected pulsed laser and the Raman scattered light; k Boltzmann's constant, h It is Planck's constant; l AS and l S These represent the wavelengths of the anti-Stokes signal and the Stokes signal, respectively. T The temperature at the cross-section of the optical fiber; R ( T (The temperature is) T The ratio of the intensity of the anti-Stokes signal to that of the Stokes signal at that time; I AS The intensity of anti-Stokes Raman scattered light; I S The intensity of Stokes Raman scattered light.

[0052] For the fiber reference cross-section, the known temperature of the fiber reference cross-section is measured as follows: i And the intensity ratio of the fiber reference section is R ( i Temperature on any cross-section of the inverted optical fiber. T : ; in, R ( i )and R ( T These are the intensity ratios calculated on the fiber reference section and the arbitrary fiber section, respectively.

[0053] Example 2: Fiber Optic Anomaly Diagnosis and Pseudo-Temperature Peak Suppression Based on Pulse Width Broadening In actual industrial environments (such as complex environments like heating networks, oil and gas wells, and transformer windings), optical fibers often face problems such as local bending, external compression, or contamination of the fiber optic connector end face.

[0054] This invention, based on time-division independent data acquisition, further introduces fiber optic anomaly diagnosis based on optical characteristics. When the system emits 1550nm pump light, the resulting Stokes signal wavelength is relatively long (approximately 1660nm), while the anti-Stokes signal wavelength is relatively short (approximately 1450nm). According to the fiber bending loss mechanism, longer wavelengths are more sensitive to macro-bending and micro-bending. The Stokes signal wavelength is longer than the anti-Stokes signal wavelength, making it more sensitive to fiber bending and stress. However, it is difficult to distinguish between localized extreme temperature and physical damage based solely on a single-wavelength anomaly step. Therefore, the core processing unit (FPGA main control module) of this invention performs fiber optic anomaly diagnosis by comparing the loss differences between the anti-Stokes and Stokes signal curves in real time, thus identifying the anomaly point.

[0055] For example, if the Stokes signal shows a significant attenuation step at a certain cross-sectional location, while the anti-Stokes signal attenuates very little at the same cross-sectional location, it can be accurately determined that a physical deformation or joint loss has occurred at that cross-sectional location, rather than a true temperature change.

[0056] Specifically, after aligning the spatial coordinates of the Stokes and anti-Stokes signal curves, the FPGA main control module performs synchronous sliding window analysis on the two backscattered signal curves, using the spatial coordinates along the fiber as a reference. First, at any cross-section of the fiber... At that location, a sliding window centered on the cross section or formed by adjacent intervals before and after the cross section is selected, and the Stokes signal and anti-Stokes signal are calculated at that cross section position. The local amplitude variation in the vicinity. Specifically, the window can be divided into a forward reference sub-window and a backward detection sub-window. The average signal intensity within each of the two window segments is taken, and the step attenuation amplitude of the Stokes signal is calculated. and the step decay amplitude of the anti-Stokes signal ,in, Characterizing the Stokes signal at this cross-section location The degree of mutation at the location, Characterizing the anti-Stokes signal at the same cross-sectional position The degree of abrupt change at the point. To reduce the impact of random noise on the judgment result, the signal strength can be the signal value after cumulative averaging, or the signal value after moving average, median filtering, and wavelet denoising. Then, the FPGA main control module calculates the attenuation difference characteristic of the two signals. This attenuation difference characteristic can be expressed by the following formula: ; in, To prevent corrections where the denominator is zero; In this embodiment, the attenuation difference characteristic is represented by the ratio of attenuation amplitudes; alternatively, the difference in attenuation amplitudes may also be used. express.

[0057] The system determines the location of the cross section when the following two conditions are met. There is a physical anomaly in the optical fiber (bending or compression): First, the Stokes signal at this cross-section location There is a significant step decay at this point, that is: ; Second, the attenuation difference between the Stokes signal and the anti-Stokes signal exceeds a set threshold, namely: ; in, The Stokes signal step attenuation threshold. This is the threshold for the difference in attenuation between the two channels. This threshold can be adaptively determined using system factory calibration, background noise statistics under initial, normal operating conditions, or historical data.

[0058] Furthermore, to avoid misjudging real temperature abrupt changes as fiber optic anomalies, the system can introduce consistency verification conditions. If neither the anti-Stokes signal nor the Stokes signal shows significant asymmetric loss at a certain cross-sectional location, and the temperature demodulation curve shows a continuous and repeatable upward or downward trend before and after that location, it is determined to be a real temperature change; if the temperature demodulation curve shows a narrow pulse-like peak, and the Stokes signal shows significant step attenuation with a significant difference in attenuation between the two channels, then the peak temperature is determined to be a pseudo-peak temperature caused by a physical anomaly in the fiber.

[0059] After identifying the anomaly, the system enters the pseudo-temperature peak suppression process. The FPGA main control module records the spatial coordinates of the anomaly. The temperature demodulation result corresponding to the anomaly point is then marked as an invalid temperature value. Subsequently, the FPGA main control module selects a preset length of adjacent effective temperature intervals on both sides of the anomaly point, calculates the average value of the adjacent temperature data before and after the anomaly point, and uses the comprehensive average value of the adjacent effective temperatures on both sides as the replacement temperature value at the location of the anomaly point.

[0060] When the system identifies a severe physical anomaly (high-loss step) at a certain point through the fiber optic anomaly diagnosis mechanism, it means that the effective signal strength behind the anomaly point will drop sharply. In response, the system automatically switches to anti-interference mode: the FPGA main control module controls the laser to further increase the second pulse width (i.e., the pulse width of the anti-Stokes acquisition channel, and if necessary, simultaneously increase the first pulse width (within the range of nonlinearity)). Increasing the pulse width brings a dual gain effect: First, it injects multiple times the single-pulse light energy into the optical fiber, forcibly penetrating high-loss anomaly points, restoring the signal-to-noise ratio of the far-end optical fiber, and avoiding the occurrence of temperature measurement blind spots; Second, the broadening of the physical pulse width is equivalent to introducing a low-pass filter with a larger sliding window in the spatial domain. The wider the pulse width, the larger the filtering window. The hardware-level low-pass filtering effect can powerfully smooth out the abrupt changes in the step signal caused by local bending or poor joints, making the transient differential step caused by the loss step of the optical fiber smoother, and making the change in the returned energy smoother. This suppresses and smooths the sharp false temperature peaks of the demodulation algorithm factor ratio mismatch output at the source, prevents the system from generating false alarms, and greatly improves the survivability and temperature measurement robustness of the system in harsh construction environments.

[0061] In summary, the core of this invention lies in breaking the parameter constraints of traditional Raman distributed fiber optic temperature sensing systems (DTS) through time-domain decoupling, encompassing time-division acquisition methods, signal processing algorithms, and hardware system architecture, specifically including the following.

[0062] (1) Core Method: A time-division acquisition method for Raman distributed fiber optic temperature measurement, which separates the acquisition of Stokes signal and anti-Stokes signal in the time domain; a first laser pulse parameter is used in the Stokes signal acquisition stage, and a second laser pulse parameter is used in the anti-Stokes signal acquisition stage; and the second laser pulse parameter is configured to provide higher effective injected light energy than the first laser pulse. Among them, the judgment rule for separation in the time domain is mainly based on the preset hardware accumulation average number or real-time signal-to-noise ratio threshold: when the acquisition accumulation number of a certain channel reaches the set threshold, the FPGA determines that the signal acquisition stage ends and triggers the timing switching instruction to enter the next stage.

[0063] (2) Key parameter regulation and adaptive mechanism: Pulse width asymmetric modulation: explicitly states that the second pulse width should be increased, i.e. the pulse width of the anti-Stokes acquisition channel, and the first pulse width should be increased simultaneously if necessary (within the range of nonlinearity).

[0064] Dynamic adaptive compensation: During the anti-Stokes signal acquisition stage, based on the flight time of the backscattered signal (i.e., the spatial distance of the optical fiber), the system sequentially transmits a sequence of interrogation pulses with different pulse widths (such as short pulses, medium pulses, and long pulses). For near-end optical fibers, high spatial resolution data segments excited by short pulses are extracted; for far-end optical fibers with severe attenuation, high signal-to-noise ratio data segments excited by long pulses are extracted. Finally, the effective data segments are spliced ​​and fused in the spatial coordinate system.

[0065] (3) Alignment and demodulation algorithm for asymmetric data: For asymmetric spatial resolution data obtained with different pulse widths, interpolation filtering is used to map and align the spatial coordinate system, and the data processing flow is substituted into the temperature measurement formula for temperature demodulation.

[0066] (4) Underlying hardware collaboration and reuse architecture: This invention provides a hardware system architecture that supports the above-mentioned time-division acquisition method, particularly including: a time-division multiplexing mechanism of dual single-channel high-speed analog-to-digital converters, and in the underlying logic chip (such as a high-capacity FPGA), high-speed on-chip storage resources (such as URAM / BRAM) are used to partition and cache and pipeline accumulate and average the massive Stokes and anti-Stokes data of up to tens of thousands of depth points (e.g., 80,000 data depths).

[0067] (5) Anomaly diagnosis method: The present invention also provides a method that utilizes the physical characteristics of the different sensitivity of Stokes Raman scattered light (long wavelength, such as 1660nm) and anti-Stokes Raman scattered light (short wavelength, such as 1450nm) to optical fiber bending / compression stress, and accurately distinguishes between real temperature change and optical fiber physical anomalies (such as macrobending, poor splicing, connector contamination, etc.) by monitoring the difference in attenuation slope or loss step of the two backscattered signals at the same spatiotemporal node.

[0068] (6) Pseudo-temperature peak suppression method based on pulse width broadening: When a physical anomaly in the optical fiber is detected or the system is in anti-interference mode, the system controls the laser to output a laser pulse with a wider pulse width (second pulse width). Utilizing the larger spatial resolution generated by the wide pulse in the optical fiber, the photodetector receives the integrated energy of the backscattered light from the optical fiber within the same sampling period. This physical process is equivalent to introducing a moving average low-pass filter in the spatial domain, smoothing out the transient loss abrupt changes caused by local stress, thereby avoiding erroneous peak temperatures output by the demodulation algorithm.

[0069] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A signal enhancement method for a Raman distributed fiber optic temperature sensing system, characterized in that, A time-division independent acquisition strategy is adopted to separate the acquisition processes of Stokes signals and anti-Stokes signals in time, and different laser pulse width configurations are used in the acquisition processes of Stokes signals and anti-Stokes signals; among them, the pulse width in the acquisition process of anti-Stokes signals is greater than the pulse width in the acquisition process of Stokes signals.

2. The signal enhancement method for the Raman distributed fiber optic temperature sensing system according to claim 1, characterized in that, The Raman distributed fiber optic temperature sensing system includes: a laser, a sensing fiber, an optical system, a spectrum acquisition module, an FPGA main control module, and a host computer; When the system is working, the laser injects pulsed laser light into the sensing fiber under the drive of the FPGA main control module; the pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect, generating Stokes Raman scattered light and anti-Stokes Raman scattered light; after the backscattered light is spectrally separated by the optical system, it enters the spectrum acquisition module for photoelectric conversion, signal conditioning and digital acquisition; the spectrum acquisition module transmits the acquired raw spectrum signal to the FPGA main control module and the host computer to complete temperature demodulation processing and visualization display.

3. The signal enhancement method for the Raman distributed fiber optic temperature sensing system according to claim 1 or 2, characterized in that, The Raman distributed fiber optic temperature sensing system operates as follows: S1, System Initialization: After the system completes fault self-check and reset, the host computer sends a start command and sets the initial pulse parameters and initial acquisition mode. S2, Stokes signal acquisition: The FPGA main control module drives the laser to emit pulsed laser light with a first pulse width. The pulsed laser light propagates in the sensing fiber and excites the Raman scattering effect. The optical system separates the Stokes Raman scattered light. The spectrum acquisition module acquires the Stokes signal, performs cumulative averaging on the acquired data, and determines whether the current accumulation count has reached the preset accumulation count. If it has, it means that the cumulative averaging is complete and the Stokes signal acquisition is complete; otherwise, continue to execute step S2 to continue acquiring the Stokes signal and performing cumulative averaging until the preset accumulation count is reached. S3, Switch Acquisition Mode: Without changing the system optical path structure, switch to anti-Stokes signal acquisition mode; S4, Anti-Stokes signal acquisition: The FPGA main control module drives the laser to emit pulsed laser light with a second pulse width greater than the first pulse width. The pulsed laser light propagates in the sensing fiber and excites Raman scattering. The optical system separates the anti-Stokes Raman scattered light. The spectrum acquisition module acquires the anti-Stokes signal, performs cumulative averaging on the acquired data, and determines whether the current accumulation count has reached the preset accumulation count. If it has, the cumulative averaging is completed, and the acquisition of the anti-Stokes signal is complete; otherwise, continue to execute step S3 to continue acquiring the anti-Stokes signal and performing cumulative averaging until the preset accumulation count is reached. S5, Temperature Demodulation: Based on the intensity ratio of the Stokes signal and the anti-Stokes signal, and combined with the system calibration parameters, the temperature data is demodulated. S6, Output Results: The acquired raw spectral signal and demodulated temperature data are transmitted to the host computer for visualization.

4. The signal enhancement method for the Raman distributed fiber optic temperature sensing system according to claim 1, characterized in that, Temperature demodulation is performed based on the acquired Stokes and anti-Stokes signals, as follows: Based on the speed of light and refractive index, spatial coordinate interpolation is performed to align Stokes signals and anti-Stokes signals. Using the aligned Stokes signal and anti-Stokes signal, calculate the intensity ratio of the anti-Stokes signal and the Stokes signal at any cross section of the optical fiber, i.e., at any spatial coordinate. For the fiber reference cross-section, the known temperature of the fiber reference cross-section is measured as follows: θ The intensity ratio of the anti-Stokes signal to the Stokes signal on the fiber reference section is . R ( θ ); Temperature on arbitrary cross-section of inverted fiber T : in, R ( θ )and R ( T These are the intensity ratios of the anti-Stokes signal and the Stokes signal calculated on the fiber reference section and the arbitrary fiber section, respectively. k Boltzmann's constant, h It is Planck's constant; v’ = Δv / c , v’ For the frequency shift of Raman scattering, c At the speed of light, Δv This is the Raman frequency shift of the fiber molecule, which is the wavenumber difference between the injected pulsed laser and the Raman scattered light.

5. The signal enhancement method for the Raman distributed fiber optic temperature sensing system according to claim 4, characterized in that, The specific method for spatial coordinate interpolation alignment is as follows: Spatial coordinates ;in, c The speed of light; n g The refractive index of the fiber core group; t The pulsed laser emitted by the laser originates from the starting end of the optical fiber and travels to a point where the fiber length is... z The time it takes for the backscattered light generated to be received by the photodetector; z These are the spatial distance coordinates along the fiber optic line, and their values ​​are taken as the fiber length. For anti-Stokes signals, spline interpolation or linear interpolation algorithms are used to resample the anti-Stokes signals and map them onto the spatial coordinates of the Stokes signals.

6. The signal enhancement method for the Raman distributed fiber optic temperature sensing system according to claim 1, characterized in that, During the anti-Stokes signal acquisition phase, based on the flight time of the backscattered signal, i.e. the optical fiber spatial distance, the system sequentially transmits a sequence of interrogation pulses with different pulse widths; for the near-end fiber, the data segment excited by the short pulse is extracted. For the distant optical fiber, extract the data segment excited by the long pulse; Finally, the extracted data segments are spliced ​​and merged in a spatial coordinate system.

7. An anomaly diagnosis method for a Raman distributed fiber optic temperature sensing system, characterized in that, Using the Stokes signal and anti-Stokes signal acquired by the signal enhancement method of the Raman distributed fiber optic temperature sensing system according to any one of claims 1 to 6, fiber optic anomaly diagnosis is performed, specifically as follows: For any cross-section of the optical fiber, a sliding window of a certain length is selected in the spatial coordinate domain, and the step attenuation amplitude of the Stokes signal intensity before and after the sliding window is calculated respectively. Step attenuation amplitude of anti-Stokes signal strength If detected If the attenuation difference between the two signals exceeds the set Stokes signal step attenuation threshold, and the attenuation difference characteristic is also greater than the set dual-channel attenuation difference threshold, then it is determined that a physical anomaly has occurred in the optical fiber at that cross-section location, and the temperature abrupt change at that cross-section location is not a true abrupt change in ambient temperature; wherein, the attenuation difference characteristic is... and The difference or ratio is expressed as a value.

8. The anomaly diagnosis method for the Raman distributed fiber optic temperature sensing system according to claim 7, characterized in that, After identifying the fiber optic anomaly, the temperature demodulation result corresponding to the anomaly is marked as an invalid temperature value. A preset effective temperature range is selected on both sides of the anomaly, and the average temperature of the two adjacent effective temperature ranges is used as the replacement temperature value at the anomaly.

9. The anomaly diagnosis method for the Raman distributed fiber optic temperature sensing system according to claim 7, characterized in that, When a physical anomaly in the optical fiber is detected or the system is in anti-interference mode, the laser is controlled to output a laser pulse with a wider pulse width.

10. A computer program product, characterized in that, It includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the anomaly diagnosis method of the Raman distributed fiber optic temperature sensing system according to any one of claims 7 to 9.

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