High spatial resolution distributed fiber temperature measurement method based on frequency self-compensation algorithm

Abstract

The application discloses a high spatial resolution distributed optical fiber temperature measurement method based on a frequency self-compensation algorithm, acquires a system response time of a distributed optical fiber temperature measurement system by using a temperature signal; constructs a series correction link according to expected dynamic characteristics, and constitutes a new system transfer function with an original transfer function to compensate for the frequency of the original system and expand the measurement frequency band of the system; and equivalent correction links are equivalent to digital filters to process the temperature signal, and amplitude correction is performed on the processed data to obtain the temperature signal after frequency self-compensation. The method has the characteristics of simple calculation process and high speed, does not increase the cost of the system, and is suitable for distributed optical fiber temperature measurement of any temperature measurement distance.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber temperature sensing, and more particularly to a high spatial resolution distributed optical fiber temperature measurement method based on a frequency self-compensation algorithm. Background Technology

[0002] Distributed fiber optic temperature measurement systems possess advantages such as resistance to electromagnetic interference, high sensitivity, long measurement distance, and small size, and are widely used for temperature monitoring in large-scale projects such as high-voltage cables, oil and gas pipelines, bridges, and tunnels. Spatial resolution characterizes the minimum distance that a distributed fiber optic temperature measurement system can distinguish during temperature monitoring. The higher the spatial resolution, the better the system's measurement performance. Therefore, improving the spatial resolution of the system has become a research hotspot and challenge.

[0003] Spatial resolution is primarily influenced by factors such as the pulse width of the light source, the bandwidth of the photodetector, and the data acquisition rate. Current techniques for improving spatial resolution fall into two categories: hardware optimization and software optimization. Hardware optimization methods mainly achieve this by reducing the pulse width of the light source, increasing the bandwidth of the photodetector, and increasing the data acquisition rate. However, this approach not only increases system cost but also drastically reduces the signal-to-noise ratio of the temperature measurement signal, affecting the accuracy of the temperature measurement. Therefore, using software technology to improve the spatial resolution of the system offers a higher cost-effectiveness. Currently proposed software optimization methods mainly include cyclic pulse coding, deconvolution algorithms, and correlation function time-domain compression demodulation. However, these methods suffer from drawbacks such as algorithm complexity and high computational cost. Furthermore, some methods still impose requirements on the light source, further increasing costs. Summary of the Invention

[0004] The purpose of this invention is to provide a high spatial resolution distributed fiber optic temperature measurement method based on a frequency self-compensation algorithm. By connecting a correction circuit in series, the measurement bandwidth of the system is broadened through frequency self-compensation, thereby improving the spatial resolution of the system.

[0005] The technical solution adopted in this invention is:

[0006] A high spatial resolution distributed fiber optic temperature measurement method based on a frequency self-compensation algorithm includes the following steps:

[0007] Step 1: Obtain the system response time of the distributed fiber optic temperature measurement system using the temperature signal, and obtain the original system transfer function based on the system characteristics of the measurement system. ;

[0008] Furthermore, the measurement system used in this invention conforms to the characteristics of a first-order system, and the original transfer function of the system is set. for:

[0009] (1);

[0010] in, Let be the system response time, and let be the transfer function, which is a function of s with respect to the complex frequency. σ is the real part of the complex frequency, j is the imaginary unit, and ω is the frequency.

[0011] Furthermore, the response time τ is obtained as follows: a 50m long fiber is taken from the end of the sensing fiber and placed in a constant temperature bath, while the rest of the sensing fiber is placed at room temperature. The temperature along the sensing fiber is measured to obtain temperature information. The temperature information is then normalized, and the system response time τ is determined based on 63.2% of the rising edge of the normalized data. That is, the time required for the temperature in the heating zone to rise from room temperature to 63.2% of the difference between the heating zone temperature and room temperature, thus obtaining the transfer function of the original system.

[0012] Furthermore, the temperature demodulation formula corresponding to the temperature information is:

[0013] (2);

[0014] Where h is Planck's constant, k is Boltzmann's constant, T is the temperature to be measured, T0 is the calibration temperature, and P s and P as These represent the power of the Stokes scattered light and the power of the anti-Stokes scattered light, respectively.

[0015] Step 2: Construct a series compensation stage, determine the bandwidth spread factor of the target after compensation, calculate the response time of the compensated system based on the bandwidth spread factor, and then obtain the transfer function of the compensation stage. ;

[0016] Specifically, the calibration stage compensates for the frequency of the original system, expanding its measurement bandwidth by a factor of A; that is, the response time of the dynamic characteristics of the system's transfer function after adding the calibration stage is shortened by a factor of A compared to the original system's transfer function, thus optimizing the system's dynamic performance. The transfer function of the calibration stage is then determined based on the response time of the calibrated system. .

[0017] Furthermore, in step 2, the transfer function of the correction element is determined. The steps are as follows:

[0018] Step 2-1, set the calibration process as follows Then the corrected system transfer function for:

[0019] (3);

[0020] in, The corrected system response time is given by a value of . .

[0021] Step 2-2, through the original transfer function and the corrected system transfer function The transfer function of the correction element is calculated. for:

[0022] (4);

[0023] Step 3: Obtain the system sampling interval T and use the backward difference method to calculate the transfer function of the correction element. The equivalent digital filter is obtained by performing a z-transform. ,Will Performing an inverse z-transform yields its computer programming formula, which is then used to correct the obtained temperature signal to obtain the system frequency-compensated temperature data. .

[0024] Furthermore, the transfer function in step 3 The formula for performing the z-transform is as follows:

[0025] (5);

[0026] in, The Z-transform, where Z is the sampling interval, is a transformation that converts a time-domain signal into an expression in the complex frequency domain. .

[0027] Furthermore, the temperature data after system frequency compensation in step 3 The calculation formula is as follows:

[0028] (6)

[0029] in, The sampling interval is... The temperature before correction. The corrected temperature is represented by k, which is the index value of the data and takes an integer value between 1 and the length of the temperature data to be corrected.

[0030] Step 4: Obtain the signal amplitude correction factor based on the system response time and bandwidth spread factor. And using amplitude correction factor Processed temperature data Amplitude correction is performed to obtain the final temperature signal after frequency self-compensation. That is, the signal after improving spatial resolution.

[0031] Furthermore, the amplitude correction factor in step 4 The calculation formula is:

[0032] (7)

[0033] Furthermore, the amplitude correction factor in step 4 The formula for amplitude correction of the processed temperature data y is as follows:

[0034] (8).

[0035] This invention employs the above technical solution, performing frequency self-compensation by cascading a link with a transfer function H(s) after the original system's transfer function. This improves the system's transfer function, compensating for the original system's insufficient dynamic performance and expanding the measurement system's bandwidth, effectively increasing the photodetector's bandwidth and thus enhancing the system's spatial resolution. The additional cascade link H(s) can be implemented using an equivalent digital filter, a simple and fast calculation process that does not increase system cost. This correction link, implemented using an equivalent digital filter, has a simple algorithm. Therefore, this invention improves the spatial resolution of the distributed fiber optic temperature measurement system while maintaining high computational speed, ensuring the real-time performance of the temperature measurement signal. This invention requires no other hardware, thus not increasing system cost and is applicable to both short- and long-distance fiber optic temperature measurement, making it valuable for applications in the field of distributed temperature measurement. Attached Figure Description

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0037] Figure 1 The flowchart shows a high spatial resolution distributed fiber optic temperature measurement method based on a frequency self-compensation algorithm.

[0038] Figure 2 This is a schematic diagram of the temperature signal acquisition system of the present invention;

[0039] Figure 3 This is a comparison diagram before and after the spatial resolution of the system temperature measurement signal is improved according to the present invention. Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0041] like Figures 1 to 3 As shown in one example, this invention discloses a high spatial resolution distributed optical fiber temperature measurement method based on a frequency self-compensation algorithm, which includes the following steps:

[0042] Step 1: Obtain the system response time of the distributed fiber optic temperature measurement system using the temperature signal. The measurement system used in this invention conforms to the characteristics of a first-order system; therefore, the original transfer function W(s) of the system is assumed to be:

[0043] (1);

[0044] In the formula, τ represents the system response time, which is obtained by placing a 50m length of fiber from the tail of the sensing fiber into a constant temperature bath, while the rest of the sensing fiber is kept at room temperature. Figure 2 The system shown measures the temperature along the sensing fiber to obtain temperature information, and its temperature demodulation formula is as follows:

[0045] (2);

[0046] In the formula, h is Planck's constant, k is Boltzmann's constant, T is the temperature to be measured, T0 is the calibration temperature, and P... s P as Let represent the power of the Stokes scattered light and the anti-Stokes scattered light. The temperature signal is normalized, and the system response time τ is determined based on 63.2% of the rising edge of the normalized data. This τ is the time required for the temperature in the heating zone to rise from room temperature to 63.2% of the difference between the heating zone temperature and room temperature. This gives the transfer function of the original system.

[0047] Step 2: Construct a series compensation element to compensate for the frequency of the original system, thus extending the measurement bandwidth of the original system by a factor of A. In other words, the response time of the dynamic characteristics of the system transfer function after adding the compensation element is shortened by a factor of A compared to the original system transfer function, optimizing the dynamic performance of the system. Assuming the compensation element is H(s), the compensated system transfer function is:

[0048] (3);

[0049] In the formula, τ' is the response time of the corrected system, and its value is τ / A. The transfer function H(s) of the corrector can be obtained from equations (1) and (3):

[0050] (4);

[0051] Step 3: Perform a z-transform on the transfer function H(s) of the correction element, as shown in the following equation:

[0052] (5);

[0053] In the formula, T is the sampling interval. The equivalent digital filter corresponding to this correction stage is obtained using the backward difference method, as shown in the following formula:

[0054] (6);

[0055] In the formula, x(k) is the temperature before correction, y(k) is the temperature after correction, and k is an integer between 1 and the length of the temperature data to be corrected. The mathematical form of this correction step is used to correct the temperature signal x obtained in step one, resulting in the temperature data y after system frequency compensation.

[0056] Step 4: Obtain the signal amplitude correction factor m based on the system response time and bandwidth spread factor, as shown in the following formula:

[0057] (7);

[0058] The processed temperature data y is subjected to amplitude correction, as shown in the following formula:

[0059] (8);

[0060] The final temperature signal g after frequency self-compensation is obtained, which is the signal after improving spatial resolution.

[0061] This invention employs the above technical solution, performing frequency self-compensation by cascading a link with a transfer function H(s) after the original system's transfer function. This improves the system's transfer function, compensating for the original system's insufficient dynamic performance and expanding the measurement system's bandwidth, effectively increasing the photodetector's bandwidth and thus enhancing the system's spatial resolution. The additional cascade link H(s) can be implemented using an equivalent digital filter, a simple and fast calculation process that does not increase system cost. This correction link, implemented using an equivalent digital filter, has a simple algorithm. Therefore, this invention improves the spatial resolution of the distributed fiber optic temperature measurement system while maintaining high computational speed, ensuring the real-time performance of the temperature measurement signal. This invention requires no other hardware, thus not increasing system cost and is applicable to both short- and long-distance fiber optic temperature measurement, making it valuable for applications in the field of distributed temperature measurement.

[0062] Obviously, the described embodiments are only a portion, not all, of the embodiments of this application. Without conflict, the embodiments and features described and illustrated herein can be combined with each other. The components of the embodiments of this application generally described and illustrated in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A high spatial resolution distributed fiber optic temperature measurement method based on a frequency self-compensation algorithm, characterized in that: It includes the following steps: Step 1: Obtain the system response time of the distributed fiber optic temperature measurement system using the temperature signal, and obtain the original system transfer function based on the system characteristics of the measurement system. ; Step 2: Construct a series compensation stage, determine the bandwidth spread factor A of the target after compensation, calculate the response time of the compensated system based on the bandwidth spread factor A, and then obtain the transfer function of the compensation stage. ; Step 3: Obtain the system sampling interval T and use the backward difference method to calculate the transfer function of the correction element. The equivalent digital filter is obtained by performing a z-transform. ,Will Performing an inverse z-transform yields the corresponding computer programming formula. Using this formula, the temperature signal is corrected to obtain the system frequency-compensated temperature data. ; Step 4: Obtain the signal amplitude correction factor based on the system response time and bandwidth spread factor. And using amplitude correction factor Processed temperature data Amplitude correction is performed to obtain the final temperature signal after frequency self-compensation. That is, the signal after improving spatial resolution.

2. The high spatial resolution distributed optical fiber temperature measurement method based on frequency self-compensation algorithm according to claim 1, characterized in that: The measurement system used conforms to the characteristics of a first-order system, and the original transfer function of the system is set. for: (1)； Among them, the transfer function It is a function with s as the independent variable, where s is the complex frequency. σ is the real part of the complex frequency, j is the imaginary unit, and ω is the frequency; This refers to the system's response time.

3. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 2, characterized in that: The response time τ is obtained as follows: a 50m long fiber is taken from the end of the sensing fiber and placed in a constant temperature bath, while the rest of the sensing fiber is placed at room temperature. The temperature along the sensing fiber is measured to obtain temperature information. The temperature information is then normalized, and the system response time τ is determined based on 63.2% of the rising edge of the normalized data. That is, the time required for the temperature in the heating zone to rise from room temperature to 63.2% of the difference between the heating zone temperature and room temperature. The transfer function of the original system is then obtained.

4. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 3, characterized in that: The temperature demodulation formula corresponding to the temperature information is: (2)； Where h is Planck's constant, k is Boltzmann's constant, T is the temperature to be measured, T0 is the calibration temperature, and P s and P as These represent the power of the Stokes scattered light and the power of the anti-Stokes scattered light, respectively.

5. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 2, characterized in that: In step 2, determine the transfer function of the correction element. The steps are as follows: Step 2-1, set the calibration process as follows Then the corrected system transfer function for: (3)； in, The corrected system response time is given by a value of . ; Step 2-2, through the original transfer function and the corrected system transfer function The transfer function of the correction element is calculated. for: (4)。 6. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 5, characterized in that: Transfer function in step 3 The formula for performing the z-transform is as follows: (5)； in, The Z-transform, where Z is the sampling interval, is a transformation that converts a time-domain signal into an expression in the complex frequency domain. .

7. The high spatial resolution distributed optical fiber temperature measurement method based on frequency self-compensation algorithm according to claim 6, characterized in that: Temperature data after system frequency compensation in step 3 The calculation formula is as follows: (6)； in, The sampling interval is... The temperature before correction. The corrected temperature is represented by k, which is the index value of the data and is an integer between 1 and the length of the temperature data to be corrected.

8. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 6, characterized in that: Step 4 Amplitude correction factor The calculation formula is: (7)。 9. The high spatial resolution distributed optical fiber temperature measurement method based on the frequency self-compensation algorithm according to claim 7, characterized in that: Step 4 Amplitude correction factor Processed temperature data The calculation formula for amplitude correction is as follows: (8)。

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