A fiber optic Raman temperature measurement device based on detection power correction

Abstract

This invention discloses a fiber optic Raman temperature measurement device based on detection power correction, comprising a pulsed laser, a wavelength division multiplexer, a fiber optic temperature calibration unit, a fiber optic interface, a photodetector, a data acquisition card, a data processing module, and a display module. The fiber optic temperature calibration unit includes a temperature calibration fiber and a temperature sensor. The fiber optic temperature calibration unit records the temperature data of the temperature calibration fiber. The data processing module combines the temperature data of the temperature calibration fiber to correct the detection power of the Raman anti-Stokes light, overcoming the influence of the pulse power emitted by the pulsed laser and the gain fluctuations of the photodetector on the temperature measurement along the tested fiber, thereby achieving high-precision distributed temperature demodulation. This invention uses Raman anti-Stokes light as the sensing signal, which not only has high sensitivity but also occupies only one data acquisition channel. Compared with conventional dual-path demodulation systems, it eliminates the need to consider position deviation correction issues, resulting in better stability.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a fiber optic Raman temperature measurement device based on fiber optic Raman anti-Stokes light detection power correction, to achieve single-path detection and single-path temperature demodulation, which can be used for temperature measurement and fire early warning in fields such as power cables, heating pipelines, oil and gas pipelines, and warehouses. Background Technology

[0002] Light propagating in optical fibers generates Rayleigh scattering, Brillouin scattering, and Raman scattering. These scattered lights exhibit different response mechanisms to external stimuli such as temperature, strain, and vibration, including variations in light intensity, frequency, polarization state, phase, and wavelength. By selecting the appropriate response mechanism, parameters such as temperature, strain, and vibration can be measured. Raman scattering includes Stokes and anti-Stokes light, and its power is affected by temperature. Based on this mechanism, Raman time-domain reflectometry (RTD) instruments have been developed to measure the temperature at various locations along the fiber optic cable, facilitating temperature event warnings and fire prevention. However, current temperature demodulation techniques using RTDs primarily employ dual-path detection, simultaneously detecting the power of both Raman and anti-Stokes signals and performing dual-path demodulation by comparing the power of the detected Raman and anti-Stokes signals. Dual-channel detection and demodulation methods can effectively overcome the influence of laser output power fluctuations and detector gain changes on temperature measurement results. However, they also have some drawbacks. For example, the difference in wavelength between Raman-Stokes and anti-Stokes light leads to different light speeds in the optical fiber, causing position drift and making drift correction difficult. This inevitably results in large positioning and temperature measurement errors. In addition, data acquisition occupies two channels, which is not convenient for integrating multiple sensing modules.

[0003] To address the aforementioned issues, the invention patent "A High-Frequency Dual-Color Coherent Anti-Stokes Raman Spectrometry Temperature Measurement Device and Method" (Publication No.: CN 112097953 A) utilizes nonlinear optical effects to generate third harmonics to obtain Stokes light and coherent anti-Stokes light. An imaging spectrometer is used to image the input coherent anti-Stokes Raman signal, and the temperature of the detected gas is calculated from the spectral data of the image. Although this scheme primarily uses Raman anti-Stokes light, its optical and circuit systems are complex, limiting its application to atmospheric optical imaging temperature measurement. The invention patent "A Distributed Fiber Raman Temperature Measurement System" (Publication No.: CN 103115693 A) employs a dual-optical-path detection and temperature demodulation scheme, utilizing a high-speed DSP digital signal processor for wavelet denoising to ensure measurement accuracy and data processing speed. However, this scheme only improves the temperature correction algorithm and does not address the fundamental problems causing measurement and positioning errors. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a fiber optic Raman temperature measurement device based on probe power correction. Based on the distributed fiber optic Raman temperature measurement principle, it uses Raman anti-Stokes light as the sensing optical signal. By setting up a temperature calibration unit, it acquires the changes in Raman anti-Stokes light at the temperature calibration position caused by fluctuations in the laser's output optical power and the photodetector's gain. A probe power correction algorithm is then used to correct the acquired Raman anti-Stokes light's time-domain voltage data. Theoretically, this can completely eliminate the influence of fluctuations in the laser's output optical power and the photodetector's gain on the temperature measurement accuracy.

[0005] This invention proposes a fiber Raman temperature measurement device based on detection power correction, comprising: a pulsed laser, a wavelength division multiplexer, a temperature calibration unit, a fiber optic interface, a photodetector, a data acquisition card, a data processing module, and a display module;

[0006] The temperature calibration unit includes: a temperature calibration optical fiber and a temperature sensor;

[0007] The temperature sensor in the temperature calibration unit transmits temperature data to the data processing module.

[0008] The data acquisition card emits an electrical pulse to drive the pulsed laser to emit an optical pulse. The optical pulse enters from the first port of the wavelength division multiplexer and is then output from the second port of the wavelength division multiplexer. It enters the temperature calibration fiber of the temperature calibration unit and then enters the fiber under test through the fiber interface.

[0009] The Raman anti-Stokes light generated during the transmission of the optical pulse in the temperature calibration fiber and the fiber under test enters through port 2 of the wavelength division multiplexer and exits from port 3.

[0010] The photodetector converts the Raman anti-Stokes light output from the third port of the wavelength division multiplexer into a voltage signal; the data acquisition card acquires the voltage signal output by the photodetector, obtains the optical time-domain reflectometry data of the Raman anti-Stokes light, and transmits the data to the data processing module for temperature demodulation to obtain the temperature information at each location along the tested optical fiber.

[0011] Before performing temperature demodulation, the data processing module first acquires a set of Raman anti-Stokes light time-domain reflection voltage data, denoted as V. A (T0,L a ), where T0 is the temperature value measured by the temperature sensor, L a This represents the distance at various locations along the tested optical fiber; a location at the tip of the tested optical fiber is denoted as L. Front As the zero point, its corresponding voltage value is denoted as V. A (T0,L FrontBased on the attenuation coefficient of the fiber under test, the distance from position L of the fiber under test is calculated. Front Voltage data V(T0,L) at various positions along the line from the end of the fiber under test, where L represents the voltage at position L of the fiber under test. Front The distance to each position along the line from the end of the fiber optic cable being tested;

[0012] The voltage value at a certain set position on the temperature calibration optical fiber is denoted as V. R (T0,L0), where L0 represents a set position on the temperature calibration fiber;

[0013] The data processing module performs temperature demodulation according to the following steps:

[0014] Step 1: Acquire a set of Raman anti-Stokes light time-domain reflectometry data, denoted as V(T,L), where T is the temperature value measured by the temperature sensor during this data acquisition process, and the position information L in the Raman anti-Stokes light time-domain reflectometry data V(T,L) corresponds one-to-one with the position information L in the voltage data V(T0,L).

[0015] The voltage value at a predetermined position on the temperature calibration fiber is denoted as V. R (T,L0), where L0 represents a set position on the temperature calibration fiber; where T is the temperature value measured by the temperature sensor (302);

[0016] Step 2: Calculate the power detection correction factor R of the Raman anti-Stokes light. Where h is Planck's constant, with a value of h = 6.626 × 10⁻⁶. -34 J·s, where k is the Boltzmann constant, with a value of k = 1.3806 × 10⁻⁶. -23 The Raman scattering bandwidth of J / K, v fiber is generally taken as v = 1.32 × 10⁻⁶. 13 Hz; Divide the optical time-domain reflectance voltage data V(T,L) of the Raman anti-Stokes light by the power detection correction coefficient R of the Raman anti-Stokes light to obtain the power-corrected optical time-domain reflectance voltage data of the Raman anti-Stokes light, denoted as V. C (T,L), that is

[0017] Step 3: Using the formula Calculate the temperature values ​​at each location along the fiber optic cable, corresponding to a distance L.

[0018] The data processing module transmits the calculation results to the display module, which displays the distance L and its corresponding temperature curves at various locations along the tested optical fiber.

[0019] Preferably, the temperature sensor is an electronic temperature sensor, and the temperature value is transmitted to the data processing module.

[0020] Preferably, the voltage value V at a certain set position on the temperature calibration fiber is... R (T0,L0) is the average value of the voltage at a point near the temperature calibration fiber centered at position L0.

[0021] Preferably, the voltage value V A (T0,L Front ) represents the position L of the fiber being measured. Front The average voltage is taken from the location of a fiber optic cable near the center.

[0022] To improve the dynamic range, spatial resolution, and temperature measurement accuracy of the temperature measuring device involved in this invention, the device is preferably as follows:

[0023] Preferably, the photodetector is an avalanche photodetector with a bandwidth of not less than 100MHz.

[0024] Preferably, the sampling rate of the data acquisition card is greater than 100 Msps.

[0025] Preferably, the data acquisition card has a data accumulation function, with a maximum accumulation count of not less than 2. 14 Second-rate.

[0026] Preferably, the length of the temperature calibration fiber is not less than 100m.

[0027] Preferably, the pulsed laser has a trigger output function, which can output a trigger level to trigger the data acquisition card to perform data acquisition.

[0028] This invention relates to a fiber optic Raman temperature measurement device based on probe power correction. Starting from the Raman distributed fiber optic temperature measurement mechanism, it fully considers the impact of laser output power fluctuations and photodetector gain conversion on temperature measurement accuracy. By setting up a fiber optic temperature calibration unit, it uses Raman anti-Stokes light signals for probe power correction and combines the attenuation coefficient of the Raman anti-Stokes light in the fiber under test to regenerate the time-domain reflection voltage data of the Raman anti-Stokes light at the calibration (reference) temperature. This device features high measurement accuracy, precise positioning, and good stability. In particular, compared with traditional dual-path detection and demodulation schemes, it eliminates the need to consider position drift correction and the resulting temperature measurement deviation. Furthermore, it saves data acquisition channels, thus facilitating the integration and application of multi-sensor systems. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a fiber optic Raman temperature measurement device based on detection power correction proposed in this invention.

[0030] Figure 2 This is a schematic diagram of the temperature calibration unit.

[0031] Figure 3 This is a schematic diagram of the optical time-domain reflection voltage data for Raman anti-Stokes light.

[0032] Figure 4 To extract the position L of the fiber under test Front This is a schematic diagram showing the distance and voltage at various locations along the line from the starting point to the end of the fiber under test.

[0033] Figure 5 This is a schematic diagram of a set position and corresponding voltage in the fiber optic area for temperature calibration during the first measurement.

[0034] Figure 6 This is a schematic diagram of the optical time-domain reflection voltage data of the Raman anti-Stokes light corresponding to the two measurements.

[0035] Figure 7 This is a schematic diagram showing a set location and corresponding voltage in the fiber optic area for temperature calibration during the next measurement.

[0036] Figure 8 This is a schematic diagram of the temperature demodulation results.

[0037] The numbers in the diagram represent: 1-Pulsed laser; 2-Wavelength division multiplexer; 3-Temperature calibration unit; 4-Fiber optic interface; 5-Photodetector; 6-Data acquisition card; 7-Data processing module; 8-Display module. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] This embodiment provides a fiber optic Raman temperature measurement device based on detection power correction, such as... Figure 1 As shown, the device includes: a pulsed laser 1, a wavelength division multiplexer 2, a temperature calibration unit 3, an optical fiber interface 4, a photodetector 5, a data acquisition card 6, a data processing module 7, and a display module 8.

[0040] The temperature calibration unit 3 includes: a temperature calibration optical fiber 301 and a temperature sensor 302, such as... Figure 2 The temperature calibration fiber optic cable 301 is 100m long and coiled into a coil with a diameter greater than 10cm. The temperature sensor is an electronic sensor, such as PT1000.

[0041] The temperature sensor 302 in the temperature calibration unit 3 transmits temperature data to the data processing module 7.

[0042] The data acquisition card 6 emits an electrical pulse to drive the pulsed laser 1 to emit an optical pulse. The optical pulse enters from the first port of the wavelength division multiplexer 2, and then exits from the second port of the wavelength division multiplexer 2. It enters the temperature calibration fiber 301 of the temperature calibration unit 3, and then enters the fiber under test through the fiber optic interface 4.

[0043] The sampling rate of the data acquisition card 6 is 100 Msps;

[0044] The Raman anti-Stokes light generated during the transmission of the optical pulse in the temperature calibration fiber and the fiber under test enters through the second port of the wavelength division multiplexer 2 and is output from the third port.

[0045] The photodetector 5 converts the Raman anti-Stokes light output from the third port of the wavelength division multiplexer 2 into a voltage signal, obtaining the optical time-domain reflectometry data of the Raman anti-Stokes light, such as... Figure 3 As shown, the data acquisition card 6 acquires the voltage signal output by the photodetector 5 and transmits the data to the data processing module 7 for temperature demodulation to obtain the temperature information at each location along the tested optical fiber.

[0046] The photodetector 5 has a bandwidth of 200MHz;

[0047] Before performing temperature demodulation, the data processing module 7 first acquires a set of Raman anti-Stokes light time-domain reflection voltage data, denoted as V. A (T0,L a ), where T0 is the temperature value measured by the temperature sensor 302, and L a This represents the distance at various locations along the tested optical fiber; a location at the tip of the tested optical fiber is denoted as L. Front L Front The 10m position can be selected as the zero point, and the corresponding voltage value is denoted as V. A (T0,L Front V A (T0,L Front The value is taken as the average of the voltages at various locations within a range of 5m to 15m; the value from location L of the tested fiber is calculated based on the attenuation coefficient of the tested fiber. Front The voltage data V(T0,L) at various locations along the line to the end of the fiber under test, such as... Figure 4 As shown, L represents the distance from the measured fiber position L. Front The distance to each position along the line from the end of the fiber optic cable being tested;

[0048] The voltage value at a certain set position on the temperature calibration optical fiber 301 is denoted as V. R(T0, L0), where L0 represents a set position on the temperature calibration fiber 301, L0 is taken at a position of 50m, and its corresponding voltage V R (T0, L0) Take the average value of the voltages at various locations within the range of 25m to 75m, such as Figure 5 As shown;

[0049] The data processing module 7 performs temperature demodulation according to the following steps:

[0050] Step 1: Acquire a set of Raman anti-Stokes light time-domain reflectometry (TDR) data, denoted as V(T,L), where T is the temperature value measured by the temperature sensor 302 during this data acquisition process. The position information L in the Raman anti-Stokes light TDR data V(T,L) corresponds one-to-one with the position information L in the voltage data V(T0,L), as follows: Figure 6 As shown;

[0051] The voltage value at a certain set position on the temperature calibration optical fiber 301 is denoted as V. R (T, L0), where L0 represents a set position on the temperature calibration fiber optic cable 301, and T is the temperature value measured by the temperature sensor 302; L0 is taken at a position of 50m, and its corresponding voltage V R (T,L0) Take the average value of the voltage at each location within the range of 25m to 75m, such as Figure 7 As shown;

[0052] Step 2: Calculate the power detection correction factor R of the Raman anti-Stokes light. Where h is Planck's constant, with a value of h = 6.626 × 10⁻⁶. -34 J·s, where k is the Boltzmann constant, with a value of k = 1.3806 × 10⁻⁶. -23 The Raman scattering bandwidth of J / K, v fiber is generally taken as v = 1.32 × 10⁻⁶. 13 Hz; Divide the optical time-domain reflectance voltage data V(T,L) of the Raman anti-Stokes light by the power detection correction coefficient R of the Raman anti-Stokes light to obtain the power-corrected optical time-domain reflectance voltage data of the Raman anti-Stokes light, denoted as V. C (T,L), that is

[0053] Step 3: Using the formula Calculate the temperature value at a distance L along the fiber optic cable under test;

[0054] The data processing module 7 transmits the calculation results to the display module 8, which displays the distance L and its corresponding temperature curves at various locations along the tested optical fiber. Figure 8 As shown.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A fiber optic Raman temperature measurement device based on detection power correction, characterized in that, The device includes: a pulsed laser (1), a wavelength division multiplexer (2), a temperature calibration unit (3), an optical fiber interface (4), a photodetector (5), a data acquisition card (6), a data processing module (7), and a display module (8); The temperature calibration unit (3) includes: a temperature calibration optical fiber (301) and a temperature sensor (302); The temperature sensor (302) in the temperature calibration unit (3) transmits temperature data to the data processing module (7); The data acquisition card (6) sends out an electrical pulse to drive the pulsed laser (1) to emit an optical pulse. The optical pulse enters from the first port of the wavelength division multiplexer (2), and then exits from the second port of the wavelength division multiplexer (2), enters the temperature calibration fiber (301) of the temperature calibration unit (3), and then enters the fiber under test through the fiber interface (4). The Raman anti-Stokes light generated during the transmission of the optical pulse in the temperature calibration fiber and the fiber under test enters through the second port of the wavelength division multiplexer (2) and is output from the third port; The photodetector (5) converts the Raman anti-Stokes light output from the third port of the wavelength division multiplexer (2) into a voltage signal; the data acquisition card (6) acquires the voltage signal output by the photodetector (5), obtains the optical time-domain reflectometry data of the Raman anti-Stokes light, and transmits the data to the data processing module (7) for temperature demodulation to obtain the temperature information at each position along the fiber under test. Before performing temperature demodulation, the data processing module (7) first acquires a set of Raman anti-Stokes light time-domain reflection voltage data, denoted as V. A (T0,L a ), where T0 is the temperature value measured by the temperature sensor (302), L a This represents the distance at various locations along the tested optical fiber; a location at the tip of the tested optical fiber is denoted as L. Front As the zero point, its corresponding voltage value is denoted as V. A (T0,L Front Based on the attenuation coefficient of the fiber under test, the distance from position L of the fiber under test is calculated. Front Voltage data V(T0,L) at various positions along the line from the end of the fiber under test, where L represents the voltage data from position L of the fiber under test. Front The distance to each position along the line from the end of the fiber optic cable being tested; The voltage value at a certain set position on the temperature calibration fiber (301) is denoted as V. R (T0,L0), where L0 represents a set position on the temperature calibration fiber (301); The data processing module (7) performs temperature demodulation according to the following steps: Step 1: Acquire a set of Raman anti-Stokes light time-domain reflectometry voltage data, denoted as V(T,L), where T is the temperature value measured by the temperature sensor (302) during this data acquisition process, and the position information L in the Raman anti-Stokes light time-domain reflectometry voltage data V(T,L) corresponds one-to-one with the position information L of the voltage data V(T0,L). The voltage value at a certain set position on the temperature calibration fiber (301) is denoted as V. R (T,L0), where L0 represents a set position on the temperature calibration fiber (301), and T is the temperature value measured by the temperature sensor (302); Step 2: Calculate the power detection correction factor R of the Raman anti-Stokes light. Where h is Planck's constant, with a value of h = 6.626 × 10⁻⁶. -34 J·s, where k is the Boltzmann constant, with a value of k = 1.3806 × 10⁻⁶. - 23 J / K, where v is the Raman scattering bandwidth of the optical fiber, typically taken as v = 1.32 × 10⁻⁶. 13 Hz; Divide the optical time-domain reflectance voltage data V(T,L) of the Raman anti-Stokes light by the power detection correction coefficient R of the Raman anti-Stokes light to obtain the power-corrected optical time-domain reflectance voltage data of the Raman anti-Stokes light, denoted as V. C (T,L), that is Step 3: Using the formula Calculate the temperature values ​​at distance L along the tested optical fiber at each location; The data processing module (7) transmits the calculation results to the display module (8), which displays the distance L and its corresponding temperature curves at each position along the tested optical fiber.

2. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The temperature sensor (302) is an electronic temperature sensor, and the temperature value is transmitted to the data processing module (7).

3. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The voltage value V at a certain set position on the temperature calibration fiber (301) R (T0,L0) is the average value of the voltage of the temperature calibration fiber (301) at a point near position L0.

4. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The voltage value V A (T0,L Front ) represents the position L of the fiber being measured. Front The average voltage is taken from the location of a fiber optic cable near the center.

5. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The photodetector (5) is selected as an avalanche photodetector with a bandwidth of not less than 100MHz.

6. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The sampling rate of the data acquisition card (6) is greater than 100 Msps.

7. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The data acquisition card (6) has a data accumulation function, with a maximum accumulation count of not less than 2. 14 Second-rate.

8. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The temperature calibration fiber (301) is not less than 100m in length.

9. The fiber optic Raman temperature measurement device based on detection power correction according to claim 1, characterized in that, The pulsed laser (1) has a trigger output function, which can output a trigger level to trigger the data acquisition card (6) to perform data acquisition.

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