Crystallizer monitoring method in high-temperature environment based on improved BOCDA

Abstract

A method for monitoring a crystallizer in a high-temperature environment based on an improved BOCDA comprises the following steps: after a sensing optical fiber is laid on the surface of the crystallizer in a two-dimensional plane mode, the sensing optical fiber and the BOCDA arranged in a normal-temperature environment are respectively connected through a dispersion compensation optical fiber (DCF); the optical fiber Brillouin frequency shift (BFS) on a specific section distance in the sensing optical fiber is obtained by setting modulation frequency parameters, and then temperature information of the surface of the crystallizer is obtained through calculation. According to the invention, the sensing optical fiber with a heat-resistant coating layer is combined with the dispersion compensation optical fiber (DCF), and the BFS of the sensing optical fiber is remotely measured by utilizing the property that the BFS of the two optical fibers is greatly different, so that the accurate temperature measurement in a high-temperature environment is realized.

Description

Technical Field

[0001] The present invention relates to a technology in the field of optical fiber sensing, in particular to a method for monitoring a crystallizer in a high-temperature environment based on an improved Brillouin coherence domain analyzer (BOCDA). Background Art

[0002] The mold, the heart of the continuous casting machine, is enclosed on all sides and contains high temperatures, making it difficult for technicians to understand the temperature of the molten steel inside. The current common solution is to use thermocouples for discrete measurements of the mold. However, the number of thermocouples is limited, typically 20 to 30, resulting in limited temperature data. Furthermore, thermocouple temperature measurement is subject to interference from the magnetic field generated by electromagnetic stirring, resulting in low measurement accuracy. Furthermore, the thermocouples must be regularly replaced, which is inconvenient. Summary of the Invention

[0003] In response to the deficiency of existing electrical component detection technology that is unable to accurately measure the temperature of a planar area in a temperature environment above 300°C, the present invention proposes a crystallizer monitoring method in a high-temperature environment based on an improved BOCDA. A sensing fiber with a heat-resistant coating is combined with a dispersion-compensating fiber (DCF). The Brillouin frequency shift (BFS) of the two optical fibers is greatly different, and the BFS of the sensing fiber is remotely measured to achieve accurate temperature measurement in a high-temperature environment.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a method for monitoring a crystallizer in a high-temperature environment based on an improved BOCDA. A sensing optical fiber is laid on the surface of the crystallizer in a two-dimensional plane. The sensing optical fiber and the BOCDA set at room temperature are respectively connected via dispersion-compensating optical fiber (DCF). The Brillouin frequency shift (BFS) of the sensing optical fiber over a specific distance is obtained by setting modulation frequency parameters, and the temperature information of the crystallizer surface is then calculated.

[0006] The BOCDA includes a DFB laser, a detection light branch, a pump light branch, a signal processing branch, and a sensing fiber. The laser light output by the DFB laser is sinusoidally modulated and then output to the detection light branch and the pump light branch, respectively. The output end of the detection light branch is connected to one end of the sensing fiber and the input end of the signal processing branch, respectively. The output end of the pump light branch is connected to the other end of the sensing fiber and the input end of the signal processing branch via a circulator.

[0007] The detection optical branch comprises: a single sideband modulator, an erbium-doped amplifier and a polarization controller connected in sequence, and the frequency of the wavelength scanning laser output by the laser is reduced by the single sideband modulator.

[0008] The pump light branch comprises an acousto-optic modulator, a delay optical fiber, a polarization switch and an erbium-doped amplifier connected in sequence. The wavelength scanning laser output by the laser is modulated into periodic pulse pump light by the acousto-optic modulator.

[0009] The signal processing branch comprises a variable attenuator (VOA), a photoelectric detector, an acquisition card and a phase-locked amplifier connected in sequence, wherein the input end of the photoelectric detector is connected to the variable attenuator and the circulator respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the structure of the present invention;

[0011] In the figure: 1 laser, 2 arbitrary waveform generator, 3 tunable microwave source, 4 single-sideband modulator, 5 polarization controller, 6 isolator, 7 acousto-optic modulator, 8 polarization switch, 9 erbium-doped amplifier, 10 sensing fiber, 11 delay fiber, 12 circulator, 13 variable attenuator, 14 photodetector, 15 acquisition card and lock-in amplifier, 16 first section of dispersion-compensating fiber, 17 second section of dispersion-compensating fiber;

[0012] Figure 2 Schematic diagram of BOCDA related peaks in the embodiment;

[0013] Figure 3 This is a schematic diagram of a polymer-coated optical fiber after being subjected to high temperature;

[0014] Figure 4 Schematic diagram of Brillouin frequency shift of polymer-coated optical fiber at high temperature;

[0015] Figure 5 Schematic diagram of Brillouin frequency shift and temperature of polymer-coated optical fiber at high temperature;

[0016] Figure 6 This is a schematic diagram of the mold test area and optical fiber laying in the continuous casting machine;

[0017] Figure 7 Schematic diagram of system measurement accuracy and energy loss simulation;

[0018] In the figure: a is the relationship between optical fiber loss and bending radius of curvature, b is the relationship between system temperature measurement accuracy and signal-to-noise ratio, and c is the relationship between temperature measurement accuracy and bending radius of curvature;

[0019] Figure 8 This is a diagram of the two-dimensional temperature distribution results of the embodiment. DETAILED DESCRIPTION

[0020] like Figure 1As shown, the embodiment relates to a BOCDA system for crystallizer temperature monitoring, comprising: a 1550nm DFB laser 1, a detection light branch, a pump light branch, a signal processing branch, and a sensing fiber 10. The laser light output by the DFB laser 1 is sinusoidally modulated and output to the detection light branch and the pump light branch, respectively. The output end of the detection light branch is connected to one end of a first section of dispersion-compensating fiber (DCF) 16 and the input end of the signal processing branch, respectively. The other end of the first section of DCF 16 is connected to one end of the sensing fiber 10. The output end of the pump light branch is connected to one end of a second section of DCF 17 and the input end of the signal processing branch via a circulator 12. The other end of the second section of DCF 17 is connected to the other end of the sensing fiber 10.

[0021] The detection light branch includes: a single sideband modulator 4, a first erbium-doped amplifier 9 and a polarization controller 5 connected in sequence. The single sideband modulator 4 reduces the frequency of the laser output to a detection light of about 11 GHz.

[0022] The pump light branch comprises an acousto-optic modulator 7, a delay fiber 11, a polarization switch 8 and a second erbium-doped amplifier 9 connected in sequence. The acousto-optic modulator 7 modulates the output laser of the laser into periodic pulsed pump light.

[0023] The signal processing branch comprises a variable optical attenuator 13, a photodetector 14, an acquisition card and a lock-in amplifier 15 connected in sequence, wherein the input end of the photodetector 14 is connected to the variable optical attenuator 13 and the circulator 12 respectively.

[0024] Preferably, in order to prevent the signals of multiple correlation peaks from affecting each other, the length of the sensing fiber 10 is less than or equal to the interval between adjacent correlation peaks, that is, the maximum sensing range d m Generally: ,in: is the core refractive index of the optical fiber, and c is the speed of light.

[0025] The Brillouin frequency shift of the DCF fibers 16 and 17 differs from that of the sensing fibers by more than 1 GHz, and will not affect the sensing fibers when measuring the Brillouin gain spectrum. Figure 2 shown.

[0026] Preferably, in order to meet the measurement requirements of higher temperatures, the exterior of the sensing optical fiber 10 is coated with a heat-resistant polymer material polyimide (PI) layer.

[0027] like Figure 3 As shown in the figure, after measuring at a high temperature of 400℃ for more than 30 minutes, the organic matter in the high temperature furnace has been carbonized, while the physical properties of the sensing fiber have not changed.

[0028] like Figure 4 As shown in the figure, in a stable high-temperature environment, the BFS of the sensing fiber does not change and can be used for higher temperature measurements.

[0029] like Figure 5 The figure shows the relationship between temperature and BFS. It can be seen that at high temperatures, BFS is no longer linearly related to temperature, so the optical fiber needs to be recalibrated when measuring at high temperatures.

[0030] The probe light and pump light are respectively sent to the sensing fiber 10 and generate stimulated Brillouin scattering. The gain spectrum of Brillouin scattering is characterized by adjusting the modulation signal frequency of the single-sideband modulator. The light source is modulated by a sine wave to form a correlation peak on the sensing fiber, such as Figure 2 As shown, the stimulated Brillouin scattering at the correlation peak position is stronger, while the stimulated Brillouin scattering at other positions is weaker. By changing the frequency of the sine wave, the correlation peak position can be changed to achieve the purpose of distributed measurement.

[0031] The range to be measured on the crystallizer is a two-dimensional plane area, and the following Figure 6 The bending radius is shown. When the bending loss coefficient , where: normalized phase constant , radial normalization constant , is the cladding refractive index, the free space wave number , is the core radius, is the propagation constant, for Bessel function of order, . The calculated results and the measured results are as follows Figure 7 (a) and Figure 7 (b) Considering the influence of multiple bending on the measurement accuracy of the BOCDA system, the results are as follows Figure 7 (c) shows that when the curvature radius is above approximately 1.5 cm, multiple bends can have little effect on the temperature measurement error. Therefore, the specific laying method used in the actual experiment is: bending with a curvature radius of 2 cm and bending seven times.

[0032] After specific actual experiments, under the specific environment setting of about 362°, a BOCDA system including 10 meters of DCF, 10 meters of sensing fiber, and 1.2 cm spatial resolution was used. After isolating the high temperature environment, the following measurements were made: Figure 8 Compared with the prior art, the present invention can achieve long-distance measurement without being affected by DCF, solves the technical difficulties of high-temperature environment measurement, and realizes high-temperature measurement at a long distance.

[0033] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA, characterized in that: After laying the sensing fiber on the surface of the crystallizer in a two-dimensional plane, the sensing fiber and the BOCDA set at room temperature are connected through dispersion-compensating optical fibers. The Brillouin frequency shift of the fiber at a specific distance in the sensing fiber is obtained by setting the modulation frequency parameters, and then the temperature information of the crystallizer surface is calculated.

2. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 1, wherein: The BOCDA includes a DFB laser, a detection light branch, a pump light branch, a signal processing branch, and a sensing fiber. The laser light output by the DFB laser is sinusoidally modulated and then output to the detection light branch and the pump light branch, respectively. The output end of the detection light branch is connected to one end of the sensing fiber and the input end of the signal processing branch, respectively. The output end of the pump light branch is connected to the other end of the sensing fiber and the input end of the signal processing branch via a circulator.

3. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 2, wherein: The detection optical branch comprises: a single sideband modulator, an erbium-doped amplifier and a polarization controller connected in sequence, and the frequency of the wavelength scanning laser output by the laser is reduced by the single sideband modulator.

4. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 2, wherein: The pump light branch comprises an acousto-optic modulator, a delay optical fiber, a polarization switch and an erbium-doped amplifier connected in sequence. The wavelength scanning laser output by the laser is modulated into periodic pulse pump light by the acousto-optic modulator.

5. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 2, wherein: The signal processing branch comprises a variable attenuator (VOA), a photoelectric detector, an acquisition card and a phase-locked amplifier connected in sequence, wherein the input end of the photoelectric detector is connected to the variable attenuator and the circulator respectively.

6. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 1, wherein: The length of the sensing fiber is less than or equal to the interval between adjacent correlation peaks, that is, the maximum sensing range .

7. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 1 or 6, wherein: The Brillouin frequency shift of the dispersion-compensating optical fiber differs from that of the sensing optical fiber by more than 1 GHz.

8. The method for monitoring a crystallizer in a high temperature environment based on an improved BOCDA according to claim 1, wherein: The two-dimensional plane laying method means that the range to be measured on the crystallizer is a two-dimensional plane area, and a curved laying method is required. When the bending radius is When the bending loss coefficient , where: normalized phase constant , radial normalization constant , is the cladding refractive index, the free space wave number , is the core radius, is the propagation constant, for Bessel function of order, , is the wavelength.

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