Improved bocda-based mold monitoring method in high temperature environment

Abstract

The application discloses a kind of crystallizer monitoring methods in high temperature environment based on improved BOCDA, after two-dimensional plane mode is laid to the surface of crystallizer by sensing optical fiber, sensing optical fiber and BOCDA in normal temperature environment are connected by dispersion compensation fiber (DCF) respectively, the optical fiber Brillouin frequency shift (BFS) in specific section distance of sensing optical fiber is obtained by setting modulation frequency parameter, and then the temperature information of the surface of crystallizer is calculated.The sensing optical fiber with heat-resistant coating layer is combined with dispersion compensation fiber (DCF) in the application, and the property that the two kinds of optical fiber Brillouin frequency shift (BFS) is very different is utilized to measure the BFS of sensing optical fiber remotely, so as to realize accurate measurement of temperature in high temperature environment.

Description

Technical Field

[0001] This invention relates to a technology in the field of fiber optic sensing, specifically a method for monitoring crystallizers under high-temperature conditions based on an improved Brillouin coherence domain analyzer (BOCDA). Background Technology

[0002] The crystallizer, as the heart of the continuous casting machine, is enclosed and the molten steel is at a high temperature, making it difficult for technicians to understand the internal temperature of the steel. Currently, the common solution is to use thermocouples for discrete measurements of the crystallizer. However, the number of thermocouples is limited, typically twenty or thirty, resulting in limited temperature data. Furthermore, thermocouple measurements are affected by the magnetic field generated by electromagnetic stirring, leading to low accuracy. Additionally, the thermocouples need to be replaced periodically, which is inconvenient. Summary of the Invention

[0003] This invention addresses the shortcomings of existing electrical device testing technologies, which cannot accurately measure the temperature of planar areas at temperatures above 300°C. It proposes a crystallizer monitoring method based on an improved BOCDA, which combines a heat-resistant coated sensing fiber with a dispersion-compensating fiber (DCF). By utilizing the significant difference in the Brillouin frequency shift (BFS) of the two fibers, the BFS of the sensing fiber is measured remotely, enabling accurate temperature measurement in high-temperature environments.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a crystallizer monitoring method under high temperature conditions based on an improved BOCDA. The method involves laying a sensing fiber in a two-dimensional plane on the surface of the crystallizer, connecting the sensing fiber and the BOCDA set up at room temperature through a dispersion compensation fiber (DCF). By setting modulation frequency parameters, the fiber Brillouin frequency shift (BFS) over a specific segment of the sensing fiber is obtained, and the temperature information of the crystallizer surface is calculated.

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

[0007] The probe light branch includes a single-sideband modulator, an erbium-doped amplifier, and a polarization controller connected in sequence. The single-sideband modulator reduces the frequency of the wavelength scanning laser output by the laser.

[0008] The pump light branch includes an acousto-optic modulator, a delay fiber, a polarization switch, and an erbium-doped amplifier connected in sequence. The acousto-optic modulator modulates the wavelength scanning laser output from the laser into periodic pulsed pump light.

[0009] The signal processing branch includes: a variable attenuator (VOA), a photodetector, a data acquisition card, and a lock-in amplifier connected in sequence, wherein the input terminal of the photodetector is connected to the variable attenuator and the circulator, respectively. Attached Figure Description

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

[0011] In the diagram: 1 Laser, 2 Arbitrary Waveform Generator, 3 Adjustable Microwave Source, 4 Single Sideband Modulator, 5 Polarization Controller, 6 Isolator, 7 Acousto-Optical 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 Dispersion Compensation Fiber, 17 Second Dispersion Compensation Fiber;

[0012] Figure 2 This is a schematic diagram of the 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 A schematic diagram of the Brillouin frequency shift of a polymer-coated optical fiber at high temperature.

[0015] Figure 5 A schematic diagram of the Brillouin frequency shift and temperature of a polymer-coated optical fiber at high temperature.

[0016] Figure 6 A schematic diagram of the test area in the crystallizer of a continuous casting machine and the fiber optic cable laying;

[0017] Figure 7 A simulation diagram illustrating the system's measurement accuracy and energy loss;

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

[0019] Figure 8 The image shows the two-dimensional temperature distribution results for an example. Detailed Implementation

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

[0021] The probe 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 probe light of about 11 GHz.

[0022] The pump light branch includes: 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 includes: a variable optical attenuator 13, a photodetector 14, a data acquisition card, and a lock-in amplifier 15 connected in sequence, wherein: the input terminal 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 correlated peaks from interfering with each other, the length of the sensing fiber 10 is less than or equal to the interval between adjacent correlated peaks, i.e., the maximum sensing range d. m Generally: ,in: ρ is the refractive index of the fiber core, and c is the speed of light.

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

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

[0027] like Figure 3 As shown, after measuring in a high-temperature environment of 400℃ for more than 30 minutes, all the organic matter in the high-temperature furnace had been carbonized, while the physical properties of the sensing optical fiber remained unchanged.

[0028] like Figure 4 As shown, the BFS of the sensing fiber remains unchanged under stable high-temperature conditions, making it suitable for measuring higher temperatures.

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

[0030] The probe light and pump light are respectively fed into the sensing fiber 10 and stimulated Brillouin scattering is generated. The gain spectrum of Brillouin scattering is characterized by adjusting the modulation signal frequency of the single-sideband modulator. The light source forms a correlation peak on the sensing fiber after sinusoidal modulation, such as... Figure 2 The stimulated Brillouin scattering at the correlation peak position is shown to be strong, while the stimulated Brillouin scattering at other positions is weak. The position of the correlation peak can be changed by changing the frequency of the sine wave, thus achieving the purpose of distributed measurement.

[0031] The area to be measured on the crystallizer is a two-dimensional planar region, and it is necessary to make such a measurement. Figure 6 The diagram shows a curved paving pattern. When the bending radius is... At that time, bending loss coefficient Where: normalized phase constant Radial normalization constant , Here, denoted as cladding refractive index and free space wavenumber, is given. , The core radius is... Let be the propagation constant. for Bessel function of order 1, . The calculated results and the actual measurements are as follows: Figure 7 (a) and Figure 7 As shown in (b). Considering the impact of multiple bending on the measurement accuracy of the BOCDA system, the results are as follows. Figure 7 As shown in (c), it can be concluded that with a radius of curvature of approximately 1.5 cm or more, multiple bends have little impact on temperature measurement error. Therefore, the laying method used in the actual experiment was: bending with a radius of curvature of 2 cm, 7 times.

[0032] Through specific practical experiments, under a specific environmental setting of approximately 362°, using a BOCDA system including a 10-meter DCF, a 10-meter sensing fiber, and a 1.2-cm spatial resolution, and after isolating the high-temperature environment, it was able to measure... Figure 8 The temperature distribution is shown in a two-dimensional plane. Compared with the prior art, the present invention can achieve long-distance measurement without being affected by DCF, solves the technical problem of high-temperature environment measurement, and realizes high-temperature measurement at a long distance.

[0033] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for monitoring crystallizers under high-temperature conditions based on improved BOCDA, characterized in that, After laying the sensing fiber in a two-dimensional plane on the surface of the crystallizer, the sensing fiber and the BOCDA set at room temperature are connected by the dispersion compensation fiber. By setting the modulation frequency parameters, the fiber Brillouin frequency shift of a specific segment in the sensing fiber is obtained, and then the temperature information of the crystallizer surface is calculated. The aforementioned two-dimensional planar laying method refers to: the area to be measured on the crystallizer is a two-dimensional planar region, requiring a curved laying method, where the bending radius is... At that time, bending loss coefficient Where: normalized phase constant Radial normalization constant , Here, denoted as cladding refractive index and free space wavenumber, is given. , The core radius is... Let be the propagation constant. for Bessel function of order 1, , For wavelength, The core refractive index of the optical fiber; The length of the sensing fiber is less than or equal to the interval between adjacent correlation peaks, i.e., the maximum sensing range. ,in: , c is the speed of light.

2. The crystallizer monitoring method based on improved BOCDA under high temperature environment according to claim 1, characterized in that, The BOCDA includes a DFB laser, a probe light branch, a pump light branch, a signal processing branch, and a sensing fiber. The laser output from the DFB laser is sinusoidally modulated and then output to the probe light branch and the pump light branch. The output of the probe light branch is connected to one end of the sensing fiber and the input of the signal processing branch. The output of the pump light branch is connected to the other end of the sensing fiber and the input of the signal processing branch through a circulator.

3. The crystallizer monitoring method based on improved BOCDA under high temperature conditions according to claim 2, characterized in that, The probe light branch includes a single-sideband modulator, an erbium-doped amplifier, and a polarization controller connected in sequence. The single-sideband modulator reduces the frequency of the wavelength scanning laser output by the laser.

4. The crystallizer monitoring method based on improved BOCDA under high temperature environment according to claim 2, characterized in that, The pump light branch includes an acousto-optic modulator, a delay fiber, a polarization switch, and an erbium-doped amplifier connected in sequence. The acousto-optic modulator modulates the wavelength scanning laser output from the laser into periodic pulsed pump light.

5. The crystallizer monitoring method based on improved BOCDA under high temperature conditions according to claim 2, characterized in that, The signal processing branch includes: a variable attenuator (VOA), a photodetector, a data acquisition card, and a lock-in amplifier connected in sequence, wherein the input terminal of the photodetector is connected to the variable attenuator and the circulator, respectively.

6. The crystallizer monitoring method based on improved BOCDA under high temperature environment according to claim 1, characterized in that, The Brillouin frequency shift of the dispersion compensation fiber differs from that of the sensing fiber by more than 1 GHz.

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