A personnel positioning system for underground mines based on dual-wavelength phase demodulation

Abstract

The invention discloses a personnel positioning system in a mine based on dual-wavelength phase demodulation. The system comprises a diode laser source, a coupler, an acousto-optic modulator, an erbium-doped fiber amplifier, a circulator, a wave splitter, a sensing fiber, a coupler, a photoelectric balance detector, a high-speed data acquisition card and a computer. A diode laser source is used to generate incident light of two wavelengths, which is divided into two paths through a coupler, and an EDFA is used to further increase the power to enter the circulator and the sensing fiber. The wave splitter is used to perform wavelength separation on the synthesized light wave, so that single-wavelength phase and dual-wavelength phase information can be obtained simultaneously; the photoelectric balance detector is used to perform coherent demodulation on the phase information; the high-speed data acquisition card is used to collect and demodulate the vibration information in the sensing fiber in real time, and all data are finally processed by a computer, and the positioning lag caused by a digital low-pass filter needs to be compensated, so as to finally obtain the relationship between the phase and the positioning distance.

Description

Technical Field

[0001] The invention belongs to the technical field of underground coal mine production safety monitoring, and relates to a personnel positioning system, in particular to a mine personnel positioning system based on dual-wavelength phase demodulation of phase optical time domain reflectometry technology. Background Art

[0002] As a major coal producer in China, mine accidents occur from time to time. How to quickly locate trapped personnel in accident mines is of great significance to the safe production of coal mines. The underground production environment of coal mines is relatively complex, mainly including dust-proof, explosion-proof and intrinsically safe production requirements for underground electronic and electrical equipment. The existence of a large amount of background noise in mines (on the one hand, such as mechanical noise caused by coal mining machines, conveyors, crushers and underground locomotives, on the other hand, electromagnetic noise caused by the closing of switches, the start and stop of large electromechanical equipment and the operation of underground substations), as well as the presence or absence of power supply conditions at the scene during emergency rescue, leads to certain deficiencies in the use of existing personnel positioning systems such as UWB, SUPER-RFID, Zigbee, micro-power and WiFi personnel positioning systems in mines. The personnel positioning system based on optical fiber sensing detection can solve the problems of the above positioning systems due to its insensitivity to electromagnetic interference and passive characteristics.

[0003] Due to the special environment underground, complex fiber optic sensing systems are often not suitable for designing personnel positioning systems. When accidents such as gas explosions, collapses or water seepage occur underground, the rescue positioning system should be able to directly connect to the existing fiber optic network underground to quickly locate personnel. Therefore, except for the sensing fiber (Sensing Fiber) part, other equipment should be carried by rescue personnel. Therefore, a relatively simple and efficient coherent detection structure is more adaptable to the production environment and accident conditions underground. In addition, the coherent detection structure can also effectively reduce noise interference. The existing underground fiber optic sensing positioning system mainly adopts a distributed fiber optic personnel positioning system based on phase optical time domain reflection technology (Φ-OTDR). Its main principle is to locate the position of the vibration signal by calculating the time delay between the incident pulse light and the received backward Rayleigh scattered light through the phase change of the Rayleigh reflected light in the optical fiber caused by vibration. Since the relationship between phase and time is a trigonometric function relationship, and the periodicity of the trigonometric function itself makes the result of demodulating the phase not necessarily the real vibration information, so positioning misjudgment often occurs.

[0004] Since the phase has the periodicity of trigonometric functions, the phase jumps every time it passes through an integer multiple of π. During traditional phase unwrapping, since the relationship between the wrapped phase and the main value phase is , the phase values ​​of two adjacent points are compared. When the phase jumps, if the phase difference between the two adjacent points exceeds 2π, the phase values ​​of this point and subsequent points are added or subtracted by 2π so that the difference between adjacent sampling points is within the range of (-π, π). However, if the final compensated difference between the two adjacent points by this method still exceeds 2π or -2π, the traditional phase unwrapping method will fail, and false positioning information will be generated.

[0005] The study found that when a laser source with a relatively long wavelength is used, the time interval for the jumps also becomes longer. Therefore, the existing fiber laser source can be used to obtain a larger synthetic wavelength through the dual-wavelength phase demodulation method in digital holography technology to avoid the phase wrapping problem and obtain accurate phase distribution. Summary of the invention

[0006] The purpose of the present invention is to provide a personnel positioning system in mines based on dual-wavelength phase demodulation. After a mine accident occurs, the trapped personnel knock on the mine wall, and the rescue personnel use the existing optical fiber network in the mine to quickly and accurately locate the trapped personnel. The false position information is eliminated through the dual-wavelength phase demodulation results in the system, and accurate positioning information is obtained through the single-wavelength phase demodulation results.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A personnel positioning system for mines based on dual-wavelength phase demodulation, comprising a diode laser source, a coupler, an acousto-optic modulator, an erbium-doped fiber amplifier, a circulator, a wave splitter 1, a wave splitter 2, a sensing fiber, a coupler 1, a coupler 2, a photoelectric balance detector 1, a photoelectric balance detector 2, a high-speed data acquisition card and a computer, wherein:

[0009] The incident laser source generates incident light of two different wavelengths, wavelength 1 and wavelength 2, which are divided into two paths through a coupler, one for reference light and the other for detection light;

[0010] The detection light enters the detection arm, passes through the acousto-optic modulator and then is amplified by the erbium-doped fiber amplifier, and then enters the sensing fiber through the circulator. The Rayleigh reflected light returns to the circulator through the sensing fiber and then enters the wavelength splitter 1 to separate two lights of different wavelengths, wavelength 1 and wavelength 2. The light of wavelength 1 enters the coupler 1, and the light of wavelength 2 enters the coupler 2.

[0011] The reference light enters the reference arm and is split into two lights of wavelength 1 and wavelength 2 with different wavelengths by the wavelength splitter 2. The light of wavelength 1 enters the coupler 1, and the light of wavelength 2 enters the coupler 2.

[0012] The Rayleigh reflected light in the detection arm and the reference light in the reference arm enter the coupler 1 and coupler 2, are coupled after being phase shifted by π / 2, enter the photoelectric balancer detector 1 and the photoelectric balancer detector 2, and are converted into photocurrent in the photoelectric balancer detector 1 and the photoelectric balancer detector 2 to obtain the difference;

[0013] The outputs of the photoelectric balancer detector 1 and the photoelectric balancer detector 2 are entered into a computer for coherent demodulation through a high-speed data acquisition card to obtain the phases of wavelength 1 and wavelength 2. The phases of wavelength 1 and wavelength 2 are subtracted to obtain a synthetic phase. The three phase results are phase unwrapped to obtain a phase curve of phase and distance. When vibration occurs, the phase of the Rayleigh reflected light is disturbed, and the phase information of the phase curve at this time and the original curve at the disturbance position will change. The specific disturbance position information can be obtained by superimposing multiple curves.

[0014] In the present invention, the wavelength 1 and the wavelength 2 need to meet the dust and explosion proof intrinsic safety requirements of mines, and the closer the wavelengths are, the better. For example, the wavelength 1 is 1310 nm and the wavelength 2 is 1550 nm.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. Use a diode laser source to generate incident light of two wavelengths, 1310nm and 1550nm, which are divided into two paths through a coupler, one for reference light and the other for detection light. The detection light has a stronger power, accounting for 90%, which can increase the intensity of Rayleigh reflected light.

[0017] 2. Use an erbium-doped fiber amplifier (EDFA) to further increase the power into the circulator and then into the sensing fiber.

[0018] 3. By using a wavelength splitter (DEMUX) to separate the synthesized light wave, single-wavelength phase and dual-wavelength phase information can be obtained simultaneously.

[0019] 4. Use balanced photoelectric detector (BPD) to coherently demodulate the phase information. In addition, BPD can also effectively remove noise.

[0020] 5. Use a high-speed data acquisition card (DAQ) to collect and demodulate the vibration information in the sensing optical fiber in real time.

[0021] 6. All data are finally processed by computer, and the positioning lag caused by digital low-pass filter needs to be compensated to finally obtain the relationship between phase and positioning distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a structural block diagram of a dual-wavelength mine personnel positioning system, 1-1310nm laser source (Laser1), 2-1550nm laser source (Laser2), 3-2×2 coupler (2×2Coupler), 4-acoustic-optic modulator (AOM), 5-erbium-doped fiber amplifier (Amplifier), 6-circulator (Circulator), 7-demultiplexer 1 (DEMUX1), 8-demultiplexer 2 (DEMUX2), 9-sensing fiber (Sensing Fiber), 10-3dB coupler 1 (3dBCoupler1), 11-3dB coupler 2 (3dBCoupler2), 12-photoelectric balanced detector 1 (BPD1), 13-photoelectric balanced detector 2 (BPD2), 14-high-speed data acquisition card (DAQ), 15-computer (Computer);

[0023] Figure 2 It is the working principle diagram of BPD, 16-diode 1, 17-diode 2, 18-transimpedance amplifier, 19-operational amplifier;

[0024] Figure 3 This is a flow chart of position determination;

[0025] Figure 4 It is the cumulative distribution curve of positioning error after multiple phase demodulations. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0027] The present invention provides a personnel positioning system in a mine based on dual-wavelength phase demodulation. Figure 1 As shown, the positioning system includes an incident laser source, a 2×2 coupler, an acousto-optic modulator, an erbium-doped fiber amplifier, a circulator, a wave splitter 1, a wave splitter 2, a sensing fiber, a 3dB coupler 1, a 3dB coupler 2, a photoelectric balanced detector 1, a photoelectric balanced detector 2, a high-speed data acquisition card and a computer, wherein:

[0028] The incident laser source adopts a diode laser source with wavelengths of 1310nm and 1550nm respectively. The 1310nm laser source and the 1550nm laser source enter the detection arm and the reference arm respectively through a 2×2 coupler;

[0029] The detection light of the detection arm accounts for 90% of the incident power. The incident light passes through the acousto-optic modulator and then amplified by the erbium-doped fiber amplifier, and then enters the original mine optical fiber network (sensing fiber) through the circulator. The Rayleigh reflected light returns to the circulator through the sensing fiber and enters the wavelength splitter 1 to separate two lights with different wavelengths. The light with a wavelength of 1310nm enters the 3dB coupler 1, and the light with a wavelength of 1550nm enters the 3dB coupler 2.

[0030] The reference light of the reference arm accounts for 10% of the incident power. The incident light is split into two lights with different wavelengths by the splitter 2. The light with a wavelength of 1310nm enters the 3dB coupler 1, and the light with a wavelength of 1550nm enters the 3dB coupler 2.

[0031] The Rayleigh reflected light in the detection arm and the reference light in the reference arm enter the 3dB coupler 1 and the 3dB coupler 2, are coupled after being phase shifted by π / 2, enter the photoelectric balancer detector 1 and the photoelectric balancer detector 2, and are converted into photocurrent in the photoelectric balancer detector 1 and the photoelectric balancer detector 2 to obtain the difference;

[0032] The outputs of the photoelectric balancer detector 1 and the photoelectric balancer detector 2 are sent to the computer for coherent demodulation through a high-speed data acquisition card to obtain the phase of the 1310nm wavelength and the 1550nm wavelength. The synthetic phase is obtained by subtracting the phase of the 1310nm wavelength and the 1550nm wavelength. The three phase results are phase unwrapped to obtain the phase curve of phase and distance. When vibration occurs, the phase of the Rayleigh reflected light is disturbed, and the phase information of the phase curve at this time and the original curve at the disturbance position will change. The specific disturbance position information can be obtained by superimposing multiple curves (disturbance will cause phase change, and the phase at the non-disturbance position remains basically unchanged).

[0033] After many experiments, it was found that the high-order low-pass digital filter used in coherent demodulation will have a lag effect on the positioning information. The specific impact is positively correlated with the order of the filter. After the lag compensation of the program, the correct positioning information is obtained.

[0034] The synthetic wavelength positioning information will be compared with the two single wavelength positioning information. If the error value is within 50 meters, the single wavelength positioning information will be used, because the smaller the wavelength, the more accurate the positioning accuracy. If the error is beyond 50 meters, the synthetic wavelength positioning information will be used, because the synthetic wavelength reduces the false alarm information caused by phase unwrapping.

[0035] In the present invention, the working principle of BPD is as follows Figure 2 described.

[0036] In the present invention, the position determination process is as follows: Figure 3 shown.

[0037] In order to verify the performance of the dual-wavelength mine personnel positioning system, a related experiment was designed. Using cylindrical piezoelectric ceramics (PZT) as an external vibration source, it was placed at the position of 1100m of the optical fiber detection arm to simulate the vibration of underground personnel hitting the mine wall. The distance of the optical cable wrapped around PZT was 3 meters to simulate the vibration range of the mine wall. The light source used was a laser diode with wavelengths of 1310nm and 1550nm respectively.

[0038] If the positioning error is within 10 meters, it can be considered as accurate positioning. If the positioning error is between 10 meters and 30 meters, it can be considered as a positioning measurement that meets general needs. When the positioning error exceeds 30 meters, the positioning information is generally considered to be false alarm information. Figure 4 It can be found that within the 20-meter positioning error range, single-wavelength phase demodulation has a clear advantage, and dual-wavelength demodulation has a larger positioning information error. Within the 30-meter positioning error range, dual-wavelength phase demodulation false alarm positioning has a clear advantage. The specific data information is shown in Table 1.

[0039] Table 1 Error ratio of two phase demodulation methods

[0040]

[0041] As can be seen from Table 1, since the PZT is wrapped with 3 meters of optical fiber to simulate the vibration of the mine wall, the accuracy of the two demodulation methods within the three-meter positioning error is relatively small, especially the dual-wavelength phase demodulation positioning accuracy is only 18.24%. When the positioning error is within 10 meters, it can be seen that the single-wavelength phase demodulation has a clear advantage, and its positioning accuracy is 71.22%. When the positioning error is required to be within 20 meters, the accuracy of the two demodulation methods is relatively close, with the single-wavelength demodulation method being 90.34% and the dual-wavelength demodulation method being 91.78%. When the positioning error is required to be 30 meters, it can be seen that the dual-wavelength positioning accuracy is significantly higher than that of the single wavelength, and at this time the accuracy of the dual-wavelength positioning reaches 98.87%. When the positioning error exceeds 30 meters, the positioning information at this time can be regarded as false alarm information. At this time, the single-wavelength positioning has a 7% false alarm rate, while the dual-wavelength positioning has only 1%. Due to the addition of a splitter, coupler and optoelectronic balancer, the dual-wavelength positioning system is slightly slower than the single-wavelength positioning system in positioning time. However, in actual engineering applications, such a time difference will not affect the specific use effect.

Claims

1. A mine personnel positioning system based on dual-wavelength phase demodulation, characterized in that The system comprises a diode laser source, a coupler, an acousto-optic modulator, an erbium-doped fiber amplifier, a circulator, a wave splitter 1, a wave splitter 2, a sensing fiber, a coupler 1, a coupler 2, a photoelectric balanced detector 1, a photoelectric balanced detector 2, a high-speed data acquisition card and a computer, wherein: The diode laser source generates two incident lights with different wavelengths, wavelength 1 and wavelength 2, which are divided into two paths through a coupler, one for reference light and the other for detection light; The detection light enters the detection arm, passes through the acousto-optic modulator and then is amplified by the erbium-doped fiber amplifier, and then enters the sensing fiber through the circulator. The Rayleigh reflected light returns to the circulator through the sensing fiber and then enters the wavelength splitter 1 to separate two lights of different wavelengths, wavelength 1 and wavelength 2. The light of wavelength 1 enters the coupler 1, and the light of wavelength 2 enters the coupler 2. The reference light enters the reference arm and is split into two lights of wavelength 1 and wavelength 2 with different wavelengths by the wavelength splitter 2. The light of wavelength 1 enters the coupler 1, and the light of wavelength 2 enters the coupler 2. The Rayleigh reflected light in the detection arm and the reference light in the reference arm enter the coupler 1 and coupler 2, are coupled after being phase shifted by π / 2, enter the photoelectric balancer detector 1 and the photoelectric balancer detector 2, and are converted into photocurrent in the photoelectric balancer detector 1 and the photoelectric balancer detector 2 to obtain the difference; The outputs of the photoelectric balancer detector 1 and the photoelectric balancer detector 2 are sent to the computer for coherent demodulation through a high-speed data acquisition card to obtain the phase of wavelength 1. and the phase of wavelength 2 The phase of wavelength 1 and the phase of wavelength 2 Subtract to get the resultant phase The three phase results are phase unwrapped respectively, and the phase-position relationship curve is drawn to obtain initial position information 1, initial position information 3 and initial position information 2; correct position 1, position 3 and position 2 caused by the position lag caused by the order of the low-pass filter, and judge the difference between position 1 and position 2. If the absolute difference between position 1 and position 2 is greater than 30m, continue to judge the difference between position 2 and position 3, otherwise output position information 1; if the absolute difference between position 2 and position 3 is greater than 30m, output position information 2, otherwise output position information 3.

2. The mine personnel positioning system based on dual-wavelength phase demodulation according to claim 1 is characterized in that The coupler is a 2×2 coupler.

3. The mine personnel positioning system based on dual-wavelength phase demodulation according to claim 1 is characterized in that The coupler 1 and the coupler 2 are 3dB couplers.

4. The mine personnel positioning system based on dual-wavelength phase demodulation according to claim 1 is characterized in that The detection light of the detection arm accounts for 90% of the incident power, and the reference light of the reference arm accounts for 10% of the incident power.

5. The mine personnel positioning system based on dual-wavelength phase demodulation according to claim 1 is characterized in that The wavelength 1 is 1310 nm, and the wavelength 2 is 1550 nm.

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