阅读说明：本技术 面向煤田采空区火源钻孔探测的分布式光纤温度传感方法 (Distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection ) 是由 李健 刘硕 王俊峰 张明江 于 2021-08-24 设计创作，主要内容包括：本发明属于煤田火源钻孔探测技术领域,具体是一种面向采空区煤田火源钻孔探测的高精度分布式光纤拉曼传感方法。包括以下步骤：S1、定标阶段：将传感光纤放置在一个温度恒定的温度场中,向传感光纤中发射单脉冲,测量激光脉冲在传感光纤中的各个位置激发的拉曼散射光信号；S2、测量阶段：向传感光纤中发射单脉冲,测量激光脉冲在传感光纤中各个位置激发的拉曼散射光信号；S3、解调得到传感光纤中温度突变点的温度。本发明可以解决传统分布式光纤拉曼传感系统因空间分辨率不足导致系统测温精度下降的问题,可应用于煤田火源钻孔探测领域。(The invention belongs to the technical field of coal field fire source drilling detection, and particularly relates to a high-precision distributed optical fiber Raman sensing method for goaf coal field fire source drilling detection. The method comprises the following steps: s1, calibration stage: placing a sensing optical fiber in a temperature field with constant temperature, transmitting a single pulse into the sensing optical fiber, and measuring Raman scattering optical signals excited by laser pulses at each position in the sensing optical fiber; s2, measurement stage: emitting a single pulse into the sensing optical fiber, and measuring Raman scattering optical signals excited by the laser pulse at each position in the sensing optical fiber; and S3, demodulating to obtain the temperature of the temperature mutation point in the sensing optical fiber. The invention can solve the problem that the temperature measurement precision of the traditional distributed optical fiber Raman sensing system is reduced due to insufficient spatial resolution, and can be applied to the field of coal field fire source drilling detection.)

1. A distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection is characterized in that a sensing device comprises a pulse laser (1) and a sensing optical fiber (4), the sensing optical fiber (4) is laid in a goaf coal field drilling area, and the sensing method comprises the following steps:

s1, calibration stage: the sensing fiber (4) is placed at a constant temperature ofT _o In the temperature field, a single pulse is emitted into the sensing optical fiber (4), and Raman scattering optical signals excited by the laser pulse at each position in the sensing optical fiber (4) are measured;

s2, measurement stage: emitting single pulse into the sensing optical fiber (4), and measuring Raman scattering optical signals excited by the laser pulse at each position in the sensing optical fiber (4);

s3, demodulation stage: calculating slope auxiliary coefficients at all positions in the sensing optical fiber, and judging temperature catastrophe points in the sensing optical fiber; calculating the temperature of a non-catastrophe point in the sensing optical fiber (4) according to Raman scattering optical signals obtained by measurement in a calibration stage and a measurement stage, demodulating the temperature of the temperature catastrophe point in the sensing optical fiber (4) according to the Raman scattering optical signal intensity of laser pulses generated in the sensing optical fiber (4) and the temperature of the non-catastrophe point in the sensing optical fiber (4) measured at two adjacent sampling moments, and further obtaining the temperature information distribution along the sensing optical fiber (4); the temperature demodulation formula of the temperature catastrophe point is as follows:

；

wherein, Deltaf ₁ And Δf ₂ Respectively for the ith and i +1 thThe number of sampling points between the pulse starting points corresponding to the sample time and the number of sampling points between the pulse end position,his the constant of the planck, and is,kis boltzmann constant, deltaupsilon is raman frequency shift,T _non-FUT temperature at a non-abrupt point, L_iAndL _i+1 respectively indicating the position of the laser pulse at the ith and (i + 1) th sampling time instants,representing the slope auxiliary coefficient.

2. The distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection as claimed in claim 1, wherein in step S3,

the calculation formula of the slope auxiliary coefficient is as follows:

；

wherein the content of the first and second substances,φ _a （L _i) Andφ _a（L _i+1) Respectively indicating laser pulses at L during the measuring period_iAndL _i+1 the intensity of the raman scattering signal excited at the location,φ _a0（L _i) Indicating the laser pulse at the calibration stage at L_i(ii) raman scattering signal intensity of raman scattering signal intensity excited at the location;

the formula for calculating the non-mutation point temperature is as follows:

；

wherein the content of the first and second substances,φ _a0（L) The Raman scattering signal light intensity excited by the laser pulse at the position of the sensing optical fiber L in the calibration stage is represented;φ _a（L) Raman scattering information for indicating the excitation of laser pulse at the position of sensing optical fiber L in the measuring stageThe sign light intensity.

3. The distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection according to claim 1, wherein in steps S1 and S2, the collected raman scattering light signal is raman scattering anti-stokes light.

4. The distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection according to claim 1, wherein the sensing device further comprises: the device comprises a wavelength division multiplexer (2), a photoelectric detector (5), a data acquisition card (7) and a computer (8);

laser pulses emitted by the pulse laser (1) are sequentially incident to the sensing optical fiber (4) after passing through the wavelength division multiplexer (2); raman scattered light generated in the sensing optical fiber (4) is output through the wavelength division multiplexer (2) and then detected by the photoelectric detector (5), and detection signals are acquired by the data acquisition card (7) and then sent to the computer (8).

5. The distributed optical fiber temperature sensing method for the coal field goaf fire source drilling detection according to claim 4, wherein the computer (8) is used for demodulating temperature information distribution along the sensing optical fiber (4) according to a detection signal of the photoelectric detector (5).

6. The distributed optical fiber temperature sensing method for the coal field goaf fire source drilling detection according to claim 4, characterized in that the sensing device further comprises an amplifier (6), and the amplifier (6) is used for amplifying the electric signal output by the photodetector (5) and then sending the electric signal to the data acquisition card (7).

7. The distributed optical fiber temperature sensing method facing the coal field goaf fire source drilling detection is characterized in that the wavelength of an optical signal output by the pulse laser (1) is 1550nm, and the wavelength of the wavelength division multiplexer (2) is 1450nm/1550 nm.

Technical Field

The invention belongs to the technical field of coal field fire source drilling detection, and particularly relates to a high-precision distributed optical fiber Raman sensing method for coal field goaf fire source drilling detection.

Background

Coal is an important industrial raw material and still remains the most important energy resource at present. In the coal mining, storing and transporting process, coal spontaneous combustion is a serious accident type which can happen, and is one of important problems which need to be solved urgently in the world, and if the coal spontaneous combustion is not properly disposed, social and ecological imbalance can be caused. In particular, in high gas mines, coal spontaneous combustion disasters can easily cause secondary disasters such as gas or coal dust explosion.

The spontaneous combustion fire of the coal seam occurs underground, and the concealment of the fire source brings great difficulty to the work of fire extinguishing, temperature monitoring and determination. Therefore, in the treatment work of drilling and fire extinguishing in the fire orientation area, the measurement and monitoring of the temperature of the drill hole and the establishment of the fire extinguishing scheme through the temperature measurement of the drill hole are effective scientific and technological means. The borehole geothermal distribution can truly reflect the geothermal field characteristics of the mining area. The temperature measurement of the drill holes is generally carried out in the coal field well logging, and the temperature distribution curve of the drill holes is utilized, so that the low-temperature field characteristics and the forming mechanism of the low-temperature field characteristics of the whole mining area can be comprehensively and objectively known through analyzing the influence factors. The distributed optical fiber Raman temperature sensing system is only sensitive to the physical quantity of temperature change, has the advantages of being distributed, resistant to electromagnetic interference, resistant to corrosion and the like, and is particularly suitable for coal field fire source drilling fire detection based on temperature mutation characteristic identification. At present, researchers at home and abroad have preliminarily applied the distributed optical fiber Raman sensing technology to coal field fire source drilling detection.

The temperature measurement precision is an important performance index of the distributed optical fiber Raman sensing technology, the monitoring capability of the system on the sudden change of the environmental temperature is reflected, and the index is very important for the fire source detection of the coal field and the roadway drilling area thereof based on the distributed optical fiber Raman sensing technology. The existing distributed optical fiber Raman sensing system is limited by meter-level spatial resolution, so that temperature change information of a tiny fire source area of a coal field is submerged in environmental noise, temperature change characteristics generated by a tiny hidden fire source are difficult to identify, the good opportunity for early detection and early treatment is finally lost, and a coal mine major safety accident is possibly caused and a secondary disaster is further caused. Therefore, in the field of safety monitoring for coal field fire source drilling detection, the application of the distributed fiber Raman temperature measurement system is limited due to the technical bottleneck that the temperature measurement precision of the system is deteriorated due to meter-level spatial resolution.

The national standard of a line-type temperature-sensing fire detector in China is specially set up a small-size high-temperature response performance, and any sensitive part of the detector with the length of 100mm is required to be capable of rapidly monitoring high-temperature change so as to timely and effectively perform early warning under the condition of small fire intensity or even small-range rapid temperature rise, thereby extinguishing the fire in a bud state. The distributed optical fiber temperature measurement technology can realize the sensing of the temperature of any point on the optical fiber, but the method is to detect the average value of the temperature in a section of area (within the size of the spatial resolution of the system), and the detection result of a heat source with the size smaller than the spatial resolution of the system (usually 1m) is far smaller than the real temperature value, so the existing Raman distributed optical fiber sensing method is difficult to be used for monitoring small-size fire sources.

Based on the above, a brand-new temperature demodulation method is needed to be invented to solve the problem that the temperature measurement accuracy of the existing distributed optical fiber raman sensing system is reduced due to low spatial resolution, so that the goaf coal field fire source drilling detection can be realized.

Disclosure of Invention

The invention provides a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection, and aims to solve the technical problem that the temperature measurement precision in the existing distributed optical fiber Raman sensing system is limited by the meter-level spatial resolution of the system, so that the detection of a drilling hidden fire source in a goaf and a coal mine roadway is difficult to realize.

In order to solve the technical problems, the invention adopts the technical scheme that: a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection is characterized in that a sensing device comprises a pulse laser and a sensing optical fiber, the sensing optical fiber (4) is laid in a goaf coal field drilling area, and the sensing method comprises the following steps:

s1, calibration stage: placing the sensing fiber at a constant temperature T_oIn the temperature field, a single pulse is emitted into the sensing optical fiber, and Raman scattering optical signals excited by the laser pulse at each position in the sensing optical fiber are measured;

s2, measurement stage: emitting a single pulse into the sensing optical fiber, and measuring Raman scattering optical signals excited by the laser pulse at each position in the sensing optical fiber;

s3, demodulation stage: calculating slope auxiliary coefficients at all positions in the sensing optical fiber, and judging temperature catastrophe points in the sensing optical fiber; calculating the temperature of a non-catastrophe point in the sensing optical fiber according to Raman scattering optical signals obtained by measurement in a calibration stage and a measurement stage, demodulating the temperature of the non-catastrophe point in the sensing optical fiber according to the Raman scattering optical signal intensity of the laser pulse generated in the sensing optical fiber and the temperature of the non-catastrophe point in the sensing optical fiber, which are measured at two adjacent sampling moments, and further obtaining the temperature information distribution along the sensing optical fiber; the temperature demodulation formula of the temperature catastrophe point is as follows:

wherein, Δ f₁And Δ f₂Respectively the number of sampling points between the pulse starting points corresponding to the ith and (i + 1) th sampling moments and the number of sampling points between the pulse end point positions, h is a Planck constant, k is a Boltzmann constant, Delnu is a Raman frequency shift, and T is_non-FUTTemperature at a non-abrupt point, L_iAnd L_i+1Respectively represents the position, phi, of the laser pulse at the ith and (i + 1) th sampling time_slopeRepresenting the slope auxiliary coefficient.

In step S3, the calculation formula of the slope auxiliary coefficient is:

wherein phi is_a(L_i) And phi_a(L_i+1) Respectively indicating laser pulses at L during the measuring period_iAnd L_i+1Intensity of Raman scattering signal excited at the position, phi_a0(L_i) Indicating the laser pulse at the calibration stage at L_i(ii) raman scattering signal intensity of raman scattering signal intensity excited at the location;

the formula for calculating the non-mutation point temperature is as follows:

wherein phi is_a0(L) the Raman scattering signal light intensity excited by the laser pulse at the position of the sensing optical fiber L in the calibration stage is shown; phi is a_aAnd (L) represents the Raman scattering signal intensity excited by the laser pulse at the position of the sensing optical fiber L in the measurement stage.

In the steps S1 and S2, the collected raman scattering light signal is raman scattering anti-stokes light.

The sensing device further comprises: the device comprises a wavelength division multiplexer, a photoelectric detector, a data acquisition card and a computer;

laser pulses emitted by the pulse laser are sequentially incident to the sensing optical fiber after passing through the wavelength division multiplexer; raman scattering light generated in the sensing optical fiber is output by the wavelength division multiplexer and then detected by the photoelectric detector, and detection signals are collected by the data acquisition card and then sent to the computer.

And the computer is used for demodulating according to the detection signal of the photoelectric detector to obtain the temperature information distribution along the sensing optical fiber.

The sensing device also comprises an amplifier, and the amplifier is used for amplifying the electric signal output by the photoelectric detector and then sending the electric signal to the data acquisition card.

The wavelength of an optical signal output by the pulse laser is 1550nm, and the wavelength of the wavelength division multiplexer is 1450nm/1550 nm.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection, the invention calculates the distributed temperature mutation information along the sensing optical fiber through the light intensity slope data of the anti-Stokes light of the slope auxiliary area along the sensing optical fiber, and further positions the spontaneous combustion hidden danger positions of the goaf and the coal mine tunnel drilling area, the invention can calculate the mutation temperature information along the sensing optical fiber by calculating the slope auxiliary coefficient based on the temperature change area of the sensing optical fiber, thereby avoiding the phenomenon that the temperature mutation information in a small area range is submerged in the noise in a pulse width scale due to the optical time domain reflection positioning principle in the traditional Raman distributed optical fiber technology, the problem of the temperature measurement precision of the traditional distributed optical fiber Raman sensing system is reduced due to insufficient spatial resolution is solved.

Drawings

Fig. 1 is a schematic structural diagram of a sensing device adopted in a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection according to an embodiment of the present invention;

FIG. 2 is a schematic illustration of laser pulse delivery in an embodiment of the present invention;

in the figure: 1-pulse laser, 2-wavelength division multiplexer, 4-sensing optical fiber, 5-avalanche photodetector, 6-amplifier, 7-data acquisition card, 8-computer, 9-temperature normal point and 10-temperature abnormal point.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a schematic structural diagram of a sensing device adopted in a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection according to an embodiment of the present invention is shown, in this embodiment, the sensing device includes: the device comprises a pulse laser 1, a wavelength division multiplexer 2, a sensing optical fiber 4, a photoelectric detector 5, a data acquisition card 7 and a computer 8.

Specifically, as shown in fig. 1, a first port a of the wavelength division multiplexer 2 is connected to a signal output end of the pulse laser 1, and a second port b of the wavelength division multiplexer 2 is connected to one end of the sensing fiber 4; the third port c of the wavelength division multiplexer 2 is connected with the avalanche photodetector 5; the wavelength division multiplexer 2 is configured to send the optical signal output by the pulse laser 1 to the sensing optical fiber 4, and is further configured to send anti-stokes light in the backscattered optical signal to the photodetector 5; the photoelectric detector 5 is used for collecting anti-stokes optical signals in backscattered light signals and converting the anti-stokes optical signals into electric signals, the data acquisition card 7 is used for collecting the electric signals and sending the electric signals to the computer 8, and the computer 8 is used for demodulating according to the anti-stokes signals to obtain distributed abrupt change temperature field information along the sensing optical fiber 4. The sensing optical fiber 4 is laid in a drilling area of the goaf coal field.

Further, as shown in fig. 2, the distributed fiber raman sensing device for coal field fire source drilling detection provided in this embodiment further includes an amplifier 6, where the amplifier 6 is configured to amplify the electrical signal output by the photodetector 5 and then send the amplified electrical signal to the data acquisition card 7.

Further, in this embodiment, the wavelength of the optical signal output by the pulse laser 1 is 1550nm, the wavelength of the wavelength division multiplexer 2 is 1450nm/1550nm, and the incident light with the wavelength of 1550nm emitted by the laser enters the wavelength division multiplexer from the a port of the wavelength division multiplexer; the b port emits light to enter the sensing optical fiber 4, the back-scattered anti-stokes light wavelengths are 1450nm respectively, the light returns to the wavelength division multiplexer 2 through the b port of the wavelength division multiplexer 2, and then the light is injected into the avalanche photodetector 5 from the c port respectively.

Specifically, the distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection provided by the embodiment includes the following steps:

s1, calibration stage: the sensing fiber 4 is placed at a constant temperature T_oEmits a single pulse into the sensing fiber 4, and measures raman scattered light signals generated by the corresponding laser pulse at various positions in the sensing fiber.

In order to compensate the influence of the sensing fiber attenuation and other parameters on the temperature demodulation result, in this embodiment, all the sensing fibers need to be placed in a constant temperature field (T) before temperature measurement_o) To perform a calibration process. When scaling processingThe light intensity of the Raman scattering signal collected based on the single pulse is shown as the formula (1).

In the formula, T₀Is the temperature of the sensing fiber 4 in the calibration phase. Wherein L is_iIs the position of the laser pulse at the ith sampling moment; k_aIs a coefficient related to the scattering cross section of the fiber, P is the incident power of the pulsed light source, λ_aIs the optical frequency of the anti-Stokes light, alpha₀And alpha_aThe optical loss coefficients of the incident light and the anti-stokes light, respectively. R_aWhich represents a modulation function that is dependent on temperature,h is the Planckian constant, k is the Boltzmann constant, and Δ upsilon is the Raman frequency shift, which is 13.2 THz.

S2, measurement stage: a single pulse is launched into the sensing fiber 4 and raman scattered light signals excited by the laser pulse at various positions in the sensing fiber 4 are measured.

S3, demodulation stage: calculating slope auxiliary coefficients at all positions in the sensing optical fiber, and judging temperature catastrophe points in the sensing optical fiber; according to Raman scattering optical signals obtained by measurement in the calibration stage and the measurement stage, the temperature of the non-catastrophe point in the sensing optical fiber 4 is obtained through calculation, and according to the Raman scattering optical signal intensity of the laser pulse generated in the sensing optical fiber 4 and the temperature of the non-catastrophe point in the sensing optical fiber 4, which are measured at two adjacent sampling moments, the temperature of the temperature catastrophe point in the sensing optical fiber 4 is obtained through demodulation, so that the temperature information distribution along the sensing optical fiber 4 is obtained.

The measurement principle and the demodulation principle of the embodiment of the present invention are explained below.

First, the measurement stage in this embodiment will be described separately in two stages.

Measurement phase 1: when the laser pulse is located at the boundary between the temperature normal point 9 and the temperature abnormal point 10 in the sensing fiber 4, i.e. the laser pulse is about to be emittedWhen the temperature normal point 9 is turned on, the Raman scattering signal light intensity phi acquired by the data acquisition card 7 at the ith sampling moment_a(L_i) Can be expressed as:

wherein R is_a(T_non-FUT)＝[exp(hΔν/kT_non-FUT)-1]^-1，R_a(T_FUT)＝[exp(hΔν/kT_FUT)-1]^-1。

In the formula, phi_a(L_i) For the ith sampling instant, i.e. the laser pulse is at L_iIntensity of the excited anti-Stokes light, K, at the location_aIs a coefficient related to the scattering cross section of the fiber, P is the incident power of the pulsed light source, λ_aThe optical frequency of the anti-stokes light, h is the planckian constant, k is the boltzmann constant, and Δ ν is the raman shift, which is 13.2 THz. Alpha is alpha₀And alpha_aThe optical loss coefficients of the incident light and the anti-stokes light, respectively. T is_non-FUTIs the absolute temperature, T, of the temperature normal point 9 in the sensing fiber 4_FUTIs the absolute temperature of the temperature anomaly point 10 in the sensing fiber 4. L is_s1The laser pulse is at L_iStarting point of laser pulse at position, L_f1The laser pulse is at L_iAt the end point of the laser pulse, L_m1Is the boundary position of a temperature normal point 9 and a temperature abnormal point 10 in the sensing optical fiber.

Measurement stage 2: at the (i + 1) th sampling moment, the laser pulse is still at the boundary position of the temperature normal point 9 and the temperature abnormal point 10 in the sensing fiber 4, and the position of the laser pulse at this moment is marked as L_i+1The light intensity phi of the Raman scattering signal collected by the data acquisition card 7_a(L_i+1) Can be expressed as:

in the formula, phi_a(L_i+1) For measuring the phase laser pulses at L_i+1Intensity of anti-Stokes light excited at a location, L_s2The laser pulse is at L_i+1Starting point of laser pulse at position, L_f2The laser pulse is at L_i+1At the end point of the laser pulse, L_m2Is the boundary position (L) of a temperature normal point 9 and a temperature abnormal point 10 in the sensing optical fiber_m2＝L_m1)。

Next, the demodulation stage in the present embodiment will be described in three stages.

Demodulation stage 1: the optical fiber attenuation coefficient can be compensated based on the light intensity ratio of the raman anti-stokes signals of formula (1) and formula (2), as shown in the following formula.

A demodulation stage 2: the optical fiber attenuation coefficient can be compensated based on the light intensity ratio of the raman anti-stokes signals of formula (2) and formula (3), as shown in the following formula.

A demodulation stage 3: based on the equations (4) and (5), the slope auxiliary coefficient φ can be calculated_slopeAs shown in formula (6).

In the formula (6), T_o、T_non-FUT、L_iAnd L_i+1Is constant, so the slope auxiliary coefficient phi_slopeWith temperature (T) of the sensing fibre region_FUT) And (4) presenting a determined functional relationship, and transforming the equation (6) to obtain an equation (7).

Wherein, Δ f₁Is a distance L_s1To L_S2Number of sampling points,. DELTA.f₂Is a distance L_f1To L_f2H is Planck constant, k is Boltzmann constant, Delnu is Raman frequency shift, and T is_non-FUTThe absolute temperature of the temperature normal point 9 in the sensing optical fiber in the measuring stage is measured, so that the actual temperature information (T) along the sensing optical fiber 4 can be demodulated based on the formula (7)_FUT)。

Further, in this embodiment, the absolute temperature T of the temperature normal point 9 in the sensing fiber in the measurement stage_non-FUTThe calculation formula of (2) is as follows:

in the formula (8), phi_a0(L) the Raman scattering signal light intensity excited by the laser pulse at the position of the sensing optical fiber L in the calibration stage is shown; phi is a_a(L) shows the light intensity of Raman scattering signal excited by laser pulse at the position of sensing optical fiber L in the measuring stage, phi_a0(L) and phi_a(L) can be obtained by measurements in a calibration phase and a measurement phase, respectively.

In summary, the invention provides a distributed optical fiber temperature sensing method for coal field goaf fire source drilling detection, which is realized based on a distributed optical fiber Raman temperature demodulation principle of a slope auxiliary demodulation technology, and is characterized in that distributed temperature mutation information along a sensing optical fiber is calculated through light intensity slope data of anti-Stokes light in a slope auxiliary region along the sensing optical fiber, and spontaneous combustion hidden danger positions of a goaf and a coal mine tunnel drilling region are further positioned.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.