A multi-parameter monitoring system and method for spontaneous combustion of coal mines

Abstract

The application is a kind of coal mine spontaneous combustion multi-parameter monitoring system and method, relating to the technical field of coal mine safety monitoring, comprising: gas sound coupling and hardware isolation module; low frequency band sound wave excitation module; acoustic echo receiving and front end conditioning module; TDR pure logic ranging and fault qualitative module. In the application, a special integrated forged tee cavity is used in combination with a high molecular sound-transparent isolation film structure, which not only realizes the physical isolation of flammable and explosive gases such as gas, toxic and harmful gases in the pipeline, but also ensures that the sound transmission rate and sound energy loss meet the preset requirements, meeting the stringent requirements of intrinsic safety and explosion prevention in coal mine underground, eliminating safety hazards caused by gas leakage, and not affecting the normal coupling transmission of sound waves.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety monitoring technology, and in particular to a multi-parameter monitoring system and method for spontaneous combustion in coal mines. Background Technology

[0002] Spontaneous combustion in coal mines is a major hazard threatening safe production. Typically, online monitoring of gases such as carbon monoxide and methane is conducted using bundled tube sampling systems. The integrity of long-distance sampling pipelines is a prerequisite for reliable monitoring data. In actual underground environments, pipelines are prone to blockages, breaks, and leaks. Traditional manual inspections are inefficient and slow to respond, failing to meet the demands of intelligent safety monitoring.

[0003] Using acoustic methods to achieve online pipeline fault detection is the mainstream direction in the industry. However, existing acoustic detection devices generally cannot achieve both efficient air-to-sound coupling and intrinsically safe explosion protection. The sound-generating and sound-collecting devices are prone to direct contact with flammable and explosive gases, which does not meet the explosion-proof safety requirements of coal mines. If a physical isolation structure is added, it will cause a significant attenuation of sound waves, making it difficult to achieve stable detection. This has become a key bottleneck restricting the application of acoustic detection technology in underground coal mines.

[0004] Existing acoustic testing technologies for coal mine pipelines mostly rely on conventional high-frequency acoustic wave detection schemes, which suffer from severe transmission defects in long-distance, narrow-diameter sampling pipelines. The ratio of high-frequency acoustic wave wavelength to pipeline inner diameter is small, easily leading to multiple reflections and scattering within the pipeline, resulting in multipath effects such as rapid signal attenuation and short transmission distances. Typically, this technology can only achieve short-distance detection within 50 meters, making it unsuitable for the hundreds of meters of long bundled pipelines found underground in coal mines.

[0005] Meanwhile, this type of technology does not optimize the frequency for the characteristics of coal mine pipelines, and does not establish a matching mechanism between pipe diameter, length and sound wave frequency band. The sound wave propagation loss is large and the echo signal is weak, making it difficult to effectively identify fault points at long distances. The detection stability and practicality are poor.

[0006] Therefore, a multi-parameter monitoring system and method for spontaneous combustion in coal mines is proposed to address the aforementioned problems. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-parameter monitoring system and method for spontaneous combustion in coal mines in order to solve the above-mentioned problems.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A multi-parameter monitoring system for spontaneous combustion in coal mines includes: The air-to-sound coupling and hardware isolation module is configured to achieve efficient sound wave coupling and strict isolation of toxic / explosive gases in the pipeline through a three-way coupling cavity, a polymer sound-permeable isolation membrane, and auxiliary fixing components. The low-frequency band acoustic excitation module is configured to emit low-frequency pulses to ensure that the acoustic waves propagate with low attenuation and without interference within the pipeline. The acoustic echo receiver and front-end conditioning module is configured to capture echoes and, through hardware conditioning, convert the echo signals into stable and recognizable electrical signals for transmission to subsequent modules. The TDR pure logic ranging and fault characterization module is configured to use a microcontroller and hardware logic, combined with temperature compensation and sound velocity formula to achieve fault point ranging, and to determine the fault type by phase reversal.

[0009] Preferably, the air-acoustic coupling and hardware isolation module specifically includes: Three-way coupling cavity: made of stainless steel, with an integral forged structure; the inner diameter of the main channel of the tee matches the inner diameter of the sampling pipeline. High-polymer sound-permeable insulation membrane: Teflon or polyimide film is selected, the diameter of the film is consistent with the inner diameter of the bypass pipe, and the edge is sealed with fluororubber sealing ring; Auxiliary fixing components include stainless steel pressure rings, sealing gaskets, and mounting brackets.

[0010] Preferably, the installation method is as follows: Before the main exhaust pipe of the existing sampling system host enters the gas chamber, a special three-way coupling cavity is connected; after connection, the gas to be tested in the main exhaust pipe flows normally to the gas chamber to complete the sampling and detection, and the bypass pipe is in a closed state. Cut the polymer acoustic barrier membrane to a size that matches the inner diameter of the bypass pipe. Place the fluororubber sealing gasket around the edge of the barrier membrane and insert them together into the groove at the end of the bypass pipe. Then, tighten the stainless steel pressure ring through the threads to compress the barrier membrane and the sealing gasket. At this point, the barrier membrane divides the bypass pipe into two sides. One side is the air-contact side, and the other side is the non-air-contact side; The speaker and microphone are fixed to the non-air-contact side of the isolation membrane using mounting brackets; The speaker and microphone are arranged coaxially to ensure that the sound waves can be incident perpendicularly on the isolation diaphragm, maximizing the sound energy coupling efficiency; the speaker and microphone leads are led out through explosion-proof flexible tubing and connected to the subsequent control circuit, and the tubing interfaces are sealed.

[0011] Preferably, the low-frequency band acoustic excitation module specifically includes: Select the appropriate frequency pulse based on the inner diameter of the sampling pipeline; The waveform of the acoustic pulse can be selected as a sine wave or a linear frequency modulated chirp signal; The microcontroller collects the action signal of the gas path switching valve and the working status signal of the air pump in the sampling system in real time. When the gas path switching valve completes its action or the air pump enters a sleep state, the acoustic excitation module is triggered to work. After being triggered, the microcontroller generates a pulse signal of a set frequency through the PWM pulse generator circuit. After being amplified by the audio power amplifier, it drives the speaker to emit low-frequency sound wave pulses. After each sound pulse is emitted, wait for a preset time before resuming normal operation of the sampling system.

[0012] Preferably, the acoustic echo receiving and front-end conditioning module specifically includes: High-sensitivity dynamic microphone: arranged on the same side as the speaker, using a condenser dynamic microphone; Analog bandpass filter: An active bandpass filter is selected, consisting of an operational amplifier, resistors, and capacitors. The center frequency is matched with the center value of the sound wave excitation frequency. The input impedance of the filter is matched with the microphone output impedance, and the output impedance is matched with the subsequent amplification circuit. Pure hardware time-gain controlled amplifier circuit: operational amplifiers are selected to form a variable gain amplifier circuit; Blind spot blocking circuit: It consists of a transistor, resistor, and capacitor, and is connected to the microphone output terminal; when the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor to conduct, briefly blocking the microphone input; Signal buffer circuit: An operational amplifier is selected to form a voltage follower.

[0013] Preferably, the method further includes: When the acoustic pulse propagates in the sampling pipeline and encounters a fault point, it will generate a reflected echo. The echo propagates in the opposite direction along the pipeline and is transmitted through the isolation membrane of the bypass pipe to the non-air-contact side, where it is captured by a high-sensitivity microphone. The microphone converts the acoustic signal into an electrical signal and transmits it to the blind zone shielding circuit. While the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor in the blind zone shielding circuit to conduct, and the microphone output is short-circuited; when the sound wave pulse is emitted, the microcontroller outputs a low-level signal, the transistor is cut off, the blind zone shielding is released, and the echo signal captured by the microphone is normally transmitted to the bandpass filter. Analog bandpass filters filter the electrical signal output by the microphone, removing low-frequency noise and high-frequency interference from the environment. The filtered signal is fed into a pure hardware TGC amplifier circuit, which automatically adjusts its gain according to the arrival time of the echo signal. The signal amplified by the TGC is fed into the signal buffer circuit, buffered by a voltage follower, and then transmitted to the ADC interface of the microcontroller. The microcontroller converts the analog signal into a digital signal and transmits it to the TDR pure logic ranging and fault characterization module for processing.

[0014] Preferably, the TDR pure logic ranging and fault characterization module specifically includes: Precise ranging, based on the formula for the speed of sound propagation, combined with temperature compensation: The microcontroller records the time when the acoustic excitation module emits acoustic pulses via a timer. ; The echo signal transmitted by the front-end conditioning module is confirmed through cross-correlation calculation, and the time it arrives at the microcontroller is... Time difference ; Real-time ambient temperature is collected using a temperature sensor. Perform sound velocity compensation to obtain the actual sound velocity inside the pipe. ; Combined with the speed of sound and time difference Calculate the distance to the fault point ; According to the principle of acoustic reflection, when a sound wave is incident from a low-impedance medium to a high-impedance medium at a hard boundary, the phase of the reflected wave is in phase with the incident wave; when a sound wave is incident from a low-impedance medium to a low-impedance medium at a soft boundary, half-wave loss occurs, and the phase of the reflected wave is out of phase with the incident wave. The phase detection circuit converts the transmitted pulse signal and the echo signal into square wave signals. The comparator compares the zero-point crossover points of the two square wave signals and determines the fault type based on the phase difference.

[0015] Preferably, the method further includes: After the microcontroller starts up, it initializes each module. When a gap in the gas path switching valve's operation or a sleep signal from the air pump is detected, the low-frequency acoustic excitation module is triggered to emit an acoustic pulse. Simultaneously, the microcontroller starts a timer to record the emission time. ; The microphone captures the echo signal, which is then processed through blind spot masking, bandpass filtering, TGC amplification, and signal buffering before being transmitted to the microcontroller's ADC interface and converted into a digital signal. The microcontroller performs cross-correlation calculations on the transmitted pulse signal and the received digital signal to identify valid echo signals and record the echo arrival time. Calculate the time difference ; Temperature sensor collects ambient temperature Calculate the actual speed of sound inside the tube. and the distance to the fault point ; The phase detection circuit detects the phase difference between the echo and the incident wave, determines the fault type based on the phase difference, and stores the fault type data.

[0016] A multi-parameter monitoring method for spontaneous combustion in coal mines, comprising: Complete the installation and deployment of the gas-acoustic coupling and hardware isolation module to achieve strict isolation of toxic and explosive gases in coal mine sampling pipelines and efficient coupling and transmission of sound waves. The low-frequency sound wave band is selected by matching the sampling pipeline parameters, and the timing pulse is emitted by the coordinated sampling system to ensure that the sound wave propagates in the pipeline with low attenuation and no interference. A high-sensitivity microphone is used to capture the weak echo at the fault point, which is then converted into a stable electrical signal through pure hardware blind zone masking, bandpass filtering, and TGC amplification and conditioning. Accurate fault location is achieved by combining TDR pure logic with temperature compensation. The type of blockage / fracture fault is determined by echo phase reversal and the result is output.

[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention employs a specially designed integrated forged three-way cavity combined with a polymer sound-permeable isolation membrane structure. This achieves physical isolation of flammable and explosive gases such as methane and toxic substances within the pipeline, while ensuring that the sound wave transmission rate and sound energy loss meet the preset requirements. This not only meets the stringent intrinsic safety and explosion-proof requirements of underground coal mines and eliminates safety hazards caused by gas leaks, but also does not affect the normal coupling and transmission of sound waves.

[0018] 2. This invention allows for direct connection to the gas circuit without requiring large-scale modifications to existing sampling pipelines. It is easy to install, has strong sealing properties, and excellent corrosion resistance, significantly reducing on-site implementation costs and modification difficulties. It breaks through the technical bottleneck that traditional acoustic detection devices cannot be used in flammable and explosive environments, providing reliable hardware support for the large-scale implementation of acoustic detection technology in the field of coal mine safety monitoring. Attached Figure Description

[0019] Further details, features, and advantages of this application are disclosed in the following description of exemplary embodiments in conjunction with the accompanying drawings, in which: Figure 1 This is a system structure diagram of the present invention; Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0020] Several embodiments of this application will now be described in more detail with reference to the accompanying drawings to enable those skilled in the art to implement this application. This application may be embodied in many different forms and for various purposes and should not be limited to the embodiments set forth herein. These embodiments are provided to make this application thorough and complete, and to fully convey the scope of this application to those skilled in the art. The embodiments described do not limit this application.

[0021] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It will be further understood that terms such as those defined in commonly used dictionaries shall be interpreted as having a meaning consistent with their meaning in the relevant field and / or the context of this specification, and shall not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0022] Example 1

[0023] Its specific implementation method is combined with the appendix Figure 1 and attached Figure 2 Please provide a detailed explanation.

[0024] Appendix Figure 1 This invention provides a structural block diagram of a multi-parameter monitoring system for spontaneous combustion in coal mines, showing the connection relationship between the gas-acoustic coupling and hardware isolation module and the TDR pure logic ranging and fault characterization module, and marking the main functional interaction flow of each module.

[0025] Appendix Figure 2 The flowchart of a multi-parameter monitoring method for spontaneous combustion in coal mines provided in this embodiment of the invention illustrates the complete steps from completing the installation and deployment of the gas-acoustic coupling and hardware isolation module to completing the accurate distance measurement of the fault point.

[0026] In this embodiment, it includes: The air-acoustic coupling and hardware isolation module is configured to achieve efficient sound wave coupling and strict isolation of toxic / explosive gases in the pipeline through a specially designed three-way coupling cavity, a polymer sound-permeable isolation membrane and auxiliary fixing components, ensuring the intrinsic safety and explosion-proof of the system without affecting the sound wave transmission; Specifically, it includes: The core physical basis for realizing the reuse of long-distance sampling pipelines as acoustic waveguides is also a key module to ensure the intrinsic safety and explosion protection of the system and to avoid leakage of toxic / explosive gases.

[0027] The core function of this module is to ensure that the sound waves emitted by the loudspeaker can enter the sampling pipeline efficiently and without attenuation (achieving air-acoustic coupling), while strictly isolating the gas to be tested (toxic, explosive, and corrosive gases) in the pipeline, ensuring that the gas will never leak into the sound-generating electronic devices (loudspeakers, microphones) and control circuits, eliminating safety hazards, and at the same time not affecting the normal transmission of sound waves.

[0028] Hardware components: The specially designed three-way coupling chamber is made of 316L stainless steel (highly corrosion-resistant, suitable for various gases to be tested in industrial environments, such as methane and toxic chemical gases). It features a one-piece forged structure with no welded seams (to prevent gas leakage). The inner diameter of the main channel of the three-way valve perfectly matches the inner diameter of the sampling pipeline, with specifications ranging from 6mm to 10mm (compatible with existing mainstream long-distance sampling pipelines; custom sizes are available upon request). The inner diameter of the bypass pipe is 8mm to 12mm (slightly larger than the main channel to ensure sufficient propagation space for sound waves and reduce coupling loss). The bypass pipe is 5cm to 8cm long and forms a 90° angle with the main channel (vertically arranged to avoid interference from airflow in the main channel on sound wave propagation in the bypass pipe). The surface of the three-way chamber is anodized to enhance wear resistance and corrosion resistance. The working pressure range is 0.1MPa to 0.3MPa (compatible with the normal working pressure of the sampling system).

[0029] High-polymer acoustic insulation membrane: PTFE or polyimide (PI) film is used, with a thickness of 0.1mm~0.2mm (excessive thickness leads to excessive sound wave attenuation, while insufficient thickness fails to guarantee gas isolation and structural strength); sound transmittance ≥90% (ensuring efficient transmission of low-frequency sound waves and reducing sound energy loss); airtightness ≤1× (Ensures 100% gas isolation and no leakage); Temperature range is -40℃ to 80℃ (suitable for high and low temperature environments in industrial sites); Corrosion resistance meets GB / T1033-2008 standard (can withstand corrosion from common toxic and harmful gases, acid and alkali gases); The membrane diameter is consistent with the inner diameter of the bypass pipe, and the edge is sealed with a fluororubber sealing ring (further enhancing airtightness).

[0030] Auxiliary fixing components include a stainless steel pressure ring, a sealing gasket, and a mounting bracket. The pressure ring is used to press and fix the isolation diaphragm to the end of the bypass pipe, with the pressure controlled at 0.1MPa-0.2MPa (ensuring a tight seal while avoiding excessive pressure that could damage the isolation diaphragm). The sealing gasket is made of fluororubber and is 1mm thick. It fits snugly against the pressure ring and the end of the bypass pipe to enhance airtightness. The mounting bracket is an L-shaped stainless steel bracket used to fix the speaker and microphone. The bracket height is adjustable (3cm~5cm) to ensure that the speaker, microphone, and isolation diaphragm maintain the optimal distance.

[0031] The installation method is as follows: The core physical mechanism of this module is pneumatic isolation and acoustic transmission. Through the special design of the isolation membrane, the gas and sound waves are separated and transmitted. The specific implementation method is as follows, and the steps are clear and operable: Piping connection: Before the main exhaust pipe (sampling pipe) of the existing sampling system host enters the gas chamber (gas detection chamber), it is connected to a specially designed three-way coupling chamber through a threaded connection to ensure that the connection between the three-way main pipe and the main exhaust pipe and the gas chamber is tight and there is no gas leakage; after connection, the gas to be tested in the main exhaust pipe flows normally to the gas chamber to complete the sampling and detection, and the bypass pipe is in a closed state (only used for sound wave transmission and does not participate in gas sampling). Installation of the isolation membrane: Cut the polymer acoustic isolation membrane to a size that matches the inner diameter of the bypass pipe. Place the fluororubber sealing gasket around the edge of the isolation membrane and insert it into the groove at the end of the bypass pipe. Then, tighten the stainless steel pressure ring through the threads to compress the isolation membrane and the sealing gasket, ensuring uniform pressure on the pressure ring (the tightening torque can be controlled to 5 N·m using a torque wrench). This achieves a complete seal at the end of the bypass pipe, at which point the isolation membrane divides the bypass pipe into two sides. One side is the gas-contact side (connected to the main T-junction and in contact with the gas to be tested), and the other side is the non-gas-contact side (connected to the outside air and used for installing electronic devices). Electronic component installation: Fix the speaker and microphone to the non-gas-contact side of the isolation diaphragm using mounting brackets. The distance between the speaker and the isolation diaphragm should be controlled between 3mm and 5mm (too close a distance will cause the speaker vibration to be directly transmitted to the microphone, causing interference; too far a distance will cause excessive sound wave attenuation); The speaker and microphone are arranged coaxially (the axis is consistent with the bypass pipe axis) to avoid deflection during sound wave propagation and ensure that the sound waves can be incident perpendicularly on the isolation diaphragm, maximizing the sound energy coupling efficiency; The speaker and microphone leads are led out through explosion-proof flexible tubing and connected to the subsequent control circuit. The tubing interfaces are sealed to prevent gas leakage through the gaps between the leads; Routine maintenance and sealing inspection: Check the integrity of the isolation membrane weekly (no damage or deformation), and check the tightness of the pressure ring and the aging of the sealing gasket monthly. If the isolation membrane is found to be damaged or the gasket is found to be aged, replace it in time (when replacing, the sampling system's air pump must be turned off first, and the gas in the pipeline must be purged to ensure safe operation); test the airtightness using the soap film method to ensure no gas leakage (no bubbles are generated in the soap film to indicate that it is qualified).

[0032] The core of this module lies in the design and application of the isolation diaphragm. Its design concept is similar to that of a speaker's "passive radiator," but it has been specifically optimized for the needs of industrial explosion protection and gas-acoustic coupling, cleverly resolving the contradiction between "efficient sound wave transmission" and "strict gas isolation." Specific advantages are as follows: When the speaker emits sound, the sound wave vibration is conducted through the air medium on the non-air-contact side to the polymer sound-permeable isolation membrane. Due to the thin thickness and high sound transmittance of the isolation membrane, it can respond quickly to the sound wave vibration and then perform a reciprocating piston-like motion. The piston-like vibration of the isolation membrane "pumps" low-frequency sound waves into the bypass tube, and then into the entire sampling pipeline (acoustic waveguide), achieving efficient coupling and transmission of sound waves with a sound energy loss of ≤10% (far lower than the sound energy loss of traditional isolation structures). At the same time, the isolation membrane has excellent airtightness, which can physically isolate the gas to be tested in the pipeline 100% on the air-contact side, and will not leak into the speaker, microphone and control circuit on the non-air-contact side. It perfectly meets the stringent requirements of intrinsic safety and explosion protection in industrial sites and solves the technical pain point that traditional acoustic testing cannot be applied to flammable and explosive environments.

[0033] Furthermore, the design of the isolation membrane does not require additional complex coupling structures, and can be directly adapted to the modification of existing sampling pipelines without the need for large-scale modifications to the original pipelines, thus reducing the implementation cost and modification difficulty of the system and making it highly practical.

[0034] The low-frequency band acoustic excitation module is configured to consist of an intrinsically safe loudspeaker, a microcontroller PWM circuit, etc., and emits low-frequency pulses of 100Hz~500Hz (extending to infrasound). The timing is optimized to avoid airflow interference and ensure that the acoustic waves propagate with low attenuation and without interference in the pipeline. Specifically, it includes: This module is one of the core modules that determines the detection distance and accuracy. Its core function is to generate low-frequency acoustic pulses of a specific frequency and timing to ensure that the acoustic waves propagate in an interference-free and low-attenuation manner within the long-distance sampling conduit (acoustic waveguide), providing a stable signal source for subsequent echo reception, fault location, and characterization. Selecting the correct acoustic frequency and optimizing the excitation timing are key to solving the problems of high attenuation and severe multipath interference in long-distance detection.

[0035] Hardware components: Intrinsically safe explosion-proof miniature loudspeaker (or piezoelectric buzzer): Utilizing an intrinsically safe explosion-proof design, with an explosion-proof rating of ExiaIICT4 (suitable for flammable and explosive industrial environments), a rated power of 0.5W~1W (excessive power may generate sparks, while insufficient power will result in inadequate sound wave propagation distance), a frequency response range of 50Hz~1000Hz (primarily covering the low-frequency range of 100Hz~500Hz), and a sound pressure level ≥85dB (measured at a distance of 1m to ensure sufficient sound wave intensity for propagation over hundreds of meters); the loudspeaker size is 20mm×15mm (miniaturized design to fit the installation space of bypass pipes), and it features a waterproof and dustproof design (IP65 protection rating) to prevent damage from industrial dust and moisture. If a piezoelectric buzzer is selected, it must meet the requirements for frequency response range and explosion-proof rating, and the sound frequency must be precisely adjustable via a microcontroller.

[0036] The microcontroller PWM pulse generation circuit uses an STM32L431RCT6 microcontroller (low power consumption, intrinsically safe design, suitable for industrial power supply environments), with an operating voltage of 3.3V and an operating frequency of 80MHz. The PWM pulse generation circuit consists of the microcontroller's GPIO port and an RC filter circuit (1kΩ resistor, 10μF capacitor), capable of generating PWM pulse signals with adjustable frequency (accuracy ±1Hz) and adjustable duty cycle (50% fixed duty cycle to ensure stable sound wave signal). A current-limiting resistor (220Ω) is connected in series in the circuit to prevent excessive current from damaging the speaker. A reverse connection protection diode is also provided to prevent the microcontroller from burning out due to reverse connection.

[0037] Audio Amplifier: The LM386 audio amplifier chip is selected (low power consumption, small size, suitable for intrinsically safe systems), with an operating voltage of 3V~5V, output power of 0.5W~1W, and adjustable gain (20dB~40dB). The input terminal of the amplifier circuit is connected to the microcontroller's PWM pulse generator circuit, and the output terminal is connected to the speaker. It is used to amplify the PWM pulse signal generated by the microcontroller and drive the speaker to emit sound waves of sufficient intensity. The amplifier chip is equipped with filter capacitors (100μF electrolytic capacitor and 0.1μF ceramic capacitor) to filter out high-frequency interference and ensure the purity of the output sound wave signal.

[0038] Power supply module: It adopts an intrinsically safe DC power supply with an output voltage of 3.3V and an output current of 1A. It has overcurrent, overvoltage and short circuit protection functions. The power supply module is connected to the microcontroller, audio amplifier and speaker to provide stable power supply for the entire excitation module and ensure long-term stable operation of the module.

[0039] Physical mechanisms and implementation methods: The core physical mechanism of this module is the one-dimensional plane wave propagation of low-frequency sound waves. Utilizing the characteristic that the wavelength of low-frequency sound waves is much larger than the pipe diameter, multipath effects and sound wave attenuation are avoided, ensuring long-distance transmission. Simultaneously, by optimizing the excitation timing, interference from the airflow of the sampling system on sound wave propagation is avoided. Specific implementation methods and parameter specifications are as follows: Frequency selection: Select the appropriate frequency pulse based on the inner diameter of the sampling pipeline; The inner diameter of the sampling pipe is usually 6mm to 10mm. The propagation characteristics of sound waves are closely related to the ratio of wavelength to pipe diameter: high-frequency sound waves have shorter wavelengths (e.g., the wavelength of a 1kHz sound wave is about 34cm), which is a smaller ratio to the pipe diameter (6mm to 10mm). The sound waves will be reflected and scattered multiple times in the pipe, resulting in multipath effect, which leads to severe sound wave attenuation and makes it impossible to achieve long-distance transmission (usually the transmission distance does not exceed 50 meters); while low-frequency sound waves have wavelengths much larger than the pipe diameter, and can propagate strictly in the form of a one-dimensional plane wave in the pipe. There is no multipath effect interference, the attenuation is minimal, and long-distance transmission of hundreds of meters can be achieved.

[0040] Based on the above principles, this system is designed to emit low-frequency pulses at a specific frequency (100Hz~500Hz), which can be extended to infrasound (20Hz-100Hz) if necessary. The specific frequency can be adaptively adjusted according to the inner diameter and length of the pipeline, based on the following criteria: When the inner diameter of the pipe is 6mm~8mm, select a low frequency pulse of 100Hz~300Hz. At this time, the wavelength of the sound wave is 1.13m~3.4m (the speed of sound v≈340m / s), the ratio of wavelength to pipe diameter is ≥113 (much greater than 10, which satisfies the one-dimensional plane wave propagation condition), and the attenuation is ≤0.5dB / 100m. When the inner diameter of the pipe is 8mm~10mm, select a low frequency pulse of 300Hz~500Hz. At this time, the wavelength of the sound wave is 0.68m~1.13m, the ratio of wavelength to pipe diameter is ≥68 (satisfying the one-dimensional plane wave propagation condition), and the attenuation is ≤0.8dB / 100m. When the pipeline length exceeds 300 meters, 20Hz~100Hz infrasound can be selected. Infrasound has less attenuation (≤0.3dB / 100m) and can achieve long-distance transmission of more than 500 meters.

[0041] The waveform of the acoustic pulse can be selected as either a sine wave or a linear frequency modulated chirp signal: sine wave pulses have good stability and are convenient for subsequent phase detection; chirp signals (frequency linearly changing from 100Hz to 500Hz, duration 10ms) have strong anti-interference ability and can improve the recognition accuracy of echo signals. The specific choice can be made according to the interference situation on site.

[0042] Work sequence: When the sampling system is working normally, the air pump is running, and there is airflow in the pipeline. This airflow can interfere with the propagation of sound waves, causing echo signal distortion and affecting detection accuracy. Therefore, the timing of this module needs to be coordinated with the air path switching and air pump operation of the sampling system to select a gap with stable and interference-free airflow for sound wave pulse emission. The specific timing is as follows: Timing trigger conditions: The microcontroller collects the action signal of the gas path switching valve and the working status signal of the air pump in the sampling system in real time (detected by the sensor). When the gas path switching valve completes its action (switching interval is 5 seconds) or the air pump enters a short sleep state (sleep time is 3~5 seconds, to avoid overheating caused by long-term operation), the acoustic excitation module is triggered to work. Pulse emission timing: After triggering, the microcontroller generates a pulse signal of a set frequency through the PWM pulse generator circuit. After being amplified by the audio power amplifier, it drives the speaker to emit a very short low-frequency sound wave pulse. The pulse duration is strictly controlled to 10 milliseconds (too long a duration will cause sound wave superposition, affecting echo recognition; too short a duration will cause insufficient sound energy and insufficient propagation distance). The pulse duty cycle is 1% (to avoid excessive power consumption due to prolonged sound emission, and at the same time reduce interference to the sampling system). Timing interval: After each sound wave pulse is emitted, wait for a preset time (1~2 seconds to ensure that the echo signal is fully received) before resuming normal operation of the sampling system (air pump operation, air path switching); the detection cycle can be set according to actual needs, usually 10 minutes to 30 minutes / time, or it can be set to manual trigger detection.

[0043] The core function of this module lies in the precise selection of low-frequency sound wave frequencies and the optimized design of the working timing: Frequency selection: Existing acoustic detection technologies mostly use high-frequency sound waves (kHz level), which are not suitable for long-distance sampling pipelines (large attenuation, multipath interference). However, this solution analyzes the relationship between the inner diameter of the pipeline and the wavelength of the sound wave, and accurately selects the low-frequency band of 100Hz~500Hz. For the first time, it has achieved stable propagation of one-dimensional plane waves in long-distance sampling pipelines, which solves the attenuation problem of long-distance acoustic detection. Moreover, the frequency can be adaptively adjusted according to the pipeline parameters to adapt to sampling pipelines of different specifications. Timing design: The timing of the acoustic excitation is coordinated with the air path switching and the working status of the air pump in the sampling system. The acoustic wave is emitted during the gap between air path switching and air pump dormancy, which avoids the interference of airflow on the propagation of the acoustic wave and improves the detection accuracy. At the same time, there is no need to add an extra independent acoustic wave transmission time, so it does not affect the normal working efficiency of the sampling system.

[0044] The acoustic echo receiver and front-end conditioning module is configured to capture weak echoes through a high-sensitivity microphone, and then convert the echo signal into a stable and recognizable electrical signal through pure hardware conditioning such as blind spot masking, bandpass filtering, and TGC amplification, which is then transmitted to the subsequent modules. Specifically, it includes: The core function of this module is to capture extremely weak acoustic echo signals (typically ≥10μPa) reflected from a fault point hundreds of meters away, and convert these weak echo signals into stable, identifiable electrical signals through front-end conditioning such as filtering, amplification, and blind zone protection. These signals are then transmitted to the subsequent TDR logic module for processing, ensuring the accuracy of fault location and characterization. Because the echo signals attenuate significantly after long-distance transmission and are subject to environmental interference (such as air pump noise and ambient noise), the performance of the front-end conditioning directly determines the detection effectiveness of the entire system.

[0045] Hardware components: High-sensitivity dynamic microphone: Located on the same side as the speaker (non-air-contact side), using a condenser dynamic microphone with a sensitivity ≥ -40dBV / Pa (ensuring the capture of weak echo signals), frequency response range 50Hz-1000Hz (matching the speaker's frequency response range to ensure the reception of echoes at corresponding frequencies), signal-to-noise ratio ≥ 60dB (reducing environmental noise interference), output impedance 1kΩ-2kΩ, and operating voltage 3.3V (consistent with the microcontroller's power supply); the microphone adopts a waterproof and dustproof design (IP65 protection rating), and its size matches the speaker (20mm×15mm). It is connected to the front-end conditioning circuit through a shielded cable to reduce electromagnetic interference.

[0046] Analog bandpass filter: An active bandpass filter is selected, consisting of an operational amplifier (LM324), resistors, and capacitors. The center frequency is 300Hz (matching the center value of the sound wave excitation frequency), the passband range is 200Hz~400Hz (precisely filtering out low-frequency ambient noise below 200Hz and high-frequency interference above 400Hz), the passband gain is ≥0dB, and the stopband attenuation is ≥40dB / decade (ensuring that interference signals are effectively suppressed). The input impedance of the filter is ≥10kΩ (matching the microphone output impedance to avoid signal attenuation), and the output impedance is ≤1kΩ (matching the subsequent amplification circuit).

[0047] The pure hardware time gain control (TGC) amplifier circuit uses an operational amplifier (LM324) to form a variable gain amplifier circuit with a gain adjustment range of 0~60dB. The adjustment method is pure hardware automatic adjustment (no software intervention required, fast response speed). The core of the TGC circuit is an RC integrator circuit (10kΩ resistor, 100μF capacitor), which can automatically adjust the amplifier gain according to the arrival time (waiting time) of the echo signal: the longer the waiting time (the farther the echo comes from the fault point), the gain increases exponentially (gain coefficient 0.1dB / ms), ensuring that the amplitude of the echo signal from near and far is consistent (0.5V~1V) when it is transmitted to the microcontroller, avoiding the problem of saturation of the echo signal from near and the weak echo signal from far being unrecognizable.

[0048] Blind spot shielding circuit: Composed of a transistor (NPN type, 9013), resistors (1kΩ, 10kΩ), and capacitor (1μF), connected to the microphone output; when the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor to conduct, briefly locking the microphone input (lock-in time 10-15ms, matching the duration of the sound wave pulse), preventing the amplifier from being saturated by strong direct sound signals from the near end, thus forming a detection blind spot protection; the response time of the blind spot shielding circuit is ≤1μs, ensuring no signal delay and not affecting the reception of the echo signal.

[0049] Signal buffer circuit: An operational amplifier (LM324) is selected to form a voltage follower with an input impedance ≥100kΩ and an output impedance ≤100Ω. It is used to buffer the front-end conditioned signal to avoid attenuation and interference during signal transmission and ensure that the signal is stably transmitted to the ADC interface of the microcontroller.

[0050] Physical mechanisms and implementation methods: The core physical mechanism of this module is weak signal capture, interference suppression, and adaptive gain adjustment. Through the coordinated work of a series of pure hardware circuits, the weak echo signal is conditioned into a stable electrical signal. The specific implementation method and signal flow are as follows: Signal flow direction: From acoustic echo to high-sensitivity microphone to blind spot shielding circuit to analog bandpass filter to pure hardware TGC amplifier circuit to signal buffer circuit to microcontroller ADC interface (analog-to-digital conversion). Detailed implementation methods for each step: Echo capture: When an acoustic pulse propagates in the sampling pipeline and encounters a fault point (blockage, breakage), a reflected echo is generated. The echo propagates in the opposite direction along the pipeline and is transmitted through the isolation membrane of the bypass pipe to the non-air-contact side, where it is captured by a high-sensitivity microphone. The microphone converts the acoustic signal (mechanical vibration) into a weak electrical signal (amplitude usually at the μV level) and transmits it to the blind zone shielding circuit.

[0051] Blind spot masking: While the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor in the blind spot masking circuit to conduct. The microphone output is short-circuited, and the signal cannot be transmitted to subsequent circuits, preventing strong direct sound signals (amplitude in the mV range) from entering the amplifier, which could cause amplifier saturation damage or signal distortion. When the sound wave pulse is emitted (10~15ms later), the microcontroller outputs a low-level signal, the transistor is cut off, the blind spot masking is released, and the echo signal captured by the microphone is normally transmitted to the bandpass filter. Interference filtering: The analog bandpass filter filters the electrical signal output by the microphone, accurately filtering out low-frequency noise (such as the noise of an air pump, which is usually below 200Hz) and high-frequency interference (such as electromagnetic interference, which is usually above 400Hz) in the environment, retaining only the echo signal of 200Hz-400Hz (matching the frequency of the excitation sound wave) to ensure signal purity; the amplitude of the filtered signal is still at the μV level and needs to be further amplified.

[0052] Adaptive gain adjustment: The filtered weak signal is fed into a pure hardware TGC amplifier circuit. The TGC circuit automatically adjusts the gain according to the arrival time of the echo signal: the earlier the echo signal arrives (the closer the fault point), the smaller the gain (to avoid signal saturation); the later the echo signal arrives (the farther the fault point), the gain increases exponentially (to ensure sufficient signal amplitude). For example, when the fault point is 100 meters away from the host, the echo arrival time is about 0.59ms (speed of sound 340m / s), and the TGC gain is adjusted to 10dB; when the fault point is 500 meters away from the host, the echo arrival time is about 2.94ms, and the TGC gain is adjusted to 60dB, ensuring that the echo signal amplitude is 0.5V-1V in both cases, which is convenient for subsequent microcontroller recognition.

[0053] Signal buffering and transmission: The signal amplified by TGC is fed into the signal buffering circuit, where it is buffered by a voltage follower to reduce signal attenuation and interference during transmission. Then it is transmitted to the ADC interface of the microcontroller (12-bit analog-to-digital conversion accuracy). The microcontroller converts the analog signal into a digital signal and transmits it to the TDR pure logic ranging and fault characterization module for processing.

[0054] Key details: Microphone and speaker spacing control: The distance between the two is 5mm-8mm, and they are arranged coaxially to avoid the speaker vibration being directly transmitted to the microphone, causing mechanical interference; at the same time, a shock-absorbing pad (silicone material, 2mm thick) is installed between the two to further reduce vibration interference.

[0055] Bandpass filter parameter calibration: Before each device leaves the factory, the center frequency and passband range of the bandpass filter must be calibrated to ensure filtering accuracy. The calibration method is as follows: input standard signals of different frequencies (100Hz-1000Hz), measure the output amplitude of the filter, and adjust the resistance and capacitance parameters so that the signal attenuation in the passband range is ≤1dB and the signal attenuation in the stopband range is ≥40dB.

[0056] TGC gain adjustment and calibration: Based on the pipeline length, preset the TGC gain adjustment curve. For example, for pipeline lengths of 0~100 meters, the gain is 0~20dB; for 100~300 meters, the gain is 20~40dB; for 300~500 meters, the gain is 40-60dB. Ensure that the gain adjustment matches the echo distance. Fine-tuning can be done using a potentiometer.

[0057] Interference suppression measures: All circuits use shielded wiring (shielding layer grounded) to avoid electromagnetic interference; the leads of microphones and speakers use shielded wires, with the length controlled within 10cm to reduce signal attenuation and interference; the front-end conditioning circuit is arranged separately from the microcontroller and power module to avoid power interference.

[0058] The TDR pure logic ranging and fault characterization module is configured based on STM32 microcontroller and pure hardware logic. It combines temperature compensation and sound speed formula to achieve accurate fault point ranging and determines the fault type (blockage / breakage) by phase reversal. Specifically, it includes: The core function is to receive digital signals transmitted from the front-end conditioning module and use classical acoustic formulas and pure hardware logic (cross-correlation algorithm) to achieve accurate distance measurement (quantitative detection) of fault points and qualitative judgment of fault types (blockage / breakage).

[0059] Hardware components: The core control unit is a single-chip microcontroller that shares the same STM32L431RCT6 microcontroller as the low-frequency acoustic wave excitation module (eliminating the need for an additional microcontroller and reducing costs). It has a built-in 12-bit ADC interface (for receiving digital signals after front-end conditioning), a timer (for recording the time difference between the transmitted pulse and the echo), and an I2C interface (for connecting a temperature sensor). It operates at a frequency of 80MHz and has a response time of ≤1μs, ensuring the accuracy of time difference measurement.

[0060] Temperature sensor: The DS18B20 digital temperature sensor is selected, with a measurement range of -20℃ to 60℃, a measurement accuracy of ±0.5℃, and a response time of ≤100ms. It is connected to the microcontroller via an I2C interface and is used to collect the ambient temperature (or gas temperature) in the sampling pipeline in real time, providing data support for sound velocity compensation. The sensor is installed in the main T-junction (gas inlet side) and is in close contact with the inner wall of the pipeline to ensure the accuracy of the measured temperature.

[0061] Cross-correlation operation circuit: It consists of the built-in arithmetic unit of the microcontroller and external logic gate circuit (74HC00). No additional dedicated arithmetic chip is required. Cross-correlation operation is implemented through pure hardware logic. The operation speed is ≥1000 times / second. It can quickly identify the correlation between the transmitted pulse and the echo signal and determine the arrival time of the echo signal. The logic gate circuit is used to enhance the stability of the operation and avoid misjudgment caused by signal interference.

[0062] Phase detection circuit: Composed of comparator (LM311) and flip-flop (74HC74), used to detect the phase difference between the echo signal and the transmitted pulse signal; the threshold voltage of the comparator is adjustable (0.3V-0.7V) to convert the echo signal into a square wave signal for easy phase detection; the flip-flop is used to lock the phase difference signal and transmit it to the microcontroller for judgment.

[0063] Display and alarm module (optional): OLED display screen (128×64 pixels) is selected and connected to the microcontroller via SPI interface to display parameters such as distance to the fault point, fault type (blockage / breakage), and ambient temperature; the alarm module consists of a buzzer and an LED indicator. When a fault is detected, the buzzer emits an alarm sound (frequency 1kHz, volume ≥80dB), and the LED indicator (red) flashes to remind staff to handle the situation in a timely manner.

[0064] Core logic: The core logic of this module is divided into two parts: precise ranging (quantitative) and fault characterization (qualitative): Precise ranging (quantitative), based on the sound speed propagation formula, combined with temperature compensation: Core principle: The speed of sound propagation within a pipe is constant (affected by temperature). By recording the time difference between the emitted sound pulse and the echo signal, and combining this with the sound speed formula, the distance between the fault point and the main unit can be calculated. The specific steps are as follows: Time difference measurement: The microcontroller records two key time points using a timer: The time for the acoustic excitation module to emit acoustic pulses ; The echo signal transmitted by the front-end conditioning module is confirmed through cross-correlation calculation, and the time it arrives at the microcontroller is... ; Time difference Measurement accuracy ±10μs (to ensure distance measurement accuracy); The core function of cross-correlation is to accurately identify the echo signal from the mixed interference signal, eliminate noise interference, and ensure the accuracy of time difference measurement. The specific operation logic is as follows: cross-correlate the transmitted pulse signal and the received signal. When the correlation coefficient reaches the maximum value (≥0.8), it is determined to be a valid echo signal, and the time at this point is recorded. .

[0065] Sound speed compensation: the speed at which sound waves travel in air The speed of sound is greatly affected by temperature. At room temperature (20℃), the speed of sound is approximately 340 m / s. For every 1℃ change in temperature, the speed of sound changes by approximately 0.607 m / s. Therefore, it is necessary to collect the ambient temperature in real time using a temperature sensor. (Temperature in Celsius), use the following formula to compensate for the sound velocity and obtain the actual sound velocity inside the pipe. : ; in, It is the reference value for the speed of sound in air at room temperature (0℃), with the unit being meters per second (m / s), and is the fundamental constant for calculating the speed of sound; This is the sound speed temperature compensation coefficient, with units of meters per second per degree Celsius (°C). It means that for every 1°C increase in temperature, the speed of sound propagation increases by approximately 0.607 m / s. It is used to correct the effect of temperature on the speed of sound. For example, when the ambient temperature is 25°C, the speed of sound =331.4+0.607×25=346.575m / s, ensuring the accuracy of the sound speed calculation.

[0066] Distance calculation: The total distance the sound wave travels from the main unit to the fault point and then reflects back to the main unit is 2. ( (Distance between the fault point and the host), combined with the speed of sound and time difference The distance to the fault point is calculated using the following classical acoustic formula. : ; For example, time difference =2ms (0.002s), speed of sound =340m / s, then = (340 × 0.002) / 2 = 0.34m, that is, the distance between the fault point and the host is 0.34 meters; the ranging accuracy is ≤ ±1 meter (when the pipeline length is ≤ 500 meters), which fully meets the detection needs of industrial sites.

[0067] Distance measurement calibration: Before each device leaves the factory, distance measurement calibration is required. A standard pipeline of known length (such as 100 meters, 200 meters, 500 meters) is selected to simulate a fault point (blockage), measure the distance to the fault point, and adjust the error of the time difference measurement to ensure that the distance measurement accuracy meets the requirements. After calibration, the microcontroller stores the calibration parameters for error correction in subsequent actual testing.

[0068] Fault characterization (qualitative analysis) utilizes phase reversal based on the principle of acoustic impedance variation: Core principle: Sound waves are reflected at the interface of media with different acoustic impedances. The phase change of the reflected wave is determined by the difference in acoustic impedance on both sides of the interface. When a pipeline is blocked or broken, there is a significant difference in acoustic impedance at the fault point, causing the phase of the reflected wave to have a different phase relationship (in-phase / out-of-phase) with the incident wave (emitted pulse). By detecting the phase relationship, the fault type can be directly distinguished. The specific judgment process is as follows: Acoustic impedance principle: Acoustic impedance , For the density of the medium, The velocity of sound varies depending on the medium; The medium in the sampling pipeline is the gas to be measured (such as air, methane, etc.), and the acoustic impedance is... The acoustic impedance varies depending on the medium at the fault location. In blockage faults (such as water seal blockage, dust accumulation, or debris blockage), the medium at the fault point is either solid (dust, debris) or liquid (water), and its acoustic impedance... Much greater than the acoustic impedance of the gas inside the pipe ( >> ), forming a hard boundary; Broken / Leaking Fault: After a pipeline break, the fault point is connected to the external tunnel space. The medium in the external space is air (or other gas), but due to the vast space, sound waves propagate without constraints, resulting in an equivalent acoustic impedance. Much smaller than the acoustic impedance of the gas inside the pipe ( << ), forming soft boundaries; Phase change law: According to the principle of acoustic reflection, when a sound wave travels from a low-impedance medium... Incident on a high impedance medium At a hard boundary, the reflected wave is in phase with the incident wave (phase difference is 0°); when the sound wave travels from a low-impedance medium... Incident on a low impedance medium At soft boundaries, half-wave loss occurs, and the phase of the reflected wave is out of phase with that of the incident wave (phase difference of 180°). Phase detection implementation: The phase detection circuit converts the transmitted pulse signal (incident wave) and the echo signal into square wave signals. A comparator compares the zero-point crossover points (rising or falling edge) of the two square wave signals, based on the phase difference. Fault type determination: If the phase difference is 0° (the rising edges of the two square waves are synchronized), the reflected wave is in phase with the incident wave, and the microcontroller determines that there is a "pipeline blockage" fault, and records the distance to the fault point at the same time. If the phase difference is 180° (the rising edges of the two square waves are opposite), the reflected wave is out of phase with the incident wave, and the microcontroller determines it as a "pipeline breakage / air leakage" fault, and records the distance of the fault point.

[0069] Misjudgment avoidance measures: To avoid misjudgment caused by interference signals, a phase detection threshold is set: when the phase difference is within the range of 0°±10°, it is judged as in phase (blockage); when the phase difference is within the range of 180°±10°, it is judged as out of phase (breakage / leakage); if the phase difference exceeds the above range, it is judged as an invalid signal, and the detection is repeated (up to 3 times; if it is still an invalid signal, an alarm is triggered, indicating "detection abnormality").

[0070] Implementation process: System initialization: After the microcontroller starts up, it initializes each module, checks the working status of the temperature sensor, microphone, speaker, and front-end conditioning circuit. If there is an abnormality, an alarm is triggered; if normal, it enters standby mode and waits for the detection trigger signal. Detection trigger: When a gap in the operation of the air circuit switching valve or a sleep signal of the air pump is detected, the low-frequency acoustic excitation module is triggered to emit an acoustic pulse, and at the same time, the microcontroller starts a timer to record the emission time. ; Echo reception and conditioning: The microphone captures the echo signal, which is then processed through blind spot blocking, bandpass filtering, TGC amplification, and signal buffering before being transmitted to the microcontroller's ADC interface and converted into a digital signal. Cross-correlation operation: The microcontroller performs cross-correlation operation on the transmitted pulse signal and the received digital signal to identify the valid echo signal and record the echo arrival time. Calculate the time difference ; Temperature Acquisition and Sound Velocity Compensation: Temperature sensor acquires ambient temperature. Substitute the values ​​into the sound velocity compensation formula to calculate the actual sound velocity inside the pipe. ; Precise distance measurement: Substitute the values ​​into the distance calculation formula to calculate the distance to the fault point. Store distance data; Fault characterization: The phase detection circuit detects the phase difference between the echo and the incident wave, determines the fault type (blockage / breakage) based on the phase difference, and stores the fault type data; Output results: The distance to the fault point, fault type, ambient temperature and other parameters are displayed on the OLED screen. If a fault is detected, a buzzer alarm is triggered and the LED indicator flashes. At the same time, the data is transmitted to the host computer (optional) for remote monitoring.

[0071] Restore standby: After the test is completed, the system returns to standby mode, waiting for the next test to be triggered.

[0072] Example 2 Please see Figure 2 A multi-parameter monitoring method for spontaneous combustion in coal mines, comprising the following parts: Complete the installation and deployment of the gas-acoustic coupling and hardware isolation module to achieve strict isolation of toxic and explosive gases in coal mine sampling pipelines and efficient coupling and transmission of sound waves. The low-frequency sound wave band is selected by matching the sampling pipeline parameters, and the timing pulse is emitted by the coordinated sampling system to ensure that the sound wave propagates in the pipeline with low attenuation and no interference. A high-sensitivity microphone is used to capture the weak echo at the fault point, which is then conditioned into a stable electrical signal through pure hardware blind zone masking, bandpass filtering, and TGC amplification. Accurate fault location is achieved by combining TDR pure logic with temperature compensation. The type of blockage / fracture fault is determined by echo phase reversal and the result is output.

[0073] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0074] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

[0075] It should be noted that, in this document, the use of relational terms such as "first" and "second" is merely for distinguishing one entity or operation from another, and does not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0076] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0077] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0078] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0079] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0080] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0081] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0082] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A multi-parameter monitoring system for spontaneous combustion in coal mines, characterized in that, include: The air-to-sound coupling and hardware isolation module is configured to achieve efficient sound wave coupling and strict isolation of toxic / explosive gases in the pipeline through a three-way coupling cavity, a polymer sound-permeable isolation membrane, and auxiliary fixing components. The low-frequency band acoustic excitation module is configured to emit low-frequency pulses to ensure that the acoustic waves propagate with low attenuation and without interference within the pipeline. The acoustic echo receiver and front-end conditioning module is configured to capture echoes and, through hardware conditioning, convert the echo signals into stable and recognizable electrical signals for transmission to subsequent modules. The TDR pure logic ranging and fault characterization module is configured to use a microcontroller and hardware logic, combined with temperature compensation and sound velocity formula to achieve fault point ranging, and to determine the fault type by phase reversal.

2. The multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 1, characterized in that, The air-acoustic coupling and hardware isolation module specifically includes: Three-way coupling cavity: made of stainless steel, with an integral forged structure; the inner diameter of the main channel of the tee matches the inner diameter of the sampling pipeline. High-polymer sound-permeable insulation membrane: Teflon or polyimide film is selected, the diameter of the film is consistent with the inner diameter of the bypass pipe, and the edge is sealed with fluororubber sealing ring; Auxiliary fixing components include stainless steel pressure rings, sealing gaskets, and mounting brackets.

3. The multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 2, characterized in that, The installation method is as follows: Before the main exhaust pipe of the existing sampling system host enters the gas chamber, a special three-way coupling cavity is connected; after connection, the gas to be tested in the main exhaust pipe flows normally to the gas chamber to complete the sampling and detection, and the bypass pipe is in a closed state. Cut the polymer acoustic barrier membrane to a size that matches the inner diameter of the bypass pipe. Place the fluororubber sealing gasket around the edge of the barrier membrane and insert them together into the groove at the end of the bypass pipe. Then, tighten the stainless steel pressure ring through the threads to compress the barrier membrane and the sealing gasket. At this point, the barrier membrane divides the bypass pipe into two sides. One side is the air-contact side, and the other side is the non-air-contact side; The speaker and microphone are fixed to the non-air-contact side of the isolation membrane using mounting brackets; The speaker and microphone are arranged coaxially to ensure that the sound waves can be incident perpendicularly on the isolation diaphragm, maximizing the sound energy coupling efficiency; the speaker and microphone leads are led out through explosion-proof flexible tubing and connected to the subsequent control circuit, and the tubing interfaces are sealed.

4. The multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 1, characterized in that, The low-frequency band acoustic wave excitation module specifically includes: Select the appropriate frequency pulse based on the inner diameter of the sampling pipeline; The waveform of the acoustic pulse can be selected as a sine wave or a linear frequency modulated chirp signal; The microcontroller collects the action signal of the gas path switching valve and the working status signal of the air pump in the sampling system in real time. When the gas path switching valve completes its action or the air pump enters a sleep state, the acoustic excitation module is triggered to work. After being triggered, the microcontroller generates a pulse signal of a set frequency through the PWM pulse generator circuit. After being amplified by the audio power amplifier, it drives the speaker to emit low-frequency sound wave pulses. After each sound pulse is emitted, wait for a preset time before resuming normal operation of the sampling system.

5. A multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 1, characterized in that, The acoustic echo receiver and front-end conditioning module specifically includes: High-sensitivity dynamic microphone: arranged on the same side as the speaker, using a condenser dynamic microphone; Analog bandpass filter: An active bandpass filter is selected, consisting of an operational amplifier, resistors, and capacitors. The center frequency is matched with the center value of the sound wave excitation frequency. The input impedance of the filter is matched with the microphone output impedance, and the output impedance is matched with the subsequent amplification circuit. Pure hardware time-gain controlled amplifier circuit: operational amplifiers are selected to form a variable gain amplifier circuit; Blind spot blocking circuit: It consists of a transistor, resistor, and capacitor, and is connected to the microphone output terminal; when the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor to conduct, briefly blocking the microphone input; Signal buffer circuit: An operational amplifier is selected to form a voltage follower.

6. A multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 5, characterized in that, Also includes: When the sound wave pulse propagates in the sampling pipeline and encounters a fault point, it will generate a reflected echo. The echo propagates in the opposite direction along the pipeline and is transmitted to the non-air-contact side through the isolation membrane of the bypass pipe, where it is captured by a high-sensitivity microphone. The microphone converts sound wave signals into electrical signals and transmits them to the blind spot shielding circuit. While the speaker emits a sound wave pulse, the microcontroller outputs a high-level signal to control the transistor in the blind zone shielding circuit to conduct, and the microphone output is short-circuited; when the sound wave pulse is emitted, the microcontroller outputs a low-level signal, the transistor is cut off, the blind zone shielding is released, and the echo signal captured by the microphone is normally transmitted to the bandpass filter. Analog bandpass filters filter the electrical signal output by the microphone, removing low-frequency noise and high-frequency interference from the environment. The filtered signal is fed into a pure hardware TGC amplifier circuit, which automatically adjusts its gain according to the arrival time of the echo signal. The signal amplified by the TGC is fed into the signal buffer circuit, buffered by a voltage follower, and then transmitted to the ADC interface of the microcontroller. The microcontroller converts the analog signal into a digital signal and transmits it to the TDR pure logic ranging and fault characterization module for processing.

7. A multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 1, characterized in that, The TDR pure logic ranging and fault characterization module specifically includes: Precise ranging, based on the formula for the speed of sound propagation, combined with temperature compensation: The microcontroller records the time when the acoustic excitation module emits acoustic pulses via a timer. ; The echo signal transmitted by the front-end conditioning module is confirmed through cross-correlation calculation, and the time it arrives at the microcontroller is... Time difference ; Real-time ambient temperature is collected using a temperature sensor. Perform sound velocity compensation to obtain the actual sound velocity inside the pipe. ; Combined with the speed of sound and time difference Calculate the distance to the fault point ; According to the principle of acoustic reflection, when a sound wave is incident from a low-impedance medium to a high-impedance medium at a hard boundary, the phase of the reflected wave is in phase with the incident wave; when a sound wave is incident from a low-impedance medium to a low-impedance medium at a soft boundary, half-wave loss occurs, and the phase of the reflected wave is out of phase with the incident wave. The phase detection circuit converts the transmitted pulse signal and the echo signal into square wave signals. The comparator compares the zero-point crossover points of the two square wave signals and determines the fault type based on the phase difference.

8. A multi-parameter monitoring system for spontaneous combustion in coal mines according to claim 7, characterized in that, Also includes: After the microcontroller starts up, it initializes each module. When a gap in the gas path switching valve's operation or a sleep signal from the air pump is detected, the low-frequency acoustic excitation module is triggered to emit an acoustic pulse. Simultaneously, the microcontroller starts a timer to record the emission time. ; The microphone captures the echo signal, which is then processed through blind spot masking, bandpass filtering, TGC amplification, and signal buffering before being transmitted to the microcontroller's ADC interface and converted into a digital signal. The microcontroller performs cross-correlation calculations on the transmitted pulse signal and the received digital signal to identify valid echo signals and record the echo arrival time. Calculate the time difference ; Temperature sensor collects ambient temperature Calculate the actual speed of sound inside the tube. and the distance to the fault point ; The phase detection circuit detects the phase difference between the echo and the incident wave, determines the fault type based on the phase difference, and stores the fault type data.

9. A method for monitoring multiple parameters of spontaneous combustion in coal mines, and a system for monitoring multiple parameters of spontaneous combustion in coal mines according to any one of claims 1-8, characterized in that, include: Complete the installation and deployment of the gas-acoustic coupling and hardware isolation module to achieve strict isolation of toxic and explosive gases in coal mine sampling pipelines and efficient coupling and transmission of sound waves. The low-frequency sound wave band is selected by matching the sampling pipeline parameters, and the timing pulse is emitted by the coordinated sampling system to ensure that the sound wave propagates in the pipeline with low attenuation and no interference. A high-sensitivity microphone is used to capture the weak echo at the fault point, which is then converted into a stable electrical signal through pure hardware blind zone masking, bandpass filtering, and TGC amplification and conditioning. Accurate fault location is achieved by combining TDR pure logic with temperature compensation. The type of blockage / fracture fault is determined by echo phase reversal and the result is output.

Images