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1、精品论文大集合The Research of Retraining Interference Signal in Mine GasEmission Monitoring by Infrasonic WaveLI Xiao, Zheng Wei, Yu ZengqiangSchool of Information and Engineering, China University of Mining and TechnologyXuzhou Jiangsu; PRC (221008)E-mail: lixiao19842008AbstractIn coal mine, the increase
2、of gas emission in coal bed can easily lead to the concentration of gas gauge in the mining，a gas explosion in the hidden dangers. But because of the dynamic response speed of the mining gas sensor is slowly at present，we cant monitor the phenomenon of mine gas emission timely.The paper investigates
3、 a kind of monitoring measure which takes advantage of infrasonic wave .When the gas release from the grime, a kind of wave whose frequency range is from 0.01 to 20hz will be generated. The infrasonic sensor can detect the signal, so we can monitor the dynamic change of mine gas emission in effect.
4、However, the interference signals are complicated as the same as other monitoring methods. We must adopt some anti-jamming measures to improve the monitoring reliability of mine gas emission. This paper introduced the sensor of infrasonic wave, the design of Infrasound monitoring device, analyzed th
5、e interference noises in the mine, and discussed the technique by hanging the wavelet transform and self-adaptive filter together to filter the interference signal. The experiment indicated that it could acquire preferable anti-jamming effect by using this improved wavelet transform and it improved
6、the discriminating reliability of the disaster information.Keywords: Gas; Infrasonic Wave; Monitoring technology; Anti-jamming1. IntroductionFor a long time，gas disaster throughout endanger the safety of coal mine, it has been the main contradiction of restricting production safety in coal mine. Gas
7、 accidents have been highly destructive and endangered production safety and the lives of miner in the coal mine. This disaster caused huge losses to the state and peoples lives and property. The gas emission easily leaded to the concentration of gas gauge in the slope, a gas explosion in the hidden
8、 dangers. Owing to the dynamic response speedof the mining gas sensor is slowly at present，we cant monitor the phenomenon of mine gas emissionpromptly. The prediction of gas emission is the necessary section. And it influences the safety and reliability of the process of coal mine production for a g
9、reater extent. This paper investigates a kind of monitoring method with predicting and analyzing the gas emission of the non-mining areas. It has important theoretical and practical value for directing mine ventilation design adopt disposition. Then we can take targeted measures to combat gas.2. The
10、 Infrasound Monitoring DeviceThe infrasound monitoring device is used the infrasonic sensor to receive the signal.Infrasonic sensor, it belongs to capacitive sensor. the sound can be converted to the voltage signal which can be enlarged, transported, recorded and analyzed. The output signals can be
11、recorded directly or processed by A / D converter for computer analyzing. Frequency response is 0.01 10Hz, sensitivity is 400 mv / Pa, dynamic range is 108 dB, temperature range is -10 45 .The figure 1 is the frequency response curve of the infrasonic sensor.- 6 -Fig.1 Frequency response curve of th
12、e sensorThe principle of capacitive infrasonic sensor is: one plate of the capacitor is a tightening thin metal diaphragm, and another plate is stationary .When the displacement of the diaphragm is changed due to the sound pressure, the change of capacitance changes into a corresponding change of vo
13、ltage. Thus a sound-electric conversion is achieving. The figure 2 is the equivalent circuit of capacitive infrasonic sensor.Fig.2 The equivalent circuit of sensorIn this paper the sound receiver of the capacitance is analog receiver. It is mainly made up of the acoustic parts and the transducer cir
14、cuit. The capacitance receiver is using AM-transducer, and the receiver circuit includes the oscillation, modulation, microphone, demodulator, DC enlargement,low pass filter, as shown in Figure 3.Oscill- ationModula- tionDemod- ulatorDCenlargementLowpass filterOutputMicrophonFig.3 Analog receivers,
15、sound principle circuit diagramThere is a bridge modulation amplifier in the sensor. The bridge is in balance when there is no infrasonic signal. When there are some infrasonic signal the bridge loses balance with the capacitance changing. Thus bridge export AM signal to complete the modulation and
16、enlargement of the infrasonic signal.The size of the device is small, and the weight is light, and it is easy-to-install and uses easily. Aportable device can be designed. It is convenient to using.3.Noise Analysis Interference Coal MineThere are mainly wind noises, electric noises and ruleless nois
17、es in the coal mine. Though large numbers of noise analysis, the noises in coal mine can be classified to be 5 kinds as follow:(1) Wind noise. Generally speaking, the wind causes the undulating changes of atmospheric pressure when it passes through obstacle. When the speed of wind in the 6.7-11.2 m
18、/ s range changes random, there is corresponding about 50Pa pressure on the random fluctuations 2 . From the wind noise spectrum analysis of McDonald 3 we can know that, when the wind velocity is between 2.8-4.3m/s, the main cycle is between 10-300 s. This shows that the scope of its cycle and the s
19、ound pressure level are all in the range of the measured infrasound.(2) Machinery noises. They are mainly from the process of every kind of mechanism equipmentwhen it works. The basic characteristic is inerratic. When the machines works, a great deal signals are produced concentratively and have obv
20、ious periodicity. That is because of the connatural running frequency, and the amplitude of the machinery noises changes very little commonly.(3) Electric noises. This kind of noise is mainly from the electric interfering of diversified electrical equipments in the coal mine. The characteristic is,
21、part of the noises belongs to white noise; part of the noises has almost changeless frequencies, and the other is sharp pulse produced by the electric equipments when they start and the amplitude may be great but the endurance time is bally short.(4) Noises of human activities. They are mainly from
22、people around when they are doing some work. This kind of noises is the most difficult to filter. Because the regularity it presents is weak, the variation range of frequency is rather wide, and the peculiarity is not obvious and some of them have very similar to the effective signal. Compared with
23、machinery noises, the quantity of signals is fewer.(5) Random noises. They are mainly from the around coal wall spalled, collapsing and the coal mine collapsing of drill inside and outside or noises aroused by sensors. The characteristic of the random noises is, some amplitude is large when other is
24、 small, and some frequency is high while other is low. However, they have relatively small number of signals.Material shows that: The frequency of machinery jamming is 150-1150Hz.The frequency of acoustic emission signal in coal seam is 300-850Hz.The frequency of electrical interference is50-100Hz.
25、The frequency band of wind coal drilling operations noise is about 500-600Hz. The frequency band of large diameter drilling rigs operating noise is about 100-200Hz. The frequency band of electricity coal drilling operations noise is about 1500-1750Hz. The frequency of vibration blasting noise is abo
26、ut 400-500Hz. The frequency of tunneling blasting noise is about 80200Hz. According to the analysis of these noises, it is not difficult to find that, machine noise and electrical noise are beyond the scope of infrasound, and these signals will not interfere measuring. So the we do not consider thes
27、e interfering factors in the use of acoustic monitoring mine gas emission. Wind noise is in the infrasound range, and it can be a serious influence. Noises of human activities and random noises also can interfere with different degrees. We need to filter the interferences in the using of monitoring
28、the mine gas emission by infrasound.4.Restrain Noise SchemeBased on the analysis of the characteristic of noises in coal mine, we must take anti-jamming measures in order to receive full acoustic signals of the gas emission. Wavelet transform comparatively fit for the denoising of noises from AE sig
29、nals. To filter the noise preferably and roundly, the self-adaptive filter is hanged together with the wavelet transform. To realize theseparation of signal and noise, the characteristic of effective AE signal or the noises must be known, then through the wavelet analyzing can filter the noises and
30、rebuild the signal. As mentioned above, the characteristic of wind noises and electric noises is known, so they can be filtered by using wavelet transform. However, the noises of human activities and random noises because of their randomicity, cant be foreknown ahead and then it cant be filtered by
31、the wavelet transform, but can be filtered by the self-adaptive filter.The block diagram as Fig.4 shows.Wavelet analysisSignals receivedWavelet transformWaveletinverse transformSignal rebuildingSelf-adaptive filterFig.4 The design of the denoising project4.1Filter of Wavelet TransformThe basic idea
32、of the wavelet transform is that one family function represents or approaches a signal or function. This function is known as the owner of the wavelet function, and it is comprised by a basic wavelet function through changing their time base and frequency.Bases on the character of the mother wavelet
33、, and combine the characteristic of infrasonic signal and the request of analysis, there are symmetrical wavelet( as B spline wavelet) and approximatively symmetrical wavelet( such as Coiflet wavelet, Symlets wavelet, Daubechies wavelet ) should be chosen.Separation of signal and noises using wavele
34、t analysis could adopt the two methods hereinafter: No.1 When the frequency component we concerned of AE signal is known, only reserve the wavelet transform result of the concerned frequency band and let the result of other frequency band to zero by wavelet transform and then rebuild the signal.No.2
35、 When the frequency extension of noises is known, the method is zero setting the frequency band of the noises component and then rebuild the signal and eliminate the noises.4.2The filtering of Self-adaptive Noise Cancellation FilterThe self-adaptive filter has the ability of self-adjustable paramete
36、rs. The design of it needs little or none of the foreknown knowledge. The self-adaptive is controlled by a self-adaptive process, and it could eliminate the noises to be the extent the direct filter difficult or cant achieve.The basic principle of self-adaptive filter is shown as Fig.2Sourceof signa
37、ldk=sk+nk+Output of systemskSourceof noisesxkThe referenced inputSelf-adaptivefilternkFig.5 The principle of self-adaptive filterThrough the filter of wavelet transform and the filtering of self-adaptive noise cancellation filter the infrasonic signal of gas emission can be received completely.5.Exp
38、eriments and AnalysisTo validate the feasibility and reliability of the infrasound in monitoring gas emission under the mine, we experimented in the lab with simulative gas emission equipment, the experimentequipment is as fig 6.Depressurizing ValveGasGas Release DeviceInfrasonicSensorLow FrequencyO
39、scillographFig. 6 Simulative gas emission equipmentIn the experiment equipment showed in fig 6, high pressure gas is put in the gas container. It goes into the release equipment through the depressurizing valve. Rows of exhaust nibs are assembled on the gas release equipment. When the high pressure
40、gas makes the pressure in the gas release equipment stable, the t depressurizing valve is turned on and the gas will spurt out to simulate the gas emission in the coal bed. The type of CDC-2B infrasonic sensor is used in the experiment, and12V DC is supplied. The output of the infrasound sensor is c
41、onnected to the low frequencyoscillograph (Type Handyscope3).In the experiment, we adjust the isobaric controlling clique to set the pressure 8Mp.If the gas pressure in the gas release equipment keep stable, we turn on the electromagnetism clique and survey the wave of the simulative gas emission, t
42、he result is as fig 7(A).Then we simulate the wind environment using exhaust fan of dia.1.2m and 80W power, the signal wave is as fig7(B）.Then we dispose with the method by hanging the wavelet transform and self-adaptive filtertogether to filter the interference signal is as fig 7（C）.A 无干扰信号时的瓦斯涌出波形
43、The gas Emission waveform without interference signalB 没有采取抗干扰措施的瓦斯涌出波形The gas emission waveform without anti-jamming stepC 采取抗干扰措施的瓦斯涌出波形The gas emission waveform with anti-jamming stepFig.7 The infrasonic waveformWe can pick up the characteristic signal (just as the peak value and frequency) from
44、the sound signal that is resulted with the filter of wavelet transform and the filter of self-adaptive.6.ConclusionThrough the above analysis, the dynamic response speed is quickly with the method of monitoring the mine gas emission based on infrasound. And the sensitivity is high. The technique by
45、hanging the wavelet transform and self-adaptive filter together to filter the interference signal can greatly improve the reliability of monitoring. There are some broad prospects for using and development. It is significant for monitoring the mine gas emission in the future.References1 Tong Min-ming , Feng Ying-bo. The Filtration of Sound Transmit In the Mine ,CISCGCT 2OO7 2 Cook, R.K .and Yound , J.M. Strange sound in the atmosphereM. Sound,1,1962：25-33.3 Xie Jin-lai ,Tu Yan , Wang Jun-sheng. The Circular Infrasound Array to Enhance Signal-to-Noise , inChinese. Acoustic Journal.1986,11(5)
