Design And Application Of Portable Transient Electromagnetic Instrument Based On WiFi

In the process of coal mining,the mine water inrush disaster will occur if it encounters water-rich caves and accumulated water.The disaster will cause huge losses to people's lives and national property.At the same time,most of the traditional TEM instruments have the disadvantages of large size,bulkiness,inconvenience,complicated operation and low construction efficiency.They are also complicated in the data export process,and need to be exported from the USB port through the serial port or U disk.Therefore,this paper designs a small,lightweight,fast operation,high reliability,multi-function portable wireless intelligent transient electromagnetic instrument to prevent mine water inrush disaster and ensure safe production in coal mines.The instrument is composed of WiFi communication module ESP8266,STM32F205 microprocessor of ARM Cortex-M3 architecture and Android tablet computer.It uses the transmitting coil to send a pulsed large current to the detection area.The current will generate an exciting magnetic field.Then using the receiving coil to receive the secondary field signal which is induced by the geological body.The signal is processed by the microprocessor and directly uploaded to the tablet computer for analysis.The results of geological advance report and two-dimensional visualization results can be obtained on the spot,which are used to analyze the geological structure and hydrogeological status of the coal mining area.This method greatly improves the detection construction efficiency.In order to complete the design of new instruments,this paper conducts research and development work on instrument function analysis,frame design,hardware circuit design,software program writing,functional testing,mine experiment and data result analysis.This paper briefly outlines the research background of the subject,the design requirements of the instrument,and the working principle of the instrument.Then the instrument design is discussed in detail.The hardware structure design is developed from the aspects of power system,transmitting module,receiving module and WiFi module communication circuit.The instrument uses the STM32F205 microprocessor as the main control chip.Firstly,the chip controls and drives the isolation device IR2110 by sending signals,and uses the weak current to control the strong current method to generate the emission current in the H-bridge circuit.Secondly,the current generates a bipolar pulsed current signal through the transmitting coil to establish a primary magnetic field and is collected by the current sensor ACS712.The secondary field signal generated by the geological body induction is captured by the receiving coil.After signal conditioning,it is converted into a digital signal by the ADS1274 sampling chip and transmitted to the microprocessor for data processing.Finally,the main control chip communicates with the WiFi module ESP8266 in SPI mode,combined with Socket communication based on TCP / IP protocol to realize wireless data collection.On the basis of hardware design,following the principle from the bottom to the top,the supporting embedded signal acquisition software was developed.The bottom part of the microprocessor program is written in C language,and is equipped with the Free RTOS real-time operating system.It uses task scheduling to achieve functions such as receiving commands,transmitting current,signal acquisition,and data transmission.The tablet PC software is developed based on the Qt platform and includes functional modules such as project file settings,test parameter settings,waveform display modules,and file management modules.In addition,a custom communication protocol is designed between the microprocessor and the tablet PC software.The tablet PC sets the transmission and acquisition parameters,and sends the start acquisition command.The microprocessor receives the command and parses the command to start the transient electromagnetic signal acquisition process.After the acquisition is complete,the data is sent to the tablet PC software.tablet PC software draws a single waveform and multi-track waveforms based on the received data and saves it as an engineering data file.Afterwards,the new instruments were tested for hardware and software such as the frequency and accuracy of the transmitted pulse current,the range and accuracy of the received voltage,the wireless transmission data rate,software functions,and ground experiments.The results show that all the important indicators of the instrument have met the requirements.In order to test the comprehensive performance of the instrument,multiple mines in Yunnan,Sichuan and Shaanxi provinces were selected as the test objects to carry out detection experiments under the mine.The experimental results are presented in a two-dimensional visualization map.According to the change of apparent resistivity in the figure,the low-resistance anomaly area,weak-abnormality area and high-resistance area are analyzed,and the result of geological advance report is obtained.This result is basically consistent with the actual geological conditions of the borehole.In particular,the low resistance anomaly area has relatively strong water replenishment and should be highly valued.Comparing the detection conditions when the emission currents are different,the result is that the greater the emission current,the farther the detection depth,but there is a deviation from the shallow information at the near point.In addition,the application of the instrument is extended to slope surface testing to detect the distribution of groundwater.All experimental results are combined to verify the effectiveness and accuracy of the instrument.In the complex site conditions,there may be strong electromagnetic interference and the impact of environmental metal objects,as well as the artificial effects of the coil detection mode,the layout of the measuring line,the distance between the measuring points,etc.,which will cause deviations in the experimental data collection.In addition,the data processing needs to be improved.The software adds artificial intelligence,classification of typical geology,establishes data and deep learning methods,and improves the level of intelligence.Also,It can provide three-dimensional visualization of the results,making the detection results more intuitive and useful.