Design Of High-density Electrical Prospecting Apparatus Based On RS485 Bus Network

During the process of mine excavation,a large amount of groundwater is often suddenly poured into the roadway,causing unnecessary casualties and economic losses.Whether the location of the water-bearing areas in the roadway can be predicted in advance has become a key technology for preventing mine water disaster.The High-density Electrical Prospecting Apparatus is an array type geophysical prospecting instrument.By laying hundreds of electrodes at a time to detect the resistivity in the geological profile,the distribution of water-bearing areas in the roadway can be obtained by this analysis.However,the electrode system of the existing domestic apparatus uses a specific electrode conversion device to connect multiple 30-core large wire cables to control the electrode pole distance and arrangement.In the actual survey,the large wire cable is too heavy to facilitate construction,And the time it takes for the electrode conversion device to switch the electrodes is too long,which greatly affects the survey efficiency,which will limit its application field,so this paper proposes a High-density Electrical Prospecting Apparatus based on RS485 bus network design method.In order to complete the design of the new instrument,this paper uses research methods such as instrument function analysis,hardware circuit design,software program writing,performance testing and experiment.The detection principle of the High-density Electrical Method is to use electrodes A and B to emit an electric current I underground to establish an electric field.By measuring the potential difference ΔV between electrodes M and N,The arrangement positions of A,B,M and N electrodes are switched in real time by the electrode conversion device controlled by the master of the apparatus.Based on this principle,it was decided to change the one-pole one-wire large wire structure of the existing apparatus to a bus-type cable network structure.The new apparatus bus cable will always use an eight-core standard cable,including 2 cores for power supply and 2 cores for control communication,AB electrode is connected to 2cores and MN electrode is connected to 2 cores.The entire electrode system adopts T-shaped three-way connection,and is made into standard equal length control cables,which is convenient for on-site construction and standardization.And by comparing the parameters of the Ethernet bus,CAN bus and RS485 bus,combined with the characteristics of the apparatus usage scenario,the advantages and disadvantages of these types of buses are analyzed in detail.Due to the small amount of communication data of the apparatus,the real-time requirements are not high,selected the RS485 bus with low cost,high reliability and long communication distance is used as a carrier for communication between the master and slave of the new apparatus.The system master sends related commands to the slave through the bus,so that the slave controls the electrode arrangement and combination,and realizes the switching connection between the host and different electrodes,thus preliminary design of the functional structure framework of the apparatus hardware system and the functional modules of embedded software architecture.Based on the hardware structure of the new High-density Electrical Prospecting Apparatus,in accordance with the design idea from the whole to the part,the functionalmodule circuits of the master and the slave are designed in detail.The Survey Control Master is based on the main control circuit of the STM32F429 processor,the excitation source H-bridge circuit,and the analog-to-digital conversion circuit.It constitutes a hardware circuit with current emission,signal acquisition,electrode control,data storage,and display functions;The Electrode Switching Slave uses the STM32F103 chip as a microcontroller,supplemented by an electrode conversion circuit,which can arrange and combine the electrodes according to the command of the master and return the feedback information to the master.Following the principle from the bottom to the upper layer,the embedded system software is divided into four levels: the peripheral driver layer,the master-slave communication protocol layer,the operating system layer,and the survey control application layer.In order to allocate peripheral resources reasonably,the RS485 communication interface driver is used to support command transmission between master and slave;the NAND Flash driver is used to support data storage;and the ADS8556 driver is used to support signal collection.The frame format of the Modbus communication protocol between the master and slave is formulated to bridge the data transmission between the master and slave.In order to realize data exchange between driver layer and application layer,Free RTOS operating system is transplanted.Then the application layer software program of the apparatus system is designed,and the functions of emission and acquisition control,hardware automatic detection,data reading and writing,display control and electrode switching are realized respectively.The performance parameter test and functional test of the electrical prospecting apparatus were carried out under laboratory conditions.The test results showed that the emission current accuracy,receiving voltage accuracy,acquisition resolution and system noise of the apparatus can all meet the design requirements,and the apparatus can complete basic functions such as relay switching,running pole control and grounding resistance measurement.In a mining area in Yunnan,a detection experiment on the water-bearing areas of the mined-out area was carried out.Four measuring lines were arranged above the approximate geographical location of the mined-out area.The poles were run through the Wenner method,and the measured data was inverted using the least square method Transformation processing and analysis.The scope of the water-bearing areas detected by the apparatus is compared with the previous measurement results of the mining company,and they are not very different,which verifies the effectiveness and accuracy of the apparatus developed in this paper to detect in the wild.When the apparatus surveys goafs with large burial depths,the deep abnormal signal attenuation is large and may not be effectively captured.It is hoped that in the future,the anti-interference method of the High-density Electrical Prospecting Apparatus can be improved to realize the survey of goafs in a larger depth range.