Design Of Acquisition And Control System For DC Resistivity Measuring Instrument

The resistivity method is an electrical exploration method,which works by using the power supply electrodes A and B to emit current to the earth,establishing a stable current field,detecting the circuit current strength and the potential difference between electrodes M and N,obtaining the resistivity at the middle point of electrodes M and N,processing the detected data in forward or inverse,drawing a cross-sectional map of the measured area,and interpreting the geological situation of the area according to the cross-sectional map.This paper improves on the traditional resistivity measuring instrument: using embedded microprocessor to drive high-speed AD acquisition chip for data acquisition,which greatly improves the acquisition efficiency;and choosing multi-core cable to connect electrodes,which reduces the complicated wiring work;using relay circuit,through the driver,the arrangement of electrodes can be changed at will,which improves the working efficiency.This paper designs a resistivity meter acquisition control system with DC power supply by analyzing functional requirements,designing hardware circuits,writing drivers and conducting performance tests.According to the functional requirements,three parts of hardware circuit are designed:master,slave and relay module.After the measuring instrument starts to work,the slave will first complete the numbering by sending and receiving commands and energize the next level of slaves until all slave sequences finish the numbering work.The master controls the slaves to arrange the electrodes,collect the current and voltage data and calculate the resistivity.The repeater is responsible for connecting the master and slaves to improve the overall efficiency of the system.The STM32F407ZET6 is selected as the master chip for the host part,together with the current detection circuit,voltage sampling circuit,AD conversion circuit and current transmitting circuit.The slave part uses STMF103 microprocessor as the core to drive the CAN communication circuit and electrode control circuit.The relay module uses two STMF103 microprocessors,each controlling two CAN communication circuits,each connected to a slave all the way,enabling the system to perform four-channel acquisition.The system software design is divided into four parts: peripheral driver layer,communication protocol layer,control application layer and upper computer operating system.The AD7609 driver is designed in the peripheral driver layer part.In the communication protocol layer part,the communication data frame and serial port communication and CAN bus communication driver between the modules of the instrument are designed.The data acquisition,data processing,PWM output control,electrode conversion and other functions are realized in the control application layer part.Finally,the touch screen communication program and operation interface are designed to complete the upper computer operating system and control the instrument work.After completing the overall system design the slave number,electrode switching,system short circuit noise and transmitter circuit stability were tested using relevant test tools.Then four-channel resistivity measurements were performed using adjustable resistors to simulate earth.The performance tests and experimental results show that the design basically achieves the expected functionality.