Design And Experimental Study Of Constant Current Excitation Source Based On Direct Current Method

The shortage of water resources has a direct impact on the development of national economy and people's living standards.With the development of industry and the growth of population,people's demand for water resources is increasing,and the demand for water quality is getting higher and higher.The efficiency and accuracy of traditional methods of water source searching can not meet people's actual needs.Geophysical water prospecting technology emerged at the historic moment,providing an efficient way for hydrogeological survey.Common geophysical prospecting methods include transient electromagnetic method,ground penetrating radar method,reflection seismic method,nuclear magnetic resonance method and electrical method.Common geophysical methods for finding water include transient electromagnetic method,geological radar method,reflection seismic method,nuclear magnetic resonance method and electric method.Electrical method is widely used in geophysical prospecting for water because of its strong environmental adaptability and high detection accuracy.The principle of water prospecting by electric method is to apply a sustained and stable electric field to the earth by exciting source,and to determine whether the detected area contains groundwater by measuring the electric field distribution on the ground surface.If the constant voltage source is used as the excitation source,when the earth resistance is too large,the current may be very small,which can not guarantee the detection effect.The constant current source is used as the excitation source,and the current output to the earth is constant.At this time,the excitation electric field is stable,which can make the detection result more accurate.Because the function of common constant current source can not meet the special needs of DC method detection,this paper designs a DC method constant current excitation source according to the needs of DC method detection system.The detection system of DC method is composed of main engine,DC constant current excitation source and industrial control unit.The industrial control computer sends control signals to the host computer,which controls the constant current source to output the excitation current.In this paper,a DC constant current source based on STM32 microcontroller is developed.The parameters of the circuit are collected and the circuit is controlled.A negative feedback circuit composed of a precision operational amplifier and a field effect transistor is designed to achieve constant current output.When the load resistance is small,in order to avoid excessive power consumption of the regulator,a low power adjustment unit is designed.Using STM32 to control the voltage output of switching power supply,the voltage drop of the regulator is limited to 5-IOV.thus reducing the power consumption of the regulator.In order to prevent current overshoot,a signal conversion program is compiled.The STM32 microcontroller is used to convert the step function control signal into the slope function control signal to avoid overshoot.In practical detection,the inductive load compensation circuit is designed to eliminate the current error caused by inductance because of the long power supply cable,which makes the load present inductive characteristics.The accuracy of feedback voltage and current under low current is improved by using the automatic switching program of feedback resistance.In order to reduce the current ripple,the anti-interference design is carried out in the program to reduce the output current ripple.