Design And Implementation Of DC Detection System

Water shortage is a common problem in the world,especially in China.Groundwater exploration has become an important research topic.At present,our country's electrical prospecting methods have reached the international advanced level.However,at present,there are few technicians engaged in this field,lacking reliable and effective detection system,and the detection accuracy has not reached the desired effect.In order to solve this problem,based on the principle of direct current method,this paper develops a direct current method detection system for surface water prospecting,which can be used for surface water prospecting in water scarce areas.The principle of water detection by DC method is to supply constant current to the earth through the supply electrodes.The voltage between the measuring electrodes will gradually increase with the supply time and tend to stabilize the saturation value.When the supply current is disconnected,the voltage between the measuring electrodes will decrease rapidly at the moment of power cut off,then decrease slowly with time,and then decay to near zero after a period of time.The charging and discharging of the earth will be collected and analyzed.The electric curve can get the relevant parameters,so as to prove the groundwater source and achieve the purpose of water prospecting.The hardware of the system mainly includes constant current source,host computer,host computer,status display module and external electrodes.Constant current source provides excitation for power supply circuit.The host computer sends instructions to the host computer and the status display module.The host computer controls the switch of electrodes and the output current of constant current source according to the instructions of the host computer.The status display module displays the current working state of the system according to the instructions of the host computer.The external electrodes are divided into supply electrodes,measurement electrodes and reference electrodes.This paper mainly introduces the design of electrode control circuit,current measurement circuit,voltage measurement circuit and status display module,and explains the data acquisition card and power module.In terms of software,combined with the advantages of graphical programming software LabVIEW and mathematical calculation software MATLAB,the upper computer software is developed through mixed programming,which mainly includes the main user interface and important functions such as data acquisition and storage,grounding resistance detection,signal filtering,parameter calculation and serial port transmission.Users can set parameters by operating the user's main interface,and control system detects in different ways.In data acquisition function,automatic range switching design is adopted to improve measurement accuracy.Grounding resistance detection function can help users quickly and accurately determine whether the contact between the electrode and the earth is good.Based on the frequency analysis of several groups of measured data,combined with the characteristics of the earth's charge-discharge curve and the actual demand,the low-pass filtering and wavelet denoising methods are used to realize the signal filtering.On this basis,according to the calculation methods of natural potential,apparent resistivity and half-life,the software is designed to realize the automatic calculation of parameters.The software also has the function of serial port sending,which can control the status display module to display the current working state of the system in real time.After the development of the system,the system was calibrated,and then the experimental platform was set up.Accuracy experiment and functional experiment were carried out,including voltage accuracy experiment,current accuracy experiment,grounding resistance experiment,detection mode experiment,natural potential and apparent resistivity experiment and half-life experiment.Through the experimental study,the system accuracy and function met the design requirements.