Research On Anti-power Frequency Harmonic Interference Method Based On Phase Cancellation For MRS Signal

At present,the problem of water shortage is worsening,particularly in arid and semi-arid areas of northern China,which has become a major factor that restricts Chinese economic development.People pay more attention to groundwater on account of the shortage of water resources.Therefore,finding a new groundwater exploration method is extremely important for solving the problem of water shortage in our country with the advantages of high-accuracy,high-efficiency and low-cost.The continuous advancement of modern science and technology has provided effective technical support and various geophysical methods for groundwater exploration.Magnetic resonance sounding(MRS)of groundwater detection technology is the unique geophysical method in the world to directly detect the groundwater recently.It has been widely used in groundwater exploration projects with its advantages of high-resolution,high-efficiency,sufficient information and uniqueness of interpretation.However,the amplitude of the acquired MRS signal is very small,resulting in a weak anti-interference ability.Which is influenced seriously by the 50 Hz power frequency harmonics from the complex noise.Especially,the interference of agricultural power is the main triggering factor that bring noise into MRS signal.Agricultural power has a poor form factor and a large number of harmonic components,due to the lack of reactive power compensation and other factors.Traditional MRS technology of groundwater detection usually adopts the superposition de-noising method to eliminate the interference on the MRS signal caused by environmental noise after data receiving.Whereas this method can not eliminate the power frequency harmonics noise and lead an inaccurate interpretation to the subsequent data inversion,making it unable to obtain the expected results in MRS detection,then limiting the scope of application of the method severely.With the purpose of overcoming the above shortcomings,this paper proposes an anti-power frequency harmonic interference method based on phase cancellation for MRS signal.This method is mainly accomplished by two major techniques of acquisition and regulation of power frequency signals and phase cancellation of MRS signals.Firstly,the work of collection of power frequency signals and evaluation of the test site is performed.In this paper,it is proposed that the power frequency signal is received through LC parallel resonance and then converted into a square wave through the corresponding signal conditioning circuit.The control module adopted as MSP430 + CPLD.The MSP430 is used to implement the parameter adjustment of signal conditioning preamplifier circuit and the AGC circuit,to guarantee the power frequency signal amplitude be in a best state.Secondly,in order to realize the phase cancellation method,the MSP430 picks up the rising edge of the power frequency signal to control the CPLD module to determine the emission timing,and successively emits excitation pulses with a phase difference of 180°.Finally,the two received MRS signals are superimposed.Then achieve the elimination of the harmonic noise of the power frequency,and the purpose of enhancing the anti-interference ability of the MRS instrument is realized.In this paper,by the study of anti-power frequency harmonic interference method based on phase cancellation for MRS signal,the anti-interference ability of MRS detection technology is improved.While retaining the conventional noise superposition ability,the influence of power harmonics on the MRS signals is eliminated to the great extent,expanding the application of MRS detection groundwater technology to a wider range of environments.Relevant theoretical simulations and field detection results show that the accuracy of MRS detection technology has been improved effectively,which verifies the effectiveness and practicality of this method.The research results of this paper will lay the foundation for subsequent data processing and inversion.