Development Of Broadband Array Full Wave MRS Acquisition System

The MRS is the only one no-invasion groundwater detection method.We can use theinversion of MRS signal to get the important hydrological parameters of the groundwater such asthe water content,depth,porosity very accurately.These make the MRS instrument develop veryfast in the recent30years.The MRS group of Jilin University started the development of the MRS instrument in2000,after the team’s effort of five years, the MRS group finally develop the first MRS prototype,andcarried out many measurements and experiments in many parts of China,and then design thecorresponding MRS method inversion software.After comparing the actual test data with thecorresponding drilling data, the results confirmed the feasibility and accuracy of the apparatus.And then comparing with the French commercial MRS instrument-NUMIS,under the samecircumstance,the JLMRS-I of Jilin University can achieve the same SNR using less stack timesthan the French apparatus-NUMIS,greatly improved the measurement efficiency and inversionaccuracy of the instrument, the detection depth is150m,reached the international advanced level.But1D MRS detection can only obtain accurate results for layered groundwater,as for the oldempty water, karst water in the special terrain of southwest China, we can only carry outdetection using the array MRS instrument, use2D MRS inversion method to get good results.In this paper,the broadband array full wave MRS acquisition system is developed in view ofthe current need, and differ from envelope acquisition method of JLMRS-I,we use the full waveacquisition in this design,so overcome the problem that the envelope acquisition brought to thesubsequent data processing and inversion explanation.We use National Instrument’s24bit fourchannel synchronous data acquisition card, it has high sampling precision, sensitivity andreliability;data is transmitted through the network cable, it can realize the fast uploading of largeamounts of data;Array measurement lay the foundation of hardware for2D inversioninterpretation and reference noise cancellation method, the measuring efficiency of instrumentalso climb a step;in the design of the amplifier, we introduced the ultra low noise amplifiertechnology,broadband low rectangle coefficient filtering technology,these techniques ensure thatthe amplifier have less hardware delay, can obtain more weak MRS signal;in the design of theinstrument system, we use the modular design method, we setup the interface, ensure themodule’s debugging convenience,the use of stainless steel framework reduces the weight of theapparatus under the effective mechanical strength, and save time and manpower. The parameters of broadband array full wave MRS acquisition system designed in thispaper are as follows: the voltage noise of preamplifier is0.7nV/Hz1/2,the bandwidth of thebandpass filter is1.6kHz,amplification of the amplifier is66dB~110dB,the dynamic range is124.4dB,the acquisition card is24bit,the sampling frequency is25kHz.Through indoor test,thevoltage noise of whole apparatus is1.5nV/Hz1/2,the four channel has a better consistency.Thehost computer control software is based on LabView,we use the communication protocol formatof JLMRS-I,and expand the communication protocol of broadband amplifier.The software isfully compatible with JLMRS-I, these make the broadband array full wave acquisition systemcan be used in conjunction with the transmission system of JLMRS-I,and ensure thepracticability of the whole system.We obtained better MRS signal in the outdoor test,this verifythe validity and reliability of the broadband array full wave MRS acquisition system.