Design And Implementation Of Low-frequency Digital Seismograph

Applying the principle of seismic exploration to geological exploration is one of the important methods which are used to detecting coal,oil,gas,and rare minerals.With the continuous advancement of the central supply-side structural reform,the demand for ore and energy expands and the development of geophysical exploration industry has a broad prospect,which puts forward higher requirements for geophysical exploration equipment.Low-frequency moving coil seismometers can sense low-frequency seismic waves,which is the core component of low-frequency digital seismograph.The existing low-frequency moving-coil geophone is bulky because its design is based on the traditional mechanical structure.Many limitations have been discovered in engineering applications of the existing low-frequency moving-coil geophone,which makes it difficult for widely using of low-frequency digital seismograph.It is important to study low-frequency compensation technology of moving-coil geophone and design seismograph which is smaller in size and more user-friendly in geophysical exploration industry.The main contents of the article as follows:(1)For the need of improving low-frequency vibration measurement capability of moving-coil geophone without changing the mechanical structure,electronic circuit is chosen to make low-frequency compensation for moving-coil geophone.After theoretically analyzing and deducing the transfer function of moving-coil geophone,an analog compensation circuit is designed based on the principle of the zero-pole compensation method.Experiments show that the scheme can realize effectively low-frequency compensation for moving coil seismometers without increasing the volume.(2)Based on the low-frequency compensated moving coil seismometer,the design scheme of low-frequency digital seismometer was proposed by referring to the function and structure of the cable-free storage seismometer and adding the functions including data acquistion and storage.The microcontrollers(MCU)LPC11U68JBD64 with kernel ARM Cortex M0+ is selected as processor,using delta-sigma analog-to-digital converter ADS1281 which is 31-bit for seismic signal acquisition.The data with FAT32 in file format is stored in TF card and "ping-pong" data cache structure is used to operate the data acquistion.In the process of component selection and circuit structure design,the requirements of parameter indexes were considered.(3)Two kinds of assistant software and two sets of index analysis program are developed after whole function of the instrument is realized.In the development of assistant software,choosing multithreading technology of Lab Windows/CVI and serial communication for the development of host computer control software,and refer CJ-T188 Data Transmission Technical Conditions to design the communication protocol which can ensure the reliability of instrument communication data.The software of seismic waveform data observation is developed by using MATLAB app designer.In the design of the index analysis program,the method of envelope analysis and cross-correlation calculation with time window are applied to research the consistency between tracks.Cross correlation method is used to analyze the noise level.(4)The two key indicators,the working frequency band and sensitivity of the designed instrument,have been tested by the national test base "National Institute of Measurement and Testing Technology".Several other key indicators such as the instrument's noise level,inter-channel consistency,interchannel crosstalk suppression and power consumption,have also been tested with professional testing equipment by the cooperating unit.It can be seen from the test results that all the indexes of the designed low-frequency digital seismograph meet the design requirements and the design purpose has been achieved.