Receiving System Design Of Time-frequency Electromagnetic Measurement

Economic development cannot leave the full use of various resources,but the rapid development of economy will inevitably lead to all kinds of resources consumption,especially in mineral resources and energy resources,etc.Especially,the explorations of mineral resources and other resources are more and more demanding depth,high precision,fast and convenient.Electromagnetic method is the main geophysical prospecting method with a rapid development in recent years.This method observes natural formation of the electromagnetic field and underground induction abnormal electromagnetic fields by the testing instrument using the electromagnetic induction principle to study abnormal electromagnetic field on the basis of the characteristics of time domain and frequency domain,to solve practical engineering problems.Electromagnetic method is not only applied in the field of looking for mineral resources,but also spread to other areas such as hydrogeology,environmental detection.This paper based on the principles of electromagnetic has designed time-frequency electromagnetic measurement receiving system with high precision and high efficiency.This article summarizes the basic principle of electromagnetic method of time domain and frequency domain at first.Based on these principles,receiving system structure of the time-frequency electromagnetic measurement has been designed on the third chapter.The system structure is divided into two parts,the analog signal processing and digital signal processing.And the circuit of electromagnetic measurement system has been designed.Analog signal processing part mainly includes the front-end receiver coil circuit design,the preamplifier circuit design,programmable amplifier circuit design and noise interference suppression circuit design.Analyzed the receiver coil of different numbers of turns and the influence of outside interference.In the design of preamplifier circuit,the signal must be enlarged,because the strength of the received signal is weak to ensure the precision and accuracy.In anti-interference design,analyzed methods for eliminating the noise existing in actual working environment.Each circuit is given in detail the design of circuit structure and the specific device type selection.In digital signal processing part,using the FPGA and microprocessor as the master control chip.Microprocessor mainly use the mainstream of C8051 F series MCU.FPGA is responsible for the entire collection of timing and control.MCU is mainly responsible for the control part of overall system.For the precision and accuracy,at the same time for signal collection,using 24-bit A/D converter ADS1274 as collection chip with high resolution and high speed.The interface circuit and communication circuit with FPGA chip has been designed.In the process of synchronization between transmitter and receiver,using GPS technology as a standard of synchronization.In the exploration process,large quantities of data will be produced.Large capacity of SD card is used to store the data.SD card can interact with the PC for data not only,also can communicate with PC via Bluetooth with corresponding interface circuit.The last part of timefrequency electromagnetic measurement receiving system is a test for the receiving system including indoor testing,acquisition card test and outdoor test.After these tests,the acquisition card of time-frequency electromagnetic measurement receiving system has a good effect after the multi-channel consistency test,crosstalk test and stability test.The acquisition card work normally,and it can meet the requirements of design.