The Development Of Controlled Source Audio-frequency Magnetotellurics Receiver

Controlled source audio frequency electromagnetic method(CSAMT) using artificial field source power supply, the frequency range of 0.1-10 kHz. In this method, field intensity, frequency and direction are controlled by human. It is a popular method for electromagnetic exploration, which overcomes the shortcomings of weak natural source signal and harsh construction condition. This paper focuses on the development of CSAMT receiver. Including the hardware framework, software design, shell and field test.A standard receiver system includes sensors and a host. Hosts need to realize the signal conditioning, analog to digital conversion, data acquisition, storage, transmission, synchronization and automatic control etc., which is a complete multichannel data acquisition system.So,apower board, 2 ADC boards, a high precision clock board, a FPGA signal processing board and aARM core board are needed to realise all the functions. All those boards are connected through a power bus and a data bus. The power supply board has a standby circuit, which can be controlled bythe core board to change the output voltages. All theoutputsare isolated from each other. It can also measure the internal temperature and input voltage to achieve over temperature protection and low voltage alarm purpose.Each ADC board has three inputs, which are called the Ex,Ey,Ez or Hx,Hy,Hz,respectively corresponding to the e-field and magnetic field.The ADC boards were not only designed for CSAMT,but also suitable for AMT,MT and SIP,we call it multi-function. The ADC boards are controlled by the FPGA, which can switch between different acquisition parameters and select the inputs for different methods. Clock board’s function is to receive GPS signals and achieve high accuracy clock output with OCXO, which can realize synchronization for all instruments. FPGA board is designed to configure ADCs, read data and achieve digital signal processing, like power frequency notch and downsampling etc.. Finally, data are sent to the arm board, which basedon Embedded Linux and FAT32 file system and can realize data storage(SD card) and Ethernet transmission etc..The software is not only based on the embedded Linux, a host computer program was also designed to achieve human-instrument interaction.Instead of a traditional LCD display, simply by a piece of string can realize the instrument’s control and data transmission.Finally, a series of laboratory tests and field tests are made to verify the function and reliability of the instrument. The results show that the hardware design of the instrument meets the requirements, the parameters are reliable, the software functions are diverse, and the operation is simple, which meets the needs of CSAMT exploration and construction.