The Design And Implementations Of Usb-based Magnetotelluric Signal Acquisition System

With the development of geophysical exploration, according to the difference among the physical properties of rock, such as density, magnetism, electrical, elasticity, radioactivity, using geophysical methods and geophysical equipments, observing the earth's various physical field distributions and changes, more and more attention should be paid to detecting the earth's internal structure and construction, seeking energy, resource and environmental monitoring and so on. Probing magneto telluric is an important geophysical method. Using it to collect the electromagnetic signal which is in the natural time-varying electromagnetic field which is stimulated by using data acquisition instruments, the signal is very weak, its amplitude level is as low asμV, its frequency range is between 10^-510³Hz , its cycle time range is very wide, so it needs higher requirement of geophysical equipment.To adapt the faster development of the equipment requirements, such as smaller size, stability and higher accuracy, this paper is based on analyzing the general data acquisition products'software architecture, hardware architecture and common features, combining with the characteristics of the magneto telluric signal, and the advantages of the USB bus technology, to design and develop a USB-based data collection and transmission system. The system was made up of hardware and software. The hardware mainly to complete the magneto telluric signal acquisition and storage, including the C8051F320 the master controller unit, the input signal conditioning unit, 4-channel high accuracy AD conversion unit, DDS self-test unit, USB interface unit and the SD card storage unit and other hardware of the data acquisition system. For the software, is to devise the firmware of the C8051F320 microcontroller, USB drivers and the PC applications whose platform was the Lab-VIEW, and that would control hardware and collect, transport, handle and display the data.The equipment use the 4-magneto telluric to collect. Two-way electric signals were Ex, Ey and two magnetic signals were Hx, Hy, and microcontroller would send the collected data to the host computer by the USB interface, then, display in real-time, or send data into SD card by the SPI interface; the PC part would control data acquisition and playback data by using the Lab-VIEW applications. The design implement USB2.0 interface, the design and debugging of the software and hardware in the both the host side and device-side. The results have showed that, hardware and software worked properly, every indicator meet the expected demand. Magneto-telluric acquisition utilized data acquisition and control circuit whose axis was the C8051F320 microcontroller, and the host computer software which based on Lab-VIEW, to achieve the multi-channel, high accuracy, low power consumption target.