Design And Implementation Of A Multi-channel Transient Electro-magnetic Exploration System

The device used for time domain transient electromagnetic method consists of a launch system and a receiving system.The theory is to pass a step current I through the transmission coil to inspire a magnetic field. During the process of the magnetic filed spread to the deep, it will inspire induced current in the underground target.The induced current varias over time will generate a new magnetic field around it, witch is called secondary field.As secondary field is generated by the induced current in the target, so it carries important information about the target.The voltage induced by the receive coil is converted to digital format by ADC and stored and uploaded to host computer.By analyzing and inversing, we can used the data for explaing the relevant physical parameters of the target body. As electronic technology and equipment advances in science, mathematics model and inversion depth theoretical study and improve, making detection and interpretation accuracy levels are rising. The application of transient electromagnetic method has been expanded to cover several areas: mineral exploration and geological, hydrological and geological surveys, environmental monitoring and survey, detection of tectonics, such as archaeological excavation. TEM in shallow exploration applications have been increasing, such as finding water, municipal construction, pollution and salinization of investigation or detection of shallow structures such as oil and gas have achieved the best results.In recent years, especially transient electromagnetic exploration in the shallow one aspect of attention is the water content of the advanced detection of Roadway. Mine Water is a common disaster in coal production, a serious threat to the safety of coal production, sometimes causing huge economic losses and casualties. Therefore, the identification of complex geological structure is a coal mine production safety is one important problem to be solved. And the third component of Transient Electromagnetic get more information on underground structures, underground structures contribute to a comprehensive understanding of the situation. However, the existing detection systems are mostly transient electromagnetic single-component can only be collected.Taking into account the needs of practical application, this paper targets specifically designed for shallow high-speed high-resolution body detection of multicomponent transient electromagnetic sounding system. Underground systems take into account the main use of small coils detect overlapping loop, the transceiver device is designed machine.In the instrument development process, summarize and analyze the existing electromagnetic detection system in terms of design features and shortcomings. Through the use of new methods, new technologies to improve it, designed to DSP and CPLD as its core control device to USB bus as the communications interface to intelligent power module for the launch system to multi-core and parallel 24-bit high speed ADC and FIFO for the acquisition system transient electromagnetic core detection system. Since the system is transmitting and receiving one machine, a portable, reliable, and low energy consumption.TEM instrument has been the launch system and the receiver separately, by wire, radio, high-precision clock synchronization or GPS. This method is suitable for large-field line or the central loop back detection, but in municipal roadway construction or advanced detection, due to limited space, and the transceiver is not very far away, this method will no longer apply. Therefore, this paper described the system design using one machine, can be observed in the narrow space layout and operation of the system.The system use TMS320LF2407A as the central controller, and use CPLD to address the aid of decoding, control logic synthesis and timing. Launch systems to intelligent power modules as the core, the receiving system Zeyi high-speed 24-bit Sigma-Delta based ADC, FIFO buffer supplemented. The system use USB100 module, by using the USB bus and the transceiver protocol to communicate with the host computer. The system's maximum sampling rate is 625Ksps, and the dynamic range of 144dB.In this system, low power DSP chip as the core, effectively reducing the system operating noise. DSP chips have the same time as the flexibility and processing power, the control system provides an ideal solution. The system selected TMS320LF2407A processor is a control and data processing for high-speed low-power DSP chip. In order to facilitate and host computer for high-speed data transmission, using USB100 USB bus transfer module.Electromagnetic launch systems require high performance instrument with high reliability, this system uses Mitsubishi Intelligent Power Modules PM20CNJ060. As for the critical and post-processing system to accept part, because of its large dynamic range of features, we use high-speed 24-bit Sigma-Delta ADC, and the use of CPLD and FIFO for automatic acquisition and storage.The transient electromagnetic detection system achieved the goal of constructing a high-speed high-resolution multi-channel acquisition system. Discussed and resolved facing multi-channel simultaneous sampling acquisition, automatic storage, channel calibration and other issues. As the system has the ability to multi-channel acquisition, the instrument can work in a variety of operating modes, with a high degree of flexibility. First, it can be collected with the same accuracy while the second field emission current waveforms and the transient waveform; second, it can be X, Y, Z simultaneous acquisition of three components. Optional mode makes it convinent for later processing and interpretation.Finally, this paper discusses the calibration of the acquisition system, and gives the test results of launch system and the acquisition system test and gives suggestions of follow-up work.