Study Of Control Technology In High Power Borehole-Ground Electromagnetic Transmitter

Borehole-Ground metal exploration is an effective method of electrical prospecting. Use tunnel of the existing mine and way of placing the electrical source under the ground and receiving the signal on the ground, so can effectively avoid the surface electromagnetic interference and increase the accuracy of exploration.Compared with the traditional electromagnetic transmitter, the separated transmitter of this design use the scheme of remote control, namely, the control module of transmitter is separated from the primary loop, and connect them with a multi-core cable. This approach has many advantages, one of the most obvious is to protect the control module from the electromagnetic interference of the main loop. This article mainly introduces the hardware and software design of control part of the transmitter.The transmitter in this paper is mainly used in CSAMT, and the frequency range is from 10kHz to 0.01 Hz. The traditional transmitters always have the problems of low frequency coverage, low work efficiency in the field environment and poor performance of synchronization in electromagnetic transmitter, the article realizes power waveform synthesis of arbitrary frequency using direct frequency synthesis technology(DDS) and programmable device(CPLD). Add a simple and reliable multi-frequency waveform on the basis of sweep launch using powerful logic operation function of CPLD. And design and implement high-precision synchronization with frequency calibration system for OCXO based on GPS. In a word, the control module is based on ARM and CPLD, the peripheral circuit mainly include DDS, RTC, high precision clock board and wireless module. The software design in the system mainly includes the sweeping transmit of frequency table, the waveform synthesis programming, and the synchronization of the PPS signal with the transmitted waveform. The waveform synthesis programming includes single frequency, multi-frequency and m sequence power waveform.Lastly, the system is tested many times in the sink and field, and mainly tests the power waveform, the synchronization precision and the work of the superior computer. Experiment results show that the waveform’s frequency is accurate and stable, multi-frequency’s energy is evenly distributed, Synchronization error is in the nanosecond level, setting of dead time is reasonable, achieves the required specifications.