| With the rapid increasing human demand on mineral resources, contradictions among limited mineral resources and human growing demand increasingly prominent. The focus of prospecting shifts gradually to looking for concealed and blind ore at concealed areas, in depth or on the periphery of a mine. Semi-aviation transient electromagnetic method is an important progress in electro-prospecting area during recent years. Transient electromagnetic method uses ungrounded loops or grounded electric dipole source to send primary field to underground, during the intermittent of primary field use the loop or electric dipole method to observe secondary vortex field. The vortex only lasts for a very short time, which requires high precision of sampling time. To make the receiving system and launch system achieve precise synchronization, it is necessary to start the measurement at a precision certain moment when emission current is shut off.Based on the nonprofit industry scientific research project of Ministry of Land and Resources "semi-aviation transient electromagnetic exploration technology research based on the UAV", this article mainly studies synchronization technology of sampling singles among ground-launched system, UAV receiving system and ground receiving system of its data acquisition system. This paper studies principle and realization of three synchronization technology including oscillator synchronization technology, wireless synchronization technology, GPS synchronization technology, and experimented via GPS synchronization technology, also the system anti-interference measures are also introduced.Oscillator synchronization technology uses programmable clock output, alarm and timer function of the clock chip PCF8563, setting TI/TP to 1 in which the interrupt signal is pulse. PCF8563 generates a pulse at/INT terminal to the microcontroller per second, and the microcontroller can read the clock in interrupt service to display. This clock is used as the synchronous time scale for emission and receiving system.The realization of the wireless synchronization technology takes advantage of the Manchester code which has rich clock information. When sending data, master will gradually send the data of OCXO and electromagnetic signal to the encoding module, t and the encoding module converts it into Manchester code. Then the code is sent to emission system after smoothing adjustment, power drive and audio transformer isolation. The decoder first sends signal through audio transformer isolation after receiving the transmitted signal from the emission system,, then through the band-pass filter, amplification plastic for square wave signals, after which the signal is sent to decoding module for decoding, and the decoder identifies whether a signal is an effective one by "terminated byte". Demodulated data realizes MCU read by interrupt request.The realization of the GPS synchronization technology is that GPS receiving module receives the time signal from satellite through the antenna, and obtains the required time signal. The signal and UTC international standard time are precisely synchronized. At the same time, calibrate the second pulse of OCXO. In FPGA, measurement modules to calculate the deviation between the clock of synchronization technology and OCXO second pulse are designed. The host computer will store and process data and uses the calculated time difference sequence to estimate statistical variance of random error for the synchronization signal. Do real-time correction to constant temperature crystals output signal and resulting in a high precision clock signal.Due to long-term continuous working in strong electromagnetic environment, the synchronous sampling device is seriously disturbed. If it is not handled correctly in time, the device may work abnormally and cause the failure of the synchronous sampling. Hence, it’s necessary to design anti-interference of synchronous sampling device. This article studies anti-interference measures for synchronous sampling device, anti-interference measures for data acquisition part, and anti-interference measures for external electromagnetic noise, effectively reducing the interference in the synchronous sampling system. |
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