Research On Key Technologies Of Multi-frequency Electromagnetic Detection Signal Acquisition System

As human society advances, follow the development on the economy and speed limit, the city's infrastructure construction is also more to the ground the following extension, such as communication cables, underground pipelines, subway, etc.. In recent years, due to the destruction of underground pipelines, the social economy caused a great loss. In the aspect of environmental geological problems, leakage of harmful chemical substances, all kinds of production and living buried waste, abnormal change of the geological structure, various engineering injury problems pose a serious security threat. Based on the above situation, the importance of exploration and mastery of the shallow surface structure is becoming more and more important. It also puts forward new requirements for shallow surface exploration.The key technology in multi-frequency electromagnetic signal acquisition system is carried out in the study are as follows,the main work includes three aspects.Weak signal collection circuit design:according to the detected signal is weak in this problem, the analog signal conditioning technology, with the method of cascade amplification, and the design of low noise preamplifier and high performance filter circuits, the signal got better amplification, obtained higher SNR. Using a high resolution analog-to-digital conversion technology, designed 32 bit analog-to-digital converter, improve the effective bits, get higher signal resolution, improve the ability of weak signal acquisition. From the point of reducing noise and improving the sampling precision and resolution, the design of the device is deeply considered from the selection of the amplifier and the filter screen.Research on collection technology of multi-frequency lock-in amplifier:according to the electromagnetic detection of weak electric field measurement of multiple frequency signals, using multi-frequency signal detection technology, select the m sequence of pseudo random signal transmission, to realize the multi-frequency signal at the same time in order to improve the detection efficiency of acquisition. The basic principle of lock-in amplifier is studied,combined with heterodyne lock-in amplifier and digital phase sensitive detector, designed a heterodyne multiple frequency digital lock-in amplifier design, low noise, high precision of frequency synthesizer and frequency mixer, low-pass filter to realize multi-frequency pseudo-random signal digital lock-in amplifier with narrowband comb filter instead of the traditional design, in the end, a digital multi-frequency phase detector is designed to realize multi-frequency pseudo random signal amplitude and phase extraction. Then the amplitude value of the original signal is calculated. A number of frequency lock-in amplifier is achieved, the efficiency of detection is improved.Performance test of data acquisition system:this paper tested the performance of the designed system, including the common mode rejection, effective resolution digits, system error and short-circuit noise.