| Nuclear Magnetic Resonance (NMR) logging is one of the most advanced logging methord in this century. Compared to traditional logging methord, NMR logging has many advantages such as high measurement accuracy, little formation influence, mass information. NMR logging apparatus consists of the DSP system, antenna snode, exciter, AUX measurement and so on. And the the DSP system is the core of whole logging tool, it provides the control signal, generates exciting pulse, captures and processes the signal and supplies many other functions.Based on the introduction of the principle of NMR logging, considering the technical problems, this paper did deep research and design of activation used in logging work. The DSP system was consisted by Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA) and many other components to implement the whole device control timming, CPMG pulse sequence, and signal's acquisition and processing. Especially, in this system, the Direct Digital Synthesis (DDS) technology was adopted to control the frequency and phase precisely of the pulse; a high speed data acquisition circuit is designed to capture the paroxysmal signal; a improved Digital Phase Senstive Detect (DPSD) arithmetic is introduced to reduce the calculation greatly and make the real-time logging possible. At the same time, it had been paid much attention to the high temperature performation in the circuit design and chip selection to fit the downhole envirament. More than these, a CAN interface circuit and communication protocol were also designed to accomplish the communication of the logging tools and the telegram systerm.It was the first to do formal research on NMR logging instrument in our country. And experiments proved that the DSP system could work with the other parts of the NMR logging device efficiently and stably. It has reached the all kinds of function requriemnts of the multi-frequency NMR logging tools.
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