Research On Weak Signal Measure Algorithm For Nuclear Magnetic Resonance Well-logging

Nuclear Magnetic Resonance (NMR) nV voltage signal measure technology is one of the key techniques in the NMR weak signal detecting system, while the algorithms for the nV voltage signal detecting is an important component of the technology. This thesis goes deeply into the principles and practical implementation of weak signal detecting algorithms, which is significant in measuring the NMR weak signal, both theoretically and practically.Through precise calculations, the principles of some weak signal measuring methods are deduced, including multi-layer autocorrelation algorithm, digital phase sensitive detection (DPSD) algorithm and cross power spectrum algorithm, etc. Besides, this thesis briefly introduces the C programming language based LabWindows/CVI virtual instrumentation program developing platform, and the program designing for weak signal measuring on the platform. In reference to measure precision and time complexity, a comparison is made among each algorithm of their performances in practical application according to multiple experiments results.Furthermore, the thesis analyzes the causes of errors in each algorithm. A conclusion is drawn that DPSD algorithm best satisfies the requirement of NMR weak signal detection. In the end, feasibility analyses are given according to the application of cross spectrum algorithm. In addition, an improved DPSD algorithm is referred with automatically adjusting frequency of reference signal in order to achieve higher measure precision.