Research And Design Of Nuclear Magnetic Resonance Logging Control System

NMR logging, with its advantage in accuracy and capacity of information compared with the traditional logging method, is proved to be an advanced logging technology at present. As the core of the entire apparatus, the design of system control module is crucial to the quality and performance of the apparatus.By introducing the theory of nuclear magnetic resonance, this thesis discussed how NMR works in logging, and then furthered the discussion into detailed analyses on the functions of the NMR logging system control module. On such basis, a new kind of NMR logging system control module, which is based on DSP digital technology by combining the previous research achievements and the newly-emerged electronic technology and signal processing algorithms, is introduced. On a hardware processing platform combined by DSP and FPGA, this system control module functions systematically as timing control circuit module, signal collecting and processing module, and logging pulse signal producing module.In hardware design, three ways of producing NMR logging pulse were discussed in this thesis. A hardware plan, in which the direct digital synthesis technology is applied to produce RF pulse, is brought up through the compare. Besides, regarding NMR logging's feature of frequent but intermittent data collection, the author made a special design, by applying two pieces of first-in-first-out queue chips (FIFO) to buffer A/D data conversion, which improves the system's ability to collect unexpected data. What's more, by comparing three high-temperature circuit plans, the author comes up with a PCB high-temperature circuit plan under limited conditions. In software design, explicitly explaining the logging control flow of the apparatus in details, the author offered a design for the sequence control software was offered, and discussed about two methods of digit processing to improve the echo signal-to-noise ratio, which are the multiple correlation and the digital phase-sensitive detection.finally, CAN-Bus is applied for the communication between the control system and the equipment outside the well. Thus, a data exchanging plan based on dual-port RAM, including the hardware and software flow designs, is offered as a solution, and the transmit-speed of CAN-bus was reached to 1Mb/s proved by experiment.