The Design And Implement Of The DSPystem Of Two-dimensional NMR Logging Instrument

Two-dimensional nuclear magnetic resonance (2D NMR) logging is an advanced technique in formation evaluation without loss the merits of one-dimensional NMR logging. 2D NMR logging will perform superior to 1D NMR logging in accuracy because it gets more information than T2 distribution. And the performance of the 2D NMR logging instrument depends on the design of the main control system for it is the core part of the whole too.The hardware and software design of the main control system is discussed in detail in this paper based on the analysis of the 2D NMR logging principle and the main board's function in the apparatus. The system is implemented mainly by Digital Signal Processor (DSP) and Field Programmable Gate Array (FPGA) and could be divided into 4 parts: CAN communication, RF signal generator, data capture and sequence control. The CAN communication module translates data between the main board and the computer. A Direct Digital Synthesis (DDS) chip is adopted in the RF signal generator module to create two orthogonal sine signals whose phases are programmable. Signal capture module converts the signal form analog to digital form. And the sequence control module generates signals to control the whole device. The software is implemented by FPGA and DSP. Nearly all control signals are generated by FPGA and the signal process algorithm-Digital Phase Signal Detection (DPSD) is programmed in DSP. Moreover, the communication protocol is made for the message could be transmitted fast, reliable, correctly.Finally, through the logging, frequency sweep and calibration experiments, the performances of the main control system have been proven to satisfy the requirement of the NMR logging. And the main board designed in this paper been successfully applied in the logging experiment of the standard oil well.