一种基于改进CORDIC算法的阵列侧向测井仪信号发生电路

A Signal Generation Circuit for Array Lateral Logging Tool Based on Improved CORDIC Algorithm

阵列侧向测井仪是目前测井工程中探测与分析复杂地质结构的一大利器。为实现5种不同探测深度的“阵列式”测井,仪器自身需要同时产生5种频率高精度正弦信号。本文对经典坐标旋转数字计算机(CORDIC)算法进行了改进与优化,改进后的算法计算量仅约为经典算法的1/3,大幅减小了DDS信号发生电路的输出时延。通过Modelsim软件仿真验证改进算法的可行性后,使用FPGA芯片编程,搭配DA/C与低通滤波电路,设计实现了一种基于DDS技术的阵列侧向测井仪信号发生电路。仪器外刻度模拟实验表明:搭载该信号发生电路的阵列侧向仪器能够在0.6Ω~100 kΩ电阻范围内保持良好的一致性,5种模式下电阻值实测误差均保持在10%以内,对于中低阻值模拟地层的测量精度达到了3%,较上一代阵列侧向仪器性能有明显提高。

Array logging tool is a powerful tool for detecting and analyzing complex geological structures in logging engineering at present.In order to realize the "array" logging with five different detection depths,the logging instrument itself needs to generate five high-precision sinusoidal signals with different frequencies at the same time.In this paper,the classical CORDIC algorithm was improved and optimized.The calculation amount of the improved algorithm is only about one third of that of the classical algorithm,which greatly reduces the output delay of DDS signal generator circuit.After the feasibility of the improved algorithm was verified by Modelsim software simulation,a signal generation circuit for array lateral logging tool based on DDS technology was designed and implemented by using FPGA chip programming,with DA/C and low-pass filter circuit.The external scale simulation test of the instrument shows that the array lateral instrument equipped with the signal generation circuit can keep a good consistency in the resistance range of 0.6 Ω~100 kΩ,whose actual measurement error of the resistance in five modes is all kept within 10%,and the measurement accuracy of the simulated formations with medium-low resistance reaches 3%,which is obviously improved compared with the previous generation array lateral instrument.