基于开关切换混频的随钻电阻率信号处理系统

Signal Processing System of Resistivity While Drilling Based on Switching Mixing

针对随钻电阻率测井仪器中电路系统工作温度高、电路板安装空间狭小、信号灵敏度低等现状,基于开关切换混频原理,设计一种随钻电阻率信号处理系统。依据原有随钻电阻率测井仪器电路系统基本结构和特点,进行优化和改进:通过FPGA对16号进行8分频实现,生成2 MHz信号;设计开关切换混频电路,实现信号由2 MHz向2 kHz的转换。FPGA的引进,降低了对温度的敏感性,压缩了电路板面积,使得随钻电阻率测井仪器可靠性得到提高,能够更加适应井下狭小空间和高温高压的恶劣环境。测试验证表明,幅度比和相位差的测量相对误差都在1%以内,完全满足随钻电阻率测量精度要求。

In view of the current situation such as high working temperature,narrow circuit board installation space and low signal sensitivity in the circuit system of the logging while drilling(LWD)instrument,a kind of signal processing system of resistivity while drilling is designed based on the principle of switching mixing.According to the basic structure and characteristics of the circuit system in the original resistivity LWD instrument,the optimization and improvement are carried out:the 16 MHz signal is divided into 8 frequencies by FPGA to generate a 2 MHz signal;the switching mixing circuit is designed to realize the signal conversion from 2 MHz to 2 kHz.With the introduction of FPGA,the sensitivity to the temperature is reduced,the area of the circuit board is compressed,the reliability of the resistivity LWD instrument is improved,which can be more suitable for the tough environment of narrow logging space,high temperature and high pressure.The test validations show that the relative errors of amplitude ratio and phase difference are within 1%,which fully meet the measurement accuracy requirements of the resistivity while drilling.