Circuit Design Of LWD Induction Logging

The formation resistivity is an important indicator for well logging interpretation of oil and gas, induction logging instrument can achieve this key measurement. The underground part of traditional induction logging instrument is mainly consist of simulation mechanism,it is susceptible to the high temperature and pressure environment.causing the inaccurate measurement. This paper on the basis of the principle of induction logging, using modern integrated electronic and digital signal processing technology, analyzing and improving the underground part of induction logging tool.Induction logging instrument underground part including two blocks:transmitting block and receiving block. According to transmitting block, using DDS direct digital frequency synthesis technology, design a phase, frequency and amplitude adjustable signal generator based on CPLD. The receiving module realizes the detection of weak signal, including signal conditioning circuit and data acquisition circuit. Signal conditioning circuit mainly realizes low noise amplifier^active filter and differential transformation of received signal. It is consist of front end circuit and band-pass filter circuit. The data acquisition and processing is designed based on DSP. In the DSP uses digital orthogonal detection method and correlation function analysis method complete the weak signal detection. All the chips in the circuit selection have the strict analysis and calculation, meanwhile use EDA simulation softwares to verify design in advance.At last, through experiment and test, the design units implement the reservation function and achieve the expected requirements under the homogeneous and non homogeneous situation. It provides a reliable basis for the development of induction logging instrument.