Design Of Data Acquisition Module For LWD Density Logging Tool

The LWD density logging tool is one of the most important instruments in the field of nuclear logging,and it is used to identify the lithologic information and calculate the effective porosity by the reaction of gamma rays with strata materials.In the process of detecting,the ultimate purpose of the LWD density logging tool is to obtain the energy amplitude spectrum,which is the original data of the detection.All of the analysis and calculation of formation data is around the energy amplitude spectrum,and the acquisition of the energy amplitude spectrum is accomplished by the data acquisition module of LWD density logging tool.The data acquisition module is a key module of the LWD density logging tool,which is used to convert the analog electronic signal provided by detection system into energy amplitude spectrum.The tool dicussed in this thesis adopt the compensated density logging technology and azimuth logging technology.There are two sources detector for long source and short source to detect formation,and this logging tool divide the well into 16 sectors.The data acquisition module needs to obtain an energy amplitude spectrum for every source and sector after processing the data collected from two sourses and the azimuth information.During the logging detection,the LWD density logging tool is in a high temperature and high pressure state and it is necessary to ensure the stability of signal gain coefficient,so this module need to regulate the voltage of the detector according the position of the peak of the energy spectrum to stable gain coefficient.The data acquisition module obtains a large amount of logging data in a single logging,which need to be transmited to a dedicated circuit to store and calculate.According to the principle and repuirement of LWD density logging tool,this module chooses FPGA to control ADC,obtain azimuth information,processe data and chooses MCU to regulate the voltage of the detector,to transmit energy spectrum data,to communication with other circuit.In the first part of the thesis,requirements of the data acquisition module are analyzed according to the structure and principle of the LWD density logging tool.In second part,design scheme of data acquisition module is put forward based on the requirement analysis.In the next part,the thesis introduces the specific design process of the data acquisition module in detail.Finally,after the completion of the whole design,experiment is carried out to test and verify the data acquisition module design.