Research Of Coding Method In Logging Cable Transmission System

Well logging as an applied technology of geophysics, has a history of more than half a century. Today, with the application of computer technology and digital technology, well logging has become an indispensably important production link in the stage of petroleum survey and geological prospecting.There will produce lots of well logging data in the process of logging, such as temperature, downhole pressure, acoustic curve and natural gamma, lateral depth,self-potential parameters,which is needed to transmit to ground unit in a effective way timely, and then through the analysis of the data, we can give a comprehensive evaluation to the layer timely and effectively, perfecting the logging process correctly.Well logging data transmission system is through appropriate communication mode, which the ground unit sends commands to downhole unit, then the downhole unit control the instrment to collect data, which is transmitted to the ground unit.The performance of the well logging transmission system is a key factor determining the quality of logging efficiency and logging. Researching and designing high speed, real time well logging transmission system is one of the most important direction of well logging technology in recent years.This thesis developed a new high-speed data transmission system applied in geological logging system. In this system4core cable is used to transmit data, ground unit and downhole unit adopts the full-duplex to communicate, the time-division multiplexing technology is used to eliminate the influence of downlink signal to the uplink signal, namely, there will be only one type of signal transmitted at the same time, it is equivalent to half duplex mode for data communication. Downlink and uplink data using pulse interval coding, the data coding is a high density of data coding, data encoding and decoding by single-chip microcomputer software program.The first chapter in the thesis introduces the source, background and research significance of the topic, and the development condition and gap of the domestic and foreign.The second chapter gives a simple introduction to the concepts in data transmission system, such as transmission medium, the performance index of the communication system, the frequency properties of the communication channel, the working method of the telecommunication line and the transmission mode of signal,then analyses the transmission properties of4core logging cable,and several encoding methods applied in well logging cable transmission system, finally introduces the concrete method realizing the high speed transmission system.The third chapter introduces the design of the hardware circuit of the system, including the ground unit circuit and underground unit circuit.The design of ground unit hardware circuit is divided into:PC interface circuit, downlink signal coding circuit, downlink signal driving circuit, uplink signal decoding circuit and uplink signal receiving circuit. The design of downhole circuit is divided into:uplink signal coding circuit, uplink signal driving circuit, downlink signal decoding circuit, downlink signal receiving circuit and downhole instrument interface circuit.The fourth chapter introduces the design of the software program of the system. it can be divided into the ground unit and underground unit. The program design of the ground unit consists of serial port interrupt program, timer interrupt coding program and pulse interrupt capture program.The program design of the downhole unit is made up of pulse capture decoding program, downhole instrument interface program and INTO plus INT1interrupt coding program.The fifth chapter are the data communication tests and result analysis between ground unit and downhole unit.Finally after test, data transmitted in the transmission system, is highly immune to the noises, reliable,having a low rate of bit error and the transmission rate can reach115kbit/s.it can completely meet the current basic data transmission rate of100kbit/s in the computerized logging unit.In addition there is room for further research of the coding method in the tramsmission system, if reducing the pulse width of "0" and "1",more data can be transmitted in the transmission channel which the bandpass is fixed.