Downhole Data Transmission System Based On Power Line Carrier

In order to control the process of oil extraction, monitoring and measuring the under-well temperature, press, and flux values is always necessary. A new idea is brought for data acquisition in this thesis. Data transmission through the existent power line in the oil well is available.The complicated environment of power line is the main obstacle for date communication. Characteristics of the low voltage power line medium are first analyzed in this paper, including impedance, attenuation and disturbance. According to our special application, a simplified channel model of the power line under the oil well is brought, and the simulation is done about the channel characteristics. On account of its ascendant capability of anti-interfere and anti-attenuation, spread spectrum communication technique can advance the reliability of the power-line carrier communication. Furthermore, because the data rate of under-well data transmission is low, spread spectrum is more suitable. In the thesis, the simulation about the advantage and the capability of anti-interfere of sine wave of Direct Sequence Spread Spectrum is done. On these bases, an under-well data transmission system which is composed of a single chip computer AT89C51 and a carrier-current chip SC1128 is developed. The system includes master and slave parts. The gathered data which is modulated by the chip SC1128 is send to power line by the slave part. The master part receives the data and demodulated it. Then the information data is transmitted to PC. Data will be graphed on the screen of PC.To improving the communication reliability of system, ensuring the reliable data transmission, enhancing the capability of anti-jamming and decreasing the rate of error, the technology of Forward Error Correction is advanced in the system. The capability of error correction of BCH (31, 16) code is simulated, and the encoding and decoding arithmetic is developed by software. The project of monitoring and measuring network is brought, and the communication protocols are issued in this thesis.This thesis mainly describes the hardware and software of the data transmission system based on power line carrier with the spread spectrum technique. Finally the experimentation shows that the system is feasible.