Marine Expendable Conductivity Temperature And Depth Measurement System

Marine Expendable Conductivity Tempurature and Depth (XCTD) measurement system is a kind of temperature salinity and depth measurement system that is researched by foreign countrier firstly and is developed rapidly. It's meaningful to the field of military affairs and marine science research, so it has been attach to our country and projected in the National 863 project.Nowdays, the research about XCTD has just began in our country. The results of this project are of great positive significance to XCTD research in our country.This paper introduces the developing situation of domestic and foreign XCTD, includeing system composition and working principle. After the transmission channel is tested, through the test data, and analyses the transmission properties of channel is got. By the characteristic curve , with the increase of the signal frequency signal amplitude will decreases quickly above 150Hz. Tis is a typical band-limited, nonlinear and variable channel. Digital signal spectrum is very rich, so direct transmission in the channel is not possible. According to the characteristics of the channel, it's determined to use baseband transmission technology to realize the wire data transmission. After analyzing the features of the base band transmission system and its feasibility, the whole system is divided into several modules for the design and debug separately. At last, each module cascade joint debugging. The entire system hardware circuit mainly divided into four parts including digital transmitting circuit, analog transmitting circuit, analog receiving circuit,and digital receiving circuit. Digital transmitting part is mainly some frequence dividing circuit, which are composed of some small scale integrated circuit. Analog transmitting part is a base-band shaping filter. Analog receiving part includes amplifying circuit, filter and pulse restoration circuit. Digital receiving circuit is recognizaed with FPGA that completes a synchronous extraction and data recovery. Through the software simulation and practical circuit experiment, the communication system is validated doubly.Compared with original frequency transmission system, the baseband transmission rate is high and circuit area is small.In laboratory environment, the system can meet data transmission rate of the front-end data collection and achieve the required Ber that is less than or equal to 10-5. Finaly the results of this topic are summarized. Some suggestions and ideas are put forward about the improvement of the future XCTD transmission technology.