The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community
Issue link: http://sea-technology.epubxp.com/i/679071
www.sea-technology.com May 2016 / st 25 A n inductively coupled data transmission system of- fers real-time, remote monitoring of underwater en- vironments. We designed such a system based on signal modulation and processing technology, combined with low power needs and high-reliability data acquisition, comprising a data acquisition controller, node communi- cator, signal coupler and plastic-covered cable. In the sig- nal circuit, the data acquisition controller communicates with each node communicator on the cable according to the communication protocol to acquire the data collected by sensors in real time. The data monitoring and transmission system applies to marine and freshwater environments, such as lakes and glaciers. It can be equipped with measuring instruments, e.g., for temperature, salinity, depth, dissolved oxygen and fow velocity, with data transmitted by inductive cou- pling in the water, then by means of wireless or satellite communications to the end- user. Design Signal matching design is necessary to meet the needs in different water environ- ments, which cause interfer- ence of the signal transmis- sion. For instance, in a 15-Ω, 500-m plastic-covered cable, the signal attenuation in fresh- water is more than 370 times than that in seawater. For the hardware, a two- stage, wide-range tunable amplifer circuit was designed to ensure that the signal is al- ways in a linear amplifcation area of the circuit. We also designed three types of flter circuits to flter out the noise during transmission and the noise caused by the circuit itself. A band-pass flter elimi- nates high- and low-frequen- cy noise produced in the cou- pling transmission process. A capacitor flter flters out the DC component of the trans- mission signal. A low-pass flter is used in the demodula- tion, fltering out the high-frequency component caused by a chip. The design also includes prevention of small signal transmissions being buried in ground noise. By using a software flter and the Modbus protocol packet for data transmission, including the header, ad- dress code, command index, content and CRC-16 check, the data acquisition controller and node communicator respectively identify and check data packets to reduce the transmission error rate. To allow for the installation of third-party underwater instruments, the system has a series of standard RS232/485 and other types of interfaces in hardware. The system uses a fxed developing packet protocol framework; users only need to complete a simple instrument setting in the ter- minal without changing the underlying communication Inductively Coupled Underwater Data Transmission System Real-Time Monitoring for Marine and Freshwater Environments By Zhang Xiaowei • Deng Yun • Jiang Fei A diagram of the inductively coupled data monitoring and transmission system.