Due to the corrosions of the ocean water, or other deep sea water motions, the offshore structure is very easy to be damaged. In order to secure the safety of this structure, the frequent inspection of each member of the structure is the most effective way. The procedure of the inspection has to be carried out by the experienced non-destructive evaluation inspector with the deep-sea diving specialty. Consequently, the automation of the inspection is essential for the further development. The most difficulties in this automatic inspection procedure are how to transmit the detecting signals with the least loss to the inspection station on the platform over the water. In order to overcome all interferences during the transmitting process under the ocean, such as temperature effect, electro-magnetic interference(EMI) and radio frequency interference(llFI), the optical signal transmission is the most suitable one. In this research, a method of signal transmission by optical fibers is introduced. First, an electrical circuit system is established for driving a LED, its sparkling frequency is proportional to the voltage of input signal. And the optical signal is transmitted by an optical fiber. At the same time, a received circuit unit at the other end is also set up for converting the optical frequency signal to the corresponding analog voltage signal. Because this transmission process is based on the frequency counting, therefore the interference coming from the deep sea environment(e.g. EMI, RFI, …, etc.) will be reduced tremendously. Finally, the experimental results will demonstrate the signal attenuation difference between copper cable and optical fiber for EMI or long distant transmission.
In the past few decades, the ocean has invaded by the petroleum drilling process and the ocean city development, and the offshore structure has been broadly used for this engineering purpose.
