| 摘要 |
PCT No. PCT/GB93/01272 Sec. 371 Date Dec. 13, 1994 Sec. 102(e) Date Dec. 13, 1994 PCT Filed Jun. 15, 1993 PCT Pub. No. WO93/26115 PCT Pub. Date Dec. 23, 1993A sub-sea oil pipeline installation comprising a production platform (10) and sub-sea facilities (15) at a plurality of well-heads (16), has a data transmission system by which data is transmitted in either direction between the master platform (10) and the sub-sea facilities (15) via communication channels formed by the electrically conducting material of the pipelines (12, 14). The data is transmitted in the form of a VLF or ELF electro-magnetic signal which comprises changes of voltage level oscillating about the DC voltage level of the pipe (12, 14) so that the mean level of the signal is the DC voltage level of the pipe (12, 14).
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