
350 Cable Survey System
DPN 402197 © TSS (International) Ltd Page 12 of 18
vey control room using the ROV multiplexer and an existing data link to the survey
control room.
The Systems default parameters for communication between the SDC and the SEP
are 9600 baud with 8 data bits, 2 stop bits and no parity.
These communication settings are valid even when you use 2-wire or 4-wire current-
loop communications. This is because the SDC converts between current-loop and
RS232 communications through a special converter card. All communication between
the SDC and the sub-sea installation passes through the relevant SDC serial port.
Communication lines between the SDC and the sub-sea components are opto-iso-
lated at both ends.
There are two further methods that you may use to establish successful communica-
tion between the SDC and the sub-sea components of the 350 System:
❐ 2-wire 20mA digital current-loop
If the umbilical cable is of good quality, experience has shown that you may use this
communication method successfully through transmission distances up to 1000
metres.
2-wire 20mA digital current-loop is carried on a twisted pair within the ROV umbilical.
To avoid possible communication conflicts, the SDC acts as the ‘Master’ and the SEP
acts as the ‘Slave’ in this link.
To ensure reliable communications through the umbilical, select a twisted pair that
has the following characteristics:
❐ 4-wire 20mA digital current-loop
You should select this method when the umbilical link to the ROV is longer than
1000 metres, or where you cannot establish reliable communication using a 2-
wire current-loop.
You will need to reconfigure the SDC and the SEP to use this communication
method. Refer to sub-section 4.2.2.1 for instructions to do this.
After you have made the necessary changes in the SEP and the SDC, perform a
simple communication check.
Table 4–3: Ideal twisted pair characteristics for successful communication
Twisted pair characteristic Ideal value
Overall resistance Less than 200Ω
Core size
0.5 to 1.0mm
2
Inter-conductor capacitance Less than 100pF per metre
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