2 – Installation
DPN 060221 Issue 1.3
© Teledyne Limited
2- 5
2.3.3 Communication link to Subsea Electronics Pod (SEP)
Use the SDC port – ‘COMMS FROM SEP’
The standard communication link between the SDC and the subsea installation uses RS232. This is a
3-wire link suitable only for communication over distances up to 15 metres. You may use this method to
transmit data to the survey control room using the ROV multiplexer and an existing data link to the
survey control room.
There are two further methods that you may use to establish successful communication between the
SDC and the subsea installation.
NOTE
Not all Teledyne TSS detection products support current-loop communication.
Check the user manual for the system to confirm. If you intend to use current-loop
communication you will need to reconfigure the SDC and the SEP to use this com-
munication method. See section 2.3.7 for instructions.
❐
2-wire 20mA digital current-loop
If the umbilical cable is of good quality, experience has shown that you may use this communica-
tion 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 pos-
sible 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 follow-
ing 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.
After you have made the necessary changes in the SEP and the SDC, perform a simple communi-
cation check.
The communication parameters used between the SDC and the SEP are 9600 baud with 8 data bits, 2
stop bits and no parity. These cannot be changed by the user.
Table 2-1: Ideal twisted pair characteristics for successful communication
Twisted pair characteristic
Ideal value
Overall resistance
Less than 200
Core size
0.5 to 1.0mm
2
Inter-conductor capacitance
Less than 100pF per metre