Operator Manual
Issue 1
TIL – Eng – Spec – 080
Page 33 of 70
SeaHub
4.6.4. ArcNet Line Termination
The ArcNet communication link normally requires termination resistors to be installed at each end of the
umbilical cable. These resistors are fitted between each line of the twisted pair.
For twisted pair cables that are below 100 metres in length, it is only necessary to install one termination
resistor of value between 47
Ω
to 100
Ω
(ohm) (68
Ω
nominally).
For twisted pair cables that are greater than 100 metres in length, two termination resistors should be
installed, one at either end of the cable. At the surface SeaHub module, a
270
Ω
resistor should be fitted.
At the subsea end of the cable, a
39
Ω
resistor should be fitted – if there is more than one Sensor
connected then this resistor should be fitted at the junction / splice point of the cable.
100 - 2500 metre
twisted pair cable
8
15
SeaHub
6w Underwater
Connector
1
2
270 ohm
Resistor
39 ohm
Resistor
NOTE
When shipped from the factory, a 270
Ω
resistor is internally fitted within the SeaHub module
across the ArcNet signal pair. However, internal “jumper-links” provide a means that allow
either 68
Ω
or 270
Ω
termination to be selected, depending on system configuration – section
7.7 provides details of how to change the termination jumpers within the module.
A
yellow
waterblock Adapter (Part No. 02648) is provided with the
system which has a 39 ohm termination resistor installed internally.
This can optionally be fitted to any subsea Sensor to provide the
ArcNet termination at the subsea end of the cabling.
The Yellow terminated waterblock should be installed directly onto the
‘Main’ connector port
(as indicated right)
of one of the subsea Sensor
heads attached to the ArcNet network.
CAUTION
!
•
Only
one yellow 39
Ω
terminated waterblock to be used per system.
•
Check that there are no other termination resistors present, other than the 270
Ω
at
the surface, prior to installation.
4.6.5. Subsea Sensor Electrical Installation
If powering Sonar head(s) down a long lead or umbilical, the maximum recommended loop resistance of
the power line must not exceed 10
Ω
for one head, 5
Ω
for two heads, and 3
Ω
for three heads. Refer to the
manual of the specific Sonar being used to determine the minimum acceptable supply voltage.
4.6.6. Ground Fault Monitoring Equipment
Within the SeaHub module, there is a small capacitive connection to the equipment chassis which should
not noticeably affect any impressed current ground fault indicator (GFI) equipment.
