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0721-SOM-00001-01
© Tritech International Ltd.
Appendix.
A
Appendix 1. ARCNET Termination
Depending on the cable length the ARCNET communication link requires a termination resistor to be installed
at each end of the umbilical cable. Normally this is supplied fitted within the ARCNET cable DA-15 or within the
SCU/SeaHub at the surface and is left for the user to fit at the sub-sea end in a convenient junction box or by
use of a special waterblock.
The purpose of these terminations is to attenuate any electrical interference or “reflections” which may occur
due to an impedance mis-match and the overall aim is to improve signal quality and negate any effects which
might otherwise be felt by other sources of impedance such as from the cable itself.
The diagram below shows best practice to use when installing termination resistors on an ARCNET network of
Tritech International Ltd sonar products.
Note
A special yellow waterblock is available from Tritech International Ltd which
contains an in-line impedance of 39Ω which will enable quick and easy
installation of the subsea termination resistor.
Waterblock Connectors
1
ARCNET A
2
ARCNET B
3
+V DC
4
-V DC
5
RS232 GND
6
Earth/Screen
Cable length
Termination
Baud rate setting
Less than 100m
Single 39Ω subsea resistor
Normal baud rate
100-1200m
270Ω at surface and 39Ω subsea
Normal baud rate
1200-2500m
270Ω at surface and 39Ω subsea
Half baud rate
Note
If there are more than one sensors connected then the sub-sea resistor should
be fitted at the junction box or splice of the cable.
1
2
3
4
5
6
Sur
face Unit
270
