Installation Manual

22 Issue 1 AIS Installation Manual
6.4 Connection terminals
The AIS Transponder has detachable terminal blocks for connection of cables. Dedicated
connections are provided for power sources, sensors, the Display and other interfaces.
Refer to the wiring diagram, attached as an appendix, for details of connections to the terminal
blocks.
6.4.1 Fuse values
The main system fuse (3.15 Amp) is located beside the connectors on the transponder chassis.
Fuse description Fuse value Part No.
Main system fuse 3.15 Amp 99-084
6.4.2 Signal line termination
RS422 signal lines may need termination by resistors, depending on the length of connecting
cable and the rate of data transmission. Suitable resistors are incorporated in the transponder
listeners and can be switched in by wire links in the corresponding screw terminal blocks – see
subsequent tables and section 6.4.4 for details. The talkers in the transponder have inbuilt
termination resistors.
Whether termination at the transponder is required depends on many factors, including how the
other units are connected and whether any of these other units provides termination for the
signal line. The following sketch shows the principle:
Note: For clarity, the sketch shows the devices connected to the twisted pair by spurs; in practice, the twisted pair is
looped through each device in turn.
There is only one talker per twisted pair; there can be several listeners. The intention is that
terminations must be provided by the devices at the ends of the line, regardless of whether they
are listeners or the talker, and that no other device should provide a termination.
A terminal is provided for the common connection at each port on the transponder; note that this
is NOT a ground connection.
It is good practice to use screened cables in all ship cable installations. Take care to connect
the cable screen to ship’s ground at one end only of the cable, as connecting at both ends may
cause ground loops and interference to the signals. The correct method of connecting the cable
screen to ground is at the talker only, as shown in the diagram above.
ListenerListener
Talker
Termination resistor
at end of line
Screen connected to ground
at talker ONLY
Twisted pair, with common and screen
Common
Listener
Termination resistor
at end of line
Listener