Westermo LD-64 AC Manuel D'installation page 14

Description of redundancy
LD-64 is connected through two parallel fibre optical rings, ring 1 and ring 2. The ring
topology introduces the possibility for the units to handle a fault on a fibre or a fibre pair
and still maintain communication. The units will automatically change the communication
path when a fault is detected. This change can take up to 4ms and all data sent during
this time needs to be resent since the modems do not have any possibility to databuffer.
One modem in the ring needs to be configured as master through switches inside the
unit. The master controls the data and prevents data to be resent through the ring. The
master is also used for monitoring of the fibre rings since all faults detected in the rings
will be sent to the master. This gives possibility to monitor the complete system through
the master unit. The other modems in the ring needs to be configured as slaves and will
be transparent during normal communication.
LD-64 is equipped with alarm signals which is used for indication of fibre
interruptions. Each unit is equipped with two alarm ports, one for each fibre channel.
These ports are marked as CE1 and CE2 on the unit. A fault will close the circuit
between indications "C" and "E" on respective port. The alarm outputs can for example
be used for connection of an external relay. See connection and examples on page 19–20.
There is also a led indication for fibre interupption. This makes it easy to locate an
interupption.
An interruption will be detected by the closest unit which will indicate a receiver alarm
and also send the error further to the master unit which will indicate a corresponding
fault for the ring.
For correct function the fibre optic rings needs to be connected correct between
each modem
Ring 1: Tx1 – Rx2 – Tx1 – Rx2 etc.
Ring 2: Tx2 – Rx1 – Tx2 – Rx1 etc.
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