User manual

Hot Standby
310
33002479 06 07/2008
Quantum Hot Standby for Unity Pro
The Hot Standby
Solution
In the hot standby solution, two identically configured PLC systems are set up to
control the same application. One PLC, the primary, runs the application and
updates the other secondary (standby) PLC. The standby maintains awareness of
the application status but does not perform any control functions. In the event of a
failure in the primary PLC, the standby PLC takes over the primary PLC responsi-
bilities. When the PLC that has failed becomes operational again, it comes back up
in the hot standby system as the new secondary PLC.
The NOEs coordinate the swapping of IP addresses. After closing both the client
and the server connections, each NOE sends a swap UDP message to its peer
NOE. The sending NOE then waits a specified timeout (500 ms) for the peer swap
of UDP messages. Either after receiving the messages or after a timeout, the NOE
changes its IP address.
COMMUNICATION FAILURE
Whenever possible, use of a switch (not a hub) to connect the NOE modules to
each other or to the network.
Schneider Electric offers switches. Contact a local sales office for more
information.
Failure to follow these instructions can result in injury or equipment damage.
UNINTENDED EQUIPMENT OPERATION
Design your application so that unmonitored modules support communication only
to noncritical parts of the application.
Failure to follow these instructions can result in death, serious injury, or
equipment damage.
Note: NOEs must communicate with each other in order to swap IP addresses.
Schneider Electric recommends that you connect the primary and secondary
NOEs to the same switch because:
z Communication failures between the NOEs increases the time to swap.
z Connecting 2 NOEs to the same switch minimizes the probability of a
communication failure.
CAUTION
WARNING