Saia-Burgess Controls AG
User Manual Standby System
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Document 27-645
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Edition E
NG 02
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2017-04-26
PCD3.M6880 Standby Controller
Standby System Overview
1-9
1
1.5.3
Switchover Criteria
Each of the Standby PCDs (CPU1) sends a „Keep Alive“ telegram to its partner for
supervision.
The STANDBY PCD switches to ACTIVE when:
■
No Keep Alive telegram has been received within the „Keep alive timeout“
period defined with the Redundant CPU‘s Device Configurator. The “Keep Alive
Timeout” can be adjusted between 100…500 ms. By this the max. switchover
latency is <100…500 ms.
■
The ACTIVE PCD‘s state is not RUN or STOP (stops sending Keep Alive).
■
A manual switchover command is executed. This is only possible if the Primary
device does not have priority, the „Primary device has priority“ option must be
„No“.
Data Synchronization and Supervision (Keep Alive)
Data Synchronisation and Program Cycle:
The used PCD medias (R, F, T/C, DB/TX) in the redundant CPU1 are cyclically
synchronized between the active and the standby PCD. The synchronization time
for all PCD media is normally less than 200 ms. This time is reduced accordingly if
only a part of the PCD media is used. The total program cycle time is calculated as
follows:
Total cycle time = program execution time + data synchronization time
The max. value for a large application can be calculated as follows: 100 ms +
200 ms = 300 ms max.
For smaller applications where less PCD media are used the cycle time is reduced
correspondingly.
