What has to be considered when PLC devices are synchronised?
Answer:
Only the task of the PLC devices with top priority can be completely synchronized.
The interval of the sync telegram must be the multiple of the interval of the task to be synchronised. Ideally, the intervals are the same.
The event, which is to be synchronous, e. g. the simultaneous start of positioning sequences, is to be controlled by the task with top priority.
Explanation:
Due to the processing of the task depending on their priority the tasks with low priority can be interrupted at different points. Consequently, they are never completely synchronous on different controllers. Only the task with top priority is always equidistant and is not interrupted. Thus, it can be synchronised in the concerned devices. If the Sync interval is no multiple of the task interval, the different controllers can synchronise to the Sync signal, the starting times of the devices' tasks can, however, differ (see sketch).
Further notes:
Detailed information regarding synchronisation of control cycles by CAN-Sync-telegrama area available in Application Report 500.0.1.
