CHAPTER 4: CREATING A STRATEGY WITH CONTROLLER REDUNDANCY
SNAP PAC Redundancy Option User’s Guide
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What Causes Synchronization to Occur
A synchronize operation is performed whenever a sync block is encountered in a transactional chart.
A sync operation is also performed for the following reasons:
•
Changes occur in
non-transactional
charts (without sync blocks) to persistent/redundant
variables and I/O.
NOTE: Changing redundant variables and I/O in non-transactional charts can cause your system to
slow down significantly because without sync block, the controllers are synchronized each time a
persistent/redundant variable changes. Therefore, in charts with persistent/redundant variables,
whenever possible use sync blocks to control when the controllers are synchronized.
•
An operator changes a value for a persistent/redundant variable in PAC Control Debug mode or
in PAC Display Runtime. Only the changed persistent/redundant variable is synchronized. In
Runtime, if an operator changes a tag that is linked to a persistent/redundant variable, the
changed variable is synchronized immediately.
Adding a Sync Block
A sync block is added to a chart in the same way that other PAC Control blocks are added (an action
or condition block, for example). For more information on adding a block and using it in a chart’s
logic, see form 1700, the
PAC Control User’s Guide
.
1.
Make sure that redundancy is enabled for the strategy. See
“Step 1. Enabling the PAC Control
2.
With the chart open and the strategy in Configure or Online mode, click the Sync block tool.
Sync block tool
3.
Move the mouse into the window, and notice an outline representing the block.
