OPTO 22 SNAP PAC Redundancy Option, User Manual

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SNAP PAC Redundancy Option User’s Guide
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4: 4: Creating a Strategy with Controller RedundancyChapter 4
4: Creating a Strategy with
Controller Redundancy
This chapter describes how to set up a PAC Control Pro strategy for controller redundancy.
Redundant controllers are configured identically. This means that they are programmed with the
same strategy, they run in lockstep with each other, and their variables and I/O have the same
values. The Active controller is in charge and informs the Backup controller of its state. This is
achieved by the Active controller telling the Backup controller every time it changes a variable, I/O,
or moves to the next instruction or flowchart block. PAC Control provides extra control for the
strategy programmer to reduce the communication overhead of synchronization; only
persistent/redundant variables and I/O are synchronized, and by using sync blocks, synchronization
is delayed until a sync block is encountered in a transactional chart.
In This Chapter
Glossary of Terms ................................................................................................................................ 31
Creating a Redundant Strategy .................................................................................................... 33
Step 1. Enabling the PAC Control Redundancy Features ........................................ 33
Step 2. Adding a Redundant Control Engine to a PAC Control Strategy ......... 33
Step 3. Configuring Persistent/Redundant Data ........................................................ 39
Step 4. Designing a Transactional Chart ......................................................................... 41
Glossary of Terms
Persistent/Redundant Data
Data generated by persistent/redundant variables that are replicated to an available backup
controller whenever synchronization occurs. See
Chapter 4: Creating a Strategy with Controller
Redundancy .
Redundant Control Engine
A control engine configured for redundant controllers. See “Creating a Control Engine for Controller
Redundancy” on page 24 .