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Transaction groups are edited through the Ignition Designer. When a group is selected, you are presented with the transaction group workspace.
The workspace is broken into several parts:
Each Item in the Transaction Group consists of several properties, but the key properties are the Value and Target Name.
In order for groups to be evaluated, they must first be enabled. This is done by selecting "Enabled" in the group title bar, and then saving the project. The group executing can be stopped by reversing the procedure and selecting "Disabled" before saving. If you want to quickly and temporarily stop the group's evaluation, toggle the "Pause" button. This will prevent execution until the group is unpaused, or until the system is restarted.
Transaction Groups exist in a project, but they execute in the global Gateway space. This means that once your groups are enabled, they will run even without a client open.
Group settings may be modified at any time, regardless of whether or not the group is executing. Modifications will be applied when the project is saved, and the group will be started or stopped as required. Some changes such as modifying items may cause features like live values to appear to be incorrect. It is therefore important to note the modified icon that appears next to the group, and to save often. If you would prefer to stop the group before making edits you can simply pause the group. Execution will begin again after the project is saved.
Generally speaking, groups work on a timer. They are set to run at a certain rate, and at that rate, then check the rest of the settings. If the trigger conditions pass, the group is executed fully. The following section provides a fuller outline of the execution cycle.
All of the groups follow a similar execution cycle. The core evaluation may differ, but the general cycle is the same.
If an error occurs at any stage besides the last stage, execution will break and the failure handshake will be written if configured. The group will attempt execution again after the next update rate period.
If the group errors are due to a bad database connection, they will need to be manually restarted once the database connection is brought back.
Transaction groups are used to store history, log events, synchronize databases tables with PLC, perform calculations, and many more data-centric tasks.
Let's create a basic History Group and start logging some PLC values to your database.