Transaction Group Workspace
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:
- Title bar - Shows the name of the currently selected group, as well as options to set it as Enabled or Disabled, and to Pause, if it's currently executing.
- Item configuration - Shows all of the items configured in the selected group. Many settings can be modified directly through the display, the rest by double-clicking the item or selecting Edit in the context menu.
- Action / Trigger / Options tabs - Defines how and when a group executes. Holds most of the options that apply to the group in general, such as the update rate, and which data connection it uses.
- Status / Events tabs - Provides information about the executing group, including the most recent messages that have been generated.
Each Item (Tag) in the Transaction Group consists of several properties, but the key properties are the Source/Latched Values and Target Name.
Source and Latched Value
The Source Value will be the value of the items source. This can be something like a Tag or a direct OPC Item if writing to the database, but can also be the value pulled from the database if in DB to OPC mode. This value can change in between executions, depending on the source type. When the source is a Tag, it will update as the Tag updates, depending on how the Tag Group for the Tag is set. However, if the source is an OPC Item, it will update only when the group executes, unless the OPC subscription rate is overridden in the group.
The Latched value will be the value that was written at execution. This can be the value that gets written to the database on execution in OPC to DB mode, or it can be the value that gets written to the Tag in DB to OPC mode. The value will only change on execution of the group.
In most cases, the Target Name is a column on the database table the Transaction Group is associated with. However, it is possible to have the Target Name 'Read-only'. When set to 'Read-only' the value of the item will not be tied to any columns in the database, but is still visible from the Transaction Group and can be used as a trigger.
Enabling Group Execution
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 enabled again, or until the system is restarted.
Editing Group Settings
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 notice 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.