Bi-directional Group
A bidirectional transaction is any transaction that synchronizes data between sources. It is not a transaction that inserts values into a database like a historical group. Bidirectional transactions are useful in a number of cases. A bidirectional transaction can update a database table with the values from an OPC location thus making the values accessible to systems that have the ability to read from databases but not OPC locations. Likewise, bidirectional transactions allow external systems to update OPC locations by interacting with the database.
A transaction group designed for bi-direction synchronization evaluates and handles the updates at the group's rate, for example every second. In the event that both the database and the OPC locations experience a change between the executions of the transaction group the group decides to synchronize the database and the OPC location in accordance with the selected update mode. The update modes can also be individually tailored for each tag and database column by choosing the correct update mode in the Mode column of the Basic OPC/Group Items section.
To create an bidirectional transaction group
Create a New Standard Group and drag tags from the OPC server or the Tag Browser into the group's Basic OPC/Group Items.
Go to the Action tab, and set the following:
- Update mode: either Bi-directional OPC wins or Bi-directional DB wins
- Data source: the appropriate source
- Table name: the appropriate name
- Automatically create table: select the check box so a table is automatically created if the table name does not already exist Table Action area: select update/select and first. You can also synchronize the OPC and database locations based on a condition by choosing custom or the key/value pairs options.
Click Enabled and save the project to start the group.