Using Exception-Based Processing

GE version 7.x drivers support exception-based processing when used with iFIX products for process control. Exception-based processing means that the software application processes data only if there is a considerable deviation from normal values.

Exception-based processing also applies to database blocks. You can enable exception-based processing for any block in the process database. After you enable this feature, the I/O driver reports any data change that exceeds the I/O driver’s deadband to the iFIX Scan, Alarm, and Control (SAC) program. This program resides in the background and works to maintain the process database continuously. Upon receiving notification of an exception, SAC polls for information on the affected database block and updates that block’s value.

 To configure a database for exception-based processing:

  1. Start the Power Tool.
  2. Add a server and a group, or modify an existing group by highlighting it in the Tree Browser window.
  3. Depending on the group's I/O, enter a deadband value as follows:
    • For asynchronous I/O:
      1. In the Group properties, select Asynchronous in the I/O Type field.
      2. Enter a value in the % Deadband field.
    • For synchronous I/O:
      1. In the Group properties, select Synchronous in the I/O Type field.
      2. Add an Item.
      3. In the Item properties, enter a value in the Exception Deadband field.
  1. Start Process Database.
  2. From the program’s spreadsheet, double-click the block you want to modify or from the Blocks menu, choose Add and then select the type of block you want to create.
  3. In the I/O Address box of the database block, enter an OPC address. Reference the group or item you configured in the Power Tool.
  4. Enter E in the Scan Time field of the database block.

If you have many database blocks, using exceptions can help reduce the demand on SAC.

NOTES:

  • Analog Register and Digital Register blocks in iFIX databases do not support exception-based processing. In addition, the OPC Client does not support using the Text block with exception-based processing.
  • The OPC Client does not support exception-based processing for database blocks that reference items configured as data arrays.

See Also