[Bug 6091] Bug in 8.1.15: Bidirectional Transaction Groups w/ Scaled OPC Items Only Scale Unidirectionally

Hey folks,

I spent several hours with IA support yesterday identifying a bug in 8.1.15 and wanted to share the results here.

This was a 7.9 to 8.1 upgrade with several transaction groups to control read/write to data-points in the PLC. The bidirectional transaction groups featured several tags that were being scaled between the PLC and the DB. In 7.9 this scaling occurred bidirectionally, while in 8.1.15 it only occurs when reading from the PLC to the DB.


  • Bidirectional transaction groups with OPC items being scaled


  • Scaling occurs normally PLC to DB.
  • Scaling DOES NOT occur DB to PLC.

Observed Impact:

  • Example: The PLC holds a setpoint of 550 that represents a value of 55.0 degrees.
    • Reading from the PLC, 550 is scaled to 55.0 in the database.
    • Writing to the PLC, a value of 55.0 is not scaled to 550, but instead written directly at 55. Effective setpoint of 5.5 degrees.
    • Reading from the PLC, this value of 55 is scaled to 5.5 in the database.

The bug has been escalated to dev, and the solution for us in the meantime was to remove scaling from the transaction group and instead scale values as queried to / from the DB.

Just wanted to share as an FYI to anyone who might encounter the issue in the future.


Hey, we are experiencing the same exact issue. I am having trouble making this happen using transaction groups, it goes in a loop updating each other (OPC <ā€”> DB) every once in a while. Did you get rid of transaction groups completely?

FYI - this bug was recently fixed for 8.1.19.

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We did not get rid of the transaction groups. Rather we disabled scaling in the transaction groups and performed the scaling in the queries we use to interface with the data table. If you need examples Iā€™m happy to share.