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NULL Tag Value via DataLink and PI-SDK

Question asked by rohanar on Jul 28, 2015
Latest reply on Jul 31, 2015 by dng

When queried via DataLink or the PI-SDK, a tag value is returning #NULL! or System.DBNull, respectively. Two tags have this issue so far at a single facility.

Is anyone familiar with how this might happen or how to reproduce a NULL PI tag value?


Sequence of events on the two tags in question..

  1. Digital tag is active for a several years.
  2. They decommission it and set scan class = 0 and change the pointsource
  3. The last value in the archive 3 years ago is a valid digital state (OFF)
  4. It’s now reading #NULL / DBNull via Datalink and PISDK.



This is via DataLink, but the same is encountered programmatically via the PI-SDK.