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..
- Digital tag is active for a several years.
- They decommission it and set scan class = 0 and change the pointsource
- The last value in the archive 3 years ago is a valid digital state (OFF)
- It’s now reading #NULL / DBNull via Datalink and PISDK.
This is via DataLink, but the same is encountered programmatically via the PI-SDK.