Edge Historian Scan Class

I recently setup up an Edge Gateway that is syncing tag history data to a Central Gateway. Both gateways are 8.1.3. The tag values are syncing fine, but I noticed today that it does not appear that the sqlth_scinfo or sqlth_sce data is making its way to the Central Gateway. I just have one row in sce with scname = _exempt_ (it should be Default) and nothing is in scinfo. Is this expected behavior with Edge syncing or should I actually be seeing scan class/tag group info in these tables?

Not urgent, but just want to give this a bump since I posted it at not an ideal time to get eyes on it.

I got an answer to this from support. Apparently it is expected behavior for the Edge gateways to NOT sync scan class information to the central gateway for tag history. It seems to me like this could cause inaccuracies in any Easy Charts or tag history calculations on the central gateway (especially if utilizing analog compression). But maybe I’m wrong? I sent a similar question into support and hope to hear back. Right now I feel like I can’t really trust the tag history data from our Edge gateways unless it is all set to simple scan class settings (and even then, without the sce data, it could be misleading)…hopefully I’m wrong!

From support:

You are correct, if there are gaps in the data it won’t be seen on the central Gateway as missing data.
In this scenario, Tag history data is being sent (stored) using the Tag Group rate but it is queried as onChange. It’s exempt, meaning that it is exempt from scan class tracking and validation.

Confirms my fears…I feel like this should be a big, bold warning in the Edge documentation. Everything I read led me to believe that the Edge Sync service would be the same as normal tag history on a full gateway…and unless you are really paying attention to the auxiliary tag history tables in the DB, you would not be aware of this limitation.

Didn’t take long for this to cause a problem…we had a power outage over the weekend cause a glitch with the Edge device and resulted in a gap in data, but the tag history uploaded to the central gateway shows it as holding the last known value (results in the runtime aggregate calculations showing 16 hours more runtime than it should have…).

Following up with support, the lack of scan class tracking and validation is not just limited to syncing, the Edge Historian does not track/validate scan class information at all (local or sync). They will be updating the documentation to call out this difference in the Edge vs Ignition Historian.

I’ve also created a new feature request to add Edge Historian Scan Class Tracking and Validation in case this is an issue for anyone else. In the mean time, custom data validation logic does not sound fun…