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Large data gaps in OPC tags

Question asked by alcanton on Mar 6, 2018
Latest reply on Mar 8, 2018 by alcanton


I'm investigating a perplexing issue with some of our OPC tags. We have noticed large gaps in the data that span weeks and months and are trying to determine the cause. The tags are coming from DeltaV, and when we open Control Studio, all the parameters and IO appear good. Watchit and OPCWatchit show the same value and Good quality. However, in PI, the current value we see in DeltaV was written for several days loosely following our Compmax policy of 8 hours. I say "loosely" because for some reason, the value was written every 7hr50min, rather than the default 8hr. Then after 49 iterations, the value stops writing. At the time of writing this post, the last value was written 10-Jan-18.


I looked in the OPC Client tool, and found that the parameter we are looking for is not browsable. We are trying to record WFI22FC100/SP.CV, but .CV is not present. We can browse .AWS, .CST and .ST, but not .CV.

NO CV.png

I manually added the .CV tag into the OPC Client tool, and it confirmed with OPCWatchit, that the value is 17, and quality is Good.

OPC Tool.png

This tag is configured as an Advise Float32 tag spanning 0-30. I understand that advise tags receive values as often as the OPC server changes them, instead of via a scan class, but I still expect the tag to follow the compression rules.

compmin: 0  compmax: 28800 compdev: 0

excmin: 0 excmax: 600 excdev: 0


Most other tags from this interface are reporting good current values, but I found other examples of other WFI units that currently seem to be suffering a similar condition.  There do not appear to be any messages in any logs (interface node and PI server) relevant to this issue. There are likewise no errors in the Windows Event Viewer that seem pertinent.


I can't figure out why we're not writing new values, and why unchanging values are written every 7hr10min vs 8hr as configured.