Tags calculated using ACE module going Stale

Discussion created by MSEConsultants on Jul 14, 2010
Latest reply on Jul 15, 2010 by michaelh



I have a single ACE module that writes to lots of "Calculated tags" on my test system. The ACE module is scheduled to run every 15 seconds. All was working well and I left it overnight to run. In the morning I found that some of the calculated tags had gone stale. To try and figure out what was going on, I concentrated on one of the stale tags (over 12 hours stale).


At the end of my ACE module all the calculated tags get written in one procedure. My stale tag update code is located between calculated tags that are updating to PI correctly, so it is clearly not dropping out of the procedure mid-way.


The log message I write back from my ACE module indicates that all went well.


When I test my ACE module using current values, the value for that tag is changing significantly.


Next I checked my archive settings for the stale tag. The tag value was stuck at 11138. My ACE test indicated that the value had changed to 12856. My archive settings for that tag were:


Typical value: 10
Zero: 0
Span: 50000
Scan: On
Archiving: On
Step: Off
Shutdown: Off
Compressing: On
Exception Deviation: 2 Eng Units
Compression Deviation: 4 Eng Units
The Max Times for exception and compression were > 1 day


I changed the Max Times to 1 Minute


Then my tag did update but the value was set to NaN


Why would my ACE test show a value for the stale tag, but the current value in SMT shows NaN? The tags that are calculated in the same module and are updating correctly, do have the same calculated value in the ACE test so the test is definitely getting the current values for the calcs.