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Streaming snapshot values via PI to PI interface

Question asked by Peter Falk on Oct 9, 2014
Latest reply on Nov 6, 2014 by Peter Falk

I recently noticed that something appears to have changed with how our PI server is receiving its data.  This server receives its data from our DCS based PI server via a PI to PI interface.


Previously when viewing data in processbook, all values would frequently update.  If you watched a trend run live, you could see small movements in the line every few seconds, but when redrawing the trend those small movements were gone since they did pass compression test to make it into the archive.


Now when I view processbook, values are only updating every few minutes instead of seconds.  When watching trends run live, no data updates for up to 30 minutes.  I just get a horizontal line that does not even follow the slope of the previous data points.  In some cases when watching a process temperature and controller setpoint trend I can see the process temperature start to change (as if the setpoint was changed), but the setpoint trend stays the same, then after 5-10 minutes the setpoint change suddenly shows up on the trend at the correct time stamp.  This makes watching live data difficult and misleading.  Another example, a pressure was trending down slowly from 60-40 psi.  The live trend indicated at 50.1 psi the pressure change stopped and was constant for 45 minutes.  Then after that 45 minutes the trend finally updates you see the pressure was actually decreasing in that time and the rate recently had changing which I think triggered a new archive value to be written.


I am assuming before the interface was streaming snapshot values and now it is only sending values when new archive values have been written to the DCS based PI server.  Does that make sense or could it be something else?  What should I check to begin looking into this change?