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Problems with PI Interface - Compression and Deviation Processing

Question asked by JulioFloresGarcia on Dec 20, 2017
Latest reply on Jan 5, 2018 by Roger Palmen

Hi all,


I have a problem/doubt with the PI Interface and the processes of exception and deviation for filter this data coming from OPC.


The following picture shows a samples of humidity.



There is an alarm behaviour saying that an alarm is triggered ON after that 5 minutes are elapsed out of thresholds (red line). The time counter of 5 minutes is decreased when the condition is ON, and it is stopped and resetted when air condition value go back inside thresholds plus a hysteresis (yellow line).


As you can see in the picture, you go out from lower threshold (RED line) between 08:16:09 and 08:16:40. If we consider 08:16:10 as first time that you are out of threshold, the alarm should be triggered ON at 08:21:10.


Here is the problem, in the report the alarm appears at 08:20:46, 24 seconds before the theoritical time.



If I go to the PI DA and take a look in the values, I see this:



As you can see the picture shows the 10 samples showed in the first trend. Considering that the alarm is triggered ON at 08:20:46 must be a value 5min before so at 08:15:46.

However the first time that the value is under 40 is at 08:16:40 so the alarm would be at 08:21:40. I don't know if the samples that trigger ON the alarm if filtered.



  • The PLC samples every 2msec.
  • Scan class of the Interface is 00:00:01.
  • Humidity sensor has a Resolution of 0,1
  • This is the configuration of my tag (loc4=1)


And don't know if the problem is coming from the machine or if it is problem from the PI System.


Thanks in advanced.


Best regards,

Julio Flores