HI,
I have a question regarding what the expected accuracy should be for some datalink functions. In particular, I was comparing the results of "PITimeFilterVal()" to those "PISamplFilDat()". My initial thought was that the "PITimeFilterVal()" would give me the most accurate results, but that is not the case. I observed the following things when running different scenarios and wanted to know if anyone can give insight into what is going on.
- In this exercise I determined the "correct" value by zooming in on a plot in Processbooks and determine the time that each filter condition was true.
- The results for PITimeFilterVal() varied depending on how large my start and end window were. A larger window gives less accurate results. My errors were between 0.5 - 2%
- When using PISamplFilDat() my results approached what I assumed to the correct results as I increased the sampling frequency. A sampling frequency of 1 minute or less resulted in almost exactly matching what I assumed to be the correct results.
I read in the help section for data link under PITimeFilterVal "Note: Time Filtered results vary slightly depending on your PI Server version.". But it does not explain how or why the results may vary. I am running version 2010. I need to understand the degree of possible error just to make sure we select the proper function to calculate values. I like the PITImeFilterVal function as it is a very convenient way to pull data.
Thanks.