2 Replies Latest reply on Dec 13, 2017 11:40 PM by DARFLET

    Analysis Questions


      Hi David,

      I have a few questions for you.  In our environment, we have PI tags setup with similar calculations that we are doing using AF.  I assume that was an older method of doing the same thing?  For example, we have a PI tag that calculates the running time of an engine over the last 24 hours using the following expression in the tag.  I assume the AF method is now the preferred method for doing this?  What is the advantage/disadvantage?

      Tagval  ('KAK_PL_K-150_COMP-ACC-RT.PV', '*') - Tagval ('KAK_PL_K-150_COMP-ACC-RT.PV',  '*-24h')


      I am working on a rollup example in my test environment (not using a template for now, just picked one element with 3 children to rollup).  I just installed analysis services in test and it seems to be working.  I created the analysis and it calculates a value when I evaluate it, I also successfully mapped and created a tag for the data, but it still says Pt Created rather than showing a value.  I also did a backfill on it and it does calculate previous data.  Not sure what I am doing wrong or is it some restriction on the test environment?





      (this question was originally asked by Darlene Fletcher in the Introduce yourself thread)

        • Re: Analysis Questions

          Hi Darlene,


          You are correct, the tags you are talking about are likely Performance Equation tags, which were a precursor to Analysis which is definitely the recommended option. Both AF Analysis and PE Tags use the same syntax, so simple calculations using data from other tags would be effectively the same between both, the main difference is that AF Analyses add a lot more functionality that are unavailable with PE tags, such as Event Frame Generation, Rollup analyses, and SQC. Another one of the biggest advantages of using Analysis over PE tags is that since it utilizes AF attributes, you are able to make use of data coming from non-PI sources in your calculations, and you can also use analysis templates to allow for more widespread deployment of calculations. The analysis service also offers better performance and makes backfilling calculations a lot easier to do. If you're looking for more information on AF Analyses, KB01123 is a great resource.


          For your second question, the analysis service needs the configured trigger criteria to be met for it to write a new value to the tag. If you are using natural scheduling but there is no data coming in, then the analysis would not be able to trigger, but a backfill would be able to go back and apply the calculation if the older data exists. Based on your earlier comments about your test system it seems like this is likely the case.


          Let me know if you have any more questions!