2 Replies Latest reply on Aug 3, 2010 12:54 AM by Bryan Owen

    PI calculated Tags


      Hi all,


      I am new to the calculation tags. I am trying to configure PI to capture a downtime scenario. Following is the scenario:


      1. We have normal PI tags - Tag 1 for temperature (say TEMP) and Tag2 for pressure (say PRES)


      2. I created two digital states - 0 (for Down) and 1 (for up).


      3. I created a new calculated tag (say DOWN). Now, I want to write an expression as if TEMP>120 OR PRES>80, then 0 else 1. I want this tag as event-scheduled monitoring two tags - TEMP or PRES. How can I do this?


      I went through the documentation and it says


      event = tagname, CalculationExpression


      Here I can put only one tagname - either PRES or TEMP. I want the expression to be evaluated when a new value is present in the snapshot of either TEMP or PRES.


      Thanks for your patience reading.




      Nageshwara Manda









        • Re: PI calculated Tags

          Unfortunately, PE cannot be configured to use multiple tags for event scheduling. An alternative option to PE would be to use PI ACE. PI ACE has the option to use multiple tags for event scheduling, so you can easily do this.


          Another option would be to create a totalizer tag that gets a new result whenever one of the 2 tags (TEMP or PRES) gets a new value.


          The totalizer tag configuration should be like the following:
          Name & Type:
          Summary Calculation
          Moving Event Weighted Total

          Sampling: Whenever the expression changes
          (IF(BadVal('Tag 1')) THEN 0 ELSE 'Tag 1') + (IF(BadVal('Tag 2')) THEN 0 ELSE 'Tag 2')

          Continue forever
          At source time (ramp)

          Compressing to off and all exception to 0.

          The downside to this is an additional tag is required.



            • Re: PI calculated Tags
              Bryan Owen

              In this case, event triggered PE may not be critical for success. Event scheduling is very important when there is latency in the inputs.  However assuming the temperature and pressure tags are from the same datasource on the same scan class, consider using scheduled PE with a matching scan class.