6 Replies Latest reply on Jun 7, 2017 6:31 PM by MPetro

    Tagavg showing bias


      Hi everyone!


      I am having an unexpected result from the Tagavg function. The average is lower than the raw data. Does anyone know what the cause might be?



      Attribute1: Value from PI point

      Attribute2: Value from a Table

      Analysis: Tagavg('Attribute1','*-5m','*')*'Attribute2'*24

                     Scheduling: every 5 minutesAttribute3: Output from Analysis saved in PI Point



      PI SE 2016 R2 SP1

        • Re: Tagavg showing bias

          Hi Mauricio,


          What are the values that you are getting for Attribute2?  I just want to make sure it's not the easy solution .

            • Re: Tagavg showing bias

              Can you execute the analysis in "Preview" and see what the table of numbers look like?  Do the numbers make sense?

              You can also right-click on attribute 1 and attribute 2 to bring up the Time Series Data dialog box and check to see if the data make sense.

              Let us know what you find.


              Steve Kwan

                • Re: Tagavg showing bias

                  Funny thing. The dummy configuration presented is slightly different from the original. Just as a last attempt, I changed the configuration to the one I showed here. It seems that it is working fine now.


                  The original configuration uses DR formula to do the multiplication. Than the average uses the formula result as input.


                  Attribute1: Value from PI point

                  Attribute2: Value from a Table

                  DR Formula: Attribute3 = Attribute1 * Attribute2

                  Analysis: Tagavg('Attribute3','*-5m','*')  Scheduling: every 5 minutes

                  Attribute4: Output from Analysis saved in PI Point


                  So now the question is: what does Tagavg do if the input is a DR formula? I have several other configurations done this way.

                    • Re: Tagavg showing bias

                      Speculating possible reasons...


                      The DR formula is


                      Default value = 0


                      I realised that the last value in a Processbook graph shows the default value (why? I don't know! Not always, but it is fairly common to see that). If the Tagavg includes the default value, in this case zero, it will always average a lower value.


                      Is this correct?

                  • Re: Tagavg showing bias

                    The Table Lookup gets a constant to make unit convertion.

                  • Re: Tagavg showing bias

                    Here what I got after some testing.


                    Formula DR with DefaultAllowed=1

                    The average function Tagavg() consider the default value in the calculation. In my case, zero, causing a bias to a lower value. Since my average is for 20 or so value, I usually get 4-5% bias.


                    Formula DR

                    The average works fine. But the result does not match exactly the average done in Excel Datalink. So it is a new kind of problem...