5 Replies Latest reply on May 7, 2013 7:56 AM by johngaytor

    DEADBAND DIGITAL

    johngaytor

      Dear All

       

      I have a user who has a digital tag that indicates the cool down of a bit of equipment...he wants us to stop it flicking up and down between states when it is hovering around the changeover point from one state to another like 230deg then 225deg and the digi changes state, then back up to 230 again then down to 229 and it changes state again.

       

       

       

      what is the best way to introduce a deadband to smooth it out so he doesnt get a bunch of alarms??? exception setting, filtercode?

       

      all contributions welcome...

       

       

       

      John

        • Re: DEADBAND DIGITAL
          hanyong

          Hi John,

           

          From what you described, it seems like your digital tag is tied to a value of a temperature tag. How is this digital tag getting its value? Is this a Performance Equation Tag? or this is collected from as a seperate status tag from the data source directly?

           

          Depending on how the digital tag gets its value, we probably can find the best way to proceed. 

            • Re: DEADBAND DIGITAL
              johngaytor

              it is a digital PE looking at a temperature tag

                • Re: DEADBAND DIGITAL
                  hanyong

                  Thanks for the elaboration. Personally I don't think there are any simple configuration on the PE tag that will do the trick. Exception deviation setting are ignored given that we are working with a digital tag, and I don't think PE uses any of the classic attribute like filtercode for processing data.

                   

                  You can choose to include some filtering logic in the equation for the digital tag. Not necessary an easy task depending on how complicated the equation is already and also how robust you want this filtering to be. A simple filter like the last change of state should not be less than 2 seconds ago, we can do something like:

                   
                  IF '*' - PREVEVENT('PEDigitalTag', '*') < 2 THEN NOOUTPUT() ELSE IF 'TemperatureTag' > 150 THEN 1 ELSE 0
                  

                   But should it be something complex like the last change of state A to state B should not be less than 2 seconds, it would be quite challenging to do this in PE.

                    • Re: DEADBAND DIGITAL

                      Hello John,

                       

                      As mentioned by Han Yong exception doesn't apply to point type Digital but I see some potential to remove the noise from the raw data (temperature) tag. I may be mistaken because I do not know your process but usually I consider temperature being slow changing data.

                       

                      If temperature is quickly changing back and forth via the process, how accurate can the measurement be? What is the change in Temperature that is really considered a change and not just signal noise for whatever reason? By answering these questions to yourself you will be able to find appropriate settings for excdev / excdevpercent.

                       

                      Because you may not want to touch the original tag while evaluating settings that work, you can create an event scheduled PE tag that duplicates the raw data. Either use this tag as the source or create a copy of your Digital PE tag. The second option allows you to compare the raw data with and without noise as well as the Digital states resulting from your equation.