Opinions on initializing PIDE instruction block

PLCGurus.NET Live & Interactive Forum PLC Questions and Answers Rockwell, Allen-Bradley, Stratix Opinions on initializing PIDE instruction block

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      I have two temperature controlled vessels.  The PIDE blocks for each vessel are exactly the same.  The operators set the temperature using an HMI menu.  Today, one of the operators told me the cooling loop was not working on one of the vessels.

      The PIDE blocks run in OperatorAuto mode.

      I looked at all the parameters on each of the PIDE blocks.  All the parameters were the same except SPProg and WindupHOut.  The WindupHOut signal was an indicator of the CV value being at a limit however, on vessel F4, SPProg=SPOper=70°F. On vessel F5, SPProg=0°F, SPOper=70°F.

      On vessel F5 I set SPProg=70°F.  Didn’t make any difference.

      I was finally able to get the loop working by changing from Operator mode to Program mode then back to Operator mode.

      Since this function has been working for all five vessels for weeks, I’m wondering if it’s possible that the PIDE block got left in an indeterminate state that messed with it’s ability to execute the control loop.  If that’s a possibility, would it be a good practice to “initialize” the PIDE block to a known state?  If so, how would you go about doing it?



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