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John McCulloch - Control Loop Tuning

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There are many software packages available to help with loop tuning; some control systems even provide self-tuning algorithms. Why, then, do we still need Control Engineers with the skill of manually tuning control loops? There are many reasons - here are some:
  • All processes are non-linear and it is important to provide a set of tuning constants that is satisfactory for all possible operating points. Automatic tuning packages cannot do this.
  • Process-linked dynamic interactions can occur between different control loops on the same process unit. It is important to recognise this and to organise the relative tuning of adjacent loops to minimise such interactions. Only the most complex automatic loop-tuning systems can attempt this.
  • There are many situations where the control objective is not to minimise variation of the measurement but to make best use of surge capacity and to prevent disturbances from propagating through the plant. Automatic tuning packages cannot do this.
  • Sometimes, process or instrument problems only become evident when trying to tune a control loop. Whilst some automatic tuning packages can give useful indications of problems, only a skilled engineer can properly identify and solve the problem.
I had a reputation, when I was with bp, for being able to tune some very difficult loops. I was the Engineer they called on when the loop was one where a minor error could trip the whole plant.

You can hire me to visit your site and advise on the tuning of difficult control loops.












This page last updated on 2013-08-06 JGM