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JAN-FEB 2019

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FAST FORWARD l APC progress has stalled, because its high cost of ownership lim- its its applicability. Most APC resources now go toward support and maintenance of existing applications, not new applications. l Most APC benefits come from a minority of variables, while costs are compounded by the number of variables, which sug- gests applying the Pareto principle (80/20 rule) to APC controller design. l Experience shows that detailed models and embedded optimizers are not always necessary for the essential role of multivariable control, which unlocks many new possibilities for APC. 8 INTECH JANUARY/FEBRUARY 2019 WWW.ISA.ORG APC paradigm now more affordable, agile, scalable, and reliable By Allan Kern, PE I n this article, as in industry, advanced pro- cess control (APC) refers primarily to multi- variable control. Multivariable control means adjusting multiple single-loop control- lers in unison, to meet constraint control and optimization objectives of an additional set of related process variables. Multivariable control is a central aspect of nearly every industrial process operation. His tor- ically, operators adjusted single-loop controller set points and outputs (i.e., "the available han - dles") to control a superset of constraint and op- timization variables (i.e., "controlled variables"). They did this based on experience, knowledge of the process, ongoing operating conditions, and input from the greater operating team, which includes supervision, process engineers, and production planning. APC endeavors to auto - mate this task, in order to capture incremental gains in capacity, efficiency, quality, etc. Figure 1 Advanced process control: Indispensable process optimization tool

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