Override Control Smith & Corripio: pp340-344 Luyben, W.L.: pp259-261 Syn: Constraint control. Def: The manipulated variable is set by any one of a number of controlled variables (Luyben). Purposes (Smith & Corripio): a protective strategy to maintain process variables within limits in order to ensure safety of personnel and equipment, and product quality as an optimization strategy to provide smooth transition between control schemes.

Override Control Flow control Example If the liquid level drops below h2, the liquid will not does not have enough NPSH, and cavitation at the pump will occur. Normal level Min. NPSH

Pump Cavitation

Override Control Solution Level < SP MVLC50 MVFC50 = ● LS = LC LS = FC

Selective Control Purposes (Smith & Corripio): for safety consideration and process optimization. Example:

Selective Control Solution: