The morning shift just started. A senior process engineer sits at a workstation reviewing overnight trends from a recently commissioned unit. Production is online, but something isn’t quite right. A few loops are oscillating substantially. The engineer soon learns that operators intervened repeatedly during the night shift to keep things within acceptable limits.

Diving into the tuning coefficients for the oscillatory PIDs, the engineer sees that large Gain values were used across the board as though their sole purpose is to tightly track Setpoint. A flow loop regulating inlet pressure is tuned just as aggressively as a controller regulating level inside a surge tank.

Whichever tuning method was followed during commissioning, one thing is now clear: Little consideration was given for the unique control objectives of these regulatory loops.