What causes control loop interaction and how is it managed?

Loop interaction occurs when control action in one loop affects the process variable of another loop (coupling). Diagnosis: Relative Gain Array (RGA) analysis quantifies interaction - diagonal elements near 1 indicate low interaction. Management: proper variable pairing (minimize RGA off-diagonal elements), decoupling control (feedforward from interacting outputs), sequential loop tuning (tune tighter loop first, detune interacting loops), detuning (reduce gains on both loops), or multivariable control (MPC handles interactions explicitly). Severe interaction may require process redesign.