Cascade control is defined as ...

• A. A control scheme that uses only proportional control
• B. A control scheme with no inner loop
• C. A control scheme in which a primary loop controls a secondary loop
• D. A control scheme that uses only feedforward control

Answer: (C)

Cascade control uses two feedback loops in series: an outer (primary) loop that regulates a slower or more influential process variable, and an inner loop that directly controls a fast-responding variable to keep its own variable near a setpoint. The outer loop sets the inner loop’s reference, so the inner loop can react quickly to disturbances and stabilize the fast dynamics, while the outer loop handles the slower, larger-scale changes. This arrangement improves disturbance rejection and reduces interaction between process dynamics, making the overall control more robust. In short, it’s a control scheme where one loop governs the setpoint of a second loop.