What is Cascade Control?

• A. When the output of a primary controller adjusts the setpoint of a secondary controller.
• B. A control strategy using two independent controllers with no interaction.
• C. A feedback loop where the secondary controller regulates the input to the primary controller.
• D. A feedforward method that predicts disturbances without feedback.

Answer: (A)

Cascade control uses two controllers in series: the outer (primary) controller provides a setpoint for the inner (secondary) controller, and the inner controller directly drives the actuator to track that setpoint. This arrangement makes the inner loop respond quickly to disturbances or fast dynamics, while the outer loop handles slower changes in the process, keeping the overall system stable and accurate.

The described statement fits this setup exactly: the primary controller’s output serves as the setpoint for the secondary controller, creating a fast inner loop and a slower outer loop that work together.

The other options describe configurations that aren’t cascade. Two independent controllers with no interaction lacks the crucial setpoint-link between the loops. A secondary controller regulating the input to the primary would invert the actual information flow in cascade, where the inner loop controls the actuator, not the outer loop’s input. A purely feedforward method with no feedback doesn’t involve nested feedback loops at all.