Which statement best describes cascade control?

• A. A control technique where a primary controller adjusts the setpoint of a secondary controller.
• B. A method of measuring pressure
• C. Automatic and Manual
• D. Output of a controller is split

Answer: (A)

Cascade control uses two controllers in sequence, where the outer loop provides a setpoint to the inner loop. The outer controller watches a slower-changing variable and tweaks what the inner controller should aim for, sending that target to the second controller. The inner loop then directly drives the manipulated variable to track its setpoint, giving fast, precise control of the fast-responding part of the process while the outer loop handles slower disturbances.

For example, in a heating/cooling scenario, the inner loop might regulate a valve to keep a jacket temperature at a chosen inner setpoint. The outer loop monitors the reactor temperature and adjusts that inner setpoint to compensate for changes in feed temperature or heat input, improving overall stability and disturbance rejection.

This description matches the idea that the primary controller is setting the target for the secondary controller, rather than being about measurement methods, operational modes, or splitting outputs.