Question

Feed forward control can be used only:

• A. If the disturbance variable is measured
• B. If the disturbance variable is manipulated
• C. If the disturbance variable is ignored
• D. If a regulatory control is needed

Hint:

Feed-forward control is "proactive" (measures disturbances).
Feedback control is "reactive" (measures the controlled output error).
Without measurement of the disturbance, feed-forward control is mathematically impossible to implement.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question asks about the primary requirement for implementing a feed-forward control scheme in a process control system.

Step 2: Detailed Explanation:

• Feed-forward control is a proactive control strategy designed to compensate for load disturbances before they can affect the process output (controlled variable).

• Unlike feedback control, which acts only after an error or deviation is detected in the output, feed-forward control acts in anticipation of disturbances.

• To execute this anticipation, the controller must calculate the exact corrective action needed based on the magnitude and direction of the incoming disturbance.

• Therefore, a feed-forward control loop can only be implemented if the disturbance variable is directly measured in real-time.

• If a disturbance is unmeasured or cannot be quantified, a feed-forward controller cannot compute the proactive corrective action, and the system must rely on feedback control instead.

Step 3: Final Answer:
Feed-forward control can be used only if the disturbance variable is measured.