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GATE 2021 CH – Question 22

Instrumentation and Process Control · Cascade and feedforward control · 1 mark · Multiple choice

A feedforward controller can be used only if

  1. the disturbance variable can be measured
  2. the disturbance variable can be manipulated
  3. the disturbance variable can be ignored
  4. regulatory control is not required

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Show answer and explanation

Correct answer: (A) the disturbance variable can be measured

Explanation

Feedforward control calculates a compensating change in a manipulated input **from the measured disturbance**, before that disturbance produces an output error. A disturbance measurement is therefore necessary for this scheme.

The disturbance itself need not be manipulable: the controller adjusts another input to offset its effect. Ignoring the disturbance defeats feedforward action, and feedforward can be combined with feedback regulatory control. **Answer: A.**