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GATE 2018 EC – Question 15

Control Systems · Routh-Hurwitz and Nyquist Stability Criteria · 1 mark · Multiple choice

The Nyquist stability criterion and the Routh criterion both are powerful analysis tools for determining the stability of feedback controllers. Identify which of the following statements is FALSE:

  1. Both the criteria provide information relative to the stable gain range of the system.
  2. The general shape of the Nyquist plot is readily obtained from the Bode magnitude plot for all minimum-phase systems.
  3. The Routh criterion is not applicable in the condition of transport lag, which can be readily handled by the Nyquist criterion.
  4. The closed-loop frequency response for a unity feedback system cannot be obtained from the Nyquist plot.

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Show answer and explanation

Correct answer: (D) The closed-loop frequency response for a unity feedback system cannot be obtained from the Nyquist plot.

Explanation

The closed-loop frequency response of a unity feedback system can be obtained from the Nyquist plot (for example with M-circles), so D is false. A, B and C are standard statements.