Stability Margins MCQs

Practice Stability Margins MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Control SystemsStability Margins

Phase margin is measured at the?

AGain crossover frequency
BPhase crossover frequency only
CNatural frequency always
DDC frequency only

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Correct Answer: A. Gain crossover frequency

Explanation: Phase margin is the additional phase lag needed to reach -180° at the gain crossover frequency.

Reference: Standard control systems: stability margins

Question 2

Control SystemsStability Margins

Gain margin is evaluated at the?

AGain crossover frequency
BPhase crossover frequency
CResonant frequency only
DSampling frequency

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Correct Answer: B. Phase crossover frequency

Explanation: Gain margin is determined from the loop magnitude at the phase crossover frequency.

Reference: Standard control systems: stability margins

Question 3

Control SystemsStability Margins

At the gain crossover frequency, the open-loop phase is -140°. The phase margin is?

A20°
B40°
C140°
D320°

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Correct Answer: B. 40°

Explanation: PM=180°+phase at gain crossover=180-140=40°.

Reference: Standard control systems: stability margins

Question 4

Control SystemsStability Margins

At the phase crossover frequency, |G(jω)H(jω)|=0.5. The gain margin as a ratio is?

A0.5
B1
C2
D4

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Correct Answer: C. 2

Explanation: Gain margin GM=1/|GH| at phase crossover=1/0.5=2.

Reference: Standard control systems: stability margins

Question 5

Control SystemsStability Margins

If the gain margin ratio is 2, its value in decibels is approximately?

A3.01 dB
B6.02 dB
C10 dB
D20 dB

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Correct Answer: B. 6.02 dB

Explanation: GM(dB)=20log10(2)≈6.02 dB.

Reference: Standard control systems: stability margins

Question 6

Control SystemsStability Margins

The gain crossover frequency is the frequency at which the open-loop magnitude is?

A0 dB
B-180 dB
C1 dB
DInfinite

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Correct Answer: A. 0 dB

Explanation: Gain crossover occurs where |G(jω)H(jω)|=1, equivalent to 0 dB.

Reference: Standard control systems: stability margins

Question 7

Control SystemsStability Margins

The phase crossover frequency is the frequency at which open-loop phase is?

A0°
B+90°
C-90°
D-180° modulo 360°

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Correct Answer: D. -180° modulo 360°

Explanation: Phase crossover is conventionally where loop phase reaches -180° (modulo 360°).

Reference: Standard control systems: stability margins