71. The correct sequence of steps needed to improve system stability is

A. insert derivative action, use negative feedback reduce gain

B. reduce gain, use negative feedback, insert derivation action

C. reduce gain, insert derivation action, use negative feedback

D. use negative feedback, reduce gain, insert derivation action.

72. The constant M-circles corresponding to the magnitude (M) of the closed loop transfer function of a linear system of values of M greater than one lie in the G-plane and to the

A. right of the M = 1 line

B. left of the M = 1 line

C. upper side of the M = +j 1 line

D. lower side of the M = ?jl line

73. The characteristics equation of a closed-loop control system is given as s2 + 4s + 16 = 0. The resonant frequency in radians/sec. of the system is

A.2

B. 2 ii-

C.4

D.2

74. The open loop transfer function of a control system is given by K(s + 10) s(s + 2)(s + a) The smallest possible value of 'a' for which this system is stable in the closed-loop for all positive values of K is

A.0

B.8

C.10

D.12

75. A phase-lag compensation will

A. improve relative stability

B. increase the speed of response

C. increase bandwidth

D. increase overshoot

76. Consider the following statements regarding a first order system with a proportional (P) controller which exhibits an offset to a step input: 1. increase the gain of the P controller 2. add derivative mode 3. add integral mode Of these statements

A. 1, 2 and 3 are correct

B. 1 and 2 are correct

C. 2 and 3 are correct

D. 1 and 3 are correct.

77. Which one of the following statements is true for gain margin and phase margin of two closed-loop system having loop transfer fuction G (s) H (s) and exp (--s) G (s) H (s)?

A. Both gain and phase margins of the two systems will be identical

B. Both gain and phase margins of G (s)H (s) will be more

C.Gain margins of the two systems are the same but phase margin of G (s) H (s) will be more

D. Phase margins of the two systems are the same but gain margin of G (s) H (s) will be less

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