Anna University Coimbatore 2008 B.E Electrical and Electronics Engineering Control system QB - Question Paper

65. What is Nichols chart?
The chart consisting if M & N loci in the log magnitude versus phase Diagram is called Nichols chart.
66. What are 2 contours of Nichols chart?
Nichols chart of M and N contours, superimposed on ordinary graph. The M contours are the magnitude of closed loop system in decibels and the N contours are the phase angle locus of closed loop system.
67. How the resonant peak (Mr), resonant frequency (wr), and band width are determined from Nichols chart?
The resonant peak is provided by the value of ?. Contour which is tangent to G (j?) locus.
The resonant frequency is provided by the frequency of G(j? ) at the tangent point.
The bandwidth is provided by frequency corresponding to the intersection point of G(j? ) and –3dB M-contour.
68. What are the advantages of Nichols chart?
The advantages are:
a. It is used to obtain the closed loop frequency response from open loop frequency response.
b. Frequency domain specifications can be determined from Nichols chart.
c. The gain of the system can be adjusted to satisfy the provided specification.
69. What is Nyquist contour?
The contour that encloses entire right half of S plane is called Nyquist contour.
70. State Nyquist stability criterion.
If the Nyquist plot of the open loop transfer function G(s) corresponding to the Nyquist contour in the S-plane encircles the critical point –1+j0 in the counter clockwise direction as many times as the number of right half S-plane poles of G(s), the closed loop system is stable.
71. What are the 2 segments of Nyquist contour?
a. A finite line segment C1 along the imaginary axis.
b. An arc C2 of infinite radius.
72. What are the effects of adding a zero to a system?
Adding a zero to a system outcomes in pronounced early peak to system response thereby the peak overshoot increases appreciably.
73. State magnitude criterion.
The magnitude criterion states that s=sa will be a point on root locus if for that value of s, | D(s) | = |G(s)H(s) | =1
74. State angle criterion.
The Angle criterion states that s=sa will be a point on root locus for that value of s,, ?D(s) = ?G(s)H(s) =odd multiple of 180°
75. Define BIBO stability.
A linear relaxed system is stated to have BIBIO stability if every bounded input outcomes in a bounded output.
76. What is the necessary condition for stability?
The necessary condition for stability is that all the coefficients of the characteristic polynomial be positive.
77. What is the necessary and sufficient condition for stability?
The necessary and sufficient condition for stability is that all of the elements in the 1st column of the Routh array should be positive.
78. What is quadrant symmetry?
The symmetry of roots with respect to both real and imaginary axis called quadrant symmetry.
79. What is limitedly stable system?
For a bounded input signal if the output has constant amplitude oscillations. Then the system may be stable or unstable under a few limited constraints such a system is called limitedly stable system.
80. Define relative stability
Relative stability is the degree of closeness of the system, it and indication of strength or degree of stability.
81. What are root loci?
The path taken by the roots of the open loop transfer function when the loop gain is varied from 0 to a are called root loci.
82. What is a dominant pole?
The poles lying close / on the imaginary axis are dominant poles.
83. What are the main significances of root locus?
a. The main root locus technique is used for stability analysis.
b. Using root locus technique the range of values of K, for as table system can be determined
84. What are the 2 kinds of compensation?
a. Cascade or series compensation
b. Feedback compensation or parallel compensation
85. What are the 3 kinds of compensators?
a. Lag compensator
b. Lead compensator
c. Lag-Lead compensator
86. What are the uses of lead compensator?
a. Speeds up the transient response
b. Increases the margin of stability of a system
c. Increases the system fault constant to a limited extent.
87. What is the use of lag compensator?
Improve the steady state behavior of a system, while nearly preserving its transient response.
88. When is lag lead compensator required?
The lag lead compensator is needed when both the transient and steady state response of a system has to be improved.
89. What is a compensator?
A device inserted into the system for the purpose of satisfying the specifications is called as a compensator.

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