JNTU
JNTU B.Tech III CONTROL SYSTEMS Previous Question Paper (November/December - 2018 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions. (Note: Graph sheets and semilog sheets are required to be provided during the examination).
Part A
Briefly discuss about the classification of control systems.
Answer
Control systems are primarily classified into Open-loop control systems, where the output has no effect on the control action, and Closed-loop (feedback) control systems, where the output is monitored and compared with the input to adjust the control action automatically.
Explain the effects of feedback with suitable examples.
Answer
Feedback reduces system sensitivity to parameter variations, improves disturbance rejection, and allows for precise control over bandwidth and steady-state error. For example, in a speed-controlled DC motor, feedback ensures the motor maintains a constant speed despite changes in load torque.
Briefly discuss about the block diagram algebra to obtain transfer function.
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Give the Mason’s gain formula and describe all the terms of it.
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Obtain the time response of First order system to impulse input.
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Briefly discuss about the effects of PD and PI systems.
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Briefly explain the concept of stability of a control system.
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Explain Routh’s stability criterion.
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Discuss about frequency domain specifications.
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Define phase margin and gain margin.
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Part B
Obtain the transfer function X(s)/F(s) for the mechanical translational system shown in Figure 1.
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Write the differential equations governing the behavior of the mechanical system shown in Figure 2. Also obtain the electrical analogy using f-I system.
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Obtain the transfer function of A.C. Servomotor.
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Obtain the overall transfer function of the following signal flow graph using Mason’s gain formula (Figure 3).
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Obtain the transient response of a second order system for a unit step input.
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Explain the time domain specifications of a transient response of a second order system.
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For the unity feedback system with G(s) = 10 / (s(s+10)), find the error series for the input r(t) = 1 + 2t + (t^2)/2.
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The characteristic equation of certain control system is given by s^4 + 3s^3 + 2s^2 + (K+10)s + 15 = 0. Determine the range of values of K for the system to be stable.
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Determine the breakaway points, angle of departure and the centroid of the root locus for the system G(s)H(s) = k(s+3) / (s(s+5)(s+6)(s^2+2s+2)). Also sketch the root locus.
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Sketch the Bode plot for the system G(s) = K / ((1+s)(1+0.1s)(1+0.01s)) and determine the value of K for which the magnitude plot crosses the 0db line at w = 15 rad/sec.
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The Open loop transfer function of a unity feedback system is given by G(s) = K*exp(-0.1s) / (s(1+0.1s)(1+s)). By using Bode plot, determine the value of K so that the gain margin of the system is 20db. And the value of K for which phase margin is 60 degree.
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