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B.E./B.Tech DEGREE EXAMINATION, APRIL- 2014Second Year Fourth Semester

MODEL EXAMINATION

EC2255- CONTROL SYSTEMSELECTRONICS AND COMMUNICATION ENGINEERING

Time: Three hours

Maximum marks: 100

Answer ALL questions

Part-A (10 x 2 = 20 marks)1. Compare open loop and closed loop system.2. Write the differential equations of the mechanical system shown in fig 2. 3. Calculate the time response of the following system if the input r(t) is unit step 4. Draw the unit step response for an under damped and over damped second order system.

5. What is transient response and steady state response?6. What are frequency domain specifications?

7. State Nyquist stability criterion.

8. Write the Hurwitz determinant for the system given by the characteristic equation 4s3 + 2s2 + 5s + 7 = 0.9. What is meant by sampled data control systems?

10. What are the advantages of state space approach?

PART B (16 x5=80marks)

11.a) (i)Reduce the block diagram and obtain its transfer function y(s)/x(s).

(8)

(ii) Obtain Signal flow graph

(8)

Or11.b) Write the differential equations of motion for the following system

(16)

12.a) (i) For the system shown in the figure, determine the value of b such that the damping ratio is 0.5. Also obtain the value of rise time and maximum overshoot in its step response. (10)

(ii) For a unity feedback control system the open loop transfer function G(s) = 10(s+2) / S2(s+1).

Find Position, velocity, acceleration error constants. (6)

Or12.b) What is meant by steady state error? Determine the steady state error for unit ramp input when k=400 in the figure below. Also determine value of k for which the steady state error to a unit ramp will be 0.02.

(16)

13.a) A servomechanism has an open loop transfer function of G(s) = 75(1+0.2s) / s(s2+16s+100).Draw the Bode plot and determine the phase and gain margin

(16)Or

b) Give polar sketch for the transfer function G(s) = K / s(1+0.5s)(1+4s) Find k when (i)GM=20db,(ii)PM=30deg.

(16)

14.a) Sketch the root loci for the system shown in Figure.

(16)

Or

b)(i) A unity feedback is characterized by the open-loop transfer function, G(s) = k/ (s+2)(s+4)(s2+ 6s+25). Using routh-stability criterion, calculate the range of values of k for system to be stable. Determine the value of K, which will cause sustained oscillations in the closed loop system. Also determine the frequency of sustained oscillations.

(10)(ii) What are the procedures for constructing root locus?

(6)

15.a) (i) Given the state equations below, write the transfer function for this system. Assume the output variable in the transfer function is y(t) which is equal to the state variable x1.

(10)

(ii) Write the following differential equation in state equation format. (6)

Or b) (i) The transfer function of a control system is given by Check for controllability (8) ( ii) A LTI system is characterized by data equation = u. Compute solution of block equation assuming initial condition =.

(8)

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