PSG College of Technology

Department of Instrumentation and Control Systems Engineering

Control Systems

NOTE: Duration:20 minutes

This question paper contains 20 questions Each correct answer carries 1 mark Each wrong answer carries -1 mark

1. The error response of a second order system to a step input is obtained as: E(t) = 1.66 e−s t sin (6t + 37°). The damping ratio is

a)0.4 b)0.5 c)0.8 d)1.0

2. If the characteristic equation of a closed-loop system is S2+2S+2=0, then the system is,

a)overdamped b)critically damped c)underdamped d)undamped

3. The laplace transform of a 4 sec transportation lag system is

a) 1/ s+4 b) e^ 4s c) e^ -4s d) e ^ -s/4

4. The open loop transfer function of a unity negative feedback control system is given by G (s) = K (s + 2) / (s + 1) (s - 7). For K > 6, the stability characteristics of the open-loop and closed loop configurations of the system are respectively

a)stable and stable b)unstable and stable c)stable and unstable d)unstable and unstable

5. As the system type increases ,steady state errora) remains constant b) increases c) decreases d) none of these

6. Mass in force-voltage analogy is analogous to a)inductance b)charge c)current d)resistance

7. The root-locus diagram for a closed loop feedback system is shown in Figure The system is overdamped

a)only if 0<K<1 b)only if 1<K<5 c)only if K>5 d)if 0 £ K < 1 or K > 5

8. A plant transfer function is given as

When the plant operates in a unity feedback configuration, the condition for the stability of the closed loop system isa) KP > KI/2 > 0 b) 2KI > KP > 0 c) 2KI < KP d) 2KI > KP

9. Addition of zeros to the transfer function causes which of the following a)Lead-compensation b)lag-compensation c)Lead-lag compensation d)None of the above

10.Which of the following points is NOT on the root locus of a system with the open loop transfer function

a)s = -j√3 b)s = -1.5 c)s = -3 d)s = -∞11.The steady state error of a stable type 0 unity feedback system, for unit step function is,

a)0 b)1 / (1+Kp ) c) infinity d)1/Kp

12.The state variable representation of a system is given as,

The response y(t) is,

a)sin(t) b)1- et c)1- cos(t) d)0

13.Phase margin of a system is used to specify which of the following ?

a)Frequency response b)Absolute stability c)Relative stability d)Time response

14.The signal flow graph of a system is shown in figure. The transfer function C(S)/R(S) of the system is

15.Which of the following statements is correct for a system with gain margin close to unity or a phase margin close to zero?

a) The system is relatively stable b)The system is highly stable c)The system is highly oscillatory d) None f the above

16.Sparking between the contacts can be reduced by

a) capacitor in series with the contacts b) capacitor in parallel with the contacts c) a reactor in the line d) a resistor in the line

17.The second order system has a transfer function

With r(t) as the unit step function, the response c(t) of the system is represented by,

18.The gain margin and phase margin of a feedback system with,

a) 0 dB, 0° b) , c), 0° d) 88.5 dB,

19.The zero input response of a system given by the state space equation,

20. A double integrator plant,G(S)=K/S2,H(S)=1 is to be compensated to achieve the damping ratio 0.5,and an undamped natural frequency, 5 n rad/s. Which one of the following compensator Gc(S) will be suitable?

ALL THE BEST!!