Control System Mcqs PDF

Preview

Summary

Control System Mcqs...

Description

CONTROL SYSTEM 1. The constant M circle for M=1 is the a) straight line x=-1/2 b) critical point (-1j0) c) circle with r= 0.33 d) circle with r=0.67 Answer: a Explanation: For M =1 the constant M circle is a straight line at x=-1/2. 2. The polar plot of a transfer function passes through the critical point (1,0). Gain margin is a) Zero b) -1dB c) 1dB d) Infinity Answer: a Explanation: Gain margin of a polar plot passing through the critical point is zero.

8. If a system has an open loop transfer function 1-s / 1+s, then the gain of the system at frequency of 1 rad/s will be a) 1 b) ½ c) Zero d) -1 Answer: d Explanation: The system is all pass system and the gain of the system at frequency of 1 rad/sec. 9. The polar plot of the open loop transfer function of a feedback control system intersects the real axis at -2. The gain margin of the system is a) -5dB b) 0dB c) -6dB d) 40dB Answer: c Explanation: Gain margin of the system is inverse of the intersect on the real axis and calculated in decibels. G(s) = 1+s / s(1+0.5s).

3. Consider the following statements: 1. The effect of feedback is to reduce the system error 2. Feedback increases the gain of the system in one frequency range but decreases in another 3. Feedback can cause a system that is originally stable to become unstable Which of these statements are correct. a) 1,2 and 3 b) 1 and 2 c) 2 and 3 d) 1 and 3 Answer: c Explanation: Feedback can cause the increase in gain and also can cause stable system to become unstable.

10. The corner frequencies are a) 0 and 1 b) 0 and 2 c) 0 and 1 d) 1 and 2 Answer: d Explanation: Corner frequency can be calculated by time constant form of the transfer function and here the corner frequencies are 1 and 2.

4. The open loop transfer function of a system is G(s) H(s)= K / (1+s)(1+2s) (1+3s) The phase cross over frequency ωc is a) V2 b) 1 c) Zero d) V3 Answer: b Explanation: Phase crossover frequency is calculated as by calculating the magnitude of the transfer function and equating it to 1 and the frequency calculated at this magnitude is phase cross over frequency.

12. The gain margin (in dB) of a system having the loop transfer function G(s) H(s) = 2 / s(s+1) is a) 0 b) 3 c) 6 d) 8 Answer: d Explanation: Gain margin of a system is calculated at the phase cross over frequency and expressed in decibels.

5. If the gain of the open-loop system is doubled, the gain margin a) Is not affected b) Gets doubled c) Becomes half d) Becomes one-fourth Answer: a Explanation: If the gain of the open-loop system is doubled, the gain margin gets doubled. 6. The unit circle of the Nyquist plot transforms into 0dB line of the amplitude plot of the Bode diagram at a) 0 frequency b) Low frequency c) High frequency d) Any frequency Answer: d Explanation: The unit circle of the Nyquist plot transforms into 0dB line of the amplitude plot of the Bode diagram at any frequency. 7. Consider the following statements: The gain margin and phase margin of an unstable system may respectively be 1. Positive, positive 2. Positive, negative 3. Negative, positive 4. Negative, negative Of these statements a) 1 and 4 are correct b) 1 and 2 are correct c) 1, 2 and 3 are correct d) 2,3 and 4 are correct Answer: d Explanation: For unstable system the signs of gain margin and phase margin are always different or they can both be negative.

11. For the transfer function G(s) H(s) = 1 / s(s+1) (s+0.5), the phase cross-over frequency is a) 0.5 rad/sec b) 0.707 rad/sec c) 1.732 rad/sec d) 2 rad/sec Answer: b Explanation: Phase cross over frequency is calculated at the point where magnitude of the polar plot is 1.

13. The gain margin for the system with open loop transfer function G(s) H(s) = G(s) =2(1+s) / s2 is a) 8 b) 0 c) 1 d) -8 Answer: 0 Explanation: Gain margin of a system is calculated at the phase cross over frequency and expressed in decibels. 14. Statement 1: In constant M circles, as M increases from 1 to 8 radius of circle increases from 0 to 8 and Centre shifts from (-1,0) to (-8,0) Statement 2: The circle intersects real axis at point (-1/2, 0) a) Statement 1 is TRUE, 2 is FALSE b) Statement 1 is FALSE, 2 is TRUE c) Statement 1 & 2 TRUE d) Statement 1 & 2 FALSE Answer: d Explanation: All the circles pass through the points (0,0) and (-1,0). 15. Assertion (A): Relative stability of the system reduces due to the presence of transportation lag. Reason (R): Transportation lag can be conveniently handled by Bode plot. a) Both A and R are true but R is correct explanation of A b) Both A and R are true but R is correct explanation of A c) A is true but R is false d) A is false but R is true Answer: b Explanation: Transportation lag can be conveniently handled on Bode plot as well without the need to make any approximation. 16. Assertion (A): The phase angle plot in Bode diagram is not affected by the variation in the gain of the system. Reason(R): The variation in the gain of the system has no effect on the phase margin of the system. a) Both A and R are true but R is correct explanation of A b) Both A and R are true but R is correct explanation of A c) A is true but R is false d) A is false but R is true Answer: c Explanation: The variation in the gain of the system has effect on the phase margin but phase plot is not affected.

17. A system has poles at 0.01 Hz, 1 Hz and 80Hz, zeroes at 5Hz, 100Hz and 200Hz. The approximate phase of the system response at 20 Hz is: a) -90° b) 0° c) 90° d) -180° Answer: a Explanation: Pole at 0.01 Hz gives -180° phase. Zero at 5Hz gives 90° phase therefore at 20Hz -90° phase shift is provided.

open loop transfer function c) Resonant frequencies of the second factors d) None of the above Answer: d Explanation: T. F. = Kp (1+Tds) There is only one zero which will give slope of +20dB/decade.

18. The constant M-circle represented by the equation x^2+2.25x+y^2=1.25 has the value of M equal to: a) 1 b) 2 c) 3 d) 4 Answer: c Explanation: Comparing with the M circle equation we have the value of M =3.

26. OLTF contains one zero in right half of s-plane then a) Open loop system is unstable b) Close loop system is unstable c) Close loop system is unstable for higher gain d) Close loop system is stable Answer: c Explanation: OLTF contains one zero in right half of s-plane then Close loop system is unstable for higher gain.

19. What is the value of M for the constant M circle represented by the equation 8x2+18x+8y2+9=0? a) 0.5 b) 2 c) 3 d) 8 Answer: c Explanation: Comparing with the M circle equation we have the value of M =3. 20. The constant N loci represented by the equation x^2+x+y^2=0 is for the value of phase angle equal to: a) -45° b) 0° c) 45° d) 90° Answer: d Explanation: Centre = (-0.5, 0) Centre of N circle is (-1/2, 1/2N) N =tanα α =90°. 21. All the constant N-circles in G planes cross the real axis at the fixed points. Which are these points? a) -1 and origin b) Origin and +1 c) -0.5 and 0.5 d) -1 and +1 Answer: a Explanation: Centre of N circle is (-1/2, 1/2N) N =tanα Constant –N circles always pass through (-1, 0) and (0, 0). 22. Consider the following statements: Nichol’s chart gives information about. i. Closed loop frequency response. ii. The value of the peak magnitude of the closed loop frequency response Mp. iii. The frequency at which Mp occurs. Which of the above statements are correct? a) 2 and 3 b) 1 and 2 c) 1 and 3 d) 1,2 and 3 Answer: d Explanation: Nichol’s chart gives information about closed loop frequency response, value of the peak magnitude of the closed loop frequency response Mp and the frequency at which Mp occurs. 23. Which one of the following statements is correct? Nichol’s chart is useful for the detailed study analysis of: a) Closed loop frequency response b) Open loop frequency response c) Close loop and open loop frequency responses d) None of the above Answer: a Explanation: Nichol’s chart is useful for the detailed study analysis of closed loop frequency response. 24. In a bode magnitude plot, which one of the following slopes would be exhibited at high frequencies by a 4th order all-pole system? a) -80dB/decade b) -40 dB/decade c) 40 dB/decade d) 80 dB/decade Answer: a Explanation: A 4th order all pole system means that the system must be having no zero or s-term in numerator and s4 terms in denominator. One pole exhibits -20dB/decade slope, so 4 pole exhibits a slope of -80 dB /decade. 25. Frequency range of bode magnitude and phases are decided by : a) The lowest and higher important frequencies of dominant factors of the OLTF b) The lowest and highest important frequencies of all the factors of the

27. The critical value of gain for a system is 40 and gain margin is 6dB. The system is operating at a gain of: a) 20 b) 40 c) 80 d) 120 Answer: a Explanation: Gm (dB) = 20logGM GM =2 As we know, GM =K (marginal)/K (desired) K desired =40/2 =20. 28. Nichol’s chart is useful for the detailed study and analysis of: a) Closed loop frequency response b) Open loop frequency response c) Close loop and open loop frequency responses d) open loop and Close loop frequency responses Answer: a Explanation: Nichol’s chart is useful for the detailed study and analysis of closed loop frequency response. 29. The roots of the characteristic equation of the second order system in which real and imaginary part represents the : a) Damped frequency and damping b) Damping and damped frequency c) Natural frequency and damping ratio d) Damping ratio and natural frequency Answer: b Explanation: Real part represents the damping and imaginary part damped frequency. 30. A minimum phase unity feedback system has a bode plot with a constant slope of -20dB/decade for all frequencies. What is the value of the maximum phase margins of the system? a) 0° b) 90° c) -90° d) 180° Answer: b Explanation: For given Bode plot, G(s) H(s) =K/jw As H(s) =1 PM (maximum) =90°. 31. The range of K for the stability of system is 00 b) (1+aTs)/(1+Ts) , a0 c) (1-aTs)/(1+Ts) , a>1 T>0 d) (1±Ts)/(1+Ts) , a0 Answer: a Explanation: For the phase lead controller in which the stability and speed of response is more for the system, the magnitude of the pole must be greater than the magnitude of the zero. 46. If the system matrix of a linear time invariant continuous system is given by Its characteristic equation is given by: a) s2+5s+3=0 b) s2-3s-5=0 c) s2+3s+5=0 d) s2+s+2=0 47. Given a unity feedback control system with G (s) = K/s(s+4), the value of K for which the damping ratio is 0.5. a) 1 b) 16 c) 64 d) 32 Answer: b Explanation: The value is found by using the Routh- Hurwitz criteria and equating one of the row of the Routh-Hurwitz criteria equal to zero and hence finding the value of K. 48. The LVDT is used in the measurement of: a) Displacement b) Acceleration c) Velocity d) Humidity Answer:a Explanation: The LVDT is the linear variable differential transformer and it is used to calculate the displacement with the inductor process. 49. A system with gain margin close to unity and phase margin close to zero is : a) Highly stable b) Oscillatory c) Relatively stable d) Unstable Answer: c Explanation: A system is relative stable not stable if the phase margin is close to zero then the stability is checked by gain margin....