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# 300+ TOP AUTOMATIC CONTROL SYSTEMS Questions and Answers pdf

## AUTOMATIC CONTROL SYSTEMS Questions and Answers :-

1. Which of the following can be used as a rotating amplifier in a control system?

1.Amplidyne
2.Separately excited dc generator
3.Synchro
4.Self excited dc generator

Select the answer from the following codes:

A. 3 and 4
B. 1 and 2
C. 1, 2 and 3
D. all

A. speeds up the transient response
B. increases the stability margin
C. increases the stability margin and speeds up the transient-response.
D. none of the above.

3. The effect of adding poles and zeros can be determined quickly by

A. Nichols chart
B. Nyquist plot
C. Bode plot
D. Root locus

4. In force current analogue, mechanical mobility is analogous to

A. impedance Z
C. reactance X
D. conductance G

5. If any term in the first column of a Routh array becomes zero, then

A. Routh criterion cannot be used to determine stability
B. Routh criterion can be used by substituting a small positive number for zero and completing the array
C. Routh criterion can be used by substituting a big positive number for zero and completing the array
D. Routh criterion can be used by substituting a small negative number for zero and completing the array

6. Which of the following features is not associated with Nichols chart?

A. (0 dB, -180°) point on Nichols chart represent critical Point (-1, 0)
B. It is symmetric about -180°
C. M loci are centred about (0 dB, -180°) point
D. The frequency at intersection of G(j?) locus and M = +3 dB locus gives bandwidth of closed loop system

7. A system is highly oscillatory if

A. gain margin is high
B. gain margin is close to 1
C. gain margin is close to 1 or phase margin is zero
D. gain margin is high and phase margin is 180°

8. Which of the following is correct?

A. Speed torque characteristics of permanent magnet dc servomotor is more flat than that of wound field dc servomotor
B. Speed torque characteristics of wound field dc servo- motor is more flat than that of permanent magnet dc servo motor
C. Speed torque characteristics of wound field and permanent magnet dc servomotor are equally flat
D. None of the above

9. A conditionally stable system is stable for the value of gain between two critical values. It is unstable if

A. the gain is increased beyond upper critical value
B. the gain is decreased below lower critical value
C. both (a) and (b)
D. none of the above

10. Transport lag usually exists in

A. thermal systems
B. hydraulic systems and thermal systems
C. pneumatic systems
D. thermal, hydraulic and pneumatic systems

11. Which of the following can act as error detecting devices

1.a pair of potentiometers
2.a pair of synchros
3.a differential transformer
5.a control transformer

Select the answer using the following codes:

A. 1, 2, 5
B. 2, 3, 4, 5
C. 1, 3, 4, 5
D. 1, 2, 3, 4

12. For type 1 system the velocity lag error is

A. inversely proportional to bandwidth of system
B. directly proportional to gain constant
C. inversely proportional to gain constant
D. independent of gain constant

13. Nyquist stability criterion uses open loop frequency response characteristics.

A. True
B. False

14. Integral control action

A. removes offset
B. may lead to oscillatory response
C. both (a) and (b)
D. neither (a) nor (b)

15. The sensor generally used in incremental optical encoder is

A. LED
B. LCD
C. photodiode
D. either (a) or (b)

16. Robotic manipulator arms mostly use

A. hydraulic actuator
B. pneumatic actuator
C. electric motor actuator
D. none of the above

17. Lag compensation permits a high gain at low frequencies.

A. True
B. False

18. If the poles lie in second quadrant, damping ratio is

A. 1
B. less than 1
C. zero
D. more than 1

19. Which of the following is used to obtain output position in a position control system?

A. Strain gauge
C. Synchro
D. Thermistor

20. DC tachogenerator can be used in

A. speed control system
B. position control system
C. both (a) and (b)
D. neither (a) nor (b)

21. For a stable system having two or more gain crossover frequencies the phase margin is measured at the highest crossover frequency.

A. True
B. False

22. In a two phasor servomotor, the direction of rotation of the rotating field depends on

A. magnitudes of voltages applied to the two stator windings
B. phase relation of voltages applied to the two stator windings
C. both magnitude and phase relationship of voltages applied to the two stator windings
D. none of the above

23. Gain margin and phase margin can be determined from Bode plots as well as Nyquist plot.

A. True
B. False

24. The permanent magnet field system of brushless dc servo- motor is generally on

A. stator
B. rotor
C. partly on stator and partly on rotor
D. either (a) or (b)

25. For any transfer function, the constant phase angle loci are

A. a family of circles
B. a family of straight lines
C. either (a) or (b)
D. neither (a) nor (b)

### AUTOMATIC CONTROL SYSTEMS Questions with Answers

26. In force current analogy, displacement x is analogous to

A. charge
C. electrostatic energy
D. voltage

27. In Bode plots the frequency at which two asymptotes meet is called corner frequency.

A. True
B. False

28. In Bode plots, frequency is plotted on log scale.

A. True
B. False

29. Nichol’s chart is symmetric about – 180° axis.

A. True
B. False

30. If poles lie in first quadrant, damping ratio is

A. 1
B. more than 1
C. less than 1
D. zero

31. Which control action can never be used alone?

A. Proportional
B. Derivative
C. Integral
D. Both (b) and (c)

32. In a simple on-off controller with differential gap, the magnitude of differential gap determines

A. the level of accuracy
B. the life of controller
C. both (a) and (b)
D. neither (a) nor (b)

33. Which dc servomotor requires strongest permanent magnet?

A. Slotted armature
B. Surface wound armature
C. Surface wound with stationary rotor
D. Either (a) or (b)

34. Nichols chart consists of

A. constant magnitude loci
B. constant phase angle loci
C. magnitude and phase angle loci in log-magnitude versus phase diagram
D. none of the above

35. Consider the following statements about root locus

1.The intersection of root locus branches with the imaginary axis can be determined by the use of Routh criterion
2.Segments of real axis having an odd number of real axis open loop poles plus zeros to their right are not parts of root locus
3.The number of root locus branches terminating on infinity is always zero

Which of the above statements are correct?

A. 1, 2 and 3
B. 1 and 2 only
C. 1 only
D. 2 and 3 only

36. The poles with greater displacement from the real axis correspond to

A. higher frequencies of oscillations
B. stable response
C. lower frequencies of oscillations
D. unbounded output

37. Which of the following is open loop system?

A. Wind screen wiper
B. Aqualing
C. Respiratory system of animal
D. System for controlling antirocket missiles

38. Consider the following statements

1.The effect of feedback is to reduce system error
2.Feedback increases the system gain at one frequency but reduces the system gain as another frequency
3.Feedback can cause an originally stable system to become unstable

Which of the above statements are correct?

A. 1, 2, 3
B. 1, 2
C. 2, 3
D. 1, 3

39. M circles are symmetrical with respect to

A. real and imaginary axis
B. M = 1 straight line and real axis
C. M = 1 straight line and imaginary axis
D. M = 1 straight line

40. A lag compensator

A. speeds up the transient response of the system
B. improves steady state behaviour of the system
C. improves steady state behaviour and speeds up the transient response of the system
D. improves steady state behaviour and preserves the transient response of the system

41. In root locus analysis the breakaway and break in points

A. lie on the real axis
B. either lie on the real axis or occur in complex conjugate pairs
C. always occur in complex conjugate pairs
D. none of the above

42. In control systems the output of sensor usually, is

A. analog electrical signal
B. digital electrical signal
C. mechanical signal
D. analog or digital electrical signal

43. Magnetic amplifier is used for

A. voltage amplification
B. power amplification
C. current amplification
D. frequency amplification

44. Temperature is analogous to

A. voltage
B. flux
C. charge
D. none of the above

45. The relative stability of a system is given by

A. gain margin alone
B. phase margin alone
C. both phase and gain margins
D. either (a) or (b)

46. Bandwidth is proportional to speed of response.

A. True
B. False

47. The complicated shapes in the polar plots are only due to time constants in the numerator of transfer functions.

A. True
B. False

48. The distance of poles from origin depends on

A. undamped natural frequency
B. damping ratio
C. both (a) and (b)
D. neither (a) nor (b)

49. In the field controlled motor the entire damping comes from

A. armature resistance
B. back emf
D. field resistance