APGENCO Placement Paper

APGENCO previous years question paper with answers

1. Electronic control systems have the serious draw?backs of
(a) low reliability (b) operational difficulty (c) temperature sensitiveness (d) all of
above
2. The system whose characteristic equation has the following roots is marginally
stable
(a) ?j, j, ?1,1 (b) ?3,?2,0 (c) ?2+3j, ?2?3j, ?2 (d) ?3,?2,?1
3. A phase log compensation will
(a) improve relative stability
(b)increase the speed of response
(c)increase band?width
(d) increase overshoot
4. For Nyquist plot we use
a. open loop function
b. closed loop function
c. characteristic equation
d. any of the above
5. A system with gain margin close to unity or a phase margin close to zero is
a. highly stable
b. oscillatory
c. relatively stable
d. none of these
6. Root locus diagram exhibits the
a. frequency response of a system
b. poles of the transfer function for a set of parameter values
c. bandwidth of system
d. all of the above
7. Increase in the gain K makes the system
a. more stable
b. unstable
c. none of above
8. The transfer function of a system is used to determine
a. the output for a given input
b. the type of system
c. the input for a given output
d. the steady state gai n
9. In a servo system the voltage induced in the control transformer rotor is the
a. error voltage
b. driving voltage
c. opposing voltage
d. none of these
10. With the feedback system, the transient response
a. decays slowly
b. decays rapidly
c. rises slowly
d. rises quickly
11. An open loop control system has its
(a) control action independent of the output or desired quantity
(b) controlling action, depending upon human judgment
(c) internal system changes automatically taken care of
(d) both (a) and (b)
(e) all (a),(b) and (c)
12. A servo system must have
(a) feedback system
(b) power amplifier to amplify error
(c) capacity to control position or its derivative
(d) all of these
(e) none of these
13. The major disadvantage of a feedback system may be
(a) Inaccuracy
(b) inefficiency
(c) Unreliability
(d) instability
(e) Insensitivity
14. Properties of a transfer function
(a) It is ratio of two polynomials is S and assumes zero initial conditions
(b) It depends on system elements and not input and output of the system
(c) Coefficients of the powers of S in denominator and numerator are all real
constant.
The order of denominator is usually greater than or equal to the order of
numerator
(d) All of these
(e) It is a function which transfer one physical system into another physical
system.
15. The classical analogous of a simple lever is
(a) Capacitor bridge
(b) transformer
(c) mutual inductor
(d) either of these
16. Two blocks G1(s) and G2(s) can be cascaded to get resultant transfer function as
(a) G1(s) + G2(s)
(b) G1(s) / G2(s)
(c) G1(s) G2(s)
(d) 1+G1(s) G2(s)
(e) 1?G1(s)G2(s)
(f) two blocks cannot be cascaded
17. The principles of homogeneity and super position can be applied to
(a) linear time invariant system
(b) non?linear time invariant system
(c) digital control system
(d) both (a) and (b)
18. Pick up the nonlinear system
(a) automatic voltage regulator
(b) d.c. servomotor with high field excitation
(c) temperature control of a furnaces using thermistor
(d) speed control using SCR
(e) all of these
19. Signal flow graph (SFG) is a
(a) polar graph
(b) semi log graph
(c) log log graph
(d) a special type of graph for analyzing modem control system
(e) a topological representation of a set of differential equations
20. Disadvantages of magnetic amplifier
(a) time lag, less flexible, non?sinusoidal waveform
(b) low power consumption and isolation of the active circuit
(c) saturation of the core
(d) all of these
21. Pick up false statement regarding magnetic amplifiers
(a) The gate coil of an ideal magnetic amplifier has either zero or infinite
inductance
(b) Resistance of control and gate winding is very small
(c) Magnetic amplifier gas dropping load characteristics
(d) Magnetic amplifiers are not used to control the speed of d.c. shunt motor
(e) Magnetic amplifiers can be used in automatic control of electric drivers of
higher rating.
22. High power amplification is achieved by using
(a) push pull amplifier
(b) amplidyne
(c) magnetic amplifier
(d) DC amplifier
(e) D.C. generator
23. Pick up false statement regarding servomotors
(a) The d.c. servomotors are lighter than equivalent a.c. servomotors
(b) The d.c. servomotors develops higher starting and reversing torque than
equivalent a.c. servomotor.
(c) A drag cup a.c. servomotor has one windings on stator and other on rotor
(d) Output power of servomotors varies from 1/20 W to 100 W
24. To reduce steady state error
(a) decrease natural frequency
(b) decrease damping
(c) increase damped frequency
(d) increase time constant
(f) increase gain constant of the system
25. A good factor for Mp should be
(a) less than 1
(b) lying between 1.1 and 1.5
(c) more than 2.2
(d) zero
(e) infinity
26. Pick up false statement. Routh?Hurwitz criterion
(a) is used for determining stability of a system
(b) is an algebraic procedure
(c) gives the exact location of roots of the characteristic equation
(d) does not indicate relative degree of stability or instability
27. Which of the following is the time domain method of determining stability of a
control system
(a) Bode plot
(b) Nyquist plot
(c) Nicholos chart
(d) Routh?Hurwitz array
(e) Constant M and (fy) locus
(f) Root locus technique
28. The technique which gives transient response quickly as well as stability
information is
(a) Nyquist plot
(b) Routh?Hurwitz criteria
(c) Bode plot
(d) Root locus plot
(e) Nichols plot
29. The bandwidth can be increased by use of
(a) phase lag network
(b) phase lead network
(c) both (a) and (b) in cascade
(d) both (a) and (b) in parallel
(e) none of these
30. Nyquist plot is drawn on
(a) semi log graph paper
(b) log log graph paper
(c) polar graph paper
(d) centimeter graph paper
31. If the gain margin is positive and the phase margin is negative the system is
(a) stable
(b) unstable
(c) indeterminist
32. The Bode plot is applicable to
(a) all phase network
(b) minimum phase network
(c) maximum phase network
(d) lag lead network
(e) none of these
33. The valid relation between setting time ts and rise time tr is
(a) tr>ts
(b) ts>tr
(c) ts=tr
(d) none of these
34. As a root moves further away from imaginary axis the stability
(a) increases
(b) decreases
(c) not affected
(d) none of these
35. Flat frequency response means that the magnitude ratio of output to input over
the bandwidth is
(a) variable
(b) zero
(c) constant
(d) none of above
36. How many octaves are between 200 Hz and 800 Hz
(a) Two octave
(b) One octave
(c) Four octave
(d) None of above
37. Human system can be considered as
(a) open loop system
(b) close loop system with single feedback
(c) close loop system with multivariable feedback
(d) none of these
38. In a feedback system the transient response
(a) Decays at constant rate
(b) gets magnified
(c) decays slowly
(d) decays more quickly
39. Transfer function of a system is used to calculate
(a) the steady state gain
(b) the main constant
(c) the order of system
(d) the output for any given input
(e) all of the above
40. Transfer function of a system is defined as the ratio of output to input in
(a) Laplace transform
(b) Z?transform
(c) Fourier transform
(d) Simple algebraic form
41. Introduction of feedback decreases the effect of
(a) disturbances
(b) noise signals
(c) error signals
(d) all the above
42. The system response of a system can be best tested with
(a) unit impulse input signal
(b) ramp input signal
(c) sinusoidal input signal
(d) exponentially decaying input signal
43. Which of the following is a closed loop system
(a) electric switch
(b) car starter
(c) de generator
(d) auto?pilot for an aircraft
44. Which of the following is used as an error detector
(a) potentiometer
(b) field controlled ac motor
(c) amplidyne
(d) armature controlled ac motor
45. The break away point of root loci are
(a) open loop poles
(b) closed loop poles
(c) open loop zeros
(d) closed loop zeros
46. Noise in a control system can be kept low by
(a) reducing the bandwidth
(b) attenuating such frequencies at which external signals get coupled into the
system
(c) both (a) and (b)
(d) none of these
47. Main cause of absolute instability in the control system is
(a) parameters of controlling system
(b) parameters of controlled system
(c) parameters of feedback system
(d) error detector where the two signals are compared
48. Basically a controller is
(a) a amplifier
(b) a clipper
(c) a comparator
(d) a summer
49. A system with gain margin close to unity or a phase margin close to zero is
(a) highly stable
(b) highly oscillatory
(c) relatively stable
(d) none of these
50. Which of following elements is not used in an automatic control system
(a) sensor
(b) error detector
(c) oscillator
(d) final control element
51. AC systems are usually preferred to the DC systems in control applications
because
(a) AC systems are cheaper
(b) AC systems are more stable
(c) AC systems have better performance characteristics and smaller in size
(d) all of these
52. A system has the transfer function (1?s)/(1+s); It is known as
(a) low pass system
(b) high pass system
(c) all pass system
(d) none of the above
53. In control systems, excessive bandwidth should be avoided because
(a) noise is proportional to bandwidth
(b) it leads to low relative stability
(c) it leads to slow speed of response
(d) none of these
54. In most systems, an increase in gain leads to
(a) larger damping ratio
(b) smaller damping ratio
(c) constant damping ratio
(d) none of these
55. A step function is applied to the input of a system and output is of the form y = t,
the system is
(a) stable
(b) unstable
(c) not necessarily stable
(d) conditionally stable
56. Which of the following can be magnified by magnetic amplifier
(a) voltage
(b) current
(c) power
(d) none of above
57. The inductance is not used in lag network because of
(a) big size
(b) time delay and hysteresis losses
(c) high reactance
(d) none of these
58. Saturation in a stable control system can cause
(a) conditional stability
(b) over damping
(c) low level oscillations
(d) high level oscillations
59. Excessive noise in control systems can cause
(a) reduction in bandwidth
(b) reduction in gain
(c) saturation in amplifying stages
(d) oscillations
60. The type?0 system has
(a) net pole at the origin
(b) no pole at the origin
(c) simple at one origin
(d) two poles at the origin