Sunday, April 25, 2010
BSNL TTA EXAM Control Systems
BSNL TTA EXAM Control Systems
1. 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)

2. 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

3. The major disadvantage of a feedback system may be
 Inaccuracy
(b) inefficiency
(c) Unreliability
(d) instability
(e) Insensitivity

4. 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.

5. The classical analogous of a simple lever is
(a) Capacitor bridge
(b) transformer
(c) mutual inductor
(d) either of these

6. 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 cascade

7. The principles of homogeneity and super position can be
applied to
 linear time invariant system
(b) non-linear time invariant system
(c) digital control system
(d) both (a) and (b)

8. 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

9. 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

10. 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
11. 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.
12. High power amplification is achieved by using
(a) push pull amplifier
(b) amplidyne
(c) magnetic amplifier
(d) DC amplifier
(e) D.C. generator
13. 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
14. 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
15. 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
16. 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
17. 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
18. 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
19. 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
20. Nyquist plot is drawn on
(a) semi log graph paper
(b) log log graph paper
(c) polar graph paper
(d) centimeter graph paper
21. If the gain margin is positive and the phase margin is
negative the system is
(a) stable
(b) unstable
(c) indeterminist
22. 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
23. 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
24. As a root moves further away from imaginary axis the
stability
(a) increases
(b) decreases
(c) not affected
(d) none of these
25. 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
26. How many octaves are between 200 Hz and 800 Hz
(a) Two octave
(b) One octave
(c) Four octave
(d) None of above
27. 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
28. In a feedback system the transient response
(a) Decays at constant rate
(b) gets magnified
(c) decays slowly
(d) decays more quickly
29. 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
30. 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
31. Introduction of feedback decreases the effect of
(a) disturbances
(b) noise signals
(c) error signals
(d) all the above
32. 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
33. Which of the following is a closed loop system
(a) electric switch
(b) car starter
(c) de generator
(d) auto-pilot for an aircraft
34. Which of the following is used as an error detector
(a) potentiometer
(b) field controlled ac motor
(c) amplidyne
(d) armature controlled ac motor
35. The break away point of root loci are
(a) open loop poles
(b) closed loop poles
(c) open loop zeros
(d) closed loop zeros
36. 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
37. 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
38. Basically a controller is
(a) a amplifier
(b) a clipper
(c) a comparator
(d) a summer
39. 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
40. Which of following elements is not used in an automatic
control system
(a) sensor
(b) error detector
(c) oscillator
(d) final control element
41. 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
42. 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
43. 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
44. 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
45. 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
46. Which of the following can be magnified by magnetic
amplifier
(a) voltage
(b) current
(c) power
(d) none of above
47. 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
48. Saturation in a stable control system can cause
(a) conditional stability
(b) over damping
(c) low level oscillations
(d) high level oscillations
49. Excessive noise in control systems can cause
(a) reduction in bandwidth
(b) reduction in gain
(c) saturation in amplifying stages