Multiple Choice Questions and Answers on Control Systems
1) Which terminology deals with the excitation or stimulus applied to the system from an external source for the generation of an output?
a. Input signal
b. Output signal
c. Error signal
d. Feedback signal
ANSWER: (a) Input signal
2) Which among the following is not an advantage of an open loop system?
a. Simplicity in construction & design
b. Easy maintenance
c. Rare problems of stability
d. Requirement of system recalibration from time to time
ANSWER: (d) Requirement of system recalibration from time to time
3) Which notation represents the feedback path in closed loop system representation?
a. b(t)
b. c(t)
c. e(t)
d. r(t)
ANSWER: (a) b(t)
4) Which among the following represents an illustration of closed loop system?
a. Automatic washing machine
b. Automatic electric iron
c. Bread toaster
d. Electric hand drier
ANSWER: (b) Automatic electric iron
5) How is an output represented in the control systems?
a. r(t)
b. c(t)
c. x(t)
d. y(t)
ANSWER: (b) c(t)
6) The output is said to be zero state response because ______conditions are made equal to zero.
a. Initial
b. Final
c. Steady state
d. Impulse response
ANSWER: (a) Initial
7) Basically, poles of transfer function are the laplace transform variable values which causes the transfer function to become ___________
a. Zero
b. Unity
c. Infinite
d. Average value
ANSWER:(c) Infinite
8) By equating the denominator of transfer function to zero, which among the following will be obtained?
a. Poles
b. Zeros
c. Both a and b
d. None of the above
ANSWER: (a) Poles
9) The output signal is fed back at the input side from the _________point
a. Summing
b. Differential
c. Take-off
d. All of the above
ANSWER: (c) Take-off
10) In a parallel combination, the direction of flow of signals through blocks in parallel must resemble to the main _______
a. Forward
b. Feedback
c. Opposite
d. Diagonal
ANSWER: (a) Forward
11) While shifting a take-off point after the summing point, which among the following should be added?
a. Summing point in series with take-off point
b. Summing point in parallel with take-off point
c. Block of reciprocal transfer function
d. Block of inverse transfer function
ANSWER: (a) Summing point in series with take-off point
12) Consider the assertions related to block diagram. Which among them represents the precise condition?
A. Block diagram is used for analysis & design of control system.
B. Block diagram also provides the information regarding the physical construction of the system.
a. A is true, B is false
b. A is false, B is true
c. Both A & B are true
d. Both A & B are false
ANSWER: (a) A is true, B is false
13) In a signal flow graph, nodes are represented by small _____
a. Circles
b. Squares
c. Arrows
d. Pointers
ANSWER: (a) Circles
14) According to signal flow graph, which among the following represents the relationship between nodes by drawing a line between them?
a. Branch
b. Self-loop
c. Semi-node
d. Mesh
ANSWER: (a) Branch
15) Which type of node comprises incoming as well as outgoing branches?
a. Source node
b. Sink node
c. Chain node
d. Main node
ANSWER: (c) Chain node
16) Where are the dummy nodes added in the branch with unity gain?
a. At input & output nodes
b. Between chain nodes
c. Both a and b
d. None of the above
ANSWER: (a) At input & output nodes
17) According to the property of impulse test signal, what is the value of an impulse at t = 0?
a. Zero
b. Unity
c. Infinite
d. Unpredictable
ANSWER: (c) Infinite
18) What is the value of parabolic input in Laplace domain?
a. 1
b. A/s
c. A/s2
d. A/s3
ANSWER: (d) A/s3
19) Which among the following is/are an/the illustration/s of a sinusoidal input?
a. Setting the temperature of an air conditioner
b. Input given to an elevator
c. Checking the quality of speakers of music system
d. All of the above
ANSWER: (c) Checking the quality of speakers of music system
20) If a system is subjected to step input, which type of static error coefficient performs the function of controlling steady state error?
a. Position
b. Velocity
c. Acceleration
d. Retardation
ANSWER: (a) Position
21) On the basis of an output response, into how many parts can the s-plane be divided?
a. 2
b. 3
c. 4
d. 6
ANSWER: (b) 3
22) If the complex conjugate poles are located at RHP, what would be the nature of corresponding impulse response?
a. Exponential
b. Damping oscillations
c. Increasing amplifier
d. Constant amplitude oscillations
ANSWER: (c) Increasing amplifier
23) Which among the following are solely responsible in determining the speed of response of control system?
a. Poles
b. Zeros
c. Speed of input
d. All of the above
ANSWER: (a) Poles
24) If a pole is located at s = -5 in left-hand plane (LHP), how will it be represented in Laplace domain?
a. 1/ s + 5
b. 1/ s – 5
c. s/ s + 5
d. s/ s – 5
ANSWER: (a) 1/ s + 5
25) In second order system, which among the following remains independent of gain (k)?
a. Open loop poles
b. Closed loop poles
c. Both a and b
d. None of the above
ANSWER: (a) Open loop poles
26) Root locus specifies the movement of closed loop poles especially when the gain of system ________
a. Remains constant
b. Exhibit variations
c. Gives zero feedback
d. Gives infinite poles
ANSWER:(b) Exhibit variations
27) Which condition is used to verify the existence of a particular point on the root locus?
a. Amplitude
b. Frequency
c. Magnitude
d. Angle
ANSWER: (d) Angle
28) While specifying the angle and magnitude conditions, angles are added whereas magnitudes get ________
a. Subtracted
b. Multiplied
c. Divided
d. All of the above
ANSWER: (b) Multiplied
29) The magnitude & phase relationship between _________input and the steady state output is called as frequency domain.
a. Step
b. Ramp
c. Sinusoidal
d. Parabolic
ANSWER: (c) Sinusoidal
30) If a linear system is subjected to an input r(t) = Asin(ωt), what output will be generated?
a. c(t) = B sin (ωt + Φ)
b. c(t) = B cos (ωt + Φ)
c. c(t) = B tan (ωt + Φ)
d. c(t) = B cot (ωt + Φ)
ANSWER: (a) c(t) = B sin (ωt + Φ)
31) Which unit is adopted for magnitude measurement in Bode plots?
a. Degree
b. Decimal
c. Decibel
d. Deviation
ANSWER: (b) Decibel
32) In an octave frequency band, the ratio of f2 / f1 is equivalent to ________
a. 2
b. 4
c. 8
d. 10
ANSWER: (a) 2
33) In polar plots, what does each and every point represent w.r.t magnitude and angle?
a. Scalar
b. Vector
c. Phasor
d. Differentiator
ANSWER: (c) Phasor
34) In polar plots, if a pole is added at the origin, what would be the value of the magnitude at Ω = 0?
a. Zero
b. Infinity
c. Unity
d. Unpredictable
ANSWER: (b) Infinity
35) Conventional control theory is applicable to ______ systems
a. SISO
b. MIMO
c. Time varying
d. Non-linear
ANSWER: (a) SISO
36) State space analysis is applicable even if the initial conditions are _____
a. Zero
b. Non-zero
c. Equal
d. Not equal
ANSWER: (b) Non-zero
37) If an error signal e(t) of an ON-OFF controller is found to be greater than zero, what would be its output?
a. 10%
b. 50%
c. 80%
d. 100%
ANSWER: (d) 100%
38) Which time is responsible for introducing an error in the temperature regulation of applications associated with ON-OFF controllers?
a. Rise time
b. Dead time
c. Switching time
d. Decay time
ANSWER: (b) Dead time
39) Which controller has the potential to eliminate/overcome the drawback of offset in proportional controllers?
a. P-I
b. P-D
c. Both a and b
d. None of the above
ANSWER: (a) P-I
40) In P-I controller, what does an integral of a function compute?
a. Density of curve
b. Area under the curve
c. Volume over the curve
d. Circumference of curve
ANSWER: (b) Area under the curve
41) Which among the following controls the speed of D.C. motor?
a. Galvanometer
b. Gauss meter
c. Potentiometer
d. Tachometer
ANSWER: (d) Tachometer
42) Into which energy signal does the position sensor convert the measured position of servomotor in servomechanisms?
a. Mechanical
b. Electrical
c. Thermal
d. Light
ANSWER: (b) Electrical
43) What is the value of steady state error in closed loop control systems?
a. Zero
b. Unity
c. Infinity
d. Unpredictable
ANSWER: (a) Zero
44) A good control system should be sensitive to __________
a. Internal disturbances
b. Environmental parameters
c. Parametric variations
d. Input signals (except noise)
ANSWER: (d) Input signals (except noise)
45) For the transfer function given below, where does the zero of the system lie?
G(s) = 5s -1 / s2 + 5s + 4
b. s = -4 & s = -1
c. s = 1/5
d. s = -1/5
ANSWER: (c) s = 1/5
46) If a signal is passed through an integrator, it _____the amplitude of noise signal.
a. Enhances
b. Reduces
c. Stabilizes
d. Factorizes
ANSWER: (b) Reduces
47) Laplace transform of an impulse response is regarded as _____function of the system
a. Analytic
b. Parabolic
c. Transfer
d. Hypothetical
ANSWER: (c) Transfer
48) The fundamental function of a tachometer is the conversion of angular _______ into voltage
a. Velocity
b. Displacement
c. Acceleration
d. Current
ANSWER: (a) Velocity
49) If finite number of blocks are connected in series or cascade configuration, then how are the blocks combined algebraically?
a. By addition
b. By multiplication
c. By differentiation
d. By integration
ANSWER: (b) By multiplication
50) Associative law for summing point is applicable only to those summing points which are __________connected to each other.
a. Directly
b. Indirectly
c. Orthogonally
d. Diagonally
ANSWER: (a) Directly
51) For the elimination of feedback loops, the derivation based on transfer function of ______ loop is used.
a. Open
b. Closed
c. Both a and b
d. None of the above
ANSWER: (b) Closed
52) In block diagram representation, what do the lines connecting the blocks, known as?
a. Branches
b. Nodes
c. Datums
d. Sources
ANSWER:(a) Branches
53) In a signal flow graph method, how is an overall transfer function of a system obtained?
a. Poisson’s equation
b. Block diagram reduction rules
c. Mason’s equation
d. Lagrange’s equation
ANSWER: (c) Mason’s equation
54) While solving signal flow graph using Mason’s gain equation, what does the second letter in two subscript notation of ‘L’ stand for?
a. Serial number of loop
b. Parallel number of loop
c. Number of touching loops
d. Number of non-touching loops
ANSWER: (d) Number of non-touching loops
55) For which systems are the signal flow graphs applicable?
a. Causal
b. Invertible
c. Linear time invariant system
d. Dynamic
ANSWER: (c) Linear time invariant system
56) Two loops are said to be non-touching only if no common ______exists between them.
a. Loop
b. Feedback path
c. Branch
d. Node
ANSWER: (d) Node
57) In time domain system, which response has its existence even after an extinction of transient response?
a. Step response
b. Impulse response
c. Steady state response
d. All of the above
ANSWER: (c) Steady state response
58) Which among the following is represented by a parabolic input signal?
a. Position
b. Force
c. Velocity
d. Acceleration
ANSWER: (d) Acceleration
59) Type 0 systems are unsuitable ___________
a. For ramp inputs
b. If the input is parabolic in nature
c. Both a and b
d. None of the above
ANSWER: (c) Both a and b
60) If a type 0 system is subjected to step input, what is its effect on steady state error?
a. It increases continuously
b. It remains constant
c. It decreases monotonically
d. It gets subjected to another input
ANSWER: (b) It remains constant
61) Consider that the pole is located at origin and its laplace representation is 1/s. What would be the nature of pole response?
a. Rising exponential
b. Decaying exponential
c. Sinusoidal
d. Constant value
ANSWER: (d) Constant value
62) In accordance to relative stability, the settling time exhibits inversely proportional nature to ________parts of roots
a. Real positive
b. Real negative
c. Imaginary positive
d. Imaginary negative
ANSWER: (b) Real negative
63) In Routh array, if zero is found in the first column, then by which term it needs to be replaced?
a. δ
b. η
c. σ
d. ε
ANSWER: (d) ε
64) In a second order system, if the damping ratio is greater than equal to ‘1’, then what would be the nature of roots?
a. Imaginary
b. Real and equal
c. Real but not equal
d. Complex conjugate
ANSWER: (c) Real but not equal
65) For drawing root locus, the angle of asymptote yields the direction along which _________branches approach to infinity.
a. p + z
b. p – z
c. p / z
d. p x z
ANSWER: (b) p – z
66) Which point on root locus specifies the meeting or collision of two poles?
a. Centroid
b. Break away point
c. Stability point
d. Anti-break point
ANSWER: (b) Break away point
67) What should be the nature of root locus about the real axis?
a. Assymetric
b. Symmetric
c. Exponential
d. Decaying
ANSWER: (b) Symmetric
68) If the system is specified by open loop transfer function G(s)H(s) = k / s(s+3) (s + 2), how many root loci proceed to end at infinity?
a. 2
b. 3
c. 5
d. 6
ANSWER: (b) 3
69) Which plots in frequency domain represent the two separate plots of magnitude and phase against frequency in logarithmic value?
a. Polar plots
b. Bode plots
c. Nyquist plots
d. All of the above
ANSWER: (b) Bode plots
70) How is the sinusoidal transfer function obtained from the system transfer function in frequency domain?
a. Replacement of ‘jω’ by ‘s’
b. Replacement of ‘s’ by ‘ω’
c. Replacement of ‘s’ by ‘jω’
d. Replacement of ‘ω’ by ‘s’
ANSWER: (c) Replacement of ‘s’ by ‘jω’
71) According to the principle of log-scales, if the ratio between two points is same, then the two points get ________equally.
a. United
b. Separated
c. Multiplexed
d. Mixed
ANSWER: (b) Separated
72) If a pole is located at origin, how does it get represented on the magnitude plot?
a. -10 log (ω) dB
b. -20 log (ω) dB
c. -40 log (ω) dB
d. -60 log (ω) dB
ANSWER: (b) -20 log (ω) dB
73) Due to an addition of pole at origin, the polar plot gets shifted by ___ at ω = 0?
a. -45°
b. -60°
c. -90°
d. -180°
ANSWER: (c) -90°
74) Consider the system represented by the equation given below. What would be the total phase value at ω = 0?
200/ [s3 (s + 3) (s + 6) (s + 10)]
b. -180°
c. -270°
d. -360°
ANSWER: (c) -270°
75) Which among the following are the interconnected units of state diagram representation?
a. Scalars
b. Adders
c. Integrators
d. All of the above
ANSWER: (d) All of the above
76) Which among the following plays a crucial role in determining the state of dynamic system?
a. State variables
b. State vector
c. State space
d. State scalar
ANSWER: (a) State variables
77) In P-D controller, the derivative action plays a significant role in increasing _______ of response.
a. Time
b. Distance
c. Speed
d. Volume
ANSWER:(c) Speed
78) In addition to storage instructions, PLC controls __________
a. Logic sequence timing
b. Counting
c. Arithmetic operations
d. All of the above
ANSWER: (d) All of the above
79) Which is the correct sequence of operational steps necessary for proper operation of an elevator (lift) control mechanism?
1. Up switch
2. Stop switch
3. Down switch
4. Start switch
a. 1-2-3-4
b. 2-1-4-3
c. 4-2-1-3
d. 3-1-2-4
ANSWER: (c) 4-2-1-3
80) How many digital inputs are present in PLCs?
a. 4
b. 8
c. 16
d. 32
ANSWER: (c) 16
81) Which system exhibits the initiation of corrective action only after the output gets affected?
a. Feed forward
b. Feedback
c. Both a and b
d. None of the above
ANSWER: (b) Feedback
82) What should be the nature of bandwidth for a good control system?
a. Large
b. Small
c. Medium
d. All of the above
ANSWER: (a) Large
83) If an impulse response of a system is e-5t, what would be its transfer function?
a. 1/ s – 5
b. 1/ s + 5
c. (s+1) / (s+5)
d. (s2 – 5s)/ (s-5)
ANSWER: (b) 1/ s + 5
84) Which among the following are the elements of rotational motion?
a. Mass, Spring, Friction
b. Inertia, Damper, Spring
c. Work, Energy, Power
d. Force, Pressure, Viscocity
ANSWER: (b) Inertia, Damper, Spring
85) Match the following notations with their meanings:
A. G(s) ———- 1) Laplace of error signal
B. H(s) ———- 2) Laplace of output signal
C. C(s) ———- 3) Forward transfer function
D. E(s) ———- 4) Feedback transfer function
a. A- 2, B- 3, C- 1, D- 4
b. A- 3, B- 4, C- 2, D- 1
c. A- 2, B- 3, C- 4, D- 1
d. A- 1, B- 2, C- 3, D- 4
ANSWER: (b) A- 3, B- 4, C- 2, D- 1
86) At summing point, more than one signal can be added or _________
a. Subtracted
b. Multiplied
c. Both a and b
d. None of the above
ANSWER: (a) Subtracted
87) The value of variables at each node is _________the algebraic sum of all signals arriving at that node.
a. Less than
b. Equal to
c. Greater than
d. None of the above
ANSWER: (b) Equal to
88) In signal flow graph, the product of all ______gains while going through a forward path is known as ‘Path gain’.
a. Branch
b. Path
c. Node
d. Loop
ANSWER: (a) Branch
89) If a type 1 system is subjected to parabolic input, what will be the value of steady state error?
b. 100
c. Constant k
d. Infinite
ANSWER: (d) Infinite
90) On which factor does the steady state error of the system depend?
a. Order
b. Type
c. Size
d. Prototype
ANSWER: (b) Type
91) Consider the equation S3 + 3s2 + 5s + 2 = 0. How many roots are located in left half of s-plane?
a. Zero
b. Two
c. Three
d. Four
ANSWER: (c) Three
92) If the system is represented by characteristic equation s6 + s4 + s3 + s2 + s + 3 = 0, then the system is_________
a. Stable
b. Unstable
c. Marginally stable
d. Unpredictable
ANSWER: (b) Unstable
93) If poles are added to the system, where will the system tend to shift the root locus?
a. To the left of an imaginary axis
b. To the right of an imaginary axis
c. At the center
d. No shifting takes place
ANSWER: (b) To the right of an imaginary axis
94) For a unity feedback system with G(s) = 10 / s2, what would be the value of centroid?
a. 0
b. 2
c. 5
d. 10
ANSWER: (a) 0
95) If ‘ξ’ approaches to zero, the peak resonance would ________
a. Also be zero
b. Be unity
c. Tend to infinity
d. Become equal to peak overshoot
ANSWER: (c) Tend to infinity
96) At which condition of ‘ξ’, resonant peak does not exist and its maximum value is considered to be unity along with zero resonant frequency?
a. 0 < ξ < 0.707
b. ξ > 0.707
c. ξ = 0
d. ξ = 1
ANSWER: (b) ξ > 0.707
97) If the damping of the system becomes equal to zero, which condition of the resonant frequency is likely to occur?
a. ωr = ωd
b. ωr > ωn
c. ωr < ωn
d. ωr = ωn
ANSWER: (d) ωr = ωn
98) If the resonant peak is estimated to be ‘5’, which among the following would be the correct value of damping?
a. ξ = 0.3
b. ξ = 1
c. ξ = 3.2
d. ξ = 5.55
ANSWER: (a) ξ = 0.3
99) If a system is said to have a damping ξ = 0.5532 with the natural frequency ωn = 2 rad/sec, what will be the value of resonant frequency (ωr)?
a. 1.2456 rad/s
b. 1.7352 rad/s
c. 2.3421 rad/s
d. 3.66 rad/s
ANSWER: (a) 1.2456 rad/s
100) In frequency response, the resonance frequency is basically a measure of _______ of response.
a. Speed
b. Distance
c. Angle
d. Curvature
ANSWER: (a) Speed
101) The frequency at which the phase of the system acquires ____ is known as ‘Phase crossover frequency’.
a. 90°
b. -90°
c. 180°
d. -180°
ANSWER: (d) -180°
102) At which frequency does the magnitude of the system becomes zero dB?
a. Resonant frequency
b. Cut-off frequency
c. Gain crossover frequency
d. Phase crossover frequency
ANSWER: (c) Gain crossover frequency
103) If the phase angle at gain crossover frequency is estimated to be -105°, what will be the value of phase margin of the system?
a. 23°
b. 45°
c. 60°
d. 75°
ANSWER: (d) 75°
104) The system is said to be marginally stable, if gain margin is ______
a. 0
b. 1
c. +∞
d. None of the above
ANSWER: (c) +∞
105) If the constant ‘k’ is positive, then what would be its contribution on the phase plot?
a. 0°
b. 45°
c. 90°
d. 180°
ANSWER: (a) 0°
106) If the unity feedback system is given by the open loop transfer function G(s) = ks2 / [(1 + 0.3s) (1+ 0.05s)], what would be the initial slope of magnitude plot?
a. 20 dB/decade
b. 40 dB/decade
c. 60 dB/decade
d. Unpredictable
ANSWER: (b) 40 dB/decade
107) If the system is represented by G(s) H(s) = k (s+7) / s (s +3) (s + 2), what would be its magnitude at ω = ∞?
a. 0
b. ∞
c. 7/10
d. 21
ANSWER: (a) 0
108) According to Nyquist stability criterion, where should be the position of all zeros of q(s) corresponding to s-plane?
a. On left half
b. At the center
c. On right half
d. Random
ANSWER: (a) On left half
109) Consider a feedback system with gain margin of about 30. At what point does Nyquist plot crosses negative real axis?
a. -3
b. -0.3
c. -30
d. -0.03
ANSWER:(b) -0.3
110) For Nyquist contour, the size of radius is _______
a. 25
b. 0
c. 1
d. ∞
ANSWER:(d) ∞
111) If a Nyquist plot of G (jω) H (jω) for a closed loop system passes through (-2, j0) point in GH plane, what would be the value of gain margin of the system in dB?
a. 0 dB
b. 2.0201 dB
c. 4 dB
d. 6.0205 dB
ANSWER: (d) 6.0205 dB
112) Which principle specifies the relationship between enclosure of poles & zeros by s-plane contour and the encirclement of origin by q(s) plane contour?
a. Argument
b. Agreement
c. Assessment
d. Assortment
ANSWER: (a) Argument
113) Which among the following constitute the state model of a system in addition to state equations?
a. Input equations
b. Output equations
c. State trajectory
d. State vector
ANSWER: (b) Output equations
114) State model representation is possible using _________
a. Physical variables
b. Phase variables
c. Canonical state variables
d. All of the above
ANSWER: (d) All of the above
115) Which mechanism in control engineering implies an ability to measure the state by taking measurements at output?
a. Controllability
b. Observability
c. Differentiability
d. Adaptability
ANSWER: (b) Observability
116) According to the property of state transition method, e0 is equal to _____
a. I
b. A
c. e-At
d. -eAt
ANSWER: (a) I
117) Which among the following is a disadvantage of modern control theory?
a. Implementation of optimal design
b. Transfer function can also be defined for different initial conditions
c. Analysis of all systems take place
d. Necessity of computational work
ANSWER: (d) Necessity of computational work
118) Which among the following is a unique model of a system?
a. Transfer function
b. State variable
c. Both a and b
d. None of the above
ANSWER: (a) Transfer function
119) Which architectural unit/block of PLC decides the sequence of different operations to be executed by means of instructions written in memory?
a. Memory
b. Programming software
c. I/O interface
d. CPU
ANSWER: (d) CPU
120) Which among the following units of PLC is adopted to convey the control plan to CPU?
a. Memory
b. Power supply unit
c. I/O interface
d. Programming software
ANSWER: (d) Programming software
