# Control Systems and PLC (CSP)

### Multiple Choice Questions (MCQs)

1   What is the value of Impulse input in Laplace domain?
(A)   1
(B)   A/s
(C)   A/s2
(D)   A/s3

2   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

3   Basically, zeros 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

4   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

5   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

6   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

7   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

8   If a pole is located at s = -1 in left-hand plane (LHP), how will it be represented in Laplace domain?
(A)   1/ s + 1
(B)   1/ s – 1
(C)   s/ s + 1
(D)   s/ s – 1

9   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%

10   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

11   A good control system should be sensitive to __________
(A)   Internal disturbances
(B)   Environmental parameters
(C)   Parametric variations
(D)   Input signals (except noise)

12   For the transfer function given below, where does the zero of the system lie? G(s) = (5s -1) / (s2 + 5s + 4)
(A)   s = -1 & s = -1/4
(B)   s = -4 & s = -1
(C)   s = 1/5
(D)   s = -1/5

13   a signal is passed through an integrator, it _____the amplitude of noise signal.
(A)   Enhances
(B)   Reduces
(C)   Stabilizes
(D)   Factorizes

14   Laplace transform of an impulse response is regarded as _____function of the system
(A)   Analytic
(B)   Parabolic
(C)   Transfer
(D)   Hypothetical

15   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

16   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

17   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

18   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

19   In a second order system, if the damping ratio is equal to ‘0’, then what would be the nature of roots?
(A)   Imaginary
(B)   Real and equal
(C)   Real but not equal
(D)   Complex conjugate

20   In P-D controller, the derivative action plays a significant role in increasing _______ of response.
(A)   Time
(B)   Distance
(C)   Speed
(D)   Volume

21   What should be the nature of bandwidth for a good control system?
(A)   Large
(B)   Small
(C)   Medium
(D)   All of the above

22   If an impulse response of a system is cos6t, what would be its transfer function?
(A)   s/ (s2 –36)
(B)   s/ (s2+36)
(C)   s/ (s+6)
(D)   (s2 – 6s)/ (s-6)

23   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

24   On which factor does the steady state error of the system depend?
(A)   Order
(B)   Type
(C)   Size
(D)   Prototype

25   If the system is represented by characteristic equation s3 + s2 + 3s + 3 = 0, then the system is_________
(A)   Stable
(B)   Unstable
(C)   Marginally stable
(D)   Unpredictable

26   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)   Central Processing Unit (CPU)

27   The acronym PLC stands for:
(A)   Pressure Load Control
(B)   Programmable Logic Controller
(C)   Pneumatic Logic Capstan
(D)   PID Loop Controller

28   Ladder logic programming consists primarily of:
(A)   Virtual relay contacts and coils
(B)   Logic gate symbols with connecting lines
(C)   Function blocks with connecting lines
(D)   Text-based code

29   The Boolean representation of this PLC program is:

(A)   AB’C + D’
(B)   C + (A + B’) D’
(C)   C + D'(A + B’)
(D)   C (AB’ + D’)

30   The difference between online and offline PLC programming is . . .
(A)   whether the PLC is running or stopped
(B)   whether the programming PC has internet connectivity
(C)   the type of programming cable used
(D)   where the edited program resides

31   What is the largest integer number that a PLC counter function can reach if it uses a 16-bit register?
(A)   32,768
(B)   65,535
(C)   32,767
(D)   65,537

32   An OR function implemented in ladder logic uses:
(A)   Normally-closed contacts in series
(B)   Normally-open contacts in series
(C)   Normally-open contacts in parallel
(D)   Normally-closed contacts in parallel

33   An AND function implemented in ladder logic uses:
(A)   Normally-closed contacts in series
(B)   Normally-open contacts in series
(C)   Normally-open contacts in parallel
(D)   Normally-closed contacts in parallel

34   An NOT function implemented in ladder logic uses:
(A)   Normally-closed contacts in series
(B)   Normally-open contacts in series
(C)   A single normally-open contact
(D)   A single normally-closed contact

35   A NAND function implemented in ladder logic uses:
(A)   Normally-closed contacts in series
(B)   Normally-open contacts in series
(C)   Normally-closed contacts in Parallel
(D)   Normally-open contacts in Parallel

36   An NOR function implemented in ladder logic uses:
(A)   Normally-closed contacts in series
(B)   Normally-open contacts in series
(C)   Normally-closed contacts in Parallel
(D)   Normally-open contacts in Parallel

37   The most popular language for PLCs is:
(A)   Ladder diagram
(B)   C++
(C)   OOP+
(D)   VHDL

38   In PLC, generally relays and valves are connected to:
(A)   Input modules
(B)   Output modules
(C)   both of these
(D)   None of the above

39   Normally open contacts are open when:
(A)   When Input is not energized
(B)   When the input is energized
(C)   When input is higher than 20 volts
(D)   None of these

40   PLCs that have a fixed amount of I/O capability built into the unit are known as:
(A)   Rack PLCs
(B)   Modular PLCs
(C)   Fixed or Packed PLCs
(D)   None of these

41   How is the speed of operation of digital controllers to conventional relay system as compared?
(A)   Very slow
(B)   Very fast
(C)   Same
(D)   Almost similar

42   __________ of PLCs can be done in very little time.
(A)   Programming
(B)   Installation
(C)   Commissioning
(D)   All of the above

43   The PLC is used in _______.
(A)   Machine tools
(B)   Automated assembly equipment
(C)   Moulding and extrusion machines
(D)   All of the above

44   Which of the following cannot be an input that is given to the PLC?
(A)   Manual switches
(B)   Relays
(C)   Sensors
(D)   None of the above

45   PLC can be ___________ in plant to change the sequence of operation.
(A)   Only programmed
(B)   Only reprogrammed
(C)   Programmed and reprogrammed
(D)   Able to give a set point

46   The capability of the PLCs for complex operations is ___________ that of convention relay systems
(A)   Poor than
(B)   Excellent than
(C)   As good as
(D)   Unpredictable as

47   When ___________ contacts are actuated, they disrupt the power supply through them.
(A)   Normally open type
(B)   Normally closed type
(C)   Both a and b
(D)   None of the above

48   The type of memory which is fast and temporarily stores the data which are immediately required for use is called as______.
(A)   HDD
(B)   ROM
(C)   RAM
(D)   SSD

49   Which one of the following is not a PLC manufacturer?
(A)   Siemens
(B)   Mitsubishi
(C)   Microsoft
(D)   ABB

50   When a relay is NOT energized:
(A)   There is an electrical path through the NO contacts
(B)   There is an electrical path through the NC contacts
(C)   Neither the NO or the NC contacts have an electrical path
(D)   Both the NO and the NC contacts have an electrical path

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