[Download pdf] Top 20 PLC MCQ – Part -3

plc and scada mcq

Hi All, In this series I explained top 20 objective questions and answer. For more questions of PLC and SCADA MCQ series. Please checkout my all MCQ series on PLC and SCADA. I have created MCQ series on Basic Electronics, Power Electronics, 8051 Microcontroller, 8086 Microprocessor.

#1 PLC and SCADA MCQ Series click here

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#4 PLC and SCADA MCQ Series click here

If you are going to attempt any competitive exam then check your skills here. This is mock test questions which is asked in previous year paper in UPPCL, RSEB, Metro rail corporation and SSC JE.

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Question 1 Which of the following statements about RLL is NOT true?

  • NO contact symbol has two parallel lines to indicate an open contact.
  • RLL stands for Relay Ladder Logic.
  • NC contact symbol has the same two parallel lines with a line across them to indicate closed contacts.
  • The right power rail is positive or the high side of the source, and the left power rail is the power return or ground.

Answer : The right power rail is positive or the high side of the source, and the left power rail is the power return or ground.

Question 2 _____ is a method of entering ladder logic representation.

  • Segment programming
  • TINT
  • Boolean mnemonics
  • All of the above

Answer : Boolean mnemonics

Question 3 When a relay is NOT energized

  • There is an electrical path through the NO contacts
  • There is an electrical path through the NC contacts
  • Neither the NO or the NC contacts have an electrical path
  • Both the NO and the NC contacts have an electrical path

Answer : There is an electrical path through the NC contacts

Question 4 In a current sinking DC input module _____

  • The current flows out of the input field device
  • Requires that a AC sources be used with mechanical switches
  • The current flows out of the input module
  • Currents can flow in either direction at the input module

Answer : The current flows out of the input field device.

Question 5 How is the speed of operation of conventional relay system as compared to digital controllers?

  • Very slow
  • Very fast
  • Same
  • Almost similar

Answer : Very slow.

Question 6 The type of memory which is fast and temporarily stores the data which are immediately required for use is called as______.

  • HDD
  • ROM
  • RAM
  • SSD

Answer : RAM.

Question 7 _____ of PLCs can be done in very little time.

  • Programming
  • Installation
  • Commissioning
  • All of the above

Answer : All of the above

Question 8 How is the noise immunity of PLCs to electrical noises as compared to that of conventional relay controllers?

  • Poor
  • Excellent
  • As good as noise immunity of conventional relay controllers
  • Unpredictable

Answer : Poor

Question 9 _____ of PLCs can be done in very little time

  • Programming
  • Installation
  • Maintenance
  • All of the above

Answer : All of the above

Question 10 Which of the following statements is correct?

  • Ladder logic is a PLC graphical programming technique introduced in the last 10 years.
  • Ladder logic program is hard to analyze because it is totally different when compared with the equivalent relay logic solution.
  • The number of ladder logic virtual relays and input and output instructions is limited only by memory size.
  • The number of contacts for a mechanical relay is limited to number of coils on the relay.

Answer : The number of ladder logic virtual relays and input and output instructions is limited only by memory size.

Question 11 PLC can be _____ in plant to change the sequence of operation.

  • Only programmed
  • Only reprogrammed
  • Programmed and reprogrammed
  • Able to give a set point

Answer : Programmed and reprogrammed.

Question 12 The PLC is used in _______.

  • Machine tools
  • Automated assembly equipment
  • Molding and extrusion machines
  • All of the above

Answer : All of the above.

Question 13 Which of the following can be the output of PLC?

  1. Relay coils
  2. Solenoids
  3. Indicators
  4. Motors
  5. Lamps
  6. Alarms

Select correct option

  • Only (1), (2), (3) and (4)
  • Only (3), (4), (5) and (6)
  • Only (1), (2), (3) and (5)
  • All the (1), (2), (3), (4), (5), and (6)

Answer : All the (1), (2), (3), (4), (5), and (6)

Question14 Instructions available in PLCs can be grouped in two categories: ________and ________ instructions.

  • basic ladder _ enhanced ladder
  • basic ladder and simple ladder
  • Enhanced ladder _relational ladder

Answer : basic ladder _ enhanced ladder

Question15 What one item in the output module circuit above should be changed to make it correct.

  • The battery polarity
  • Output module should be sourcing
  • Field device should be sinking
  • Current flow direction

Answer : Current flow direction

Question 16 Which of the following cannot be an input that is given to the PLC?

  • Manual switches
  • Relays
  • Sensors
  • None of the above

Answer : None of the above

Question 17 An AND function implemented in ladder logic uses

  • Normally-closed contacts in series
  • Normally-open contacts in series
  • A single normally-closed contact
  • Normally-open contacts in parallel

Answer : Normally-open contacts in series

Question 18 Ladder contacts can be programmed in

  • series-parallel
  • series or parallel
  • a and b both true
  • All of the above

Answer : a and b both true

Question 19 PLC instructions ___________.

  • Uses the same symbols as relay logic.
  • were copied using the original relay instructions
  • Were added to the original relay instructions to make PLCs more powerful.

Answer : Were added to the original relay instructions to make PLCs more powerful.

Question 20 The L2 rail side of an electromechanical circuit is represented by _____________.

  • The left side of the rail
  • The right side of the ladder rung.
  • sub-script lettering with arrows

Answer : The right side of the ladder rung.


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#4 Top 50 PLC and SCADA MCQ

Important 50 Multiple Choice Question based on PLC and SCADA


Question 1: What is the full form of SCADA?

  • Supervisory Control and Document Acquisition
  • Supervisory Control and Data Acquisition
  • Supervisory Column and Data Assessment
  • Supervisory Column and Data Assessment

Answer: Supervisory Control and Data Acquisition

Question 2: DCS is a ______

  • Distributed Control System
  • Data Control System
  • Data Column System
  • Distributed Column System

Answer: Distributed Control System

Question 3 The control in SCADA is _____________

  • Online control
  • Direct control
  • Supervisory control
  • Automatic control

Answer: Supervisory control

Question 4 What is SCADA?

  • Software
  • Process
  • System
  • Hardware

Answer: Process

Question 5 Which of the following is not the component of a SCADA system?

  • Database server
  • I/O system
  • PLC controller
  • Sparger controller

Answer: Sparger controller

Question 6 When did the SCADA start?

  • 1980s
  • 1990s
  • 1970s
  • 1960s

Answer:1960s

Question 7 When did Windows become the world standard operating system?

  • 1980s
  • 1990s
  • 1970s
  • 1960s

Answer: 1990s

Question 8 How many levels are present in a complex SCADA system?

  • 3 – levels
  • 5 – levels
  • 4 – levels
  • 6 – levels

Answer: 4 – levels

Question 9 What is the full form of RAID

  • Redundant Array of Independent Drives
  • Redundant Array of Inexpensive Disks
  • Redundant Array of Independent Disks
  • All of the above

Answer: All of the above

Question 10 Which of the following is used for centralized network databases?

  • RAID 2
  • RAID 5
  • RAID 1
  • RAID 2

Answer: RAID 5

Question 11 Which of the following is the heart of a SCADA system?

  • PLC
  • HMI
  • Alarm task
  • I/O task

Answer: I/O task

Question 12 Which of the following is an example of the SCADA system?

  • Emerson Delta V
  • Honeywell Plant Scape
  • Yokogawa CENTUM
  • Power Studio Deluxe

Answer: Power Studio Deluxe

Question 13 What does NC stands for?

  • New Configuration
  • Normally Close
  • Normal Classes
  • Never Closing

Answer: Normally Close

Question 14 What is nominal DC voltage given to PLC?

  • +10V
  • +24V
  • +5V
  • +12V

Answer: +5V

Question 15 In which of the following is a PLC Programming tool.

  • RS Logix 500
  • RS view 32
  • Keil u vision
  • Core Vision AVR

Answer: RS Logix 500

Question 16 Among following which one is a PLC Programming Language

  • Assembly
  • Ladder Logic
  • Java
  • HTML

Answer: Ladder Logic

Question 17 In which of the following is the SCADA Software?

  • OrCAD
  • RS View32
  • Keil u vision
  • Porteous

Answer: RS View32

Question 18 Ladder logic programming consists primarily of:

  • Virtual relay contacts and coils
  • Logic gate symbols with connecting lines
  • Function blocks with connecting lines
  • Text-based code
  • Hieroglyphics

Answer: Virtual relay contacts and coils

Question 19 Examine-on instruction in PLC language is symbolically represented by what shape?

  • -] [-
  • -( )-
  • -]/[-
  • None of these

Answer: -] [-

Question 20 The symbol -(L)- represent what instruction in the PLC language?

  • OUT output unlatch instruction.
  • OTL output latch instruction
  • Examine off instruction.
  • Output energize instruction

Answer: OTL output latch instruction

Question 21 In a PLC, the scan time refers to the amount of time in which …..

  • The technician enters the program
  • Timers and counters are indexed by
  • One “rung” of ladder logic takes to complete
  • The entire program takes to execute
  • Transmitted data communications must finish

Answer: The entire program takes to execute

Question 22 The Boolean representation of this PLC program is:

  • ABC + D
  • C + (A + B)D
  • C + D(A + B)
  • ABC + BD
  • C(AB + D)

Answer: C(AB + D)

Question 23 What is the color used for NO type switches?

  • Red
  • Green
  • non of the above

Answer: non of the above

Question 24 To reset the time for a PLC what condition must be true?

  • Reset rung of TON must be true.
  • Reset rung of TON must be false.
  • RST instruction with timer address must be true.
  • RST instruction with associated timer address must be false

Answer: RST instruction with timer address must be true.

Question 25 The below rung would represent what Boolean equation?

  • X • Y = Z
  • X + Y = Z
  • X • Y’ = Z
  • None of the above.

Answer: X • Y’ = Z

Question 26 To increase the number of inputs and outputs of the PLC, one can use expansion modules.

  • True.
  • False.
  • None of the above.

Answer: True.

Question 27 Solenoids, lamps, motors are connected to:

  • Analog output.
  • Digital output.
  • Analog input.
  • Digital input

Answer: Digital output.

Question 28 The _____ is moved toward the relay electromagnet when the relay is on.

  • Armature
  • Coil
  • NO contact
  • NC contact

Answer: Armature

Question 29 In a current sinking DC input module _____

  • The current flows out of the input field device
  • Requires that a AC sources be used with mechanical switches
  • The current flows out of the input module
  • Currents can flow in either direction at the input module

Answer: The current flows out of the input field device

Question 30 AC output field devices can interface to _____

  • AC output modules
  • Relay output modules
  • Both a and b
  • Neither a or b

Answer: Both a and b

Question 31 The difference between online and offline PLC programming is . . .

  • Whether the PLC is running or stopped
  • Whether the programming PC has internet connectivity
  • The type of programming cable used
  • Where the edited program resides
  • The type of programmer used

Answer: Where the edited program resides

Question 32 In PLC programming, a retentive function is one that:

  • Defaults to the “on” state
  • Comes last in the program
  • Defaults to the “off” state
  • Cannot be edited or deleted
  • Is not reset after a power cycle

Answer: Is not reset after a power cycle

Question 33 Normally open contacts are open when:

  • When Input is not energized
  • When the input is energized
  • When input is higher than 20 volts
  • None of these

Answer: When Input is not energized

Question 34 What is the largest integer number that a PLC counter function can reach if it uses a 16 bit register?

  • 32,768
  • 65,535
  • 65,536
  • 65,537
  • 32,767

Answer: 65,535

Question 35 An NOR function implemented in ladder logic uses:

  • Normally-closed contacts in series
  • Normally-open contacts in series
  • A single normally-closed contact
  • Normally-open contacts in parallel
  • Normally-closed contacts in parallel

Answer: Normally-closed contacts in series

Question 36 Which of the following instruction enables a jump to a subroutine?

  • JMP
  • SBR
  • RET
  • None of the above

Answer: JMP

Question 37 What are the features of SCADA?

  • Control feature using a graphical representation
  • Alarm Handling
  • Security Management
  • All of the above

Answer: All of the above

Question 38 Leading SCADA providers companies are.

  • Siemens WinCC
  • Microsoft
  • TCS
  • All of the above

Answer: Siemens WinCC

Question 39 What is Scripts in SCADA?

  • Scripts are basically a form
  • Scripts are basically a function
  • Scripts are basically a facility
  • Scripts are basically a favorite

Answer: Scripts are basically a function

Question 40 What is CIMPLICITY?

  • SCADA package
  • SCADA hardware
  • SCADA software
  • SCADA handler

Answer: SCADA package

Question 41 A good application for a timed interrupt in a PLC program would be:

  • A communications function block
  • A PID function block
  • A math function block
  • A motor start/stop rung
  • A “watchdog” timer

Answer: A PID function block

Question 42 What is the full form of RTU ?

  • Remote Terminate Unit
  • Remote Terminal Unit
  • Remote Translation Unit
  • Remote Transfer Unit

Answer: Remote Terminal Unit

Question 43 What is the full form DDE?

  • Dynamic Data Exchange
  • Data Dynamic Exchange
  • Domain Data Exchange
  • Different Data Exchange

Answer: Dynamic Data Exchange

Question 44 What is the difference between SCADA and HMI.

  • Both are same
  • HMI is not related with SCADA
  • HMI can be a part of SCADA but SCADA can’t be a part of HMI.
  • SCADA is a part of HMI

Answer: HMI can be a part of SCADA but SCADA can’t be a part of HMI.

Question 45 What are the differences between PLC and SCADA?

  • PLC is a hardware part while SCADA is a software part.
  • PLC is a  software  part while SCADA is a hardware part.
  • Both are hardware unit
  • Both are software

Answer: PLC is a hardware part while SCADA is a software part.

Question 46 A PLC consists of

  • Processor Unit
  • Program Memory
  • Input/output Section
  • Display Device
  • All of the above

Answer: All of the above

Question 47 An OR function implemented in ladder logic uses:

  • Normally-closed contacts in series
  • Normally-open contacts in series
  • A single normally-closed contact
  • Normally-open contacts in parallel
  • Normally-closed contacts in parallel

Answer: Normally-open contacts in parallel

Question 48 What is the full form of NEMA ?

National Electronics Manufacturing Association
National Electrical Manufacturing Association 
National Electrotechnical Manufacturing Association 
National Electromechanical Manufacturing Association 

Answer: National Electrical Manufacturing Association 

Question 49 Which of the following is not element of SCADA:

  • SCADA Communication
  • Mono Terminal Units
  • PLCs
  • RTUs

Answer: Mono Terminal Units

Question 50 Identify the problem in this motor control PLC program:

  • Coil
  • Start contact
  • Seal-in contact
  • Stop contact
  • Power source

Answer: Seal-in contact


#2 PLC MCQ

Top 10 Multiple choice questions on Programmable logic controller


Question 1: The PLC was invented by.

  • Bill Gates
  • Dick Morley
  • Bill Landis
  • Tod Cunningham

Answer: Dick Morley

Question 2: The first company to build PLCs was.

  • General Motors
  • Allen Bradley
  • Square D
  • Modicon

Answer: Modicon

Question 3: Which part of plc monitors the inputs and makes decisions in a PLC.

  • Sensor
  • CPU
  • Input Module
  • Output Module

Answer: CPU

Question 4: One of the following is an input device.

  • Motor
  • Light
  • Valve
  • Sensor

Answer: Sensor

Question 5: Which one of the following is not a PLC manufacturer.

  • Siemens
  • Mitsubishi
  • Microsoft
  • ABB

Answer: Microsoft

Question 6: Solenoids, lamps, motors are connected to:

  • Analog output
  • Digital output
  • Analog input
  • Digital input

Answer: Digital output

Question 7: In a PLC “I” is used for output and “Q” is used for input.

  • True
  • False
  • None of the above

Answer: False

Question 8: To increase the number of inputs and outputs of the PLC, one can use expansion modules.

  • True
  • False
  • None of the above

Answer: True

Question 9: An example of discrete (digital) control is:

  • Varying the volume of a music system
  • Turning a lamp ON or OFF
  • Varying the brightness of a lamp
  • Controlling the speed of a fan

Answer: Turning a lamp ON or OFF

Question 10: Which of the following statements is NOT correct?

  • The status of each input can be checked from one location and outputs can be forced on and off.
  • All symbols in the RLL represent actual components and contacts present in the control system.
  • PLCs are not as reliable as electromechanical relays in RLL.
  • Input (-| |-) and output (- ( ) -) instruction symbols in the ladder logic represent only data values stored in PLC memory.

Answer: PLCs are not as reliable as electromechanical relays in RLL.

#4 PLC MCQ

Programmable Logic controller

Multiple choice questions

Question 1: 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

Answer: RAM

Question 2: 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. 65,536
d. 65,537
e. 32,767

Answer: 65,535

Question 3: How is the speed of operation of conventional relay system as compared to digital controllers?

a. Very slow
b. Very fast
c. Same
d. Almost similar

Answer: Very slow

Question 4: The PLC is used in _______.

a. Machine tools
b. Automated assembly equipment
c. Moulding and extrusion machines
d. All of the above

Answer: All of the above

Question 5: 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

Answer: programmed and reprogrammed

Question 6: __________ of PLCs can be done in very little time.

a. Programming
b. Installation
c. Commissioning
d. All of the above

Answer: All of the above

Question 7: How is the noise immunity of PLCs to electrical noises as compared to that of conventional relay controllers?

a. poor
b. excellent
c. as good as noise immunity of conventional relay controllers
d. unpredictable

Answer: Poor

Question 8: The most popular language for PLCs is:

a. Ladder diagram
b. C++
c. OOP+
d. VHDL

Answer: Ladder diagram

Question 9: An AND function implemented in ladder logic uses:

a. Normally-closed contacts in series
b. Normally-open contacts in series
c. A single normally-closed contact
d. Normally-open contacts in parallel
e. Normally-closed contacts in parallel

Answer: Normally-open contact in series

Question 10: The PLC Can be categorized according to the

a. Power rating of the I/O module
b. Cost of the I/O module
c. Current rating of the I/O module
d. Number of I/O point

Answer: Number of I/O point