[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.

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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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#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

Top 10 PLC MCQ questions asked in previous year paper

Programmable Logic controller Multiple Choice Question

Top 10 PLC Programmable logic controller questions asked in various competitive exam. Please give this exam. This is free mock test and check your score.

First give this exam. If your answer is wrong then check below video for detail description of question

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Series#1 ( Top 10 Questions )

Question 1 The acronym PLC stands for:

  1. Pressure Load Control
  2. Programmable Logic Controller
  3. Pneumatic Logic Capstan
  4. PID Loop Controller
  5. Pressure Loss Chamber

Answer: Programmable Logic Controller

Question 2 Ladder logic programming consists primarily of:

  1. Virtual relay contacts and coils
  2. Logic gate symbols with connecting lines
  3. Function blocks with connecting lines
  4. Text-based code
  5. Hieroglyphics

Answer: Virtual relay contacts and coils

Question 3 In a PLC, the scan time refers to the amount of time in which …..

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

Answer: The entire program takes to execute

Question 4 Identify the problem in this motor control PLC program:

  1. Coil
  2. Start contact
  3. Seal-in contact
  4. Stop contact
  5. Power source

Answer: Seal-in contact

Question 5 The Boolean representation of this PLC program is:

  1. ABC + D
  2. C + (A + B)D
  3. C + D(A + B)
  4. ABC + BD
  5. C(AB + D)

Answer: C(AB + D)

Question 6 The difference between online and offline PLC programming is . . .

  1. Whether the PLC is running or stopped
  2. Whether the programming PC has internet connectivity
  3. The type of programming cable used
  4. Where the edited program resides
  5. The type of programmer used

Answer: Where the edited program resides

Question 7 In PLC programming, a retentive function is one that:

  1. Defaults to the “on” state
  2. Comes last in the program
  3. Defaults to the “off” state
  4. Cannot be edited or deleted
  5. Is not reset after a power cycle

Answer: Is not reset after a power cycle

Question 8 Normally open contacts are open when:

  1. When Input is not energized
  2. When the input is energized
  3. When input is higher than 20 volts
  4. None of these

Answer: When Input is not energized

Question 9 An OR function implemented in ladder logic uses:

  1. Normally-closed contacts in series
  2. Normally-open contacts in series
  3. A single normally-closed contact
  4. Normally-open contacts in parallel
  5. Normally-closed contacts in parallel

Answer: Normally-open contacts in parallel

Question 10 A good application for a timed interrupt in a PLC program would be:

  1. A communications function block
  2. A PID function block
  3. A math function block
  4. A motor start/stop rung
  5. A “watchdog” timer

Answer: A PID function block

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FAQ’s

1. What is PLC ?

PLC stand for “Programmable Logic Controller”. It is a general purpose computer modified specifically to perform control task . It is a hardware device having microprocessor based control system. It is used in industrial automation.

2. What do you mean by PLC scan time?

PLC Scan Time is the time taken by the PLC to read the inputs, solve the Logic, and update the output is called a PLC Scan Time. This time is measured in millisecond .

3. Which is the most popular language in plc programming ?

The most popular language in plc programming is Ladder Logic Diagram.

4. What are the applications of PLC ?

PLC is used in industrial automation. These controllers can automate a specific process, machine function, or even an entire production line.

5. What are components of PLC system ?

There are major 6 components of PLC:
•Processor (CPU)
•Rack/Mounting
•Input Module
•Output Module
•Power Supply
•Programming Device/Unit

6. What is ladder diagram ?

Ladder diagram is the most popular programming language used in Plc programming. Ladder diagrams expresses a program as a series of “coils” and “contacts”, simulating the operation of electromechanical relays.
The advantage of ladder diagram is the familiarity many electricians have with the simple operation of relays.


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