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

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.

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______.

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.