PLC Programmable Logic Controllers Interview Questions and Answers

Programmable Logic Controllers (PLC) Interview Questions and Answers:

What are different comonents in PLC?

Answer: 1. Input Interface 2. Memory Section 3. Central Processing Unit (CPU) 4. Programmable Language 5. Programming tool 6. An output Interface

Advantages of PLCs than Hard wired Relay?

Answer: PLCs are highly reliable, easily programmable, Small and Inexpensive, PLCs can be designed with the communication capabilities so they can converse with the local or remote computer, They can sustain in robust environment less maintenance.

What is the programmable language used in PLC?

Answer: The general language program consists of Ladder Diagrams. Relay logic control scheme is represented in Ladder diagrams. Alternative languages uses Boolean representation of these control schemes as base of the computer representation.

What does Central Processing Unit (CPU) of PLC consists?

Answer: CPU is the brain of the system and consists of
Microprocessor: To carryout arithematic and logical operations
Memory: The area in the CPU in which the information is stored and reterived
Power Supply: The electrical supply that converts the ac voltage to various DC operating voltages.

What is SCAN in PLC ?

Answer: The sequential operation of the controller that goes through the ladder diagram from top to bottom of the ladder. In this process it updates all the outputs corresponding to the inputs. SCAN takes place from left to right of each rung. Usually SCAN time is in milliseconds and it is a continuous process.


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