PLC (Programmable logic controller) Interview questions


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1.What is PLC?

PLC are solid state members of the computer family using integrated circuit instead of electromechanical devices to implement control functions.

2.What are the two basic sections of PLC?
CPU
The Input/Output interface system

3.What are the three major components of CPU?
Processor
Memory system
System power supply

4.Explain logic functions of “AND” and “OR” gate?

5.Explain logic functions of “NOT” gate?

6.Explain timer instructions in ladder logic programming ?

7.Explain counter instructions in ladder logic plc programming ?

8.Differentiate SCADA and PLC?

9.Common PLC programming languages ?
Ladder logic
Functional Block diagram
Sequential Function Chart

10.How to select a PLC (Selection Criteria ) ?

Cost of Hardware and Software
Reliability Flexibility Scalability
Ease of database configuration
Graphics development
Interlocks and batch processing
Integration of high level application

11.Leading PLC brands?

  1. American

Allen Bradley
Modicon
Texas Instruments
General Electric

  1. European

Siemens
Festo
Telemechanique

3.Japanese

Toshiba
Omron
Fanuc
Mistubishi