PLC Introduction

What is PLC?

• Definition:-

               "PLC is basically a programmed interface between input devices like Push buttons, Limit switches,etc and final control element like Actuators,Relays,Motors,Solenoid valves and Status indicating output devices like Lamp,Led,Hooters etc."

•   Definition Of PLC given by "NEMA" (National Electrical Manufacturers Association):-

          "PLC is a digital electronics device that uses programmable memory to store instruction and to implement specific function such as logic,sequence,timing,counting and arithmetic operation to control machines and process."

• Types Of PLC :-

          1. Compact PLCs. 
          2. Modular PLCs.

•  PLC Advantage:-

1. Grate life and Reliability.
2. Tremendous Flexibility. 
3. Shorter Project time.
4. Ease of maintenance.
5. Economical.
6. Easier Storage and Documentation.
7. Energy Saving.
8. Required less space.

• Features Of PLC:- 
  

1. Sequential Logic Solver.
2. Bit Operation.
3. Data Transfer.
4. Text handling.
5. PID Calculation.
6. Subroutines.

•  PLC Components/Hardware:-

1. Rack (Rail).
2. Bus Systems.
3. Power Supply.
4. Input Modules.
5. Output Modules.

• PLC Programming Languages:-

1. Ladder Diagram.(Note:- Mostly use every where.)
2. Function Block Diagram.(FBD)
3. Sequential Function Chart.(SFC)
4. Structured Text Language.(ST)

• PLC Selection Criteria:-

1. Inputs and Outputs Requirement.
2. CPU Memory.
3. Compatible Protocol. 
4. Integration Of High-Level Application.
5. Reliability.
6. Flexibility.
7. Spare Parts and Maintenance.
8. Cost of Hardware.
9. Local Support Availability.

• Leading PLC Vendors:-

1. Siemens
2. Allen Bradley.
3. Schneider.
4. Beckhoff.
5. Mitsubishi.
6. Messung.
7. GE-Fanuc.
8. Omron.