introduction to PLC

PLC stands for Programmable Logic Controller.

   What is PLC?

1. PLC is just like a control system which takes in the input and produces outputs as per the programs written by the user.
2. most common way in which programs are written in plc is via Ladder diagrams.
3. the most common manufacturers of PLC include Rockwell automation,siemens etc
4. The basic elements of a PLC include input modules or points, a Central Processing Unit (CPU), output modules or points, and a programming device
5. the output or input of plc can be analog or digital.
6. Output modules convert control signals from the CPU into digital or analog values that can be used to control various output devices.
7.  PLC’s input circuit converts the signals provided by various switches and sensors into logic signals that can be understood by the CPU.
8. The PLC's can be divided into five groups:

•  micro PLCs
•  small PLCs
•  medium PLCs
•  large PLCs
•  very large PLCs

9. PLC architecture is modular and flexible, allowing hardware and

software elements to expand as the application requirements change.

10. before PLCs,  control tasks were performed by contactors, control relays and other electromechanical devices.Referred to as hard-wired control.

11. Some of the advantages of PLCs are as follows:

•  Smaller physical size .
•  Easier and faster to make changes.

• Applications can be immediately documented.
• Easy fault finding
• Cost effective
• flexible

12. PLCs have software which convert ladder diagrams into code.

13.plc hardware consists of :

• Power supply module
• Input module
• Output module
• Processor module
• Output relays
• terminal units with fuse

14.A PLC works by continually scanning a program which includes three main steps .(for beginners to understand)