Architecture of PLC- Part 1

    PLC system contains of the following parts

• Power supply
• CPU 
• Input modules
• Output modules
• Programming Device

Power Supply:

 This module supplies power to the CPU, input and output modules. It can be built into the PLC or be an external unit. Common voltage levels required by the PLC (with and without the power supply) are

24Vdc, 120Vac, 220Vac.

CPU (Central Processing Unit):

This module is considered as the brain of the PLC system and where 

ladder logic is stored and processed.

•The memory contains the data and the ladder program.

It contains an “Executive” program that tells the PLC how to:

• Execute the control Instructions

• User’s Program

• Communicate with other devices

• Other PLCs, Programming devices, I/O devices, etc.

• Perform Housekeeping activities

• Diagnostics, etc

This program is stored in “nonvolatile” memory

• Meaning that the program will not be lost if power is removed.