Monday, 14 July 2014

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.

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