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PLC Basic


A programmable logic controller, also called a PLC. This computer type device used to control equipment in an industrial facility. PLC provide softwiring advantage. It is one of the most important features of PLCs.
Softwiring makes changes in the control system easily. If you want a device in a PLC system to behave differently all you have to do is change the control program. In a traditional system, for making this type of change you have to change the wiring between the devices physically, which is costly.
Let’s say that two push buttons, PB1 and PB2, are connected to a PLC. Two pilot lights, PL1 and PL2, are also connected to the PLC. The way these devices are connected now pressing push button PB1 turns on
pilot light PL1 and pressing push button PB2 turns on pilot light PL2. Let’s say that you want to change this around so that PB1 controls PL2 and PB2 controls PL1. In a traditional system, you would have to rewire
the circuit so that the wiring from the first push button goes to the second pilot light and vice versa. However, because these devices are connected to a PLC, making this change is as simple as making a small
change in the control program.




What Exactly is a PLC:-

A PLC basically consists of two elements:
• the central processing unit
• the input/output system

The Central Processing Unit:-
The central processing unit(CPU) is the part of a programmable controller that retrieves, decodes, stores, and processes information. It also executes the control program stored in the PLC’s memory. In essence, the CPU is the “brains” of a programmable controller.
CPU has three parts:-
• the processor
• the memory system
• the power supply





The Input/Output System:-
 The input/output (I/O) systemis the section of a PLC to which all of the field devices are connected. The I/O system is what actually physically carries out the control commands from the program stored in the PLC’s memory.
The I/O system consists of two main parts:
• the rack
• I/O modules

This is very basic. I will keep posting advance stuff from basic. Next, I will post about some PLC programing. If you have any question, please let me know.