What is PLC?

Hello, my Internet Friends my name is Akash Mishra and today we are going to Understand what is PLC in most easy in (PURE ENGLISH😜) way.

The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires.

To Understand PLC lets take a simple example(Don't Worry I said SIMPLE😜). Consider you have one switch and one light bulb, you can on and off light bulb using that switch. beyond that, you don't have any control.

Bulb and Switch

now if your BOSS comes and say.

BOSS: Hey, I want That Bulb 30 Seconds ON and 30 Second OFF till 5 Hour

Now you Can't Toggle that switch for 5 hours. (You can but you will look Fool)

it's you without PLC

So here PLC Saves the day Now consider the same device with a PLC in the middle.  The switch is fed as an input into the PLC and the light is controlled by a PLC output.  by Implementing a delay in this system is easy since all that needs to be changed is the program in the PLC to use a delay timer.

Switch and bulb with PLC

Now let PLC do its work and you.......

Free Worker After PLC installation

So a programmable logic controller(PLC) is a specialized computer used to control machines and processes.

PLCs can perform

• relay-switching tasks.
• conduct counting, calculation, and comparison of analog process values.
• responds to the changes in process parameters within fractions of seconds.
• improve the overall control system reliability.

And PLCs is cost-effective for controlling complex systems. and it can be worked with the help of the HMI (Human-Machine Interface) computer(I promise I will discuss it later if you all will show your support.)

How PLCs Work?

We can divide the PLCs process into three parts

1.Input Processing
2.Program Processing
3.Output Processing

Working of PLC

1.Input Processing

During the Input scan PLC reads the ON/OFF status of Inputs and stores them to the Input image memory before execution of Program This information is stored and held valid till next scan of the input module.

2.Program Processing

The PLC executes the user program taking into consideration the states of input and depending upon the logic the output image memory is updated.

3.Output Processing

After Completing the execution of all instructions the above-stored output memory is transferred to an output module.

PLC Scan Cycle

PLC is a dedicated controller it will only process this one program over and over again.

One cycle through the program is called a scan time and involves reading the inputs from the other modules, executing the logic based on these inputs and then updated the outputs accordingly.  

The scan time happens very quickly (in the range of 1/1000th of a second). 

The memory in the CPU stores the program while also holding the status of the I/O and providing a means to store values,

PLC scan cycle

How to Program PLC?

PLC's can be programmed by using the ladder logic diagram, Instruction List, Function Block diagram, sequential function chart, and Structure text. The most widely used form of programming is called ladder logic.  Ladder logic uses symbols, instead of words, to emulate the real world relay logic control.

The completed program looks like a ladder so it is called ladder logic Program. it represents an electrical circuit. The left and right rails indicate the positive and ground of a power supply.

The rungs represent the wiring between the different components.

Here is one simple ladder logic Program,

Simple ladder logic diagram

Thanks for reading

and, if you have any questions feel free to ask I will reply it ASAP.