Programmable Logic Controller PLC

Programmable Logic Controller PLC is a computer used for industrial automation. These controllers automate a specific process, machine function, or even an entire production line.

The PLC can control Utility Plants, Batch Control Application, Chemical Processing, Conveyor systems, food processing machinery, auto assembly lines and many more process system.

Could you imagine your life without using your Brain, that is exactly looks like when you get into the “Automation” without the complete knowledge of PLCs.

Today we are going to speak about the major element in the Industrial Automation Field “Programmable Logic Controllers”.

We will discuss classifications of PLCs and also difference between PLC and Microcontroller.

In addition to the best vendors of PLCs all over the world, all of that and more is here so please stay tuned.

What is a PLC device?

PLC stands for “programmable logic controllers”, it is a microprocessor-based computer OR if you want to be more detail, we can say it is an Industrial Computer that used to monitor input signals to process it through a pre-programmed code.


After processing these signals the PLC translates that into decisions and transfers it to the output peripherals.

You could say that, PLCs act exactly like our brains with higher capabilities.

They can handle a large amount of input and output signals with a high speed and accuracy that you cannot imagine.

What is the difference between PLC & Microcontroller?

You might be confused when you are comparing PLC and microcontroller together as:

  • The both are a microprocessor-based device.
  • The both have RAM (Random Access Memory) and ROM (Read Only Memory).
  • We use both of them for the same principle that is called “AUTOMATION”.
  • Both have an input/output peripheral.

But “simply” we can say that a PLC is a larger scale of the microcontroller:

  • As we knew the both have a microprocessor but you have to consider that a PLC has a larger processing ability than the microcontroller.
  • The same principle with (RAM, ROM, Number of in/out signals) the PLC has a higher ability than a microcontroller.
  • An important point to consider that in almost every industrial environment, you’ll find systems that create electronic noise, along with magnetic fields.

An inexpensive microcontroller could go into fault mode or lose its program if the interference is significant enough.

But a PLC has a better level of protection. It can stand standard electronic noise without issue.

So, we could summary all of that “The both used for the same principle AUTOMATION, but PLCs have larger abilities and they could stand against noisy environments”.

PLC Block Diagram

plc architecture

A PLC has CPU and memory. It gets data from the field devices, process it and outputs signal according to the programming.

Classification of PLC devices

We could classify the PLC devices based on:

  • The application size:

It is clear that we have a wide range of applications that we could use PLCs with it, the number of I/O signals and the whole volume of your process definitely affect on your PLC size.

types of plc

So, when you select a PLC for your application you have to select the unique size.

  • Hardware setup:

For this point we have two main PLC types that you can deal with:

Compact PLC

that is a one-unit device, it has its own built-in power supply with the CPU module and limited (in most cases also fixed) number of I/O peripherals.

So, when you get it you to take it all, you have no choice to add or remove any of the unit modules.

Modular PLC

this type of a PLC refers to a rack-based device, in this case we have the option to select and change any module from the PLC unit beginning with the power supply, CPU module, function modules and the various IO modules.

Who are the best PLCs vendors all over world?


Most of Automation Engineers agreed on that company is the clear leader in PLCs, Siemens has approximately 30 to 40 per cent market share. Beside its simple and reliable PLCs, it offers a great software (TIA Portal) that enables you to program and configure all of its products just in one software.

siemens -plc manufacturer
  • Rockwell Automation / Allen Bradley

Here we are talking about the leader of the American markets in this industry. Its PLC offerings range from large down to tiny “nano” systems.

allen bradeley PLC manufacturer
  • ABB

ABB is also one of the world’s largest manufacturers of industrial robots, so it follows that it has a wide range of PLCs on offer.

Abb- plc manufacturer
  • Schneider Electric

Modicon, one of Schneider Electric’s brands, it has produced the first PLC in the US back in 1968. Then, through a series of mergers and acquisitions, Schneider Electric emerged in 1999.

schneider- plc manufacturer

Advantages of PLC circuits over Classic control circuits

  • Simply the Modern control (PLCs, Microcontroller based devices) is a compact form of the classic control, concept is the same but PLCs would help to minimize volume of control panel.
  • The PLCs also provide a great advantage over the classic control circuits with is the programming and the ease of rewiring and designing of control signals.
  • Power consumption by a PLC-based system is very less compared to relay-based systems. The average power consumption of a PLC is just 1/10th of power consumed by an equivalent relay-based control.

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