What is a PLC and Why You Need It?

Industrial Internet of Things or Industry 4.0 is what we call the application of IoT solution in manufacturing. It has the power speed up both the acquisition and access huge amounts of data, make it efficient and work with it. Although some modern machines propose modern hardware in this respect, it is not an easy task to substitute a machine in a production line. Here come the PLCs. They are well established systems used widely in factories, but they are also a bridge to IIoT.

PLCs (programmable language controllers) are widely used industrial computers designed to manage system processes remotely. Instead of having multiple devices and employees managing various systems and tasks, PLCs can handle all of them at once (just like controlling automatic doors, traffic lights switching, etc.)

How PLCs emerged?

Back in the 60s electromechanical relays were used to perform similar processes in the industry. However, these were very big and heavy objects, difficult to maintain and to operate with. This pushed engineers to come up with new technologies of production and, eventually, to the development of the PLC prototype by Richard Morley.

Why you may need a PLC?

The creators put a lot of effort to make sure that their invention solved existing issues being much easier to use. Modern PLCs are much more advanced than the electromechanical relays in terms of speed, reliability, cost-effectiveness, and data management and the ability to adjust them. This means PLCs could adapt to changes and different requirements and are also able to perform diagnostics and identify system flaws.

PLCs consist of:

  • Central processing unit (CPU) giving instructions to the PLC on how to function. It contains the memory of the computer and stores all the data needed for diagnostics and operation of different machines. The CPU can communicate with other devices and PLC systems.
  • Input/Output modules that pipe the necessary information to the CPU and communicate tasks repeatedly. These could be digital or analog devices. Examples for input devices are sensors or switches, and for output devices – lights, valves or others.

PLC Setup

As any other device, PLCs need “instructions” on how to perform. They are usually given via programming devices or software and are downloaded into the PLC RAM or memory. Various programming languages could be used for programming a PLC (Instruction List; Structured Text; Function Block Diagram, and others) but Ladder Logic is the most used one, being quite easy to read and program.

PLC Functioning

After writing the program and setting the input/output modules the PLC processes the information, performs the given instructions, and brings the final output. Once inputs and outputs are defined, the PLC works in a repeating mode. The process includes steps during which input scanning is conducted, then the program created by the user is run, followed by output scanning and communicating with other devices and performing diagnostics.

Unitary and Modular PLC

There are two types of PLCs you can use depending on your needs. Unitary PLCs are more compact and simpler, with given number of I/O points and usually could be directly connected to the devices or applications. Modular PLCs, on the other side, give you more flexibility in terms of customization and adding I/O modules.

Before choosing the right PLC for your needs you’d better be aware of whether you are implementing it in a new or existing system, how many I/O points does it require, how complex are the processes you will be controlling, what programming language you will be using, and in what type of environment your PLC will be run.

PLCs are still very widely used and will remain in focus in most industries, although they need to adapt to the new technologies of production being implemented. In the next years they must be more adaptive to climate changes and remote operation and compatible with Industrial Internet of Things for better data management.

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