What is a PLC (programmable logic controller)?

Automation has become necessary with the rise of saving time as much as possible. You see automation all around you. Many things have been replaced with simple commands, whether it’s a washing machine or an Alexa device. They require no human physical movement any longer.


A PLC or programmable logic controllers are resistant machines made to help in manufacturing processes. PLCs come in many sizes.

In this article, we’ll also take a look at the following:

  • What they’re used for
  • Pros & cons
  • Different types

What is a Programmable Logic Controller? (programmable logic controller)

Computers are widely used to aid manufacturing processes and industrial tasks. These computers are known as Programmable Logic controllers. They have been specially adapted to resist the wear and tear of the production process, in assembly lines, for instance. They can vary from pocket-sized to large enough to accommodate whole mechanical plants.

They work in three processes: input, output, and CPU.

programmable logic controller

What are PLCs used for?

PLCs are used for several big-picture data. Here are some examples of the same:

  • Cement manufacturing
  • Glassmaking
  • Wind turbines
  • Virtual modeling

Cement manufacturing

A PLC can determine the type of quality and the quantity needed to produce the best product within the kiln. If any discrepancy occurs, it can also warn you against the same.

Making of glass

The making of glass has involved the use of PLC since the early 1980s. The ratio of the material is calculated using the PLC and in the production of flat glasses. PLC alone cannot accomplish this complicated task; thus, bus technology is used to assist in this process.

Wind turbines

Turbines generate plenty of essential electricity but must be protected during bad weather conditions. The wind and direction sensors consider several data factors used to operate the turbine more efficiently. This way, the turbine will be protected from bad weather and experience less downtime.

Virtual modeling

Rather than manufacturing and testing new machines, virtual modeling through PLCs allows us to test models online before creating them. You can move on to the production process when you fit one that works perfectly.

Programable Logic Controllers book

Civil life

Your daily life is full of examples of PLC use. You’ll be using multiple such devices daily without even realizing it. Washing machines, traffic lights, and elevators all have PLCs governing their ease of use. All such examples will also remind you of the ruggedized adaptation they go through. Traffic lights will be on during rain, sleet, or snow because PLCs are designed to withstand every condition out there.

Paper production

You will often find PLCs in use while printing large books. Even newspapers will use this type of technology to administer high speeds and high-volume production.

Plastic industry

You can find many plastic products that will use this technology in their factories. Whether it’s injections or silo feeding, PLCs will overlook the process to aid in ease of use.

Advantages of using PLCs

There are certain pros over other controllers that PLCs offer.


The programming language of PLCs is simpler compared to other industrial control systems. If you want your workers not to waste too much time learning, this is the perfect solution because it is easy to catch on.


The electricity used is comparatively less, and PLCs work more efficiently. It helps save capital which can then be used elsewhere. It brings us to the next big pro.


Their electricity usage is lesser compared to others. The downtime remains low due to its rugged exterior; hence, maintenance charges are also low. Fewer components make for the replacement of fewer parts and, thus, even lower cost. Overall, you’re looking at a lot of cost savings with this device.

Something for everyone

There is so much variety in this technology that there are numerous price points. One can opt for the budget-friendly option or go all out with the full package deal. Moreover, PLCs are so versatile that they will fit in with various electromechanical processes.

PLC MicroLogix

Disadvantages of using PLC

Like any other machine, this has its downsides too. Let’s look at a few of them.

Can’t handle complexity

Unlike a smartphone or laptop that operates multiple tasks simultaneously, PLCs run on a series basis. They cannot handle large complex amounts of data or tasks at once. Either you will have to install a distributed control system or use another industrial device to aid electromechanical automation.

Electrical malfunction

Since they are like any other computer device, PLCs can also experience malfunctions like interference and corruption of memory or other failures in programming.

Incompatible with other PLCs

Since all manufacturers will use their programming software, PLCs bought from different brands will not be interoperable. If you want this feature, you will be restricted from buying from the same brand again.

What are the different types of PLC?

There are two types of PLCs. Let us look at them in detail below.

Below are the types based on the hardware setup.


Also known as the I/O PLC or compact type, the I and O stand for input and output. It means the I and O are part of the same microcontroller. To translate into easier words, the input, and output remain determined by the manufacturer and aren’t expandable either.


As the name suggests, this type is expandable into multiple ‘I’s and ‘O’s. Each component remains separate from the other and hence does not depend on the other either. The communication module, inputs, outputs, and power supply are outside the microcontroller. Although this is great since it means all components are independent of each other, it also means you need to hook up the inputs to make your device manually.

How does a programmable logic controller work?

The functioning is just like any other PC. The CPU is the brain where a command is created and sent. There are several modes on this CPU. The programming mode is first operated so the logic can be downloaded from the PC. In run mode, this logic is executed as commands to the rest of the components. Once this program is run, the inputs on other modules are read, and outputs are updated accordingly. This cycle runs over and over based on the originally downloaded logic. It’s the CPU’s memory that stores this program.

Choosing a PLC

You might be in a manufacturing business where electromechanical processes need automation that PLCs provide. In this case, assessing which kind of machine you require becomes crucial. These are the factors to consider before you head to the market.

Mark your needs

Before starting anything, you need to make a list of the basic needs you want to be fulfilled by the machine. Is it automating the right ratio of mixing cement? Is it the functioning of an assembly line smoothly? Write it down, and then hunt for the right device. The right device might already exist or be made from scratch according to your requirements.


Input and Outputs are the key players. After the first step, you’ll easily know how many I/O you need and their location. Is it key that you need to alter the I/O frequently? If so, you must buy a modular type to connect the cables with whichever devices are needed at the moment. Modular-type devices are also great if you have plenty of remote I/Os that need plugging.


The second key factor is, of course, the CPU, which is the brain of every computer. The more complex the number of I/O, the more CPU speed will be required. As the programs you run become more and more detailed and the number rises, the CPU’s memory will also increase proportionately. The scan time must also be considered. It is how long it takes for one program cycle to run successfully.


It is crucial since it translates to the programming language used in the system. More complex programs will require a complex language like C, while simpler ones will make do with BASIC. Your language should be apt for the maintenance and troubleshooting that will come up during its working.

Programming a PLC

This programming varies according to the machine you want to program for. The ends you want to meet will decide the program. Thus you must follow the steps below

  • Identify the outcomes you want to achieve
  • Decide on the input, output, and sensor devices needed based on your desired outcomes.
  • Find the programming language you want to use based on the program’s complexity level.
  • Start coding and make sure to install safety measures like an emergency stop button or proximity detector.

Difference between PLC and DCS

DCS stands for distributed control systems, and the following are the basic difference between them and PLCs.

  • A DCS works with multiple machines at the same time, while PLCs will work with no other programs running in the background. Thus their Operating system is also simple. It also makes them faster than DCS.
  • PLC can be designed according to your need. They have room for flexibility depending on the program you require. However, DCS does not.
  • DCS will use higher-level languages, while logic controllers will use lower-level languages because of their simple series tasks.
  • While DCS operates whole buildings, plants, and factories, logic controllers were only meant to replace relay-based controls and thus control one machine.

Best programmable logic controllers

Here’s a look at our favorite picks:

Starter kit

It is surely an investment at this cost, but it’s worth it. With 12 Input and 8 outputs, this is a power-packed controller. It comes with a manual for programming and hardware setup. The operational wattage is 24V, and the great thing is the power supply is included.

CompatibleFor Windows 10 at 32bit
FeaturesProgrammable via RS232 or USB Interface
Package Dimensions12.48 x 8.66 x 2.05 inches
Specs12 DC Inputs, 8 Relay Output 5 Amp


  • Nice interface
  • Good starter kit


  • It was expensive.
  • Not that many reviews


Here’s a small but super smart device. The module connects to both the text screen and touch screen for programming. It has been rated superbly for use in industrial control applications.

FeaturesSmall body and stable performance.
Size6.85 x 3.94 x 1.18 inches
Weight1.01 Pounds


  • Nice price
  • Good delivery
  • Good speed


  • Mixed reviews


The speed on this machine is unmatchable. It uses a 32-bit MCU with anti-interference details. It uses ladder logic programming for the best industrial control. And at this cost, it’s a bargain.

Voltage24 Volts
Item Dimensions LxWxH0.39 x 0.39 x 0.39 inches
Item Weight0.36 Kilograms
Made ofindustrial-grade 32-bit MCU


  • Good performance


  • Not great delivery

We will be happy to hear your thoughts

Leave a reply

Passion Plans
Login/Register access is temporary disabled