What is a PLC? How does it work? What is it for?


You want to know what is a PLC? You have come to the right blog, because here we will explain everything you need to know to understand what a programmable logic controller (Programmable Logic Controller – PLC).

A PLC is a “brain” that activates machinery components to carry out activities that are potentially dangerous for people, very slow or imperfect.

It is important that you do not confuse the PLC (Power Line Communications) that are used in communication networks with the automaton industryHe, then, although they share a name, the uses are totally different.

This second one, which we are not going to delve into, transmits the internet connection through the electrical network. This type of PLC repeater It is used to expand the Wi-Fi network and the Ethernet connection.

now that you know What does the acronym PLC mean?, it is time for you to understand how it works and the utility that an industrial automation computer can provide.

How does a PLC work?

It is important to know that functionality is a tailored aspect in PLC development. Well, the provider develops the functions according to the needs of control, registration, monitoring... of the project that is being developed.

This equipment like a computer, where the main parts They are the CPU, a memory and input/output module, the power supply and the programming unit. In order for it to work, then, it is necessary to carry out a programming prior to the function that it is going to perform.

To carry out this programming, specific software adapted to the brand and the programming language to be developed is needed.

Basically, the function of a PLC is to detect various types of signals from the process, and prepare and send actions according to what has been programmed. In addition, it receives configurations from the operators (programmers) and reports to them, accepting programming modifications when necessary.

How are PLC devices born?

With the development of the Internet and electronic technologies, a way was sought to replace control systems based on electrical circuits of combinational logic, with relays and switches.

In the late 60's the first appeared types of programmable controllers, with very simple characteristics and a very long useful life.

The aim was to achieve industrial automation, where the use of electronic devices would alleviate the burden of repetitive tasks in factories. Thus, a work evolution occurred where the professional stopped doing the work and began to ensure that the machine worked correctly.

In 1982, the first standardized commercialized PLC was sold for more than a million dollars. However, now this type of technology is available from $49 (€43).

When history was still understanding what a PLC is, microprocessors were incorporated into its composition. Thus, PLCs were created with the ability to communicate with each other and control the processors telematically. Technological improvements were also implemented to improve the data obtained.

In the 80s, the programming and communications protocol was standardized, making improvements to the programming system so that it could be carried out with personal computers instead of with programming terminals. In addition, other design improvements were implemented that improved its performance.

Starting in the 90s, and up to now, the physical characteristics of the devices and the programming modules have been modernized, opening the possibilities of programming, control and communication channels.

What types of PLC are there?

As we have seen in the evolution of PLCs, the modifications and improvements that have been made have resulted in different types of PLCs that can be grouped into four main categories.

compact type

Do you want to know what a compact PLC is? It is one that conforms to the generic specifications of PLCs: it has the power supply, the CPU and the different modules built in.

There are compact PLCs in nano size, which have a super small size, although the basic operation of the PLC is more limited by its characteristics. All our equipment has inputs to connect our sensors of temperature, pressure, humidity, etc.. With which you can perform a precision control of your machinery and equipment.

modular type

This type of PLC is characterized by being composed of expandable modules, which gives it more powerful features than the compact model. It works with more complex programs, has greater memory capacity and operability.


When you know what a modular PLC is, it is easier to understand rack mounting. It is practically the same, but there are differences in the rack where the PLC modules are placed.

In the case of rack mounting, the exchange of information between the different modules is allowed, this allows a higher speed of information transmission and, therefore, optimizes the operation of the PLC.

PLC with built-in HMI

He HMI (Human Machine Interface) is a programmable device, a graphic interface, which combined with the PLC allows to optimize the experience of programming and use of the machine. Reduces wiring of PLC elements and displays them on a graphical display as programmed.

What use can I give to this technology?

This technology of simple implementation and fast execution, allows us to automate the processes of our project with low maintenance and customized installation.

To finish understanding what this equipment is and how it works, we are going to give the example of an automatic car wash:

It will be programmed so that, every 500 meters, it collects the signals from different sensors of temperature, pressure, presence of vehicles, levels of oxide and carbon dioxide, and the water level of the tank.

Depending on the sensors, the input and output devices will be activated: traffic lights, warning lights, fans and water pump. Furthermore, by having remote access, operators can access the machine interface and view the status of the process, in addition to modifying it if necessary.

In short, safety levels will be established in the presence of toxic gases, vehicle speed, etc., and the PLC will check that the data is within that parameter and, if it is not, it will activate the measures scheduled security.

Now that you know perfectly well what a PLC is, we inform you that at SRC we have a development line for these products. Our engineers are also in charge of developing the automation systems to connect our sensors. temperature, pressure, humidity, etc.. With which you can perform a precision control of your machinery and equipment.

get in contact Contact us and we will solve all the doubts that have arisen in this regard, in addition to informing you in depth about the types of PLCs with which we work.