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Known as the brain of industrial automation, PLCs play a crucial role in everything from factories and elevator systems to water treatment plants and transportation networks. If you’ve got 10 minutes, this guide will give you clear and simple answers to the basics: What is a PLC? Where is it used? What does it actually do? And what programming languages are commonly used for PLCs? We’ll walk through these questions step-by-step and cover other important details you might be curious about. First up, let’s start with some key technical definitions to set the stage.
In the world of industrial automation, safely, flexibly, and efficiently controlling complex processes is essential. At the same time, digitalizing systems and optimizing production have become necessities. In this transformation, PLCs (Programmable Logic Controllers)—often called the heart of industrial control systems—have become the cornerstone of engineering applications. In today’s manufacturing technologies, where automation is widespread, PLCs help make systems more reliable, sustainable, and cost-effective.
The acronym PLC stands for Programmable Logic Controller. As mentioned earlier, PLCs are specialized control computers programmed to perform specific tasks within automation systems, bridging the physical and digital worlds. The very first PLC was developed about 60 years ago, in 1968, by the company Modicon. Since then, with advancing technology, PLCs have become indispensable equipment across nearly every industry.
We’ve explained what a PLC is with technical details, but the full picture becomes clearer when we explore it through examples rather than just its literal meaning.
PLCs are embedded systems that detect physical events and respond to them based on predefined rules. They sense physical parameters like temperature, pressure, level, and speed, and generate system outputs accordingly. In short, they serve as an automation command center that can be programmed by the user.
Thanks to these systems, production processes can continue without manual intervention, reducing production errors and minimizing human mistakes. This is why PLCs can be customized to meet the automation needs of different industries, giving them a wide range of applications.
One of the most remarkable features of PLC systems is their flexibility, allowing easy integration into various processes. They can handle tasks ranging from temperature control in a manufacturing plant to controlling conveyor belt movements. This versatility makes them indispensable not only in large industrial facilities but also in areas like energy management, water treatment plants, smart buildings, and even agriculture.
We will dive deeper into these applications in the section dedicated to PLC use cases.
Thanks to their programmable nature, PLCs can be coded specifically to meet the needs of each facility. This enables the same hardware components to be used in different scenarios. With evolving industrial dynamics, PLCs have gone beyond mere control functions and now play an active role in data collection, analysis, and system optimization.
Additionally, the modular architecture of PLCs allows new input-output units to be easily added as the system grows. This means a system initially set up for a small automation need can be expanded over time, resulting in a cost-effective and sustainable solution.
Having taken a detailed look at the technical definition of PLCs and their significance in industry, let’s now move on to answer other common questions by exploring PLC components, software, and programming languages.
A typical PLC system consists of the following basic components:
Note: PLCs have revolutionized systems by replacing traditional relay control panels. Their smaller footprint, high reliability, and flexible programmability have allowed PLCs to take on a critical role in automation.
When communicating with the outside world, PLC systems use many input and output devices. Let’s take a closer look at these input and output elements separately.
Input Devices:
Output Devices:
A PLC circuit is a complete system where these devices are properly connected to the controller, with protection elements in place.
You might be wondering, "What exactly is a controller?" Don’t worry—we’ll cover the definition of a controller in detail when we discuss what a PLC is and where it’s used.
The working principle of a PLC consists of three main cyclical stages. To summarize these stages briefly:
Since this cycle repeats within a few milliseconds, the system can respond in real time.
We’ve touched on this topic briefly, but the answer to what a PLC does is much more extensive. The primary purpose of PLCs is to automate and control specific processes, machines, or systems. For example, in a production line, PLC systems precisely manage operations like running conveyor belts, activating motors based on timing, or adjusting heaters according to a set temperature. As we mentioned earlier, this greatly reduces both production and human errors.
If we summarize the tasks performed by PLCs under one umbrella, they include:
Note: Especially in systems requiring uninterrupted operation, PLCs enhance safety through backup functions. In case of a fault, they don’t just stop the system—they can activate alternative paths, preventing a complete process shutdown. In this way, PLCs serve not only as controllers but also as safety and continuity providers for the process.
Thanks to these capabilities, PLC systems improve production quality while lowering operational costs. We will examine these advantages in more detail in the later sections of this guide.
Before diving into PLC programming languages, let’s first answer the question: What is PLC programming? This will make the topic much clearer.
PLC programming is the process of configuring a digital controller that manages industrial control processes using languages such as Ladder Logic, Structured Text (ST), Function Block Diagram (FBD), Instruction List (IL), or Sequential Function Chart (SFC). These programs are developed following the IEC 61131-3 standard, which covers various programming languages and allows engineers to choose the most suitable one based on system requirements.
For example, in a conveyor system, if you want the motor to start rotating and send the product to the next station whenever a sensor detects an item, you need to define that logic in the PLC. This definition is what PLC programming is all about.
Now, let’s take a detailed look at the main PLC programming languages:
Depending on the programming language used, different levels of optimization are possible. For applications requiring complex algorithms, the Structured Text (ST) language is preferred, while Ladder Diagram is favored where visual monitoring and quick intervention are important. This flexibility makes both system design and field implementation much easier for programmers.
In the next part of our guide, we will break down how these programs work step by step. But first, let’s focus on PLC software.
Different manufacturers have developed specialized software for their own PLC models. For example:
Thanks to PLC software, users can directly interact with physical processes in the field through a virtual environment. This speeds up troubleshooting and simplifies maintenance tasks. Additionally, a well-configured PLC software can contribute to optimizing many outputs—from energy efficiency to production quality.
Throughout this guide, we’ve given examples of where PLCs are used. Now, let’s briefly summarize the most common application areas:
As can be understood from their application areas, PLCs are fundamental building blocks of the digital transformation era. With Industry 4.0 and the Internet of Things (IoT), PLCs no longer serve solely as machine controllers; they also take on roles such as data collection, analysis, and remote monitoring. Moreover, they can be easily integrated with HMI panels, SCADA systems, and cloud-based software.
For example, a 2018 laboratory study on energy management using PLC-supported SCADA systems demonstrated that these systems provide high precision in energy monitoring processes while significantly improving operational efficiency by minimizing operator intervention (Üstünsoy & Sayan, 2018). This flexibility and broad usage scope position the PLC not just as a control device but also as a central element of digital transformation.
Globally, the PLC segment in industrial automation and control systems generated revenue of USD 43.39 billion in 2023 and is projected to grow at an average annual rate of 10.3%, reaching approximately USD 85.31 billion by 2030 (Grand View Research, 2025).
Advanced PLC models also feature built-in hardware-level diagnostic functions. These features can detect faults or deviations early and alert operators, thus preventing potential production losses.
As we’ve seen from the details provided so far, the PLC is the backbone of industrial automation systems. Especially in complex production lines, PLC automation systems ensure that all processes run in the correct sequence and remain synchronized. Thanks to these systems, machines can communicate with each other, respond to specific conditions, and operate efficiently without the need for operator intervention. The references we mentioned earlier also support this fact.
One of the biggest advantages of PLC automation is minimizing human error. Automating a manual process eliminates variations in the workflow, standardizing quality. Additionally, monitoring production processes, collecting data, and performing retrospective analyses become much easier. This is a significant benefit for large-scale manufacturing facilities, both in operational control and strategic planning.
As mentioned earlier, modern PLC automation systems are no longer limited to physical control tasks; they also integrate with higher-level software such as SCADA and MES. This integration is crucial because data from the field is fed into the enterprise’s overall decision-making processes. This connection is a key component of the Industry 4.0 vision, which forms the foundation of digital factories.
The unit that analyzes the data collected in the system and generates appropriate commands is called a controller. PLCs are a type of controller, but unlike them, microcontrollers, DCS (Distributed Control Systems), and industrial computers can also serve as controllers. PLCs are especially preferred in industrial environments due to their robustness and ease of programming.
Logic forms the foundation of decision-making processes. Logical structures expressed through gates like AND, OR, and NOT play a crucial role in PLC programming. In Ladder diagrams, these logical operations are represented graphically, defining how the system responds to different conditions.
Let’s summarize the information we’ve covered so far. PLCs are an integral part of modern manufacturing technology. These systems analyze input data and send commands to outputs based on programmed rules, ensuring quality, speed, and efficiency in production. With this guide supported by software, hardware, and practical examples, we’ve provided comprehensive answers to the questions: What is a PLC?, What does a PLC do?, and Where are PLCs used?
Of course, you may want to explore these topics further. You can find more detailed information by browsing other content on our website or contacting us directly.
One final note before we close: In the near future, PLC systems will evolve even further through integration with artificial intelligence, data analytics, and IIoT (Industrial Internet of Things), continuing to serve as foundational components of autonomous production lines.
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Muhammet Kılınç
Sales and Project Manager
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