Programmable logic controller (PLC): all-rounder in automation technology

Learn all about programmable logic controllers in automation, machines and systems - from design and principles to applications, benefits and features to PLCs at electronica.

The programmable logic controller: automation in real time

A high degree of automation is the key to success in machine and plant construction and throughout the manufacturing industry, and programmable logic controllers (PLC) play a key role in that, despite questions regularly arising about their justification in times of digitalization and large volumes of data. Condition monitoring, data analytics, or predictive maintenance bring industrial PCs (IPC) to mind rather than a control technology from the 1970s.

However, robustness, millisecond response times, long life cycles, IT security, and, not least, the hardware base installed by the millions continue to be an argument for PLC automation. What’s more, modern plc systems increasingly meet requirements regarding IT functionality (OT meets IT), standardized communication (OPC UA), the integration of cloud and edge functionality, and artificial intelligence.

Analysts also see further growth in the PLC industry. In a recent study, Mordor Intelligence projects the market for programmable logic controllers (PLC) to increase from USD 11.75 billion this year to USD 14.46 billion by 2028, with an average annual growth rate (CAGR) of 4.23 percent. In the same year, the IMARC Group expects revenue of USD 20.2 billion for the PLC industry.

PLC structure and principle

The operating principle of programmable logic controllers has remained the same since they were first launched. They receive input signals (sensors, switches, etc.) from systems and machines, process them sequentially and cyclically using programmed logic – typically in milliseconds – in order to then use the results to activate corresponding output signals for actuators such as motors, valves and relays.

In other words, a processor, memory, power supply unit, and the input and output modules (I/O modules) were enough for half a century to automate sequential or repetitive production processes little fault tolerance in sometimes the harshest industrial environments via PLC.

programmable logic controller in industries
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Areas of application for PLC automation

Today, programmable logic controllers (PLCs) play a central role in almost all industries and sectors. Their efficiency and versatility have made them indispensable tools in plant engineering and automation. Applications for PLC automation range from manufacturing automation to critical infrastructure such as water treatment. In the following, we take a closer look at PLC technology, its use in various fields and how they contribute to process optimization, quality assurance and increased efficiency:

  1. Manufacturing automation: On production lines, PLCs control the production processes, move materials, and perform quality checks.
  2. Machine control: From miniature controllers to CNC and robot controllers – controlled by PLC.
  3. Building automation: PLCs control the heating, ventilation, air conditioning, lighting, and security systems in buildings.
  4. Traffic and transport systems: PLCs monitor and control traffic lights, elevators, conveyor belts, automatic doors, and other aspects of traffic and transport systems.
  5. Power generation: PLCs monitor and regulate power generation plants such as hydroelectric power plants, wind turbines, or solar power plants.
  6. Chemical and pharmaceutical industry: PLCs control and monitor chemical processes to ensure safety and product quality.
  7. Food and beverage industry: PLCs control filling and packaging processes, temperature monitoring, and hygiene standards.
  8. Water treatment: PLCs ensure drinking water quality in water treatment plants.

The benefits of programmable logic controllers

Unlike the originally hard-wired programmed logic controllers based on relay switches, PLC innovation means that modern, programmable, and connected control technology scores points with:

  • high flexibility and reliability,
  • low installation effort,
  • simple duplicability and expandability,
  • better diagnostic options,
  • fast function change,
  • and low power consumption and space needs.

There are only a few drawbacks in comparison to the PLC advantages. For example, it’s not worth using PLC automation for simple control tasks that don’t often change. In addition, the programmable version requires a corresponding technical infrastructure with digital devices and trained personnel.

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Control technology—modular, soft, or virtual

Programmable logic controllers are used as a modular system, a compact device, or an embedded chip solution. Software-based controllers (soft PLC) are becoming increasingly important for less safety-critical use. They usually run on universal PC hardware with an operating system enhanced with real time.

Virtual controllers (vPLC) represent the next step in control technology and, unlike the soft PLC, function completely independently of the hardware. The path to the cloud finally enables integration into Industry 4.0 solutions and IIoT platforms to implement smart and adaptive production environments.

Smart production solutions for the smart factory

This is difficult to achieve with the current variety of protocols. OPC UA (Open Platform Communications Unified Architecture) is a platform-independent, unified communications standard designed to ensure the seamless flow of information between devices from different vendors. Enhanced by TNS (Time-Sensitive Networking) and the so-called publish/subscribe mechanism, OPC UA not only meets the interoperability requirements, but also the real-time requirements of the PLC industry.

The non-profit organization (UAO) is also committed to vendor-independent control technology. With the IEC 61499 standard, the organization is declaring war on proprietary automation systems. As an extension of the IEC 61131 industry standard, it defines a model for distributed control systems. Event orientation allows function blocks to react to events without being closely tied to a central control logic. This improves the flexibility, reusability, and scalability of PLC automation.

Whether it is IIoT integration, edge computing, AI applications, or increased cybersecurity, standardized, secure communication from the field device to the cloud is a prerequisite for more powerful, intelligent, and connected PLCs. To realize their full potential, companies must keep pace with these emerging trends.

© Messe München GmbH

PLC at electronica 2024

The PLC is a mature, robust and highly survivable technology and one of the most successful control components ever. It is as indispensable as the relay. Both technologies have been declared obsolete many times and are still going strong. However, the relay offers performance that is far from being achieved with semiconductors.

At electronica, the PLC joins the variety of intelligent components. It competes successfully with modern microprocessor and microcontroller-based solutions, and especially with embedded boards and modules of all kinds, as well as with embedded PCs. The programmable logic controller is an indispensable component for the all-electric society of today and tomorrow.

Embedded Platforms and Industrial Control

With the Embedded Platforms Forum and the Industrial Control Forum,electronica from 2024 will focus even more strongly on applications in mechanical engineering and automation. The two forums offer hardware and software developers, system designers, product managers, development managers and device manufacturers a platform for exchanging knowledge and openly discussing the challenges and solutions for embedded systems and industrial control and automation systems.

The PLC Guide: Frequently asked questions on the subject of programmable logic controllers

At the heart of most industrial control and factory automation systems is the programmable logic controller (PLC). Here are some frequently asked questions (FAQs) about PLCs:

What is a programmable logic controller?

A programmable logic controller (PLC) is an electronic device used to control automation processes in industrial applications.

What are the main components of a PLC?

The main components of a PLC are the CPU (central processing unit), input and output (I/O) modules, memory, communication interfaces, and a programming interface.

What is the difference between PLC and VPS?

VPS (connection programmed control) is a hard-wired control system. In a PLC (stored program control), the control is done by software. The more advanced solution is a PLC because the control can be made by a customized program.

How does a programmable logic controller work?

A PLC reads input signals from sensors, processes them based on a pre-programmed control program, and then outputs corresponding output signals to actuators.

What are the advantages of using a PLC?

The advantages include flexibility in programming, easy adaptation to different processes, reliability and the ability to monitor equipment in real time.

What applications can a PLC be used for?

PLC systems are used in a wide variety of machinery and industrial equipment, including manufacturing plants, processing plants, warehouses, robotic systems, and more.

What programming languages are used for PLCs?

The most commonly used programming languages for PLCs are IEC 61131-3 compliant languages such as Ladder Logic, Function Block Diagram (FBD), Structured Text (ST) and Sequential Function Chart (SFC).

How can I program a PLC?

A PLC is usually programmed using special software that allows the control program to be created, loaded and monitored. The programming language depends on the software used.