PLCs are well-established industrial automation systems used widely in factories. They are the bridge to Industrial Internet of Things (IIoT) or Industry 4.0, which is the application of IoT solutions in manufacturing.
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IIoT has the power to speed up the acquisition and access of huge amounts of data, making it efficient and easy to work with. It does that with the help of smart sensors that collect information.
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Get a demoAlthough some modern machines come with such IIoT hardware improvements, it's costly to replace all the equipment in a production line with more sophisticated versions. That's where PLCs step in to streamline manufacturing processes.
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Earlier editions of the IEC 61131-3 standard defined five programming languages for PLCs; the current 2025 edition defines four after removing Instruction List, though all five are still worth knowing because legacy controllers use them. Most modern controllers support several of them, and real projects often mix languages within a single program.
The language choice matters for maintenance as much as for engineering. When a controller from Siemens or Allen-Bradley stops a line, the technician who can read the program finds the true cause faster. Our guides on Siemens S7 SF fault LED troubleshooting and Allen-Bradley major fault codes cover the most common failure paths.
PLCs are often compared with programmable automation controllers (PAC), distributed control systems (DCS), and plain microcontrollers. All four execute control logic, but they target different problems, plant sizes, and engineering teams.
| Controller | Best suited for | Key characteristics |
|---|---|---|
| PLC | Machine and line control with fast, discrete logic | Rugged hardware, deterministic scan cycle measured in milliseconds, simple to maintain |
| PAC | Mixed discrete, motion, and process control on one platform | PLC ruggedness combined with PC style processing power, memory, and communications |
| DCS | Large continuous processes such as chemicals, power, and refining | Plant wide architecture with thousands of analog control loops and central operator stations |
| Microcontroller | Embedded control inside a single product or device | Low cost chip for embedded designs, needs supporting electronics and firmware built around it |
In practice the boundaries blur. Modern PLCs have absorbed many PAC capabilities, and hybrid plants routinely run PLCs on individual machines alongside a DCS in the continuous process area. For most discrete manufacturers, the PLC remains the default choice at the machine level.
Because nothing has beaten them at their core job: deterministic, real time control in harsh environments. A PLC executes its scan cycle in milliseconds, tolerates vibration, dust, and temperature swings, and often runs for a decade or more with minimal attention. Modern factories build on that reliability by feeding PLC signals into systems that track downtime and OEE, turning raw machine states into improvement decisions.
Automotive, food and beverage, packaging, pharmaceuticals, plastics, water treatment, and energy are the heaviest users. Any operation built on repeatable machine sequences (conveyors, robotic cells, filling lines, palletizers) almost certainly runs on PLCs.
A traditional PLC is dedicated hardware with its own real time operating system. A soft PLC is control software running on an industrial PC or edge device. Soft PLCs offer more computing power and flexibility for data heavy tasks, while hardware PLCs are prized for determinism, simplicity, and proven long term stability, which is why they dominate at the machine level.
Only if they are treated as part of the network rather than as isolated boxes. Legacy PLC protocols were designed for closed systems, so connected controllers need network segmentation, strict access control, and disciplined firmware updates. Standards such as IEC 62443 give manufacturers a practical framework for securing control systems as PLCs connect to IT and cloud platforms.
A PLC or programmable lоgic controller is an industrial computer that has been designed to remotely control manufacturing operations and equipment, such as machines, production lines, robotic devices, or any process that requires high reliability, programming and fault detection.
Instead of having multiple devices and employees managing various systems and tasks, PLCs can handle all of them at once.
Manufacturers need PLC controllers because they help automate industrial operations. Their implementation provides a competitive edge to all types of factory-based manufacturing.
The rapid operation of internal timers, sequencers and relays in PLCs far surpasses that of traditional time delay relay systems. Consequently, an assembly machine using a PLC would achieve a significantly higher productivity rate.
Moreover, PLCs are extremely reliable real-time production control systems and are easy to program. They can seamlessly be adapted to emerging sensor technologies and sophisticated human-machine interface (HMI) devices, which means they progress in tandem with modern technological advancements.
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Book a demoWhen it comes to programmable logic controllers' advantages, there are several key points:
Programmable logic controller inventors put a lot of effort into making sure that their control systems solved existing issues and were easy to use.
Back in the 60s, electromechanical relays were used to perform similar processes in the manufacturing 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 (Dick) Morley.
Modern PLCs are much more advanced than electromechanical relays in terms of speed, reliability, cost-effectiveness, 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.
There are two types of PLCs you can use depending on your needs:
Before choosing the right PLC type, you should know whether you are implementing it in a new or existing system, how many I/O points it requires, 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 essential elements in industrial process automation. They function based on instructions stored in a memory module that contains programmed commands and data. The system receives input from sensors and executes logical operations on the data to generate the desired output.
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As with 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. PLC runs on various programming languages (Instruction List, Structured Text, Function Block Diagram and others) but Ladder Logic is the most used one, being quite easy to read and program.
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 communicating with other devices and performing diagnostics.
PLCs are very widely used and will remain in focus in the manufacturing industries for years to come. Although they need to adapt to the new technologies of production, they are easy to program and modify.
In the future, they will become more adaptive to climate changes and remote operations and more compatible with Industrial Internet of Things (IIoT) for better data management.
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