Why are PLCs used for industrial control instead of embedded systems?

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PLCs and embedded systems are used in industrial control; it’s not accurate to say that PLCs are used in most cases. In embedded applications, if you pay close attention, standard industrial products that are manufactured in bulk and require some complex calculations usually make use of embedded systems. Such as frequency converters, standard industrial robotic arms, some specialized equipment, and so on. Some products are manufactured in bulk. When embedded systems were first developed for specific purposes, significant financial and human resources had to be invested in research, debugging, and so on. Once the development is completed, the initial R&D costs are allocated directly to each individual product produced in bulk later on, which significantly reduces the overall cost associated with product development. If it is only for mass-producing equipment, it can be said that the hardware cost of embedded systems is much lower than that of PLCs. Furthermore, in many scenarios, using a PLC is not ideal. For example, some products require extensive complex calculations, such as the numerous motor drive and control algorithm computations found in frequency converters, or algorithms like SLAM navigation used in modern automated handling robots; such tasks are only suitable to be carried out by embedded high-performance processors, as PLCs are unable to handle such complex algorithms. Furthermore, there are situations in which PLCs cannot be used either, such as with frequency converters or sophisticated industrial devices. Although a PLC could be used in these cases, where would its size fit? At least one voltage regulation module is required, as well as several input and output modules, and at least one communication module as well. If all these components are packed into a standard, compact industrial device, it simply won’t look reasonable in terms of design. Another point is that it is a standard industrial product; if it is controlled by a PLC, there are usually many competitors for such products. If it is built using an embedded system, there are relatively fewer competitors. It also shows indirectly that control systems built with PLCs can be easily replicated; at least by opening the control cabinet, one can see how such a control system is structured – what input and output modules are used, and which sensors are connected to them, etc. In embedded systems, designers have to design the peripheral integrated circuits themselves, which relatively results in better protection. For an industrial device with high added value that is controlled solely by a PLC, if there are few competitors, it’s likely that the difference between their control system and those of others isn’t significant; the advantage lies rather in the mechanical design, patent protection, or knowledge of the manufacturing process. Control systems that do not rely on embedded systems often involve a high level of control technology and complex algorithms; embedded systems, with their built-in programs, are therefore valuable and come with certain technical barriers. In cases where industrial PLCs are used, various industrial devices in reality need to be put into use in specific projects for testing, and projects themselves come in a wide variety of forms. The most important requirement for industrial projects, as those working in industrial control surely know, is “stability”. You can take a look – any company that produces PLCs is definitely not a small one; their PLC products are highly popular and are used in various industries and fields, with countless examples of such use. PLCs can be found in control systems for power transmission and distribution networks, in stackers in automated warehouse systems, in certain equipment in the petrochemical industry, and also in steel-making control systems in the steel industry. And each of these projects has already helped other users verify how stable this PLC is. At the same time, to enhance stability, the PLC also has specialized modules designed; if one of these modules fails, it is sufficient to replace it with a new one, allowing the system to continue operating. The replacement speed is also very fast. Imagine that a company wins a bid to undertake a project with a deadline of 100 days. If Team A approaches the development of the control system using an embedded approach, then while they are working on designing the circuit boards, Team B, which uses the PLC approach, has already started writing control ladder diagrams for the PLC modules they have purchased. And this doesn’t even take into account the aspects related to embedded systems: the methods used to control outputs and the coupling circuits used to acquire inputs from the field. For PLCs, none of this is necessary; all they need to do is go to the PLC manufacturer and select the appropriate modules to be installed in their own control cabinets. Furthermore, if the project timeline is long enough and an embedded system is finally developed using high-tech methods, the process layout for future projects will be completely different; in that case, the embedded system used this time would also have to be discarded due to its lack of versatility. Furthermore, even if the embedded system is developed, it is the first of its kind; who can guarantee that no problems will arise in subsequent systems? What to do if a problem occurs – replace the control system entirely? What if the designer who created this embedded system has changed jobs? What should be done then? And for the PLC mentioned above, all that needs to be done is to buy another module to replace the existing one. In short, each PLC and embedded system has its own suitable applications, and it’s not possible to make generalizations.