Virtual PLCs Explained: Why Manufacturers Are Revisiting Their Approach to Controllers

Programmable logic controllers have been the backbone of industrial automation for decades. They are purpose-built, reliable and well understood by engineers and maintenance teams. For most manufacturers, PLC hardware is not something to experiment with lightly, and for good reason.

That said, at Outlier Automation, virtual PLCs keep coming up in our conversations with customers working through their first wave of physical AI projects.

So, just what are virtual PLCs and why are tech-forward companies and automation vendors focusing on them now? 

The idea behind virtual PLCs is to run PLC control logic in a containerized or app-based environment that can operate on general computing hardware, such as a server managed by IT onsite or offsite with a cloud service provider. This is different from a traditional physical PLC installed near a manufacturing line. It is also a significant evolution of the “soft PLC,” a related concept that is still typically tied to a physical, ruggedized industrial PCs (IPCs) installed near industrial equipment.

The main allure of the virtual PLC is that it fits into the broader shift toward software-defined automation, where more functionality is handled in software and managed using software engineering and IT-style workflows, rather than being tightly tied to specific hardware or vendors. This shift is driven in part by the fact that manufacturing systems are under pressure to become more flexible as product mixes change faster, lines are reconfigured more often and downtime becomes increasingly expensive. 

In response, major automation vendors are now offering virtual PLC products that integrate into the IT stack to unlock software-defined automation benefits. A few examples include:

• Codesys Virtual Control SL is an extension of their existing soft PLC framework that can be deployed in containers or hypervisors. 
• Beckhoff’s TwinCAT Runtime is making similar expansions into virtual PLCs backed by a Linux operating system. 
• Siemens, which is known for physical PLC hardware as well as industrial PCs, recently released its S7-1500V PLC that can be deployed on its Industrial Edge platform.

Considering these developments, let’s dive into some of the reasons why virtual PLCs could be enticing for manufacturers.

Failure recovery

Rapid redeployment to keep lines running when a hardware failure occurs is one major advantage of virtualized PLCs. In a traditional setup, if a PLC fails, recovery usually means replacing that specific piece of hardware. The correct PLC model must be on hand, firmware versions must match and the right program must be loaded. Even with good preparation, this process can take hours. 

With a virtual PLC architecture, because the controller exists as software, the system can detect that a failure has occurred and automatically restart the control instance on another available computing resource with the latest version that was running. 

In traditional PLC environments, PLC redundancy and automatic backup management are typically cost-prohibitive and complicated.  Most IT server environments already use established approaches for redundancy, failover and backups for very high reliability.  Virtual PLC architecture aims to use and adapt these capabilities within the industrial control realm.

Rapid development, testing and deployment

Virtual PLCs running in IT-managed stacks could significantly reduce the time it takes to develop and commission automated systems, whether for new installations or retrofits and expansions of existing lines. From a computing standpoint, a virtual PLC’s processing capacity is inherently flexible and can be increased quickly to handle more I/O or a larger system. With a traditional physical PLC, that kind of growth typically requires swapping to a larger controller while also needing to revisit hardware and panel decisions.

More than that, developing automated systems concepts and code in a virtual PLC environment allows control systems teams to more easily program and test their code in a development environment that does not require special hardware. Concepts like digital twins and virtual commissioning become much easier to realize by having logic processing (in a virtual PLC) within the same environment for communication, simulation and version control.

Knowing and validating that control system logic works prior to having access to the physical equipment being built can save OEMs, integrators and end users significant amounts of time and money. In addition, this type of workflow — which helps manufacturers know that their code changes will be right the first time — applies not only to initial commissioning, but also to updates and feature improvements during production.

It’s still early

Virtual PLC products are still in the early phases of development. There are certainly cautions that must be addressed when it comes to applications requiring safety controllers or control that needs tight millisecond accuracy, such as real-time or synchronized motion control. However, there are many control system applications where cycle time is not as critical and the ability to integrate tightly with software would unlock rapid scaling, manufacturing flexibility, the application of physical AI and more.

For now, the most practical takeaway is awareness of what is possible. Manufacturers don’t need to deploy virtual PLCs today to benefit from understanding them. But as software-defined automation continues to evolve, virtual PLCs are likely to play an increasing role in how control systems are designed, maintained and upgraded.

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