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Long live the PLC!

17 May 2021

David Humphrey offers some thoughts on the changing role for a machine control stalwart – the Programmable Logic Controller (PLC) – as the industrial technology space continues to evolve at a rapid pace. 

The PLC has been declared dead many times. In the mid-1990s the first soft PLC hit the market  offering ‘openness’, a concept mostly unknown in the industry at the time. But the PLC endured in its classic form while the soft PLC remained a niche solution. In reality, the PLC will never go away. Its function will endure, but its look, shape and form factors will change to adapt to the needs of applications and automation architectures that today are now getting an IT makeover.

The influence of initiatives like Industry 4.0 and the Industrial Internet of Things (IIoT) is driving evolution in industrial technology at an uncommonly rapid pace. In short, the convergence of Operational Technology (OT) and Information Technology (IT) means that automation architectures are looking more like IT architectures.

The IT-ification of automation architectures got its first boost in 2004 when Industrial Ethernet solved the connectivity dilemma of industrial devices. Where it ends is anyone’s guess. Will IT giants move into the industrial space currently dominated by automation suppliers? Will automation hardware become a commodity and will future automation solutions be purely software-based? The answers to these questions lie somewhere between the Edge and the Cloud – the domains where OT technology is quickly evolving under the influence of IT. 

So what about the future of the PLC? Industrial users have clung to the hardware PLC for decades. A PLC is reliable and repeatable – it can be picked up, dropped, swapped out, and reprogrammed without a deep knowledge of programming languages. Over decades, these features have saddled PLCs with ever more tasks like high-speed motion control, data handling and even process control. While the PLC excels at some of these tasks, complex data processing is its Achilles heel because PLCs lack the data structures and the programming tools necessary for complex data operations. Fortunately, reaching this limit has helped industry users realise the real value of the PLC and seek out other ways of handling the rest of the solution.

Arguably, recognising the PLC’s limitations is what gave birth to the industrial edge. The IT-ification of automation technology is taking place, but clearly the PLC is not the right vehicle for this evolution. Instead, the PLC should be viewed simply as one of many functions that collectively make up a complete automation solution. This function is primarily logic control – monitoring inputs for change and setting outputs according to a programmed set of rules. Like most functions, logic control can be virtualised so that it can run on a different platform alongside other machine or process functions. As more tasks are off-loaded to the Cloud, automation systems now have a critical need to share data and communicate with cloud-based apps that have access to more data and processing power than are typically available locally on an industrial machine. 

So, what will the PLC of the future look like? Instead of a piece of ruggedised hardware, most future PLCs will be virtualised software functions that run on a server, either on-premise or in the Cloud, as part of a complete, mostly software-based solution. Programming tools will remain the same so that logic functions can be troubleshooted easily by plant floor staff. Private 5G networks will ensure that the PLC function can be accessed easily from anywhere in the plant without having to open electrical cabinets. In the same way, machine builders will be able to connect to a virtualised PLC during all building phases, from machine construction to factory acceptance testing to on-site commissioning. In fact, machine builders stand the most to benefit from PLC virtualization as they learn to use this technology as the basis for lucrative aftersales revenue streams generated from new digital services.

The PLC is not dead yet. Quite the opposite – it is aging well by adapting to the winds of change.

David Humphrey is research director, Europe at ARC Advisory Group.


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