Part Two: PLCs are Challenged

You are reading Part 2 of the History of PLCs series. In this series of blogs, we write about the PLC industry. Its challenges. And how to overcome them. Enjoy!

Last time, we concluded that when they came into being; PLCs had four great advantages — however, over the years, this situation has changed.

There has been a significant shift in the performance, methods, and means of creating systems, which enable fast delivery and many new features in information technology since the '70s. However, no comparable development happened for the control systems — until now, information technology and control systems have lived in isolation from each other.

The price of hardware has decreased significantly. Today, the cost of more powerful hardware is a fraction of the cost of a PLC system — precisely the opposite of how it was decades ago. It is worth mentioning that today's smart devices, computing power, storage, and other equipment; exceed the capabilities of PLCs. If we compare a system like Arduino or Raspberry Pi, their performance and storage easily outperform that of PLCs at a fraction of the cost.

The robustness of commonly used devices is unprecedented compared to the past. In the past, the main reasons for the limited resilience were moving parts such as HDD hard drives (today replaced by SSD) and ventilator cooling (replaced by passive heat dissipation methods). Just one look at your mobile phone brings back memories of many accidents that would have ended the life of a similar device in the past. Times have changed. The weakest factor in the life of smart devices has become their moral aging, not their construction.

Determinism is the most critical feature of PLC systems in real-time control. Commonly used operating systems (Windows, Linux, Android) do not guarantee determinism under normal circumstances. However, there have also been significant developments in this area. Hardware performance is now much higher than when PLC systems were born, and more importantly, there are reliably proven solutions for deterministic programming. These are primarily systems capable of running alongside the operating system or in complete isolation. At the same time, they use the same hardware and thus allow rapid communication with a conventional operating system.

The life cycle issue (hardware availability and support) loses importance because of the ability to virtualize the run-time environments of the control system. In the past, the running of a particular program was firmly tied to a given type of hardware; virtualization allows for running the same program on different types of hardware. The guarantee of the program's functioning even extends to the hardware produced in the future. In other words, if the control program runs on hardware X today, it will run on hardware Y tomorrow; reducing the need to keep morally obsolete devices alive.

Do PLC systems still make sense?

It should be clear that PLC systems belong to the past, and we must replace them with something new. As usual, things are complicated, and simple solutions usually overlook that the devil hides in the detail.

There are some legitimate reasons why we should be patient with PLC systems. These are mainly the amount of available I/O hardware, industrial buses, and the large amount of human potential that still exists for both industrial automation component manufacturers and industrial equipment manufacturers. Also, the run-time model of input reading (program run) the real-time update of outputs; reduces the complexity that occurs with event (reactive) control. There is, however, a profound need for a shift towards PC-based PLC systems. Such a shift, in contrast to classical PLC systems, would open wider possibilities and higher performance; all at the same or an even lower price.

Part one: Rise of the PLC Systems
Part two: PLCs are Challenged
Part three: Differences in PLC Programming Languages
Part four: What Can Australian Natives Teach Us About Modern PLCs?
Part five: Will Industry 4.0 Save Us?
Part six: PLC Performance Challenges
Part seven: Why Beckhoff PLCs?
Part eight: Connecting PLCs to the .NET Environment

Tags: History of PLCs

Peter Kurhajec
CTO of Inxton

Peter Kurhajec

Hello! I'm the CTO of Inxton! More than a decade ago my pet project turned into a full-time job - INXTON. Now I'm on a mission to bring industrial automation and information technologies together.