Future of the PLC

PLCs are evolving and continue to be the best option for a variety of industrial automation applications. Greater programming flexibility and ease, scalability, more memory, smaller sizes, very high-speed (Gigabit) Ethernet, and built-in wireless are among evolving programmable logic controller features.

By Jeff Payne August 26, 2014

If you use PLCs or are thinking of doing so, you may consider them to be a mature technology with little room for improvement as they’ve been around for nearly 50 years. But like their close counterparts in the world of consumer electronics, significant improvements continue with no end in sight, promising faster, smaller, and lower cost solutions.

The PLC’s hardened embedded processor, running a real-time proprietary operating system, has proven to be a mainstay of the industrial automation world, fighting off all challengers to its supremacy. Microsoft Windows-based open systems have made inroads but lag behind PLCs, a trend expected to continue as the PLC with its purpose-built hardware, specially designed software, and one-supplier support model remains a solid choice for many industrial control applications.

From the beginning, when the PLC was typically replacing scores if not hundreds of relays and timers, there’s been a push to decrease automation system size and to simplify support and maintenance. Over the years the relay panels have been replaced with smaller rack-based PLCs (Figure 1), or smaller yet PLCs with remote I/O. In terms of software, ladder logic programming initially mimicked automation systems based on relays and timers, and continues to be the most widely used PLC programming language. But other options have emerged—specifically, the IEC 61131-3 suite of PLC programming options.

In the future, PLCs will continue to evolve while adapting technology improvements in hardware, communications, and software. Part of the evolution will include merging of PLC and programmable automation controller (PAC) functionality, along with advancements to span communications from the plant floor to the top floor.

[A PAC is generally recognized as a hardened modular industrial controller that uses a PC-based processor and allows programming options beyond the IEC 61131-3 languages. Industrial PC or IPC is another term often used interchangeably with PAC.]

Smaller, faster, better

Today’s processors, circuit boards, and components are shrinking throughout the electronics industry. These technology improvements are slowly making it to the PLC, although the need for stability, reliability, and ruggedness slows acceptance. Current enhancements include faster processors for improved cycle time, added memory capacity, and new communication features.

In response to market demands, many features and functions are migrating from higher to lower-end PLCs. For example, we can expect that small PLCs will evolve to include many of the features of higher-level PLCs, and mid- and high-range PLCs will offer a smaller, more compact solution to meet users’ needs.

PLCs are also taking advantage of dramatic declines in solid-state memory costs and size. This permits greatly increased local data storage, allowing the use of a PLC in many applications formerly requiring expensive data acquisition systems. It also opens the door to other features, such as the on-board storage of product information, which can expedite troubleshooting.

Today’s PLCs are already benefiting from USB technology, making it easier than ever before to get online, program, and monitor your control system. This technology is continuing to evolve, and with the availability of smaller micro and mini USB connectors, you can expect to see this communication option on more of the smaller PLCs.

Another example of a feature from the fast-moving consumer electronics world that’s quickly penetrating the industrial controls market is nonvolatile portable memory devices. These offer great benefit to the PLC customer by providing an enormous amount of additional memory in a small package. These options include USB devices to SD, miniSD, and microSD cards, adding up 32 GB of additional memory to a PLC as needed by the end user, machine builder, or system integrator.

PLC and PAC Merge

Many industrial controller suppliers tout the differences between PLCs and PACs, but future automation engineers may not care about the nomenclature, focusing instead on performance and the available features when specifying their systems. Just as the definition and features of each have changed over the years, PLCs and PACs will continue to merge as they each evolve.

During this evolution, there will be plenty of room in the market for low- and high-end processors. With advances in hardware technology and the passage of time, it is inevitable that advanced features will make their way into the lower-end processors as well. This will in turn put pressure on suppliers to include even more features and options in their higher-end products.

Higher-speed processors and more memory will opens the floodgate for advanced features such as motion control, vision system integration, and simultaneous support for multiple communication protocols-while still maintaining much of the simplicity that makes the PLC so attractive to many users.

During this period of PAC versus PLC, we have seen a much faster advancement of both classes of the product. PACs have allowed users to stretch the envelope of what is considered traditional industrial automation, encouraging suppliers to grow products to meet their demands.

These demands have challenged product designers to find new ways to support the available components and build them into a system that will be rugged and stand up to the punishment of an industrial environment. The challenge continues with providing the connectivity, memory expansion, and processing power improvements required to handle ever more complicated applications, while maintaining or even lowering the cost of the final product.

Ladder logic: Never say good-bye

Fifty years ago, hardwired relay logic was replaced with ladder diagram. This language kept things simple for technicians and engineers who had grown up with relay logic, but it had some limitations, particularly in terms of process control and data handling.

The IEC 61131-3 standard introduced other programming languages for industrial controllers, but ladder diagram responded with advancements of its own and has shown surprising staying power. There are applications where sequential function chart is better, particularly for process control. Structured text works well for data manipulation, and other IEC languages have their strong points. But ladder diagram forges on, and remains the leader by a wide margin in terms of PLC programming languages.

Suppliers and their customers support a large installed base of equipment controlled by PLCs programmed in ladder logic. There’s also a large group of engineers, technicians, electricians, and maintenance personnel who prefer this simple programming technology. Regardless of the hardware involved, this language has gone a long way to making the PLC the industry standard, and this trend is expected to continue.

While ladder logic is the anchor of machine control simplicity, function block programming techniques can reduce the amount of code, particularly as PLC coding merges into one programming environment.

One programming environment

The combining of PLC, motion control, and human-machine interface (HMI) programming into one environment is a trend that will progress over the next several years. The integration of the PLC and HMI processor into the same rack may likely follow suit, with the monitor either included as part of the package or provided as an external option. Whether it’s the same processor or an HMI module added to a PLC I/O rack doesn’t matter as even current technology enables either configuration.

Having a unified programming environment is ideal for most users, as long as it’s not too overwhelming. Key benefits to marrying these packages include a reduced learning curve and less total development time. However, if the tool is not properly thought-out, it can become cumbersome and uneasy to navigate.

A good step in the right direction toward a fully unified programming environment is ensuring devices can share the same tag name database. The tag names are the key link between program and process, and creating the database is a time-consuming task. Eliminating duplication of this task drastically reduces the overall development time and reduces the chance for errors.

Let’s talk communications

Over the last several decades and especially in the early 1990s, an excessive variety of communication networks and protocols were developed and used for industrial communication. Over time, these contenders were narrowed down to a select few leaders. This trend will continue and will further focus on plug-and-play solutions that self-configure, once again following a trend from consumer electronics, in this case the PC and its peripherals. In terms of determinism, there will be no need to focus on whether or not these communication technologies are actually real-time, as the raw speed of Ethernet and many other industrial control networks will be much greater than what’s required for the vast majority of applications.

Regarding a universal interface to local memory and other devices, USB shows promise but has its limitations. USB is plug-and-play, but integrating software and hardware for USB use requires an additional investment by device suppliers. Because of this, slow-to-change industrial hardware vendors, such as weigh scale or bar code reader suppliers, will keep RS232 around for the short term.

In its present form, a high-end PLC includes many communication ports to support multiple protocols (Figure 2). Long term, this promises to change, as users demand more standardized options, possibly just Ethernet and wireless, with industrial Bluetooth a possible option in the latter category.

It is a wireless age; however, industry does require a more robust wireless technology with improved range and the preservation of data integrity before we see a large convergence of commercial and industrial wireless communication protocols. [See Industrial Wireless Tutorials.]

We have seen advancements in this field, from the latest Wi-Fi (802.11n) and ZigBee (802.15.4) protocols to the use of ad hoc and mesh networking and the rise of Bluetooth and Near Field Communication (NFC)-but none of these has emerged as a suitable solution for mission critical plant floor applications. The future will encompass wider adoption of wireless, as it works well for applications like remote terminal units (RTUs) where line-of-sight is available, and also in many less critical monitoring applications where real-time control isn’t required.

Connected factory

Perhaps the most dramatic change in the PLC’s future will be the integration of enterprise resource planning (ERP) and other higher level computing systems to the factory floor. [See Information Integration Study.] In the past, it was a major integration task to extract machine or process data and feed it upstream to these system, but future technologies will include the hooks, functions, and features needed to simplify this integration (Figure 3).

With this in mind, controller manufacturers need to consider the user’s needs and provide a solution where the PLC is not only controlling the application, but also providing the tools to seamlessly manipulate and present process data to the users who need it.

This could include providing access to data through a web browser or via mobile apps, or including the tools to interface with a database. This is a natural progression for the PLC. The enhanced communications capabilities, improved processing power, and greater memory capacity all give the PLC the ability to now manage the data it has always created.

In the future, PLC likely will still be the nomenclature used for many industrial automation controllers, although significant changes will be made to form, purpose, and performance (see Table). The PLC’s size will continue to be reduced, and hardware improvements will expand the features, functions, and capabilities of this rugged, long-lasting industrial controller. Software and communication capabilities will also evolve, creating a new industrial automation platform with an old name.

– Jeff Payne is product manager — Automation Controls Group, AutomationDirect (formerly known as PLCDirect). Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, mhoske@cfemedia.com.

Key concepts

  • Programmable logic controllers (PLCs) continue to evolve for industrial automation applications.
  • Future PLCs will include greater programming flexibility and ease, scalability, industrial construction, more memory, smaller sizes.
  • PLC communications will integrate very high-speed (Gigabit) Ethernet and wireless capabilities.

Consider this

Just because an old PLC still works doesn’t mean it wouldn’t be worth the investment to look at new, easier, more effective PLC options.

ONLINE extra


This online article for September has additional links, including research on PLCs and industrial communications; see a PLC history article, also in this issue.

See Industrial Wireless Tutorials.

See Information Integration Study and Mobility, Ethernet, and Wireless Study from Control Engineering.

Global economy decreases PLC demand but U.S. economic growth brings expanded PLC use: see related PLC article links below.