In the world of industrial automation, the terms PLC, PAC and IPC get thrown around as if they’re interchangeable. The problem is in many ways they are. And, as the technologies on all three categories of devices advance, their unique features and benefits converge and their differences become less noticeable.
So, how are these three technologies different, how are they the same, which one is best for which application and what are the pros and cons of each? Let’s take a look. But first, a little history lesson.
The Evolution of Controllers
Toward the end of the 1960s, programmable logic controllers (PLCs) began proliferating in industrial automation. The primary reason for their development was to eliminate the cumbersome and high-cost relay-based machine control systems that supported the U.S. car manufacturing industry. PLCs were small, simple, cheap and reprogrammable versions of the old relay racks using ladder-logic programming.
Today, PLCs automate the processes, machine functions and even entire production lines inside manufacturing plants. They provide several advantages over earlier automation systems: they tolerate the industrial environment, they are more reliable and more compact, and they require less maintenance than relay systems. They also use simple programming language and are easily extensible with additional I/O modules.
Industrial Personal Computers (IPCs) came along during the 1990s. They run on operating systems like Windows or Linux, giving them access to a ton of connectivity options and software tools. Their increased processor speeds, smaller footprints (compared to traditional PCs) and lower costs (also compared to traditional PCs) helped establish them as a viable alternative to PLCs in industrial automation. However, the first iterations were ill-suited for the dust, high temperatures and vibrations common in industrial environments.
The early 2000s saw the introduction of Process Automation Controllers (PACs). They can be described as industrial controllers that combine the functionality of a PLC with the processing capability of a PC. However, with no standard definition, the distinction between PACs and PLCs remains fuzzy. Higher-end PLCs incorporate many of the attributes once unique to PACs: standard programming languages, the ability to expand functionality through add-on modules, connectivity to various bus systems and monitoring and controlling a large number of I/O.
So What’s the Different?
Unfortunately, the differences between PLCs, PACs and IPCs remain shades of gray rather than black and white. To make matters worse, manufacturers are purposely blurring the lines even further by calling their devices PLCs, PACs or IPCs depending on what term their target audience calls a control device, regardless of which traditional category the device actually fits into.
That said, the simplest way to view these three devices is: a PLC can be thought of as the standard, base controller; the PAC is similar to a PLC but with additional features; and, the IPC runs the same software found on a PAC but with the full features of a personal computer.
Let’s Take a Closer Look
PLCs have a small footprint and usually use ladder logic to control discrete machinery or processes. They offer a wide range of features, from analog I/O to advanced communication protocols, and are relatively inexpensive, making them the go-to option in small scale projects. The more advanced PLCs are capable of remote I/O and motion control.
PACs are better suited for more complex automation solutions dealing with advanced process control, motion control, visualization and more. Also, PACs use exception-based logic instead of ladder-based. They are larger and much more expensive than PLCs, but they provide greater scalability, support a huge number of control I/O, offer the possibility to add other PACs for redundancy and much more.
IPCs offer the same advantages that PACs offer but with even more capabilities. They are becoming more suitable for industrial environments both on the hardware side (more rugged construction) and the software side (more applications). IPCs are being used for anything that needs the CPU power and the versatility of operative systems like Windows or Linux. Some are being used as a control center or database center for other control devices, such as PLCs and PACs.
Which Controller Is Right for You?
The neat and tidy answer is: it depends. One industry professional suggested, “If you’re looking at a standalone machine, a PLC may be the right choice. But if you want to also address motion and safety or controlling remote I/O, a PAC is often the way to go. And if you need to layer on additional features and software beyond what a PAC can do, that’s when you might start looking at an IPC.”
Price will always be an important determinant. However, are you talking about upfront costs or lifetime costs? In some cases, a large initial investment might be cheaper in the long run when you consider future scalability needs and data mining and analytic capabilities for continuous process improvement. Ultimately, the final selection will be determined by a variety of factors that apply to your specific application including functional requirements, future expansion plans, company/vendor relationships, experience with specific automation platforms, experience with customer support and, yes, cost.
If you need help determining what’s right for your particular application, Real Time Automation can help. We’ve been delivering innovative communications solutions to the industrial automation market since 1989. Our products seamlessly integrate your process equipment so you can collect, analyze and interpret the real-time data you need to improve productivity and maximize efficiencies.
RTA specializes in making easy-to-use connectivity products, including industrial protocol gateways, embedded source code stacks and customized OEM solutions. Our products are used by control engineers on factory floors all over the world and come backed by our industry-leading Enginerd® tech support to help you save time, money and aggravation. And, our products come with a 5-year warranty, are made in America and are always in stock, ready to ship the same day you place an order.
At RTA, we move your data…so you can move your business forward.