Know the differences among a PLC, PAC and IPC

A programmable logic controller (PLC), process automation controller (PAC) and industrial PC (IPC) have unique features and benefits, but those traits are blurring as technology becomes more sophisticated.

By Jon Breen May 1, 2020

Is a programmable logic controller (PLC) always a PLC, or is it a process automation controller (PAC) or an industrial PC (IPC)? What’s the difference? Which one is needed for my process or machine? Let’s start by filling in some historical context and defining each term. 


Programmable logic controllers (PLCs) are industrial computers used for automation and control. A PLC system monitors inputs, makes decisions based on its program, and controls outputs to run a process or automated machine. This description also fits PACs and IPCs. 

So what’s the difference? There must be some clear definition between the three, right? Not quite. The truth is, there’re only very general guidelines that describe the differences, and there’s a lot of overlap among the three.  


By traditional definition, PACs are considered to be more decentralized, able to connect to remote input/output (I/O) and other PACs. They’re also touted as having more advanced programming capabilities compared to a PLC’s ladder logic language. This definition may have worked 20 years ago, but virtually all PLCs today have these features, as well.  

A more modern definition for PAC is elusive. The cRIO platform from National Instruments (NI) is a good example of a modern controller with the PAC label. It has features like a built-in field programmable gate array (FPGA) that aren’t seen on PLCs, but what exactly constitutes a PAC? A basic way of viewing it is a PAC is a PLC with a couple extra bells and whistles. Some of these extra bits will be adopted by the PLCs of tomorrow, which confuses the issue further. 


IPCs, like their non-industrial counterparts run operating systems (OSs) like Windows or Linux, giving them access to nearly endless software tools and connectivity options. Early IPCs were different from PLCs, bu like PACs, the technology is converging. Devices that run Microsoft Windows, but still look and feel like PLCs, have been around for years. For example, Beckhoff Automation sells IPCs that mount in a rack with I/O cards and can be programmed with ladder logic. It’s possible Microsoft Windows will be the norm in 20 years and the term “PLC” will swallow up IPC just like it did with PACs. 

PLC, PAC, IPC use vs. emotion

The terms PLC, PAC, and IPC are as much about branding as about capabilities. Each one has all the power to incite emotion that any logo ever did. PLCs may feel comfortable, predictable, known, reliable, safe, boring, limited. PACs may feel futuristic, exciting, scary, unknown or powerful. IPCs may feel unstable, unreliable, powerful, stable or reliable.  

Emotional responses vary depending on the individual, and may be extreme or dogmatic. For example, a person whose primary goal is to keep a production facility running may view everything in an extremely conservative way. This person may strongly prefer the term PLC because of its feeling of known, stable, reliable. Someone might things called PAC or IPC at all costs with thoughts like, “PCs get viruses, break down, require updates, etc.” and “Nobody knows how to troubleshoot a PAC if something breaks.”  

None of these thoughts is subjectively true across all devices with those names. In fact, many devices could easily be classified under two or all of those names. This is emotional rather than rational thinking; manufacturers know their audience and play to thatFor example, a manufacturer targeting a user base in production will use the term “PLC” to describe even its most advanced offering that fits the definition of PAC. A manufacturer focusing on R&D, test and measurement, and datalogging will choose the term “PAC” even for its simplest offerings. These labels are chosen as much for an emotional branding effect as they are to describe a technical difference.  

Controller to fit the application

So what’s the difference between a PLC, PAC, and IPC? It’s not always clear, but fortunately, that doesn’t have to get in the way of selecting a controller. Consider your goals and find something that works for the specific application. What is locally supported? What do other people use in similar situations? Know that each specific term is generally marketed towards certain industries and certain types of people.  

Understanding the target audience of a term and your general position might help narrow down the options a bit, despite the vagueness of the definitions. Beware the emotional branding effect of the terms – emotional responses affect decisions. Focus on specific and tangible benefits and capabilities while selecting a controller. 

Jon Breen, founder/owner, Breen Machine Automation Services, a Control Engineering content partner. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, 


Keywords: PLC, PAC, industrial controller 

The terms PLC, PAC and IPC are meant to imply different things, but there is a lot of overlap. 

When it comes to general capabilities, a PLC, PAC and IPC can do many of the same things. 

There are some situations and applications where one is better suited over the other. 

Consider this 

What criteria do you use when choosing among a PLC, PAC or IPC? 

Original content can be found at

Author Bio: Jon Breen, owner, Breen Machine Automation Services, LLC