Understanding the Differences Between PLCs and PACs

Programmable logic controllers (PLCs) and programmable automation controllers (PACs) have many similarities, and as technology advances the lines between the two are blurring, which can make understanding the difference between them more difficult.

Both PLCs and PACs are industrial computers intended for use in automated environments. Their primary purpose is to control automation equipment. Nearly every piece of automation equipment is built with either a PLC or a PAC. While they perform essentially the same functions, the two are different on a technical level.

Defining Programmable Automation Controllers (PACs)

The most distinct difference between PLCs and PACs is that PACs leverage a different programming interface. Typically, PACs use C or C++ programming languages for more sophisticated control functions. PACs have an open architecture, allowing them to easily operate with multiple devices, networks, and systems. 

PACs also utilize a modular design. This simplifies the expansion process, making adding or removing components easier. In addition to monitoring and controlling thousands of input/output (I/O) points, PACs also allow for tag-based programming where a single database of tag-names is used for development. 

PACs offer robust monitoring and control features when compared to PLCs, which are more basic in design. 

Defining Programmable Logic Controllers (PLCs)

PLCs are more simplistic in their design and function. They usually leverage a programming interface called Ladder Logic, as opposed to the more complex C or C++ programming interface leveraged by PACs. 

While PLCs have simple program execution scans and more limited memory, they’re capable of high-speed I/O, sequencing, and proportional-integral derivative control. Most PLCs come with built-in networks that allow for communication between multiple PLCs, human machine interfaces (HMIs), and/or supervisory control and data acquisition (SCADA) systems. 

PLCs may offer a lower cost and streamlined control solution for certain applications, particularly those with lower levels of automation. 

PACs and PLCs perform essentially the same functions, but they do so very differently. From their programming interfaces to their methods of communication, they differ in how they provide control of automation equipment.