A programmable automation controller (PAC) is a compact controller that combines the features and capabilities of a PC-based control system with that of a typical programmable logic controller (PLC). PACs are most often used in industrial settings for process control, data acquisition, remote equipment monitoring, machine vision, and motion control. Additionally, because they function and communicate over popular network interface protocols like TCP/IP, OLE for process control (OPC) and SMTP, PACs are able to transfer data from the machines they control to other machines and components in a networked control system or to application software and databases.
Programmable Automation Controllers were first introduced by Control Technology Corporation in 1985 as an alternative to traditional PLC technology. The ARC Advisory Group, an analyst group focused on the manufacturing industry, is generally credited for popularizing the acronym "PAC". It was first coined in 2001 as a way to help users of control hardware better define their needs, and to give the leading control hardware vendors a term to more clearly communicate the capabilities of their products.
PAC - PLC Comparison
Generally, PACs and PLCs serve the same purpose. Both are primarily used to perform automation, process control, and data acquisition functions such as digital and analog control, serial string handling, PID, motion control, and machine vision. The parameters within which PACs operate to achieve this, however, sometimes run counter to how a PLC functions.
Unlike PLCs, PACS offer open, modular architectures, the rationale being that because most industrial applications are customized, the control hardware used for them needs to allow engineers to pick and choose the other components in the control system architecture without having to worry whether or not they will be compatible with the controller.
PACs and PLCs are also programmed differently. PLCs are often programmed in ladder logic, a graphical programming language resembling the rails and rungs of ladders that is designed to emulate old electrical relay wiring diagrams. PAC control programs are usually developed with more generic software tools that permit the designed program to be shared across several different machines, processors, HMI terminals or other components in the control system architecture.
PAC processing and I/O scanning is also very different. Unlike PLCs, which constantly scan all the I/O inputs in the control system at very high rates of speed, PACs utilize a single tagname database and a logical address system to identify and map I/O points as needed.