Programmable automation controller (PAC) is a term that is loosely used to describe any type of automation controller that incorporates higher-level instructions. The systems are used in industrial control systems (ICS) for machinery in a wide range of industries, including those involved in critical infrastructure.
A PAC makes it possible to provide more complex instructions to automated equipment, enabling much the same capabilities as PC-based controls in an all-in-one package like a programmable logic controller (PLC).
PLCs were created in the 1960s as an improvement over relay-based systems. Although more advanced than relay, PLCs still functioned by simple ladder logic that resembled the appearance of wiring diagrams of relay systems. In the beginning, PLCs had limited memory, required proprietary terminals and lacked remote I/O (input/output) capabilities. Additional abilities required adding hardware cards. PC-based programming of PLC was introduced in the 1980s and offered greater abilities, more memory and sequential control.
Early PACs came on the scene at the beginning of the 21st century. PACs offered a combination of the abilities and technologies of distributed control systems (DCS) and remote terminal units (RTU) as well as some of the abilities offered by PC control. PACs offered more connectivity options and broader control while maintaining smaller packaging and durability for environmental stresses and shock. With these new improvements, PACs were widely adopted.
Controllers of both types (PAC and PLC) have advanced since their creation. With the increased capabilities of PLC, the differentiating lines between the two have blurred. Higher-end PLCs with increased capabilities are often marketed as PAC.