By Dan Hebert, Senior Technical Editor
Many process control applications require much more than just real-time control, and extensive communications and data handling can tax the functionality of PLCs. In these instances, a programmable automation controller (PAC) can be a good fit. Most PACs are derived from the PC world; hence their relative strength when it comes to communications and data handling.
A good example of using a PAC instead of a PLC or a DCS is a recently implemented mercury emissions sampling system for monitoring stack gasses in a coal-fired power plant. A DCS would be too expensive and not rugged enough, and a PLC would struggle with the required communication and data handling tasks...