Programmable logic controllers have been around for decades, and programmable automation controllers for not quite so long, but each has its special role in the manufacturing hierarchy.
Both PLCs and PACs can come in small or large packages and range in price from about a hundred dollars or more to thousands of dollars. Knowing which to specify for an application depends on your needs and may include, for example, cost, performance, bandwidth (number and type of I/O and processing speed), type of process (discrete, analog/PID or a combination thereof), data sharing and manipulation, and/or maintenance—keeping track of sensor and actuator health in a machine—or monitoring motor and bearing wear on pumps, compressors and the like.
No one article can pretend to have all the answers, but it can provide some bullet points to consider how much technology you need to solve an automation problem. When you purchase a machine, it already includes the necessary controllers to meet its needs. (For more on PLCs and PACs in machine control, see FE, September 2016.) However, unless you buy all of the equipment on a single line from the same manufacturer, there may be some additional controls that need to be added, for example, conveyor controls that link to a machine controller. Often, this might be the role of a “cell controller,” a device taking the appearance of a PAC with some kind of PC-based framework. No doubt, this will require additional system integration.