The programmable logic controller (PLC) and programmable automation controller (PAC) are integral parts of most automation operations. The devices have been around so long and have such reliability that when adding them to a new line, the choice might be taken for granted. That’s a mistake, said Jeff Payne of AutomationDirect. 

“The difficult part can be deciding whether to run a single program on a large PLC, or to deploy the same project on multiple smaller PLCs, each only executing the parts of the program needed to run the specific subsystem,” he writes. “It’s more complex than picking a PLC, PAC, or PC-based controller-size, capabilities, and functions enter into the discussion.” Payne notes the hardware, software and operational needs of the plant have to be identified first, because those decisions may have an impact on other parts of the network. “In addition to distributed I/O, communication among multiple PLCs, peripheral devices, and enterprise-level systems may be required. The extent of these communication needs must be determined early in the process with the expectation that whatever they are now, they will only get more complex going forward.”

Bob Vavra, content manager at CFE Media, bvavra@cfemedia.com.