PAC Vs PLC: What's the Difference?

A few years ago, the term PAC (Programmable Automation Controller) started to appear. Many PLC manufacturers began to market new PAC's along with their traditional line of PLC's. If you use AutomationDirect.com as an example, their traditional line of PLC's (DL05, DL06, and others) are still available - and still fairly inexpensive. The new Programmable Automation Controller in contrast, is predictably more expensive and has many more options for networking, expandability, and user interface. This seems to be the differentiation between the traditional PLC and the newer PAC: Relative cost, expandability, functionality, and user options. A more telling indication of the new standard of higher-end PLC's being referred to as PAC's, is with the Rockwell/Allen-Bradley products. The Rockwell site used to list the ControlLogix and CompactLogix platforms as higher-end PLC's; however, now these systems are listed as PAC systems. Schneider/Telemecanique has seem to fallen into step and created their own PAC with the new M340 series. The new M340 series does not have more capability than the Premium or Quantum lines; however, Schneider has chosen to market this platform as a PAC.
Though there's no official differentiation between the term PLC and PAC, I like to think of the differences in terms of how the system is applied: If the system is controlling 1 or 2 machines or processes, then I refer to that as a PLC. If a system is controlling a complete factory floor, then I would tend to refer that system as a PAC. I also tend to refer to a controller as a PAC if it is taking the place of a traditional DCS system. Since DCS systems are usually designed to control many different processes, any off-the-shelf system used as a DCS system can be safely regarded as a PAC system. One other qualifying aspect of a PAC would be if a business front-end were integrated with the system. For example, if you have SAP running an order-picker application and SAP is communicating with a automation system, then that system could be regarded as a PAC.
The difference between PLC and PAC is really up to the interpretation of each user. To the OEM or integrator; however, the difference between the PLC and the PAC will be most visible with the cost of new purchase parts. PAC's will almost invariably be more expensive than platforms referred to as PLC's. Additionally, the software required to program these systems will also be more expensive than the software required to purchase their respective PLC counterparts.

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