PLCs and PACs End Courtship, Get Hitched

Like many of us, PLCs have been around for decades. Also like many of us, they are improving as they grow in age and intelligence. PACs are a newer creation, originating in the 21st century. Now, it looks like these two product categories are coming together, with the result being the PLC-based PAC.

This new name makes sense because PLC-based PACs combine the best of two technologies, delivering the performance you need at a price you can afford. The PLC world brings ruggedness, dependability and a history of reliable performance. The PAC (programmable automation controller) contributes new, low-cost technologies borrowed from PCs and mobile. And as with any good marriage, the whole is greater than the sum of its parts.

Ignoring the ties to the PLC and just calling this new class of controllers PACs never seemed right to us, as it was obvious there was a strong connection between the two. Hence, we christen this new class of controllers PLC-based PACs, a moniker that may be a bit unwieldy but very descriptive.

P2000 CPU

Not to overly confuse things, but many suppliers are still hanging on to the PAC name for their high-end and high-priced offerings, creating three classes of controllers: PLCs, PLC-based PACs and PACs.

Alike in Many Ways

Here at AutomationDirect, we make PLCs and PLC-based PACs, as do many other suppliers, many of whom also make PACs. We find all of these industrial controllers share similarities.

Scan times are faster than ever before, advancing along with the processor chips found inside the controllers. More and more, industrial controllers are allowing the use of tag names instead of fixed addresses, greatly simplifying programming and maintenance. After all, what’s easier to remember, a descriptive tag such as LSH-101 to denote a level switch high, or a cryptic controller address?

Tag naming was made possible by lower cost memory, and many end users are taking advantage of this newly abundant storage capacity by loading program documentation into the controller, a very welcome addition for maintenance and troubleshooting.

Can We Talk?

Another similarity among all types of modern industrial controllers is the proliferation of comm ports and protocols. Older PLCs often had just one port and one proprietary protocol, but rare is the new controller without multiple ways to communicate with other controllers, HMIs and upper level computing systems.

Most every industrial controller has an Ethernet port, and popular Ethernet-based protocols include EtherNet/IP and Modbus TCP/IP. Many controllers also provide serial Modbus and ASCII communications to talk with bar code scanners, message displays, scales, VFDs, temperature controllers, timers/counters and other similar devices.

PLC-based PAC

Just the Same, but Different

While modern industrial controllers share many characteristics, there are some important distinctions between a PLC-based PAC and a PAC, best expressed in this table:

Differences between PLC-based PAC and PAC

As can be seen from the table, PLC-based PACs are a good fit for all but the largest and most complex applications.

Picking the Right Product

When you’re ready to design your next control system, don’t get hung up on the name. Instead, select the best product for your application, whether it’s a PLC, a PLC-based PAC or a PAC.

This blog post is based on the article titled Blurred Lines: PLCs and PACs Converge. This article was authored by Jeff Payne, Product Manager of Automation and Controls, AutomationDirect. This copy originally appeared in the June 2015 issue of Applied Automation.

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