Jon Giardina
Omron Electronics Inc.
Schaumburg, Ill.

The ZEN logic controller from Omron measures 70 X 90 X 56 mm and comes standard with 10 I/O lines. Ladder logic programs can be as large as 96 lines.

After more than a decade of articles touting the benefits of PC-based control over a programmable logic controller and predictions of the PLC's demise, this much is clear: both PCs and programmable logic controllers ( PLCs ) have their place in contemporary control systems. In many cases, they will work as a team.

In lower-end process industries such as food plants where the programmable logic controller ( PLCs ) is strongly entrenched, there is little interest in switching to PC-based control. The reason is the programmable logic controller's ( PLCs ) suitability. Sequential logic control provided by a programmable logic controller ( PLCs ) is best suited for round-the-clock operations common in those industries. In particular, a programmable logic controller ( PLCs ) can offer repeatable, reliable control conducive to high-speed, repetitive processes. Dedicated performance and a high level of security are also benefits of a programmable logic controller (PLCs ). The packaging side of a food plant lends itself well to sequential logic control which makes a programmable logic controller ( PLCs ) the best choice for conveying and sorting applications.

Five years ago, the prediction was that PCs were going to take traditional programmable logic controller ( PLCs ) applications by storm. The reason they didn't is that the programmable logic controller ( PLCs ) has continued to be a good, low-cost control option. For instance, a programmable logic controller ( PLCs ) with highspeed counter inputs, loop controls, analog points, and basic math calculations are available in the $200 to $400 range with 100 or more I/O and with options for expansion. On the other hand, even buying an inexpensive PC requires loading software, setting it up, and making sure it's robust enough to not crash.

However, PC-based control has its merits. Specifically, it has greater number-crunching capability, more communication options, and is geared more toward data logging and trending, plant monitoring, report generation, and documentation. The key reasons to switch to PC-based control include networking the control system to higher-level applications such as ERP, handling complex mathematical applications such as vision inspection systems, and connecting to bar-code scanners, in-motion weigh scales, and other devices. In short, most users believe that when data must be transferred from the controller into a database for analysis, the transfer goes more smoothly when the data is already on a PC-based system.

Programmable Logic Controller ( PLCs ): Motion Controller Information