The personal computer (PC) has been a boon to the control of industrial systems. The PC provides many advantages over the traditional PLC, like the ability to do complex calculations, connect to the outside world, offer feature-rich operator interfaces, and collect and analyze real-time data. Through the use of PLC emulation software, PCs can even do things that have been traditionally the work of PLCs. These abilities make the PC an indispensable part of many industrial systems.

However, the PC has a major disadvantage when applied to industrial systems. PC software and hardware tend to have a much shorter lifecycle than that of industrial controls and devices. Most of the solenoids, transducers, motor starters, etc., that we had in 1994 we have today. In addition, many of the PLCs in use in 1994 are still available (or at least supported) today. However, in 1994, the typical high-end PC had an Intel 386 processor running the MS-DOS operating system. Many of the compilers and canned operator interfaces that ran on those systems have been converted to Microsoft Windows operating systems. In addition, many of the new processors of today are incapable of even running the old MS-DOS operating system, not to mention finding a person today that can effectively work in the MS-DOS environment.

What can be done to lengthen the life of that PC resource? Listed are a few of the support strategies that can be employed.

• Strategy #1 —Hold on tight. In this strategy, no extraordinary support is provided for the PC on the industrial system. Although the original software may be backed up, little other support is provided. This strategy is the lowest cost and easiest-to-implement strategy, but the PC will only have a maximum life of about four years.
• Strategy #2 —Technology freeze. In this strategy, exact duplicate(s) of the PC are purchased and loaded with the proper software and hardware. The hardware and software is not updated as time goes on and is essentially "frozen" in time. This is a mid-cost strategy that can extend the life of the PC control to a maximum of 10 years.
• Strategy #3 —Latest and greatest. At predefined intervals of between two to four years, the old PC hardware and software is totally replaced with the newest hardware and software. All support costs to the OEM are paid, all updates to software are installed, and old code is updated. This is the costliest of all strategies, but it does guarantee that the PC control will last indefinitely.

What is the best strategy to employ? The answer depends on how important your industrial system is and how long it needs to last. "Holding on tight" only works for the most non-critical, least important, or most short-lived systems in your plant. Unfortunately, this is an all-too-common strategy. Although the "technology freeze" strategy is better than the "hold on tight" strategy for critical systems, it is only delaying the inevitable; the PC control will have to be totally replaced some day. Grudgingly and through bitter experience, many companies have come to realize that the "latest and greatest" strategy is really the only way to support their critical PC systems.

The key to effectively protecting the PC resource is the control professional. While management may choose what seemingly is the cheapest and easiest support route, it is up to the control professional to do what is best for the long-term operation of the system. Through the use of cost analysis tools and an honest dialog, the proper support for the PC resource can be established. Employing the proper support strategy can ensure that the PC resource will be protected for many years to come.

The opinions presented in this column are those of the author and not necessarily those of Control Engineering or Reed Business Information.

If you would like to step onto the Soapbox, contact David Greenfield, editorial director, at dgreenfield@reedbusiness.com