The PLC versus the PC
By Joseph R. Garber

OREO COOKIES, robotized offshore oil rigs and The Phantom of the Opera are governed by a common technology: PLCsprogrammable logic controllers.

Although the PLC business is a $6 billion hardware industry growing at 20% per year, few people but factory automation experts know it exists. That seems unfair to me. After all, while personal computers and the Internet get most of the publicity, it's PLCs that do the world's real work.

At heart, a PLC is an industrial-strength microcomputer. In contrast to PCs, which are designed to do many jobs, programmable controllers are intended to perform only one chore, but to perform it flawlessly. Often it's to run a sequential manufacturing process.

Heavy manufacturing is an unforgiving environment. General Motors estimates that production line downtime costs it $15,000 a minute. A seemingly trivial but repetitive task like dropping the Phantom's chandelier right on cue (or stamping out millions of Oreos) is actually a high-precision job. Nor is there much leeway in tipping cauldrons of molten steel or pumping propane refrigerant. In some businesses, a millisecond's mistiming can mean a multimillion-dollar lossor body parts strewn over an acre's area.

Given the frequency with which both Wintel and Apple computers crash (a weekly certainty in my experience), putting either in charge of a precision production process could be a recipe for disaster. Instead, you want a machine that, unlike PCs, will do exactly the same things at exactly the same intervals for as long as you let it run. You want something with a mean time between failure in the neighborhood of five years, not five days. PLCs fill the bill. It's no surprise that industry leaders Siemens and Rockwell's Allen-Bradley subsidiary (neck-and-neck for number one) are doing very well.
Putting a PC in charge of a precision production process could be a recipe for disaster.

Once markedly dissimilar, there's no longer much visible difference between the guts of a PLC and the innards of a personal computeropen either up and you'll find a motherboard, processor, memory, expansion slots and all the rest. But though they look the same, they behave quite differently. PCs are vain and idle creatures; they spend most of their time updating their displays and waiting for commands from their masters. Moreover, they're easily distractedgive them an order via keyboard or mouse and, no matter what they're doing, they'll pause momentarily to react. Imperceptible to us humans, such hiccups can throw an entire factory out of kilter. PLCs don't hiccup. Nor are they ever idle. And only potentially serious situations (for example, plummeting pressure) can distract them from their job.

Will personal computer and programmable controller technologies ever converge? According to Randall Freeman, Allen-Bradley's Milwaukee-based vice president of global marketing, the answer is someday, but not soon. Technical differences notwithstanding, the PC and PLC industries are starting to look more alike. First, there's miniaturization. According to Freeman, where once it took a flatbed truck and a team of sweaty guys in T-shirts to deliver controllers to customers, today's PLCs are sleekly compact. A $300 baby PLC fits neatly into a coin-operated coffee machine.

More important than size, modern PLCs are no longer the closed and impenetrably proprietary boxes of an earlier generation. True, the controller manufacturers' definition of "open architecture" is far more restrictive than Intel's or Microsoft's. Nonetheless, their tardy tolerance of third-party plug-ins to their boxes has sparked no small entrepreneurial boom. These days more than 1,000 independent innovators sell PLC add-in boards or other peripherals. At least twice that many develop custom or packaged PLC software. To my eyes that makes the PLC industry look a lot like the PC industry a dozen years agoor the Klondike in 1897.

With PLC prices falling (although you can spend up to $20,000 for one of the things), PLCs seem to be finding their way into places no one imagined, to do things never conceived of. That means new opportunities for hi-tech innovators.

Entrepreneurs take note: It could just be that the next big gold rush won't be the Internetor much else to do with personal computers. Programmable logic controllers may be where the real action is.


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