Personal Computers Lose the Pretty Face

PC-based control gains acceptance with new and more practical form factors

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It could be an episode of "Fear Factor": A control systems engineer is forced to perform control of a critical process using a desktop Windows PC!

Rational or not, many end users and system integrators fear using PCs for real-time process control. "We have not implemented PC-based control, and I am not aware of any client applications. Everyone I speak to expresses many reservations regarding PC-based control," says David Kennedy, PE, a control systems engineer with Fresno, Calif., system integrator Ginosko (

Many engineers and technicians believe PCs are unreliable, and many others don't see a need for PCs in process control. "PCs have too much overhead, which results in bugs in the Windows software that cause crashes, hang-ups, and re-boots," says Paul Parker, a plant engineer with KSL Services at Los Alamos National Labs in Los Alamos, N.M. "Why stress out over this, when PLCs cost less than PCs? What is the advantage?" he asks.

When we visited this topic two years ago, we showed concrete reasons for using PCs instead of PLCs in process control. These reasons are shown in Table I, and perusal of the table shows how PCs can be a cost-effective alternative when there is a need for more than just simple discrete and analog control.

Even if one or more of these reasons apply to your application, it still would not make sense to use a PC unless it proved to be a reliable, inexpensive, and accepted alternative to a PLC or DCS.

Industry acceptance is coming along slowly but surely. PC-based control is a mainstay of discrete parts manufacturing, most notably in the auto industry. According to the Venture Development (, a technology market research group, PC control also has a significant and fast-growing presence in process control.

Table I: Top Ten Reasons for Using a PC Instead of a PLC


Networking to higher-level platforms


Advanced control algorithms


Extensive database manipulation


HMI functionality in one platform


Integrated custom control routines


Complex process simulation


Very fast CPU processing


Memory requirements exceed PLC specs


Interfaces thorough multiple protocols


Wireless access


"Distributed and remote I/O for use with PC-based control systems in industrial process industry applications is forecast to increase from $143 million in 2001 to $254 million in 2005. This gives PC-based control about 10.6% of the total control market in 2001 and a projected 14.5% of the total in 2005," according to Jim Taylor, a group manager with Venture Development.

Industry acceptance is growing, but what about cost effectiveness? This is perhaps the area where PCs have made their greatest inroads, and this trend is sure to accelerate.

Office-grade PCs decline in price on a seemingly daily basis, and industrial grade PCs now follow the same trend. "Several years ago the cost ratio of an industrial PC to an office-grade was about 4:1, but now the ratio has declined to around 2:1 or less," says Ed Boutilier, president and CEO of Stealth Computer (

Industry acceptance is on the rise and costs are declining, so the only hurdle left for PCs in process control is reliability. Unfortunately for PC-based control vendors and their supporters in the user community, this is a high hurdle, largely due to poor past implementations of PC-based control.

Windows Won't Work

It is hard to escape history, and PCs in process control have a rather unpleasant past. Many users have fallen to the temptation of using low-cost desktop Windows-based PCs for critical process control, often with disastrous results. "The whole PC-based control scenario is riddled with amateurish implementations," observes George Turnbull, managing director of Open Automation and Control in Essex, England (

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