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Personal Computers Lose the Pretty Face
PC-based control gains acceptance with new and more practical form factors
05/22/2003
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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 (www.oacg.co.uk).
One of the main problem areas has been the Windows operating system. Desktop Windows is primarily designed for non-real time and non-critical applications. Earlier versions of Windows (prior to NT) were especially plagued by unexplained glitches, the blue screen of death, and frequent re-boots.
As detailed in our May 2002 cover story, this problem has largely been alleviated by the use of real-time PC-based operating systems. In addition to the various embedded versions of Windows, such as CE and embedded XP, real-time PC operating systems are also available in Linux. Firms such as VxWorks (www.windriver.com), QNX (www.qnx.com), and LynxOS (www.lynuxworks.com) also offer rock-solid real-time operating systems.
Table II: Industrial Grade PCs vs. Office PCs
|
Features to consider |
Industrial Grade |
Office Grade |
|
Can it withstand extended temperatures? |
Yes |
No |
|
Can it withstand shock & vibration? |
Yes |
No |
|
Is it dust proof, or does it have filtering? |
Yes |
No |
|
Is it splash proof? |
Yes |
No |
|
Does it have RFI/EMI shielding? |
Yes |
No |
|
Does it have power surge protection? |
Optional |
No |
|
What type of chassis construction? |
Cold rolled steel, rigid |
Flimsy, often plastic |
|
Does it meet industry classifications? |
NEMA/IP, MIL, etc. |
None |
|
What type of security does it provide? |
Locking doors & drive bays |
None |
|
How much lifecycle technical support? |
3-5 years |
6-12 months |
|
Does it provide Intrinsic Safety? |
Optional |
No |
|
Mean Time Between Failure Data |
Sometimes provided |
Not provided |
|
Mean Time to Repair |
5-15 minutes |
1-2 hours plus |
|
Mounting & enclosures |
Multiple Options |
desktop or tower style |
|
Is it fault tolerant? |
Optional |
No |
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