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From: "andrew queisser"
Subject: Re: Avoiding PLCs
Date: Thu, 17 Oct 2002 12:18:23 -0700
Organization: Hewlett Packard Corvallis Site
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NNTP-Posting-Date: 17 Oct 2002 19:23:37 GMT
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"Bill Shymanski" wrote in message
I'm not arguing with the usefulness of PLCs or the difficulty of using PCs
for factory automation, but...
> Backward compatiblity? Oh really ? Where can I buy:
> - 5 1/4 inch disk drives
> - MFM hard drives
> - 5 1/4 inch floppy disks!
> - XT-compatible keyboards
> - Anything that can plug into an AT backplane
> - An EGA monitor
You probably wouldn't need to buy any of those things unless the software
you were using was somehow hardcoded to use MFM, EGA, etc. Even
at the time the hardware you mention was standard nobody needed to depend
on MFM vs. SCSI or EGA vs. VGA.
> etc. etc. The PC is a moving target and can't be maintained for more than
> a couple of years. New laptops don't even come with RS 232 ports!
Our industrial PC vendor guarantess availability for five years. Beyond that
we can stock up with a reasonable amount of spares.
In the last couple of years our PC platform has been much more stable than
our PLC platform. Everytime I turn around they've upgraded to a new version
of RSLogix or this or that module has changed. The PCs have been running
NT 4.0 or Win2K for years now and no plan to go anywhere else, not on
our part and not on the part of the PC software vendors. The PC software
runs transparently on either flavor of Windows.
PLCs are great at doing PLC stuff and PCs are great at doing PC stuff
but the boundaries aren't as clear as they used to be.
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