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From: "Bill Shymanski"
References: <email@example.com> <firstname.lastname@example.org>
Subject: Re: Avoiding PLCs
X-Newsreader: Microsoft Outlook Express 5.00.2919.6600
Date: Wed, 16 Oct 2002 18:39:50 -0500
NNTP-Posting-Date: Wed, 16 Oct 2002 18:38:57 CDT
Organization: MTS Internet
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
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!
One of the reasons a PLC is a Z80 in a $5000 box is that you'll be able to
buy replacement parts for it for
20 years. Most control applications are not processor-limited. ( Yes, I'm
aware that more powerful processors are available in PLCs but there's
still thousands of Z80s out there doing the world's work.)
A cheap desktop machine isn't even fit to be used on a desktop. By the
time you "harden up" a PC to be useful for control applications, the darn
thing costs as much as a
real PLC and crashes roughly 3 orders of magnitude more often.
The only time I crashed an Allen-Bradley PLC 2 processor was when I
delibrately did something that a recall notice told me would stall the
processor. Desktop PCs stall...a lot more frequently.
Now, a PC, doing all the data logging and sending data to your networked
office automation system, standing between the "office" world and the PLC
world, is a really good thing - and you don't mind replacing it every
couple of years. Of course, if they stop selling PCs with serial ports,
it's going to be really hard getting it to talk to that 1770-KF2
"Pat Ford" wrote in message
> One reason is that PC's will be available for a long time, and
> have amazing backwards compatibility. I can still run some programs from
> at on my 2GHz machine. Another reason is that they are available no 30
> delivery. The processing power in a modern PC combined with the low
> also a good reason.
> As far as a 3 month PC being obsolete may be true but the software
> still work and why upgrade if it works.
> "Kevin Carney" wrote in message
> > I am just lurking but here is my $ 2 (adjusted for inflation) . With
> > the rapid changes in the P.C. market (operating systems, hardware
> > etc.), Why would a company want to put a PC as the controller for a
> > they may use for 15 years ? What if the PC poops after 3 years, you
> > able to get the same interface cards to work with a new operating
> > My thoughts are that the latest and greatest every 6 months,
> > year old PC has killed the PC market. People aren't going to spend $
> > every 2-3 years for the latest & greatest.
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