From: Don Pearce
Subject: Re: Avoiding PLCs
Date: Thu, 17 Oct 2002 11:06:54 +0430
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <2jqr9.76172$oq6.18550@sccrnsc01> <firstname.lastname@example.org>
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On Thu, 17 Oct 2002 16:15:58 +1000, "Cameron Dorrough"
>"Don Pearce" wrote in message
>> On Thu, 17 Oct 2002 04:26:21 GMT, email@example.com (Mike
>> Harding) wrote:
>> >On Thu, 17 Oct 2002 13:56:53 +1000, "Cameron Dorrough"
>> > wrote:
>> >>And that's one of the *best* reasons not to use custom PC's with custom
>> >>software right there..
>> >>If the PLC ever needs to be upgraded/replaced, simply translate the
>> >>ladder logic, PID loops, etc to the new platform. It is very easily
>> >>(especially something like Siemens to AB or vice-versa).
>> >>Heaven help you if your plant is reliant on custom PC software written
>> >>particular (eg. Microsoft) operating system that is no longer supported,
>> >>a PC chipset (eg. x86) that you can't buy parts for.. That's just
>> >>for trouble. Been ther done that.. remember DOS? ;-)
>> >Yep. And we should still be using it for any kind of control
>> >system running on a PC. By version 5 and 6 it was/is
>> >pretty stable and has all the features we need.
>> Remember Dr DOS? Now that was the one to use in my books. I had a PC
>> with that on it until very recently.
>Guys, the biggest problem with DOS (any flavour) is that you can't even
>*buy* it, let alone expect your clients to be able to get support!
>Dunno about the rest of you, but a "what do I type in now?" request from an
>operator at 2:00am is not what I'm looking for in a control system...
Why would a decent control system require an operator to remember what
to type in next? Whether in Windows or DOS, the options should be
clear and well presented. The main difference is that with DOS you
won't be getting the "The cursor is stuck and there is a green square
flashing in the corner" request in the middle of the night.
And of course you can still get DOS, no problem.