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Subject: Re: Avoiding PLCs
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Sun, 13 Oct 2002 14:42:46 +0100
NNTP-Posting-Date: Sun, 13 Oct 2002 14:42:49 BST
Organization: ntlworld News Service
The reasons users want you to use 'the make of controller already in use by
them' are sensible - they want to reduce their training and maintenance
costs. Using another type of controller will not help those users.
I suggest that you produce a detailed but system independent functional
specification that can then be implemented on any suitable PLC. It is good
practise anyway, and you can use an IEC-61131 type approach for this
functional specification so that it can be easily implemented on an
IEC-61131 type PLC.
"Spehro Pefhany" wrote in message
> "JohnS" wrote in message
> > We have run into a problem, hope someone here can make a helpful
> > suggestion! We have a digital control system which is fairly easily
> > using a plc. (Lots of interlock logic, timers, 4/20 mA circuits, 4 line
> > display, etc) Unfortunately every customer then seems to insist that we
> > build using the make of controller already in use by them. In order to
> > this I am looking for modular electronic systems that we can program in
> > whatever so we can avoid using a PLC, but still have the flexibility to
> > I/O etc as required.
> > We could design from the ground up, but there must be suitable systems
> > there, ideally with CE and UL approval!. Any pointers to possibles
> > much appreciated.
> Other than PC-based systems (which would be hard to recommend for a
> variety of reasons), I don't really think there *is* much out there.
> On the PC platform (various packaging, but all really PCs underneath)
> you have to worry about the availability of IO's and service bits off
> into the future. I think you will have little success (for good reason)
> convincing your customer to go with something other than what they are
> using on large projects. On small projects, you may well be able to talk
> them into a micro-PLC because of the low cost of both the controller and
> the software you will develop for them. From a business POV it's probably
> best to concentrate on the major brands of PLC and/or those your major
> prospects and customers use.
> The only ray of hope I can offer is that you may be able to IEC-61131
> compatible controllers, but selling that to your customer base is
> another thing. See: http://www.plcopen.org
> I've cross-posted the reply to sci.engr.control and
> alt.engineering.electrical as it's appropriate in those newsgroups.
> Best regards,
> Spehro Pefhany
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