Here is where I would use a PIC:

Where the ultimate product is mass produced and is cost sensitive
Where the ultimate product is a one-off prototype that I will build myself
and nobody else will ever have to maintain
Where the control sequence is extremely complex.
Where I don't want other people to mess around with the internal details
(assuming they don't know PICs)
Where a relatively large investment in setting up the program and building
the control is justified


Here is where I would use a PLC:

Where the ultimate product is not cost-sensitive, and has to work no matter
what
Where the ultimate product may be a one-off, or will be reporeduced in small
quantities
Where the ultimate product will probably be maintained or expanded by people
with a lot less skill than I have
Where the facility already has a base of people who know PLC's.
Where the control sequence is fairly complex
Where a medium investment in building and programming the control is
justified

Here is where I would use actual (gasp!) relays:

Where the ultimate product is a one-off
Where people of minimal electrical skill will maintain it
Where ease of maintenance is paramount
Where the control sequence is not very complex
Where the only thing being controled is 120VAC signals (or 240VAC) and the
extra hassle of a power supply and low voltage control is not needed.
Where the most minimal investment in "programming" (i.e. banging out a
wiring schamtic and handing it to a drooling hillbilly with a screwdriver)
is justified.


I still design things with relay logic all the time, usually they consist of
no more than a microswitch, a relay and a motor or some such simple thing.

--Lawrence




----- Original Message -----
From: "Gabriel Caffese" <gabrielsdi@IMPSAT1.COM.AR>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, July 08, 2002 12:07 PM
Subject: [PIC]: When to use PIC or PLC ??


> Hello everyone,
>
>    I would like you to tell me wich are the the most important reasons why
> a PIC microcntroller would (or would not) be able to replace a PLC.
>    For example, supose the need for replacing the semaphore PLC control in
> a city.
>
>    Thanks,
>         Gabriel.-
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.