From: Christopher Browne <cbbrowne@acm.org>
Subject: Re: SQL to PLC to diverter gate, can this be done?
Date: Fri, 07 Nov 2003 08:47:45 -0500
Organization: cbbrowne Computing Inc
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To: pgsql-sql@postgresql.org

Centuries ago, Nostradamus foresaw when razorbak71@yahoo.com (Razorbak71) would write:
> First, I know nothing about PLC's, but I was wondering is there a
> way to extract data from a SQL database file, feed that to a PLC is
> some manner, and then have the PLC trigger a diverter gate based on
> the value in the table exceeding a certain value, to divert parts to
> another location.
>
> Am I off base, or is there something out there that will allow or
> help me to do this.  Any help would be greatly appreciated.

It all depends on how you are able to program the PLC.  They tend to
have pretty proprietary tools that are very much dependent on the
vendor.

My little brother works for Omron, and does some pretty fancy things
with their PLCs.  But since the languages Omron uses aren't the same
as are used with similar products from (say) Siemens, knowing one
platform doesn't necessarily help with the other.  (They commonly use
languages resembling BASIC...)

I think you need to know a LOT more about the PLC system in question,
and that knowledge is not likely to be found here.  What you want is
probably feasible in some sense, although it's likely to be rather
fiddly.  

And your use of the term "SQL database file" suggests some confusion
on your part as to how the SQL side would work.  While PostgreSQL
implements tables in files, you don't read data from the files, but
instead ask the "postmaster" to give it to you.  You might need to
drop the data into a separate file outside the database in order to
get it into a form that the PLC can get at...
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