[Mike Wrote]>
> Beautiful rant. I er um had to fib to a customer once to get his head out
of the Cutler
> Hammer PLC cloud. I told him I wouldn't guarantee that it would handle the
speeds
> required to make his machine go faster. The app was not much different
from
> controlling a linear actuator, which leads me to ask if you've ever been
asked to use
> PLC's and how you talk the customer into an embedded solution. I've seen a
lot of
> machines in plants completely controlled by PLC's programmed by
technicians. I
> even saw an ad in the paper for a "control engineer." The requirements
were H.S.
> education,  AutoCAD, and PLC experience. Companies get off cheap around
here.
> That really gags me.
>
> Regards,
> Mike
>
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I look at PLC's as complimentary to embedded systems, rather than
competition. I use them often for short-run or prototype machines. For any
given application, an embedded system will generally be quite a bit cheaper
than a PLC, once you get it designed, built, and programmed. The PLC,
however, doesn't have any front-end cost in bux or time to get to the
programming phase. PLC's make a lot of sense for the situation where you
have to put together a prototype that may have a bunch of additional air
cylinders, valves, motors or the like added during the design. I do a lot of
work for the cut-flower handling industry. Things like flower bucket water
fillers, washers, underwater stem cutters, etc. This equipment is handling
materials that are not at all uniform. A lot of kluges get added to a design
after the prototype is built to make it all work. My strategy here is to use
a PLC until the design attains some stability, then sell a custom controller
for production. I get paid to do the programming twice. Life is good!

I would rather program in PIC assembler any day than ladder logic, but I do
what I have to. My first engineering job in 1968 was to design relay logic
controllers for automatic assembly equipment, which used panels of 4-500
A-B Bulletin 700 relays to make the machine work. It is amusing to me that I
can draw schematics just like I did 35 years ago and have the same result as
I did then, even though there isn't any clanking or buzzing involved.

Edward Gisske, P.E.
Gisske Engineering
608-523-1900
gisske@offex.com

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