Re: [CAD_CAM_EDM_DRO] PLC's and industrial automation

In a message dated 4/9/01 12:01:18 PM Eastern Daylight Time,
peteryco@... writes:

> Dough
> some moer info?
> I agree most plc´s are simple 70's stuff but much cheaper
> than in yhose days.
>
> Sven Peter
>
> Doug Fortune wrote:
>
> > Doug Harrison wrote:
> >
> >> Try www.automationdirect.com and look for the DL-05 or DL-105. The 05
> >> starts at $99 and the 105 at $149. I got the software for an additional
> >> $99, though I think its now $199. AB, GE, etc are often available in the
> >> dumpsters but the software will kill your bank account if you have to
> buy it.
> >
> >
> > OK, no-one has said just what the darn things are! Just a quick overview
> > please. Is it just a little loop logic and input/output relays?
> >
> > I'll give you a counter-example: A Scenix (now Ubicom) SX-28
> > programmable microcontroller chip:
> >
> > http://www.ubicom.com/hardware/sx28ac.html
> >
> > programmers available (~$200 range) from:
> > http://www.parallaxinc.com/html_files/sxtech/sxtech_home.htm
> >
> > It gives you 20 I/O (dedicated or multiplexed), analog in & out,
> > and 50 or 75 MIPs (millions of instructions/sec). If you prefer
> > not to use assembly, there are C compilers (at least one is free).
> > I have one very complex program that is 35 pages long, and am
> > still only using half the ROM! The chip is only $5.
> >
> >
> > The SX-52 runs at 100 MIPs and has 40 I/O pins, and twice the
> > ROM storage. This chip is around $10.
> >
> > - - - -
> >
> > I am assuming the PLC's have no where near this sophistication,
> > so unless someone tells me otherwise, I am still going to assume
> > PLC's are 1970's technology, and it is more worthwhile to spend
> > time learning something new ( like high performance microcontrollers)
> > vs something old (like PLC's). The only two advantages to PLC's is
> > perhaps that they are field programmable & integrated with high current
> > drivers - but really that is no different than putting some relays and
> > programming pins on a little SX circuitboard.
> >
> > ....unless I'm way off base, of course.
> >
> > Doug Fortune
> > http://www.cncKITS.com
> >
> >
> >
> >
> >
> >
>

Doug:

Actually, PLCs are more like IF-THEN statements that act on the inputs and
turn on or off an output according to the data on the inputs. Of course it
is a little more complex but that is the simple version. I make some of my
own PLC units using the 8052 family of Microcontrollers, with some peripheral
chips you can get 64 I/O very easily and with a bit of creativity up to 256
for about or even less than $75 and, some time of course. One can even have
analog inputs (using ADC), and read quadrature encoders with a little time
spent on the programming (there are low cost chips out there that will
process the encoder signals and output the data directly to the data/address
buss). When you get into the analog, counter, and encoder part of commercial
PLCs you are still going to pay a lot for those capabilities as well as more
money if you need additional I/O. As had already been stated the software
alone can be quite costly and you STILL have to write the ladder and/or
statement programs for the PLC.

Of course, if you only have a few inputs and outputs and no analog or encoder
signals to process then the Logo etc. are good choices if you can get the
software cheaply.

Regards,

Randy Abernathy
Woodworking Machinery Specialist
4626 Old Stilesboro Road NW
Acworth, GA 30101
Ph/Fax: 770-974-5295
E-mail: cnc002@...


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