Re: [Biofuel] Attn. Pack Rats -- (maybe) A cheap Process Control Idea

Paddy O'Reilly 22 Feb 2005 17:29:58 -0000

always a rush of adrenalin when you run your own program and wait inanticipation to see if your programming skills don't blow up yourbasement ;o)


Kirk McLoren wrote:

Computers are great. I like them. But they aren't as
reliable as simple physical systems. As for the delta
T a bimetal can operate over it is a question of
mechanical design. An electronic controller may
theoretically switch over a change of a milli degree
but in the real world the conductivity from the heater
to the mass, the rate of heating, amount of mixing in
a tank, rates of cooling etc can make for some
temperature differences that are enormously larger
than the sensitivity of the controller.

As for upset my daughters computer lost its CMOS
settings when the wrong breaker was thrown. Failed
CMOS battery? Doesn't lose setup info if powered down.
Doesn't lose it every time either. She also lost a
satellite internet transponder due to a glitch on the
powerline last year. Expensive spike that one.
You will also note Windows users are warned to not use
windows for critical control applications such as life
support. In industry numerical controllers are widely
used but critical operations have staff during
operation and redundant controls if failure analysis
indicates.

Redundant controls and voting? That helps failure rate
but it is still not perfect. I think if you size the
heater so that if it fails on while unattended so that
it cannot cause a fire or other danger then maybe your
computer controller is an acceptable risk. Maybe
include a bimetal disk cutout at 10 or 20 above
highest temp ever used. Appliance clothes dryers have
a backup cutout. They have to. Too many fires
otherwise and those controllers are much more reliable
than windoze.

I think old computers are great for data logging but
be damn careful when you include them in the loop for
control. Always have a backup safety or you may have a
situation not bargained for.

Kirk


--- Michael Redler <[EMAIL PROTECTED]> wrote:

OK Kirk.

Thanks for the reply.

I have a couple of follow-up questions:
First, Is accuracy of your temperature set points
(or other I/O) a critical issue for controlling a
process? Because, a PID or Smith compensator control
can give you far better control of your process than
a bi-metallic strip for example.

Second, I'd like to rephrase the question: Is there
any way (in your opinion) that obsolete computers
can be put to use for the purposes of generating
alternative energy?

Lastly: Can anything really be called "foolproof"?
If I count the number of times that I have a power
outage/lightning strike on my property, I still come
up with a good risk assessment -- especially since
set points can be stored in memory while power is
down and I'm not sure if any control system aside
from a purely mechanical one, would be effective
during those relatively rare times that a mishap
occurs.

I've made all of my arguments (so far) without
touching on the potential of a computer like a 486
as a platform for control and data acquisition --
all for the price of a ....bi-metallic strip. So,
after reading your reply and agreeing with its
logic, I'm still not convinced that the idea of
using "obsolete" computers is too far off base.

Mike

Kirk McLoren <[EMAIL PROTECTED]> wrote:
A temperature controller that would not upset
because
of lightning or other power line disturbance and
would
not lose its settings with power supply failure may
prove superior especially if less expensive.

Thus a bimetal strip may prove best in the long run.

I am in favor of data logging and alarms via
computer
but fool proof and ultra reliable control usually

means no computer.

Kirk

--- Michael Redler wrote:

Hi everyone,

For those of you who are working on your process
control for ethanol/methanol or biodiesel
production, I was wondering about something.

I hate to send anything to the land fill or scrap
yard that I might be able to use later and I'm

sure

you feel the same way. This philosophy has caused

me

to become a bit of a pack rat (and dumpster

diver).

My basement is neatly organized with old (486 and
P1) computers, motors, and other
mechanical/electrical devices from dissected
printers and other obsolete or broken down
equipment.

I was thinking of developing generic software (in

or assembler) for old computers to convert them

into

process controllers. For example, it might make an
effective temperature controller for your still.

If

this works, I would take the programs and put them
on a web page for download. If it's truly generic
(compatible with all XX86 architecture), it will

be

a matter of copying the executable file to the

hard

drive of a computer, adding a line to the
autoexec.bat file and making a harness
(serial/parallel port to solid state relays and
sensors).

Has anyone tried this already and if so, can that
person please share their experience with me and
those interested in this thread?

Thanks!

Regards,

Mike


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Re: [Biofuel] Attn. Pack Rats -- (maybe) A cheap Process Control Idea

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