On 2013-12-09, RogerN wrote:
"Jim Wilkins" wrote in message ...


I considered similarly overengineering a computerized draft regulator for
my woodstove, with inputs from firebox, stack and outdoor air temperature
and the draft vacuum, all of which I was monitoring. It would be fun and a
considerable accomplishment to tune it properly. I've designed relay-ladder
controls for industrial production test and burn-in stations and
wired/programmed simulations of the rest of the system for circuit board
test and calibration fixtures.

For the woodstove I decided instead to add a remote thermocouple
temperature display above this computer's monitor, so I know at a glance to
go down and attend to it when it has reached operating temperature or needs
more wood. A second channel tells me when a pot on the stove is nearing
boil.

When I sandblast with an inadequate compressor I hang a large pressure
gauge on the wall nearby and attack a new area with hammer and chisel until
the pressure recovers enough to continue.

I've learned to be cautious of designing complex things for other people's
use that only the designer can fix.
jsw

I wired an Allen Bradley PLC 5 to a Brinkman Gourmet Electric Smoker. Had a
PanelView 550 for operator interface. A RTD probe for the meat and another
for the temperature inside the smoker. The meat set point temperature
ramped up over 12 hours as the smoker temperature was kept within limits.
After the temperature was reached, it was held for a period of time to allow
it to even out, then brought down to a set point of 140 degrees for "keep
warm". It worked great but was a pain to drag out & set up then put back
up. I need to mount the controller in a box and use plugs for the
temperature probes and power. It was done for fun but made pretty good BBQ,
need an automatic smoke wood feeder!

Next step I could use some actuators for the air inlets and control my Weber
Smokey Mountain smoker!

PLC 5's are a bit old but their cards are cheap since the 1771 racks date
back to PLC 2's. The downside is the programming software but I have it on
my work laptop.

What is OK for an outdoor smoker, is not OK for an indoor wood fired
stove, a much more dangerous device.

i