John Baymore on sun 4 jul 99
------------------
(clip)
There are times the probe readings indicate that I will have exquisite reds
beyond my expectations...only to find out that is not the case (The entire
reason I purchased the tool) Other times the indications and results are
reversed.
(snip)
One thing to keep in mind is that a sensor only measures the property it
was designed to measure in the exact location of the probe itself. There
is no implication from the sensor unit that it will monitor factors
anywhere other than at that point. This is the same with thermocouple-type
pyrometers and CO2 analyzers, and Oxy probes.
The variations between probe location and the conditions in the rest of the
kiln are a function of kiln design and the choice in siting the probe
location.
When chosing a location you need to select one that is typically
representative of the chamber as a whole.....particularly the stacking
area. For example.... it would be a bad choice to locate a thermocouple or
oxyprobe in the area directly in the firebox above the burners and expect
the reading to be consistent with the stacking area. (Unless you wanted to
monitor firebox conditions =3Cg=3E=3E)
The variations exhibited in the kiln described here are typical of many
craft potter type kilns. The variations tend to come from marginal kiln
and combustion system design.... and are caused by poor mixing and gas (not
gas as in fuel but gasseous) flow in the chamber. This makes the kiln very
susceptable to stacking variations, wind, barometric pressure, slight
changes in control settings, and the like.
To sort of visualize this issue of the flow and mixing pattern in a kiln,
picture a shallow riverbed filled with stones. Take a strong viscous blue
dye and inject it at one point in the slowly flowing river. As the water
flows through the rocks the dye mixes slowly into the water. Eventually
you get an even light blue water. But in some areas closer to the dye
injection point, the concentration of blue dye is greater in some areas
than in others.
If you happen to locate your =22blue color tester=22 probe in one of the
locations that the dye concentration is higher, you don't get an accurate
reading of the average conditions a little farther down the stream. If you
want a certain shade of blue, you could be mislead based on the available
probe data to change the amount of dye you pump in.....but this would be in
error.
Best,
................................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
=22Earth, Water, and Fire climbing kiln firing workshop Aug. 20-29,1999=22
Bill Downs on tue 6 jul 99
Does it make sense to locate the oxyprobe in the low end of the chimney?
Bill on the Big Island
Ben Shelton on tue 6 jul 99
OK so let us open a whole can o' worms.
Say I've got a kiln like a giel geil whatever! Nice and cube like with
burners from the bottom etc. Nice tight door...
Where would be the best location for an oxyprobe? The middle of the door
seems a good start as there wouldn't be a direct blast from the burners. The
back wall at mid level would also seem good as long as you don't get to
close to the exit flue..
What about TDC (top dead center)? I assume you're readings would be off
here, no?
As an aside. It was once suggested that an automotive oxygen sensor placed
into the exhaust (chimney) might be used as an oxygen probe. I've looked
into this but I'm not sure how to get readings from the sensor. This of
course would be only the beginning of the kinks that would have to be worked
out if one could make that work. Any thoughts??
-----Original Message-----
From: John Baymore
To: CLAYART@LSV.UKY.EDU
Date: Sunday, July 04, 1999 5:34 PM
Subject: Reduction and Oxyprobes
----------------------------Original message----------------------------
------------------
(clip)
There are times the probe readings indicate that I will have exquisite reds
beyond my expectations...only to find out that is not the case (The entire
reason I purchased the tool) Other times the indications and results are
reversed.
(snip)
One thing to keep in mind is that a sensor only measures the property it
was designed to measure in the exact location of the probe itself. There
is no implication from the sensor unit that it will monitor factors
anywhere other than at that point. This is the same with thermocouple-type
pyrometers and CO2 analyzers, and Oxy probes.
The variations between probe location and the conditions in the rest of the
kiln are a function of kiln design and the choice in siting the probe
location.
When chosing a location you need to select one that is typically
representative of the chamber as a whole.....particularly the stacking
area. For example.... it would be a bad choice to locate a thermocouple or
oxyprobe in the area directly in the firebox above the burners and expect
the reading to be consistent with the stacking area. (Unless you wanted to
monitor firebox conditions >)
The variations exhibited in the kiln described here are typical of many
craft potter type kilns. The variations tend to come from marginal kiln
and combustion system design.... and are caused by poor mixing and gas (not
gas as in fuel but gasseous) flow in the chamber. This makes the kiln very
susceptable to stacking variations, wind, barometric pressure, slight
changes in control settings, and the like.
To sort of visualize this issue of the flow and mixing pattern in a kiln,
picture a shallow riverbed filled with stones. Take a strong viscous blue
dye and inject it at one point in the slowly flowing river. As the water
flows through the rocks the dye mixes slowly into the water. Eventually
you get an even light blue water. But in some areas closer to the dye
injection point, the concentration of blue dye is greater in some areas
than in others.
If you happen to locate your "blue color tester" probe in one of the
locations that the dye concentration is higher, you don't get an accurate
reading of the average conditions a little farther down the stream. If you
want a certain shade of blue, you could be mislead based on the available
probe data to change the amount of dye you pump in.....but this would be in
error.
Best,
................................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore@compuserve.com
John.Baymore@GSD-CO.COM
"Earth, Water, and Fire climbing kiln firing workshop Aug. 20-29,1999"
John Baymore on thu 8 jul 99
------------------
(clip)
Does it make sense to locate the oxyprobe in the low end of the chimney?
(snip)
Bill,
IF ... and that is a BIG if...... the kiln has good mixing properties it is
possible to locate the probe at the very base of the chimney.... but
probably NOT the best overall choice. It'd have to be in the area where
the effluent is somewhat representative of the conditions in the chamber
(see my other prior post). This zone in the base of the chimney would be
pretty small.... and would be in the VERY base area of the chimney near the
inlet fron the kiln chamber. If there is a long path from the actual ware
chamber to the chimney .....I'd say forget it for sure. For SURE it would
have to be below any active (slab type) or passive (adjustable holes)
dampers.
For optimal firing performance (balance of adequate reduction and maximum
fuel efficiency) in reduction your goal is to have the flame front just
burning off as it leaves the working chamber and enters the chimney. So if
you are actually doing this.... the readings in the base of the chimney
would be sampling in an area that is less consistent than the atmosphere in
the chamber. As the front is burning off the sampling from one spot a
couple of inches from another spot may vary within the firing and from
firing to firing.
Like with any sensor/display system..... you can get used to the meaning of
the readings you obtain even if they are not the actual =22real=22 readings.
For example.... most potters using the cheap type K analog pyrometers make
the mental shift to the relative reading on the pyrometer vs the actual
temperature in the kiln..... and are not concerned when the pyrometer is
showing ...say...2200F when cone 10 is going down. They know that cone 10
should be going down at that temp reading cause that is what typically
happens...and the display numbers are not accurate in the =22real world=22
sense. You can extrapolate results based on readings.... given a good
experience base from which to compare. At first however.... you'll be
shooting in the dark as to a comparison between the readings in the place
you chose to sample and the conditions in the place where it MATTERS =
=3Cg=3E.
You also lose the usefullness of the pyrometer function of the probe.
Unless of course you are interested in chimney temperature =3Cg=3E. (Which =
IS
an interseting thig to monitor... as a function affecting efficiency of
firing.)
I typically site them in the ware chamber as close to a section of the
actual ware as I can get. Depending on the design of the kiln either in
the top center of the arch/roof and sometimes in the rear center of the
back wall in the upper third of the kiln chamber (coming in at an angle
through the refratories if it is a downdraft and I have to contend with the
chimney being there on the outside). No matter where you site it.... watch
out on loading.... they are fragile=21 You don't get too many =22chances=22=
to
bump it without damage. In that sense....the base of the chimney protects
it pretty well =3Cg=3E.
Best setup would have multiple probes running into a multichannel PC data
logger..... but that is more the province of the industrial realm due to
the costs. That'll tell you something about the mixing situation in your
kiln too =3Cg=3E.
BEst,
....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
=22Earth, Water, and Fire climbing kiln firing workshop Aug. 20-29,1999=22
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