C. A. Sanger on fri 23 may 03
We're about to build one of those auto sniffers as written up in CM
recently. Can anyone give me an idea of the range of "numbers" one
looks for when firing? None of the literature I have found mentions
specific numbers. Thanks! C. A. Sanger
ShardRock Clay Studio <:)}}}><
Herington, Kansas
Roger Graham on mon 26 may 03
For C.A.Sanger who was asking about the range of "numbers" to be expected
from an auto EGO sensor during a reduction firing. The short answer is,
somewhere between 600 and 900 millivolts, depending on the intensity of
reduction.
Some figures from a typical firing, with an $800 oxyprobe deep in the kiln,
and an EGO sensor in the exhaust stream at the kiln damper: Began reduction
at 700 degrees Celsius, by closing the damper until the probes showed a
sudden rise in readings. The $800 oxyprobe read 730 mV, and the EGO sensor
read 925 mV.
Somewhat later in the firing at 980 degrees C, the readings were 720 mV
(oxyprobe) and 899 mV (EGO sensor).
Later still, at 1180 degrees C, the readings were 520 mV (oxyprobe) and 790
mV (EGO sensor).
I kept detailed kiln logs during all the test firings when the exhaust
sniffer idea was being developed, and drew pretty graphs showing the rise
and fall of readings from the various probes in use. Unfortunately the
Ceramics Monthly people chose not to include a printout of such a graph in
the CM article, somewhat to my disappointment. The graphed results were
convincing evidence that the sniffer works.
Since EGO sensors come in a variety styles, it seemed a good idea to run a
firing with two different probes side by side in the same exhaust stream.
Not surprisingly, the readings from the two probes were a little different,
but similar enough to reassure me that this wasn't likely to be a problem.
Example figures: At 1200 degrees C, the $800 oxyprobe read 520 mV. One EGO
sensor read 789 mV, and the other was 744 mV. The kiln log graphs for this
firing show the three traces for the three probes rising and falling
together throughout, as always seems to happen.
If contacted off list, I can email copies of typical kiln log graphs. I'd be
grateful for feedback from other potters who fit an exhaust sniffer, to know
whether it's a success in other kilns.
Roger Graham, near Gerringong, Australia
http://members.optusnet.com.au/~rogergraham
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