Karen Terpstra on mon 4 nov 02
someone posted me privately with a good question. basically it said, =
"shouldn't the pyrometer match the cones?"
My answer: We have the pyrometer at the top and side of the first =
chamber in the wood kiln. It protrudes into the kiln only 1 to 2 =
inches. Probably not the best place to put it. (What was I thinking?!) =
And perhaps I should have ordered a longer one. I don't get as accurate =
a reading as with cones. the cones are placed all over the kiln and =
read very accurately because they are farther inside the kiln. =20
We had to replace the pyrometer on our gas kiln last month. Our old one =
consistantly read 2160F to 2167F when cone 10 would start to bend. Our =
new one reads 2280F when cone 10 goes. It is also placed in an upper =
corner of the kiln.=20
Works the same way with electric kilns. Rarely if ever an exact match. =
Maybe someone on the list can explain more about the workings of =
pyrometers? my answer doesn't really explain all of the reasons. =20
I remember that it's been said on Clayart before, "Always trust the =
cones before the pyrometer." Probably more info in the archives.
karen terpstra
La Crosse, WI
ps. off clayart until the weekend. Branfman's Raku workshop here this =
week. still room if you want to come.
And, thanks for all the private and public responses from my posts this =
weekend.
vince pitelka on mon 4 nov 02
Karen Terpstra wrote:
"someone posted me privately with a good question. basically it said,
'shouldn't the pyrometer match the cones?'"
Let me elaborate on Karen's answer. It isn't a question of whether the
pyrometer should or shouldn't match the cones. The truth is that it cannot
match the cones. The whole point of cones is that they respond to
temperature, atmosphere, and duration of the firing, while a pyrometer only
responds to temperature. That's why you cannot fire a programmable kiln
purely on the temperature reading. You have to place test conepacks
throughout the kiln to measure your thermocouple's accuracy, and then adjust
your firing temperatures accordingly.
Also, as Karen pointed out, the pyrometer only measures the temperature at
the location of the thermocouple. In a wood kiln we place cone packs all
over the kiln, including in the front just above the firebox, the very
hottest place in the kiln. No one would ever place a pyrometer thermocouple
in such a location, because the ash slag would kill it pronto. As is, the
ash slag in that location causes the cones to drop at least one cone before
their true temperature.
Our firings are long and slow, and our digital pyrometer, with the
thermocouple in the crown port halfway back the kiln, never reaches anywhere
near 2350, while we generally drop cone 12 at most of the cone packs.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
KLeSueur@AOL.COM on tue 5 nov 02
Use both. A good pyrometer measures the progress of the kiln. Are you climbing too fast. Need to slow it down. How hot is it before you start to open. But use the cones to know when the glazes have matured. All of these things are tools. The more tools you have, the better you can control your firings.
Kathi LeSueur
Steve Mills on fri 8 nov 02
Absolutely.
Also if you're intending to be consistent; keep a graph of each firing,
and keep the graph of your best firing on a piece of Acetate, and
overlay it on the current firing graph, so's you can reproduce it as
near as possible.
Steve
Bath
UK
In message , KLeSueur@AOL.COM writes
>Use both. A good pyrometer measures the progress of the kiln. Are you cli=
>mbing too fast. Need to slow it down. How hot is it before you start to o=
>pen. But use the cones to know when the glazes have matured. All of these=
> things are tools. The more tools you have, the better you can control yo=
>ur firings.
>
>Kathi LeSueur
--
Steve Mills
Bath
UK
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