wayneinkeywest on wed 3 mar 04
Just got through (my first) firing of my electric to ^10, monitoring
it with
a new Ultimax digital pyrometer . Thermocouple in the middle peep,
BTW.
Kiln sitter shut off at what the pyrometer said is 1274C
though according to the large Orton cone (10) I had inside,
it would have been a bit closer to 1300. The large Orton was
wobbly,
but not over far enough to be considered a true 10, far as I can
tell.
(Bent more than 45 degrees, right?)
The pyro is accurate at 76F through 450F, (I checked with an oven
thermometer) but I can't think of a way to calibrate it
for the higher temps. According to the instructions, once the
"offset" is adjusted
it should then be accurate _"for that temp"_.
Am I just confusing myself? Could I have had a bad cone in the
sitter?
The cone bar in the sitter was made by Bell Research (not Orton).
Or does that pyro need more work? Am I just being psychotic and
worrying too much?
Does anyone have any idea on how to come up
with a true temp reading with which to calibrate a pyrometer at high
temps?
To me a 26C difference is too large an error to be comfortable with.
Any advice would be appreciated.
TIA
Wayne Seidl
Dave Finkelnburg on wed 3 mar 04
Wayne baby,
Relax, be cool, chill! Your pyrometer is plenty close enough for all
practical purposes. I doubt it's off 26C. The sitter is not a high
precision instrument. And from your description, you didn't reach a full
cone 10.
Your number 10 cone on the shelf is what you want to end the firing by.
I tend to put the tip of cone 10 so it just touches the shelf. To me that's
a perfect 10!
To get cone 10 down like that on the shelf you probably need an 11 in
the sitter. At least my electric, and others I've heard about, tend to fire
about a cone cooler than the small cone in the sitter.
Besides, you can't calibrate the thermometer accurately by the cone.
What you will see is the thermometer letting you know when to watch the
witness cone. Then fire by it to get the clay and glaze results you seek.
And, the thermometer should read the same every firing, so you'll know when
you're getting close to wanting to open the peep and inspect the cone.
Good firing!
Dave Finkelnburg, watching a cottontail rabbit on the snow under the
spreading spruce tree boughs in the pre-dawn in Idaho
----- Original Message -----
From: "wayneinkeywest"
Sent: Wednesday, March 03, 2004 6:53 AM
> Just got through (my first) firing of my electric to ^10, monitoring
> it with
> a new Ultimax digital pyrometer . Thermocouple in the middle peep,
> BTW.
> Kiln sitter shut off at what the pyrometer said is 1274C
> though according to the large Orton cone (10) I had inside,
> it would have been a bit closer to 1300. The large Orton was
> wobbly,
> but not over far enough to be considered a true 10, far as I can
> tell.
> (Bent more than 45 degrees, right?)
> The pyro is accurate at 76F through 450F, (I checked with an oven
> thermometer) but I can't think of a way to calibrate it
> for the higher temps. According to the instructions, once the
> "offset" is adjusted
> it should then be accurate _"for that temp"_.
>
> Am I just confusing myself? Could I have had a bad cone in the
> sitter?
> The cone bar in the sitter was made by Bell Research (not Orton).
> Or does that pyro need more work? Am I just being psychotic and
> worrying too much?
>
> Does anyone have any idea on how to come up
> with a true temp reading with which to calibrate a pyrometer at high
> temps?
> To me a 26C difference is too large an error to be comfortable with.
> Any advice would be appreciated.
Arnold Howard on wed 3 mar 04
Here's a simple way to calibrate a pyrometer:
1) Place a self-supporting witness cone in a central area of your firing
chamber where you can see the cone through a peephole.
2) Fire the kiln. During the last hour of firing, the rate of temperature
rise should be 108°F (60°C).
3) When the witness cone bends so that the tip of the cone is even with the
top of the self-supporting base, adjust the pyrometer to match the Orton
cone chart. (Use the 108°F column in the chart.)
Note: The self-supporting cone is very slightly over-fired when the tip
touches the shelf. The tip should be even with the top of the cone's tapered
base.
Sincerely,
Arnold Howard
Paragon Industries, L.P.
arnoldhoward@att.net
From: "wayneinkeywest"
> Does anyone have any idea on how to come up
> with a true temp reading with which to calibrate a pyrometer at high
> temps?
> To me a 26C difference is too large an error to be comfortable with.
> Any advice would be appreciated.
> Wayne Seidl
Craig Martell on wed 3 mar 04
Wayne observed:
>Kiln sitter shut off at what the pyrometer said is 1274C
>though according to the large Orton cone (10) I had inside,
>it would have been a bit closer to 1300. The large Orton was
>wobbly,
>but not over far enough to be considered a true 10, far as I can
>tell.
Hello Wayne:
Congratulations on a successful jouney to cone 10.
The deal with pyrometers is that they measure temperature only, not heat
work. Cones are the most accurate measure of heat work, which is a
function of time and temperature. Sitter cones are affected differently
than free standing large cones and they also have the sitter rod weight to
contend with. What I'm getting at is the standing cones in the kiln should
have the last word on maturation of the ware and glazes. The sitter cone
and pyrometer are indicators and safety devices only. I cringe when I hear
potters say that they leave kilns unattended and trust the sitter to
shutdown at the exact, correct time.
The only time I give more credence to the pyrometer is when I'm firing the
salt kiln. Cones are affected by the salt vapor and don't give as true an
indication of heat work so I use the pyrometer and also fire "by eye",
looking at the fire inside the kiln and the glow of pots and refractories.
I bisque fire to cone 03 which is about 1988 F. When the kiln is packed to
the gills and the temp rise is slower, cone 03 is down before the pyro says
1988. It's usually about 1965-70F. If the kiln is packed lightly and the
temp rise is faster, the pyro will sometimes read as high as 2020F before
the large, standing cone 03 bites the dust. It's heat work that makes the
difference.
hope this helps, Craig Martell Hopewell, Oregon
Fredrick Paget on wed 3 mar 04
>
>Does anyone have any idea on how to come up
>with a true temp reading with which to calibrate a pyrometer at high
>temps?
>To me a 26C difference is too large an error to be comfortable with.
>Any advice would be appreciated.
>Wayne Seidl
Wayne,
Pyrometers are usually calibrated electrically. An expensive piece of
test equipment that is itself kept calibrated by approved means
generates the minuscule voltages that the thermocouple in good
condition puts out. The output voltage of all types of thermocouples
is given in a set of standards. Then it is just a matter of
calibration, You could have it done by an instrument lab if you live
in a metropolitan area where these are based, Nominal charge of
course.
I used to send out test equipment for calibration routinely in the
Boston Area when I was working. I trained at GE where we were not
allowed to use test equipment that was more than 90 days from
calibration.
At low temps the boiling point of pure water at standard pressure and
the freezing point are good check points, There are a lot of other
substances that have known melting and boiling points too but that is
a major pain in the but to set up and carry out . Anyone for the
melting point of platinum?
Fred
in sunny California where spring is here (Temporarily)
william schran on thu 4 mar 04
Wayne wrote:>Kiln sitter shut off at what the pyrometer said is 1274C
though according to the large Orton cone (10) I had inside,
it would have been a bit closer to 1300<
>Am I just confusing myself? Could I have had a bad cone in the
sitter? The cone bar in the sitter was made by Bell Research (not Orton).
Or does that pyro need more work?<
Since the weight of the rod part of the Kilnsitter presses down on
the cone, you can't judge the firing by that. I would expect the shut
off before cone 10 was bent. Better idea would be a cone 11 in the
sitter and fire by the witness cones. I also wouldn't worry that the
pyrometer doesn't provide an absolute accurate temperature reading
you're expecting. Use the pyrometer to monitor rate of temperature
heating & cooling.
I fire cone 6 crystalline glazes. My firings from cold kiln to cone 6
last 4 hours - then slight cool down and holding temperature. I use a
=46luke 50S with a type K bimetal thermocouple. Cone 6 at 3 o'clock I
get readings from 1030=B0C to 1058=B0C.
Bill
Ivor and Olive Lewis on fri 5 mar 04
Dear Fredrick Paget,
MP Pt.1772=BAC
Regards,
Ivor Lewis. Redhill, South Australia
| |
|
