Marcia Selsor on fri 9 dec 05
I have a Bartell retro fitted computer controller on my big oval
kiln. For the last two firings to ^6 my digital reading was 100
degrees cooler than what was inside the kiln. After the first firing
which I shut off when I saw ^8 was dropping the kiln setter as the
digital readout was 20 degrees below ^6, I called my supplier. Then
next firing I put witness cones 6,7 in and logged the digital. Again
the reading was off but not as much. The first kiln had 14 shelves,
bowl sets, smaler work, the second firing had teapots, larger bowls.
etc.
Anyone know how to adjust this. The manual says I can adjust to 50
cooler shut off but then how do you fire down? That was why I had a
^8 in the setter, so I could fire down.
Marcia
Arnold Howard on fri 9 dec 05
Marcia, your thermocouple may be ready to fail. I would replace it instead
of adjusting the controller. The reason the controller can be recalibrated
only up to 50 degrees is that an adjustment greater than that indicates a
bad thermocouple.
If you don't want to change the thermocouple, you could use the Ramp-Hold
mode and just fire to a cooler temperature. I know people who never use
Cone-Fire, because in some ways, Ramp-Hold is simpler.
Or you could program a cone 4 or 5 firing in Cone-Fire mode.
By the way, if you adjust Thermocouple Offset, the controller's room
temperature reading will be off. That is normal.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
From: "Marcia Selsor"
>I have a Bartell retro fitted computer controller on my big oval
> kiln. For the last two firings to ^6 my digital reading was 100
> degrees cooler than what was inside the kiln. After the first firing
> which I shut off when I saw ^8 was dropping the kiln setter as the
> digital readout was 20 degrees below ^6, I called my supplier. Then
> next firing I put witness cones 6,7 in and logged the digital. Again
> the reading was off but not as much.
Marcia Selsor on fri 9 dec 05
Arnold,
The room temp is correct. The thermocouple looks pristine. It isn't
very old and I was gone a lot last year. It has been fired to several
bisques and two ^6. U susally fire all my bisque for raku in that kiln.
Maybe the tight load had more to do with it but it has been tripping
the cone in the setter regularly.
Thanks for the advice.
Marcia
On Dec 9, 2005, at 12:17 PM, Arnold Howard wrote:
> Marcia, your thermocouple may be ready to fail. I would replace it
> instead
> of adjusting the controller. The reason the controller can be
> recalibrated
> only up to 50 degrees is that an adjustment greater than that
> indicates a
> bad thermocouple.
>
> If you don't want to change the thermocouple, you could use the
> Ramp-Hold
> mode and just fire to a cooler temperature. I know people who never
> use
> Cone-Fire, because in some ways, Ramp-Hold is simpler.
>
> Or you could program a cone 4 or 5 firing in Cone-Fire mode.
>
> By the way, if you adjust Thermocouple Offset, the controller's room
> temperature reading will be off. That is normal.
>
> Sincerely,
>
> Arnold Howard
> Paragon Industries, L.P., Mesquite, Texas USA
> ahoward@paragonweb.com / www.paragonweb.com
>
> From: "Marcia Selsor"
>> I have a Bartell retro fitted computer controller on my big oval
>> kiln. For the last two firings to ^6 my digital reading was 100
>> degrees cooler than what was inside the kiln. After the first firing
>> which I shut off when I saw ^8 was dropping the kiln setter as the
>> digital readout was 20 degrees below ^6, I called my supplier. Then
>> next firing I put witness cones 6,7 in and logged the digital. Again
>> the reading was off but not as much.
>
> ______________________________________________________________________
> ________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Maurice Weitman on thu 15 dec 05
At 1:23 PM -0600 on 12/15/05, Arnold Howard wrote:
>Last week I suggested that the problem above may be due to a faulty
>thermocouple. This morning I thought of another reason: The thermocouple
>reading will be cooler than the actual kiln temperature if the thermocouple
>is not pushed far enough into the firing chamber. This is especially likely
>if the thermocouple is not permanently mounted to the kiln. (Some people use
>a portable controller on several kilns one at a time, and the thermocouple
>is mounted through a drilled peephole plug.)
Hello, Arnold,
I use such a setup: an outboard (Bartlett) controller with a
thermocouple inserted into a hole in the side of the kiln.
Two weeks ago I was firing my small (Aim 88) test kiln with about 15
raw-glazed test tiles to cone 6. I had the (S-type) 'couple inserted
incorrectly; it was only about 1/8" into the kiln. Luckily, I was
using witness cones and found near the time that 6 should have been
at 2:00, 5 had barely budged; the kiln was underfiring big time. So
I compensated by adding a soak until I saw the target cone drop.
My point (you were wondering, huh???) is that it made sense to me at
the time that since the tip of the thermocouple was so close to the
hottest part of the kiln, the bricks and elements, it would be
reading high, thus underfiring.
What do you think about that theory?
Regards,
Maurice
Arnold Howard on thu 15 dec 05
----- Original Message -----
> From: "Marcia Selsor"
>>I have a Bartell retro fitted computer controller on my big oval
>> kiln. For the last two firings to ^6 my digital reading was 100
>> degrees cooler than what was inside the kiln. After the first firing
>> which I shut off when I saw ^8 was dropping the kiln setter as the
>> digital readout was 20 degrees below ^6, I called my supplier. Then
>> next firing I put witness cones 6,7 in and logged the digital. Again
>> the reading was off but not as much.
Last week I suggested that the problem above may be due to a faulty
thermocouple. This morning I thought of another reason: The thermocouple
reading will be cooler than the actual kiln temperature if the thermocouple
is not pushed far enough into the firing chamber. This is especially likely
if the thermocouple is not permanently mounted to the kiln. (Some people use
a portable controller on several kilns one at a time, and the thermocouple
is mounted through a drilled peephole plug.)
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
Marcia Selsor on thu 15 dec 05
the kiln came with the hole. it sticks in about 1.5 to 2" I made
sure is was in as far as it could go.
But that is a good idea.
Marci
On Dec 15, 2005, at 12:23 PM, Arnold Howard wrote:
> ----- Original Message -----
>> From: "Marcia Selsor"
>>> I have a Bartell retro fitted computer controller on my big oval
>>> kiln. For the last two firings to ^6 my digital reading was 100
>>> degrees cooler than what was inside the kiln. After the first firing
>>> which I shut off when I saw ^8 was dropping the kiln setter as the
>>> digital readout was 20 degrees below ^6, I called my supplier. Then
>>> next firing I put witness cones 6,7 in and logged the digital. Again
>>> the reading was off but not as much.
>
> Last week I suggested that the problem above may be due to a faulty
> thermocouple. This morning I thought of another reason: The
> thermocouple
> reading will be cooler than the actual kiln temperature if the
> thermocouple
> is not pushed far enough into the firing chamber. This is
> especially likely
> if the thermocouple is not permanently mounted to the kiln. (Some
> people use
> a portable controller on several kilns one at a time, and the
> thermocouple
> is mounted through a drilled peephole plug.)
>
> Sincerely,
>
> Arnold Howard
> Paragon Industries, L.P., Mesquite, Texas USA
> ahoward@paragonweb.com / www.paragonweb.com
>
> ______________________________________________________________________
> ________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
William & Susan Schran User on fri 16 dec 05
On 12/16/05 1:10 AM, "Maurice Weitman" wrote:
> My point (you were wondering, huh???) is that it made sense to me at
> the time that since the tip of the thermocouple was so close to the
> hottest part of the kiln, the bricks and elements, it would be
> reading high, thus underfiring.
>
> What do you think about that theory?
My two cents would be the thermocouple needs to have a certain length
exposed to the kiln interior to produce a correct reading. When part of the
thermocouple is not exposed to the interior atmosphere, it is in the wall of
the kiln and the thermal mass of the brick is absorbing the heat, creating a
cooler area around the part of the thermocouple still in the wall.
If one is moving a thermocouple from kiln to kiln, and the kilns have
similar wall thickness, simply insert the thermocouple in a kiln to the
correct point, then make a pencil mark on the protection tube/ceramic holder
at the point where it comes out of the kiln on the exterior, then insert in
any other kiln up to the pencil mark.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
William & Susan Schran User on mon 19 dec 05
On 12/18/05 10:20 PM, "Ivor and Olive Lewis" wrote:
> Correct me if I misread you, but I understood absorption of heat resulted in
> increased temperature !
I also understood absorption of heat would increase temperature, but
wouldn't the heat be dissipated as it moves towards the cold face of the
brick?
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Marcia Selsor on mon 19 dec 05
Bill,
would the thermocouple misread on the interior of the kiln?
Marcia
On Dec 19, 2005, at 6:48 AM, William & Susan Schran User wrote:
> On 12/18/05 10:20 PM, "Ivor and Olive Lewis"
> wrote:
>
>> Correct me if I misread you, but I understood absorption of heat
>> resulted in
>> increased temperature !
>
> I also understood absorption of heat would increase temperature, but
> wouldn't the heat be dissipated as it moves towards the cold face
> of the
> brick?
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
> ______________________________________________________________________
> ________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
William & Susan Schran User on mon 19 dec 05
On 12/19/05 10:19 AM, "Marcia Selsor" wrote:
> would the thermocouple misread on the interior of the kiln?
The original response was to a question about a thermocouple perhaps not
being inserted into the kiln the proper amount.
My response was that if less than the proper length were inserted into the
kiln interior, then the thermocouple would send incorrect readings to the
pyrometer/controller as it would be cooler due to the surrounding brick.
So, yes, the thermocouple would misread the interior of the kiln.
I'm also assuming the tip of the thermocouple actually reads the
temperature, but I would think the tip needs to be at a certain distance
inside the kiln to "read" the temperature without being over heated by the
radiance of an element, and I would think it best if the ware/shelf/posts
were also a certain distance from the thermocouple.
This is all my conjecture. Someone who designs/builds these devices would
probably explain it better.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Fredrick Paget on mon 19 dec 05
>On 12/19/05 10:19 AM, "Marcia Selsor" wrote:
>
> > would the thermocouple misread on the interior of the kiln?
Thermocouples are pretty simple devices.
A tiny voltage is generated when two dissimilar metals are in contact
and is conducted out to the cold end. The cold end is another
junction and for a true reading has to be at a reference temperature.
All this is taken into account in the design of the controller.
Now when the hot end is inside the kiln it registers the temperature
at the tip. The wire from the tip to the outside is a heat conductor
but a very small one. Also if there is a draft of cool air coming in
alongside the thermocouple through the thermocouple hole due to the
kiln vent, that can slightly cool the tip. The result is slight over
firing.
The answer is to get the tip well into the kiln and to plug up the
hole so a draft doesn't affect the temperature at the tip and the
thermocouple wire for a short distance back from the tip is at kiln
temperature.
To avoid another competing thermo-junction at the outside of the
kiln where the flexible wire to the controller is attached the wire
must be either of the same metal as the thermocouple so it is not
dissimilar, as for example with a type k or if platinum ( at $10 an
inch) a special cheaper alloy that has near zero dissimilarity for a
small range around room temperatures.
If plain copper wire is used there is another pair of junctions
right outside the kiln and an erroneous reading results.
--
From Fred Paget,
Marin County, CA, USA
fredrick@well.com
http://homepage.mac.com/fredrick/FileSharing1.html
Charter Member Potters Council
Ivor and Olive Lewis on mon 19 dec 05
Dear William,
You write <certain length
exposed to the kiln interior to produce a correct reading. >>
It is the interface between the two metal of the thermocouple that =
provides the electric potential under the influence of Heat. Your =
statement is true if the location of the junction is not at the tip of =
the sheath. A projecting length would overcome the difference.
<<... it is in the wall of the kiln and the thermal mass of the brick is =
absorbing the heat, creating a cooler area around the part of the =
thermocouple still in the wall....>>=20
Correct me if I misread you, but I understood absorption of heat =
resulted in increased temperature !
All the best,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on wed 21 dec 05
Dear William ,
<wouldn't the heat be dissipated as it moves towards the cold face of the
brick?>>
Yes, you are correct. Heat will be conducted into the outer reaches of =
the insulation. The outer face will increase in temperature until =
equilibrium is established. At which point it might be expected that =
temperature becomes a function of distance from the original source of =
energy. Because of the geometry of a kiln this is not necessarily a =
linear function and it may be that the wall adjacent to the Pyrometer =
probe will have a lower temperature.
Be of good Cheer this Yule Tide.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
| |
|
