Snail Scott on wed 17 feb 10
As some of you know, I teach at a college with a
very limited clay program. We have two sections of
Ceramics I and only one kiln, a 12-sided Olympic
with a Bartlett controller. I rely heavily on the
automatic controller since I work other teaching
jobs on alternate days of the week and cannot be
there to monitor the kiln while firing.
In the three years I have taught there, the kiln has
consistently fired a bit high, but rather than program
the offset, I just tell it to fire to ^5, and it gives me a
perfect ^6 firing according to the witness cones. It's
done this without variation for hundreds of firings
over the last three years, through three thermocouple
replacements, new fuses, new wall wiring, new box
connectors and a full set of new elements.
I replaced the thermocouple again in January, and
ran about six bisque firings in it. I just did the first ^6
firing on the new thermocouple, setting it to ^5 as
usual, but it overfired dramatically, well past the
guard cone in the witness cone pack. Based on the
level of vitrification of the clay and the extreme flow
of the normally stable glazes, I'd estimate perhaps
^9. However, the controller still thinks it only went to
^5 as usual, though with a much longer firing time.
Not enough to generate an error message, though.
I don't generally use witness cones in the bisque, so
it may have overfired previously, but I didn't notice
any visible discrepancy at the time. So, the error
may have been present before but gone unnoticed
until the glaze firing occurred, or it may be a new
problem that merely coincided with the first glaze
firing.
I have checked the connections on the new
thermocouple, and they seem fine. It is a different
style than the previous, but our supplier says it's
still the correct type K for the unit. (It does give an
accurate room-temperature reading.)
I will be asking the Monday-Wednesday sculpture
instructor to keep an eye on it today. He may not be
able to read the cone pack accurately during the
firing, but as a blacksmith, he may be able to read
the color closely enough to do a shutdown if it gets
badly overfired again. I've got it set for ^3 this time,
hoping for the best rather than letting the work go
unfired altogether. At least he can shut it down if
it runs the nominal firing duration and doesn't shut
itself off.
This is our only kiln, and I already have to come in
on weekends to keep up with the firing schedule;
any downtime at all will cripple our program severely.
If anyone out there has experience with this type of
controller or has seen similar symptoms, please let
me hear your suggestions. I will beg funds to replace
the circuit board or thermocouple if needed, but I have
to be certain what the problem is first as funds are
very tight. Help me troubleshoot this thing, please?
-Snail
Arnold Howard on wed 17 feb 10
From: "Snail Scott"
> I replaced the thermocouple again in January, and
> ran about six bisque firings in it. I just did the first
> ^6
> firing on the new thermocouple, setting it to ^5 as
> usual, but it overfired dramatically, well past the
> guard cone in the witness cone pack.
-------------
Snail, I would check the thermocouple wires for damaged
insulation. The thermocouple wires should also be away from
the element-to-relay wires.
Is the thermocouple pushed into the firing chamber far
enough? (It should extend into the chamber four times the TC
diameter.) Someone may have bumped it back into the wall
with a shelf. That will overfire the kiln.
Though the thermocouple connector screws are tight, the
thermocouple itself, under a screw, may be broken.
If the wires and thermocouple position are okay, I would
replace the thermocouple again. You may have received a
defective one.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
Larry Kruzan on wed 17 feb 10
Hi Snail,
I have some type K thermocouples that I picked up surplus. I'd be happy to
send you one to try. They are 12" long but I just cut them to the same
length as the old one.
I'm no expert but always thought type k was type k as long as wire gage was
the same. I could be very wrong.
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Snail Scott
Sent: Wednesday, February 17, 2010 10:17 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: Bartlett controller issue
As some of you know, I teach at a college with a
very limited clay program. We have two sections of
Ceramics I and only one kiln, a 12-sided Olympic
with a Bartlett controller. I rely heavily on the
automatic controller since I work other teaching
jobs on alternate days of the week and cannot be
there to monitor the kiln while firing.
In the three years I have taught there, the kiln has
consistently fired a bit high, but rather than program
the offset, I just tell it to fire to ^5, and it gives me a
perfect ^6 firing according to the witness cones. It's
done this without variation for hundreds of firings
over the last three years, through three thermocouple
replacements, new fuses, new wall wiring, new box
connectors and a full set of new elements.
I replaced the thermocouple again in January, and
ran about six bisque firings in it. I just did the first ^6
firing on the new thermocouple, setting it to ^5 as
usual, but it overfired dramatically, well past the
guard cone in the witness cone pack. Based on the
level of vitrification of the clay and the extreme flow
of the normally stable glazes, I'd estimate perhaps
^9. However, the controller still thinks it only went to
^5 as usual, though with a much longer firing time.
Not enough to generate an error message, though.
I don't generally use witness cones in the bisque, so
it may have overfired previously, but I didn't notice
any visible discrepancy at the time. So, the error
may have been present before but gone unnoticed
until the glaze firing occurred, or it may be a new
problem that merely coincided with the first glaze
firing.
I have checked the connections on the new
thermocouple, and they seem fine. It is a different
style than the previous, but our supplier says it's
still the correct type K for the unit. (It does give an
accurate room-temperature reading.)
I will be asking the Monday-Wednesday sculpture
instructor to keep an eye on it today. He may not be
able to read the cone pack accurately during the
firing, but as a blacksmith, he may be able to read
the color closely enough to do a shutdown if it gets
badly overfired again. I've got it set for ^3 this time,
hoping for the best rather than letting the work go
unfired altogether. At least he can shut it down if
it runs the nominal firing duration and doesn't shut
itself off.
This is our only kiln, and I already have to come in
on weekends to keep up with the firing schedule;
any downtime at all will cripple our program severely.
If anyone out there has experience with this type of
controller or has seen similar symptoms, please let
me hear your suggestions. I will beg funds to replace
the circuit board or thermocouple if needed, but I have
to be certain what the problem is first as funds are
very tight. Help me troubleshoot this thing, please?
-Snail
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William & Susan Schran User on thu 18 feb 10
On 2/17/10 11:16 AM, "Snail Scott" wrote:
> This is our only kiln, and I already have to come in
> on weekends to keep up with the firing schedule;
> any downtime at all will cripple our program severely.
>
> If anyone out there has experience with this type of
> controller or has seen similar symptoms, please let
> me hear your suggestions. I will beg funds to replace
> the circuit board or thermocouple if needed, but I have
> to be certain what the problem is first as funds are
> very tight. Help me troubleshoot this thing, please?
Hi Snail, ain't technology wonderful?
After I make any repairs to my programmable kilns, changing out elements or
thermocouples, I program the firings the same as before the repair, but I
make sure I am there when the anticipated completion of the firing will
occur. Watching the witness cones, I can enter a "skip step" when the prope=
r
cone has bent if the kiln has not completed the heating cycle. I'm afraid
this is what you will need to do for both bisque and glaze firings until yo=
u
find the proper set temperature to enter.
Have same kiln in my studio as at school. Mine has APM elements and "S" typ=
e
thermocouples. Kiln at school has very HD elements and "K" type
thermocouples. Getting to the same ^6, set point in my kiln is 2210, at
school it is 2185. I know my elements are beginning to wear down, because
I've reset set temperature to 2195 for ^6 as the firings are slowing a bit
and I have more work heat acting on the pots.
I don't necessarily think it's your controller. My kilns are L&L and they
have Barlett controllers. I think your issue is probably the new
thermocouples, the signal that is being sent to the controller and you'll
need to conduct a test firing to find the proper temperature set point.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Snail Scott on fri 19 feb 10
Thanks to all who offered their suggestions
regarding my college's kiln controller failure.
Just to reiterate briefly - Being present to monitor
the firing would indeed be desirable, but I work
elsewhere on alternate days and can't be there
to watch it go through its paces. If this continues,
I suppose I could run each load with a 30 hour
time delay, so that it would be reaching temperature
while I am there on my next teaching day. There
is enough inherent lag time in ceramics anyway
that I hate to make that a routine practice, but it is
possible. (I'm firing the work of 27 students in just
one kiln, so efficiency rules. To avoid limiting the
size of their work, I already drive in on the
weekends - my own studio time - to get it all fired.)
So, I did actually take time to drive in on my 'other'
work day and check it out in person around the time
it should have ended. (Couldn't be quite exact in my
timing.) I had set the controller to ^3, just in case I
couldn't make it in after all, thinking that maybe it
might overfire less than the last time if I couldn't be
there. Well, it went to just over ^4 - the exact offset
error that it has had for as long as I have used it,
so, essentially normal in every respect. Dangit.
So, it worked perfectly (by my standards), and I still
have no idea what went wrong last time. Crossing
my fingers for next time...I surely don't want a repeat
of the meltdown (I'm still resurfacing the shelves),
but I may not ever know what happened if it doesn't
repeat. Ignorance ain't bliss, but it's better than a
meltdown!
-Snail
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