Fara Shimbo on tue 3 feb 04
Good morning (well, I was told it is anyway, I don't
believe there's any such thing)
I have a Skutt 818 kiln with a controller on it that consistantly
reads only 96% of the actual temperature. At room temp
this makes no difference but when the Skutt pyrometer is
telling me I've got 1233 C, my Fluke pyrometer is telling me
I'm at 1280 C. When I tried to fire to cone 05 to break in
a new set of elements, cone 03 was down before I just shut the
thing off.
I've tried changing the thermocouple and even have had the
motherboard replaced. Neither made a difference.
Is there any way I can reprogram the Skutt to give me an
actual temperature reading?
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Fara Shimbo, Master Crystalliere, Certified Public Nuisance
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Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.272.0442
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
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WHC228@AOL.COM on tue 3 feb 04
Fa
Is the wire from the thermocouple and your meter thermocouple wire? The wire
is specific.
Bill Campbell
Arnold Howard on tue 3 feb 04
It's normal for a digital controller to be out of adjustment by at least a
few degrees. So it is not surprising that your kiln reads 1233 while the
Fluke pyrometer reads 1280.
The Fluke could be off, too. A pyrometer or controller is only as accurate
as the thermocouple connected to it. You are probably using Type-K
thermocouples, which drift in temperature as they age. (The more expensive
Type-S thermocouples last much longer without drift.)
Using witness cones on the shelf, as you have done, is the best way to check
the accuracy of your digital controller. It would be a good idea to place
the cones in several locations to get an average cone reading.
Your Skutt controller is made by Bartlett Instruments. I don't know which
version you have, so I can't tell you how to adjust the temperature. If you
look through the manual, you will probably find instructions for one or two
types of adjustments. The last Barlett controller that Paragon used had two
adjustments: "Cone Offset" and "Thermocouple Offset."
Adjusting Cone Offset affects only the cone you are adjusting. The other
cones in Cone Fire mode remain unaffected. Thermocouple Offset affects all
cones in Cone Fire mode and all temperatures in Ramp Hold mode. Example:
Adjusting Thermocouple Offset so the kiln fires 10 degrees hotter affects
all firings. Making that adjustment for cone 05 in Cone Offset affects only
cone 05 firings.
If you don't want to make a controller adjustment, you could also fire to a
lower cone number or add a hold time.
If the controller is off by more than 50 degrees F, it is probably because
the thermocouple is failing. Or it may not be pushed into the firing chamber
far enough. A 1/4" diameter thermocouple should protrude into the firing
chamber by 1". Since your controller is off by around two cones, the
thermocouple may be failing. Another possibility is that a shelf is too
close to the thermocouple. That can change the reading.
One way to check the thermocouple for wear is to reach inside the kiln while
it is cold and move the thermocouple tip with your fingers. If the
temperature display on the controller jumps, the thermocouple is about to
fail.
At any rate, replacing a thermocouple takes just a few minutes once you've
done it a couple of times. Most likely the controller is operating normally.
Sincerely,
Arnold Howard
Paragon Industries, L.P.
arnoldhoward@att.net
From: "Fara Shimbo" I have a Skutt 818 kiln with a
controller on it that consistantly
> reads only 96% of the actual temperature. At room temp
> this makes no difference but when the Skutt pyrometer is
> telling me I've got 1233 C, my Fluke pyrometer is telling me
> I'm at 1280 C. When I tried to fire to cone 05 to break in
> a new set of elements, cone 03 was down before I just shut the
> thing off.
Ivor and Olive Lewis on wed 4 feb 04
Dear Fara Shimbo,
I am not sure if this is applicable to the situation you describe.
Pyrometers have two important connections called Junctions which are
necessary of the Electro Thermal Effect to work. These are the Hot
Junction, in the kiln and the Cold Junction which is associated with
the metering device, be it analogue or digital. If there is a
difference between the temperature to which an instrument was
calibrated by the maker and the temperature at which it is being used
then it is not possible to get a valid reading from the meter.
Somewhere in each system there should be a way of making an adjustment
for this temperature difference. Your system may have been calibrated
with a cold junction at room temperature, or at the freezing point of
water or to some agreed national standard, possibly 15=BA C.
I have an analogue Pyro. I can adjust the needle setting, while the
kiln is cold, to the ambient temperature of the day. I have assumed I
am doing the correct thing. But I do not rely on my pyrometer as a
true temperature gauge. I place my trust in good old Orton Cone.
Perhaps you might inquire about the nature of resetting your system to
ambient temperature to compensate for difference in cold junction
calibration.
But I may be wrong on this one.
Best regards,
Ivor Lewis. Redhill, South Australia
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