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Cone offset


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#1 Claypple

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Posted 02 May 2013 - 10:33 PM

Why do all new kilns require reprogramming? I mean the cone offsetting?
I was glazing at ^6 on a new kiln and had a big over-firing (it went up to cone 7 instead).
I checked the temperature and found the glazing at ^6 was programmed to go up to 2238F instead of 2199F as the manual suggested.

Yes, I know, the Temperature is not equal to cone, it is all about the heat-work, but it was not firing for a shorter time either.
Yes, I did the test firing with the kiln furniture in.
I also realize that the thermocouple requires a tune-up at first, but I do not think I was off-setting the thermocouple but the final temperature programmed by the manufacture, did I?

#2 bciskepottery

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Posted 03 May 2013 - 07:46 AM

An offset is required because thermocouples have a sheathing around them . . . so you need to compensate because the sheathing prevents a true temperature reading. The sheathings prevent the thermocouples from being knocked by shelves and breaking. My kiln reads 2232 for cone 6.

A new kiln, or an old kiln with new elements, may fire hotter at first. As the elements age, they become less efficient. You may find the offset you use now will need to be adjusted latter. When you adjust the offset, your are really "tricking" the kiln into thinking it has reached a certain cone level by manipulating the temperature.

Did you do any type of hold at peak temperature? If so, that would also contribute to reaching a higher cone level.

#3 OffCenter

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Posted 03 May 2013 - 08:41 AM

Why do all new kilns require reprogramming? I mean the cone offsetting?
I was glazing at ^6 on a new kiln and had a big over-firing (it went up to cone 7 instead).
I checked the temperature and found the glazing at ^6 was programmed to go up to 2238F instead of 2199F as the manual suggested.

Yes, I know, the Temperature is not equal to cone, it is all about the heat-work, but it was not firing for a shorter time either.
Yes, I did the test firing with the kiln furniture in.
I also realize that the thermocouple requires a tune-up at first, but I do not think I was off-setting the thermocouple but the final temperature programmed by the manufacture, did I?


Maybe bciskepottery knows more about thermocouples than I do but I don't see how the thermocouple being inside a ceramic tube would affect the reading very much if at all. When you first turn on the kiln at room temp, it might take the air inside the tube a little longer to warm up than the air just outside the tube but once they are equalized they should stay the same with maybe an insignificant delay. What does Dolomite Neil have to say about this?

Obviously, you know how cones work so I won't insult you by describing heat work, but your new kiln was probably rated at a ramp rate of about 110 F/hr at which cone 6 is very close to 2238. For cone 6 to be 2199 the ramp rate would have had to be somewhere around 50 F/hr. Before you start making adjustments find our how quickly your kiln fires. Also, How did the glazes look?

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#4 neilestrick

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Posted 03 May 2013 - 09:12 AM

When the kiln reaches it's desired temp, the elements turn off, but they are still hot for a while so they radiate heat for a few minutes. New elements run hotter, so they can radiate longer and cause a little overfiring sometimes. In my opinion it is more common in small kilns. Plus thermocouples are not 100% accurate, especially type K like we use at or above their recommended peak. But they are affordable, and generally accurate enough. However some tweaking of the system can be necessary. You have two options: adjust the thermocouple offset, which will affect your firings at every temperature, or put in a cone offset for cone 6.

1. Did you have several cones throughout the kiln? Was every section too hot? If they weren't all running hot, then you'll likely need to adjust the thermocouple for that section. If they all ran hot, then I recommend doing a cone offset, rather than the thermocouples. Is it accurate at bisque temps? If so, then you definitely want to adjust the cone offset for cone 6, rather than the thermocouples.

2. Were the cones near the edge of the shelf? They can run hot if too close to the elements.

I have put in an offset for cone 6 on my small kiln, as it runs a little hot. In my large kiln, I have adjusted the thermocouple offset for the bottom ring, as it runs a bit cold down there. This is part of owning a digital kiln. Once you get it dialed in it won't be an issue.
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#5 Claypple

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Posted 03 May 2013 - 10:43 AM

Thank you all!

Offcenter: The glaze didn't look good at all. Got over-fired (I was only doing samples).
I don't think my kiln is rated at 110 F/h, that's the point!
The manual said it should go up to 2199, but the kiln was programmed to fire itself up to 2238.

Neil: No, I didn't do several cones through the kiln. The difference in the temperature that I was telling to Offcenter drew my attention and I concentrated only on that, so I did the cone offset for the ^6. I then checked how other programs were programed and found that all of them were programmed to be fired at a higher temp than the manual was saying. The difference is insignificant for the low cones, but is noticeable at the high cones.

I have not done the cone offset for the other cones yet. In fact, I do not think I am going to do it for the bisque firing at all, as it is not that crucial. The bisque turned out well. The low fire glazing looked good too, so why mess with what is not broken.

Again, I do not think it is the thermocouples but the programming.

Other than that, I did already a lot of firing and glazing, and I think the kiln is working beautifully, has an even temp through the kiln, very reliable. I love it!

#6 OffCenter

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Posted 03 May 2013 - 11:04 AM

Thank you all!

Offcenter: The glaze didn't look good at all. Got over-fired (I was only doing samples).
I don't think my kiln is rated at 110 F/h, that's the point!
The manual said it should go up to 2199, but the kiln was programmed to fire itself up to 2238.


Well, I'm not going to argue with the manual except to say that the kiln will have to fire pretty slowly for 2199 to bend cone 6. When I fire to cone 6 the temp is above 2238. Also, maybe this is just me and my glazes, I don't consider reaching cone 7 a drastic over-firing. Somewhere between an almost flat 6 and a bending 7 is where they look best.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#7 Claypple

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Posted 03 May 2013 - 11:14 AM

[quote name='OffCenter' date='03 May 2013 - 09:04 AM' timestamp='1367597081' post='34031']
[quote name='Claypple' date='03 May 2013 - 11:43 AM' timestamp='1367595792' post='34027']
Well, I'm not going to argue with the manual except to say that the kiln will have to fire pretty slowly for 2199 to bend cone 6. When I fire to cone 6 the temp is above 2238. Also, maybe this is just me and my glazes, I don't consider reaching cone 7 a drastic over-firing. Somewhere between an almost flat 6 and a bending 7 is where they look best.

Jim
[/quote]

Hmm, I used Coyote glazes, and they all looked greyish other than how they were supposed to look.
I used slow glaze program, so it was firing pretty slow.
I agree, all the glazes and kilns are different.

That is why we call pottery an art, not a science, right? Posted Image

#8 neilestrick

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Posted 03 May 2013 - 11:43 AM

They may have made changes to the programming, but not the manual. As the manufacturer of the controller makes changes to the system, the paperwork doesn't always keep up. I run into this with every brand of kiln. Factory thermocouple offsets will be different from year to year, as well as cone temps. The technology is always changing. But like I said, once you get yours figured out it'll be good to go.
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#9 Arnold Howard

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Posted 03 May 2013 - 12:38 PM

Why do all new kilns require reprogramming? I mean the cone offsetting?
I was glazing at ^6 on a new kiln and had a big over-firing (it went up to cone 7 instead).
I checked the temperature and found the glazing at ^6 was programmed to go up to 2238F instead of 2199F as the manual suggested.

Yes, I know, the Temperature is not equal to cone, it is all about the heat-work, but it was not firing for a shorter time either.
Yes, I did the test firing with the kiln furniture in.
I also realize that the thermocouple requires a tune-up at first, but I do not think I was off-setting the thermocouple but the final temperature programmed by the manufacture, did I?


I would first make sure the thermocouple(s) extends into the firing chamber by the correct distance.

The actual temperature that the kiln reached doesn't matter as much as the bending of witness cones. You could program a cone 5 instead of 6 in Cone-Fire, use Ramp-Hold mode and incrementally adjust the temperatures, or adjust Cone Offset. Adjust the controller to bend the witness cones.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com

#10 timbo_heff

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Posted 03 May 2013 - 01:43 PM

I thought that the offset is to compensate for the different power ones' electric company delivers: if you are on 240 service the power company can legally deliver + or - 10% so if you have poor power or good power you can calibrate the controller to knock down the right cone at the given program.

#11 neilestrick

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Posted 03 May 2013 - 02:51 PM

I thought that the offset is to compensate for the different power ones' electric company delivers: if you are on 240 service the power company can legally deliver + or - 10% so if you have poor power or good power you can calibrate the controller to knock down the right cone at the given program.


Nope. The cone and thermocouple offsets are to compensate for the inaccuracy of the thermocouples. If your power is high or low 10% it doesn't matter. The kiln is trying to ramp at a certain rate. If the power is high, the elements will run a little hot, and the computer will simply have to power them up for less time to get the desired rate of climb. If the power is low, it will power them up longer to compensate. Of course, if the power is too low it won't bea able to heat like ti wants to and will give you and error code.
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#12 timbo_heff

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Posted 03 May 2013 - 03:21 PM


I thought that the offset is to compensate for the different power ones' electric company delivers: if you are on 240 service the power company can legally deliver + or - 10% so if you have poor power or good power you can calibrate the controller to knock down the right cone at the given program.


Nope. The cone and thermocouple offsets are to compensate for the inaccuracy of the thermocouples. If your power is high or low 10% it doesn't matter. The kiln is trying to ramp at a certain rate. If the power is high, the elements will run a little hot, and the computer will simply have to power them up for less time to get the desired rate of climb. If the power is low, it will power them up longer to compensate. Of course, if the power is too low it won't bea able to heat like ti wants to and will give you and error code.


That makes sense. Of course if it's running hot it still up the the thermo and the controller to make the call regardless of the relative temp of the elements. I should have intuited that... long week... ugg!

#13 Claypple

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Posted 03 May 2013 - 06:40 PM

The technology is always changing. But like I said, once you get yours figured out it'll be good to go.


Yep! It is working great since I tuned it up. I just wanted to figure out why, how come, etc.
I like understanding how the things work.

I find it great that every kiln is special. That makes our work unique.




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