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Bad Experience With Rohde Kiln - But Is Nabertherm Any Better?

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You can find mention of thermocouple (TC) drift with type K TC's on any of the kiln manufactures websites. It is also on the Orton website. From Orton:

"Thermocouples All controllers depend on thermocouples placed in the kiln to measure temperature. With time, the output of most thermocouples will change, this is called drift. When drift occurs, the thermocouple no longer measures the same temperature as it did when it was new. Typically, drift causes the kiln temperature to be higher than the temperature displayed by the controller. Type K thermocouples drift more than Type S and these need to be replaced after 50-100 firings, or when damaged. Orton recommends that Type K thermocouples normally not be used at higher temperatures (above 2100°F, unless they are made of 8 gage wire or enclosed in a protective sheath. Smaller diameter (14 gage) wire are not advisable for repeat firings above 2100°F. Type S can be used when firings regularly exceed 2100°F."

It's really not a big deal to place a cone pack in the kiln to verify the TC is reading accurately. If it's badly worn then replace it, if not then recalibrate. 

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I have run into a lot of situations that 'shouldn't happen' with kilns and electricity that happen anyway- TC drift the wrong way, element ohms that age the wrong way, elements that measure fine but won't get to temp, etc. I had a discussion about this a few months back with one of the engineers at L&L. Some people in his office swear that it's impossible for a kiln to be a lemon, because if all the parts work, then the kiln works. Others, including him (and me), believe that a kiln can be a lemon, and some things happen that aren't necessarily backed up by textbooks.

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37 minutes ago, Min said:

You can find mention of thermocouple (TC) drift with type K TC's on any of the kiln manufactures websites. It is also on the Orton website. From Orton:

"Thermocouples All controllers depend on thermocouples placed in the kiln to measure temperature. With time, the output of most thermocouples will change, this is called drift. When drift occurs, the thermocouple no longer measures the same temperature as it did when it was new. Typically, drift causes the kiln temperature to be higher than the temperature displayed by the controller. Type K thermocouples drift more than Type S and these need to be replaced after 50-100 firings, or when damaged. Orton recommends that Type K thermocouples normally not be used at higher temperatures (above 2100°F, unless they are made of 8 gage wire or enclosed in a protective sheath. Smaller diameter (14 gage) wire are not advisable for repeat firings above 2100°F. Type S can be used when firings regularly exceed 2100°F."

It's really not a big deal to place a cone pack in the kiln to verify the TC is reading accurately. If it's badly worn then replace it, if not then recalibrate. 

Totally agree, replacing them is always easy. This has been an issue for more than fifty years In industry, well researched and still debated with respect to testing. Drift actually is the movement downward whereas normal aging is the movement upward. Both conditions usually apply but drift (downward movement)  is often the superior effect.  It’s actually an extremely complicated issue in process control which has been extensively debated and discussed. I try not to over emphasize it in kiln control because it is most often an outlier or insignificant.  Most thermocouple compositions  have unique drift issues in various environments. A possibility but rarely a primary cause and really difficult to quantify. We write software to automatically correct for anticipated drift only after years of data collection and  regular successful calibration.
 

More often there are real physical issues or  firing issues especially when cone theory and use is not understood. For kilns generally they are replaced before we start to worry about a five degree drift. I  like to stress the basics before confusing what can be a quite advanced discussion.

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19 minutes ago, neilestrick said:

I have run into a lot of situations that 'shouldn't happen' with kilns and electricity that happen anyway- TC drift the wrong way, element ohms that age the wrong way, elements that measure fine but won't get to temp, etc. I had a discussion about this a few months back with one of the engineers at L&L. Some people in his office swear that it's impossible for a kiln to be a lemon, because if all the parts work, then the kiln works. Others, including him (and me), believe that a kiln can be a lemon, and some things happen that aren't necessarily backed up by textbooks.

Maybe,

Having tested and quantified things most of my life I have not ever found an element increase in resistance but put out more heat. It’s usually down to If I can find the true underlying cause.  Generally the mystery lemon products ended up to be underlying causes that I was not able to quantify at the time. Some processes take more time and analysis than often is worthwhile to solve so changing parts by trial and error is justified. I have not found a contradiction to the basic laws of physics but when I do, I will publish. Probably no hope though as I have been at it for more than fifty years.

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I think what's going on here is a difference in semantics. When I quoted Orton's blurb on TC's and drift I was reading it as a potter. @Bill Kielb, I believe when you say: "Drift actually is the movement downward whereas normal aging is the movement upward. Both conditions usually apply but drift (downward movement)  is often the superior effect." I'm going to assume you are writing this as an electrician. To a non electrician and potter such as myself and those to whom Orton and all the kiln manufacturers are speaking, the term drift does not mean drift is only a downward movement. Potters speak isn't the same as electrician speak in all situations.

 

 

 

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1 hour ago, Min said:

I think what's going on here is a difference in semantics. When I quoted Orton's blurb on TC's and drift I was reading it as a potter. @Bill Kielb, I believe when you say: "Drift actually is the movement downward whereas normal aging is the movement upward. Both conditions usually apply but drift (downward movement)  is often the superior effect." I'm going to assume you are writing this as an electrician. To a non electrician and potter such as myself and those to whom Orton and all the kiln manufacturers are speaking, the term drift does not mean drift is only a downward movement. Potters speak isn't the same as electrician speak in all situations.

 

 

 

Just lots of years of thermocouple speak for me actually and those industries that use thermocouples. Google thermocouple drift, lots to read from .... thesis papers to manufacture analysis.

It’s  an interesting fact for potters, electricians and engineers that choose to use it.  For potters it’s significant to note that it’s known tendency is to move downward so the tendency would be to begin to make your kiln overfire.  However without the context that it is really not super significant for most small kilns it only serves as another gremlin to chase, other than maybe a last gremlin to chase.

Folks choose to get what they want to out of things. If Orton cited drift, they probably actually did mean drift in the technical sense. Had they included the definition it would have provided more content to those willing to gain new knowledge. How one chooses to learn or ignore new facts they are not experienced in is totally up to them regardless of occupation or title.

Offering something you are aware of is for the benefit of others just part of each one teach one in my view. If I misunderstand  a process I prefer credible correction so that I don’t offer incorrect information to others. I am not going to be a nuclear physicist at this point in life but I am fascinated to discover cold fusion has existed since the forties using muons instead of electrons. Never knew that till I spoke with a physicists. I enjoy knowing and glad she shared. Also glad she told me it cannot be sustained more than a few micro seconds. I never would have known.

Edited by Bill Kielb

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