Calibrate new Thermocouple or change old elents

[leelee52]

Hello. I recently replaced my  original thermocouple in my 15+ year old Skutt 1018KM because of an overfired glaze firing( yes witness cones used).  In my next bisque(04), it was underfired though reached temp according to controller. Solutions please. The elemts are original as well. I generally fire Bisque 04 and Glaze Cone 5 with 15 min hold. Thank you! 

[neilestrick]

Hi @leelee52, welcome to the forum!

Can you post pics of the cones? How far off were they?

Have you measured the resistance of the elements? How do they look- are the coils starting to lay over and bunch up?

[Dick White]

Measuring the resistance of the elements is the most accurate way to determine if they are sufficiently worn that the kiln will have trouble heating, and thus the elements should be replaced. However, if one takes a close look at Ohms Law that mathematically relates volts, amps, resistance, and watts, amperage is an inverse proxy for resistance. Skutt kilns manufactured after 2006 all contain a current sensor that can measure the amperage being pulled by each section (some from before this date might have one too). This amperage measurement is built into the controller diagnostics and can be retrieved without opening the control column.  If you do not have a copy of the user manual, you can download one here - https://skutt.com/skutt-resources/manuals/kilnmaster-manuals/. The original specification for the amperage of each section of a 1018 is 20 amps (both sections are the same). If the amperage readings are 18 or below, the elements are worn.

[Leecat52]

Hello and thank you for your responses! 
The forum wouldn’t let me log in to respond so that  was the delay for my response. I called Skutt and learned   my kiln is actually 22 years old( Manufactured 2001).  Scotty helped me check  the resistance on my elements  and according to him ( 11.7 Ohms) for new, mine were in acceptable range. Though 22years old? 
They are sagging a bit on the bottom( broken brick) but burn brightly when observed. 
The  Self-supporting 04 cones bent to only 

[Dick White]

Age in years is less of an issue than the number of times they have been fired to maximum temperature. At the community studio I manage, the glaze kilns rated to cone 8 that are constantly fired to cone 6, we get about 75-80 firings in a year before they are too worn to finish. The bisque kilns are still firing to cone 06 on the same elements for 10 years now.

[Bill Kielb]

On 4/28/2023 at 8:38 AM, leelee52 said:

Cone 5 with 15 min hold

Cone 5 with a 15 minute hold ought to get you near cone 6, especially brand new. 22 year old elements that measure exactly to original specification  would be very surprising if you have been firing to cone 5/6 with any regularity in the last 22 years. At 12.8 ohms these elements are ready for replacement so the meter needs to be relatively accurate. Might be worth a careful accurate remeasure or measure the amperage, it should be 39.4 amps, if the problem continues and gets more pronounced, look for bad connections, worn relay contacts, over heating breaker …… somewhere a voltage drop is likely occurring. Most items in a kiln need some sort of service within 22 years, so relays that last that long would also be a pleasant surprise as well.