fgvanatta Posted December 10, 2015 Report Share Posted December 10, 2015 I have a fairly new Skutt KM822 (about 20 firings). As I was waiting for the cycle to complete yesterday, I noticed that the temperature went to 2241° before the kiln shut off. When the firing was complete I used "Review" to check the "Highest Temperature Reached" and it reported 2236°. I don't know if this is normal for this controller or something is wrong or it can be accounted for as heat work instead of temperature. I emailed Skutt about this yesterday morning, but haven't received any reply yet. Anyone else out there have any ideas about this? Link to comment Share on other sites More sharing options...
Mark C. Posted December 10, 2015 Report Share Posted December 10, 2015 5 degrees off-I would not sweat it. Mark Link to comment Share on other sites More sharing options...
fgvanatta Posted December 10, 2015 Author Report Share Posted December 10, 2015 I use cones on every shelf for every firing and they have all been @ 90°, so I'm not really concerned about the amount of temperature difference - I was just concerned about the reason for the inaccuracy. (If the controller has a "slight" problem in one area, what might be lurking elsewhere in its innards?) Link to comment Share on other sites More sharing options...
Mark C. Posted December 11, 2015 Report Share Posted December 11, 2015 Does this kiln have S thermocouples or K thermocouples? The s thermocouples are more accurate and longer lasting. I assume it's a zone controlled kiln as well?Neil is really the expert on this stuff maybe he will chine in. Mark Link to comment Share on other sites More sharing options...
fgvanatta Posted December 11, 2015 Author Report Share Posted December 11, 2015 The kiln uses a type K thermocouple; it's not zone controlled. I got a reply from Skutt; they just said the discrepancy is "normal" - no explanation why. Obviously not a situation to worry about, but I prefer to have a better handle on the way things work. Frank Link to comment Share on other sites More sharing options...
bciskepottery Posted December 12, 2015 Report Share Posted December 12, 2015 Is your thermocouple enclosed in a sheath and, if so, does your kiln have an offset programmed for the covered thermocouple? Link to comment Share on other sites More sharing options...
fgvanatta Posted December 14, 2015 Author Report Share Posted December 14, 2015 Everything but the tip is enclosed in a ceramic shield. Current TCOS setting is 15 (Kiln firing 15° cooler). I didn't set this; it's the way the kiln came (slightly used). This doesn't seem to make sense, as the kiln is firing properly - according to the pyrometric cones - @ cone 6 and the reported highest temp, 2236°, is reasonable. To further complicate things, bisque firing @ cone 06 also seems to be at the right temperature according to the pyrometric cones, but the reported highest temp is 1805°, considerably lower than the 1828° shown in the Orton cone chart, even with the offset. I'm tempted to go back to Skutt and get some answers. At the same time, my "if it ain't broke, don't fix it" mantra is kicking in. Methinks the best course of action at this point is to leave well enough alone and keep monitoring via the cones until an actual problem occurs. Link to comment Share on other sites More sharing options...
Dennis Bednarek Posted December 14, 2015 Report Share Posted December 14, 2015 Having worked for years in the electronics field I will say a 5 degree temperature difference is not extreme by any means. Looking at your temperature of 2241 with a 5 degree questionable difference is 0.22% accuracy difference. Many electronic devices start at 10% accuracy and when you increase the accuracy each step more accurate will double the price of the component. Yes you can usually tune a system to be considerably more accurate however movement, and atmospheric changes can require repeated needs to re tune the device. Note the difference between a cone 9 and cone 10 is 45 degrees roughly or 9 times the difference your looking at. A 1% accuracy should be more than enough for your purpose. Link to comment Share on other sites More sharing options...
S. Dean Posted December 15, 2015 Report Share Posted December 15, 2015 Here's the Orton Cone chart. Notice that the temperature attributed to a cone varies according to the rate of temperature climb. https://www.ortonceramic.com/files/2676/File/orton-cone-chart.pdf The chart contains the following explanation: Temperatures shown on the charts were determined under controlled firing conditions in electric kilns and an air atmosphere. Temperatures are shown for specific heating rates. These heating rates are for the last 100°C or 200°F of the firing. Different heating rates will change the equivalent temperature. The temperature will be higher for faster heating rates and lower for slower heating rates. There's also the issue of converting the bend angle to a temperature equivalent. https://www.ortonceramic.com/Resources/Pyrometric_Cones/ In sum, unless your firing rate exactly matches Orton's test conditions, you will see differences in temperature due to heat work. Throw in further variability between the manufacturing of the cones, accuracy of the thermocouple and accuracy in the way you read a bend in the cone, I wouldn't worry about what you are seeing. Link to comment Share on other sites More sharing options...
fgvanatta Posted December 15, 2015 Author Report Share Posted December 15, 2015 I appreciate all the info. As mentioned, the kiln is firing fine according to the cones (my final ramp is 100°/hour, fairly close to the 108° in the cone charts) and the cones on all shelves are bent to 90° after the firing. The real issue is that the controller reports the final temperature as it is firing - 2241°; then, when the firing is over, the same controller reports the highest temperature reached as 2236°. Why is it reporting two different temperatures? Skutt says this is normal. My suspicion is that the temperature reported as the kiln is firing is a direct reading from the thermocouple, while the "highest temperature" value shown after the firing is complete is the controller's attempt to report heat work. In any case, the firings is OK, so the question becomes a simple question of logic. Thank you all again for all the information. Link to comment Share on other sites More sharing options...
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