KNOWLEDGEBASE

The center of my kiln gets too hot compared to the top and bottom.

Assuming that the loading is even and the TC offsets are set equally, uneven temps in the kiln can be a simple programmable setting issue: L&L Kilns with the DynaTrol 12-key controller made from 1/06 until 9/08(?) have their PID setting set to 100 rather than the factory setting of 65. This is not a really big deal but it can add to an existing problem. When the kilns were fired before the PID setting existed, the center zone of the kiln only had to be on 30% to 40% of the time to keep up with the top zone and bottom zone- when the top and bottom zones were at 100%. In order to get the kiln to heat more quickly at the upper temps, the PID setting was added. It allows you to set the middle zone to come on at a set percentage- higher than 30%- 40% just to add more heat to the load when the bottom and top fire at 100%. With the PID set to 100, the middle stays on 100% when the bottom and top stay on 100%. Because there is no top or bottom slab in the middle zone to suck away heat, the middle gets hotter and hotter and sometimes even results in an E-d/ Errd. As the elements age this setting will come on sooner and sooner because the elements are more and more tired and are working at 100% sooner and sooner. Loading heavily in the bottom or using shorter posts between shelves in the bottom will make the PID come on sooner as well. The sooner PID comes on, the more time it has to make the kiln fire more and more unevenly, until it is enough for the operator to notice. Initially from 4/03 to about 4/04 or so the factory setting for PID was 85 (%). Around 4/04 it was lowered to 65 where it has stayed except for the controllers made between 1/06 and 9/08. 1/06 was the beginning of the 700 series boards and for some reason all these came with PID set to 100. Bartlett pre-sets a lot of settings in our DynaTrols and this is not checked when the kilns are made. (It is checked now until they start to come with the PID set to 65 again). PID setting is easy to find. When the kiln says IDLE, press OTHER/ 4/ 4/ 3/ then press OTHER again and again until it reads PID. Press ENTER and see the setting. Ones made after 1/06 will just read a number like 100 or 65. Ones made before 1/06 will read a number flashing back and forth with 'PCt' meaning 'percent'. With either, set it to 65- or as low as 40 if they still complain the center is too hot.