SINGLE ZONE VS MULTI-ZONE
Many kilns on the market have all elements controlled as one zone. Typically in such designs the elements are graded in power output from top to bottom (to adjust for temperature uniformity due to greater heat losses at the top and bottom). There are two problems with this. First, there is no way to adjust for varying load conditions. Second, as the elements age and change in power output (and they will do that at varying rates because of their different designs) the built in adjustment will change. The only way for you to fix this is to change all the elements at one time - an expensive proposition. In most L&L sectional kilns (Easy-Fire, Jupiter and DaVinci), both manual and automatic, each section is a separate zone controlled by individual contactors or zone switches. Either the automatic control automatically adjusts the zones or, in manual kilns, you can adjust the zones.
What about graded elements?
Graded elements are great when a kiln is brand new. For instance, we have test fired the leading competitor's 7 cubic foot kiln out of the box. Using graded elements it fires about as evenly under real world conditions as an e23T Easy-Fire kiln with zone control. However, elements age and with different elements in the same kiln they will age at different rates. If you have to change one element (ruined by glaze, for instance) and not the whole set of elements, your kiln may not be so even. Zone control dynamically deals with any such changes and maintains its evenness over time and under different loading conditions.
Does Multi-zone control slow down a firing?
Multi-zone control can slow down a firing as the control adjusts the firing. Yes - it is helpful to have more power with zone control. That is why we substantially increased the power in our new Easy-Fire kilns. The fact is that in side-by-side tests the leading competitor's 7 cubic foot kiln and the e23T kiln with the exact same load took almost the same time to fire (actually the L&L was a little faster). In side by side tests with an identical 87 pound load, no vent and fired to cone 7 on Fast (for the other kiln) and Fast Glaze (for the e23T) the other kiln took 6 hours 11 minutes, 58 KWh, and was between a ¼ to a ½ cone from top to bottom. The L&L e23T with 3-zone control took 6 hours, 55 KWh and witness cones were dead even top to bottom.
Note that you can get e23T elements in a JD230 kiln at no extra charge.
Years of Experience
L&L has over 50 years of real life experience with zone control. It works. We have built millions of dollars worth of high-tech multi-zone furnaces to heat treat superconductors, process optical glass and make aerospace parts. Several 200 cubic foot kilns we recently built have 27 zones and are accurate to within plus or minus 2°C. One of our multi-zone furnaces was used to calibrate all the furnaces at Corning Inc. - it was so accurate they had to measure it with chromatic glass, which is far more accurate than any thermocouple available.
MANUAL MULTI-ZONE CONTROL WITH INFINITE ZONE SWITCHES
L&L pioneered multi-zone control for manual kilns over 30 years ago. Each 9" high section of the kiln is controlled by an infinitely variable input switch. These switches allow you to adjust the gradients in the kiln by reducing the amount of energy that flows to hotter sections. Especially when used in conjunction with L&L's Tru-View Pyrometer system you can dynamically (in real time) control gradients to prevent uneven heating. On smaller single phase Jupiter kilns these switches are the complete power control. Because they are limited to 15 amps when use them in conjunction with power contactors for larger kilns that require more power. These infinite switches have an off position.
The alternate way you typically see manual kilns controlled is with simple High-Medium-Low type switches. The High-Medium-Low switches are fine for controlling heating ramp rates but will give you almost no control over the heat gradients in the kiln.
DYNAMIC ZONE CONTROL FOR AUTOMATIC KILNS
The DynaTrol features Dynamic Zone Control. It is like having three controls in one. The DynaTrol separately measures temperatures in the bottom, middle and top of the kiln and automatically adjusts the heat output of three separate heating zones even as the kiln is heating up. Kiln temperatures are automatically evened out to within 1/2 cone or better top to bottom. There is no manual intervention with input switches. There are separate thermocouples (heat sensors) and contactors (power controls) for each of the three zones. You have the ability to adjust the “lag” or differential between zones, (anywhere from 5 degrees to 99 degrees). The finer the control the slower the kiln because the faster zones get slowed down while the slower zones catch up. You may place your load to best advantage without regard to temperature differences. Perfect firings are possible at all times. Minimize refiring. No more tedious and inexact adjustment of manual switches. This is true automation.
Another important control feature is automatic tuning within the DynaTrol to eliminate temperature over-shoot. This is a true industrial type PID control (with Proportional, Integral, and Derivative mathematical calculations). There are adjustable offsets for each thermocouple as well as the ability to match control performance with actual witness cones. All this adds up to the very best automatic control on the market.
[Go to Top]
