Inside of kiln showing quartz support tubes
The inside area of the kiln is 16 inches square. The kiln is insulated with 2-inch thick Type M Board made by Thermal Ceramics Corp., contained by an expanded metal frame.
The quartz halogen bulbs are enclosed in transparent quartz tubes to reduce the exposure of the bulbs to organic burn-off and to cool the bulb ends. Both of these strategies should help lengthen element life. Clear quartz tubes are suspended in the middle of kiln, between the upper and lower elements. This eliminates the need for kiln furniture and reduces he thermal mass of non-fired ware in the kiln to virtually zero.
Control is provided by a Fuji Proportional-Integral-Derivative (PID) controller, with a 4-20 milliamp signal to an Omega phase-angle Silicon Controlled Rectifier (SCR). Patching into the 4-20 milliamp control signal is an Onset “Hobo” data acquisitor. Sampling rate is set at one point per second. Data is transferred to a spreadsheet, where a correlation is made between milliamp output and kiln watt input (unfortunately, SCR input signal to output power is non-linear). Total kiln wattage is from eight-1600 watt 240 volt quartz bulbs, totaling 12,800 watts at 100 percent output. Milliamp control signal is limited to 75 percent control output (95 percent power output) to assure long life for the elements.
On initial checkout, the elements proved to be so responsive that it has been difficult to optimize the PID parameters for steady control. The main control strategy at this point is proportional. Integral and derivative contributions to control are minor.