Kiln Temperature Controller Project

(Originally Posted December 2000)

These pages document the construction of an automatic temperature controller for a basic glass annealing kiln.  The kiln is a 120 volt model rated at 14 amperes (1680 watts).  The kiln's original controller is a variable "power" type, with an infinitely variable control adjustable between LO and HI.  This type of control is not unlike that on electric stovetops.  There is no temperature sensing by this control.  A separate thermocouple pyrometer is used to provide a visual readout of temperature on a panel meter, and the operator adjusts the power manually to maintain the desired temperature.

This automatic temperature controller project is based on the Fuji PXZ4 controller, but there are other choices available.  The Fuji provides for a manual setpoint temperature at which the kiln is held indefinitely until the ramp/soak program is initiated.  Up to four ramp/soak pairs are provided, with each temperature and time duration independently set.  The design of this project does not require ANY modifications to be made to the kiln.  The kiln is plugged into the controller, and the controller into the wall plug.

Disclaimer:  Although this project is pretty simple electrically, it DOES involve 120 volt household current, which can be lethal.  Common sense can go a long ways to making the project safe.

Here's how the completed project looks:

The kiln plugs into an outlet in the back, half of which is controlled by the Fuji, the other half remains live as an accessory outlet.  The type K thermocouple exits the case on the right.  The red push button on the front panel turns the unit on, while the black button turns it off.  I wired the controller so that its power is obtained by a relay configured such that the relay "latches" on by the red button.  In the event of a power interruption, the relay unlatches and cannot turn itself on when the power returns.  Without this feature, the Fuji would reset with the Kiln in the on condition, and with its temperature at the manual setpoint where it would operate forever until manually shut off.

Bill of Materials       Construction Information       Wiring Diagram 110v /220v       Controller Programming