Thermocouple Placement in the Firing Chamber

A thermocouple reads the temperature inside the kiln. It is used on pyrometers and digital controllers. It looks like a ceramic or metal rod protruding into the firing chamber through a kiln wall.

The thermocouple must extend into the firing chamber far enough to pick up an accurate temperature reading. If a shelf bumps against the thermocouple and pushes it out of the firing chamber, a digital kiln may over-fire. This is because the thermocouple will measure the cooler temperature inside the kiln wall rather than inside the firing chamber. The controller will try to compensate by making the kiln fire hotter.

So, every time you load the kiln, be sure the thermocouple extends into the firing chamber by the correct amount. Your instruction manual should include that information. As a rule of thumb, the thermocouple must extend into the firing chamber four times its diameter. Example: a 1/4" wide thermocouple should extend into the firing chamber by 1".

Some thermocouples are housed inside a separate ceramic sheath, which protects the thermocouple from the harsh kiln atmosphere. It is possible for the sheath to extend into the firing chamber by the correct amount, yet the thermocouple may not be pushed far enough into the sheath. In this case, the thermocouple will appear to extend the correct distance into the firing chamber even though it does not. This can cause an over-fire. When you install that type of thermocouple, be sure to push it into the ceramic sheath by the correct amount. That information should be included with the installation instructions.

Copyright 2002, by Paragon Industries, Inc.