So what is a Thermocouple ?
Thermocouples exist in most modern kilns of today and serve as temperature sensors during firings. Thermocouples are found on the inside of the kiln and extend out from the kiln walls, into the interior space of the kiln, where they detect temperature changes. There are two general types of thermocouples used in ceramics: Type-K thermocouples and Type-S thermocouples.
Type-K thermocouples are the most commonly used thermocouples. They are relatively inexpensive, strong and durable. These thermocouples typically last a long time, and do not need to be replaced very often. Type-K thermocouples function over a temperature range of -300F to 2450F. A Type K thermocouple is made up of two dissimilar metals: alumel and chromel. Alumel is an alloy consisting of approximately 95% nickel, 2% manganese, 2% aluminum and 1% silicon. Chromel is made up of 90% nickel and 10% chromium. Where the two metals meet they are welded together to form the tip which is where the heat is sensed. When heated, the two alloys produce a voltage proportional to a temperature difference, between either ends of the metal conductors. Essentially these two metals heat at different rates, and by comparing that difference, a true temperature is defined. The chromel metal is referred to as positive and designated with a yellow + symbol, the alumel metal is negative and marked with a red - symbol. Keeping this polarity connected correctly through the thermocouple wire and to the kiln controller is critical. A reversed thermocouple can appear to read backwards, which means your temperature indicator will go down, and/or, it may simply read as an error.
Type-S thermocouples are quite rare and are only used in a small number of kiln models. Kilns that require S-type thermocouples are typically used in crystalline glaze firings, which require high temperatures and longer hold times. These thermocouples can withstand these firing conditions more readily than Type-K thermocouples. Types S thermocouples are considerably more expensive because they use platinum and rhodium metals. There life is 10 to 20 times longer than Type-K thermocouples, depending on usage.
It is important to recognize when your thermocouple needs to be replaced to avoid inaccuracy in temperature readings. As thermocouples age, their accuracy declines and so often temperature readings will be off. If this is the case, it is time to change your thermocouple. You accurately test the temperature of your kiln during firings by using self-supporting, or “witness” cones.
Purchasing a thermocouple is not as difficult as it may seem. Many thermocouples are interchangeable among kilns. However, it is important to know the length and diameter of the thermocouple you need. the length is determined by the thickness of a kiln’s wall, and the diameter is the insertion point of the thermocouple in your kiln. Often you will find thermocouples protected in a porcelain sleeve like on Skutt kilns or in a tube, as in the case of L&L kilns. Thermocouples can come braided, as with the thermocouples for Amaco front loaders, and Olympic and Paragon kilns sometimes use a metal sheath over the thermocouple.
We carry thermocouples for all kiln models that we sell. They are available with and without thermocouple mounting blocks. Please click on the thermocouple product listings in this department or contact us for more information.
