Not Just Hot Air: Understanding Thermocouples in Your Kiln

For centuries, ceramic kilns have been the fiery hearts of the studio. But behind the scenes, a tiny but mighty device ensures your ceramics reach their full potential: the thermocouple. In this article, we dive into the world of ceramic kiln thermocouples, exploring the different types available, their respective applications, and why you should consider using certain types over others.

For a kiln firing to go smoothly, your kiln controller depends on getting the right temperature information from your kiln. That’s where thermocouples come in. Before getting into the specific types of thermocouples used in ceramic kilns, let’s first understand what a thermocouple is and how it functions. Simply put, a thermocouple is a sensor used to measure temperature in the kiln. They are made of two different wires that are joined at one end called the junction. When the junction gets heated, the two metals react differently, producing a small electrical voltage. This phenomenon is referred to as the Seebeck Effect. The other end of the thermocouple wires connects to a reference point. By measuring the voltage produced, the sensor can figure out the temperature difference between the hot and cold ends. This lets the thermocouple calculate the hot end’s temperature, usually within 1° or 2° Celsius of the actual temperature.

These simple, affordable, and dependable sensors can handle a wide range of temperatures. From kilns and ovens to home thermostats, cars, airplanes, and countless industrial and scientific applications, thermocouples are the go-to for reliable temperature measurement. 

Not all thermocouples are created equal. Here are the three main types you’ll encounter in the world of ceramics:

The Workhorse: Type K Thermocouples

Type K thermocouples are the most commonly used thermocouples in ceramic kilns. They are composed of chromel (an alloy of nickel and chromium) and alumel (an alloy of nickel, aluminum, and silicon) wires.  Temperature range is noted by manufacturers as -270 °C to 1,260°C.  Our Review:  Type K are the most widely used thermocouples found in US built kilns.  We don’t recommend them as we often find these to be not very accurate at the higher temperatures.  In our experience, they tend to spit and break down quickly.

The Perfectionist: Type S Thermocouples

For those who demand the ultimate accuracy, Type S thermocouples are often used in high-temperature applications.  Made with platinum and rhodium wires, Type S thermocouples offer a narrower temperature range (0°C to 1,480°C) compared to Type K thermocouples but provide superior accuracy and long-term stability.   Our Review:  CMW highly recommends them.  We use them in all of our kilns and we’ve never had one go bad as they are designed for years of use.  Although they are more expensive than Type K, we think they are worth the investment.  

The High-Heat Specialist: Type R Thermocouples

Similar to Type S in accuracy and built to withstand even higher temperatures (0°C to 1,480°C, Type R thermocouples are also composed of platinum and rhodium wires but have a higher percentage of rhodium.   They are commonly used in applications where the temperature exceeds the capabilities of Type K or S thermocouples, such as certain types of high-temperature ceramics and refractories.  Our Review:  Very accurate.  We typically use Type S, as it works with our firing temperatures, but when we’ve tried them, they’ve been within 0.01°C of a perfect Cone 6.

Finding the Perfect Match for Your Firing Needs

There are other specialty thermocouples available, but for most ceramic artists, Type K, S or R, will be what you’ll come across most often. For example, Type N thermocouples, made of Nicrosil (a nickel-chromium-silicon alloy) and Nisil (a nickel-silicon alloy), measure temperature ranges similar to Type K thermocouples but with improved accuracy and stability, making them suitable for certain high-temperature ceramic processes.

To sum up, ceramic kiln thermocouples are essential components that ensure precise temperature control during the firing process, ultimately influencing the quality and properties of the finished ceramics. By understanding the different types of thermocouples available and how to best use them, kiln operators and ceramic artists can make informed decisions to optimize their firing processes and achieve the best results possible. Whether it’s the common Type K thermocouple or the precision of Type S and Type R thermocouples, the right choice of thermocouple can be a game changer.

If you are interested, the For Flux Sake team discusses this topic in Episode 41.  Check it out here or on our Community Resources.

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