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The furnace found on a production line may operate in a similar way to the oven in your home but they rely on a much smaller margin of error. While a home oven is typically off by at least 25-50°F, most industrial furnaces, ovens, and kilns need to be much more precise.
While many factors affect the accuracy of a furnace, the component most important to that accuracy is called a thermocouple. It’s important to choose the right one and to understand when it’s failing.
A thermocouple is a tool for temperature measurement, yet it doesn’t measure temperature directly. Instead, two wires made up of different types of metal (using the “thermoelectric effect") inside a metal sheath (often stainless steel, as it best protects the thermocouple) measure the voltage created by those two wires. Without getting too detailed, these two metals will create a temperature differential based on the voltage created. This voltage is converted into temperature by a thermocouple data logger, where it can easily be interpreted by the operator.
To put it simply, thermocouples are the sensors that tell an operator what the temperature of an oven is. Some thermocouples are more accurate than others and some work better than others are different temperature ranges. Picking the right thermocouple is your best defense against a thermocouple error!
With correct use, a thermocouple can last you a few good years. However, if you exceed the thermocouple’s temperature range it could easily burn out and need to be replaced.
Anyone that owns an industrial oven understands that the oven will almost certainly outlast its thermocouples. It's not unusual to replace thermocouples even every year if used at high temperatures. Luckily, replacing a thermocouple is one of the most straightforward repairs one can make to an oven. Industrial ovens, after all, are big investments and are meant to be repaired. An oven, kiln, or furnace that is regularly maintained, correctly repaired, and operated within its parameters should last you close to a decade.
There are many types of thermocouples, all with their own temperature ranges and margins of error. The industry breaks thermocouples down by letter type (K, J, T, E, R, S, B) and are categories by the two metals used.
Type K thermocouples are the industry standard and the most widely used thermocouple on the market.
Slightly less expensive but with less of a lifespan, Type J thermocouples are still popular.
Type T thermocouples are most often used for measuring extremely low temperatures such as industrial freezers.
More accurate in lower-temperature ovens, Type E thermocouples are great for high accuracy in ovens that operate at 537°C or lower.
Type N is the most common “noble metal” thermocouple. Noble metals are great at exceptional accuracy at high temperatures.
Type S and R thermocouples have a wide range that they can take accurate temperatures but, due to their reliable high-temperature readings, they are most commonly used in high-temperature ovens. The differences between the two, other than their Rhodium content, is minimal.
Type B thermocouples are used for high-temperature readings and have the highest temperature threshold of any other type of thermocouple.
