As previously mentioned, Thermocouples comes in a wide range of calibrations. Among these calibrations Type K is the most popular choice for high temperature measurement. But does this mean it’s the best option for you? Today we look at what you should consider before purchasing your Type K Thermocouple.
This should always be your first step when purchasing a temperature device. A type K thermocouple is suitable for temperatures up to 1350°C. Although, you should always keep in mind measuring higher temperatures for long periods of time causes a Type K to drift in accuracy.
If you require an accurate temperature measurement under 100°C a RTD would be better suited. The RTD PT100 is the temperature measurement device of choice within Home brewer circles for this reason.
Suitability to the conditions
Type K Thermocouples operate well in oxidizing atmospheres. If, however, a mostly reducing atmosphere (such as hydrogen with a small amount of oxygen) comes into contact with the wires, the chromium in the chromel alloy oxidizes. This reduces the emf output and the thermocouple reads low. This phenomenon is known as green rot, due to the colour of the affected alloy. Although not always distinctively green, the chromel wire will develop a mottled silvery skin and become magnetic. An easy way to check for this problem is to see if the two wires are magnetic. (Normally, chromel is non-magnetic.)
Type K thermocouples are also vulnerable to sulphur attack and in turn should never be used in atmospheres that contain sulphur.
Type K Drift
Type K thermocouples are known to drift when exposed to high temperatures (+500°C) for prolonged periods of time. This drift can be up to 3°C but at higher temperatures (1000°C) This can increase up to 5°C out. If accuracy over a prolonged period of time is important other options available to you.
Although, Type K is the most common general purpose thermocouple and is relatively inexpensive. It is important to look at your application and find what it the perfect solution for you project.
Our sales team have over 20 years’ experience assisting clients with their temperature measurement solutions, and will be happy to help you find the perfect thermocouple for your application.