The advantages of thermocouples like self powered, simple, inexpensive and useful for wide temperature ranges often times overcome the disadvantages like non-linear, least sensitive and least stable.
High temperature thermocouples are defined as sensors used at temperatures of 2000˚F and beyond. These sensors are generally made from noble metals or refratory ceramics (Molybdenum, Tantalum, Alumina, Circonia or Quartz).This type of thermocouples can measure temperatures up to 5000˚F and are used in high temperture furnaces, rocket engines and amunitions. Thermocouples made out of noble materials are expensive. It may make sense to use instead non-contact temperature measuring methods like infrared sensors. (also called Pyrometer, Spectralmeter)
Thermocouples must be selected to meet application conditions. Selection considerations are:
- Temperature (select type J, K, M, T or other)
- Response time (larger diameter reduce response time)
- Service life (larger diameter increases service life)
There are hugely different styles of thermocouples available for different industries like plastic, pharmaceutical, food. For example: the plastic industry prefers cost effective thermocouples without MgO, spring adjustable and bayonet cap style for quick install. Other industries do like thermocouple assemblies consisting of thermo-elements swaged in hard packed Magnesium Oxide (MgO) encased in an annealed metal sheath so they can be formed and bent into a radius twice the size of its outer sheath.