There are a number of different types of thermocouple to choose from in the high temperature range in accordance with DIN EN 60584. The temperature range and the limiting deviation, among other things, are of decisive importance when selecting the type.

Color code	Type	Inner conductor / thermocouple + / -	Application temperature range
	Type S	Platinum-rhodium10% / platinum	0 to 1600°C
	Type R	Platinum-rhodium13% / platinum	0 to 1600°C
	Type B	Platinum-rhodium30% / platinum-rhodium 6%	800 to 1700°C
	TYPE C	Tungsten-5%Rhenium / Tungsten-26%Rhenium	0 to 2315°C
	TYPE A	Tungsten-5%Rhenium / Tungsten-20%Rhenium	0 to 2300°C

The choice of sheath material for sheathed thermocouples is of central importance as it protects the measuring point and the thermocouple from external influences. Extreme temperatures and a high level of interaction between the sheath material, temperature, atmosphere and area of application prevail in the high temperature range.

Particularly for type A and type C high-temperature thermocouples in inert, reducing or oxidizing atmospheres, specific sheath materials are required for the respective application. The correct design increases the resistance and therefore also the service life of the thermocouple.

When selecting the right sheath material for thermocouples for the high temperature range, it should be noted that some sheath materials are flexible and bendable in their design, while others can only be used in a rigid design. We would be happy to help you develop a solution for your application.

High-temperature thermocouples also differ from conventional thermocouples in the choice of insulator, i.e. the insulation material. Usually, magnesium oxide is used as insulation between the thermocouple and the sheath of the thermocouple for thermocouples up to 1300°C. However, both magnesium oxide and aluminum oxide show a decreasing insulation resistance with increasing temperatures. However, magnesium oxide as well as aluminum oxide show a decreasing insulation resistance and a reduced ductility at increasing temperatures. For high temperature thermocouples type A and type C, hafnium oxide and beryllium oxide are often used as insulation material up to temperatures of 2500°C.

Hafnium oxide as insulation material in high-temperature thermocouples tends to be rather coarse-grained. Its ductility is lower than that of beryllium oxide, which is why the material is often used for high-temperature thermocouples in rigid designs. Beryllium oxide as an insulator in high-temperature thermocouples, on the other hand, is very suitable for flexible designs.