Mineral-insulated high-temperature thermocouples up to 2300°C

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Mineral-insulated sheathed thermocouples for the high-temperature range are used in industry and research to measure very high temperatures, sometimes under particularly difficult conditions. The selection of the respective thermocouple is significantly influenced by the environmental influences, temperature requirements and mechanical stress. The thermocouple pair (inner wires) and the sheath material of mineral-insulated high-temperature thermocouples are made of high-quality precious metals. With the exception of a few designs, these are generally flexible and can measure temperatures of up to 2300°C, depending on their composition. They offer the usual advantages of high measuring accuracy, short response times and a long service life. An indispensable product with a wide range of applications in industry and research.

Typical application examples

  • Aerospace
  • Petrochemical industry
  • Scientific apparatus engineering
  • Laser and plasma research
  • Medical technology
  • Chemical/thermal reactions
  • Temperature measurement in combustion chambers
  • Gas chromatographs
  • Vacuum chambers and ovens
  • Coating process
  • Analysis technology and research

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 codeTypeInner conductor / thermocouple + / -Application temperature range
ssType SPlatinum-rhodium10% / platinum0 to 1600°C
ssType RPlatinum-rhodium13% / platinum0 to 1600°C
bbType BPlatinum-rhodium30% / platinum-rhodium 6%800 to 1700°C
ddTYPE CTungsten-5%Rhenium / Tungsten-26%Rhenium0 to 2315°C
ccTYPE ATungsten-5%Rhenium / Tungsten-20%Rhenium0 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.

Jacket materialApplication temperature rangeMinimum bending radiusAreas of application
Inconel600 (I)0 to 750°C5x diameterInert and oxidizing atmosphere, vacuum
Platinum (PR)0 to + 1550°C5x diameterInert and oxidizing atmosphere
Tantalum (TA)0 to + 2200°C12x diameterInert atmosphere, vacuum
Molybdenum (MO)0 to + 2000°CRigid versionReducing atmosphere, vacuum, inert atmosphere
Rhenium (RE)0 to + 2200°CRigid versionInert and oxidizing atmosphere
Tungsten (W)*0 to + 2300°C Vacuum, very low outgassing
Molybdenum, 50% rhenium *0 to + 2300°C Inert, hydrogen-containing, nitrogen-containing and ammonia-containing atmosphere, vacuum
*Only on request  
Sheath material Outer diameter in mm
1,0 1,5 1,6 2,0 3,2
Platinum (PR) x x x x x
Tantalum (TA) x x x
Molybdenum (MO) x x
Rhenium (RE) x x
Molybdenum 50% Rhenium (MR) On request

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.

TypeMaterial designationApplication temperature rangeProperties
MgOMagnesium oxide0 to 1600°CVery hygroscopic, common insulation material in sheathed thermocouples. Only limited resistance behavior at high temperatures
AL2O3Aluminum oxide0 to 1550°CVery good application behavior with the use of platinum
HFO2Hafnium oxide0 to 2200°CGood properties at high temperatures, very good alternative to beryllium oxide, non-toxic, but with poor bending properties
BeO*Beryllium oxide0 to 2200°CVery good conductivity in the high-temperature range, very good resistance behavior
*Caution is advised when using berrylium oxide. Beryllium oxide is considered a toxic material. Incorrect or improper handling can lead to health problems

Uninsulated fine wires consist of a positive leg and a negative leg of a thermocouple. They are available in type S, type B, type R, type C and type A thermocouples. The wire thickness of the thermocouples is available in thicknesses of 0.25 mm, 0.35 mm, 0.51 mm and 0.81 mm. The respective legs are wound separately on a roll and can be supplied in individual lengths. The fine wires correspond to the DIN EN 60584 thermocouples.

TypeThermocouple + / -Wire diameter in mm   
Type SPlatinum-rhodium10% / platinumxxxx
Type RPlatinum-rhodium13% / platinumxxxx
Type BPlatinum-rhodium30% / platinum-rhodium 6%xxxx
TYPE CTungsten-5%Rhenium / Tungsten-26%Rheniumxxxx
TYPE ATungsten-5%Rhenium / Tungsten-20%Rheniumxxxx