Temperature measurement with sheathed thermocouples

The measurement of temperature is a very important element in many areas of research and industry. Using thermocouples is a well-known and proven method in temperature measurement.

Accurate and fast measurements, easy fitting, simple utilisation and interchangeability as well as low-cost production are the reasons for the widespread use of the thermocouples.
They are resistant to heat and pressure and relatively insensitive to parasites.

Specific technical requirements like within nuclear reactors, in space- research or in medical fields led to the development of sheathed thermocouples that are small in size with high insulation resistance and high resistance to corrosive media.
All this is being fulfilled by miniature sheated thermocouples.

Construction of the THERMOCOAX thermocouple

THERMOCOAX manufactures a wide range of thermocouples with many advantages in a large number of applications.
Most of the THERMOCOAX thermcouples manufactured are a combination of conductors, insulation and metal protective sheath.

Thanks to the highly compact insulating powder and the excellent metallographic state of the conductors and the sheath, the THERMOCOAX thermocouples are very flexible and may be bent to a radius equal to three times the outer diameter without causing any damage.
With certain precautions, this can even be reduced.

THERMOCOAX Mineral Insulated Thermocouples

An important criteria for the quality of sheated thermocouples is the insulation resistance.
Due to the small size of M.I thermocouples, very little space remains for the insulating conductor between conductor and between conductors and sheath.

Thermocouple Products

Thermocoax provides the following thermocouple products:

-200ºC ~ 1200ºC, these thermocouples use no precious metals
- Type K, Alumel®, temperature range: -200ºC ~ 1200ºC, accuracy: 41μV/℃, most commonly used.
- Type J, Iron-Constantan®, temperature range: -40ºC ~ 750ºC, accuracy: 55μV/℃
- Type E, Chromel®-Constantan, temperature range: -200ºC ~ 950ºC, accuracy: 68μV/℃, non-magnetic
- Type N, Nicrosil®-Nisil®, temperature range:  temperature up to 1200ºC in normal atmosphere, up to 1300ºC in vacuum or controlled atmosphere, accuracy: 39μV/℃ at 900ºC, stability better than platinum-based thermocouples.
- Type T, Copper-Constantan®, temperature range: -200ºC ~ 350ºC, not to be widely used any more.

0ºC ~ 1600ºC, platinum/rhodium thermocouple
- Type S, Platinum 10% Rhodium-Platinum, often seen in oxidizing atmosphere, temperature up to 1600ºC, accuracy: 6-12μV/℃.
- Type R, Platinum 13% Rhodium-Platinum, similar to Type S, accuracy: 6-14μV/℃.
- Type B, Platinum 30% Rhodium-Platinum 6% Rhodium, temperatures up to 1700ºC, very high stability but low accuracy, especially in low temperatures. Type B thermocouple has been a basis for high temperature measurement despite its high cost and low thermoelectric power.
0ºC ~ 2300ºC, Tungsten/Rhenium thermocouple
- Type C, Tungsten-Rhenium 5%Re- Tungsten-Rhenium 26%Re, for extremely high temperature measurement up to 2300ºC, in reducing and neutralizing atmosphere. The alloy has a very high melting point, very low vapor pressure, but has no ductility. Soft thermocouple can measure temperatures up to 1800ºC.  

Heating Elements

Types Ends Codes Diameters in mm
0.5 1.0 1.5 2.0 2.5 3.0 4.0
Single Core With cold ends Standard SEI      
Standard SEA        
On request ZEZ  
On request ZUZ    
Withou cold end 1 Nc
1 Hc  
With true cold ends TET or TUT      
With median swaging        
Self-regulated 1 N (nickel)      
1 Ba (Balco)          
With coiled core NWN, NWNN, NWBaN            
Twin Core Without cold end 2 NcNc
2 NN    
2 BaBa        
With cold ends 2 ZE