Technical Information

Thermocouples

1. Structure and function mode 2. Thermocouples according to DIN EN 60584 3. Thermoelectric laws 4. Selection of the types of element 5. Limiting deviation for thermocouples 6. Maximum application temperatures of thermocouples 7. Aging of thermocouples 8. Information about temperature measurements with PtRh thermoelectric-elements

Compensation and thermoelectric cables

6. Maximum application temperatures of thermocouples

For the maximum application temperature of a thermocouple apart from the indicated temperature of the wire diameters given in the tables of DIN EN 60584, the surrounding conditions, as well as the sheath material for sheath thermocouples is of crucial importance. In the VDI/VDE 3511 sheet 2 recommendations regarding the selection of the wire diameters as well as for outside diameters and sheath material of sheath thermocouples are given:

ø in mm	0,2	0,35	0,5	0,8	1,0	1,38	1,6	2,0	3,0
CuCuNi Typ T, U	200°C	200°C	200°C	200°C	300°C	300°C	300°C	400°C	400°C
Fe-CuNi Typ J, L	300°C	400°C	400°C	400°C	500°C	600°C	600°C	700°C	700°C
NiCr-Ni Typ K,N	600°C	700°C	700°C	800°C	800°C	900°C	900°C	1000°C	1000°C
PtRh-Pt Typ S, R	---	1300°C	1300°C	---	---	---	---	---	---
PtRh-PtRh Typ B	---	1500°C	1500°C	---	---	---	---	---	---

Tab. 3: Maximum application temperature in °C of thermowires according to DIN 43712

Sheath Material	NiCr-Steel				NiCr-Alloy
ø in mm	≤ 0,5	1,5	3,0	6,0	≤ 0,5	1,5	3,0	6,0
CuCuNi Typ T, U	400°C	400°C	400°C	500°C	400°C	400°C	400°C	500°C
Fe-CuNi Typ J, L	500°C	800°C	800°C	800°C	700°C	900°C	900°C	900°C
NiCr-Ni Typ K,N	500°C	800°C	800°C	800°C	800°C	1000°C	1100°C	1100°C
PtRh-Pt Typ S, R	---	---	---	---	1000°C	1300°C	---	---
PtRh-PtRh Typ B	---	---	---	---	1000°C	1300°C	---	---

Tab. 4: Maximum application temperatures into °C of sheath thermocouples according to DIN 43712

Sheath thermocouples with thermocouple types R, S or B should be used only briefly over 1000 °C, as due to the catalytic effect of platinum in reducing atmospheres, it results in a reduction of the metal oxide (MgO) of the insulation material.

The Platinum enters into a combination with the magnesium and silicon which leads to a change of the thermovoltage.

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