21
4 Thermocouples
Limit deviations according to DIN EN 60584
If the data has been specified both as the admissible limit deviation in °C and as a function of the tem-
perature, the higher value applies in each case.
Limit deviations according to DIN EN 43710
4.4 Type K thermocouples
A symptom known as green rot may occur on type K thermocouples (NiCr-Ni). It usually occurs between
800 and 1050 °C. If a type K thermocouple is used in environments containing oxygen or water vapor,
the chromium will oxidize but the nickel will not. This results in green rot, which can cause measurement
errors of up to several 100 K.
Over time, this will destroy the thermocouple. In the temperature range from 400 to 600 °C, the positive
leg undergoes a reversible change in structure, amounting to changes of up to 5 K in the output signal.
Thermo-
couple
type
Admissible limit deviations (±°C) Validity limits for temperature (°C)
Class 1 Class 2 Class 3 Class 1 Class 2 Class 3
Type T 0.5 °C or
0.004 × |t|
1°C or
0.0075 × |t|
1°C or
0.015 × |t|
-40 to +350 -40 to +350 -200 to +40
Type E 1.5 °C or
0.004 × |t|
2.5 °C or
0.0075 × |t|
2.5 °C or
0.015 × |t|
-40 to +800 -40 to +900 -200 to +40
Type J 1.5 °C or
0.004 × |t|
2.5 °C or
0.0075 × |t|
- -40 to +750 -40 to +750 -
Type K 1.5 °C or
0.004 × |t|
2.5 °C or
0.0075 × |t|
2.5 °C or
0.015 × |t|
-40 to +1000 -40 to +1200 -200 to +40
Type N 1.5 °C or
0.004 × |t|
2.5 °C or
0.0075 × |t|
2.5 °C or
0.015 × |t|
-40 to +1000 -40 to +1200 -200 to +40
Type R
Type S
t<1100°C:
1°C,
t>1100°C:
(1 + 0.003 ×
[t - 1100])
1.5 °C or
0.0025 × |t|
- 0 to 1600 0 to 1600 -
Type B - 1.5 °C or
0.0025 × |t|
4°C or
0.005 × |t|
- 600 to 1700 600 to 1700
Type C - 0.01 × |t| - - 426 to 2315 -
Type A - 0.01 × |t| - - 1000 to 2500 -
Element Tolerance classes
Fe-CuNi Type L 100 to 400 °C ±0.0075 × |t| ±3 K
400 to 900 °C ±0.0075 × |t| ±3 K
Cu-CuNi Type U 100 to 400 °C ±0.0075 × |t| ±3 K
400 to 600 °C ±0.0015 × |t| ±3 K
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