ETAS ES420.1, User Manual, Page: 22 / 100

ETAS Hardware Description
ES420.1 - User’s Guide 22
Example 2
A thermocouple of type K with an internal resistance R
i
of 150  is used to
measure a temperature T
m
of 400 °C (673.15 K; 752 °F) at an ambient tempera -
ture T
a
of 50 °C (122 °F).
 T
g
= ( | T
m
- T
0
| * 0.025 %) + 0.25 K
 T
g
= ( | 673.15 K - 298.15 K | * 0.025 %) + 0.25 K
 T
g
= 0.34 K
 T
d
= 0.005 K/K * | T
a
- T
0
|
 T
d
= 0.005 K/K * | 50 °C - 25 °C |
 T
d
= 0.13 K
 T
i
= 0.004 K/  * R
i
 T
i
= 0.004 K/  * 150 
 T
i
= 0.60 K
 T
cjc
= 1 K
 T
dcjc
= 0.008 K/K * | T
a
- T
0
|
 T
dcjc
= 0.008 K/K * | 50 °C - 25 °C |
 T
dcjc
= 0.20 K
The maximum total inaccuracy is:
 T = 
T
g
+ 
T
d
+ 
T
i
+ 
T
cjc
+ 
T
dcjc
 T = 0.34 K + 0.13 K + 0.60 K + 1 K + 0.20 K
 T = 2.27 K
In this example the maximum total inaccuracy is determined by the inaccuracy
of the cold junction compensation and the part of the inaccuracy that depends
on the internal resistance of the thermocouple.