Appendix B
Measuring Temperature with Resistive Transducers
SCXI-1581 User Manual
B-2
ni.com
The Relationship Between Resistance and Temperature in RTDs
Compared to other temperature-measurement devices, the output of an
RTD is relatively linear with respect to temperature. The temperature
coefficient, called alpha (
α
), differs between RTD curves. Although various
manufacturers specify alpha differently, alpha is most commonly defined as
the change in RTD resistance from 0 to 100 °C, divided by the resistance at
0 °C, divided by 100 °C:
where
R
100
is the resistance of the RTD at 100 °C.
R
0
is the resistance of the RTD at 0 °C.
For example, a 100
Ω
platinum RTD with
α
= 0.003911 has a resistance of
139.11
Ω
at 100 °C.
Figure B-1 displays a typical resistance-temperature curve for a 100
Ω
platinum RTD.
α Ω Ω
⁄
°
C
( )
⁄
(
)
R
100
R
0
–
R
0
100
°
C
×
-----------------------------
=