Appendix B
Measuring Temperature with Resistive Transducers
©
National Instruments Corporation
B-3
SCXI-1581 User Manual
Figure B-1.
Resistance-Temperature Curve for a 100
Ω
Platinum RTD,
α
= 0.00385
Although the resistance-temperature curve is relatively linear, accurately
converting measured resistance to temperature requires curve fitting. The
following Callendar-Van Dusen equation is commonly used to approximate
the RTD curve:
where
R
T
is the resistance of the RTD at temperature
T
.
R
0
is the resistance of the RTD at 0 °C.
A
,
B
, and
C
are the Callendar-Van Dusen coefficients shown in
Table B-1.
T
is the temperature in °C.
Most platinum RTD curves follow one of three standardized curves—the
DIN 43760 standard, the U.S. Industrial or American standard, or the
International Temperature Scale (ITS-90) used with wire-wound RTDs.
480
400
320
240
160
80
320 400 480 560 640 720 800 880
0
80 160 240
960
R
T
R
0
1
AT BT
2
C T
100
–
(
)
3
+
+
+
[
]
=