Appendix B
Measuring Temperature with Resistive Transducers
SCXI-1581 User Manual
B-4
ni.com
For temperatures above 0 °C, coefficient
C
equals 0, reducing this equation
to a quadratic. If you pass a known current,
I
EX
, through the RTD and
measure the output voltage developed across the RTD,
V
0
, you can solve
for
T
as follows:
where
V
0
is the measured RTD voltage.
I
EX
is the excitation current.
You can create a virtual channel to convert RTD voltages into temperature
readings. To create an RTD virtual channel, refer to either the
Creating an
RTD Virtual Channel Using Traditional NI-DAQ
section or the
Creating
an RTD Virtual Channel Using NI-DAQmx
section, depending on the
version of NI-DAQ you are using.
Creating an RTD Virtual Channel Using Traditional
NI-DAQ
To create an RTD virtual channel using traditional NI-DAQ, complete the
following steps:
1.
Launch MAX.
2.
Right-click
Data Neighborhood
and select
Create New
.
3.
Select
Traditional NI-DAQ Virtual Channel
and click
Finish
.
4.
Select
Analog Input
from the drop-down listbox and click
Next
.
Table B-1.
Callendar-Van Dusen Coefficients
Standard
Temperature
Coefficient
α
A
B
C
DIN 43760
0.003850
3.9080
×
10
–3
–5.8019
×
10
–7
–4.2735
×
10
–12
American
0.003911
3.9692
×
10
–3
–5.8495
×
10
–7
–4.2325
×
10
–12
ITS-90
0.003926
3.9848
×
10
–3
–5.870
×
10
–7
–4.0000
×
10
–12
T
R
0
V
0
I
EX
-------
–
–0.5
R
0
A
R
0
2
A
2
4
R
0
B R
0
V
0
I
EX
-------
–
–
+
------------------------------------------------------------------------------------------------
=