©
National Instruments Corporation
9
SCC-TC Series Thermocouple Input Modules User Guide
Cold-Junction Sensor
The cold-junction sensor voltage output varies from 1.91 to 0.58 V over a
0 to 55
°
C temperature range.
Note
NI-DAQ includes thermistor conversion utilities that implement the equations listed
below. Refer to your software documentation for more information on these utilities.
You can use the following formulas to convert the cold-junction sensor
voltage to cold-junction temperature:
where
T
K
is the temperature in kelvin.
where
a
= 1.295361
×
10
–3
b
= 2.343159
×
10
–4
c
= 1.018703
×
10
–7
R
T
is the resistance of the thermistor in ohms.
where
V
TEMPOUT
is the output voltage of the cold-junction sensor.
where
T
(
°
F) and
T
(
°
C) are the temperature readings in degrees Fahrenheit
and Celsius, respectively.
Note
V
TEMPOUT
varies from 1.91 V (at 0 °C) to 0.58 V (at 55 °C). For best resolution, use
the maximum gain for this range on the analog input channel.
For the cold-junction sensor measurement accuracy, refer to the
section.
For more information about how to configure the SCC-TC using
NI-DAQmx, refer to the
SCC Quick Start Guide
.
T
°
C
( )
T
K
273.15
–
=
T
K
1
a b
R
ln
T
(
)
c
R
ln
T
(
)
3
+
+
[
]
--------------------------------------------------------------
=
R
T
5 000
V
TEMPOUT
2.5
V
TEMPOUT
–
--------------------------------------
,
=
T
°
F
( )
T
°
C
( ) ]
9
[
5
------------------------
32
+
=
