Programming instructions

Chapter 21 Common SCXI Applications
LabVIEW Data Acquisition Basics Manual 21-4
© National Instruments Corporation
If you want to read the cold-junction temperature sensor in
dtemp
mode,
you can read the following onboard channels for these modules.
For example, you can run the Getting Started Analog Input VI, found in
labview\examples\daq\run_me.llb
, with the channel string
ob0!sc1!md1!mtemp
to read the temperature sensor on the terminal block
that is connected to the module in slot 1 of SCXI chassis 1.
SCXI terminal blocks have two different kinds of sensors: an Integrated
Circuit (IC) sensor or a thermistor. For terminal blocks that have IC sensors,
such as the SCXI-1300 and the SCXI-1320, you can multiply the voltage
read from the IC sensor by 100 to get the ambient temperature in degrees
Centigrade at the terminal block. For terminal blocks that have thermistors,
such as the SCXI-1303, SCXI-1322, SCXI-1327, and SCXI-1328, use the
Thermistor Conversion VI from
Functions»Data Acquisition»Signal
Conditioning
to convert the raw voltage data into units of temperature.
You cannot sample other SCXI channels from the same module while you
are sampling the
mtemp
sensor. However, if you are in parallel mode, you
can sample the
dtemp
sensor along with other channels on the same
module at the same time because you are not performing any multiplexing
on the SCXI module. You also can sample the
cjtemp
sensor along with
other channels on the SCXI-1102, but
cjtemp
must be the first channel in
the channel list.
For greater accuracy, take several readings from the temperature sensor and
average those readings to yield one value. If you do not want to average
several readings, take a single reading using the Easy Analog Input VI, AI
Sample Channel.
For more information, look at the SCXI Thermocouple example VIs, found
in
labview\examples\daq\scxi\scxi_ai.llb
. These VIs use the
mtemp
string to read the temperature sensor and use the reading for
thermocouple cold junction compensation.
Modules Channel
SCXI-1100 1
SCXI-1120/SCXI-1120 15 (use referenced single-ended mode)
SCXI-1121 4
SCXI-1122 1