Programming instructions

Chapter 21 Common SCXI Applications
LabVIEW Data Acquisition Basics Manual 21-6
© National Instruments Corporation
VI Examples
If you use the DAQ Channel Wizard to configure your channels, you
can simplify the programming needed to measure your signal. LabVIEW
configures the hardware with the appropriate input limits and gain, and
performs cold-junction compensation, amplifier offsets, and scaling for
you. To measure a channel using a channel name, you can use the Easy VIs
or the Continuous Transducer VI located in
labview\examples\daq\
solution\transduc.llb
, as shown in Figure 21-1. Enter the name of
your configured channel in the
channels
input. The device input value is
not used by LabVIEW when you use channel names. The acquired data is
in the physical units you specified in the DAQ Channel Wizard.
Figure 21-1.
Continuous Transducer Measurement VI
The remainder of this section describes how to measure temperature with
the SCXI-1100 and SCXI-112x modules using thermocouples when you do
not use the DAQ Channel Wizard. The temperature examples below use
both cold-junction measurements and amplifier offsets. In SCXI analog
input examples, you cannot set the scaling constants with the Easy VIs
(determined by the amplifier offset). With the Intermediate VIs, you can
change the scaling constants before acquisition begins, while the Advanced
VIs include functions that are not necessary to accurately measure
temperature with SCXI modules. The examples described in this section
use Intermediate VIs along with transducer-specific VIs.
First, you should learn how to measure temperature using the SCXI-1100
with thermocouples. You can use the example SCXI-1100 Thermocouple
VI located in
labview\examples\daq\scxi\scxi_ai.llb
. Open the
VI and continue reading this section.
To reduce the noise on the slowly varying signals produced by
thermocouples, you can average the data and then linearize it. For greater
accuracy, you can measure the amplifier offset, which helps scale the data
and lets you eliminate the offset error from your measurement. The