Programming instructions

Chapter 21 Common SCXI Applications
LabVIEW Data Acquisition Basics Manual 21-14
© National Instruments Corporation
The SCXI-1121 and the SCXI-1122 modules are commonly used with
strain gauges because they include voltage or current excitation and internal
Wheatstone bridge completion circuits. You can also use the signal
conditioning device SC-2043SG as an alternative to SCXI modules. The
device is designed specifically for strain gauge measurements. For more
information on this device, refer to your National Instruments catalog.
You can set up your SCXI module to amplify strain gauge signals or filter
noise from signals. In order to set up the excitation level, gain, and filter
settings, consult your
Getting Started with SCXI
manual for the necessary
hardware configuration and Chapter 2,
Installing and Configuring Your
Data Acquisition Hardware
, for software configuration.
To build a strain gauge application in LabVIEW, you can use the Easy I/O
analog input VIs. If you are measuring multiple transducers on several
different channels, you need to scan the necessary channels as quickly as
possible. Because the Easy I/O VIs reconfigure your SCXI module every
time the VI is called, you should use the Intermediate analog input VIs as
well as the Strain Gauge Conversion VI, as shown in the following
example. The Convert Strain Gauge Reading VI, located in
Functions»DAQ»DAQ Utilities
, converts the voltage read by the strain
gauge to units of strain.
Using the DAQ Channel Wizard to configure your channels simplifies the
programming required to measure your signal, as shown in Figure 21-8.
LabVIEW configures the hardware with the appropriate input limits and
gain, measures the strain gauge, and scales the measurement for you. Enter
the name of your configured channel in the
channels
input. You do not
need to wire the
device
or
input limits
input. The acquired data is in the
physical units you specified in the DAQ Channel Wizard.