Programming instructions

Chapter 3 Basic LabVIEW Data Acquisition Concepts
LabVIEW Data Acquisition Basics Manual 3-14
© National Instruments Corporation
Function and VI Reference Manual
for more information on how to assign
limit settings to a particular analog channel using the Advanced VIs, the
Group Config VI and the Hardware Config VI, or refer to the LabVIEW
Online Reference
, by selecting
Help»Online Reference...
.
In analog applications, you not only specify the range of the signal, you
must also specify the range and the polarity of the device. A
unipolar range
is a range containing either positive or negative values, but never both.
A
bipolar range
is a range that has both positive and negative values.
Whenadevice uses jumpers or dip switches to select its range and polarity,
you must enter the correct jumper setting in the configuration utility.
In DAQ hardware manuals and in the configuration utility, you may find
reference to the concept of
gain
. Gain is the amplification or attenuation
ofa signal. Most National Instruments DAQ devices have programmable
gains (no jumpers), but some SCXI modules require the use of jumpers
ordip switches. For all DAQ devices used with LabVIEW, the gain is
determined by limit settings. However, for some SCXI modules, you must
enter the gain in the configuration utility.
Data Organization for Analog Applications
If you acquire data from more than one channel multiple times, the data is
returned as a two-dimensional (2D) array. If you were to create a 2D array
and label the index selectors on a LabVIEW front panel, the array might
look like Figure3-10.
Figure 3-10.
Example of a Basic 2D Array
The two vertically-arranged boxes on the left are the row and column index
selectors for the array. The top index selects a row and the bottom index
selects a column.
You can organize data for a 2D array in one of two ways. First, you can
organize the data by rows. If the array contained data from analog input
channels, this would mean that each row holds data from one channel.
Selecting a row selects a channel. Selecting a column selects a scan of data.
This ordering method is often referred to as
row major order
. When you
create data in a nested For Loop, the inner loop creates a row for each