Programming instructions

Chapter 6 One-Stop Single-Point Acquisition
© National Instruments Corporation 6-3 LabVIEW Data Acquisition Basics Manual
Multiple-Channel Single-Point Analog Input
With a multiple-channel, single-point read (or scan), LabVIEW returns the
value on several channels at once. Use this type of operation when you have
multiple transducers to monitor and you want to retrieve data from each
transducer at the same time. Your DAQ device executes a scan across each
of the specified channels and returns the values when finished. Refer to
Appendix B,
Hardware Capabilities
, in the
LabVIEW Function and VI
Reference Manual
, for the number of channels your device can scan at one
time. You also can refer to the LabVIEW
Online Reference
, available by
selecting
Help»Online Reference…
.
The Easy I/O VI, AI Sample Channels, acquires single values from
multiple channels. The AI Sample Channels VI performs a single A/D
conversion on the specified channels and returns the scaled values in a
1-dimensional (1D) array. The expected range for all the signals, specified
by
high limit
and
low limit
inputs, applies to all the channels. Figure 6-3
shows how to acquire a signal from multiple channels with this VI.
Note
Remember to use commas to delimit individual channels in the channel string,
or use a colon to indicate an inclusive list of channels.
Figure 6-3.
Acquiring a Voltage from Multiple Channels with the AI Sample Channels VI
You can benefit from using the Easy Analog Input VIs because you only
need one icon in your diagram to perform the task, there are only a few
basic inputs to the VIs, and the VIs have built-in error checking; however,
the lack of programming flexibility with these VIs can be a limitation.
Because Easy VIs have only a few inputs, you cannot implement some of
the more detailed features of DAQ devices, such as triggering or interval
scanning. In addition, these VIs always reconfigure at start-up. When you
need a hi-speed or efficiently-run program, these configurations can slow
down processing time. When you need speed and more efficiency, use
the Intermediate VIs, which configure an acquisition only once and then
continually acquire data without ever re-configuring. The Intermediate VIs