Programming instructions

Chapter 3 Basic LabVIEW Data Acquisition Concepts
LabVIEW Data Acquisition Basics Manual 3-12
© National Instruments Corporation
Note
Refer to Appendix B, Hardware Capabilities, in the LabVIEW Function and VI
Reference Manual for the number of channels your device can acquire data from
at one time, or refer to the LabVIEW Online Reference, by selecting Help»Online
Reference....
Limit Settings
Limit settings
are the maximum and minimum values of the analog
signal(s) you are measuring or generating. The pair of limit setting values
can be unique for each analog input or output channel. For analog input
applications, the limit setting values must be within the range for the
device. For more information on the range for your device, refer to
Chapter 5,
Things You Should Know about Analog Input
.
Each pair of limit setting values forms a cluster. (Analog output limits have
a third member, the reference source; but, for simplicity, LabVIEW refers
to limit settings as a pair of values.) LabVIEW uses an array of these
clusters to assign limits to the channels in your
channel
string array.
If you use the DAQ Channel Wizard to configure your analog input
channels, the unit applied to the limit settings is the physical unit you
specified for a particular channel name in the DAQ Channel Wizard. For
example, if you configured a channel in the DAQ Channel Wizard to have
physical units of
Deg C
, the limit settings are treated as limits in degrees
Celsius. LabVIEW configures your hardware to make the measurement in
terms of your channel name configuration. Unless you need to overwrite
your channel name configuration, do not wire this input; allow LabVIEW
to set it up for you.
If you are not using the DAQ Channel Wizard, the default unit applied to
the limit settings is usually volts, although the unit applied to the limit
settings may be volts, current, resistance, or frequency, depending on the
capability and configuration of your device.
The default range of the device, set in the configuration utility or by
LabVIEW according to the channel name configuration in the DAQ
Channel Wizard, is used whenever you leave the limit settings terminal
unwired or you enter
0
for your upper and lower limits.
As the previous
Channel, Port, and Counter Addressing
section explains,
LabVIEW uses an array of strings to specify which channels belong to a
group. Also, remember LabVIEW lists as few as one channel to as many as
all of the device’s channels in a single array element in the
channel
string
array. LabVIEW also assigns all the channels listed in a
channel
string