Chapter 5 Using the SCXI-1125
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National Instruments Corporation
5-25
support virtual channels using Data Neighborhood (DAQ Channel Wizard)
in MAX. In LabWindows/CVI, C, or C++ development environments,
several NI-DAQ function calls need to be made to set up each module
involved in the scan, the chassis, and the E Series DAQ device controlling
the scan. In Measurement Studio, SCXI channels must be configured as
virtual channels (tags) in MAX.
A discussion describing how to implement multiplexed scanning in the
different ADEs follows. Refer to your ADE manual and the DAQ analog
input examples that come with your application software for more detailed
information on programming the SCXI modules for scanning in
multiplexed mode.
LabVIEW and the SCXI Channel String
For LabVIEW, and Visual Basic, the channel string determines the
sequence in which SCXI channels are scanned. In LabVIEW, an array of
these channel strings configures multiple modules in the scan list. When the
application program runs, the channel string is used for programming the
channel information into the SCXI system. The format of the channel string
is as follows:
ob
x
! sc
y
! md
z
!
channels
where
•
ob
x
is the onboard E Series DAQ device channel, with
x
representing
a particular channel where the multiplexed channels are sent. This
value is 0 for DAQ channel 0 in a single-chassis system. In a
multichassis or remote chassis system, however, the E Series DAQ
device channel
x
corresponds to chassis number
n
–1, where DAQ
device channel x is used for scanning the nth chassis in the system.
•
sc
y
is the SCXI chassis ID, where
y
is the number you chose when
configuring your chassis.
•
md
z
is the slot position where the module is located, with
z
being the
particular slot number. The slots in a chassis are numbered from left to
right, starting with 1.
Note
The
ob
x
!
specifier is optional and causes the gains on the module and E Series
DAQ device to be automatically set to fit the input limits parameter. When this specifier is
omitted, the default gain on the E Series DAQ device, usually the lowest gain, is used, but
the SCXI-1125 gain is adjusted to fit the input limits.
