National Instruments Module SCXI-1125, Руководство пользователя

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Chapter 5 Using the SCXI-1125
SCXI-1125 User Manual 5-26 ni.com
The last parameter, channels , is the list of channels that are scanned for
module z . It can have several formats:
•
ob
x
! sc
y
! md
z
!
n , where n is a single input channel.
•
ob
x
! sc
y
! md
z
!
n1:n2 , where n1 and n2 represent a sequential
list of input channels, inclusive.
•
ob
x
! sc
y
! md
z
! cjtemp
, where
cjtemp
is the CJC channel.
You can scan this channel with other analog input channels. For
compatibility reasons, you can use
mtemp
in place of
cjtemp
.
•
ob
x
! sc
y
! md
z
!
(n1, n2, n3:n4, n1, n5, n2) , where n1 , n2 , and
n5 represent single channels, not necessarily sequential, and n3 and n4
represent the endpoints of a sequential list of channels, inclusive . In
this case, channels n1 and n2 have explicitly been repeated in the
channel list. This random scanning format is not supported on all SCXI
modules.
•
ob
x
! sc
y
! md
z
! calgnd
n1:n2 where n1 and n2 represent a list of
autozeroed channels, inclusive. In this case autozero channels cannot
be scanned with input channels or the cold-junction channel, but must
be scanned separately. This feature is useful for measuring offsets that
appear due to temperature drifts in the analog circuitry. You can
subtract these offsets from subsequent input readings to correct for
temperature drift. Refer to Appendix A,
Specifications , for
determining how temperature drift can affect your measurement
accuracy.
Note Repeating channels or having channels out of sequence in a scan list is not supported
on all SCXI modules. Please refer to the manual of each module for information on this
feature.
LabVIEW and the Virtual Channel String
For LabVIEW, Measurement Studio, and Visual Basic, the channel string
can also contain virtual channels. For the SCXI-1125, these virtual
channels are analog input channels you create that have custom names
(
called tags in Measurement Studio), that perform scaling, linearization,
autozeroing, and CJC transparently without additional code. Virtual
channels are useful when sensors requiring different scaling factors are
used on the same SCXI-1125 channel. Using virtual channels, sensors
needing special scaling can be used in a generic analog input application
without performing hard-coded scaling or linearization. If the scaling
changes or you want to connect a different sensor to the SCXI-1125, no
changes are needed in the application. All that is required is creating a
different virtual channel and using its name in the channel string.