National Instruments SCXI-1125 LabVIEW and the Virtual Channel String

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

! sc

! md

! n, where n is a single input channel.

•ob

! sc

! md

! n1:n2, where n1 and n2 represent a sequential

list of input channels, inclusive.

•ob

! sc

! md

! 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

! sc

! md

! (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

! scy ! mdz ! 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.