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Valid SCXI Channel String Arrays under LabVIEW

Primary Software: Driver Software>>NI-DAQ
Primary Software Version: 7.2
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: SCXI

Problem:
I'm getting errors from my SCXI channel string array in LabVIEW 6.x or below. Can you give examples of good and bad channel strings, and explain why I get these errors?

Solution:
For LabVIEW, Measure, 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. In LabVIEW 6.0 and higher, the same format applies to the DAQ Channel Name control or to the array of DAQ Channel Name controls. (Tip: With the Wiring Tool, you can right-click on the channel input of the DAQ VI and choose Create Control to bring up the appropriate control.)

Note: If you are using NI-DAQmx with LabVIEW 7, please refer to the KnowlegeBase listed below in the Related Links section since SCXI channel strings have changed significantly with this new software. The remainder of the text found below in this article is in reference to NI-DAQ and LabVIEW versions prior to version 7.

The format of the channel string is as follows:

obx ! scy ! mdz ! channels

obx is the onboard 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 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.

scy is the SCXI chassis ID, where y is the number you chose when configuring your chassis.

mdz 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 obx ! specifier is optional and causes the gains on the module and DAQ device to be automatically set to fit the input limits parameter. When this specifier is omitted, the default gain on the DAQ device, usually the lowest gain, is used. In the case where the gain on the SCXI module is set programatically, the most appropriate gain on the module will be set.

channels is the list of channels that are scanned for module z. It can have several formats:

obx ! scy ! mdz ! n

where n is a single input channel.

obx ! scy ! mdz ! n1:n2

where n1 and n2 represent a sequential list of input channels, inclusive.

obx ! scy ! mdz ! (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.

Note: Repeating channels or having channels out of sequence in a scan list is not supported on all SCXI modules and is never supported through the C API. Please refer to each module's documentation for more information on this feature.

Related Links:
KnowledgeBase 2XC9KPOK: Using SCXI Channels with NI-DAQmx
KnowledgeBase 25BE4GHE: Why Is My DAQ Gain Affected When I Remove "ob0" from My SCXI Channel String?
KnowledgeBase 1P89SMEV : Scanning Multiple, Non-sequential Channels from SCXI Modules
KnowledgeBase 22UB2R8U : Why Am I Getting -10680 at AI Group Config When Acquiring from SCXI Channels?
KnowledgeBase 2CEAJPXH: Scanning with SCXI
KnowledgeBase 2ILD4BXH : SCXI and DAQ Channel Scanning
KnowledgeBase 0Z63B4AQ : How Can I Address and Use Cold Junction Compensation (CJC) with SCXI Modules?

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Report Date: 02/06/1995
Last Updated: 05/05/2006
Document ID: 065GM6NI

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