DAQmx - Sequence of Devices in Lists and Ranges

[alysko]

   Dear NI support,

I have tried to specify the DAQmx Physical Channel as "Dev1/ai3:Dev3:ai2" and ... LabView 7.1 crashed. As you can see, the problem can be either in "negative" counting of the analog inputs, or in the "stepping" through the physical devices (1 and 3 present, and there is no Dev2 in the system), or both.

Could you please let me know:

1) if this problem is present in LabView 8.5?

2) if the stepping through the devices is actually supported by design?

3) if LabView understands "negative" channel counting (e.g. ai5:3)?

4) if the DAQmx Physical Channel controls and constants still allow such combinations (in LV 8.5)?

Thanking you in advance.

Sincerely

Albert

[Speedy_Badger]

Hello Albert,

I've looked into the issues you brought up and I have some answers for you. LabVIEW 8.5 is no different in that you cannot "step" through devices in a single physical channel. If you attempt to do this you will receive an error which I have included in the figure below. This is simply because you cannot have two independent devices within a single task. The work around for this is to create two tasks, one for each device, and then later combine the data on your graph or file. To answer your question regarding the "negative" channel counting, this is perfectly acceptable. For instance, if you run the shipping example "Cont Acq&Graph Voltage-Int Clk.vi" and select Dev1/ai5:ai0 you will see that LabVIEW accounts for the reverse ordering in the way it indexes the data.



Both of these characteristics are dependent upon the DAQmx drivers, not on the version of LabVIEW. If you would like to see a device stepping feature added in future versions of DAQmx drivers, I would point you to the Product Suggestion Center on our website. This is a great way for our engineers to get feedback from customers on what new functionality is desired.

Hope this clears up your questions.

Regards,

Message Edited by Speedy Badger on 11-20-2007 10:07 AM