Changing Physical Channel Via DAQmx Channel Property Node

[Hooman91]

Hi,

I am working on a VI for frequency response analysis. The test should consist of two rounds. In each round different analoge output should be used. So I need to change the physical channel for analoge output task in the second iteration of the loop. I tried to do so by using DAQmx Channel Property Node. However the "PhysicalChanName" element of the node only accepts input channels! Furthermore, the "ChanType" element reads as "Analoge Input" and the "Change To Write" option is deactivated for this element. Any idea how can I fix this?

I am using NI PXI-4461 and LabView 16.0 64-bit.

[bahannah]

Hooman91,

The reason that you cannot see Analog Output options in the constant feeding into the property node is because you must right click on the constant, select I/O Name Filtering..., and change the I/O Type to Analog Ouput. However, this will most likely not fix your problem, because for DSA devices like the PXI-4461, you cannot set properties while the task is running. 

Is it possible to do two separate tasks for each of the rounds? That would be the simplest way to get around this issue.

Regards,

Hannah

Applications Engineering 

National Instruments 

www.ni.com/support 

[Hooman91]

Thanks for your reply.

Initially I tried using two taks like below:

The first round is run smoothly but at the beginning of second round I get this error:

For the record after each round I call DAQmx stop task and clear task.

[Hooman91 · Accepted solution]

I figured a way for my problem: I use two create virual channel VIs but connect both of them to the same task. Later when writing signal values for this task, one should simply append two waveforms and feed the 2D array into the DAQmx Write VI. (Needless to say, the N Chan N Sample variation should be selected.). Each subarray will then automatically be assigned to one of the physical channel.

However I have to say that this kind of design concept is not trivial at first. One should spend a lot of time figuring out the possible solutions. And NI does not provide sufficient documentation for that.