How to get properties of local virtual channels in a task

[HolgerF]

Hello community,

I'm a bit confused, that I'm apparently not be able to get informations (properties) of local virtual channels of a DAQmx task.

My use-case is, that I would like to set my DAQmx device into save state on application shutdown, which means to set analog out tasks to 0V and digital out tasks to FALSE.

What I tried do to was, to iterate through a list of my tasks and get the channel types of the associated channels to determine if I have to do a analog or digital write operation.

Does anybody have a idea, or do I have to memory manua, which task does which operation?

Thanks in advance

Holger

[GerdW]

Hi Holger,

you should know the properties of your DAQmx tasks right from the start of your program!

So why do you need to regain this knowledge at the end of your program?

[HolgerF]

Hi GerdW,

of course I know the properties of my tasks. But why do I have to remember them in my application, when the driver also have them and I can ask them?

The question can be more general, why channel properties do not work on local virtual channels?

In the meantime I talked to NI support and they told me, my solution for which I needed my shown vi, is not a good one. So I have to change my architecture and would not need it anymore.

Thank you GerdW for your answer. But some behavior of DAQmx is very strange.

Regards

Holger

[Bob_Schor]

One of my earlier LabVIEW/DAQ challenges was dealing with a PXI box that had Digital Outputs connected to various pieces of Lab equipment -- when the PXI was turned on, its DO lines were (as I recall) allowed to drift to +5v, which made the Lab equipment, particularly audio, start to hum loudly.  [I fixed it by creating a PXI Start-up routine that set all of the DO lines to 0v].

So I looked at my own code, and tried to see if, knowing nothing about the rest of the program and what was connected to what, I could "deduce" (from DAQmx Property Nodes) which DAQ devices I was using.  I think that, if this is possible at all (and I don't think it is), it will be very difficult, and thus prone to error.  For example, one of my routines uses "internally-created Tasks" (i.e. I don't pre-define the Task in MAX or in the Project) for a USB-6009, a multi-function AI/AO/DI/DO unit.  Looking at my own code, it became clear that unless I programmed it into the code, there was no "query" to tell what Channels I was using, whether they were Input or Output, Analog or Digital.

Thus I agree with GerdW -- at the time you start designing the code, you know what the devices and channels are, and can easily write both the initialization code and the (sorry for this made-up word) finalization code at the same time (so you won't forget to do it later).

Bob Schor