Problem using a counter to simultaneously trigger AO and AI

[tycho75]

Hi all,

I'm currently working on a VI with one AO task and one AI task running in parallel. These tasks are generating/acquiring the same (finite) number of samples and at the same rate. In addition, the two tasks are triggered with the same counter (Ctr0).

While running the VI, I can look at the counter output and the signal generated by the AO on a scope. Both look fine. The AO use Ctr0InternalOutput as trigger source.

My problem is that the AI task never sees the trigger. I tried different solutions for the trigger source of the AI (using Ctr0InternalOutput, using ao/StartTrigger), to no avail.

Can somebody have a look and tell me if there is something obvious I missed ? I looked at the forums and didn't find any solution.

I'll also appreciate comments to improve the design ! 

The main program is Metal.vi. The AO task is in the sub-vi Metal_DAQ_Start.vi. The counter task is in Metal_FG.vi.

Thanks a lot for your help !

All the best,

Julien

NB: I'm using a USB-6251 and Labview 2014.

[tycho75]

Hi,

I'm still investigating on this problem.

I wrote a smaller "quick and dirty" VI with only the AO, AI and counter tasks to help understanding what happen.

• When I disable the AI loop, I can see on the scope the output of the counter and the output of the AO task: it works fine.
• When I disable the AO loop, and enable the AI loop, the AI task works fine.
• The problem is there only when the two tasks are running in parallel: in that case, the AO works OK, but the AI always go in time out.

I don't know what to do next...

I attach my test program (for Labview 2014).

Thanks for your help !

[tycho75]

Ok, problem solved.

When using two tasks in parallel on the same device, it seems to be necessary to use the internal memory for one of the tasks.

When I use internal memory with the AO, it works.