DAqmx in timed loop

[Dan_55]

Hi,

I seem to be experiencing some strange behaviour with a DAQmx application I am putting together. Basically, I set up a continuous DAQmx task across 2 PXI-6133 cards to acquire all 16 channels at 200kHz. I also setup a digital task to acquire digital samples from one of the cards. All 3 tasks are synchronised to the same clock source and trigger event to start the acquisition. So far so good.... Next I unload a fixed number of samples (100k which is .5 seconds) inside a while loop. If there is no delay inside the while loop then the Read multiple DAQmx function uses all my CPU resources. As a workaround, I use a wait for ms with around 450ms which produces a stable output, no errors. If however I replace the while loop with a timed loop, I immediately get DAQ error -200279. Even reducing the period on the timed loop to 10 ms does not seem to be enough to stop the error. Any ideas are appreciated, I also tried putting the whole thing inside a timed loop and using a case structure so that the initialise section only happened on first call but this did not work either. Attached is the VI.

Dan

[Kenny_K]

try adding shift registers to your while loop for all of the DAQmx tasks.

[Dan_55]

Thanks kenny, I tried that as well as changing to a timed loop and using shift registers on the timed loop. There is also another problem in that even when using the while loop with delay method, adding a timed loop anywhere else on the block diagram (even if it is doing nothing) causes the daqmx task to fail. I'll log it as a tech problem and see how I go.

Dan