DAQmx Read VI returns empty waveform

[duwaar]

So, I'm writing an interface for the NI USB-6229 in LabVIEW 2018 on Windows 10.

The DAQmx Read VI will usually write data to the file just fine (unless I change the "number of samples" control, but I think that is an unrelated issue), but the main problem is that no matter what settings I use for that VI it always returns an array of empty waveforms. Why is it doing this? Am I using it wrong? Is it a gotcha-type of problem? I need those waveforms so I can display the data as it is being collected. I am stumped and would appreciate any feedback.

P.S. Sorry the block diagram is so big.

[RavensFan · Accepted solution]

Are you sure it is empty?  Did you put probes on the Waveform wires coming from the DAQmx Read?  Do you get any error message?

One thing odd I see.  You take the array data and do an array size on that.  Then you proceed to do an index array on that value.

Well if you have a 3 waveform array, the number 3 comes out.  But those are elements 0, 1, and 2.  So when you try to index waveform 3, it doesn't exist.  It will give you an empty array.

[duwaar]

Woohoo! That issue that you pointed out wasn't the problem, itself, but fixing that mistake led me to the actual problem; I needed to put a shift register in the for loop after 22 in the attached image.

Thank you so much!