frequency plot not showing

[yazan206]

hi everyone,

im using NI USB6009 in order to acquire two different voltage plots as well as a frequency plot, everything seems to work properly except that nothing is being plotted on the frequency plot. i have attached the vi, so could anyone detect what my problem could be.

Cheers 

[RavensFan · Accepted solution]

You've set your task up for 2 channels ai0 and ai1.  You are getting N channels thus a 1-D array of waveforms that will contain 2 waveforms.  Then you are indexing that array to get 2 Voltage display, and a 3rd waveform that you are feeding to frequency.

That waveform is empty because you never acquired it!

I imagine you probably want to do the frequency off of one of the two voltage waveforms you acquired.

PS.  You don't need the constants 0, 1, 2 on the Index Array.  It will give you those indices by default.