sampling rate problem labview pda

[lav]

hi, im testing my pda labview system to see what speeds i can actually acquire at. im using a signal generator as an analogue input generating a sin wave at 2khz and around 2V amplitude. im using finite acquisiton to acquire between 50-200 samples using the ai finite acquire pda example
when i acquire at 5khz [well above nyquist] i get rubbish data hinting that the system can actually reach 5khz, yet when i increase the sampling rate to 10, 15, 20 and 200khz the data improves and actually looks like a sin wave. does this mean that its only achieveing a certain percentage of the specified sampling rate each time?
yet when i input a square wave the representations seems correct - ie start to foul up when i approach the nyquist limit.
ive stuck a zip file of photos of the pda acquiring at the different rates.
thanks alot
andy

[arvin_labrat]

What version of the PDA Module are you using and what DAQ are you using?

[lav]

labview 8.2 +pda module, daq mx base 2.2 and a cf-6004 with ipaq 5550 and expansion sleeve
cheers

[arvin_labrat]

Hey Lav

Here is an tutorial on sampling and Nyquist

http://zone.ni.com/devzone/cda/tut/p/id/3000

I think the data you are collecting is expected.  You are only collecting 2.5 samples/ Cycle not enough to reconstruct your waveform.

I think you will find your PDA is working as well as a PC Daq when it comes to sampling the signal you are trying to acquire.