Spectrum problem with EX92016 DAQ Board

[AdiNocera]

Hi People, I've done a simple soft to acquire an analog signal with the EX92016 DAQ and display its power spectrum. I cannot make this work. I've tried with the Express Palette (using the Spectral VI) and the Signal Processing Palette (using the FFT PS and PSD) and none of this options worked.

The problem, I think is with the tipes of data, because the DAQ delivers a single scalar tipe of signal. So, I converted it to Double and then to Dynamic Data (Singal Manipulation "To DDT") to connect it to the Spectral VI and the output of the Spectral VI I've connected to a Waveform Graph. When I run the program, the X scale of the Waveform Graph (set to Autoscale) automatically starts from -1 and goes to 1 and shows no values. I also tried to create an array and storage the signal values (as scalar with double precision), but the values shown didn't correspond with reality and the scales were incorrect.

I hope some of you know the solution and help me. Thanks a lot!

I Attached some images of the block diagram to help understanding. Regards,

Adi.

[Pete.Dunc]

Hi Adi,

Welcome to the community!  Thanks for coming 

In the "Convertion.JPG" you are taking the FFT of a single data point - this doesn't really make sense.  You would typically have an array of time based data and transpose it into the frequency domain.  For example, an integer number of periods of a perfect sine wave (time domain) will give you a single spike in the frequency domain at the rate of oscillation.

You will need to build up an array of data to perform the operation on.  You may be able to acquire an array, rather than a single point - or read the single point multiple times, and build up the results.  You can use a For Loop with an auto-indexing output tunnel, or build up an array in a While Loop.

[AdiNocera]

Pete! Thanks a lot! That's what I've done, and I've sent the screen image named "Using Array". The thing is tha when I buid the array, connect everything and run the program, the graph shows wrong values. I will attach a scree capture of the Graph. Again thanks for answering so fast! Regards,

Adi.

P.S.: I'm sorry, I'm not at the Lab right now, so I can't send the screen capture, but I'll try to explain what hapenned. When I put a sin wave from an external Waveform Gen in to the DAQ Board input, the graph shows something that seems to be the power spectrum, but the values were so wrong. The sin wave amplitude was 1V and its frequency was 234Hz. The amplitude values in the graph oscillated between 0 an 150V and the frequency was at 0.9 Hz aprox. Even when I move the Gen frequency, at the graph it remains at 0.9Hz. The Block Diagram connection is the one you can see at "Using array" image.