LabVIEW

cancel
Showing results for 
Search instead for 
Did you mean: 

Change in voltage during acquisition altered frequency profile

I changed my acquistion rate in my labview VI from +/- 2V to +/- 0.1V to improve the resolution.  I made the change in both labview and measurement and automation explorer and adjusted the conversion factor from bits to volts accordingly.  However, I have noticed my frequency profile has changed, in some regions where there are peaks there now aren't and vice versa.  I understand how the amplitude could change but I'm not sure why the frequency would.

 

undefined

0 Kudos
Message 1 of 8
(3,036 Views)

Hello Chemgineer,

 

What is your sampling rate and what hardware are you using to acquire this signal?


Regards,
Glenn
0 Kudos
Message 2 of 8
(3,007 Views)

My sampling rate is 40,000 Hz and I am using a 6036E DAQ.... also I accidently clicked solved, obviously it's not solved.

0 Kudos
Message 3 of 8
(3,003 Views)
You can unselect solved by using the options button in the right hand corner of his reply.
Now Using LabVIEW 2019SP1 and TestStand 2019
0 Kudos
Message 4 of 8
(2,998 Views)
What happens when you try some intermediate voltage resolutions? (+/- 1 , +/- 0.5 etc)?
0 Kudos
Message 5 of 8
(2,994 Views)
I haven't tried intermediate values, but I have seen something similar when going between +/-10 and +/- 2 for a different application.
0 Kudos
Message 6 of 8
(2,973 Views)

I notice that you are plotting signal to noise ratio.  What are the peak values of signal and noise?  Can you measure them with an oscilloscope or other independent instrument to confirm?  Do you expect the signal and noise spectra to be similar or different?

 

Can you apply a known, clean signal of 50 mV peak to peak to both configurations and see what happens?

 

Lynn 

0 Kudos
Message 7 of 8
(2,969 Views)

The signal-to-noise ratio was calculated by computing the power spectral density for the process and dividing by the power spectral density of the background. I expect the process to have a higher intensity than the background.  I believe the problem lies in the raw data being recorded this was just the easiest graph to show it on.  I do not have another instrument to measure with, I suppose I could artificially generate a signal in the VI and see how it records at the different voltages to eliminate a software problem.   

0 Kudos
Message 8 of 8
(2,961 Views)