Level Measurement

[Zuc_Lab]

Hi,

in my VI I need to measure the frequency and the level (possibly in dBm) of a certain tone which last about 500ms. With the instrument in my lab I have found that the tone is around -20 dBm and 1000Hz. I have tried different VIs for the signal processing but I don’t understand why they estimated the level always lower that the one check by the instrument (around -35 dB). I used the same VIs for other programs in which the duration of the tone is longer, about 2-3 seconds, and the level is checked correctly with a ±2 dB of difference. So the only factor that I can notice is that the tone is so short to cause problem to the Vis. So if someone knows the characteristics of the following VI:

• Extract Single Tone Information.vi
• FFT Power Spectrum and PSD.vi

And have some hints it will very helpful!

For sake of completeness i am using an USB-6211.

Thanks for the help!

Best Regards,

Zuc

[GerdW]

Hi Zuc,

it really would help when you would cleanup your VI and when you would provide some useful measurement data in your graph (by setting default values)!

Please see this snippet of your data analysis:

Use this as a subVI in your main VI. Run the main VI until there are useful data in the subVI, then stop the main and set all current values of the subVI as default. Re-attach this subVI so we can analyze your data!

[Zuc_Lab]

Hi,

here after the data you asked for the limit in dimension i have added them separated.

Thank you!

Best Regards,

Zuc

[Henrik_Volkers]

Tonedetection would like to have more than 10 periodes, so it should be usefull for frequencies > 20 Hz (@ 500 ms duration).

However you should cut out the constant amplitude part 🙂

uncertainty increases for less periodes mainly due to leakage , so maybe a two step process for a cutout will help.

Another method is sine approximation (again for the constant amplitude part)

link to some info on tonedetection here

link to sinefitting paper

[Zuc_Lab]

Hi,

in my vi I measure a signal (duration around 500ms) and compute its FFT checking a frequency at 1000Hz. The vi works manually but when I call it more times in a sequence of TestStand I obtain the following warning which stop the execution until the operator close it (observe the screenshot). From other posts I read that this warning is related to the filter part which prompts the pop-up when you pass waveforms which havedifferent frequencies of acquisition or data which have no indication of the t0 (https://forums.ni.com/t5/LabVIEW/Error-20352/td-p/3133660). But each time that I call the vi the frequency used for sampling is always the same and I pass a waveform to the filter configurator. So why do I obtain thin warning and how i can solve it?

The work around is to use directly the filter whitout configuring it with the Filter Express VI

Thank you for the help!

Best Regards,

Zuc