Power Spectrum Density - units and averages

Hi,

I'm using MATLAB to calculate and plot PSD. I need some help about this operation to do this correctly.

I use NI DAQ card to sample signal by some time. I can set sampling frequency and time of recording signal.

Then I load my result's to workspace and calculate PSD.

My questions:

1. What is the best way to calculate PSD?

I'm using this

https://www.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html

and to compare this

https://www.mathworks.com/help/signal/ref/pwelch.html

and it work's but I must sure if I receive good results. I know correct results from dedicated spectrum analyser.

Now i must do this in MATLAB by DAQ card and check results. My spectrum analyser return in dbV/sqrt(Hz) and Vrms/sqrt(Hz)

What are the units of above functions. For example if I calculate PSD using method described in https://www.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html and enter to function my DAQ results which are in Volts, I obtain dBV/Hz units? What are result units? dB/Hz?

2. How to convert dB/Hz or dBV/Hz to dbV/sqrt(Hz) or Vrms/sqrt(Hz). I need units in sqrt(Hz).

3. I have problem with averaging. For example: I'm sampling signal by some time for example 10ksps and 10 seconds. I obtain 100 000 samples. My spectrum is very wide in y axis. Now i would like to calculate PSD with averaging for better readable spectrum. How to do this? I can set DAQ parameters.

Thanks a lot for any answers.