Need Help. NI Labview, SignalExpress, power spectrum (spectra)

[dho]

the top plot is in time domain the signal from an accelerometer. the bottom plot is in frequency domain.
i do not understand the unit of the power, (dB ref 1.0E+0 V/sqrt (Hz).
can anyone shine me some light?
thansk.

 

[IRstuff]

Not sure what you mean, what did you expect it to be? Your time domain signal was in volts, so your PSD is on volts/rt-Hz

TTFN
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[dho]

i expect to see Volt^2/Hz.
thanks.

 

[IRstuff]

Then you simply need to square the ordinate

TTFN
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[amanuensis]

The scare fades in the dB unit.

A simple analogy with the pressure level allows to understand.

Lp=10*Log10(p^2/pref^2) with pref= 2.10^(-5)Pa (and not pref = 2.10^(-5)Pa^2 ...)

Here the operation is 10*Log10((V^2/Hz)/Ref^2) where Ref is in V/sqrt(Hz) and equals 1