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

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

(OP)
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.

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

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

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

(OP)
i expect to see Volt^2/Hz.
thanks.

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

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

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