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# NI Labview, SignalExpress, Power Spectrum (Spectra)

## 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?
thanks.

### RE: NI Labview, SignalExpress, Power Spectrum (Spectra)

The answer in your other thread was correct. you need to enter a calibration for your accelerometer, telling the ADC how many g a given 1V signal represents.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: NI Labview, SignalExpress, Power Spectrum (Spectra)

(OP)
would you please explain it "mathematically" ?
thanks.

### RE: NI Labview, SignalExpress, Power Spectrum (Spectra)

TTFN
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### RE: NI Labview, SignalExpress, Power Spectrum (Spectra)

dB=20*log10(psd in engineering units per sqrt(Hz)/1.0)

The slight oddity is they have use V/sqrt(Hz) rather than V^2/Hz, but that is not uncommon, and the relationship is obvious.

I suggest you read and understand the section on engineering units and dB in this

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: NI Labview, SignalExpress, Power Spectrum (Spectra)

Sorry that equation assumes you want dBref = 1 engineering unit, if you wanted 0 dB to be at any other reference replace the 1.0 by that figure

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

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